Association of Skin Microbiome Dynamics With Radiodermatitis in Patients With Breast Cancer

Importance

The interindividual differences in severity of acute radiation dermatitis are not well understood. To date, the pathomechanism and interplay of microbiome and radiodermatitis before and during treatment remain largely unknown.

Objective

To assess the association of skin microbiome baseline composition and dynamics with severity of radiodermatitis in patients undergoing adjuvant radiotherapy for breast cancer.

Design, Setting, and Participants

A longitudinal prospective pilot observational study was conducted between January 2017 and January 2019. Sequencing results were received in March 2021, and the data were analyzed from August 2021 to March 2023. This study was performed at an urban academic university cancer center. A total of 21 female patients with breast cancer after surgery were consecutively approached, of which 1 patient withdrew consent before the study started.

Exposure

Adjuvant radiotherapy for breast cancer for 7 weeks.

Main Outcomes and Measures

The main outcome was the association of baseline skin microbiome composition and its dynamics with the severity of radiodermatitis. A total of 360 skin microbiome samples from patients were analyzed, taken before, during, and after radiotherapy, from both the treated and contralateral healthy sides. The skin microbiome samples were analyzed using 16S (V1-V3) amplicon sequencing and quantitative polymerase chain reaction bacterial enumeration.

Results

Twenty female patients with breast cancer after surgery who underwent radiotherapy enrolled in the study had a median (range) age of 61 (37-81) years. The median (range) body mass index of the patients was 24.2 (17.6-38.4). The 16S sequencing revealed that low (<5%) relative abundance of commensal skin bacteria (Staphylococcus epidermidis, Staphylococcus hominis, Cutibacterium acnes) at baseline composition was associated with the development of severe radiodermatitis with an accuracy of 100% (sensitivity and specificity of 100%, P < .001). Furthermore, in patients with severe radiodermatitis, quantitative polymerase chain reaction bacterial enumeration revealed a general non-species-specific overgrowth of skin bacterial load before the onset of severe symptoms. Subsequently, the abundance of commensal bacteria increased in severe radiodermatitis, coinciding with a decline in total bacterial load.

Conclusions and Relevance

The findings of this observational study indicated a potential mechanism associated with the skin microbiome for the pathogenesis of severe radiodermatitis, which may be a useful biomarker for personalized prevention of radiodermatitis in patients undergoing adjuvant radiotherapy for breast cancer.

Dosiomics and radiomics-based prediction of pneumonitis after radiotherapy and immune checkpoint inhibition: The relevance of fractionation

OBJECTIVES

Post-therapy pneumonitis (PTP) is a relevant side effect of thoracic radiotherapy and immunotherapy with checkpoint inhibitors (ICI). The influence of the combination of both, including dose fractionation schemes on PTP development is still unclear. This study aims to improve the PTP risk estimation after radio(chemo)therapy (R(C)T) for lung cancer with and without ICI by investigation of the impact of dose fractionation on machine learning (ML)-based prediction.

MATERIALS AND METHODS

Data from 100 patients who received fractionated R(C)T were collected. 39 patients received additional ICI therapy. Computed Tomography (CT), RT segmentation and dose data were extracted and physical doses were converted to 2-Gy equivalent doses (EQD2) to account for different fractionation schemes. Features were reduced using Pearson intercorrelation and the Boruta algorithm within 1000-fold bootstrapping. Six single (clinics, Dose Volume Histogram (DVH), ICI, chemotherapy, radiomics, dosiomics) and four combined models (radiomics + dosiomics, radiomics + DVH + Clinics, dosiomics + DVH + Clinics, radiomics + dosiomics + DVH + Clinics) were trained to predict PTP. Dose-based models were tested using physical dose and EQD2. Four ML-algorithms (random forest (rf), logistic elastic net regression, support vector machine, logitBoost) were trained and tested using 5-fold nested cross validation and Synthetic Minority Oversampling Technique (SMOTE) for resampling in R. Prediction was evaluated using the area under the receiver operating characteristic curve (AUC) on the test sets of the outer folds.

RESULTS

The combined model of all features using EQD2 surpassed all other models (AUC = 0.77, Confidence Interval CI 0.76-0.78). DVH, clinical data and ICI therapy had minor impact on PTP prediction with AUC values between 0.42 and 0.57. All EQD2-based models outperformed models based on physical dose.

CONCLUSIONS

Radiomics + dosiomics based ML models combined with clinical and dosimetric models were found to be suited best for PTP prediction after R(C)T and could improve pre-treatment decision making. Different RT dose fractionation schemes should be considered for dose-based ML approaches.

Enhanced RBE of Particle Radiation Depends on Beam Size in the Micrometer Range

High-linear energy transfer (LET) radiation, such as heavy ions is associated with a higher relative biological effectiveness (RBE) than low-LET radiation, such as photons. Irradiation with low- and high-LET particles differ in the interaction with the cellular matter and therefore in the spatial dose distribution. When a single high-LET particle interacts with matter, it results in doses of up to thousands of gray (Gy) locally concentrated around the ion trajectory, whereas the mean dose averaged over the target, such as a cell nucleus is only in the range of a Gy. DNA damage therefore accumulates in this small volume. In contrast, up to hundreds of low-LET particle hits are required to achieve the same mean dose, resulting in a quasi-homogeneous damage distribution throughout the cell nucleus. In this study, we investigated the dependence of RBE from different spatial dose depositions using different focused beam spot sizes of proton radiation with respect to the induction of chromosome aberrations and clonogenic cell survival. Human-hamster hybrid (AL) as well as Chinese hamster ovary cells (CHO-K1) were irradiated with focused low LET protons of 20 MeV (LET = 2.6 keV/µm) beam energy with a mean dose of 1.7 Gy in a quadratic matrix pattern with point spacing of 5.4 × 5.4 µm2 and 117 protons per matrix point at the ion microbeam SNAKE using different beam spot sizes between 0.8 µm and 2.8 µm (full width at half maximum). The dose-response curves of X-ray reference radiation were used to determine the RBE after a 1.7 Gy dose of radiation. The RBE for the induction of dicentric chromosomes and cell inactivation was increased after irradiation with the smallest beam spot diameter (0.8 µm for chromosome aberration experiments and 1.0 µm for cell survival experiments) compared to homogeneous proton radiation but was still below the RBE of a corresponding high LET single ion hit. By increasing the spot size to 1.6-1.8 µm, the RBE decreased but was still higher than for homogeneously distributed protons. By further increasing the spot size to 2.7-2.8 µm, the RBE was no longer different from the homogeneous radiation. Our experiments demonstrate that varying spot size of low-LET radiation gradually modifies the RBE. This underlines that a substantial fraction of enhanced RBE originates from inhomogeneous energy concentrations on the µm scale (mean intertrack distances of low-LET particles below 0.1 µm) and quantifies the link between such energy concentration and RBE. The missing fraction of RBE enhancement when comparing with high-LET ions is attributed to the high inner track energy deposition on the nanometer scale. The results are compared with model results of PARTRAC and LEM for chromosomal aberration and cell survival, respectively, which suggest mechanistic interpretations of the observed radiation effects.

In Vivo Microbeam Radiation Therapy at a Conventional Small Animal Irradiator

Microbeam radiation therapy (MRT) is a still pre-clinical form of spatially fractionated radiotherapy, which uses an array of micrometer-wide, planar beams of X-ray radiation. The dose modulation in MRT has proven effective in the treatment of tumors while being well tolerated by normal tissue. Research on understanding the underlying biological mechanisms mostly requires large third-generation synchrotrons. In this study, we aimed to develop a preclinical treatment environment that would allow MRT independent of synchrotrons. We built a compact microbeam setup for pre-clinical experiments within a small animal irradiator and present in vivo MRT application, including treatment planning, dosimetry, and animal positioning. The brain of an immobilized mouse was treated with MRT, excised, and immunohistochemically stained against γH2AX for DNA double-strand breaks. We developed a comprehensive treatment planning system by adjusting an existing dose calculation algorithm to our setup and attaching it to the open-source software 3D-Slicer. Predicted doses in treatment planning agreed within 10% with film dosimetry readings. We demonstrated the feasibility of MRT exposures in vivo at a compact source and showed that the microbeam pattern is observable in histological sections of a mouse brain. The platform developed in this study will be used for pre-clinical research of MRT.

What MRI Sequences are Necessary for Automated Neural Network-Based Metastasis Segmentation - An Ablation Study

PURPOSE/OBJECTIVE(S)

Brain metastasis (BM) delineation is a time-consuming process in both daily clinical practice and research. Automated BM segmentation algorithms can be used to assist in this task. Most approaches to brain tumor segmentation, such as algorithms trained on the BraTS challenge, use four magnetic resonance imaging (MRI) sequences as input, making them susceptible to missing or corrupted sequences and increase the number of sequences necessary for MRI RT planning. The goal of this project is to compare neural networks with different combinations of input sequences for the segmentation of the contrast-enhancing metastasis and the surrounding FLAIR hyperintense edema. All models were tested in a multicenter international external test cohort. This allows us to determine which MRI sequences are needed for effective automated segmentations.

MATERIALS/METHODS

In total, we had T1-weighted sequences without (T1) and with contrast enhancement (T1-CE), T2-weighted sequences (T2), and T2 fluid-attenuated inversion recovery (FLAIR) sequences from 339 patients with at least one brain metastasis from seven centers available. Preprocessing yielded co-registered, skull-stripped sequences with an isotropic resolution of 1 millimeter. The contrast-enhancing metastasis as well as the surrounding FLAIR hyperintense edema were manually segmented to create reference labels. A baseline 3D U-Net with all four sequences as well as six additional U-Nets with different clinically plausible combinations (T1-CE; T1; FLAIR; T1-CE+FLAIR; T1-CE+T1+FLAIR; T1-CE+T1) of input sequences were trained on a cohort of 239 patients from two centers and subsequently tested on an external cohort of 100 patients from the remaining five centers.

RESULTS

All models that included T1-CE in their selected sequences showed similar performance for metastasis segmentation with a median Dice similarity coefficient (DSC) of 0.93-0.96. T1-CE alone likewise achieved a performance of 0.96 (IQR 0.93-0.97). The model trained with only FLAIR performed worse (DSC = 0.73, IQR 0.54-0.84). For edema segmentation, models that included both T1-CE and FLAIR performed best (median DSC = 0.93), while the remaining four models without simultaneous inclusion of these two sequences (T1-CE; T1; FLAIR; T1-CE+T1) reached a median DSC of 0.81-0.89.

CONCLUSION

Automatic segmentation of brain metastases with less than four input sequences is feasible with minimal or no loss of quality. A T1-CE-only protocol suffices for metastasis segmentation. In contrast, for edema segmentation, the combination of T1-CE and FLAIR seems to be important. Missing either T1-CE or FLAIR decreases performance. These findings may improve future imaging routines by omitting unnecessary sequences, thus speeding up procedures in daily clinical practice while allowing for optimal neural network-based target definitions.

