Radiation-induced rib fractures after hypofractionated stereotactic body radiation therapy of non-small cell lung cancer: a dose- and volume-response analysis

Practice and principles of stereotactic body radiation therapy for spine and non-spine bone metastases

Radiotherapy is the dominant treatment modality for painful spine and non-spine bone metastases (NSBM). Historically, this was achieved with conventional low dose external beam radiotherapy, however, stereotactic body radiotherapy (SBRT) is increasingly applied for these indications. Meta-analyses and randomized clinical trials have demonstrated improved pain response and more durable tumor control with SBRT for spine metastases. However, in the setting of NSBM, there is limited evidence supporting global adoption and large scale randomized clinical trials are in need. SBRT is technically demanding requiring careful consideration of organ at risk tolerance, and strict adherence to technical requirements including immobilization, simulation, contouring and image-guidance procedures. Additional considerations include follow up practices after SBRT, with appropriate imaging playing a critical role in response assessment. Finally, there is renewed research into promising new technologies that may further refine the use of SBRT in both spinal and NSBM in the years to come.

Symptomatic radiation-induced rib fractures after stereotactic body radiotherapy for early-stage non-small cell lung cancer

Background and purpose

The present study investigated the relationships between the risk of radiation-induced rib fractures (RIRF) and clinical and dosimetric factors in stereotactic body radiotherapy (SBRT) for early-stage non-small cell lung cancer (NSCLC). We also examined dosimetric parameters associated with symptomatic or asymptomatic RIRF and the dosimetric threshold for symptomatic RIRF.

Materials and methods

We reviewed 244 cases of early-stage NSCLC treated with SBRT. Gray's test and the Fine-Gray model were performed to examine the relationships between clinical and dosimetric factors and grade ≥ 2 (i.e., symptomatic) RIRF. The effects of each dose parameter on grade ≥ 1 and ≥ 2 RIRF were assessed with the Fine-Gray model. The t-test was used to compare each dose parameter between the grade 1 and grade ≥ 2 groups. Optimal thresholds were tested using receiver operating characteristic (ROC) curves.

Results

With a median follow-up period of 48 months, the 4-year cumulative incidence of grade ≥ 1 and grade ≥ 2 RIRF were 26.4 % and 8.0 %, respectively. Regarding clinical factors, only age was associated with the development of grade ≥ 2 RIRF (p = 0.024). Among dosimetric parameters, only V40Gy significantly differed between the grade 1 and grade ≥ 2 groups (p = 0.015). The ROC curve analysis of grade ≥ 2 RIRF showed that the optimal diagnostic thresholds for D3cc, D4cc, D5cc, and V40Gy were 45.86 Gy (area under the curve [AUC], 0.706), 39.02 Gy (AUC, 0.705), 41.62 Gy (AUC, 0.702), and 3.83 cc (AUC, 0.730), respectively. These results showed that V40Gy ≤ 3.83 cc was the best indicator of grade ≥ 2 RIRF. The 4-year incidence of grade ≥ 2 RIRF in the V40Gy ≤ 3.83 cc vs. > 3.83 cc groups was 1.8 % vs. 14.2 % (p = 0.001).

Conclusion

The present results recommend V40Gy ≤ 3.83 cc as the threshold for grade ≥ 2 RIRF in SBRT.

Predictors of pathologic fracture and local recurrence following stereotactic body radiation therapy to 505 non-spine bone metastases

PURPOSE

Stereotactic Body Radiation Therapy (SBRT) is increasingly applied to treat non-spine bone metastases (NSBM) though data remains limited on this approach. In this retrospective study, we report outcomes and predictors of local failure (LF) and pathological fracture (PF) post-SBRT for NSBM using a mature single-institution database.

METHODS

Patients with NSBM treated with SBRT between 2011 and 2021 were identified. The primary objective was to assess the rates of radiographic LF. Secondary objectives were to assess the rates of in-field PF, overall survival (OS), and late grade ≥ 3 toxicity. Competing risks analysis was used to assess rates of LF and PF. Univariable regression and multivariable regression (MVR) were performed to investigate predictors of LF and PF.

RESULTS

A total of 373 patients with 505 NSBM were included in this study. Median follow-up was 26.5 months. The cumulative incidence of LF at 6, 12, and 24 months were 5.7%, 7.9%, and 12.6%, respectively. The cumulative incidence of PF at 6, 12, and 24 months were 3.8%, 6.1%, and 10.9%, respectively. Lytic NSBM (HR = 2.18; p < 0.01), a lower biologically effective dose (HR = 1.11 per 5 Gy10 decrease; p = 0.04), and a PTV ≥ 54 cc (HR = 4.32; p < 0.01) predicted for a higher risk of LF on MVR. Lytic NSBM (HR = 3.43; p < 0.01), mixed (lytic/sclerotic) lesions (HR = 2.70; p = 0.04), and rib metastases (HR = 2.68; p < 0.01) predicted for a higher risk of PF on MVR.

CONCLUSION

SBRT is an effective modality to treat NSBM with high rates of radiographic local control with an acceptable rate of PF. We identify predictors of both LF and PF that can serve to inform practice and trial design.

Predictors and characteristics of Rib fracture following SBRT for lung tumors

BACKGROUND

The utilization of stereotactic body radiation therapy (SBRT) is increasing for primary and secondary lung neoplasms. Despite encouraging results, SBRT is associated with an increased risk of osteoradionecrosis-induced rib fracture. We aimed to (1) evaluate potential clinical, demographic, and procedure-related risk factors for rib fractures and (2) describe the radiographic features of post-SBRT rib fractures.

METHODS

We retrospectively identified 106 patients who received SBRT between 2015 and 2018 for a primary or metastatic lung tumor with at least 12 months of follow up. Exclusion criteria were incomplete records, previous ipsilateral thoracic radiation, or relevant prior trauma. Computed tomography (CT) images were reviewed to identify and characterize rib fractures. Multivariate logistic regression modeling was employed to determine clinical, demographic, and procedural risk factors (e.g., age, sex, race, medical comorbidities, dosage, and tumor location).

RESULTS

A total of 106 patients with 111 treated tumors met the inclusion criteria, 35 (32%) of whom developed at least one fractured rib (60 total fractured ribs). The highest number of fractured ribs per patient was five. Multivariate regression identified posterolateral tumor location as the only independent risk factor for rib fracture. On CT, fractures showed discontinuity between healing edges in 77% of affected patients.

CONCLUSIONS

Nearly one third of patients receiving SBRT for lung tumors experienced rib fractures, 34% of whom experienced pain. Many patients developed multiple fractures. Post-SBRT fractures demonstrated a unique discontinuity between the healing edges of the rib, a distinct feature of post-SBRT rib fractures. The only independent predictor of rib fracture was tumor location along the posterolateral chest wall. Given its increasing frequency of use, describing the risk profile of SBRT is vital to ensure patient safety and adequately inform patient expectations.

Safety and efficacy of stereotactic ablative brachytherapy as a salvage therapy for recurrent chest wall cancer: A retrospective, multicenter study

Purpose

To evaluate the safety and efficacy of stereotactic ablative brachytherapy (SABT) as a salvage therapy for patients with recurrent chest wall cancer (rCWC) who have previously received external beam radiotherapy (EBRT) or surgery.

Materials and methods

Between November 2013 and October 2020, a total of 130 patients (including 75 men with a median age of 63 years) with rCWC treated with SABT were enrolled in this multicenter retrospective study. There were 97 cases of non-small-cell lung carcinoma, 24 cases of breast cancer, and 9 cases of thymic cancer. Of the patients included, 102 patients previously received surgery and 58 patients received EBRT, with systemic treatment progressing after recurrence. None of them were suitable or refused to undergo salvage EBRT or surgery again.

Results

During the 22 (4-70)-month median patient follow-up, 59 patients died. The local control (LC) rates at 6, 12, 24, and 36 months were 88.3%, 74.3%, 50.4%, and 36.7%, respectively. The 1-, 2- and 3-year survival rates were 85%, 56%, and 42%, respectively. The median overall survival was 26 months (95% CI, 18.9-33.1 months). The pain relief rate was 81%, and the median to remission time was 10 days. Univariate and multivariate analyses showed that independent prognostic factors for LC included tumor size and postoperative D90. On the other hand, independent prognostic factors for survival include the Karnofsky performance status (KPS) score, tumor size, and D90 19 patients (14.6%) developed grade I/II skin reaction complications. No grade III or severer complications occurred.

Conclusion

SABT is safe and effective as a salvage therapy for rCWC following EBRT/surgery. For patients with a KPS score greater than 80, prescribed dose greater than 130 Gy, and tumor size less than 4 cm may bring better results.

