Applicability of the linear-quadratic formalism for modeling local tumor control probability in high dose per fraction stereotactic body radiotherapy for early stage non-small cell lung cancer

Dose prescription for stereotactic body radiotherapy: general and organ-specific consensus statement from the DEGRO/DGMP Working Group Stereotactic Radiotherapy and Radiosurgery

PURPOSE AND OBJECTIVE

To develop expert consensus statements on multiparametric dose prescriptions for stereotactic body radiotherapy (SBRT) aligning with ICRU report 91. These statements serve as a foundational step towards harmonizing current SBRT practices and refining dose prescription and documentation requirements for clinical trial designs.

MATERIALS AND METHODS

Based on the results of a literature review by the working group, a two-tier Delphi consensus process was conducted among 24 physicians and physics experts from three European countries. The degree of consensus was predefined for overarching (OA) and organ-specific (OS) statements (≥ 80%, 60-79%, < 60% for high, intermediate, and poor consensus, respectively). Post-first round statements were refined in a live discussion for the second round of the Delphi process.

RESULTS

Experts consented on a total of 14 OA and 17 OS statements regarding SBRT of primary and secondary lung, liver, pancreatic, adrenal, and kidney tumors regarding dose prescription, target coverage, and organ at risk dose limitations. Degree of consent was ≥ 80% in 79% and 41% of OA and OS statements, respectively, with higher consensus for lung compared to the upper abdomen. In round 2, the degree of consent was ≥ 80 to 100% for OA and 88% in OS statements. No consensus was reached for dose escalation to liver metastases after chemotherapy (47%) or single-fraction SBRT for kidney primaries (13%). In round 2, no statement had 60-79% consensus.

CONCLUSION

In 29 of 31 statements a high consensus was achieved after a two-tier Delphi process and one statement (kidney) was clearly refused. The Delphi process was able to achieve a high degree of consensus for SBRT dose prescription. In summary, clear recommendations for both OA and OS could be defined. This contributes significantly to harmonization of SBRT practice and facilitates dose prescription and reporting in clinical trials investigating SBRT.

ONE SHOT - single shot radiotherapy for localized prostate cancer: 18-month results of a single arm, multicenter phase I/II trial

PURPOSE

To assess in a prospective, multicenter, single-arm phase I/II study the early safety and efficacy profile of single fraction urethra-sparing stereotactic body radiotherapy (SBRT) for men with localized prostate cancer.

MATERIAL AND METHODS

Patients with low- and intermediate-risk localized prostate cancer without significant tumor in the transitional zone were recruited. A single-fraction of 19 Gy was delivered to the prostate, with 17 Gy dose-reduction to the urethra. Intrafraction motion was monitored using intraprostatic electromagnetic transponders with intra-fraction correction of displacements exceeding 3 mm. Genitourinary (GU), gastrointestinal (GI), and sexual toxicity during the first 18 months were evaluated using the CTCAE v4.0 grading scale. Quality of life was assessed using the International Prostate Symptom Score, the Expanded Prostate Cancer Index composite 26 score, and the International Index of Erectile Function score.

RESULTS

Among the 45 patients recruited in 5 centers between 2017 and 2022, 43 received the single fraction without protocol deviations, and 34 had a minimal follow-up of 18 months. The worst GU toxicity was observed at day-5 after SBRT (42.5 % and 20 % with grade 1 and 2, respectively), returning to baseline at week-12 and month-6 (<3% with grade 2), with a 12 % grade 2 flare at month 18. Gl toxicity was mild in the acute phase, with no grade ≥ 2 events (12 % grade 1 at month 6). Grade-3 proctitis was observed in one patient at month 12, with < 3 % grade 2 toxicity at month 18. Mean GU and GI bother scores showed a decline at day 5, a complete recovery at month 6, and a flare between month 12 and 18. Mean PSA dropped from 6.2 ng/ml to 1.2 ng/ml at month 18 and 0.7 ng/ml at month 24. After a median follow-up time of 26 months, 3 biochemical failures (7 %) were observed at month 17, 21 and 30.

CONCLUSIONS

In this multicenter phase I/II trial, we demonstrated that a 19 Gy single-fraction urethra-sparing SBRT is feasible and associated with an acceptable toxicity rate, mostly returning to the baseline at week-12 and with a symptoms flare between months 12 and 18. Longer follow-up is needed to assess the potential long-term adverse effects and the disease control efficacy.

Stereotactic body radiotherapy in lung cancer: a contemporary review

The treatment of early stage non-small cell lung cancer (NSCLC) has improved enormously in the last two decades. Although surgery is not the only choice, lobectomy is still the gold standard treatment type for operable patients. For inoperable patients stereotactic body radiotherapy (SBRT) should be offered, reaching very high local control and overall survival rates. With SBRT we can precisely irradiate small, well-defined lesions with high doses. To select the appropriate fractionation schedule it is important to determine the size, localization and extent of the lung tumor. The introduction of novel and further developed planning (contouring guidelines, diagnostic image application, planning systems) and delivery techniques (motion management, image guided radiotherapy) led to lower rates of side effects and more conformal target volume coverage. The purpose of this study is to summarize the current developments, randomised studies, guidelines about lung SBRT, with emphasis on the possibility of increasing local control and overall rates in "fit," operable patients as well, so SBRT would be eligible in place of surgery.

Simulating the Potential of Model-Based Individualized Prescriptions for Ultracentral Lung Tumors

Purpose

The use of stereotactic body radiation therapy for ultracentral lung tumors is limited by increased toxicity. We hypothesized that using published normal tissue complication probability (NTCP) and tumor control probability (TCP) models could improve the therapeutic ratio between tumor control and toxicity. A proposed model-based approach was applied to virtually replan early-stage non-small cell lung cancer (NSCLC) tumors.

Methods and Materials

The analysis included 63 patients with ultracentral NSCLC tumors treated at our center between 2008 and 2017. Along with current clinical constraints, additional NTCP model-based criteria, including for grade 3+ radiation pneumonitis (RP3+) and grade 2+ esophagitis, were implemented using 4 different fractionation schemes. Scaled dose distributions resulting in the highest TCP without violating constraints were selected (optimal plan [Planopt]). Planopt predictions were compared with the observed local control and toxicities.

Results

The observed 2-year local control rate was 72% (95% CI, 57%-88%) compared with 87% (range, 6%-93%) for Planopt TCP. Thirty-nine patients had Planopt with TCP > 80%, and 14 patients had Planopt TCP < 50%. The Planopt NTCPs for RP3+ were reduced by nearly half compared with patients' observed RP3+. The RP3+ NTCP was the most frequent reason for TCP of Planopt < 80% (14/24 patients), followed by grade 2+ esophagitis NTCP (5/24 patients) due to larger tumors (>40 cc vs ≤40 cc; P = .002) or a shorter tumor to esophagus distance (≥5 cm vs <5 cm; P < .001).

Conclusions

We demonstrated the potential for model-based prescriptions to yield higher TCP while respecting NTCP for patients with ultracentral NSCLC. Individualizing treatments based on NTCP- and TCP-driven simulations halved the predicted relative to the observed rates of RP3+. Our simulations also identified patients whose TCP could not be improved without violating NTCP due to larger tumors or a near tumor to esophagus proximity.

Predicting cancer relapse following lung stereotactic radiotherapy: an external validation study using real-world evidence

Purpose

For patients receiving lung stereotactic ablative radiotherapy (SABR), evidence suggests that high peritumor density predicts an increased risk of microscopic disease (MDE) and local-regional failure, but only if there is low or heterogenous incidental dose surrounding the tumor (GTV). A data-mining method (Cox-per-radius) has been developed to investigate this dose-density interaction. We apply the method to predict local relapse (LR) and regional failure (RF) in patients with non-small cell lung cancer.

Methods

199 patients treated in a routine setting were collated from a single institution for training, and 76 patients from an external institution for validation. Three density metrics (mean, 90th percentile, standard deviation (SD)) were studied in 1mm annuli between 0.5cm inside and 2cm outside the GTV boundary. Dose SD and fraction of volume receiving less than 30Gy were studied in annuli 0.5-2cm outside the GTV to describe incidental MDE dosage. Heat-maps were created that correlate with changes in LR and RF rates due to the interaction between dose heterogeneity and density at each distance combination. Regions of significant improvement were studied in Cox proportional hazards models, and explored with and without re-fitting in external data. Correlations between the dose component of the interaction and common dose metrics were reported.