High Salt Diet Exacerbates Intestinal Radiotoxicity by Promoting Intestinal Epithelial Barrier Dysfunction after RT

PURPOSE/OBJECTIVE(S)

Intestinal side effects have a substantial impact on patients' quality of life and constrain radiation therapy (RT) of abdominal and pelvic tumors. We aim at gaining a better understanding of the pathogenesis of intestinal radiotoxicity and identifying contributing factors. A high salt diet is common among countries of the Global North. The effects of an increased sodium-chloride (NaCl) intake on the development of intestinal side effects have not been investigated.

MATERIALS/METHODS

C57BL/6 wild-type (WT) mice were fed a high salt diet (HSD) or normal salt diet (NSD) and irradiated with 12 Gy total body irradiation (TBI) or 13 Gy abdominal irradiation (ABI). Following TBI the mice received a syngeneic bone marrow transplant to reconstitute hematopoiesis. Readouts after RT included weight monitoring, histopathological analysis and assessment of intestinal epithelial barrier function. To corroborate our findings in vitro, murine organoids of the small intestine were cultivated, treated with varying NaCl concentrations (110-200 mM) and irradiated with 2 or 4 Gy. Organoid survival and growth were determined using multiple methods. Additionally, colony formation assays (CFA) of murine MC38 colon carcinoma cells were performed after stimulation with NaCl. Mechanistically, we analyzed the apoptosis rates of MC38 cells and intestinal epithelial organoids.

RESULTS

Irradiated HSD animals showed increased acute weight loss, reduced weight regeneration, a more severe dysfunction of the intestinal barrier (enhanced FITC-dextran permeability) and increased histopathological damage when compared with NSD animals. Murine intestinal organoids and MC38 cells showed decreased survival after RT in hypernatremic conditions. Interestingly, our preliminary data show that there are no increased rates of apoptotic cells in vitro, suggesting a different mechanism affecting the increased radiosensitivity in hypernatremic conditions.

CONCLUSION

Our data show a NaCl induced intensification of intestinal tissue injury following RT. These findings can potentially pave the way for investigating the effect of high salt diet on intestinal radiotoxicity in clinical trials.

Influence of Bacterial Metabolites on the Systemic Antitumor Immune Response after Radiation Therapy in Combination with Immune Checkpoint Inhibitors

PURPOSE/OBJECTIVE(S)

The gut microbiome influences the pathogenesis of many diseases and numerous medical therapies. In addition, it is well known that cancer patients are often treated with antibiotics during the course of their disease, which can lead to intestinal dysbiosis. Importantly, experimental and clinical studies have already shown that this has implications for tumor therapies and that immune-active bacterial metabolites can play a central mechanistic role. However, little is known about the influence of the bacterial microbiota or its metabolites on the outcome of radiotherapy (RT) in combination with immune checkpoint inhibitors (ICIs).

MATERIALS/METHODS

We used a bilateral tumor model (MC38 tumor cells) to investigate the influence of the intestinal microbiota and selected bacterial metabolites on the abscopal effect after RT in combination with ICIs. In brief, RT (1 × 8 Gy) of the right tumor was performed 7 days after tumor induction, followed by application of α-CTLA4 or α-PD1 for three weeks. Antibiotics (ampicillin, neomycin, metronidazole, and vancomycin) or selected immune-activating metabolites were administered daily by gavage. We used bacterial metabolites that are described in the literature as having strong immune-modulating properties.

RESULTS

In mice, combined treatment with different antibiotics had neither a significant effect on tumor growth of the irradiated tumor nor on tumor progression of the unirradiated tumor after RT in combination with α-CTLA4. In contrast, supplementation of specific bacterial metabolites had different effects depending on the type of ICI and the specific type of bacterial metabolite. Specifically, we identified bacterial metabolites that led to enhanced tumor progression of the unirradiated abscopal tumor after RT combined with ICIs, resulting in reduced survival rates.

CONCLUSION

To the best of our knowledge, we are presenting here for the first-time experimental data on the influence of the intestinal microbiome on the abscopal effect after RT combined with ICIs. Our data clearly show that specific immune-active bacterial metabolites can negatively influence the abscopal effect after combined radioimmunotherapy. This implies the design of further experimental studies aimed at using specific strategies (e.g., antibiotics) to decimate certain gut bacteria and reduce the amount of certain bacterial metabolites to improve response rates after radioimmunotherapy.

The Value of Equivalent Dose Calculation for Dosiomics and Radiomics-Based Prediction of Pneumonitis after Thoracic Radiotherapy with Immune Checkpoint Inhibition

PURPOSE/OBJECTIVE(S)

Post-therapy pneumonitis (PTP) is a relevant side effect after thoracic radiotherapy (RT) and immunotherapy with checkpoint inhibitors (ICI). The impact of the combination of both is unclear. We aim to improve risk estimation by prediction of PTP with and without ICI therapy. To analyze the influence of different fractionation schemes, the value of voxel-wise 2 Gy equivalent dose (EQD2) is investigated.

MATERIALS/METHODS

Clinical data from 100 patients who received fractionated RT (single dose ≤ 3Gy) RT were collected. 36 patients received additional ICI therapy. PTP of all grades were monitored. Planning Computed tomographies (CTs), segmentations and 3D dose data were extracted and converted to EQD2. Dosiomics and radiomics features were extracted using 1000-fold bootstrapping using Pearson intercorrelation and the Boruta algorithm for 5 single and 4 combined predictive models. Machine learning algorithms (random forest (rf), logistic elastic net regression, support vector machine, logitBoost) were trained and tested using a 5-fold nested cross validation approach and Synthetic Minority Oversampling Technique resampling in R. Analysis was performed using the area under the receiver operating characteristic curve (AUC) on the test sets of the outer folds.

RESULTS

All investigated models predicted PTP better than random (AUC>.5) (Table 1). Dosiomics+Radiomics models based on EQD2 using rf classifier resulted in the highest predictive performance (AUC = .83 (95% Confidence Interval .83-.84)) and performed worse on physical dose data (AUC = .72 (.71-.73)). For single models, radiomics and dosiomics achieved the best prediction (AUC = .73 (.72-.74), AUC = .8 (.79-.81)) for physical dose and EQD2, respectively. Clinical factors and ICI therapy (AUC = .6 (.59-.62)) had minor impact on PTP prediction. Table 1: AUC and 95% confidence intervals (CI) for all investigated Machine Learning models for EQD2 and physical doses (D).

CONCLUSION

Dosiomics+Radiomics machine learning models have strong capability of PTP prediction and could contribute to pre-treatment decision making. Fractionation schemes should be considered for dose-based prediction strategies. Additional ICI therapy has limited impact on PTP prediction.

Contact of the Tumor with the Internal Mammary Perforator Vessels as Risk Factor for Internal Mammary Lymph Node Involvement Based on Dynamic Contrast Enhancing MRI Imaging in Breast Cancer Patients

PURPOSE/OBJECTIVE(S)

Distant metastasis free and overall survival of high-risk breast cancer patients can be improved with irradiation of the lymphatic system. However, inclusion of internal mammary region (IMN) markedly increases the dose to the heart. Hence, an estimation of the individual risk of subclinical involvement is necessary in order to balance the oncological benefit versus the cardiac toxicity. In randomized studies the risk stratification for IMN involvement is mainly based on the tumor location (medial, central vs. lateral). The aim of this study was to evaluate whether the contact of the tumor with the internal mammary perforator vessels (IMPV) is an additional risk factor for IMN involvement.

MATERIALS/METHODS

For this trial we retrospectively examined 104 sets of pre-treatment dynamic contrast enhanced magnetic resonance imaging (DE-MRI) scans of locally advanced breast cancer patients. All patients had ipsilateral clinical suspect lymph nodes in the axillary region and either positive (n = 52) or negative lymph nodes (n = 52) in the internal mammary region. Based on the DE-MRI we assessed the tumor location as well as contact to the internal mammary perforating vessels (IMPV). Contact between tumor and IMPV was classified into either predominant, minor or no contact. Criteria for a predominant IMPV contact was defined as: main vessel contact or contact to multiple (> = 5) side branches.

RESULTS

The tumor location of IMN+ patients were medial in 19.2% (10/52), central in 26.9% (14/52), lateral in 28.8% (15/52) and multicentric in 25.0% (13/52) of. In IMN- patients, tumor location was medial in 9.6% (5/52), central in 26.9% (14/52), lateral in 42.3% (22/52) and multicentric in 21.2% (11/52) in IMN- patients. The tumor size ranged from T1-T4 with most patients staged as T2 (48.1% (IMN+) vs. 38.5% IMN-). Most patients had hormone receptor positive / Her2neu negative disease (36.5% (IMN+) vs. 46.2% (IMN-). 100 % of tumors in IMN+ patients had contact with IMPV: in 94.2% (49/52) criteria for predominant IMPV contact was fulfilled; in the remaining 3 cases (5.8%) the tumor had minor IMPV contact. In IMN- patients however, 36/52 of cases (69.2%) had direct IMPV contact. Predominant contact was found in only 23.1% (12/52), minor IMPV contact in 46.2% (24/52).

CONCLUSION

Predominant contact of the tumor with IMPV appears to be a potential risk factor for IMN involvement in breast cancer patients and could be used for stratification for IMN-irradiation in future trials.

Experimental Investigation of Lung Toxicity after Radiation Therapy Combined with Immune Checkpoint Inhibitors

PURPOSE/OBJECTIVE(S)

The combination of radiation therapy (RT) with immune checkpoint inhibitors (ICIs) has resulted in prolonged survival in patients with locally advanced lung cancer (NSCLC). However, RT and ICIs carry the risk of inflammatory and irreversible lung damage and might have synergistic effects on these adverse events. Importantly, only little is known about the risk of enhanced side effects of the lung and which factors modulate such toxicity. In addition, there is a need for sensitive diagnostics for the early detection of lung injury after combined radioimmunotherapy. Recently, experimental x-ray dark-field radiography was able to detect radiation-induced lung injury earlier than conventional radiography in mice.

MATERIALS/METHODS

The right thorax of mice was irradiated with unfractionated RT (1x15 Gy or 1x30 Gy) or fractionated RT (5x9 Gy). In addition, indicated experimental groups received ICIs (a-PD1, a-CTLA4 or combination) for one month. After four months, the mice were analyzed using different methods to quantify lung damage: lung coefficient as surrogate marker for lung fibrosis, histopathological staining of fibrosis, conventional x-ray, and dark-field radiography.

RESULTS

We found enhanced signs of lung fibrosis (lung coefficient and histopathological score) after unfractionated RT in combination with ICIs. Surprisingly, combination of ICIs with RT resulted in opposite effects. Specifically, concomitant combination of ICIs with fractionated RT resulted in reduced lung coefficients and lower histopathological signs of lung fibrosis in mice treated in this way. Importantly, in vivo x-ray dark-field radiographs showed the same trend as the ex vivo assessment of the lungs.

CONCLUSION

To the best of our knowledge, this is the first experimental study to find that the combination of RT with ICIs has an impact on the risk of pulmonary fibrosis. Strikingly, ICIs (a-PD1 + a-CTLA4) combined with unfractionated RT resulted in increased lung damage, while concomitant use of ICIs (a-PD1 + a-CTLA4) with fractionated RT resulted in reduced lung toxicity. In the field of radioimmunotherapy, such studies are of great value for the interpretation of clinical studies and of importance for the design of further clinical trials.