Clinical experience of volumetric-modulated flattening filter free stereotactic body radiation therapy of lesions in the lung with deep inspiration breath-hold

This clinical study aimed to evaluate lung cancer patients' ability to perform deep inspiration breath-hold (DIBH) during CT simulation and throughout the treatment course of stereotactic body radiation therapy (SBRT). In addition, target sizes, organ at risk (OAR) sizes, and doses to the respective volumes in filter-free volumetric-modulated arc therapy plans performed under free-breathing (FB) and DIBH conditions were evaluated. Twenty-one patients with peripheral lesions were included, of which 13 were eligible for SBRT. All patients underwent training for breath-hold during CT, and if they complied with the requirements, two CT scans were obtained: CT scan in DIBH and a four-dimensional CT scan in FB. The treatment plans in FB and DIBH were generated, and the dose parameters and volume sizes were compared. The endpoints for evaluation were patient compliance, target dose coverage, and doses to the OARs. This clinical study showed high patient DIBH compliance during both CT simulation and treatment for patients with lung cancer. A significant reduction in target volumes was achieved with SBRT in DIBH, in addition to significantly decreased doses to the heart, chest wall, and lungs. DIBH in SBRT of lung lesions is feasible, and a routine to manage intra-fractional deviation should be established upon implementation.

Effect of adherence to treatment guidelines on overall survival in elderly non-small-cell lung cancer patients

OBJECTIVES

Mean age at diagnosis of lung cancer is increasing with increasing age in Western populations. The present study was designed to evaluate the effect of adherence to first-line treatment guidelines on overall survival (OS) in elderly patients with non-small-cell lung cancer (NSCLC) and reasons for non-adherence to treatment guidelines.

MATERIALS AND METHODS

All patients aged ≥ 65 years diagnosed with NSCLC in Ostrobothnia, Finland, during the years 2016 to 2020 were identified from hospital registries. Adherence of first-line treatment to contemporary treatment guidelines was analysed based on diagnosis, tumour stage and performance status (PS), as was the effect of adherence on OS.

RESULTS

A review of hospital registries identified 238 NSCLC patients aged ≥ 65 years. Guideline adherence by stage decreased significantly with age, with 66.4% of patients aged 65 to 74 years, but only 33.3% of those aged > 80 years treated according to guidelines (p < 0.001). Other factors associated with non-adherence to guidelines included poor PS, frailty, and limited lung function. Of the patients with PS 0-2, 26.9% were under-treated according to guidelines. Reasons for under-treatment included comorbidities, decreased lung function, physician decision to reduce treatment intensity or recommend best supportive care, patient choice and PS decline before treatment initiation. Guideline adherence increased overall OS of elderly NSCLC patients in all stages. Elderly PS 2 patients appear to benefit from guideline adherence and active treatment. In contrast, active treatment did not benefit patients with PS 3-4.

CONCLUSIONS

Guideline adherence was associated with increased OS in elderly NSCLC patients. Almost 10% of elderly and otherwise fit NSCLC patients were not treated according to guidelines and could have benefitted from more intensive treatment.

Radiomic Modeling of Bone Density and Rib Fracture Risk After Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer

Purpose

Our purpose was to determine whether bone density and bone-derived radiomic metrics in combination with dosimetric variables could improve risk stratification of rib fractures after stereotactic body radiation therapy (SBRT) for early-stage non-small cell lung cancer (NSCLC).

Methods and Materials

A retrospective analysis was conducted of patients with early-stage NSCLC treated with SBRT. Dosimetric data and rib radiomic data extracted using PyRadiomics were used for the analysis. A subset of patients had bone density scans that were used to create a predicted bone density score for all patients. A 10-fold cross validated approach with 10 resamples was used to find the top univariate logistic models and elastic net regression models that predicted for rib fracture.

Results

A total of 192 treatment plans were included in the study with a rib fracture rate of 16.1%. A predicted bone density score was created from a multivariate model with vertebral body Hounsfield units and patient weight, with an R-squared of 0.518 compared with patient dual-energy x-ray absorptiometry T-scores. When analyzing all patients, a low predicted bone density score approached significance for increased risk of rib fracture (P = .07). On competing risk analysis, when stratifying patients based on chest wall V30 Gy and bone density score, those with a V30 Gy ≥30 cc and a low bone density score had a significantly higher risk of rib fracture compared with all other patients (P < .001), with a predicted 2-year risk of rib fracture of 28.6% (95% confidence interval, 17.2%-41.1%) and 4.9% (95% confidence interval, 2.3%-9.0%), respectively. Dosimetric variables were the primary drivers of fracture risk. A multivariate elastic net regression model including all dosimetric variables was the best predictor of rib fracture (area under the curve [AUC], 0.864). Bone density variables (AUC, 0.618) and radiomic variables (AUC, 0.617) have better predictive power than clinical variables that exclude bone density (AUC, 0.538).

Conclusion

Radiomic features, including a bone density score that includes vertebral body Hounsfield units and radiomic signatures from the ribs, can be used to stratify risk of rib fracture after SBRT for NSCLC.

Doses, fractionations, constraints for stereotactic radiotherapy

This paper describes how to select the most appropriate stereotactic radiotherapy (SRT ) dose and fractionation scheme according to lesion size and site, organs at risk (OARs) proximity and the biological effective dose. In single-dose SRT, 15-34 Gy are generally used while in fractionated SRT 30 and 75 Gy in 2-5 fractions are administered. The ICRU Report No. 91, which is specifically dedicated to SRT treatments, provided indications for dose prescription (with its definition and essential steps), dose delivery and optimal coverage which was defined as the best planning target volume coverage that can be obtained in the irradiated district. Calculation algorithms and OAR s dose constraints are provided as well as treatment planning system characteristics, suggested beam energy and multileaf collimator leaf size. Finally, parameters for irradiation geometry and plan quality are also reported.

Effects of Tumor-Rib Distance and Dose-Dependent Rib Volume on Radiation-Induced Rib Fractures in Patients with Breast Cancer

This study aimed to investigate the effects of tumor-rib distance and dose-dependent rib volume on radiation-induced rib fractures (RIRFs) in patients with breast cancer. We retrospectively included 510 women with breast cancer who underwent surgical resection with adjuvant radiotherapy. The tumor-rib distance was measured using preoperative computed tomography (CT) images. Postoperative chest wall thickness and dose-dependent rib volumes, which are absolute rib volumes receiving >20 Gy (V20), 30 Gy (V30), 40 Gy (V40), 45 Gy (V45), and 50 Gy (V50), were measured from the stimulation CT images for radiation treatment planning. We assessed the relationship of RIRF with tumor-rib distance, postoperative chest wall thickness, and dose-dependent rib volumes. Patients with high values of tumor-rib distance and postoperative chest wall thickness had significantly lower risks of RIRF than those with low values. Patients with high values of V20, V30, V40, V45, and V50 had significantly higher risks of RIRF than those with low values. In a multivariate analysis, tumor-rib distance and all five dose-dependent rib volumes, as well as osteoporosis and radiation field, were independent risk factors for RIRF. Tumor-rib distance and dose-dependent rib volume were independent risk factors for RIRF in patients with breast cancer.

Early-Stage Non-Small Cell Lung Cancer Stereotactic Body Radiation Therapy Outcomes in a Single Institution

Introduction

The gold standard treatment of stage I non-small cell lung cancer (NSCLC) is surgical resection. For medically inoperable patients, stereotactic body radiation therapy (SBRT) can provide comparable local control (LC) and overall survival (OS). The objectives of this study are to determine the three-year LC and OS for SBRT compared to early-stage NSCLC patients treated with alternative radiation modalities at our institution.

Materials and methods

This retrospective study included a total of 139 consecutive patients who were diagnosed with stage I (T1-2 N0 M0) NSCLC and treated with radiation therapy at our institution between 2015 and 2020. Patient demographics and clinical data were obtained from chart reviews. Treatment subgroups were: SBRT (48Gy/4 or 60Gy/8), hypofractionation (60Gy/15), conventional fractionation (60Gy/30 or 50Gy/20), and palliative radiation (20Gy/5, 30Gy/10, or 40Gy/15). Kaplan-Meier curves were plotted for LC and OS. We also performed Cox’s proportional hazard regression analysis.