Results

Local relapse occurred at a rate of 6.5% in the training cohort, and 18% in the validation cohort, which included larger and more centrally located tumors. High peritumor density in combination with high dose variability (0.5 - 1.6cm) predicts LR. No interactions predicted RF. The LR interaction improved the predictive ability compared to using clinical variables alone (optimism-adjusted C-index; 0.82 vs 0.76). Re-fitting model coefficients in external data confirmed the importance of this interaction (C-index; 0.86 vs 0.76). Dose variability in the 0.5-1.6 cm annular region strongly correlates with heterogeneity inside the target volume (SD; ρ = 0.53 training, ρ = 0.65 validation).

Conclusion

In these real-world cohorts, the combination of relatively high peritumor density and high dose variability predicts increase in LR, but not RF, following lung SABR. This external validation justifies potential use of the model to increase low-dose CTV margins for high-risk patients.

Stereotactic Body Radiation Therapy for Spinal Metastases: Benefits and Limitations

Progress in biological cancer characterization, targeted systemic therapies and multimodality treatment strategies have shifted the goals of radiotherapy for spinal metastases from short-term palliation to long-term symptom control and prevention of compilations. This article gives an overview of the spine stereotactic body radiotherapy (SBRT) methodology and clinical results of SBRT in cancer patients with painful vertebral metastases, metastatic spinal cord compression, oligometastatic disease and in a reirradiation situation. Outcomes after dose-intensified SBRT are compared with results of conventional radiotherapy and patient selection criteria will be discussed. Though rates of severe toxicity after spinal SBRT are low, strategies to minimize the risk of vertebral compression fracture, radiation induced myelopathy, plexopathy and myositis are summarized, to optimize the use of SBRT in multidisciplinary management of vertebral metastases.

Translational study for stereotactic body radiotherapy against non-small cell lung cancer, including oligometastases, considering cancer stem-like cells enable predicting clinical outcome from in vitro data

BACKGROUND

Curative effects of stereotactic body radiotherapy (SBRT) for non-small cell lung cancer (NSCLC) have been evaluated using various biophysical models. Because such model parameters are empirically determined based on clinical experience, there is a large gap between in vitro and clinical studies. In this study, considering the heterogeneous cell population, we performed a translational study to realize the possible linkage based on a modeling approach.

METHODS

We modeled cell-killing and tumor control probability (TCP) considering two populations: progeny and cancer stem-like cells. The model parameters were determined from in vitro survival data of A549 and EBC-1 cells. Based on the cellular parameters, we predicted TCP and compared it with the corresponding clinical data from 553 patients collected at Hirosaki University Hospital.

RESULTS

Using an all-in-one developed model, the so-called integrated microdosimetric-kinetic (IMK) model, we successfully reproduced both in vitro survival after acute irradiation and the 3-year TCP with various fractionation schemes (6-10 Gy per fraction). From the conventional prediction without considering cancer stem cells (CSCs), this study revealed that radioresistant CSCs play a key role in the linkage between in vitro and clinical outcomes.

CONCLUSIONS

This modeling study provides a possible generalized biophysical model that enables precise estimation of SBRT worldwide.

The minimal FLASH sparing effect needed to compensate the increase of radiobiological damage due to hypofractionation for late-reacting tissues

PURPOSE

Normal tissue (NT) sparing by ultra-high dose rate (UHDR) irradiations compared to conventional dose rate (CONV) irradiations while being isotoxic to the tumor has been termed "FLASH effect" and has been observed when large doses per fraction (d ≳ 5 Gy) have been delivered. Since hypofractionated treatment schedules are known to increase toxicities of late-reacting tissues compared to normofractionated schedules for many clinical scenarios at CONV dose rates, we developed a formalism based on the biologically effective dose (BED) to assess the minimum magnitude of the FLASH effect needed to compensate the loss of late-reacting NT sparing when reducing the number of fractions compared to a normofractionated CONV treatment schedule while remaining isoeffective to the tumor.

METHODS

By requiring the same BED for the tumor, we derived the "break-even NT sparing weighting factor" W_BE for the linear-quadratic (LQ) and LQ-linear (LQ-L) models for an NT region irradiated at a relative dose r (relative to the prescribed dose per fraction d to the tumor). W_BE was evaluated numerically for multiple values of d and r, and for different tumor and NT α/β-ratios. W_BE was compared against currently available experimental data on the magnitude of the NT sparing provided by the FLASH effect for single fraction doses.

RESULTS

For many clinically relevant scenarios, W_BE decreases steeply initially for d > 2 Gy for late-reacting tissues with (α/β)_NT ≈ 3 Gy, implying that a significant NT sparing by the FLASH effect (between 15% and 30%) is required to counteract the increased radiobiological damage experienced by late-reacting NT for hypofractionated treatments with d < 10 Gy compared to normofractionated treatments that are equieffective to the tumor. When using the LQ model with generic α/β-ratios for tumor and late-reacting NT of (α/β)_T  = 10 Gy and (α/β)_NT  = 3 Gy, respectively, most currently available experimental evidence about the magnitude of NT sparing by the FLASH effect suggests no net NT sparing benefit for hypofractionated FLASH radiotherapy (RT) in the high-dose region when compared with W_BE . Instead, clinical indications with more similar α/β-ratios of the tumor and dose-limiting NT toxicities [i.e., (α/β)_T  ≈ (α/β)_NT ], such as prostate treatments, are generally less penalized by hypofractionated treatments and need consequently smaller magnitudes of NT sparing by the FLASH effect to achieve a net benefit. For strongly hypofractionated treatments (>10-15 Gy/fraction), the LQ-L model predicts, unlike the LQ model, a larger W_BE suggesting a possible benefit of strongly hypofractionated FLASH RT, even for generic α/β-ratios of (α/β)_T  = 10 Gy and (α/β)_NT  = 3 Gy. However, knowledge on the isoeffect scaling for high doses per fraction (≳10 Gy/fraction) and its modeling is currently limited and impedes accurate and reliable predictions for such strongly hypofractionated treatments.

CONCLUSIONS

We developed a formalism that quantifies the minimal NT sparing by the FLASH effect needed to compensate for hypofractionation, based on the LQ and LQ-L models. For a given hypofractionated UHDR treatment scenario and magnitude of the FLASH effect, the formalism predicts if a net NT sparing benefit is expected compared to a respective normofractionated CONV treatment.

Endorectal contact radiation boosting: Making the case for dose AND volume reporting

INTRODUCTION

The various rectal endoluminal radiation techniques all have steep, but different, dose gradients. In rectal contact brachytherapy (CXB) doses are typically prescribed and reported to the applicator surface and not to the gross tumor volume (GTV), clinical target volume (CTV) or organs at risk (OAR), which is crucial to understand tumor response and toxicity rates. To quantify the above-described problem, we performed a dose modeling study using a fixed prescription dose at the surface of the applicator and varied tumor response scenarios.

METHODS

Endorectal ultrasound-based 3D-volume-models of rectal tumors and the rectal wall were used to simulate the delivered dose to GTV, CTV and the rectal wall layers, assuming treatment with Maastro HDR contact applicator for rectal cancer with a fixed prescription dose to the applicator surface (equivalent to 3 × 30 Gy CXB) and various response scenarios.

RESULTS

An identical prescribed dose to the surface of the applicator resulted in a broad range of doses delivered to the GTV, CTV and the uninvolved intestinal wall. For example, the equieffective dose in 2 Gy per fraction (EQD2) D90% of the GTV varied between 63 and 231 Gy, whereas the EQD2 D2cc of the rectal wall varied between 97 and 165 Gy.

CONCLUSION

Doses prescribed at the surface are not representative of the dose received by the tumor and the bowel wall. This stresses the relevance of dose reporting and prescription to GTV and CTV volumes and OAR in order to gain insight between delivered dose, local control and toxicity and to optimize treatment protocols.

Imaging of GBM in the Age of Molecular Markers and MRI Guided Adaptive Radiation Therapy

Glioblastoma (GBM) continues to be one of the most lethal malignancies and is almost always fatal. In this review article, the role of radiation therapy, systemic therapy, as well as the molecular basis of classifying GBM is described. Technological advances in the treatment of GBM are outlined as well as the diagnostic imaging characteristics of this tumor. In addition, factors that affect prognosis such as differentiating progression from treatment effect is discussed. The role of MRI guided radiation therapy and how this technology may provide a mechanism to improve the care of patients with this disease are described.