Radiobiological Characterization of Pancreatic Cancer Patient-Derived Organoids

PURPOSE/OBJECTIVE(S)

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most aggressive and lethal tumors with a 5-year survival rate of less than 10%. Neoadjuvant radio(chemo)therapy aiming tumor downsizing fails in about 70% due to high heterogeneity, strong desmoplastic stroma and intrinsic radioresistance. In this project, pancreatic cancer patient-derived organoids (PDOs) are characterized regarding radioresponse, DNA-damage, proliferation and hypoxia, and clinical patients' outcome is correlated with the preclinical radiobiological data. In contrast to 2D monolayer cultures, PDOs maintain similar appearance, organization and functionality as the original tissue and therefore might have the potential as advanced preclinical model in radiation oncology.

MATERIALS/METHODS

The radiation response of nine different pancreatic cancer PDO lines was determined by 3D cell viability assay. PDOs were irradiated with 0, 2, 4, 6, and 8 Gy (CellRad, Precision, USA) 24h after seeding and the ATP-dependent viability assay was performed 72h and 7d after irradiation (RT). Changes in morphology, number, and size were investigated by microscopy at different time points after RT. PDOs were characterized immunohistochemically by y-H2AX (DNA damage), and Ki-67 (proliferation) staining. RNA sequencing data of treatment-naive PDOs were analyzed by gene set enrichment analyses (GSEA) regarding radioresistance. Preclinical results were correlated with corresponding clinical data of PDAC patients.

RESULTS

After optimization of the experimental set-up, PDOs showed a dose-dependent decrease in viability 7d after RT and heterogeneity in radioresponse. PDO lines were classified into radiosensitive, -intermediate, and -resistant subclasses. Immunohisto-chemical staining showed a significant increase in DNA double-strand breaks after RT. A correlation between radiosensitivity and enhanced proliferation index Ki67 was observed. Based on RNA sequencing data, OXPHOS- and hypoxia-dependent genes, amongst others, were identified as pathways significantly differentially regulated between the subclasses by GSEA. Preclinical radioresistance was associated with worse survival and poor clinical outcome.

CONCLUSION

The results of the preclinical experiments demonstrate the heterogeneity among PDOs in response to RT reflecting the clinical situation of patients with PDAC. The findings from the GSEA show promising aspects for further experiments to understand the role of hypoxia in PDAC and its effect on radioresistance. PDOs have the potential as a novel translational research platform in radiation oncology. Prospectively, we aim to implement the screening of the radiosensitivity of PDOs in clinical practice for the realization of truly personalized radiotherapy in PDAC patients.

Hypofractionated Stereotactic Radiotherapy vs. Single Fraction Stereotactic Radiosurgery to the Resection Cavity of Brain Metastases after Surgical Resection (SATURNUS trial): A Prospective, Randomized Phase III Trial

PURPOSE/OBJECTIVE(S)

The brain is a common site for metastases. Resection of large or symptomatic metastases is followed by stereotactic radiotherapy to prevent local recurrence. The optimal fractionation scheme is subject of ongoing research. Supported by emerging retrospective data, we hypothesize that hypofractionated stereotactic radiotherapy (HFSRT) is superior to single-fraction stereotactic radiosurgery (SRS) in terms of local control (LC). We designed the SATURNUS trial to prospectively demonstrate the superiority of HFSRT over SRS after resection of brain metastases in terms of LC.

MATERIALS/METHODS

The SATURNUS trial is a prospective, randomized phase III trial, currently recruiting patients at a single institution. Patients are 1:1 allocated to HFSRT or SRS using permuted block randomization. Affiliation to the treatment arm is solely blinded to the neuroradiologist assessing therapy response. HFSRT will be delivered with 6 - 7 x 5 Gy and SRS with 1 x 12-20 Gy, prescribed to the surrounding isodose, depending on cavity size and proximity to structures at risk. For SRS, doses do not exceed the maximum doses according to RTOG 90-05. Case number calculation was based on own institutional data on HFSRT (mean LC rate of 88% at 12 months) and data from large phase III trials on SRS (pooled mean LC rate of 66% at 12 months). Using a Chi-squared test of equal proportions (odds ratio = 1), setting test significance level (α) to 0.05, and allocating an equal number of patients to both treatment arms, 114 patients are needed to detect the superiority of HFSRT in terms of LC at 12 months (primary endpoint) with a power of at least 80%. Estimating a dropout rate of 10%, the case number was set to 126. The trial was registered with clinicaltrials.gov (NCT05160818). The first patient was enrolled in May 2021 and recruitment is ongoing. Patients with up to three resected brain metastases are considered for study participation. Further eligibility criteria are histologically confirmed solid tumor disease, resection cavity diameter ≤ 4 cm, consent to perform adjuvant radiotherapy by an interdisciplinary tumor board, completed wound healing, resection within the last six weeks at the time of study inclusion, age ≥ 18 years, KPS ≥ 60%, adequate contraceptive measures for fertile women / men and written informed consent. Patients are followed up clinically and with MRI at 6 weeks and 3, 6, 9 and 12 months after treatment. LC is assessed according to RANO-BM. Toxicity (CTCAE v4.03) is assessed as a secondary endpoint. The rather broad dose corridors allowed within the trial do justice to clinical reality, however, may represent a limitation of the trial. They are therefore addressed with a predefined subgroup analysis, as will be cavity size, among others. Participation of further study centers is desired. To the best of our knowledge, the SATURNUS trial is the only randomized phase III trial adequately powered to detect the superiority of HFSRT over SRS with regard to LC for resected brain metastases.

RESULTS

To be determined.

CONCLUSION

To be determined.

Towards Clinical Translation of Microbeam Radiation Therapy (MRT) with a Compact Source

PURPOSE/OBJECTIVE(S)

MRT is an innovative concept of spatially fractionated radiation therapy that has demonstrated substantially improved normal tissue tolerance while achieving local tumor control in a wealth of preclinical studies. In MRT a collimator shapes a few micrometers wide planar x-ray beams with a spacing of a few 100 µm. MRT has the potential to improve cancer treatment substantially. However, until now, only a few large 3rd generation synchrotrons provide beam parameters that would allow patient treatments and therefore, MRT has not yet become clinically available. For a clinical translation, compact x-ray sources are required, that produce high dose rate orthovoltage x-rays from a micrometer sized emitter.

MATERIALS/METHODS

We developed and built a first prototype of a line focus x-ray tube (LFxT) dedicated to preclinical MRT research. By exploiting the heat capacity limit, the LFxT can deliver dose rates above 100 Gy/s from a just 50 µm-wide focal spot without destroying the rapidly (>200 Hz) rotating x-ray target. A bespoke collimator splits the homogeneous x-ray field into 50 µm wide high-dose peaks separated by 350 µm wide low-dose troughs (valleys). While the prototype in our lab is restricted to a power of 90 kW and 10 Gy/s at 300 kVp, we have started the development of the first clinically usable LFxT-2 at 1.5 MW power and >100 Gy/s at 600 kVp beam quality. We investigated the clinical applicability of the LFxT-2 by performing retrospective treatment planning studies. In particular, we were examining, whether 600 kVp photons would suffice to meet clinical dose constraints in MRT treatments treatment scenarios for first clinical use of MRT. We coupled the open source platform 3D Slicer with an in-house developed dose calculation algorithm for MRT treatment planning. For comparability of spatially fractionated MRT doses with conventional broad beam treatments, the MRT dose was converted to equivalent uniform dose (EUD) and equivalent doses in 2-Gy-fractions (EQD2). The 3D Slicer RT toolkit enabled the dosimetric analysis based on dose volume histograms (DVHs).

RESULTS

We installed a preclinical prototype of the LFxT that is currently put into operation and commissioned. Simulations show the feasibility of the next generation LFxT-2 with more than 100 Gy/s peak dose rate. Planned MRT dose distributions with the LFxT-2 meet established radiotherapy dose constraints in many of the investigated clinical cases. However, treatment planning procedures are not yet optimal and require improvement.

CONCLUSION

In a next step, we will build the LFxT-2 and aim for first clinical MRT trials at this source. In order to further improve calculated MRT dose distributions, we will implement inverse treatment planning techniques.

Post-Operative Stereotactic Radiotherapy for Resected Brain Metastases: Results of the Multicenter Analysis (AURORA) of the German Working Group "Stereotactic Radiotherapy"

PURPOSE/OBJECTIVE(S)

While the results of prospective studies support the use of postoperative stereotactic radiotherapy (RT) to the resection cavity (RC) as the standard of care after surgery, there are several issues that need to be investigated such as factors for improving local control, risk of leptomeningeal disease and radiation necrosis. Further, the optimal dose and fractionation is still under debate.

MATERIALS/METHODS

The working group "Stereotactic Radiotherapy" of the German Society of Radiation Oncology (DEGRO) analyzed its multi-institutional database with 661 patients who received postoperative stereotactic RT to the RC. Treatment was performed at 13 centers between 2008 and 2021. Patient characteristics, treatment details, and follow-up data including overall survival (OS), local control (LC) were evaluated. Cox Regression and Kaplan-Meier curves with Log-rank Tests were calculated for selected variables.

RESULTS

In this retrospective study, overall survival was 61.5% at 1 year, 47.6% at 2 years, and 35.5% at 3 years, and local control was 84.6% at 1 year, 74.8% at 2 years, and 72.8% at 3 years. 96% of patients were treated with hypofractionated stereotactic radiotherapy (HSRT), only 26 patients received single fraction radiosurgery (4%). Prognostic factors associated with overall survival were Karnofsky Performance Status, RPA and GPA class, controlled primary tumor and absence of extracranial metastases, whereas prognostic factor associated with local control was planning target volume (23 mL or less).

CONCLUSION

HSRT is the most common fractionation form in the treatment of RCs in this multicenter analysis. This approach results in excellent OS and LC outcomes. OS in patients with resected brain metastases is mainly influenced by performance status. In regard to local control, RT of large cavities remain a challenge with significantly worse outcome.

Equivalent Uniform Dose (EUD) and the Evaluation of Cell Survival in Spatially Fractionated Radiotherapy (SFRT)

PURPOSE/OBJECTIVE(S)

SFRT has shown promise as a treatment modality to decrease normal tissue sparing without compromising tumor coverage, i.e., an increase in the therapeutic window compared to more conventional uniform radiation therapy (RT). The aim of this work is to examine and test several alternative bio-dosimetric parameters for the prediction of cell survival for normal-tissue and tumor cell lines irradiated in vitro with uniform and microbeam radiotherapy (MRT).

MATERIALS/METHODS

A bespoke tungsten collimator with 50 parallel, 50 µm wide slits and 400 µm slit spacing was mounted into an x-ray cabinet. Human fibroblast (MRC5) and two human tumor cell lines (LN18 and A549) were irradiated with a range of doses (< 10 Gy) for uniform and MRT (50um slits, 400um center spacing) using kV X-rays. Average, mean and valley dose as useful predictive metrics of cell survival are compared to the equivalent uniform dose (EUD) with biological parameters estimated from uniform-dose experiments.