Results

The median patient age was 74 (range 52-91). The numbers of patients in each treatment subgroup were: SBRT (44), hypofractionation (78), conventional fractionation (8), and palliative (9). Differences in age, gender, and histopathological cell type between subgroups were not statistically significant. Metastatic progression was the most common outcome amongst treatment failures, followed by local recurrence and regional spread. Median post-treatment follow-up in months for each subgroup was: SBRT (20.2), hypofractionated (20.7), conventional fractionation (13.9), and palliative (14.4). Post-treatment three-year LC was found to be significantly better with SBRT (94%) versus hypofractionation (71%), conventional fractionation (80%), and palliative (71%). OS at three years were SBRT (67%), hypofractionation (59%), conventional fractionation (66%), and palliative (44%). As a whole, 72% (100/139) of patients had biopsy-proven NSCLC. Analysis showed biopsy status had no statistical significance with regards to LC or OS. Every 20 years of age had a 3.2x risk of death (95% CI: 1.425-7.268). Concerning the treatment modalities, there were significant differences for the hazard of death compared to SBRT: hypofractionation had 2.58x increased risk while palliative had 5.83x increased risk.

The proportion of patients who experienced post-treatment radiation pneumonitis or dermatitis were: SBRT (7%, 2%), hypofractionation (8%, 3%), conventional fractionation (13%, 25%), and palliative (0%, 0%), respectively. No patients who experienced grade III or higher toxicities were observed as defined by Common Terminology Criteria for Adverse Events (CTCAE). 

Conclusion

Our experience confirms SBRT can provide durable three-year local control with a comparable rate of post-treatment complications versus other radiation modalities for early-stage NSCLC. SBRT appears to be non-inferior to hypofractionation with regards to three-year LC.

Influence of target dose heterogeneity on dose sparing of normal tissue in peripheral lung tumor stereotactic body radiation therapy

OBJECTIVE

To evaluate the influence of target dose heterogeneity on normal tissue dose sparing for peripheral lung tumor stereotactic body radiation therapy (SBRT).

METHODS

Based on the volumetric-modulated arc therapy (VMAT) technique, three SBRT plans with homogeneous, moderate heterogeneous, and heterogeneous (HO, MHE, and HE) target doses were compared in 30 peripheral lung tumor patients. The prescription dose was 48 Gy in 4 fractions. Ten rings outside the PTV were created to limit normal tissue dosage and evaluate dose falloff.

RESULTS

When MHE and HE plans were compared to HO plans, the conformity index of the PTV was increased by approximately 0.08. The median mean lung dose (MLD), V₅, V₁₀, V₂₀ of whole lung, D_2%, D_1cc, D_2cc of the rib, V₃₀ of the rib, D_2% and the maximum dose (D_max) of the skin, and D_2% and D_max of most mediastinal organs at risk (OARs) and spinal cord were reduced by up to 4.51 Gy or 2.8%. Analogously, the median D_max, D_2% and mean dose of rings were reduced by 0.71 to 8.46 Gy; and the median R_50% and D_2cm were reduced by 2.1 to 2.3 and 7.4% to 8.0%, respectively. Between MHE and HE plans there was little to no difference in OARs dose and dose falloff beyond the target. Furthermore, the dose sparing of rib V₃₀ and the mean dose of rings were negatively correlated with the rib and rings distance from tumor, respectively.

CONCLUSIONS

For peripheral lung tumor SBRT, target conformity, normal tissue dose, and dose falloff around the target could be improved by loosening or abandoning homogeneity. While there was negligible further dose benefit for the maximum target dose above 125% of the prescription, dose sparing of normal tissue derived from a heterogeneous target decreased as the distance from the tumor increased.

Delivered dose-effect analysis of radiation induced rib fractures after thoracic SBRT

BACKGROUND AND PURPOSE

Anatomical changes during the stereotactic body radiation therapy (SBRT) of early stage non-small cell lung cancer (NSCLC) may cause the delivered dose to deviate from the planned dose. We investigate if normal tissue complication probability (NTCP) models based on the delivered dose predict radiation-induced rib fractures better than models based on the planned dose.

MATERIAL AND METHODS

437 NSCLC patients treated to a median dose of 3x18 Gy were included. Delivered dose was estimated by accumulating EQD2-corrected fraction doses after being deformed with daily CBCT-to-planning CT deformable image registration. Dosimetric parameters D_x (dose to a relative volume x) were extracted for each rib included in the CBCTs field-of-view. An NTCP model was constructed for both planned and delivered dose, optimizing the parameters TD₅₀ (dose with 50% toxicity risk), m (steepness of the curve) and x, using maximum likelihood estimation. Best NTCP model was determined using Akaike weights (Aw). Differences between the models were tested for significance using the Vuong's test.

RESULTS

Median time to fracture of 110 fractured ribs was 22.5 months. The maximum rib dose, D₀, best predicted fractures for both planned and delivered dose. The average delivered D₀ was significantly lower than planned (p < 0.001). NTCP model based on the delivered D₀ was the best, with Aw = 0.95. The models were not significantly different.

CONCLUSION

Delivered maximum dose to the ribs was significantly lower than planned. The NTCP model based on delivered dose improved predictions of radiation-induced rib fractures but did not reach statistical significance.

Imaging of the post-radiation chest in lung cancer

Radiation therapy using conventional fractionated external-beam or high-precision dose techniques including three-dimensional conformal radiotherapy, stereotactic body radiation therapy, intensity-modulated radiation therapy, and proton therapy, is a key component in the treatment of patients with lung cancer. Knowledge of the radiation technique used, radiation treatment plan, expected temporal evolution of radiation-induced lung injury and patient-specific parameters, such as previous radiotherapy, concurrent chemoradiotherapy, and/or immunotherapy, is important in imaging interpretation. This review discusses factors that affect the development and severity of radiation-induced lung injury and its radiological manifestations with emphasis on the differences between conventional radiation and high-precision dose radiotherapy techniques.

Preliminary pre-clinical studies on the side effects of breast cancer treatment

Purpose: Technological advancement in the treatment of cancer together with early detection and diagnosis have considerably improved the survival of breast cancer patients. On the other hand, the potential of patients developing side effects from cancer treatment are not negligible. Despite the progress that has been made in terms of early diagnosis, therapy, and survival, including improvements in the chemotherapeutic agents, radiation and molecular targeted therapies, cardiotoxicity of cancer therapy is still cause for concern. Radiation therapy for breast cancer is associated with increased risk of heart disease and myocardial infarction. Furthermore, the association of radiation therapy to chemotherapy is an important aspect to be considered in the development of cardiac disease, as this could play an additional role as a risk factor. Besides the heart effect, other side effects can be observed in the bone, ovary, uteri, and other organs. This paper aims to review the recent literature to present the current understanding of side effects associated with breast cancer treatment. The focus is on recent preclinical studies that have assessed potential changes in different organs that may be injured after breast cancer treatment, both due to both radiation and chemotherapy agents.Conclusion: Radiation-induced heart disease is one important side effect that must be considered during the treatment planning and patient follow-up. The cardiac damage can be potentialized when chemotherapy is associated to radiotherapy, and the literature findings indicate that heart fibrosis plays an important role at the radio-chemotherapy induced cardiac damage. Literature findings also showed important side effects at the bone, that can lead to ospeoporosis, due to the decrease of calcium, after radio or chemotherapy treatments. This decrease could be explained by the ovarian failure observed at rats after chemotherapy treatment. It is of great importance to acknowledge the complications originating from the treatment, so that new strategies can be developed. In this way, it will be possible to minimize side effects and improve the patients' quality of life.

Clinical validation of ring-mounted halcyon linac for lung SBRT: comparison to SBRT-dedicated C-arm linac treatments

Stereotactic body radiotherapy (SBRT) of lung tumors via the ring‐mounted Halcyon Linac, a fast kilovoltage cone beam CT‐guided treatment with coplanar geometry, a single energy 6MV flattening filter free (FFF) beam and volumetric modulated arc therapy (VMAT) is a fast, safe, and feasible treatment modality for selected lung cancer patients. Four‐dimensional (4D) CT‐based treatment plans were generated using advanced AcurosXB algorithm with heterogeneity corrections using an SBRT board and Halcyon couch insert. Halcyon VMAT‐SBRT plans with stacked and staggered multileaf collimators produced highly conformal radiosurgical dose distribution to the target, lower intermediate dose spillage, and similar dose to adjacent organs at risks (OARs) compared to SBRT‐dedicated highly conformal clinical noncoplanar Truebeam VMAT plans following the RTOG‐0813 requirements. Due to low monitor units per fraction and less multileaf collimator (MLC) modulation, the Halcyon VMAT plan can deliver lung SBRT fractions with an overall treatment time of less than 15 min (for 50 Gy in five fractions), significantly improving patient comfort and clinic workflow. Higher pass rates of quality assurance results demonstrate a more accurate treatment delivery on Halcyon. We have implemented Halcyon for lung SBRT treatment in our clinic. We suggest others use Halcyon for lung SBRT treatments using abdominal compression or 4D CT‐based treatment planning, thus expanding the access of curative ultra‐hypofractionated treatments to other centers with only a Halcyon Linac. Clinical follow‐up results for patients treated on Halcyon Linac with lung SBRT is ongoing.