Cellular bases of hypofractionated radiotherapy protocols for lung cancer

The extreme demand on health systems due to the COVID-19 pandemic has led to reconsider hypofractionation. Although the best clinical efficacy of these schemes is being demonstrated, the biological bases have not been established. Thus, after validating basic clinical parameters, through complementary in vitro models, we characterized the cellular and molecular mechanisms of hypofractionation protocols. Cell cultures of human lung cancer cell line A549 were irradiated with 0, 2, 4, 8, 12, 16 and 20 Gy. The clastogenic, cytotoxic, proliferative and clonogenic capacities and bystander effect were evaluated. In addition, we assessed survival and toxicity in a retrospective study of 49 patients with lung cancer. Our findings showed that the greater efficacy of ablative regimens should not only be attributed to events of direct cell death induced by genotoxic damage, but also to a lower cell repopulation and the indirect action of clastogenic factors secreted. These treatments were optimal in terms of 1- and 2-year overall survival (74 and 65%, respectively), and progression-free survival at 1 and 2 years (71 and 61%, respectively). The greater efficacy of high doses per fraction could be attributed to a multifactorial mechanism that goes beyond the 4Rs of conventional radiotherapy.

Tumor Control Probability following Radiosurgery of Brain Metastases with and without Retreatment

PURPOSE

To develop and compare tumor-control-probability (TCP) models for single-fraction stereotactic radiosurgery (SRS) for brain metastasis (BMs) with and without retreatment.

METHODS

We developed three different schemas to model TCP of BMs treated with LINAC-based SRS. Dose to 99% of each planning-target-volume (PTV D₉₉) and six-month local-control was fit using linear-quadratic-linear (LQ-L) models based on equivalent-dose conversions in 2Gy (EQD2). The M1 schema had separate LQ-L TCP models for initial dose (M1-initial) and retreatment dose (M1-retreat), and the M2 schema had an LQ-L model using the sum of 50% of the initial SRS dose plus the retreatment SRS dose. The M1-initial and M1-retreat schema modeled local control following 1^st SRS to 48 lesions (patients=22) and 2^nd SRS to 46 lesions (patients=21). The M0 schema included a whole dataset of 349 lesions (patients=136) receiving first SRS (no retreatment and M1-initial).

RESULTS

LQ-L models fitted the data well (Chi-2=0.059-0.525 and p=0.999-1.000). For M0 and M1-retreat, the fitted models EQD2₅₀ and γ₅₀ parameters, were similar. The LQ-L fitted EQD2₅₀ was ∼8.0Gy for M0 and M1-retreat, ∼24Gy for M1-initial, and ∼19Gy for M2. The model fitted γ₅₀ was 0.1Gy for M0, M1-retreat, and M2 and 0.5 for M1-initial. For the PTV D₉₉ of 10Gy and 20Gy, the steepest to shallowest dose-response or largest change in TCP, i.e., TCP_20Gy - TCP_10Gy was observed in M1-initial (0.49) and M2 (0.17). M0 and M1-retreat showed a similar change in TCP of 0.21.

CONCLUSION

The model fitted parameters predict the recurrent BMs required a higher threshold dose and had a steeper dose-response for 1^st SRS vs. 2^nd SRS and M0. Alternatively, the recurrent BMs required ∼2Gy higher predicted PTV D₉₉ dose for 1^st SRS to achieve the same TCP of 0.75 when compared to 2^nd SRS and M0. Further investigations on larger patient cohorts are needed for validating our findings in predictive modeling of recurrent brain metastases.

Practical considerations of single-fraction stereotactic ablative radiotherapy to the lung

Stereotactic ablative radiotherapy (SABR) is a well-established treatment for patients with medically inoperable early-stage non-small cell lung cancer (NSCLC) and pulmonary oligometastases. The use of single-fraction SABR in this setting is supported by excellent local control and safety profiles which appear equivalent to multi-fraction SABR based on the available data. The resource efficiency and reduction in hospital outpatient visits associated with single-fraction SABR have been particularly advantageous during the COVID-19 pandemic. Despite the increased interest, single-fraction SABR in subgroups of patients remains controversial, including those with centrally located tumours, synchronous targets, proximity to dose-limiting organs at risk, and concomitant severe respiratory illness. This review provides an overview of the published randomised evidence evaluating single-fraction SABR in primary lung cancer and pulmonary oligometastases, the common clinical challenges faced, immunogenic effect of SABR, as well as technical and cost-utility considerations.

Stereotactic Body Radiotherapy of adrenal metastases - A dose-finding study

Optimal doses for the treatment of adrenal metastases with stereotactic radiotherapy (SBRT) are unknown. We aimed to identify dose-volume cut-points associated with decreased local recurrence rates (LRR). A multicenter database of patients with adrenal metastases of any histology treated with SBRT (biologically effective dose, BED10 ≥ 50Gy, ≤ 12 fractions) was analyzed. Details on dose-volume parameters were required (planning target volume: PTV-D98%, PTV-D50%, PTV-D2%; gross tumor volume: GTV-D50%, GTV-mean). Cut-points for LRR were optimized using the R maxstat package. 196 patients with 218 lesions were included, the largest histopathological subgroup was adenocarcinoma (n = 101). Cut-point optimization resulted in significant cut-points for PTV-D50% (BED10: 73.2Gy; p = 0.003), GTV-D50% (BED10: 74.2Gy; p = 0.006), GTV-mean (BED10: 73.0Gy; p = 0.007), and PTV-D2% (BED10: 78.0Gy; p = 0.02) but not for the PTV-D98% (p = 0.06). Differences in LRR were clinically relevant (LRR ≥ doubled for cut-points that were not achieved). Further dose-escalation was not associated with further improved LRR. PTV-D50%, GTV-D50%, and GTV-mean cut-points were also associated with significantly improved LRR in the adenocarcinoma subgroup. Separate dose optimizations indicated a lower cut-point for the PTV-D50% (BED10: 69.1Gy) in adenocarcinoma lesions, other values were similar (< 2% difference). Associations of cut-points with overall survival (OS) and progression-free survival were not significant but durable freedom from local recurrence was associated with OS in a landmark model (p < 0.001). To achieve a significant improvement of LRR for adrenal SBRT, a moderate escalation of PTV-D50% BED10 > 73.2Gy (adenocarcinoma: 69.1Gy) should be considered. This article is protected by copyright. All rights reserved.

Variability of α/β ratios for prostate cancer with the fractionation schedule: caution against using the linear-quadratic model for hypofractionated radiotherapy

BACKGROUND

Prostate cancer (PCa) is known to be suitable for hypofractionated radiotherapy due to the very low α/β ratio (about 1.5-3 Gy). However, several randomized controlled trials have not shown the superiority of hypofractionated radiotherapy over conventionally fractionated radiotherapy. Besides, in vivo and in vitro experimental results show that the linear-quadratic (LQ) model may not be appropriate for hypofractionated radiotherapy, and we guess it may be due to the influence of fractionation schedules on the α/β ratio. Therefore, this study attempted to estimate the α/β ratio in different fractionation schedules and evaluate the applicability of the LQ model in hypofractionated radiotherapy.

METHODS

The maximum likelihood principle in mathematical statistics was used to fit the parameters: α and β values in the tumor control probability (TCP) formula derived from the LQ model. In addition, the fitting results were substituted into the original TCP formula to calculate 5-year biochemical relapse-free survival for further verification.

RESULTS

Information necessary for fitting could be extracted from a total of 23,281 PCa patients. A total of 16,442 PCa patients were grouped according to fractionation schedules. We found that, for patients who received conventionally fractionated radiotherapy, moderately hypofractionated radiotherapy, and stereotactic body radiotherapy, the average α/β ratios were 1.78 Gy (95% CI 1.59-1.98), 3.46 Gy (95% CI 3.27-3.65), and 4.24 Gy (95% CI 4.10-4.39), respectively. Hence, the calculated α/β ratios for PCa tended to become higher when the dose per fraction increased. Among all PCa patients, 14,641 could be grouped according to the risks of PCa in patients receiving radiotherapy with different fractionation schedules. The results showed that as the risk increased, the k (natural logarithm of an effective target cell number) and α values decreased, indicating that the number of effective target cells decreased and the radioresistance increased.

CONCLUSIONS

The LQ model appeared to be inappropriate for high doses per fraction owing to α/β ratios tending to become higher when the dose per fraction increased. Therefore, to convert the conventionally fractionated radiation doses to equivalent high doses per fraction using the standard LQ model, a higher α/β ratio should be used for calculation.

A Combined Model to Improve the Prediction of Local Control for Lung Cancer Patients Undergoing Stereotactic Body Radiotherapy Based on Radiomic Signature Plus Clinical and Dosimetric Parameters

PURPOSE

Stereotactic body radiotherapy (SBRT) is an important treatment modality for lung cancer patients, however, tumor local recurrence rate remains some challenge and there is no reliable prediction tool. This study aims to develop a prediction model of local control for lung cancer patients undergoing SBRT based on radiomics signature combining with clinical and dosimetric parameters.