RESULTS

We find that EUD, with linear-quadratic (LQ) model parameters, is more predictive for survival after SFRT than maximum, minimum or average dose. The maximum and average doses are correlated very poorly with in vitro cell survival. The difference in cell survival between uniform and MRT irradiation as a function of EUD is cell-type and dose dependent. The report results suggest that MRT is more effective at cell killing of tumor-cell lines than uniform irradiation for both tumor cell lines. However, MRT is less effective at killing normal tissue cells than uniform irradiation.

CONCLUSION

EUD is a superior predictor of in vitro cell survival than other metrics sometimes used in the SFRT literature, including mean dose, maximum dose, and valley dose. The reported studies provide some evidence that SFRT may increase the therapeutic ratio by producing spatial dose distributions that effectively reduce normal-tissue damage with little or no change in biological damage to tumor cells. Additional studies are needed to further extend and generalize our results and to test our conclusions against a larger dose range, low and high linear energy transfer (LET) radiations and additional cell lines.

Regional nodal irradiation in breast cancer patients: Effects of deep inspiration breath hold on the internal mammary chain location

The purpose of this study was to investigate the impact of deep inspiration breath hold (DIBH) on the positioning of thoracic structures and provide treatment planning recommendations for internal mammary chain (IMC) irradiation in breast cancer patients. Thirty-two breast cancer patients from our database underwent both DIBH and free breathing (FB) treatment planning. Contouring of the axillary lymph node clinical target volumes (CTVs: level I, II, III, IV, and IMC according to ESTRO), the internal mammary artery (IMA), the heart, and the left anterior descending artery (LAD) was performed. The following were then analyzed: the distance between the IMA and the heart, the craniocaudal distance in which IMC-CTV and heart coexist, the craniocaudal distance between the lower end of the of level III and IV and the upper end of the heart. Several significant geometric differences were observed between DIBH and FB that explain the efficacy of the DIBH for regional nodal irradiation. In >80% of patients the cranial origin of the LAD lies below the lower edge of the IMC-CTV in DIBH. In addition the slices in which the heart/LAD and IMC-CTV coexist decrease during DIBH. The IMA-heart distance is significantly larger in DIBH. Also the craniocaudal distance between the lower border of the CTV level III and IV and the upper border of the heart is larger in DIBH. The observed mechanisms during DIBH contribute significantly to the dose reduction in regional nodal irradiation. To further enhance the benefits of DIBH for the irradiation of the IMC-CTV, it is recommended to implement steep dose gradients in the caudal plane.

Dosiomics and radiomics to predict pneumonitis after thoracic stereotactic body radiotherapy and immune checkpoint inhibition

Introduction

Pneumonitis is a relevant side effect after radiotherapy (RT) and immunotherapy with checkpoint inhibitors (ICIs). Since the effect is radiation dose dependent, the risk increases for high fractional doses as applied for stereotactic body radiation therapy (SBRT) and might even be enhanced for the combination of SBRT with ICI therapy. Hence, patient individual pre-treatment prediction of post-treatment pneumonitis (PTP) might be able to support clinical decision making. Dosimetric factors, however, use limited information and, thus, cannot exploit the full potential of pneumonitis prediction.

Methods

We investigated dosiomics and radiomics model based approaches for PTP prediction after thoracic SBRT with and without ICI therapy. To overcome potential influences of different fractionation schemes, we converted physical doses to 2 Gy equivalent doses (EQD2) and compared both results. In total, four single feature models (dosiomics, radiomics, dosimetric, clinical factors) were tested and five combinations of those (dosimetric+clinical factors, dosiomics+radiomics, dosiomics+dosimetric+clinical factors, radiomics+dosimetric+clinical factors, radiomics+dosiomics+dosimetric+clinical factors). After feature extraction, a feature reduction was performed using pearson intercorrelation coefficient and the Boruta algorithm within 1000-fold bootstrapping runs. Four different machine learning models and the combination of those were trained and tested within 100 iterations of 5-fold nested cross validation.

Results

Results were analysed using the area under the receiver operating characteristic curve (AUC). We found the combination of dosiomics and radiomics features to outperform all other models with AUCradiomics+dosiomics, D = 0.79 (95% confidence interval 0.78-0.80) and AUCradiomics+dosiomics, EQD2 = 0.77 (0.76-0.78) for physical dose and EQD2, respectively. ICI therapy did not impact the prediction result (AUC ≤ 0.5). Clinical and dosimetric features for the total lung did not improve the prediction outcome.

Conclusion

Our results suggest that combined dosiomics and radiomics analysis can improve PTP prediction in patients treated with lung SBRT. We conclude that pre-treatment prediction could support clinical decision making on an individual patient basis with or without ICI therapy.

Influence of radiotherapy on cardiac implantable device lead parameters

Purpose

Incidences of both cardiac implantable electronic devices (CIED) and malignant tumors are rising, likewise the number of patients undergoing radiotherapy (RT) while having CIED increases. There is evidence that there is a higher failure rate with increasing cumulative dose at device and higher – neutron-inducing – photon beam energy above 10 MV. There is a paucity of data regarding lead function, lead insertion site dose and analysis of change of lead parameter during RT treatment. Aim of this work is a detailed analysis of CIED malfunctions and technical alterations in patients treated at our clinic with a special focus on device lead parameters.

Methods

In a total of 54 patients treated at our department, we evaluated the dose statistics for the leads and devices as well as lead parameters aggregated through telemetric device interrogations. Irradiation mostly took place in the thoracic (32%), pelvic (24%) and the head region (22%). A total of 80% of all patients had implanted a pacemaker and 17% an implantable cardioverter defibrillator. Two Patients (4%) were under cardiac resynchronization therapy. Overall 33% of patients were device-dependent.

Dose statistics for myocardial lead insertion sites and CIED were calculated. We collected interrogation data (intrinsic pacing impedance, pacing threshold, signal amplitude) before and after RT treatment (median number of interrogations was 3, range 1–22) and information about any CIED malfunction.

We assessed whether lead parameters changes exceeded predefined thresholds of 30% in pacing impedance, 50% in pacing threshold, or 50% in signal amplitude.

Results

24 of the 54 patients received a measurable dose at the device (median dose of patients with thoracic RT: 1.82 Gy, range 0.18–14.88 Gy). Dose data was available for atrial leads of 12 patients (median dose 7.27 Gy, ranging from barely measurable to 46.02 Gy) and right-ventricular leads of 13 patients (median dose 0.83 Gy, range 0.004–42.66 Gy).

There was no lead parameter threshold violation for pacing impedance detected, however predefined thresholds of signal amplitude and pacing threshold were exceeded in 14% and 15% of cases, respectively. These threshold violations did not compromise device function. There was no significant difference of lead parameter changes when patient groups receiving more and less than 10 Gy at lead insertion site were compared.

Two CIEDs (4%) showed a malfunction (electric restart of device) during RT, however no clinically relevant complication was reported. Both patients underwent thoracic RT (esophageal cancer) with a beam energy of 10 and 15 MV.

Conclusion

In the observed patient group, lead parameter threshold violation was neither able to predict a device malfunction nor dependent of cumulative dose at myocardial insertion side. Device malfunction occurred rarely and only at higher beam energies, however with no life-threatening outcome.

Funding Acknowledgement

Type of funding sources: None.

P11.22.A Prognostic and predictive relevance of immunohistochemically determined p53 mutation in glioblastoma

Background

It can be expected that molecular biomarkers will increasingly affect clinical decisions and lead to the development of more personalized therapies in glioblastoma (GBM) in the future. In several other tumor entities TP53 gene mutation or p53 immunoreactivity (IR) serve as a prognostic marker, significantly affecting overall survival (OS) and progression-free survival (PFS). Such an association has not yet sufficiently been demonstrated in GBM. However, there are known prognostic markers in GBM, notably MGMT promotor methylation (mMGMT) which also serves as an important predictive marker leading to a better response to temozolomide chemotherapy. Our aim was to evaluate retrospectively if p53 mutation determined via immunohistochemistry (IHC) could act as a prognostic or predictive marker in GBM.

Material and Methods

Tumor samples of 195 treatment-naïve patients with IDHwt GBM that had been stained with the p53 antibody DO-7 were subdivided into 2 different groups by p53 IHC. Samples were considered as p53mut when strong p53 IR was detected in ≥10% of all tumor cells and as p53wt when in &lt;10%. Treatment, further molecular and survival data were gathered retrospectively for all patients. Statistical analyses were performed with SPSS.

Results

The frequency of p53mut was 36.4% (71/195). p53mut tumors showed a significantly higher IR with Ki-67 proliferation marker (p=0.005) and p53wt seemed to be associated with multifocal primary tumor localization, though not statistically significant (p=0.107). There was no significant difference between p53wt and p53mut regarding gender, age, extent of resection, adjuvant therapy, occurrence of seizures, mMGMT or ATRX loss. The p53 status was not associated with OS or PFS. Factors that univariately led to significantly longer OS and PFS were younger age, unilateral or unifocal primary tumor localization, gross-total resection, higher Karnofsky Performance Status (KPS), mMGMT and adjuvant treatment via Stupp regimen instead of radiotherapy alone, the latter being significantly better than best supportive care. In multivariate survival analyses only age &lt;65 years, the Stupp regimen more than radiotherapy alone and KPS ≥80% significantly prolonged both OS and PFS. Unifocal primary tumor localization led to longer OS and mMGMT led to longer PFS independently. The p53 status did not significantly affect the response to different adjuvant therapy regimens neither concerning OS nor PFS.

Conclusion

Based on our study, p53 IR has no prognostic or predictive significance in IDHwt GBM. There have been previous studies with similar and others with contradicting results. Remarkable is the discordance of the used IR thresholds between different studies. Further studies should aim to revalidate the staining threshold and improve the concordance between TP53 gene sequencing and p53 IHC in IDHwt GBM.

Dual energy CT for a small animal radiation research platform using an empirical dual energy calibration

Objective. Dual energy computed tomography (DECT) has been shown to provide additional image information compared to conventional CT and has been used in clinical routine for several years. The objective of this work is to present a DECT implementation for a Small Animal Radiation Research Platform (SARRP) and to verify it with a quantitative analysis of a material phantom and a qualitative analysis with an ex-vivo mouse measurement. Approach. For dual energy imaging, two different spectra are required, but commercial small animal irradiators are usually not optimized for DECT. We present a method that enables dual energy imaging on a SARRP with sequential scanning and an Empirical Dual Energy Calibration (EDEC). EDEC does not require the exact knowledge of spectra and attenuation coefficients; instead, it is based on a calibration. Due to the SARRP geometry and reconstruction algorithm, the calibration is done using an artificial CT image based on measured values. The calibration yields coefficients to convert the measured images into material decomposed images. Main results. To analyze the method quantitatively, the electron density and the effective atomic number of a material phantom were calculated and compared with theoretical values. The electron density showed a maximum deviation from the theoretical values of less than 5% and the atomic number of slightly more than 6%. For use in mice, DECT is particularly useful in distinguishing iodine contrast agent from bone. A material decomposition of an ex-vivo mouse with iodine contrast agent was material decomposed to show that bone and iodine can be distinguished and iodine-corrected images can be calculated. Significance. DECT is capable of calculating electron density images and effective atomic number images, which are appropriate parameters for quantitative analysis. Furthermore, virtual monochromatic images can be obtained for a better differentiation of materials, especially bone and iodine contrast agent.