Dosimetric evaluation of SBRT treatment plans of non-central lung tumours: clinical experience

Objectives:

Lung cancer is the most commonly diagnosed cancer in Canada and the leading cause of cancer-related mortality in both men and women in North America. Surgery is usually the primary treatment option for early-stage non-small cell lung cancer (NSCLC). However, for patients who may not be suitable candidates for surgery, stereotactic body radiation therapy (SBRT) is an alternative method of treatment. SBRT has proven to be an effective technique for treating NSCLC patients by focally administering high radiation dose to the tumour with acceptable risk of toxicity to surrounding healthy tissues. The goal of this comprehensive retrospective dosimetric study is to compare the dosimetric parameters between three-dimensional conformal radiation therapy (3DCRT) and volumetric-modulated arc therapy (VMAT) lung SBRT treatment plans for two prescription doses.

Methods:

We retrospectively analysed and compared lung SBRT treatment plans of 263 patients treated with either a 3DCRT non-coplanar or with 2–3 VMAT arcs technique at 48 Gy in 4 fractions (48 Gy/4) or 50 Gy in 5 fractions (50 Gy/5) prescribed to the planning target volume (PTV), typically encompassing the 80% isodose volume. All patients were treated on either a Varian 21EX or TrueBeam linear accelerator using 6-MV or 10-MV photon beams.

Results:

The mean PTV V95% and V100% for treatment plans at 48 Gy/4 are 99·4 ± 0·6% and 96·0 ± 1·0%, respectively, for 3DCRT and 99·7 ± 0·4% and 96·4 ± 3·4%, respectively, for VMAT. The corresponding mean PTV V95% and V100% at 50 Gy/5 are 99·0 ± 1·4% and 95·5 ± 2·5% for 3DCRT and 99·5 ± 0·8% and 96·1 ± 1·6% for VMAT. The CIRI and HI5/95 for the PTV at 48 Gy/4 are 1·1 ± 0·1 and 1·2 ± 0·0 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The corresponding CIRI and HI5/95 at 50 Gy/5 are 1·1 ± 0·1 and 1·3 ± 0·1 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The mean R50% and D2cm at 48 Gy/4 are 5·0 ± 0·8 and 61·2 ± 7·0% for 3DCRT and 4·9 ± 0·8 and 57·8 ± 7·9% for VMAT. The corresponding R50% and D2cm at 50 Gy/5 are 4·7 ± 0·5 and 65·5 ± 9·4% for 3DCRT and 4·7 ± 0·7 and 60·0 ± 7·2% for VMAT.

Conclusion:

The use of 3DCRT or VMAT technique for lung SBRT is an efficient and reliable method for achieving dose conformity, rapid dose fall-off and minimising doses to the organs at risk. The VMAT technique resulted in improved dose conformity, rapid dose fall-off from the PTV compared to 3DCRT, although the magnitude may not be clinically significant.

Low Rates of Chest Wall Toxicity When Individualizing the Planning Target Volume Margin in Patients With Early Stage Lung Cancer Treated With Stereotactic Body Radiation Therapy

PURPOSE

Chest wall (CW) toxicity is a potentially debilitating complication of stereotactic body radiation therapy for non-small cell lung cancer, occurring in 10% to 40% of patients. Smaller tumor-to-CW distance has been identified as a risk factor for CW toxicity. We report our experience with individualizing the planning target volume (PTV) along the CW in an effort to reduce the volume of this organ at risk receiving 30 Gy to 50 Gy.

METHODS AND MATERIALS

We performed an institutional review board-approved retrospective analysis of patients with stage I (T1-2aN0M0) non-small cell lung cancer who received stereotactic body radiation therapy between June 2009 and July 2016. Four-dimensional computed tomography was used for treatment planning. A uniform 5-mm expansion of the internal target volume was generated for the PTV. Areas of overlap with the CW were removed from the PTV. Treatment was delivered with cone beam computed tomography guidance. CW toxicity was assessed per the Common Terminology Criteria for Adverse Events, version 5. Descriptive statistics were used to analyze outcomes.

RESULTS

The median follow-up time was 36.8 months. A total of 260 tumors were treated in 225 patients. 225 tumors in 203 patients were peripheral. The internal target volumes for 143 tumors (63.6%) were located within 5 mm of the CW. The median total dose was 48 Gy (range, 42-60 Gy) in 4 fractions (range, 3-5 fractions). The overall rate of grade 1 to 2 CW toxicity was 2.2%, and 2.8% for tumors located within 5 mm of the CW. There were no grade 3/4 cases and no increase in local recurrences with the use of a truncated PTV with a 3-year local control of 92.1% (95% confidence interval, 87.4%-96.8%).

CONCLUSIONS

Truncation of the PTV margin along the CW resulted in a marked reduction of CW toxicity for tumors in close proximity to the CW, with only a 2.8% rate of grade 1 to 2 CW toxicity. Despite PTV reduction, there was no appreciable increase in local failures. A multi-institutional validation of this technique is needed before general incorporation into clinical practice.

On the use of single‐isocenter VMAT plans for SBRT treatment of synchronous multiple lung lesions: Plan quality, treatment efficiency, and early clinical outcomes

Cone‐beam computed tomography (CT)‐guided volumetric‐modulated arc therapy (VMAT) plans for stereotactic body radiotherapy (SBRT) treatment of synchronous multiple lung lesions with a flattening filter‐free (FFF) beam is a safe and highly effective treatment option for oligometastases lung cancer patients. Fourteen patients with metastatic non–small‐cell lung cancer (NSCLC) lesions (two to five) received a single‐isocenter VMAT SBRT treatment in our clinic. Four‐dimensional (4D) CT‐based treatment plans were generated using advanced AcurosXB‐based dose calculation algorithm using heterogeneity corrections with a single isocenter placed between/among the lesions. Compared to 10X‐FFF and traditional flattened 6X (6X‐FF) beams, 6X‐FFF beam produced highly conformal radiosurgical dose distribution to each target volume, reduced dose to adjacent organs at risk (OAR), and significantly reduced the lung SBRT fraction duration to < 3.5 min/fraction for 54/50 Gy treatments in 3/5 fractions — significantly improving patient convenience and clinic workflow. Early follow‐up CT imaging (mean, 9 months) results show high local control rates (100%) with no acute lung or rib toxicity. Longer clinical follow up in a larger patient cohort is ongoing to further validate the outcomes of this treatment approach.

A novel and clinically useful dynamic conformal arc (DCA)-based VMAT planning technique for lung SBRT

Purpose

Volumetric modulated arc therapy (VMAT) is gaining popularity for stereotactic treatment of lung lesions for medically inoperable patients. Due to multiple beamlets in delivery of highly modulated VMAT plans, there are dose delivery uncertainties associated with small‐field dosimetry error and interplay effects with small lesions. We describe and compare a clinically useful dynamic conformal arc (DCA)‐based VMAT (d‐VMAT) technique for lung SBRT using flattening filter free (FFF) beams to minimize these effects.

Materials and Methods

Ten solitary early‐stage I‐II non‐small‐cell lung cancer (NSCLC) patients were treated with a single dose of 30 Gy using 3–6 non‐coplanar VMAT arcs (clinical VMAT) with 6X‐FFF beams in our clinic. These clinically treated plans were re‐optimized using a novel d‐VMAT planning technique. For comparison, d‐VMAT plans were recalculated using DCA with user‐controlled field aperture shape before VMAT optimization. Identical beam geometry, dose calculation algorithm, grid size, and planning objectives were used. The clinical VMAT and d‐VMAT plans were compared via RTOG‐0915 protocol compliances for conformity, gradient indices, and dose to organs at risk (OAR). Additionally, treatment delivery efficiency and accuracy were recorded.

Results

All plans met RTOG‐0915 requirements. Comparing with clinical VMAT, d‐VMAT plans gave similar target coverage with better target conformity, tighter radiosurgical dose distribution with lower gradient indices, and dose to OAR. Lower total number of monitor units and small beam modulation factor reduced beam‐on time by 1.75 min (P < 0.001), on average (maximum up to 2.52 min). Beam delivery accuracy was improved by 2%, on average (P < 0.05) and maximum up to 6% in some cases for d‐VMAT plans.