METHODS

The radiomics model, clinical model and combined model were developed by radiomics features, incorporating clinical and dosimetric parameters and radiomics signatures plus clinical and dosimetric parameters, respectively. Three models were established by logistic regression (LR), decision tree (DT) or support vector machine (SVM). The performance of models was assessed by receiver operating characteristic curve (ROC) and DeLong test. Furthermore, a nomogram was built and was assessed by calibration curve, Hosmer-Lemeshow and decision curve.

RESULTS

The LR method was selected for model establishment. The radiomics model, clinical model and combined model showed favorite performance and calibration (Area under the ROC curve (AUC) 0.811, 0.845 and 0.911 in the training group, 0.702, 0.786 and 0.818 in the validation group, respectively). The performance of combined model was significantly superior than the other two models. In addition, Calibration curve and Hosmer-Lemeshow (training group: P = 0.898, validation group: P = 0.891) showed good calibration of combined nomogram and decision curve proved its clinical utility.

CONCLUSIONS

The combined model based on radiomics features plus clinical and dosimetric parameters can improve the prediction of 1-year local control for lung cancer patients undergoing SBRT.

Preclinical Model of Stereotactic Ablative Lung Irradiation Using Arc Delivery in the Mouse: Is Fractionation Worthwhile?

Lung stereotactic body radiation therapy is characterized by a reduction in target volumes and the use of severely hypofractionated schedules. Preclinical modeling became possible thanks to rodent-dedicated irradiation devices allowing accurate beam collimation and focal lung exposure. Given that a great majority of publications use single dose exposures, the question we asked in this study was as follows: in incremented preclinical models, is it worth using fractionated protocols or should we continue focusing solely on volume limitation? The left lungs of C57BL/6JRj mice were exposed to ionizing radiation using arc therapy and 3 × 3 mm beam collimation. Three-fraction schedules delivered over a period of 1 week were used with 20, 28, 40, and 50 Gy doses per fraction. Lung tissue opacification, global histological damage and the numbers of type II pneumocytes and club cells were assessed 6 months post-exposure, together with the gene expression of several lung cells and inflammation markers. Only the administration of 3 × 40 Gy or 3 × 50 Gy generated focal lung fibrosis after 6 months, with tissue opacification visible by cone beam computed tomography, tissue scarring and consolidation, decreased club cell numbers and a reactive increase in the number of type II pneumocytes. A fractionation schedule using an arc-therapy-delivered three fractions/1 week regimen with 3 × 3 mm beam requires 40 Gy per fraction for lung fibrosis to develop within 6 months, a reasonable time lapse given the mouse lifespan. A comparison with previously published laboratory data suggests that, in this focal lung irradiation configuration, administering a Biological Effective Dose ≥ 1000 Gy should be recommended to obtain lung fibrosis within 6 months. The need for such a high dose per fraction challenges the appropriateness of using preclinical highly focused fractionation schedules in mice.

Acute and Late Esophageal Toxicity Following Stereotactic Ablative Radiotherapy to Thoracic Tumors near or Abutting the Esophagus

PURPOSE

To evaluate the incidence of acute and late esophageal toxicity in patients with thoracic tumors near or abutting the esophagus treated with stereotactic ablative radiotherapy (SABR).

METHODS AND MATERIALS

Among patients with thoracic tumors treated with SABR, we identified those with tumors near or abutting the esophagus. Using the linear-quadratic model with an α/ß ratio of 10, we determined the correlation between dosimetric parameters and esophageal toxicity graded using the Common Terminology Criteria for Adverse Events (CTCAE), version 5.0.

RESULTS

Out of 2200 patients treated with thoracic SABR, 767 patients were analyzable for esophageal dosimetry. We identified 55 patients with tumors near the esophagus (52 evaluable for esophagitis grade), 28 with PTV overlapping the esophagus. Median follow-up and overall survival were 16 and 23 months respectively. Thirteen patients (25%) developed temporary grade 2 acute esophageal toxicity, 11 (85%) of whom had PTV overlapping the esophagus. Symptoms resolved within 1-3 months in 12 patients, and 6 months in all patients. No grade 3-5 toxicity was observed. Only 3 patients (6%) developed late or persistent grade 2 dysphagia or dyspepsia of uncertain relationship to SABR. Cumulative incidence of acute esophagitis was 15% and 25% at 14 days and 60 days respectively. Acute toxicity correlated on univariate analysis with esophageal D_max, D_1cc, D_2cc, D_max/D_prescription and whether the PTV was overlapping the esophagus. Esophageal D_max (BED₁₀) < 62 Gy, D_1cc (BED₁₀) < 48 Gy, D_2cc (BED₁₀) < 43 Gy, and D_max/D_prescription < 85% was associated with <20% risk of grade 2 acute esophagitis. Only 2 local recurrences occurred.

CONCLUSIONS

Although 25% of patients with tumors near the esophagus developed acute esophagitis (39% of those with PTV overlapping the esophagus), these toxicities were all grade 2 and all temporary. This suggests the safety and efficacy of thoracic SABR for tumors near or abutting the esophagus when treating with high conformity and sharp dose gradients.

Technical Note: Break-even dose level for hypofractionated treatment schedules

PURPOSE

To derive the isodose line R relative to the prescription dose below which irradiated normal tissue (NT) regions benefit from a hypofractionated schedule with an isoeffective dose to the tumor. To apply the formalism to clinical case examples.

METHODS

From the standard biologically effective dose (BED) equation based on the linear-quadratic (LQ) model, the BED of an NT that receives a relative proportion r of the prescribed dose per fraction for a given α/β-ratio of the tumor, (α/β)_T , and NT, (α/β)_NT , is derived for different treatment schedules while keeping the BED to the tumor constant. Based on this, the "break-even" isodose line R is then derived. The BED of NT regions that receive doses below R decreases for more hypofractionated treatment schedules, and hence a lower risk for NT injury is predicted in these regions. To assess the impact of a linear behavior of BED for high doses per fraction (>6 Gy), we evaluated BED also using the LQ-linear (LQ-L) model.

RESULTS

The formalism provides the equations to derive the BED of an NT as function of dose per fraction for an isoeffective dose to the tumor and the corresponding break-even isodose line R. For generic α/β-ratios of (α/β)_T  = 10 Gy and (α/β)_NT  = 3 Gy and homogeneous dose in the target, R is 30%. R is doubling for stereotactic treatments for which tumor control correlates with the maximum dose of 100% instead of the encompassing isodose line of 50%. When using the LQ-L model, the notion of a break-even dose level R remains valid up to about 20 Gy per fraction for generic α/β-ratios and D T = 2 ( α / β ) .

CONCLUSIONS

The formalism may be used to estimate below which relative isodose line R there will be a differential sparing of NT when increasing hypofractionation. More generally, it allows to assess changes of the therapeutic index for sets of isoeffective treatment schedules at different relative dose levels compared to a reference schedule in a compact manner.

Possible Overcoming of Tumor Hypoxia with Adaptive Hypofractionated Radiosurgery of Large Brain Metastases: A Biological Modeling Study

OBJECTIVE

The present biological modeling study evaluated possible application of adaptive hypofractionated stereotactic radiosurgery (HSRS), which involves escalation of the prescription dose according to the gradual decrease in the tumor volume between treatment sessions separated by 2- to 3-week intervals, in the management of large brain metastases.

METHODS

To investigate the effects of dose escalation during three-stage adaptive HSRS, a generalized biologically effective dose (gBED) model was applied. Accounting for both a nonuniform dose distribution inside the target and tumor hypoxia was implemented, and normal brain radiation dose distributions were assessed.

RESULTS

In comparison with conventional three-stage HSRS (with an identical prescription dose of 10 Gy at each treatment session), adaptive HSRS resulted in a 30-40% increase in gBED. This effect was especially prominent in late-responding targets (with α/β ratios from 3 to 10 Gy) and in neoplasms containing a high percentage of hypoxic cells. Despite dose escalation in the target, irradiation of the adjacent normal brain tissue was kept within safe limits at a level similar to that applied in conventional three-stage HSRS.

CONCLUSION

Adaptive HSRS theoretically results in significant enhancement of gBED in the target and may possibly overcome resistance to irradiation, which is caused by tumor hypoxia. These advantages may translate into higher treatment efficacy in cases of large brain metastases.