Treatment Planning Study for Microbeam Radiotherapy Using Clinical Patient Data

Microbeam radiotherapy (MRT) is a novel, still preclinical dose delivery technique. MRT has shown reduced normal tissue effects at equal tumor control rates compared to conventional radiotherapy. Treatment planning studies are required to permit clinical application. The aim of this study was to establish a dose comparison between MRT and conventional radiotherapy and to identify suitable clinical scenarios for future applications of MRT. We simulated MRT treatment scenarios for clinical patient data using an inhouse developed planning algorithm based on a hybrid Monte Carlo dose calculation and implemented the concept of equivalent uniform dose (EUD) for MRT dose evaluation. The investigated clinical scenarios comprised fractionated radiotherapy of a glioblastoma resection cavity, a lung stereotactic body radiotherapy (SBRT), palliative bone metastasis irradiation, brain metastasis radiosurgery and hypofractionated breast cancer radiotherapy. Clinically acceptable treatment plans were achieved for most analyzed parameters. Lung SBRT seemed the most challenging treatment scenario. Major limitations comprised treatment plan optimization and dose calculation considering the tissue microstructure. This study presents an important step of the development towards clinical MRT. For clinical treatment scenarios using a sophisticated dose comparison concept based on EUD and EQD2, we demonstrated the capability of MRT to achieve clinically acceptable dose distributions.

Integration of radiation oncology teaching in medical studies by German medical faculties due to the new licensing regulations : An overview and recommendations of the consortium academic radiation oncology of the German Society for Radiation Oncology (DEGRO)

The new Medical Licensing Regulations 2025 (Ärztliche Approbationsordnung, ÄApprO) will soon be passed by the Federal Council (Bundesrat) and will be implemented step by step by the individual faculties in the coming months. The further development of medical studies essentially involves an orientation from fact-based to competence-based learning and focuses on practical, longitudinal and interdisciplinary training. Radiation oncology and radiation therapy are important components of therapeutic oncology and are of great importance for public health, both clinically and epidemiologically, and therefore should be given appropriate attention in medical education. This report is based on a recent survey on the current state of radiation therapy teaching at university hospitals in Germany as well as the contents of the National Competence Based Learning Objectives Catalogue for Medicine 2.0 (Nationaler Kompetenzbasierter Lernzielkatalog Medizin 2.0, NKLM) and the closely related Subject Catalogue (Gegenstandskatalog, GK) of the Institute for Medical and Pharmaceutical Examination Questions (Institut für Medizinische und Pharmazeutische Prüfungsfragen, IMPP). The current recommendations of the German Society for Radiation Oncology (Deutsche Gesellschaft für Radioonkologie, DEGRO) regarding topics, scope and rationale for the establishment of radiation oncology teaching at the respective faculties are also included.

Outcomes after stereotactic radiosurgery of brain metastases in patients with malignant melanoma and validation of the melanoma molGPA

INTRODUCTION

Malignant melanoma is the third most common primary in the diagnosis of brain metastases. Stereotactic radiosurgery (SRS) is a well-established treatment option in limited brain disease. We analyzed outcomes of SRS with a particular focus on the graded prognostic assessment (GPA, melanoma molGPA), prognostic factors, and toxicity.

METHODS

We evaluated 173 brain metastases in 83 patients with malignant melanoma. All were treated with SRS median dose of 20 Gy prescribed to the 80 or 100% isodose line between 2002 and 2019. All patients were followed-up regularly, including contrast-enhanced brain imaging as well as clinical examination, initially 6 weeks after treatment, then in quarterly follow-up.

RESULTS

The median age was 61 years (range 27-80); 36 female and 47 male patients were treated. After a median follow-up of 5.7 months, median OS (overall survival) was 9.7 months 95%-KI 4.7-14.7). LC (local control) at 6 months, 12, 24 months was 89%, 86%, and 72%, respectively (median was not reached). Median DBC (distant brain control) was 8.2 months (95%-KI 4.7-11.7). For OS, a KPS ≥ 80%, a positive BRAF mutation status, a small PTV (planning target volume), the absence of extracranial metastases, as well as a GPA and melanoma molGPA > 2 were prognostic factors. In the MVA, a small PTV and a melanoma molGPA > 2 remained significant.

CONCLUSION

The present survival outcomes support the use of the disease-specific melanoma molGPA as reliable prognostic score. Favorable outcomes for SRS compared to other studies were observed. In the treatment of brain metastases of malignant melanoma patients, a multidisciplinary approach consisting of surgery, SRS, chemotherapy, and immunotherapy should be considered.

Patient individual phase gating for stereotactic radiation therapy of early stage non-small cell lung cancer (NSCLC)

Stereotactic body radiotherapy (SBRT) applies high doses and requires advanced techniques to spare surrounding tissue in the presence of organ motion. In this work patient individual phase gating is investigated. We studied peripheral and central primary lung tumors. The internal target volume (ITV) was defined including different numbers of phases picked from a 4D Computed tomography (CT) defining the gating window (gw). Planning target volume (PTV) reductions depending on the gw were analyzed. A treatment plan was calculated on a reference phase CT (rCT) and the dose for each breathing phase was calculated and accumulated on the rCT. We compared the dosimetric results with the dose calculated when all breathing phases were included for ITV definition. GWs including 1 to 10 breathing phases were analyzed. We found PTV reductions up to 38.4%. The mean reduction of the lung volume receiving 20 Gy due to gating was found to be 25.7% for peripheral tumors and 16.7% for central tumors. Gating considerably reduced esophageal doses. However, we found that simple reduction of the gw does not necessarily influence the dose in a clinically relevant range. Thus, we suggest a patient individual definition of the breathing phases included within the gw.

An easy way to determine bone mineral density and predict pelvic insufficiency fractures in patients treated with radiotherapy for cervical cancer

Purpose

The aim of this study was to investigate whether bone mineral density (BMD) as measured in planning computed tomographies (CTs) by a new method is a risk factor for pelvic insufficiency fractures (PIF) after radio(chemo)therapy (R(C)T) for cervical cancer.

Methods

62 patients with cervical cancer who received definitive or adjuvant radio(chemo)therapy between 2013 and 2017 were reviewed. The PIF were detected on follow-up magntic resonance imaging (MRI). The MRI of the PIF patients was registered to the planning CT and the PIF contoured. On the contralateral side of the fracture, a mirrored structure of the fracture was generated (mPIF). For the whole sacral bone, three lumbar vertebrae, the first and second sacral vertebrae, and the PIF, we analyzed the BMD (mg/cm³), V50Gy, Dmean, and Dmax.

Results

Out of 62 patients, 6 (9.7%) had a fracture. Two out of the 6 patients had a bilateral fracture with only one of them being symptomatic. PIF patients showed a significantly lower BMD in the sacral and the lumbar vertebrae (p < 0.05). The BMD of the contoured PIF, however, when comparing to the mPIF, did not reach significance (p < 0.49). The difference of the V50Gy of the sacrum in the PIF group compared to the other (OTH) patients, i.e. those without PIF, did not reach significance.

Conclusion

The dose does not seem to have a relevant impact on the incidence of PIF in our patients. One of the predisposing factors for developing PIF after radiotherapy seems to be the low BMD. We presented an easy method to assess the BMD in planning CTs.

Toxicity of internal mammary irradiation in breast cancer. Are concerns still justified in times of modern treatment techniques?

BACKGROUND

The purpose of this study was to estimate the additional risk of side effects attributed to internal mammary node irradiation (IMNI) as part of regional lymph node irradiation (RNI) in breast cancer patients and to compare it with estimated overall survival (OS) benefit from IMNI.

MATERIAL AND METHODS

Treatment plans (n = 80) with volumetric modulated arc therapy (VMAT) were calculated for 20 patients (4 plans per patient) with left-sided breast cancer from the prospective GATTUM trial in free breathing (FB) and in deep inspiration breath hold (DIBH). We assessed doses to organs at risk ((OARs) lung, contralateral breast and heart) during RNI with and without additional IMNI. Based on the OAR doses, the additional absolute risks of 10-year cardiac mortality, pneumonitis, and secondary lung and breast cancer were estimated using normal tissue complication probability (NTCP) and risk models assuming different age and risk levels.

RESULTS

IMNI notably increased the mean OAR doses. The mean heart dose increased upon IMNI by 0.2-3.4 Gy (median: 1.9 Gy) in FB and 0.0-1.5 Gy (median 0.4 Gy) in DIBH. However, the estimated absolute additional 10-year cardiac mortality caused by IMNI was <0.5% for all patients studied except 70-year-old high risk patients (0.2-2.4% in FB and 0.0-1.1% in DIBH). In comparison to this, the published oncological benefit of IMNI ranges between 3.3% and 4.7%. The estimated additional 10-year risk of secondary cancer of the lung or contralateral breast ranged from 0-1.5% and 0-2.8%, respectively, depending on age and risk levels. IMNI increased the pneumonitis risk in all groups (0-2.2%).

CONCLUSION

According to our analyses, the published oncological benefit of IMNI outweighs the estimated risk of cardiac mortality even in case of (e.g., cardiac) risk factors during VMAT. The estimated risk of secondary cancer or pneumonitis attributed to IMNI is low. DIBH reduces the estimated additional risk of IMNI even further and should be strongly considered especially in patients with a high baseline risk.

Hypo- vs. normofractionated radiation therapy in breast cancer: A patterns of care analysis in German speaking countries

Aim and background

To assess the use of hypofractionated (HG-RT) versus normofractionated radiation therapy (NF-RT) in Breast Cancer in German speaking countries.

Materials and methods

Between July 2017 and August 2017, an email-based survey was sent to all 1408 physicians that are members of the German Society of Radiation Oncology (DEGRO). The survey was completed by 180 physicians including 10 private practice owners and 52 heads of departments. The majority (82.1%) of the participants had >15 years of experience in radiation therapy (RT).

Results

The majority (83.9%) of the heads of the departments agreed on using the normofractionated regimen of RT as standard treatment for breast cancer. Several physicians were skeptical about HF-RT with 6.5% of the heads refusing to use HF-RT. 40.3% of the departments had not seen the new German guidelines suggesting HF-RT as the standard treatment for all patients as positive or merely adopted a neutral position toward the guidelines (33.9%). The main points of criticism were increased side effects, an impaired toxicity profile and insufficient data. Most departments (46.8%) that perform HF-RT do so in an individual based manner.

Conclusions

HF-RT remains controversial in German speaking countries. Our data shows that NF-RT remains the predominant method of treatment. HF-RT is only used in a defined group of patients as most German physicians agree that particular patients, especially those at higher risk of RT late effects, may benefit from a less intense, extended fractionation schedule.