Conclusion

This simple d‐VMAT technique provided excellent plan quality, reduced intermediate dose‐spillage, and dose to OAR while providing faster treatment delivery by significantly reducing beam‐on time. This novel treatment planning approach will improve patient compliance along with potentially reducing intrafraction motion error. Moreover, with less MLC modulation through the target, d‐VMAT could potentially minimize small‐field dosimetry errors and MLC interplay effects. If available, d‐VMAT planning approach is recommended for future clinical lung SBRT plan optimization.

A simple, yet novel hybrid-dynamic conformal arc therapy planning via flattening filter-free beam for lung stereotactic body radiotherapy

Purpose

Due to multiple beamlets in the delivery of highly modulated volumetric arc therapy (VMAT) plans, dose delivery uncertainties associated with small‐field dosimetry and interplay effects can be concerns in the treatment of mobile lung lesions using a single‐dose of stereotactic body radiotherapy (SBRT). Herein, we describe and compare a simple, yet clinically useful, hybrid 3D‐dynamic conformal arc (h‐DCA) planning technique using flattening filter‐free (FFF) beams to minimize these effects.

Materials and Methods

Fifteen consecutive solitary early‐stage I‐II non‐small‐cell lung cancer (NSCLC) patients who underwent a single‐dose of 30 Gy using 3–6 non‐coplanar VMAT arcs with 6X‐FFF beams in our clinic. These patients’ plans were re‐planned using a non‐coplanar hybrid technique with 2–3 differentially‐weighted partial dynamic conformal arcs (DCA) plus 4–6 static beams. About 60–70% of the total beam weight was given to the DCA and the rest was distributed among the static beams to maximize the tumor coverage and spare the organs‐at‐risk (OAR). The clinical VMAT and h‐DCA plans were compared via RTOG‐0915 protocol for conformity and dose to OAR. Additionally, delivery efficiency, accuracy, and overall h‐DCA planning time were recorded.

Results

All plans met RTOG‐0915 requirements. Comparison with clinical VMAT plans h‐DAC gave better target coverage with a higher dose to the tumor and exhibited statistically insignificance differences in gradient index, D_2cm, gradient distance and OAR doses with the exception of maximal dose to skin (P = 0.015). For h‐DCA plans, higher values of tumor heterogeneity and tumor maximum, minimum and mean doses were observed and were 10%, 2.8, 1.0, and 2.0 Gy, on average, respectively, compared to the clinical VMAT plans. Average beam on time was reduced by a factor of 1.51. Overall treatment planning time for h‐DCA was about an hour.

Conclusion

Due to no beam modulation through the target, h‐DCA plans avoid small‐field dosimetry and MLC interplay effects and resulting in enhanced target coverage by improving tumor dose (characteristic of FFF‐beam). The h‐DCA simplifies treatment planning and beam on time significantly compared to clinical VMAT plans. Additionally, h‐DCA allows for the real time target verification and eliminates patient‐specific VMAT quality assurance; potentially offering cost‐effective, same or next day SBRT treatments. Moreover, this technique can be easily adopted to other disease sites and small clinics with less extensive physics or machine support.

Similar-cases-based planning approaches with beam angle optimizations using water equivalent path length for lung stereotactic body radiation therapy

This study aimed to propose automated treatment planning approaches based on similar cases with beam angle optimizations using water equivalent path length (WEPL) to avoid lung and rib doses for lung stereotactic body radiation therapy (SBRT). Similar cases to an objective case were defined as cases, which were close to the objective case with respect to the Euclidean distances based on geometrical features. Initial similar-case-based (ISC) plans were generated by applying lung SBRT plans of similar cases to objective cases. Similar cases were selected using the Euclidean distances based on lung shape and geometrical features from a radiation treatment planning database with 174 cases. Beam angles of the ISC plans were optimized using a greedy algorithm based on a cost function to include absorbed doses in the lung and ribs in the WEPL. The 12 dose evaluation indices for the planning target volume, lung, spinal cord, and ribs were evaluated in the original plans, ISC plans, and optimized similar-case-based (OSC) plans with and without WEPL for 20 test cases to investigate its dosimetric impact. These findings revealed that V10 and the mean dose for the lung and V20, V30, and V40 for the ribs in the OSC plan with WEPL improved more significantly than those in the original and ISC plans. This study indicates a potential of similar cases, whose beam angle configurations were optimized with WEPL to avoid lung and rib doses in lung SBRT plans.

FFF-VMAT for SBRT of lung lesions: Improves dose coverage at tumor-lung interface compared to flattened beams

Purpose

To quantify the differences in dosimetry as a function of ipsilateral lung density and treatment delivery parameters for stereotactic, single dose of volumetric modulated arc therapy (VMAT) lung stereotactic body radiation therapy (SBRT) delivered with 6X flattening filter free (6X‐FFF) beams compared to traditional flattened 6X (6X‐FF) beams.

Materials/methods

Thirteen consecutive early stage I–II non‐small‐cell‐lung cancer (NSCLC) patients were treated with highly conformal noncoplanar VMAT SBRT plans (3–6 partial arcs) using 6X‐FFF beam and advanced Acuros‐based dose calculations to a prescription dose of 30 Gy in one fraction to the tumor margin. These clinical cases included relatively smaller tumor (island tumors) sizes (2.0–4.2 cm diameters) and varying average ipsilateral lung densities between 0.14 g/cc and 0.34 g/cc. Treatment plans were reoptimized with 6X‐FF beams for identical beam/arc geometries and planning objectives. For same target coverage, the organs‐at‐risk (OAR) dose metrics as a function of ipsilateral lung density were compared between 6X‐FFF and 6X‐FF plans. Moreover, monitor units (MU), beam modulation factor (MF) and beam‐on time (BOT) were evaluated.

Results

Both plans met the RTOG‐0915 protocol compliance. The ipsilateral lung density and the tumor location heavily influenced the treatment plans with 6X‐FFF and 6X‐FF beams, showing differences up to 12% for the gradient indices. For similar target coverage, 6X‐FFF beams showed better target conformity, lower intermediate dose‐spillage, and lower dose to the OAR. Additionally, BOT was reduced by a factor of 2.3 with 6X‐FFF beams compared to 6X‐FF beams.

Conclusion

While prescribing dose to the tumor periphery, 6X‐FFF VMAT plans for stereotactic single‐dose lung SBRT provided similar target coverage with better dose conformity, superior intermediate dose‐spillage (improved dose coverage at tumor interface), and improved OAR sparing compared to traditional 6X‐FF beams and significantly reduced treatment time. The ipsilateral lung density and tumor location considerably affected dose distributions requiring special attention for clinical SBRT plan optimization on a per‐patient basis. Clinical follow up of these patients for tumor local‐control rate and treatment‐related toxicities is in progress.

Imaging of Novel Oncologic Treatments in Lung Cancer Part 2: Local Ablative Therapies

Conventional approaches to the treatment of early-stage lung cancer have focused on the use of surgical methods to remove the tumor. Recent progress in radiation therapy techniques and in the field of interventional oncology has seen the development of several novel ablative therapies that have gained widespread acceptance as alternatives to conventional surgical options in appropriately selected patients. Local control rates with stereotactic body radiation therapy for early-stage lung cancer now approach those of surgical resection, while percutaneous ablation is in widespread use for the treatment of lung cancer and oligometastatic disease for selected other malignancies. Tumors treated with targeted medical and ablative therapies can respond to treatment differently when compared with conventional therapies. For example, after stereotactic body radiation therapy, radiologic patterns of posttreatment change can mimic disease progression, and, following percutaneous ablation, the expected initial increase in the size of a treated lesion limits the utility of conventional size-based response assessment criteria. In addition, numerous treatment-related side effects have been described that are important to recognize, both to ensure appropriate treatment and to avoid misclassification as worsening tumor. Imaging plays a vital role in the assessment of patients receiving targeted ablative therapy, and it is essential that thoracic radiologists become familiar with these findings.

Adjacent level fracture incidence in single fraction high dose spinal radiosurgery

Background

Vertebral body compression fracture (VCF) is a complication following spinal stereotactic radiosurgery (SRS). However, the incidence of VCF in vertebrae adjacent to the level of SRS is unknown. This study aimed to determine the incidence of adjacent level VCF (adjVCF) following spinal SRS.

Methods

A retrospective review of 239 lesions treated with single-fraction SRS from 2011-2014 was performed. Clinical and pathologic factors were collected including evaluation of VCFs in adjacent levels to SRS site. In patients with adjVCFs, dose-volume histograms for adjacent-level endplates were calculated. Cox regression analysis was performed to determine any association among clinical factors and adjVCF occurrence.