Higher biologically effective dose is associated with improved survival in patients with squamous cell carcinoma of the lung treated with stereotactic body radiation therapy

BACKGROUND

Multiple studies have suggested that patients with early-stage SCC of the lung treated with SBRT are more susceptible to local failure compared to other NSCLC histologies. It is unknown if higher BED leads to improved outcomes in this patient population. We evaluated the effect of "high" BED versus "low" BED SBRT on overall survival (OS) in SCC and non-SCC NSCLC patients.

METHODS

The National Cancer Database was used to identify patients with cT1-2N0M0 NSCLC diagnosed between 2006-2016 treated with 3-5 fraction SBRT. Patients were grouped by BED_high (>150 Gy) and BED_low (≤132 Gy). Univariate and multivariable analysis using Kaplan-Meier and Cox proportional hazards regression modeling were performed. Propensity-score matched analysis with inverse probability of treatment (IPTW) weighting was used to account for selection bias.

RESULTS

We identified 4,717 eligible SCC patients and 8,807 eligible non-SCC NSCLC patients. In SCC patients, BED_high was associated with improved OS in both univariate and multivariate analysis (MVA HR 0.84 95% CI 0.76-0.92, p < 0.001), with estimated IPTW-adjusted 3-year OS of 49% compared to 41% for the BED_low group. In contrast, BED_high was not associated with improved OS compared to BED_low for non-SCC NSCLC patients (MVA HR 0.94 95% CI 0.86-1.04, p = 0.23), with estimated IPTW-adjusted 3-year OS of 54% and 53%, respectively.

CONCLUSIONS

Our analysis suggests that in patients with early-stage NSCLC, SBRT regimens with BED > 150 Gy may confer a survival benefit in patients with SCC histology. Histology-based dose modification should be considered, and prospective validation may be warranted.

Ablative radiotherapy for ultracentral lung cancers: Dosimetric, geometric, and volumetric predictors of outcomes and toxicity

BACKGROUND

Ultracentral lung cancers arise near the proximal bronchial tree (PBT), trachea, or esophagus, and have been associated with worse outcomes and increased toxicity after radiotherapy. We sought to associate dosimetric and anatomic factors with oncologic outcomes and toxicities.

METHODS

One-hundred ten patients treated with ablative, curative-intent radiotherapy for ultracentral, node-negative, non-small cell lung cancer were included. Dosimetric and geometric data obtained using custom software that calculated volumes of target structures and organs-at-risk and measured the shortest vector length between these volumes were associated with outcomes and toxicity.

RESULTS

Common dose/fractionation schemes included 50 Gy in 5 fractions (57%), 60 Gy in 8 fractions (15%), and 48 Gy in 4 fractions (13%). Overall survival at 1, 2, and 5 years was 78%, 57%, and 32%, respectively. Factors significantly associated with death included endobronchial tumor, gross tumor volume (GTV) or planning target volume (PTV) contacting PBT, shorter distance from GTV to PBT or esophagus, volume of PBT receiving prescription dose, higher pericardium max dose, lung V20Gy, and mean lung dose. Local progression at 1, 2, and 5 years was 4%, 16%, and 21%. Factors associated with local progression were lower GTV minimum dose and higher GTV/PTV volume ratio. Acute and late grade 2 + toxicity was seen in 18% and 27%, respectively. Four patients (4%) had fatal toxicity.

CONCLUSIONS

Lower GTV minimum dose and smaller volumetric PTV expansions may increase risk of local progression, and should be balanced against normal tissue doses including pericardium maximum dose, lung V20Gy, and mean lung dose.

[Stereotactic body radiotherapy for locally advanced pancreatic cancer: A systemic review]

Stereotactic body radiation therapy (SBRT) for locally advanced pancreatic cancer (LAPC) is an emerging treatment option. Most studies showed local control of approximately 75% with no evidence of improved overall survival. Gastrointestinal toxicities could be significant, ranging up to 22% for acute toxicities≥grade 3+ and 44% for late toxicities≥grade 3+. Currently, no standardized guidelines for treatment and management scheme. We conducted a systemic review of published prospective and retrospective trials to evaluate the efficacy, safety, technical data, and discuss future directions.

Revisiting the formalism of equivalent uniform dose based on the linear-quadratic and universal survival curve models in high-dose stereotactic body radiotherapy

Purpose

To examine the equivalent uniform dose (EUD) formalism using the universal survival curve (USC) applicable to high-dose stereotactic body radiotherapy (SBRT).

Materials and methods

For nine non-small-cell carcinoma cell (NSCLC) lines, the linear-quadratic (LQ) and USC models were used to calculate the EUD of a set of hypothetical two-compartment tumor dose–volume histogram (DVH) models. The dose was varied by ±5%, ±10%, and ±20% about the prescription dose (60 Gy/3 fractions) to the first compartment, with fraction volume varying from 1% and 5% to 30%. Clinical DVHs of 21 SBRT treatments of NSCLC prescribed to the 70–83% isodose lines were also considered. The EUD of non-standard SBRT dose fractionation (EUD_SBRT) was further converted to standard fractionation of 2 Gy (EUD_CFRT) using the LQ and USC models to facilitate comparisons between different SBRT dose fractionations. Tumor control probability (TCP) was then estimated from the LQ- and USC-EUD_CFRT.

Results

For non-standard SBRT fractionation, the deviation of the USC- from the LQ-EUD_SBRT is largely limited to 5% in the presence of dose variation up to ±20% to fractional tumor volume up to 30% in all NSCLC cell lines. Linear regression with zero constant yielded USC-EUD_SBRT = 0.96 × LQ-EUD_SBRT (r² = 0.99) for the clinical DVHs. Converting EUD_SBRT into standard 2‑Gy fractions by the LQ formalism produced significantly larger EUD_CFRT than the USC formalism, particularly for low \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha /\beta$$\end{document}α/β ratios and large fraction dose. Simplified two-compartment DVH models illustrated that both the LQ- and USC-EUD_CFRT values were sensitive to cold spot below the prescription dose with little volume dependence. Their deviations were almost constant for up to 30% dose increase above the prescription. Linear regression with zero constant yielded USC-EUD_CFRT = 1.56 × LQ-EUD_CFRT (r² = 0.99) for the clinical DVHs. The clinical LQ-EUD_CFRT resulted in median TCP of almost 100% vs. 93.8% with USC-EUD_CFRT.

Conclusion

A uniform formalism of EUD should be defined among the SBRT community in order to apply it as a single metric for dose reporting and dose–response modeling in high-dose-gradient SBRT because its value depends on the underlying cell survival model and the model parameters. Further investigations of the optimal formalism to derive the EUD through clinical correlations are warranted.

Electronic supplementary material

The online version of this article (10.1007/s00066-020-01713-w) contains supplementary material, which is available to authorized users.

Correlating Dose Variables with Local Tumor Control in Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer: A Modeling Study on 1500 Individual Treatments

BACKGROUND

Large variation regarding prescription and dose inhomogeneity exists in stereotactic body radiation therapy (SBRT) for early-stage non-small cell lung cancer. The aim of this modeling study was to identify which dose metric correlates best with local tumor control probability to make recommendations regarding SBRT prescription.

METHODS AND MATERIALS

We combined 2 retrospective databases of patients with non-small cell lung cancer, yielding 1500 SBRT treatments for analysis. Three dose parameters were converted to biologically effective doses (BEDs): (1) the (near-minimum) dose prescribed to the planning target volume (PTV) periphery (yielding BEDmin); (2) the (near-maximum) dose absorbed by 1% of the PTV (yielding BEDmax); and (3) the average between near-minimum and near-maximum doses (yielding BEDave). These BED parameters were then correlated to the risk of local recurrence through Cox regression. Furthermore, BED-based prediction of local recurrence was attempted by logistic regression and fast and frugal trees. Models were compared using the Akaike information criterion.

RESULTS

There were 1500 treatments in 1434 patients; 117 tumors recurred locally. Actuarial local control rates at 12 and 36 months were 96.8% (95% confidence interval, 95.8%-97.8%) and 89.0% (87.0%-91.1%), respectively. In univariable Cox regression, BEDave was the best predictor of risk of local recurrence, and a model based on BEDmin had substantially less evidential support. In univariable logistic regression, the model based on BEDave also performed best. Multivariable classification using fast and frugal trees revealed BEDmax to be the most important predictor, followed by BEDave.

CONCLUSIONS

BEDave was generally better correlated with tumor control probability than either BEDmax or BEDmin. Because the average between near-minimum and near-maximum doses was highly correlated to the mean gross tumor volume dose, the latter may be used as a prescription target. More emphasis could be placed on achieving sufficiently high mean doses within the gross tumor volume rather than the PTV covering dose, a concept needing further validation.