Influence of localization of PSMA-positive oligo-metastases on efficacy of metastasis-directed external-beam radiotherapy-a multicenter retrospective study

PURPOSE

Approximately 40-70% of biochemically persistent or recurrent prostate cancer (PCa) patients after radical prostatectomy (RPE) are oligo-metastatic in ⁶⁸gallium-prostate-specific membrane antigen positron emission tomography (⁶⁸Ga-PSMA PET). Those lesions are frequently located outside the prostate bed, and therefore not cured by the current standards of care like external-beam radiotherapy (EBRT) of the prostatic fossa. This retrospective study analyzes the influence of oligo-metastases' site on outcome after metastasis-directed radiotherapy (MDR).

METHODS

Retrospectively, 359 patients with PET-positive PCa recurrences after RPE were analyzed. Biochemical recurrence-free survival (BRFS) (prostate-specific antigen (PSA) < post-radiotherapy nadir + 0.2 ng/mL) was assessed using Kaplan-Meier survival and Cox regression analysis.

RESULTS

All patients were initially clinically without distant metastases (cM0). Seventy-five patients had local recurrence within the prostatic fossa, 32 patients had pelvic nodal plus local recurrence, 117 patients had pelvic nodal recurrence, 51 patients had paraaortic lymph node metastases with/without locoregional recurrence, and 84 patients had bone or visceral metastases with/without locoregional recurrence. Median PSA before MDR was 1.2 ng/mL (range, 0.04-47.5). Additive androgen deprivation therapy (ADT) was given in 35% (125/359) of patients. Median PSA nadir after MDR was 0.23 ng/mL (range, < 0.03-18.30). After a median follow-up of 16 months (1-57), 239/351 (68%) patients had no biochemical recurrence. Patients with distant lymph node and/or distant metastases, the so-called oligo-body cohort, had an overall in-field control of 90/98 (91%) but at the same time, an ex-field progress of 44/96 (46%). In comparison, an ex-field progress was detected in 28/154 (18%) patients with local and/or pelvic nodal recurrence (oligo-pelvis group). Compared with the oligo-pelvis group, there was a significantly lower BRFS in oligo-body patients at the last follow-up.

CONCLUSION

Overall, BRFS was dependent on patterns of metastatic disease. Thus, MDR of PSMA PET-positive oligo-metastases can be offered considering that about one-third of the patients progressed within a median follow-up of 16 months.

MRI based neuroanatomical segmentation in breast cancer patients: leptomeningeal carcinomatosis vs. oligometastatic brain disease vs. multimetastastic brain disease

Purpose

Pathogenesis of brain metastases/meningeal cancer and the emotional and neurological outcomes are not yet well understood. The hypothesis of our study is that patients with leptomeningeal cancer show volumetric differences in brain substructures compared to patients with cerebral metastases.

Methods

Three groups consisting of female breast cancer patients prior to brain radiotherapy were compared. Leptomeningeal cancer patients (LMC Group), oligometastatic patients (1–3 brain metastases) prior to radiosurgery (OMRS Group) and patients prior to whole brain radiation (WB Group) were included. All patients had MRI imaging before treatment. T1 MRI sequences were segmented using automatic segmentation. For each patient, 14 bilateral and 11 central/median subcortical structures were tested. Overall 1127 structures were analyzed and compared between groups using age matched two-sided t-tests.

Results

The average age of patients in the OMRS group was 60.8 years (± 14.7), 65.3 (± 10.3) in the LMC group and 62.6 (± 10.2) in the WB group. LMC patients showed a significantly larger fourth ventricle compared to OMRS (p = 0.001) and WB (p = 0.003). The central corpus callosum appeared smaller in the LMC group (LMC vs OMRS p = 0.01; LMC vs WB p = 0.026). The right amygdala in the WB group appeared larger compared with the OMRS (p = 0.035).

Conclusions

Differences in the size of brain substructures of the three groups were found. The results appear promising and should be taken into account for further prospective studies also involving healthy controls. The volumetrically determined size of the fourth ventricle might be a helpful diagnostic marker in the future.

Irradiation of regional lymph node areas in breast cancer - Dose evaluation according to the Z0011, AMAROS, EORTC 10981-22023 and MA-20 field design

OBJECTIVE

The purpose of this study was to estimate the dose distribution from randomized trials (MA.20, EORTC 22922-10925 (EORTC), AMAROS and the Z0011 trial) on lymph node (LN) irradiation on a large LN atlas.

METHODS

580 F¹⁸-FDG-PET/CT positive LN metastases of 235 patients were transferred rigidly and non-rigidly to three "template CTs" (standard, obese and slender patient). Further, the LN clinical target volumes (CTVs) were contoured according to the ESTRO-guidelines. Treatment plans were designed (each for the left and right side) for all patients based on the study protocols of the MA.20, EORTC, AMAROS and Z0011 trial. Subsequently, the dose distribution in the ESTRO-CTVs and in the 580 LNs were assessed.

RESULTS

Our results reveal variable dose coverage (26.8 ± 17.3 Gy-53.0 ± 1.8 Gy) in the targeted LN areas (ESTRO-CTV and LN) in dependence of the treatment planning design and the patients' body shape. None of the treatment plan designs provided full dose coverage to the lymphatic drainage system. High tangent irradiation resulted in a similar dose distribution in L I and II compared to the AMAROS field design.

CONCLUSION

Inclusion of the entire lymphatic system may not be necessary for all patients to reproduce the oncologic benefit shown in the randomized LN-irradiation trials. Inclusion of axillary level II and extension of the supraclavicular CTV can be considered in selected high-risk patients, based on dose recalculation of the MA.20 trial. Further, our results amplify earlier assumptions that irradiation may have accounted for the good results after SLND alone in the Z0011 trial.

Outcomes of immediate oncoplastic surgery and adjuvant radiotherapy in breast cancer patients

BACKGROUND

Oncoplastic surgery techniques lead to a rearrangement of the breast tissue and impede target definition during adjuvant radiotherapy (RT). The aim of this study was to assess local control rates after immediate oncoplastic surgery and adjuvant RT.

METHODS

This study comprises 965 patients who underwent breast-conserving therapy and adjuvant RT between 01/2000 and 12/2005. 288 patients received immediate oncoplastic surgery (ONC) and 677 patients breast-conserving surgery only (NONC). All patients were treated with adjuvant external tangential-beam RT (total dose: 50/50.4 Gy; fraction dose 1.8/2.0 Gy). An additional boost dose of 10-16 Gy to the primary tumor bed was given in 900 cases (93.3%). Local control rates (LCR), Progression free survival (PFS) and overall survival (OS) were assessed retrospectively after a median follow-up period of 67 (Q25-Q75: 51-84) months.

RESULTS

No significant difference was found between ONC and NONC in regard to LCR (5-yr: ONC 96.8% vs. NONC 95.3%; p = 0.25). This held also true for PFS (5-yr: ONC 92.1% vs. NONC 89.3%; p = 0.09) and OS (5-yr: ONC 96.0% vs. NONC 94.8%; p = 0.53). On univariate analyses G2-3 (p = 0.04), a younger age (p = 0.01), T-stage (p < 0.01) lymph node involvement (p < 0.01) as well as triple negative tumors (p < 0.01) were identified as risk factors for local recurrence. In a propensity score stratified Cox-regression model no significant impact of oncoplastic surgery on local control rate was found (HR: 2.05, 95% CI [0.93; 4.51], p = 0.08).

CONCLUSION

Immediate oncoplastic surgery seems not to affect the effectiveness of adjuvant whole breast RT on local control rates in breast cancer patients.

Incidental dose distribution to locoregional lymph nodes of breast cancer patients undergoing adjuvant radiotherapy with tomotherapy - is it time to adjust current contouring guidelines to the radiation technique?

Purpose/objective(s)

Along with breast-conserving surgery (BCS), adjuvant radiotherapy (RT) of patients with early breast cancer plays a crucial role in the oncologic treatment concept. Conventionally, irradiation is carried out with the aid of tangentially arranged fields. However, more modern and more complex radiation techniques such as IMRT (intensity-modulated radio therapy) are used more frequently, as they improve dose conformity and homogeneity and, in some cases, achieve better protection of adjacent risk factors. The use of this technique has implications for the incidental- and thus unintended- irradiation of adjacent loco regional lymph drainage in axillary lymph node levels I-III and internal mammary lymph nodes (IMLNs). A comparison of a homogeneous “real-life” patient collective, treated with helical tomotherapy (TT), patients treated with 3D conformal RT conventional tangentially arranged fields (3DCRT) and deep inspiration breath hold (3DCRT-DIBH), was conducted.

Materials/methods

This study included 90 treatment plans after BCS, irradiated in our clinic from January 2012 to August 2016 with TT (n = 30) and 3D-CRT (n = 30), 3DCRT DIBH (n = 30). PTVs were contoured at different time points by different radiation oncologists (> 7). TT was performed with a total dose of 50.4 Gy and a single dose of 1.8 Gy with a simultaneous integrated boost (SIB) to the tumor cavity (TT group). Patients irradiated with 3DCRT/3DCRT DIBH received 50 Gy à 2 Gy and a sequential boost. Contouring of lymph drainage routes was performed retrospectively according to RTOG guidelines.

Results

Average doses (DMean) in axillary lymph node Level I/Level II/Level III were 31.6 Gy/8.43 Gy/2.38 Gy for TT, 24.0 Gy/11.2 Gy/3.97 Gy for 3DCRT and 24.7 Gy/13.3 Gy/5.59 Gy for 3DCRT-DIBH patients. Internal mammary lymph nodes (IMLNs) Dmean were 27.8 Gy (TT), 13.5 Gy (3DCRT), and 18.7 Gy (3DCRT-DIBH). Comparing TT to 3DCRT-DIBH dose varied significantly in all axillary lymph node levels and the IMLNs. Comparing TT to 3DCRT significant dose difference in Level I and IMLNs was observed.

Conclusion

Dose applied to locoregional lymph drainage pathways varies comparing tomotherapy plans to conventional tangentially arranged fields. Studies are warranted whether dose variations influence loco-regional spread and must have implications for target volume definition guidelines.

Deep inspiration breath-hold for left-sided breast irradiation: Analysis of dose-mass histograms and the impact of lung expansion

Background

The aim of this study was to compare dose-volume histogram (DVH) with dose-mass histogram (DMH) parameters for treatment of left-sided breast cancer in deep inspiration breath-hold (DIBH) and free breathing (FB). Additionally, lung expansion and anatomical factors were analyzed and correlated to dose differences.

Methods

For 31 patients 3D conformal radiation therapy plans were retrospectively calculated on FB and DIBH CTs in the treatment planning system. The calculated doses, structures and CT data were transferred into MATLAB and DVHs and DMHs were calculated. Mean doses (Dmean), volumes and masses receiving certain doses (Vx, Mx) were determined for the left lung and the heart. Additionally, expansion of the left lung was evaluated using deformable image registration. Differences in DVH and DMH dose parameters between FB and DIBH were statistically analyzed and correlated to lung expansion and anatomical factors.