Results

Median follow-up was 14.7 months. Twenty-six adjVCFs occurred (10.8%). Of the adjVCFs, 19 had metastases following SRS, and seven did not (2.9% of total treatments). Median time to fracture post-SRS was 13.5 months. In adjVCFs, median of the mean dose to adjacent level fractured endplate was 23.3 Gy, and median of the mean dose of sixteen non-fractured endplates immediately adjacent to the SRS site was 19.1 Gy. Age, gender, and histology were not associated with adjVCF.

Conclusions

AdjVCF after spinal SRS occurs at a rate of 2.9%, when excluding metastatic sites of disease. Adjacent level endplates should be investigated as an organ at risk during SRS planning.

The evolving toxicity profile of SBRT for lung cancer

Stereotactic body radiation therapy (SBRT) is an effective and well tolerated treatment for early stage non-small cell lung cancer (NSCLC). The high doses used in thoracic SBRT can sometimes cause adverse effects ranging from mild fatigue and transient esophagitis to fatal events such as pneumonitis or hemorrhage. Efforts continue to expand in both the utility of this technique as well as our understanding of the mechanisms of the adverse effects it can cause. In this review, we discuss the current literature regarding the potential mechanisms, dosimetric constraints and toxicities associated with SBRT alone and in conjunction with definitive chemoradiotherapy and immunotherapy. As the use of SBRT expands to these spheres, we examine the available recommendations for mitigating potential associated treatment related toxicities.

Effect of Tumor Location and Dosimetric Predictors for Chest Wall Toxicity in Single-Fraction Stereotactic Body Radiation Therapy for Stage I Non-Small Cell Lung Cancer

PURPOSE

Dosimetric parameters to limit chest wall toxicity (CWT) are not well defined in single-fraction (SF) stereotactic body radiation therapy (SBRT) phase 2 trials. We sought to determine the relationship of tumor location and dosimetric parameters with CWT for SF-SBRT.

METHODS AND MATERIALS

From a prospective registry of 1462 patients, we identified patients treated with 30 Gy or 34 Gy. Gross tumor volume was measured as abutting, ≤1 cm, 1 to 2 cm, or >2 cm from the chest wall. CWT was prospectively graded according to Common Terminology Criteria for Adverse Events version 3.0, with grade 2 requiring medical therapy, grade 3 requiring procedural intervention, and grade 4 being disabling pain. Grade 1 CWT or radiographic rib fracture was not included. Logistic regression analysis was used to identify the parameters associated with CWT and calculate the probability of CWT with dose.

RESULTS

This study included 146 lesions. The median follow-up time was 23.8 months. The 5-year local control, distant metastasis, and overall survival rates were 91.8%, 19.2%, and 28.7%, respectively. Grade 2 to 4 CWT was 30.6% for lesions abutting the chest wall, 8.2% for ≤1 cm from the chest wall, 3.8% for 1 to 2 cm from the chest wall, and 5.7% for >2 cm from the chest wall. Grade ≥3 CWT was 1.4%. Tumor abutment (odds ratio [OR]: 6.5; P = .0005), body mass index (OR: 1.1; P = .02), rib D1cc (OR: 1.01/Gy; P = .03), chest wall D1cc (OR: 1.08/Gy; P = .03), and chest wall D5cc (OR: 1.10/Gy; P = .01) were significant predictors for CWT on univariate analysis. Tumor abutment was significant for CWT (OR: 7.5; P = .007) on multivariate analysis. The probability of CWT was 15% with chest wall D5cc at 27.2 Gy and rib D1cc at 30.2 Gy.

CONCLUSIONS

The rate of CWT with SF-SBRT is similar to the rates published for fractionated SBRT, with most CWT being low grade. Tumor location relative to the chest wall is not a contraindication to SF-SBRT, but the rates increase significantly with abutment. Rib D1cc and chest wall D1cc and D5cc may be used as predictors of CWT.

Chest Wall Toxicity After Stereotactic Body Radiation Therapy: A Pooled Analysis of 57 Studies

PURPOSE

The significance of clinical and dosimetric risk factors in relation to chest wall (CW) injury after stereotactic body radiation therapy (SBRT) for lung tumors were analyzed through a meta-analysis of 57 published studies.

METHODS AND MATERIALS

Studies related to CW injury after lung SBRT were obtained through searching PubMed, Embase, and Cochrane electronic databases. An estimate of the incidence of CW pain (CWP) or rib fracture (RF) was derived using a Bayesian hierarchical model. Linear regression analysis was performed to assess the relationship between CWP or RF and clinical or dosimetric factors.

RESULTS

A total of 57 studies incorporating 5985 cases reporting clinical data on CW injury after SBRT were analyzed. The overall CWP and RF rates by Bayesian hierarchical modeling were 11.0% (95% confidence interval [CI], 8.0-14.4) and 6.3% (95% CI, 3.7-9.7), respectively. The rates of grade ≥2 and grade ≥3 CWP were 6.2% (95% CI, 3.88-8.93) and 1.2% (95% CI, 0.48-2.12), respectively. Sex was significantly correlated with RF (P < .001), with female patients having a greater risk of RF than male patients (hazard ratio = 0.59; 95% CI, 0.46-0.76). No correlation was found between RF, grade ≥2 CWP, or grade ≥3 CWP, with the clinical and dosimetric factors of age, tumor size, origin of lung tumor, gross tumor volume, planning target volume, fractional dose, number of fractions, or biologically effective dose. However, tumor to CW distance (<16-25 mm), body mass index, maximum dose (Dmax) of 0.5 to 5 cm³, and the volume of CW or ribs receiving >30 Gy were significantly associated with CWP and RF.

CONCLUSIONS

The overall rates of RF and grade ≥2 CWP after thoracic SBRT are relatively low. Sex, tumor to CW distance, maximum dose, and the radiation exposure of the CW or ribs are factors associated with the risk of CW toxicity after SBRT.

Exploratory analysis using machine learning to predict for chest wall pain in patients with stage I non-small-cell lung cancer treated with stereotactic body radiation therapy

Background and purpose

Chest wall toxicity is observed after stereotactic body radiation therapy (SBRT) for peripherally located lung tumors. We utilize machine learning algorithms to identify toxicity predictors to develop dose–volume constraints.

Materials and methods

Twenty‐five patient, tumor, and dosimetric features were recorded for 197 consecutive patients with Stage I NSCLC treated with SBRT, 11 of whom (5.6%) developed CTCAEv4 grade ≥2 chest wall pain. Decision tree modeling was used to determine chest wall syndrome (CWS) thresholds for individual features. Significant features were determined using independent multivariate methods. These methods incorporate out‐of‐bag estimation using Random forests (RF) and bootstrapping (100 iterations) using decision trees.

Results

Univariate analysis identified rib dose to 1 cc < 4000 cGy (P = 0.01), chest wall dose to 30 cc < 1900 cGy (P = 0.035), rib Dmax < 5100 cGy (P = 0.05) and lung dose to 1000 cc < 70 cGy (P = 0.039) to be statistically significant thresholds for avoiding CWS. Subsequent multivariate analysis confirmed the importance of rib dose to 1 cc, chest wall dose to 30 cc, and rib Dmax. Using learning‐curve experiments, the dataset proved to be self‐consistent and provides a realistic model for CWS analysis.

Conclusions

Using machine learning algorithms in this first of its kind study, we identify robust features and cutoffs predictive for the rare clinical event of CWS. Additional data in planned subsequent multicenter studies will help increase the accuracy of multivariate analysis.

Case report of a dose-volume histogram analysis of rib fracture after accelerated partial breast irradiation: interim analysis of a Japanese prospective multi-institutional feasibility study

We initiated the first multi-institutional prospective study of accelerated partial breast irradiation for early breast cancer in Japan. Our early clinical results showed that the treatment methods were technically reproducible between institutions and showed excellent disease control at a median follow-up of 26 months in our previous report. At present, total 46 patients from six institutions underwent the treatment regimen from October 2009 to December 2011, and the median follow-up time was 60 months (range, 57-67 months). In 46 patients, we experienced one patient who had rib fracture as a late complication. The dose-volume histogram (DVH) result of this patient was analyzed. The D_0.01cc, D_0.1cc, and D_1cc values of the patient were 913, 817, and 664 cGy per fraction, respectively. These values were the highest values in 46 patients. The average D_0.01cc, D_0.1cc, and D_1cc values of the other 45 patients were 546, 500, and 419, respectively, cGy per fraction. From this result, DVH values showing high-dose irradiated volume (D_0.01cc, D_0.1cc, and D_1cc) seem to be a good predictive factor of rib fracture for accelerated partial breast irradiation. However, further investigation is necessary because of the small number of patients investigated.