Radiobiology of stereotactic ablative radiotherapy (SABR): perspectives of clinical oncologists

Stereotactic ablative radiotherapy (SABR) is a novel radiation treatment method that delivers an intense dose of radiation to the treatment targets with high accuracy. The excellent local control and tolerance profile of SABR have made it become an important modality in cancer treatment. The radiobiology of SABR is a key factor in understanding and further optimizing the benefits of SABR. In this review, we have addressed several issues in the radiobiology of SABR from the perspective of clinical oncologists. The appropriateness of the linear-quadratic (LQ) model for SABR is controversial based on preclinical data, but it is a reliable tool from the perspective of clinical application because the biological effective dose (BED) calculated with it can represent the tumor control probability (TCP). Hypoxia is a common phenomenon in SABR in spite of the relatively small tumor size and has a negative effect on the efficacy of SABR. Preliminary studies indicate that a hypoxic radiosensitizer combined with SABR may be a feasible strategy, but so far there is not adequate evidence to support its application in routine practice. The vascular change of endothelial apoptosis and blood perfusion reduction in SABR may enhance the response of tumor cells to radiation. Combination of SABR with anti-angiogenesis therapy has shown promising efficacy and good tolerance in advanced cancers. SABR is more powerful in enhancing antitumor immunity and works better with immune checkpoint inhibitors (ICIs) than conventional fractionation radiotherapy. Combination of SABR with ICIs has become a practical option for cancer patients with metastases.

Dose prescription in SBRT for early-stage non-small cell lung cancer: are we all speaking the same language?

INTRODUCTION

Stereotactic body radiation therapy is increasingly used in the treatment of early-stage lung cancers. Guidelines provide indications regarding the constraints to the organs at risk (OARs) and the minimum coverage of the planning target volume but do not suggest optimal dose distribution. Data on dose distribution from the different published series are not comparable due to different prescription modalities and reported dose parameters.

METHODS

We conducted a review of the published data on dose prescription, focusing on the role of homogeneity on local tumor control, and present suggestions on how to specify and report the prescriptions to permit comparisons between studies or between cases from different centers.

CONCLUSIONS

To identify the dose-prescription modality that better correlates with oncologic outcomes, future studies should guarantee a close uniformity of dose distribution between cases and complete dose parameters reporting for treatment volumes and OARs.

Synergistic effects of anti-PDL-1 with ablative radiation comparing to other regimens with same biological effect dose based on different immunogenic response

Introduction

Irradiation can induce multiple inhibitory and stimulatory effects on the immune system. In recent studies, it has been noted that administration of radiation with various doses and fractionation plans may influence on immune responses in microenvironment of tumor. But in radiobiology, the Biologically Effective Dose (BED) formula has been designed for calculating isoeffect doses in different regimens of daily clinical practice. In other words, BED has also been used to predict the effects of fractionation schedules on tumor cells.

Methods

In our study, three different regimens with BEDs of 40 gray (Gy) were analyzed in BALB/c mice. These included conventional fractionated radiotherapy (RT) (3Gyx10), high-dose hypofractionated RT (10Gyx2), and single ablative high-dose RT (15Gyx1).

Results

As BED predicts, all three similarly decreased tumor volumes and increased survival times relative to controls, but after high dose exposure in ablative group, the expression of IFNγ was increased following high infiltration of CD8 cells into the tumor microenvironment. When anti-PDL-1 was combined with RT, single ablative high-dose radiation enhanced antitumor activity by increasing IFNγ in tumors and CD8⁺ tumor-infiltrating lymphocytes; as a result, this combining therapy had enhanced antitumor activity and lead to control tumor volume effectively and improve significantly survival rate and finally the recurrence of tumor was not observed.

Conclusion

Results show distinct radiation doses and fractionation schemes with same BED have different immunogenic response and these findings can provide data helping to design regimens of radiation combined with immune checkpoint blockers (ICBs).

Cone-beam CT radiomics features might improve the prediction of lung toxicity after SBRT in stage I NSCLC patients

Background

Stereotactic body radiotherapy (SBRT) is the standard care for inoperable early stage non‐small cell lung cancer (NSCLC). The purpose of our study was to investigate whether a prediction model based on cone‐beam CT (CBCT) plus pretreatment CT radiomics features could improve the prediction of tumor control and lung toxicity after SBRT in comparison to a model based on pretreatment CT radiomics features alone.

Methods

A total of 34 cases of stage I NSCLC patients who received SBRT were included in the study. The pretreatment planning CT and serial CBCT radiomics features were analyzed using the imaging biomarker explorer (IBEX) software platform. Multivariate logistic regression was conducted for the association between progression‐free survival (PFS), lung toxicity and features. The predictive capabilities of the models based on CBCT and CT features were compared using receiver operating characteristic (ROC) curves.

Results

Five CBCT features and two planning CT features were correlated with disease progression. Six CBCT features and two planning CT features were related to lung injury. The ROC curves indicated that the model based on the CBCT plus planning CT features might be better than the model based on the planning CT features in predicting lung injury. The other ROC curves indicated that the model based on the planning CT features was similar to the model based on the CBCT plus planning CT features in predicting disease progression.

Conclusions

Both pretreatment CT and CBCT radiomics features could predict disease progression and lung injury. A model with CBCT plus pretreatment CT radiomics features might improve the prediction of lung toxicity in comparison with a model with pretreatment CT features alone.

Key points

Significant findings of the study: A model with cone‐beam CT radiomics features plus pre‐treatment CT radiomics features might improve the prediction of lung toxicity after SBRT in stage I NSCLC patients.

What this study adds: In the prediction of PFS and lung toxicity in early‐stage NSCLC patients treated with SBRT, CBCT radiomics could be another effective method.

Biologically Effective Dose in Stereotactic Body Radiotherapy and Survival for Patients With Early-Stage NSCLC

INTRODUCTION

Stereotactic body radiotherapy (SBRT) results in excellent local control of stage I NSCLC. Radiobiology models predict greater tumor response when higher biologically effective doses (BED₁₀) are given. Prior studies support a BED₁₀ greater than or equal to 100 Gy with SBRT; however, data are limited comparing outcomes after various SBRT regimens. We therefore sought to evaluate national trends and the effect of using "low" versus "high" BED₁₀ SBRT courses on overall survival (OS).

METHODS

This retrospective study used the National Cancer Data Base to identify patients diagnosed with clinical stage I (cT1-2aN0M0) NSCLC from 2004 to 2014 treated with SBRT. Patients were categorized into LowBED (100-129 Gy) or HighBED (≥130 Gy) groups. A 1:1 matched analysis based on patient and tumor characteristics was used to compare OS by BED₁₀ group. Tumor centrality was not assessed.

RESULTS

O 25,039 patients treated with LowBED (n = 14,756; 59%) or HighBED (n = 10,283; 41%) SBRT, 20,542 were matched. Shifts in HighBED to LowBED SBRT regimen use correlated with key publications in the literature. In the matched cohort, 5-year OS rates were 26% for LowBED and 34% for HighBED groups (p = 0.039). On multivariate analysis, receipt of LowBED was associated with significantly worse survival (hazard ratio = 1.046, 95% confidence interval: 1.004-1.090, p = 0.032).

CONCLUSIONS

LowBED SBRT for treating stage I NSCLC is becoming more common. However, our findings suggest SBRT regimens with BED₁₀ greater than or equal to 130 Gy may confer an additional survival benefit. Additional studies are required to evaluate the dose-response relationship and toxicities associated with modern HighBED SBRT.

A mathematical model for predicting the changes of non-small cell lung cancer based on tumor mass during radiotherapy

This study aims to build a feasible mathematical model to analyze the mass evolution of NSCLC during standard fractionated radiotherapy. Seventy-three cases of NSCLC who were received radiotherapy with prescription dose of 2 Gy  ×  30 fx were selected retrospectively and divided into adenocarcinoma (ADC) group and squamous cell carcinoma (SCC) group according to the pathological type. A total of six sets of CT/CBCT images were collected. The tumor masses were measured according to each set of images. We build a mathematical model (Linear Quadratic_Repopulation&Reoxygenation& Dissolution model, LQ_RRD model), which was used to fit the first five sets of measured mass into a smooth curve. By adjusting the model parameters (λ, ν and µ), the optimal fitting results can be obtained. In order to verify the accuracy of model prediction, we measured the mass of the review images (MV, measured values), and found out the estimate point of the corresponding time (EV, estimated value) on the fitting curve. The difference and correlation between MV and EV were compared. It was found that the model could substantially simulate the tumor mass changes during radiotherapy, and it had a good fit to the clinical data (%RMSE-Median  =  5.52, %RMSE-Range  =  [3.19, 10.73]). Comparing the differences of model parameters between ADC and SCC group, there was no significant difference in λ (t  =  1.622, p   =  0.109), but the difference was significant in ν and µ (z  =  -7.270, p   =  0.000 and t  =  -10.205, p   =  0.000). Moreover, linear correlation analysis showed that there was a linear correlation between MV and EV no matter mass or volume (r  =  0.960, p   =  0.000 versus r  =  0.926, p   =  0.000). Nevertheless, the deviation between MV and EV of volume was larger than that of mass (z  =  -1.897, p   =  0.058 versus z  =  -3.387, p   =  0.001), and the deviation was more pronounced in larger tumors. We suggest that this mathematical model is more suitable to predict the tumor mass than volume for NSCLC during radiotherapy.