Results

DIBH reduced Dmean (DVH) and relative V20 (V20 [%]) of the left lung in all patients, on average by − 19 ± 9% (mean ± standard deviation) and − 24 ± 10%. Dmean (DMH) and M20 [%] were also significantly reduced (− 12 ± 11%, − 16 ± 13%), however 4 patients had higher DMH values in DIBH than in FB. Linear regression showed good correlations between DVH and DMH parameters, e.g. a dosimetric benefit smaller than 8.4% for Dmean (DVH) in DIBH indicated more irradiated lung mass in DIBH than in FB. The mean expansion of the left lung between FB and DIBH was 1.5 ± 2.4 mm (left), 16.0 ± 4.0 mm (anterior) and 12.2 ± 4.6 mm (caudal). No significant correlations were found between expansions and differences in Dmean for the left lung. The heart dose in DIBH was reduced in all patients by 53% (Dmean) and this dosimetric benefit correlated to lung expansion in anterior.

Conclusions

Treatment of left-sided breast cancer in DIBH reduced dose to the heart and in most cases the lung dose, relative irradiated lung volume and lung mass. A mass related dosimetric benefit in DIBH can be achieved as long as the volume related benefit is about ≥8–9%. The lung expansion (breathing pattern) showed no impact on lung dose, but on heart dose. A stronger chest breathing (anterior expansion) for DIBH seems to be more beneficial than abdominal breathing.

Concepts and terms for dose/volume parameters in carbon-ion radiotherapy: Conclusions of the ULICE taskforce

PURPOSE

The Union of Light Ion Centers in Europe (ULICE) program addressed the need for uniting scientific results for carbon-ion radiation therapy obtained by several institutions worldwide in different fields of excellence, and translating them into a real benefit to the community. Particularly, the concepts for dose/volume parameters developed in photon radiotherapy cannot be extrapolated to high linear energy transfer particles.

METHODS AND MATERIALS

The ULICE-WP2 taskforce included radiation oncologists involved in carbon-ion radiation therapy and International Commission on Radiation Units and Measurements, radiation biologists, expert physicists in the fields of carbon-ion radiation therapy, microdosimetry, biological modeling and image-guided radiotherapy. Consensual reports emerged from multiple discussions within both the restricted group and the wider ULICE community. Public deliverables were produced and disseminated to the European Commission.

RESULTS

Here we highlight the disparity in practices between treating centers, then address the main topics to finally elaborate specific recommendations. Although it appears relatively simple to add geometrical margins around the clinical target volume to obtain the planning target volume as performed in photon radiotherapy, this procedure is not appropriate for carbon-ion radiation therapy. Due to the variation of the radiation quality in depth, there is no generic relative biological effectiveness value for carbon-ions outside of an isolated point, for a given fractionation and specific experimental conditions. Absorbed dose and "equieffective dose" for specified conditions must always be reported.

CONCLUSIONS

This work contributed to the development of standard operating procedures for carbon-ion radiation therapy clinical trials. These procedures are now being applied, particularly in the first phase III international, multicenter trial (PHRC Étoile).

Impact of Inter-Individual Variance in the Expression of a Radiation-Responsive Gene Panel Used for Triage

In previous studies we determined a gene expression signature in baboons for predicting the severity of hematological acute radiation syndrome. We subsequently validated a set of eight of these genes in leukemia patients undergoing total-body irradiation. In the current study, we addressed the effect of intra-individual variability on the basal level of expression of those eight radiation-responsive genes identified previously, by examining baseline levels in 200 unexposed healthy human donors (122 males and 88 females with an average age of 46 years) using real-time PCR. In addition to the eight candidate genes ( DAGLA, WNT3, CD177, PLA2G16, WLS, POU2AF1, STAT4 and PRF1), we examined two more genes ( FDXR and DDB2) widely used in ex vivo whole blood experiments. Although significant sex- (seven genes) and age-dependent (two genes) differences in expression were found, the fold changes ranged only between 1.1-1.6. These were well within the twofold differences in gene expression generally considered to represent control values. Age and sex contributed less than 20-30% to the complete inter-individual variance, which is calculated as the fold change between the lowest (reference) and the highest Ct value minimum-maximum fold change (min-max FC). Min-max FCs ranging between 10-17 were observed for most genes; however, for three genes, min-max FCs of complete inter-individual variance were found to be 37.1 ( WNT3), 51.4 ( WLS) and 1,627.8 ( CD177). In addition, to determine whether discrimination between healthy and diseased baboons might be altered by replacing the published gene expression data of the 18 healthy baboons with that of the 200 healthy humans, we employed logistic regression analysis and calculated the area under the receiver operating characteristic (ROC) curve. The additional inter-individual variance of the human data set had either no impact or marginal impact on the ROC area, since up to 32-fold change gene expression differences between healthy and diseased baboons were observed.

Evaluation of radiation-related invasion in primary patient-derived glioma cells and validation with established cell lines: impact of different radiation qualities with differing LET

PURPOSE

Glioblastoma multiforme (GBM) is the most common primary brain tumor and has a very poor overall prognosis. Multimodal treatment is still inefficient and one main reason is the invasive nature of GBM cells, enabling the tumor cells to escape from the treatment area causing tumor progression. This experimental study describes the effect of low- and high-LET irradiation on the invasion of primary GBM cells with a validation in established cell systems.

METHODS

Seven patient derived primary GBM as well as three established cell lines (LN229, LN18 and U87) were used in this study. Invasion was investigated using Matrigel® coated transwell chambers. Irradiation was performed with low- (X-ray) and high-LET (alpha particles) radiation. The colony formation assay was chosen to determine the corresponding alpha particle dose equivalent to the X-ray dose.

RESULTS

4 Gy X-ray irradiation increased the invasive potential of six patient derived GBM cells as well as two of the established lines. In contrast, alpha particle irradiation with an equivalent dose of 1.3 Gy did not show any effect on the invasive behavior. The findings were validated with established cell lines.

CONCLUSION

Our results show that in contrast to low-LET irradiation high-LET irradiation does not enhance the invasion of established and primary glioblastoma cell lines. We therefore suggest that high-LET irradiation could become an alternative treatment option. To fully exploit the benefits of high-LET irradiation concerning the invasion of GBM further molecular studies should be performed.

New insights in the relative radiobiological effectiveness of proton irradiation

BACKGROUND

Proton radiotherapy is a form of charged particle therapy that is preferentially applied for the treatment of tumors positioned near to critical structures due to their physical characteristics, showing an inverted depth-dose profile. The sparing of normal tissue has additional advantages in the treatment of pediatric patients, in whom the risk of secondary cancers and late morbidity is significantly higher. Up to date, a fixed relative biological effectiveness (RBE) of 1.1 is commonly implemented in treatment planning systems with protons in order to correct the physical dose. This value of 1.1 comes from averaging the results of numerous in vitro experiments, mostly conducted in the middle of the spread-out Bragg peak, where RBE is relatively constant. However, the use of a constant RBE value disregards the experimental evidence which clearly demonstrates complex RBE dependency on dose, cell- or tissue type, linear energy transfer and biological endpoints. In recent years, several in vitro studies indicate variations in RBE of protons which translate to an uncertainty in the biological effective dose delivery to the patient. Particularly for regions surrounding the Bragg peak, the more localized pattern of energy deposition leads to more complex DNA lesions. These RBE variations of protons bring the validity of using a constant RBE into question.

MAIN BODY

This review analyzes how RBE depends on the dose, different biological endpoints and physical properties. Further, this review gives an overview of the new insights based on findings made during the last years investigating the variation of RBE with depth in the spread out Bragg peak and the underlying differences in radiation response on the molecular and cellular levels between proton and photon irradiation. Research groups such as the Klinische Forschergruppe Schwerionentherapie funded by the German Research Foundation (DFG, KFO 214) have included work on this topic and the present manuscript highlights parts of the preclinical work and summarizes the research activities in this context.

SHORT CONCLUSION

In summary, there is an urgent need for more coordinated in vitro and in vivo experiments that concentrate on a realistic dose range of in clinically relevant tissues like lung or spinal cord.

DVH- and NTCP-based dosimetric comparison of different longitudinal margins for VMAT-IMRT of esophageal cancer

Purpose

To cover the microscopic tumor spread in squamous cell carcinoma of the esophagus (SCC), longitudinal margins of 3–4 cm are used for radiotherapy (RT) protocols. However, smaller margins of 2–3 cm might be reasonable when advanced diagnostic imaging is integrated into target volume delineation. Purpose of this study was to compare the dose distribution and deposition to the organs at risk (OAR) for different longitudinal margins using a DVH- and NTCP-based approach.

Methods

Ten patients with SCC of the middle or lower third were retrospectively selected. Three planning target volumes (PTV) with longitudinal margins of 4 cm, 3 cm and 2 cm and an axial margin of 1.5 cm to the gross target volume (GTV) were defined for each patient. For each PTV two treatment plans with total doses of 41.4 Gy (neoadjuvant treatment) and 50.4 Gy (definite treatment) were calculated. Dose to the lungs, heart, myelon and liver were then evaluated and compared between different PTVs.

Results

When using a longitudinal margin of 3 cm instead of 4 cm, all dose parameters (Dmin, Dmean, Dmedian and V5-V35), except Dmax could be significantly reduced for the lungs. Regarding the heart, a significant reduction was seen for Dmean and V5, but not for Dmin, Dmax, Dmedian and V10-V35. When comparing a longitudinal margin of 4 cm to a longitudinal margin of 2 cm, a significant difference was calculated for Dmin, Dmean, Dmedian and V5-V35 of the lungs and for Dmax, Dmean and V5-V35 of the heart. Nevertheless, no difference was seen for median heart dose. An additional dose reduction for V10 of the heart was achieved for definite treatment plans when using a longitudinal margin of 3 cm. The NTCP-based risk of pneumonitis was significantly reduced by a margin reduction to 2 cm for neoadjuvant and definite treatment plans.

Conclusion

Reduction of longitudinal margins from 4 cm to 3 cm can significantly reduce the dose to lungs and Dmean of the heart. Despite clinical benefit and oncologic outcome remain unclear, reduction of the longitudinal margins might provide the opportunity to reduce side effects of chemoradiation (CRT) for SCC in upcoming studies.

Interobserver variability of patient positioning using four different CT datasets for image registration in lung stereotactic body radiotherapy

PURPOSE

To assess the impact of different reference CT datasets on manual image registration with free-breathing three-dimensional (3D) cone beam CTs (FB-CBCT) for patient positioning by several observers.

METHODS

For 48 patients with lung lesions, manual image registration with FB-CBCTs was performed by four observers. A slow planning CT (PCT), average intensity projection (AIP), maximum intensity projection (MIP), and midventilation CT (MidV) were used as reference images. Couch shift differences between the four reference CT datasets for each observer as well as shift differences between the observers for the same reference CT dataset were determined. Statistical analyses were performed and correlations between the registration differences and the 3D tumor motion and the CBCT score were calculated.

RESULTS

The mean 3D shift difference between different reference CT datasets was the smallest for AIPvsMIP (range 1.1-2.2 mm) and the largest for MidVvsPCT (2.8-3.5 mm) with differences >10 mm. The 3D shifts showed partially significant correlations to 3D tumor motion and CBCT score. The interobserver comparison for the same reference CTs resulted in the smallest ∆3D mean differences and mean ∆3D standard deviation for ∆AIP (1.5 ± 0.7 mm, 0.7 ± 0.4 mm). The maximal 3D shift difference between observers was 10.4 mm (∆MidV). Both 3D tumor motion and mean CBCT score correlated with the shift differences (R_s = 0.336-0.740).