Radiobiological Optimization in Lung Stereotactic Body Radiation Therapy: Are We Ready to Apply Radiobiological Models?

Lung tumors are often associated with a poor prognosis although different schedules and treatment modalities have been extensively tested in the clinical practice. The complexity of this disease and the use of combined therapeutic approaches have been investigated and the use of high dose-rates is emerging as effective strategy. Technological improvements of clinical linear accelerators allow combining high dose-rate and a more conformal dose delivery with accurate imaging modalities pre- and during therapy. This paper aims at reporting the state of the art and future direction in the use of radiobiological models and radiobiological-based optimizations in the clinical practice for the treatment of lung cancer. To address this issue, a search was carried out on PubMed database to identify potential papers reporting tumor control probability and normal tissue complication probability for lung tumors. Full articles were retrieved when the abstract was considered relevant, and only papers published in English language were considered. The bibliographies of retrieved papers were also searched and relevant articles included. At the state of the art, dose–response relationships have been reported in literature for local tumor control and survival in stage III non-small cell lung cancer. Due to the lack of published radiobiological models for SBRT, several authors used dose constraints and models derived for conventional fractionation schemes. Recently, several radiobiological models and parameters for SBRT have been published and could be used in prospective trials although external validations are recommended to improve the robustness of model predictive capability. Moreover, radiobiological-based functions have been used within treatment planning systems for plan optimization but the advantages of using this strategy in the clinical practice are still under discussion. Future research should be directed toward combined regimens, in order to potentially improve both local tumor control and survival. Indeed, accurate knowledge of the relevant parameters describing tumor biology and normal tissue response is mandatory to correctly address this issue. In this context, the role of medical physicists and the AAPM in the development of radiobiological models is crucial for the progress of developing specific tool for radiobiological-based optimization treatment planning.

Organs at risk in lung SBRT

Lung stereotactic body radiotherapy (SBRT) is an accurate and precise technique to treat lung tumors with high 'ablative' doses. Given the encouraging data in terms of local control and toxicity profile, SBRT has currently become a treatment option for both early stage lung cancer and lung oligometastatic disease in patients who are medically inoperable or refuse surgical resection. Dose-adapted fractionation schedules and ongoing prospective trials should provide further evidence of SBRT safety trying to reduce toxicities and complications. In this heterogeneous scenario, a non-systematic review of dose constraints for lung SBRT was performed, including the main organs at risk in the thorax.

Exposure to Low-Dose X-Ray Radiation Alters Bone Progenitor Cells and Bone Microarchitecture

Exposure to high-dose ionizing radiation during medical treatment exerts well-documented deleterious effects on bone health, reducing bone density and contributing to bone growth retardation in young patients and spontaneous fracture in postmenopausal women. However, the majority of human radiation exposures occur in a much lower dose range than that used in the radiation oncology clinic. Furthermore, very few studies have examined the effects of low-dose ionizing radiation on bone integrity and results have been inconsistent. In this study, mice were irradiated with a total-body dose of 0.17, 0.5 or 1 Gy to quantify the early (day 3 postirradiation) and delayed (day 21 postirradiation) effects of radiation on bone microarchitecture and bone marrow stromal cells (BMSCs). Female BALBc mice (4 months old) were divided into four groups: irradiated (0.17, 0.5 and 1 Gy) and sham-irradiated controls (0 Gy). Micro-computed tomography analysis of distal femur trabecular bone from animals at day 21 after exposure to 1 Gy of X-ray radiation revealed a 21% smaller bone volume (BV/TV), 22% decrease in trabecular numbers (Tb.N) and 9% greater trabecular separation (Tb.Sp) compared to sham-irradiated controls (P < 0.05). We evaluated the differentiation capacity of bone marrow stromal cells harvested at days 3 and 21 postirradiation into osteoblast and adipocyte cells. Osteoblast and adipocyte differentiation was decreased when cells were harvested at day 3 postirradiation but enhanced in cells isolated at day 21 postirradiation, suggesting a compensatory recovery process. Osteoclast differentiation was increased in 1 Gy irradiated BMSCs harvested at day 3 postirradiation, but not in those harvested at day 21 postirradiation, compared to controls. This study provides evidence of an early, radiation-induced decrease in osteoblast activity and numbers, as well as a later recovery effect after exposure to 1 Gy of X-rays, whereas osteoclastogenesis was enhanced. A better understanding of the effects of radiation on osteoprogenitor cell populations could lead to more effective therapeutic interventions that protect bone integrity for individuals exposed to low-dose ionizing radiation.

A dosimetric parameter to limit chest wall toxicity in SABR of NSCLC

OBJECTIVE

Chest wall (CW) toxicity (rib fracture and/or pain) is a recognized complication of stereotactic ablative radiotherapy (SABR) for non-small-cell lung cancer. The aim of this study was to evaluate the frequency of CW toxicity following SABR and to propose a new dosimetric parameter.

METHODS

We reviewed the charts and SABR plans from patients treated for T1-T2N0 peripheral non-small-cell lung cancer between 2009 and 2015. The CW structure was created through a 3-cm expansion of the lung. The median dose delivered to the planning target volume was 60 Gy. SABR was delivered in three fractions for patients with CW V₃₀ < 30 cm³. If the CW V₃₀ exceeded 30 cm³, five fractions were used, and the plan was optimized based on CW V₃₇ (biologically equivalent to the V₃₀ of three-fraction plans).

RESULTS

In 6 years, 361 lesions from 356 patients were treated (3 fractions: 297; 5 fractions: 64). The median follow-up was 16 months. 23 patients (6.5%) developed CW toxicity after a median time of 10 months following treatment. The mean CW V₃₀/V₃₇ was 21 cm³ for patients with CW toxicity and 17 cm³ for patients without toxicity (p < 0.05). The 2-year local control and the CW toxicity rates were similar, whether patients received three or five fractions (97% vs 96% and 7% vs 5%).

CONCLUSION

When the CW V₃₀ is >30 cm³, altered fractionation combined with V₃₇ optimization can limit CW toxicity. Advances in knowledge: The CW V₃₇ is a suggested dosimetric parameter adapted to fractionation that may potentially limit CW toxicity after lung SABR.

Dosemetric Parameters Predictive of Rib Fractures after Proton Beam Therapy for Early-Stage Lung Cancer

Proton beam therapy (PBT) is the preferred modality for early-stage lung cancer. Compared with X-ray therapy, PBT offers good dose concentration as revealed by the characteristics of the Bragg peak. Rib fractures (RFs) after PBT lead to decreased quality of life for patients. However, the incidence of and the risk factors for RFs after PBT have not yet been clarified. We therefore explored the relationship between irradiated rib volume and RFs after PBT for early-stage lung cancer. The purpose of this study was to investigate the incidence and the risk factors for RFs following PBT for early-stage lung cancer. We investigated 52 early-stage lung cancer patients and analyzed a total of 215 irradiated ribs after PBT. Grade 2 RFs occurred in 12 patients (20 ribs); these RFs were symptomatic without displacement. No patient experienced more severe RFs. The median time to grade 2 RFs development was 17 months (range: 9-29 months). The three-year incidence of grade 2 RFs was 30.2%. According to the analysis comparing radiation dose and rib volume using receiver operating characteristic curves, we demonstrated that the volume of ribs receiving more than 120 Gy3 (relative biological effectiveness (RBE)) was more than 3.7 cm(3) at an area under the curve of 0.81, which increased the incidence of RFs after PBT (P < 0.001). In this study, RFs were frequently observed following PBT for early-stage lung cancer. We demonstrated that the volume of ribs receiving more than 120 Gy3 (RBE) was the most significant parameter for predicting RFs.

Predictors of chest wall toxicity after stereotactic ablative radiotherapy using real-time tumor tracking for lung tumors

Background

To evaluate the incidence of chest wall toxicity after lung stereotactic ablative radiotherapy (SABR) and identify risk factors for the development of rib fracture.

Methods

Thirty-nine patients with 49 lesions underwent SABR for primary or metastatic lung tumors using Cyberknife® with tumor tracking systems. Patient characteristics, treatment factors and variables obtained from dose-volume histograms (DVHs) were analyzed to find the association with chest wall toxicity. Four-dimensional (4D) dose calculations were done to investigate the effect of respiratory motion on dose to the ribs.