Stereotactic body radiotherapy for primary non-small cell lung cancer patients with clinical T3-4N0M0 (UICC 8th edition): outcomes and patterns of failure

The evidence for stereotactic body radiotherapy (SBRT) is meagre for patients with clinical T3-4N0M0 non-small cell lung cancer (8th Edition of the Union for International Cancer Control (UICC)). This study retrospectively investigated clinical outcomes following SBRT for such patients. Among consecutive patients treated with SBRT, patients staged as cT3-4N0M0 by all criteria were examined, most of whom were unsuitable to chemoradiotherapy due to their fragile characters. Clinical outcomes were evaluated and factors associated with outcomes were investigated. Between 2005 and 2017, 70 eligible patients (T3: 58, T4: 12; median age 81 (63-93) years) were identified. Median follow-up duration was 28.6 (1.0-142.5) months. No adjuvant chemotherapy was administered. The 3-year local recurrence rates were 15.8% and 16.7% in T3 and T4 patients, respectively, and they were significantly lower in the high-dose group (3.1% vs 28.6%, P < 0.01). Multivariate analyses showed that the dose-volumetric factor was the significant factor for local recurrence. The 3-year regional and distant metastasis rates, cancer-specific mortality, and overall survival in T3 and T4 patients were 22.7% and 25.0%, 26.5% and 33.3%, 32.2% and 41.7%, and 39.5% and 41.7%, respectively. Only age was correlated with overall survival. Radiation pneumonitis ≥grade 3 and fatal hemoptysis occurred in 3 and 1 patients, respectively. SBRT for cT3-4N0M0 lung cancer patients achieved good local control. Survival was rather good considering that patients were usually frail, staged with clinical staging, and were not given adjuvant chemotherapy, and it may be comparable to surgery. To validate these outcomes following SBRT, a prospective study is warranted.

Estimation of the α/β ratio of non-small cell lung cancer treated with stereotactic body radiotherapy

BACKGROUND

High-dose hypofractionated radiotherapy should theoretically result in a deviation from the typical linear-quadratic shape of the cell survival curve beyond a certain threshold dose, yet no evidence for this hypothesis has so far been found in clinical data of stereotactic body radiotherapy treatment (SBRT) for early-stage non-small cell lung cancer (NSCLC). A pragmatic explanation is a larger α/β ratio than the conventionally assumed 10 Gy. We here attempted an estimation of the α/β ratio for NSCLC treated with SBRT using individual patient data.

MATERIALS AND METHODS

We combined two large retrospective datasets, yielding 1294 SBRTs (≤10 fractions) of early stage NSCLC. Cox proportional hazards regression, a logistic tumor control probability model and a biologically motivated Bayesian cure rate model were used to estimate the α/β ratio based on the observed number of local recurrences and accounting for tumor size.

RESULTS

A total of 109 local progressions were observed after a median of 17.7 months (range 0.6-76.3 months). Cox regression, logistic regression of 3 year tumor control probability and the cure rate model yielded best-fit estimates of α/β = 12.8 Gy, 14.9 Gy and 12-16 Gy (depending on the prior for α/β), respectively, although with large uncertainties that did not rule out the conventional α/β = 10 Gy.

CONCLUSIONS

Clinicians can continue to use the simple LQ formalism to compare different SBRT treatment schedules for NSCLC. While α/β = 10 Gy is not ruled out by our data, larger values in the range 12-16 Gy are more probable, consistent with recent meta-regression analyses.

Calculating the individualized fraction regime in stereotactic body radiotherapy for non-small cell lung cancer based on uncomplicated tumor control probability function

BACKGROUND

To calculate the individualized fraction regime (IFR) in stereotactic body radiotherapy (SBRT) for non-small cell lung cancer (NSCLC) patients using the uncomplicated tumor control probability (UTCP, P⁺) function.

METHODS

Thirty-three patients with peripheral lung cancer or lung metastases who had undergone SBRT were analyzed. Treatment planning was performed using the dose regime of 48 Gy in 4 fractions. Dose volume histogram (DVH) data for the gross tumor volume (GTV), lung, chest wall (CW) and rib were exported and the dose bin was multiplied by a certain percentage of the dose in that bin which ranged from 1 to 200% in steps of 1%. For each dose fraction, P⁺ values were calculated by considering the tumor control probability (TCP), radiation-induced pneumonitis (RIP), chest wall pain (CWP) and radiation-induced rib fracture (RIRF). UTCP values as a function of physical dose were plotted and the maximum P⁺ values corresponded to the optimal therapeutic gain. The IFR in 3 fractions was also calculated with the same method by converting the dose using the linear quadratic (LQ) model.

RESULTS

Thirty-three patients attained an IFR using the introduced methods. All the patients achieved a TCP value higher than 92.0%. The IFR ranged from 3 × 10.8 Gy to 3 × 12.5 Gy for 3 fraction regimes and from 4 × 9.2 Gy to 4 × 10.7 Gy for 4 fraction regimes. Four patients with typical tumor characteristics demonstrated that the IFR was patient-specific and could maximize the therapeutic gain. Patients with a large tumor had a lower TCP and UTCP and a smaller fractional dose than patients with a small tumor. Patients with a tumor adjacent to the organ at risk (OAR) or at a high risk of RIP had a lower UTCP and a smaller fractional dose compared with patients with a tumor located distant from the OAR.

CONCLUSIONS

The proposed method is capable of predicting the IFR for NSCLC patients undergoing SBRT. Further validation in clinical samples is required.

Comparison of the Efficacy of Stereotactic Body Radiotherapy versus Surgical Treatment for Early-Stage Non-Small Cell Lung Cancer after Propensity Score Matching

BACKGROUND

The objective of this study was to evaluate the clinical efficacy of stereotactic body radiotherapy (SBRT) and surgical treatment for stage I-II non-small cell lung cancer (NSCLC).

METHODS

This retrospective analysis included 879 patients with primary NSCLC who underwent SBRT or surgical treatment in Zhejiang Cancer Hospital, Hangzhou, China from January 2012 to December 2017.

RESULTS

Propensity score matching (PSM) analysis was performed between the two groups. Each group included 66 patients who met the inclusion criteria. The median follow-up in the SBRT and surgery groups was 30.8 and 48.4 months, respectively. In the SBRT group, the 1- and 3-year overall survival rates were 98.5 and 83.9%, respectively. In the surgery group, these rates were 98.5 and 89.4%, respectively (P = .248). The 3-year cancer-specific survival rates in the SBRT and surgery groups were 89.1 and 95.2%, respectively (P = .056).

CONCLUSIONS

In these propensity score matched early-stage NSCLC patients, the 1- and 3-year overall survival rates associated with SBRT were similar to those observed with surgery. In addition, there was no significant difference in cancer-specific survival between the two groups.

Stereotactic body radiation therapy with higher biologically effective dose is associated with improved survival in stage II non-small cell lung cancer

OBJECTIVES

The role of stereotactic body radiation therapy (SBRT) in treating stage II non-small cell lung cancer (NSCLC) remains unclear. This study evaluates SBRT dose prescription patterns and survival outcomes in Stage II NSCLC using the National Cancer Database (NCDB).

MATERIALS AND METHODS

Patients diagnosed with Stage II NSCLC and treated with SBRT between 2004-2013 were identified in NCDB. The biologically effective dose with α/β = 10 Gy (BED₁₀) was calculated. Overall survival (OS) was analyzed using the Kaplan-Meier method and Cox regression models.

