Estimating the tolerance of brachial plexus to hypofractionated stereotactic body radiotherapy: a modelling-based approach from clinical experience.

BACKGROUND: Brachial plexopathy is a potentially serious complication from stereotactic body radiation therapy (SBRT) that has not been widely studied. Therefore, we compared datasets from two different institutions and generated a brachial plexus dose-response model, to quantify what dose constraints would be needed to minimize the effect on normal tissue while still enabling potent therapy for the tumor. METHODS: Two published SBRT datasets were pooled and modeled from patients at Indiana University and the Richard L. Roudebush Veterans Administration Medical Center from 1998 to 2007, as well as the Karolinska Institute from 2008 to 2013. All patients in both studies were treated with SBRT for apically located lung tumors localized superior to the aortic arch. Toxicities were graded according to Common Terminology Criteria for Adverse Events, and a probit dose response model was created with maximum likelihood parameter fitting. RESULTS: This analysis includes a total of 89 brachial plexus maximum point dose (Dmax) values from both institutions. Among the 14 patients who developed brachial plexopathy, the most common complications were grade 2, comprising 7 patients. The median follow-up was 30 months (range 6.1-72.2) in the Karolinska dataset, and the Indiana dataset had a median of 13 months (range 1-71). Both studies had a median range of 3 fractions, but in the Indiana dataset, 9 patients were treated in 4 fractions, and the paper did not differentiate between the two, so our analysis is considered to be in 3-4 fractions, one of the main limitations. The probit model showed that the risk of brachial plexopathy with Dmax of 26 Gy in 3-4 fractions is 10%, and 50% with Dmax of 70 Gy in 3-4 fractions. CONCLUSIONS: This analysis is only a preliminary result because more details are needed as well as additional comprehensive datasets from a much broader cross-section of clinical practices. When more institutions join the QUANTEC and HyTEC methodology of reporting sufficient details to enable data pooling, our field will finally reach an improved understanding of human dose tolerance.

Potential Clinical Significance of Overall Targeting Accuracy and Motion Management in the Treatment of Tumors That Move With Respiration: Lessons Learnt From a Quarter Century of Stereotactic Body Radiotherapy From Dose Response Models.

OBJECTIVE: To determine the long-term normal tissue complication probability with stereotactic body radiation therapy (SBRT) treatments for targets that move with respiration and its relation with the type of respiratory motion management (tracking vs. compression or gating). METHODS: A PubMed search was performed for identifying literature regarding dose, volume, fractionation, and toxicity (grade 3 or higher) for SBRT treatments for tumors which move with respiration. From the identified papers logistic or probit dose-response models were fitted to the data using the maximum-likelihood technique and confidence intervals were based on the profile-likelihood method in the dose-volume histogram (DVH) Evaluator. RESULTS: Pooled logistic and probit models for grade 3 or higher toxicity for aorta, chest wall, duodenum, and small bowel suggest a significant difference when live motion tracking was used for targeting tumors with move with respiration which was on the average 10 times lower, in the high dose range. CONCLUSION: Live respiratory motion management appears to have a better toxicity outcome when treating targets which move with respiration with very steep peripheral dose gradients. This analysis is however limited by sparsity of rigorous data due to poor reporting in the literature.

Benefit of Radiotherapy in Extraskeletal Myxoid Chondrosarcoma: A Propensity Score Weighted Population-based Analysis of the SEER Database.

OBJECTIVES: Extraskeletal myxoid chondrosarcoma (EMC) is a rare malignancy for which the role of radiotherapy is not well-defined. We examine the effect of external beam radiotherapy (EBRT) on cancer-specific survival (CSS) for patients with localized EMC, in a propensity score weighted, population-based analysis. MATERIALS AND METHODS: The Surveillance, Epidemiology, and End Results database (1973 to 2012) was queried for cases of localized EMC arising from soft connective tissues of the trunk and extremities treated with surgery and/or EBRT. Inverse probability treatment weighting was utilized, with survival analysis by weighted Cox regression and Kaplan-Meier analysis with log-rank testing. The primary endpoint was CSS. RESULTS: One hundred seventy-two patients were identified, diagnosed from 2004 to 2012. Ninety-four percent and 32% of 156 assessable patients underwent surgery and EBRT, respectively. By inverse probability treatment weighting, balancing covariates of age group, sex, race, grade, T stage, N stage, receipt of surgery, and anatomic site, we observed CSS of 97% versus 85% and 94% versus 85% in patients receiving EBRT versus no EBRT, at 3 and 5 years, respectively, at median follow-up of 33 months, P=0.01. A trend toward an overall survival benefit associated with EBRT was noted, P=0.06. Further adjusting for type of resection performed, CSS benefit persisted, 97% versus 85% at 3 years and 94% versus 85% at 5 years, P=0.02, with trend toward an overall survival benefit, P=0.08. CONCLUSIONS: The receipt of EBRT is associated with a CSS benefit in localized EMC. Aggressive local therapy, including EBRT, should be considered in these patients.

Update on Radiotherapy for Central Nervous System Malignancies.

Malignancies arising from the central nervous system are rare. Brain metastases, in contrast, are perhaps the most common neurologic complication of cancer. Radiotherapy, as part of combined modality therapy, continues to evolve with the advancement of stereotactic radiosurgery indications, the addition of new technologies, such as alternating electric field therapy, and mounting advances in the complex biology of these entities. The explosion of new clinical trials combined with newly discovered molecular markers suggest the beginning of a paradigm shift in the management of these challenging malignancies that will allow for future risk-stratification strategies.

Use of image-guided stereotactic body radiation therapy in lieu of intracavitary brachytherapy for the treatment of inoperable endometrial neoplasia.

PURPOSE: Retrospective analysis of patients with invasive endometrial neoplasia who were treated with external beam radiation therapy followed by stereotactic body radiation therapy (SBRT) boost because of the inability to undergo surgery or brachytherapy. METHODS AND MATERIALS: We identified 11 women with stage I-III endometrial cancer with a median age of 78 years that were not candidates for hysterectomy or intracavitary brachytherapy secondary to comorbidities (91%) or refusal (9%). Eight patients were American Joint Committee on Cancer (AJCC) stage I (3 stage IA, 5 stage IB), and 3 patients were AJCC stage III. Patients were treated to a median of 4500 cGy at 180 cGy per fraction followed by SBRT boost (600 cGy per fraction×5). RESULTS: The most common side effect was acute grade 1 gastrointestinal toxicity in 73% of patients, with no late toxicities observed. With a median follow-up of 10 months since SBRT, 5 patients (45%) experienced locoregional disease progression, with 3 patients (27%) succumbing to their malignancy. At 12 and 18 months from SBRT, the overall freedom from progression was 68% and 41%, respectively. Overall freedom from progression (FFP) was 100% for all patients with AJCC stage IA endometrial carcinoma, whereas it was 33% for stage IB at 18 months. The overall FFP was 100% for International Federation of Obstetrics and Gynecology grade 1 disease. The estimated overall survival was 57% at 18 months from diagnosis. CONCLUSION: In this study, SBRT boost to the intact uterus was feasible, with encouragingly low rates of acute and late toxicity, and favorable disease control in patients with early-stage disease. Additional studies are needed to provide better insight into the best management of these clinically challenging cases.