CONCLUSION

The applied reference CT dataset impacts image registration and causes interobserver variabilities. The 3D tumor motion and CBCT quality affect shift differences. The smallest differences were found for AIP which might be the most appropriate CT dataset for image registration with FB-CBCT.

Correlation between delivered radiation doses to the brainstem or vestibular organ and nausea & vomiting toxicity in patients with head and neck cancers - an observational clinical trial

Objective

Today intensity modulated radiation therapy (IMRT) can be considered the standard of care in patients with head and neck tumors. IMRT treatment plans are proven to reduce acute treatment related side effects by optimal sparing of organs at risk (OAR). At the same time, areas that were out of the former 3D fields now receive low radiation doses. Amongst those areas the brainstem (BS) and the vestibular system (VS) are known to be physiologically connected to nausea and vomiting (NV). In our study we tried to find out, if doses to these areas are linked to NV.

Material & Methods

NV were assessed at different time points during treatment in 26 patients leading to 98 documented toxicity scores that were later correlated to dose deposition in the described areas. Patients were either treated with normo-fractionated or simultaneously integrated boost IMRT plans in a curative approach. Subareas of the BS as well as the VS were delineated. Toxicity was rated based on the common toxicity criteria (CTCAE Version 4.0). Other factors such as age, gender, chemotherapy, location of the tumor, irradiated volume and unilateral dose to the VS were taken into account and analyzed also.

Results

The majority (65.4%) of our patients experienced an episode of NV at least once during treatment. NV was more frequent when treating the oropharyngeal region compared to the hypopharyngeal region, as well as when patients were female and/ or of a younger age. Nevertheless, upon statistical analysis (ROC analysis, ‘within/ between analysis’) no significant association between delivered doses to subareas and toxicity could be demonstrated.

Conclusion

In our analysis, no significant correlation between radiation dose to the BS or the VS and the occurrence of NV could be found. Therefore, until conclusive data are available, we recommend to rely on the published data regarding OAR tolerance within the BS and not to compromise on dose coverage.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-017-0846-4) contains supplementary material, which is available to authorized users.

Tangential Field Radiotherapy for Breast Cancer-The Dose to the Heart and Heart Subvolumes: What Structures Must Be Contoured in Future Clinical Trials?

Background and purpose

The aim of the present study was to evaluate if it is feasible for experienced radiation oncologists to visually sort out patients with a large dose to the heart. This would facilitate large retrospective data evaluations. And in case of an insufficient visual assessment, to define which structures should be contoured and which structures can be skipped as their dose can be derived from other easily contoured structures for future clinical trials.

Material and methods

Planning CTs of left-sided breast cancer patients treated with 3D-conformal radiotherapy by tangential fields were visually divided into two groups: with an estimated high dose (HiD) and with an estimated low dose (LoD) to the heart. For 46 patients (22 HiD and 24 LoD), the heart, the left ventricle, the left anterior descending artery (LAD), the right coronary artery, and the ramus circumflexus were contoured. A helper structure (HS) around the LAD was generated in order to consider if contouring uncertainties of the LAD could be acceptable. We analyzed the mean dose (Dmean), the maximum dose, the V10, V20, V30, V40, and the length of the LAD that received 20 and 40 Gy.

Results

The two groups had a significant different Dmean of the heart (p < 0.001). The average Dmean to the heart was 4.0 ± 1.3 Gy (HiD) and 2.3 ± 0.8 Gy (LoD). The average Dmean to the LAD was 26.2 ± 7.4 Gy (HiD) and 13.0 ± 7.5Gy (LoD) with a very strong positive correlation between Dmean LAD and Dmean HS in both groups. The Dmean heart is not a good surrogate parameter for the dose to the LAD since it might underestimate clinically significant doses in 1/3 of the patients in LoD group.

Conclusion

A visual assessment of the dose to the heart could be reliable if performed by experienced radiation oncologists. However, the Dmean heart is not always a good surrogate parameter for the dose to the LAD or for the Dmean to the left ventricle. Thus, if specific late toxicities are evaluated, we strongly recommend contouring of the specific heart substructures as a heart Dmean is not highly specific.

Helical TomoTherapy for locally advanced or recurrent breast cancer

Purpose

We report our experience of using helical tomotherapy (HT) to treat large and irregular shaped loco-regional advanced breast cancer target volumes embracing various organs at risk.

Patients and methods

We retrospectively analyzed 26 patients treated for very large, irregular shaped breast cancers. Patients were treated either with the intent to achieve local control in a primary setting (n = 14) or in a reirradiation setting (n = 12). The recurrence group was heavily pretreated with systemic therapy. Tumors were characterized by wide infiltration of the skin, encompassing mostly a complete hemithorax. The primary group underwent irradiation of supraclavicular, infraclavicular, axillary and parasternal lymphonodal region. Radiotherapy was combined with chemotherapy (n = 11). We assessed the PTV volume and its craniocaudal extension, the dose to the organs at risk, acute toxicity and survival.

Results

Median PTV was 2276 cm³ (1476–6837 cm³) with a median cranio-caudal extension of 28 cm (15–52 cm). The median dose to PTV was 40 Gy (32–60Gy). HT could be carried out in all patients without interruption. The acute toxicities were mild to moderate. The median LRFS and OS after radiotherapy was 21 and 57 months for the primary group versus 10 and 11 months for the recurrence group. Median PFS was 18 months (primary group) and 7 months (recurrence group).

Conclusions

HT is feasible for advanced thorax embracing target volumes with acceptable acute toxicity. Both curative and palliative indications can be considered good indications based on treatment volume and anatomical constellation.

[Radiotherapeutic management of lymphatic fistulas : An effective but disregarded therapy option]

BACKGROUND

Lymphatic fistulas and lymphoceles are known complications after vascular surgery of the groin and after extended surgical interventions in the pelvic region. Unfortunately, conservative standard therapies are not always successful.

OBJECTIVES

Evaluation of the therapeutic efficacy and related side effects of percutaneous low-dose irradiation in patients with lymphorrhea and definition of its importance.

MATERIAL AND METHODS

Current presentation of previously published case series, reviews and guidelines.

RESULTS

The use of low-dose irradiation therapy with single doses of 0.3-0.5 Gy leads to a cessation of the lymphatic flow in a high percentage of patients when standard therapies do not show a sufficient effect. With cessation of lymphorrhea irradiation should be terminated. Acute side effects have not been reported and the risk of tumor induction is almost negligible.

CONCLUSION

Low-dose irradiation is an effective and very well-tolerated therapeutic alternative in the treatment of lymphatic fistulas and lymphorrhea when conservative therapies are unsuccessful.

Proton therapy in paediatric oncology: an Irish perspective

BACKGROUND

Proton therapy (PT) is a radiotherapy treatment modality that uses protons, rather than conventional photons. PT is often used in paediatric oncology due to its reported capability to reduce acute and late adverse treatment effects. As PT is unavailable in Ireland, patients are referred abroad for treatment.

AIMS

To: (1) produce a descriptive study of Irish children referred abroad for PT, and (2) discuss the case for PT in general.

METHODS

A retrospective review of all children referred for PT before October 2015 was performed. Information was gathered regarding demographics, diagnosis, referral timeline, adverse effects attributable to PT, current status and cost. A review of the relevant literature was performed.

RESULTS

Seventeen children treated in Ireland have been referred abroad for PT. The largest number was in the 0-4 year old group. At initial diagnosis the median age was 4.8 years. The average cost per child was €37,312. Two patients suffered disease relapse. Four have encountered PT-related adverse effects.

CONCLUSION

Despite the fact that >100,000 patients worldwide have been treated with PT, the level of published evidence to support superiority over conventional treatment remains low. It is debated that randomised control trials in this area would be inconsistent with the principle of clinical equipoise. In contrast, there is a call for level 1 evidence to justify drastic changes in patient care, particularly in light of recent reports of unexpected toxicities. In time, careful evaluation, follow-up and clinical trials will likely support the preferential use of PT in children.

Dosimetric advantages of proton therapy over conventional radiotherapy with photons in young patients and adults with low-grade glioma

Background and purpose

Low-grade glioma (LGG) is a very common brain tumor in pediatric patients typically associated with a very good prognosis. This prognosis makes it imperative that the risk of long-term treatment-related side effects be kept at an absolute minimum. Proton therapy (PRT) provides a radiation technique that has the potential to further reduce the genesis of radiogenic impairment.

Materials and methods

We retrospectively assessed 74 patients with LGG who underwent PRT. Conventional three-dimensional photon and PRT plans were generated after contouring structures of neurogenesis, crucial neuronal structures, and areas susceptible to secondary malignancies. Target volume coverage was evaluated using the homogeneity index (HI) and inhomogeneity coefficient (IC). Results were compared using the Wilcoxon-signed rank test, with p < 0.05 being statistically significant.

Results

Target volume coverage was comparable for the photon and proton plans. Overall, we could show an essential reduction in maximal, mean, and integral doses in critical neurologic structures, areas of neurogenesis, and structures of neurocognitive function. The study indicated specifically how contralaterally located structures could be spared with PRT.

Conclusion

PRT is a highly conformal radiation technique offering superior dosimetric advantages over conventional radiotherapy by allowing significant dose reduction for organs at risk (OAR) that are essential for neurologic function, neurocognition, and quality of life, thus demonstrating the potential of this technique for minimizing long-term sequelae.

Implications of free breathing motion assessed by 4D-computed tomography on the delivered dose in radiotherapy for esophageal cancer

The aim of this study was to assess the effect of breathing motion on the delivered dose in esophageal cancer 3-dimensional (3D)-conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and volumetric modulated arc therapy (VMAT). We assessed 16 patients with esophageal cancer. All patients underwent 4D-computed tomography (4D-CT) for treatment planning. For each of the analyzed patients, 1 3D-CRT, 1 IMRT, and 1 VMAT (RapidArc-RA) plan were calculated. Each of the 3 initial plans was recalculated on the 4D-CT (for the maximum free inspiration and maximum free expiration) to assess the effect of breathing motion. We assessed the minimum dose (Dmin) and mean dose (Dmean) to the esophagus within the planning target volume, the volume changes of the lungs, the Dmean and the total lung volume receiving at least 40Gy (V40), and the V30, V20, V10, and V5. For the heart we assessed the Dmean and the V25. Over all techniques and all patients the change in Dmean as compared with the planned Dmean (planning CT [PCT]) to the esophagus was 0.48% in maximum free inspiration (CT_insp) and 0.55% in maximum free expiration (CT_exp). The Dmin CT_insp change was 0.86% and CT_exp change was 0.89%. The Dmean change of the lungs (heart) was in CT_insp 1.95% (2.89%) and 3.88% (2.38%) in CT_exp. In all, 4 patients had a clinically relevant change of the dose (≥ 5% Dmean to the heart and the lungs) between inspiration and expiration. These patients had a very cranially or caudally situated tumor. There are no relevant differences in the delivered dose to the regions of interest among the 3 techniques. Breathing motion management could be considered to achieve a better sparing of the lungs or heart in patients with cranially or caudally situated tumors.