RESULTS

Of 56,543 patients with Stage II NSCLC, 451 (0.8%) received SBRT. There were 360 patients (79.8%) with node-negative and 91 patients (20.2%) with node-positive disease. The most common prescriptions were 10 Gy x 5 (35.9%) and 12 Gy x 4 (19.3%). The mean and median BED₁₀ were 114.9 Gy and 105.6 Gy, respectively. With median follow-up of 19.3 months, overall median survival was 23.7 months. Median survival was 22.4 months for those treated with BED₁₀ < 114.9 Gy versus 31.5 months for BED₁₀ ≥ 114.9 Gy (p = 0.036). On multivariate analysis, BED₁₀ as a continuous variable (hazard ratio [HR] 0.991, p = 0.009) and ≥ 114.9 Gy (HR 0.63, p = 0.015) were associated with improved survival in node-negative patients. BED₁₀ as a continuous variable (HR 0.997, p = 0.465) and ≥ 114.9 Gy (HR 0.81, p = 0.546) were not significant factors for predicting survival in node-positive patients.

CONCLUSION

SBRT is infrequently utilized to treat Stage II NSCLC in the United States. Treatment with higher BED₁₀ was associated with improved survival, and the benefit was limited to patients with node-negative disease.

Simulation analysis for tumor radiotherapy based on three-component mathematical models

OBJECTIVE

To setup a three-component tumor growth mathematical model and discuss its basic application in tumor fractional radiotherapy with computer simulation.

METHOD

First, our three-component tumor growth model extended from the classical Gompertz tumor model was formulated and applied to a fractional radiotherapy with a series of proper parameters. With the computer simulation of our model, the impact of some parameters such as fractional dose, amount of quiescent tumor cells, and α/β value to the effect of radiotherapy was also analyzed, respectively.

RESULTS

With several optimal technologies, the model could run stably and output a series of convergent results. The simulation results showed that the fractional radiotherapy dose could impact the effect of radiotherapy significantly, while the amount of quiescent tumor cells and α/β value did that to a certain extent.

CONCLUSIONS

Supported with some proper parameters, our model can simulate and analyze the tumor radiotherapy program as well as give some theoretical instruction to radiotherapy personalized optimization.

ICRU report 91 on prescribing, recording, and reporting of stereotactic treatments with small photon beams : Statement from the DEGRO/DGMP working group stereotactic radiotherapy and radiosurgery

The International Commission on Radiation Units and Measurements (ICRU) report 91 with the title "prescribing, recording, and reporting of stereotactic treatments with small photon beams" was published in 2017. This extensive publication covers different relevant aspects of stereotactic radiotherapy such as small field dosimetry, accuracy requirements for volume definition and planning algorithms, and the precise application of treatment by means of image guidance. Finally, recommendations for prescribing, recording and reporting are given.

Comparison of Three Radiobiological Models in Stereotactic Body Radiotherapy for Non-Small Cell Lung Cancer

Objective: The applicability of the linear quadratic (LQ) model to local control (LC) modeling after hypofractionated radiotherapy to treat lung cancer is highly debated. To date, the differences in predicted outcomes between the LQ model and other radiobiological models, which are characterized by additional dose modification beyond a certain transitional dose (d_T), have not been well established. This study aims to compare the outcomes predicted by the LQ model with those predicted by two other radiobiological models in stereotactic body radiotherapy (SBRT) for non-small cell lung cancer (NSCLC). Methods: Computer tomography (CT) simulation data sets for 20 patients diagnosed with stage Ⅰ primary NSCLC were included in this study. Three radiobiological models, including the LQ, the universal survival curve (USC) and the modified linear quadratic and linear (mLQL) model were employed to predict the tumor control probability (TCP) data. First, the d_T values for the USC and mLQL models were determined. Then, the biologically effective dose (BED) and the predicted TCP values from the LQ model were compared with those calculated from the USC and mLQL models. Results: The d_T values from the USC model were 29.6 Gy, 33.8 Gy and 44.5 Gy, whereas the values were 90.2 Gy, 84.0 Gy and 57.3 Gy for the mLQL model for 1-year, 2-year and 3-year TCP prediction. The remarkable higher d_T values obtained from the mLQL model revealed the same dose-response relationship as the LQ model in the low- and high-dose ranges. We also found that TCP prediction from the LQ and USC models differed by less than 3%, although the BED values for the two models were significantly different. Conclusion: Radiobiological analysis reveals small differences between the models and suggested that the LQ model is applicable for modeling LC using SBRT to treat lung cancer, even when an extremely high fractional dose is used.

A novel index for assessing treatment plan quality in stereotactic radiosurgery

OBJECTIVE

Stereotactic radiosurgery (SRS) is characterized by high levels of conformity and steep dose gradients from the periphery of the target to surrounding tissue. Clinical studies have backed up the importance of these factors through evidence of symptomatic complications. Available data suggest that there are threshold doses above which the risk of symptomatic radionecrosis increases with the volume irradiated. Therefore, radiosurgical treatment plans should be optimized by minimizing dose to the surrounding tissue while maximizing dose to the target volume. Several metrics have been proposed to quantify radiosurgical plan quality, but all present certain weaknesses. To overcome limitations of the currently used metrics, a novel metric is proposed, the efficiency index (η50%), which is based on the principle of calculating integral doses: η50% = integral doseTV/integral dosePIV50%.

METHODS

The value of η50% can be easily calculated by dividing the integral dose (mean dose × volume) to the target volume (TV) by the integral dose to the volume of 50% of the prescription isodose (PIV50%). Alternatively, differential dose-volume histograms (DVHs) of the TV and PIV50% can be used. The resulting η50% value is effectively the proportion of energy within the PIV50% that falls into the target. This value has theoretical limits of 0 and 1, with 1 being perfect. The index combines conformity, gradient, and mean dose to the target into a single value. The value of η50% was retrospectively calculated for 100 clinical SRS plans.

RESULTS

The value of η50% for the 100 clinical SRS plans ranged from 37.7% to 58.0% with a mean value of 49.0%. This study also showed that the same principles used for the calculation of η50% can be adapted to produce an index suitable for multiple-target plans (Gη12Gy). Furthermore, the authors present another adaptation of the index that may play a role in plan optimization by calculating and minimizing the proportion of energy delivered to surrounding organs at risk (OARη50%).

CONCLUSIONS

The proposed efficiency index is a novel approach in quantifying plan quality by combining conformity, gradient, and mean dose into a single value. It quantifies the ratio of the dose “doing good” versus the dose “doing harm,” and its adaptations can be used for multiple-target plan optimization and OAR sparing.

Abscopal Effects With Hypofractionated Schedules Extending Into the Effector Phase of the Tumor-Specific T-Cell Response

PURPOSE

Hypofractionated radiation therapy (hRT) combined with immune checkpoint blockade can induce T-cell-mediated local and abscopal antitumor effects. We had previously observed peak levels of tumor-infiltrating lymphocytes (TILs) between days 5 and 8 after hRT. Because TILs are regarded as radiosensitive, hRT schedules extending into this period might be less immunogenic, prompting us to compare clinically relevant, short and extended schedules with equivalent biologically effective doses combined with anti-programmed cell death 1 (PD1) antibody treatment.

METHODS AND MATERIALS

In mice bearing 2 B16-CD133 melanoma tumors, the primary tumor was irradiated with 3 × 9.18 Gy in 3 or 5 days or with 5 × 6.43 Gy in 10 days; an anti-PD1 antibody was given weekly. The mice were monitored for tumor growth and survival. T-cell responses were determined on days 8 and 15 of treatment. The role of regional lymph nodes was studied by administering FTY720, which blocks lymph node egress of activated T cells. Tumor growth measurements after combination treatment using short or extended hRT and control treatment were also performed in the wild-type B16 melanoma and 4T1 breast carcinoma models.

RESULTS

In the B16-CD133 model, growth inhibition of irradiated primary and nonirradiated secondary tumors and overall survival were similar with all 3 hRT/anti-PD1 combinations, superior to hRT and anti-PD1 monotherapy, and was strongly dependent on CD8⁺ T cells. TIL infiltration and local and systemic tumor-specific CD8⁺ T-cell responses were also similar, regardless of whether short or extended hRT was used. Administration of FTY720 accelerated growth of both primary and secondary tumors, strongly reduced their TIL infiltration, and increased tumor-specific CD8⁺ T cells in the lymph nodes draining the irradiated tumor. In the 4T1 model, local and abscopal tumor control was also similar, regardless of whether short or extended hRT was used, although the synergy between hRT and anti-PD1 was weaker. No synergies were found in the B16 wild-type model lacking an exogenous antigen.

CONCLUSIONS

Our data suggest that combination therapy with hRT schedules extending into the period during which treatment-induced T cells infiltrate the irradiated tumor can provoke local and systemic antitumor effects similar to those with therapy using shorter schedules, if the regional lymph nodes supply sufficient tumor-specific T cells. This has implications for planning clinical RT/immune checkpoint blockade trials.