Results

After follow-up of median 26.7 months (range: 8.4 – 80.0), 8 patients (20.5%) experienced rib fractures and among these patients, three (37.5%) had chest wall pain at 2–3 months after SABR. Median time to rib fracture was 13.4 months (range: 8.0 – 38.5) and the 2-year actuarial risk of rib fracture was 12.2%. Dose to the 4.6 cc of the ribs (D_4.6cc) and rib volume received 160 Gy or more (V₁₆₀) were significant predictor for rib fracture. No significant differences between three-dimensional (3D) and 4D dose calculations were found.

Conclusions

Parameters from DVH are useful in predicting the risk of chest wall toxicity after SABR for lung tumors. Efforts should be made to reduce the risk of the rib fracture after lung SABR.

Radiobiology of stereotactic body radiation therapy (SBRT)

Recent advances in the technology of radiotherapy have enabled the development of new therapeutic modalities that deliver radiation with very high accuracy, reduced margins and high dose conformation, allowing the reduction of healthy tissue irradiated and therefore minimizing the risk of toxicity. The next step was to increase the total tumor dose using conventional fractionation (which remains the best way to relatively radioprotect healthy tissues when large volumes are treated) or to use new fractionation schemes with greater biological effectiveness. Based on the experience gained in radiosurgery, the latter way was chosen for small and well-defined tumors in the body. Stereotactic body radiotherapy delivers high doses of radiation to small and well-defined targets in an extreme hypofractionated (and accelerated) scheme with a very high biological effectiveness obtaining very good initial clinical results in terms of local tumor control and acceptable rate of late complications. In fact, we realize a posteriori that it was not feasible to administer such biologically equivalent dose in a conventional fractionation because the treatment could last several months. So far, these new therapeutic modalities have been developed due to technologic advances in image guidance and treatment delivery but without a solid biological basis. It is the role of traditional radiobiology (and molecular radiobiology) to explain the effects of high doses of ionizing radiation on tumor and normal tissues. Only through a better understanding of how high doses of ionizing radiation act, clinicians will know exactly what we do, allowing us in the future to refine our treatments. This article attempts to describe through simple and understandable concepts the known aspects of the biological action of high doses of radiation on tumor and normal tissues, but it is clear that we need much more basic research to better understand the biology of high doses of radiation.

Dosimetric and radiobiological comparison of TG-43 and Monte Carlo calculations in 192Ir breast brachytherapy applications

PURPOSE

To investigate the clinical significance of introducing model based dose calculation algorithms (MBDCAs) as an alternative to TG-43 in ¹⁹²Ir interstitial breast brachytherapy.

MATERIALS AND METHODS

A 57 patient cohort was used in a retrospective comparison between TG-43 based dosimetry data exported from a treatment planning system and Monte Carlo (MC) dosimetry performed using MCNP v. 6.1 with plan and anatomy information in DICOM-RT format. Comparison was performed for the target, ipsilateral lung, heart, skin, breast and ribs, using dose distributions, dose-volume histograms (DVH) and plan quality indices clinically used for plan evaluation, as well as radiobiological parameters.

RESULTS

TG-43 overestimation of target DVH parameters is statistically significant but small (less than 2% for the target coverage indices and 4% for homogeneity indices, on average). Significant dose differences (>5%) were observed close to the skin and at relatively large distances from the implant leading to a TG-43 dose overestimation for the organs at risk. These differences correspond to low dose regions (<50% of the prescribed dose), being less than 2% of the prescribed dose. Detected dosimetric differences did not induce clinically significant differences in calculated tumor control probabilities (mean absolute difference <0.2%) and normal tissue complication probabilities.

CONCLUSION

While TG-43 shows a statistically significant overestimation of most indices used for plan evaluation, differences are small and therefore not clinically significant. Improved MBDCA dosimetry could be important for re-irradiation, technique inter-comparison and/or the assessment of secondary cancer induction risk, where accurate dosimetry in the whole patient anatomy is of the essence.

Long-term outcomes of stereotactic body radiation therapy (SBRT) with fiducial tracking for inoperable stage I non-small cell lung cancer (NSCLC)

Background

Stereotactic body radiation therapy (SBRT) for stage I non-small cell lung cancer (NSCLC) is considered standard of care in the medically inoperable patient population. Multiple methods of SBRT delivery exist including fiducial-based tumor tracking, which allows for smaller treatment margins and avoidance of patient immobilization devices. We explore the long-term clinical outcomes of this novel fiducial-based SBRT method.

Methods

In this single institutional retrospective review, we detail the outcomes of medically inoperable pathologically confirmed stage I NSCLC. Patients were treated with the Cyberknife SBRT system using a planning target volume (PTV) defined as a 5-mm expansion from gross tumor volume (GTV) without creation of an internal target volume (ITV). Dose was delivered in three or five equal fractions of 10 to 20 Gy. Pretreatment and posttreatment pulmonary function test (PFT) changes and evidence of late radiological rib fractures were analyzed for the majority of patients. Actuarial local control, locoregional control, distant control, and overall survival were calculated using the Kaplan-Meier method.

Results

Sixty-one patients with a median age of 75 years were available for analysis. The majority (80 %) of patients were deemed to be medically inoperable due to underlying pulmonary dysfunction. Eleven patients (18 %) developed symptomatic pneumothoraces secondary to fiducial placement under CT guidance, which precipitously dropped to 0 % following transition to bronchoscopic fiducial placement. The 2-year rib fracture risk was 21.4 % with a median time to rib fracture of 2.9 years. PFTs averaged over all patients and parameters demonstrated small absolute declines, 5.7 % averaged PFT decline, at approximately 1 year of follow-up, but only the diffusing capacity of lung for carbon monoxide (DL_CO) demonstrated a statistically significant decline (10.29 vs. 9.01 mL/min/mmHg, p = 0.01). Five-year local control, locoregional control, and overall survival were 87.6, 71.8, and 39.3 %, respectively.

Conclusions

Despite reduced treatment margins and lack of patient immobilization, SBRT with fiducial-based tumor tracking achieves clinically comparable long-term outcomes to other linac-based SBRT approaches.

Ablative Approaches for Pulmonary Metastases

Pulmonary metastases are common in patients with cancer for which surgery is considered a standard approach in appropriately selected patients. A number of patients are not candidates for surgery due to a medical comorbidities or the extent of surgery required. For these patients, noninvasive or minimally invasive approaches to ablate pulmonary metastases are potential treatment strategies. This article summarizes the rationale and outcomes for non-surgical treatment approaches, including radiotherapy, radiofrequency and microwave ablation, for pulmonary metastases.

Vertebral compression fractures after stereotactic body radiation therapy: a large, multi-institutional, multinational evaluation

OBJECTIVE

The purpose of this study was to identify factors contributing to an increased risk for vertebral compression fracture (VCF) following stereotactic body radiation therapy (SBRT) for spinal tumors.

METHODS

A total of 594 tumors were treated with spinal SBRT as primary treatment or re-irradiation at 8 different institutions as part of a multi-institutional research consortium. Patients underwent LINAC-based, image-guided SBRT to a median dose of 20 Gy (range 8–40 Gy) in a median of 1 fraction (range 1–5 fractions). Median patient age was 62 years. Seventy-one percent of tumors were osteolytic, and a preexisting vertebral compression fracture (VCF) was present in 24% of cases. Toxicity was assessed following treatment. Univariate and multivariate analyses were performed using a logistic regression method to determine parameters predictive for post-SBRT VCF.

RESULTS

At a median follow-up of 10.1 months (range 0.03–57 months), 80% of patients had local tumor control. At the time of last imaging follow-up, at a median of 8.8 months after SBRT, 3% had a new VCF, and 2.7% had a progressive VCF. For development of any (new or progressive) VCF following SBRT, the following factors were predictive for VCF on univariate analysis: short interval from primary diagnosis to SBRT (less than 36.8 days), solitary metastasis, no additional bone metastases, no prior chemotherapy, preexisting VCF, no MRI used for target delineation, tumor volume of 37.3 cm3 or larger, equivalent 2-Gy-dose (EQD2) tumor of 41.8 Gy or more, and EQD2 spinal cord Dmax of 46.1 Gy or more. Preexisting VCF, solitary metastasis, and prescription dose of 38.4 Gy or more were predictive on multivariate analysis. The following factors were predictive of a new VCF on univariate analysis: solitary metastasis, no additional bone metastases, and no MRI used for target delineation. Presence of a solitary metastasis and lack of MRI for target delineation remained significant on multivariate analysis.

CONCLUSIONS

A VCF following SBRT is more likely to occur following treatment for a solitary spinal metastasis, reflecting a more aggressive treatment approach in patients with adequately controlled systemic disease. Higher prescription dose and a preexisting VCF also put patients at increased risk for post-SBRT VCF. In these patients, pre-SBRT cement augmentation could be considered to decrease the risk of subsequent VCF.