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PurposeWe sought to investigate the tumor control probability (TCP) of vestibular schwannomas after single-fraction stereotactic radiosurgery (SRS) or hypofractionated SRS over 2 to 5 fractions (fSRS).Methods and materialsStudies (PubMed indexed from 1993-2017) were eligible for data extraction if they contained dosimetric details of SRS/fSRS correlated with local tumor control. The rate of tumor control at 5 years (or at 3 years if 5-year data were not available) were collated. Poisson modeling estimated the TCP per equivalent dose in 2 Gy per fraction (EQD2) and in 1, 3, and 5 fractions.ResultsData were extracted from 35 publications containing a total of 5162 patients. TCP modeling was limited by the absence of analyzable data of 12 Gy. Using linear-quadratic-based dose conversion, the 3- to 5-year TCP was estimated at 95% at an EQD2 of 25 Gy, corresponding to 1-, 3-, and 5-fraction doses of 13.8 Gy, 19.2 Gy, and 21.5 Gy, respectively. Single-fraction doses of 10 Gy, 11 Gy, 12 Gy, and 13 Gy predicted a TCP of 85.0%, 88.4%, 91.2%, and 93.5%, respectively. For fSRS, 18 Gy in 3 fractions (EQD2 of 23.0 Gy) and 25 Gy in 5 fractions (EQD2 of 30.2 Gy) corresponded to TCP of 93.6% and 97.2%. Overall, the quality of dosimetric reporting was poor; recommended reporting guidelines are presented.ConclusionsWith current typical SRS doses of 12 Gy in 1 fraction, 18 Gy in 3 fractions, and 25 Gy in 5 fractions, 3- to 5-year TCP exceeds 91%. To improve pooled data analyses to optimize treatment outcomes for patients with vestibular schwannoma, future reports of SRS should include complete dosimetric details with well-defined tumor control and toxicity endpoints.

PurposeDosimetric and clinical predictors of radiation-induced optic nerve/chiasm neuropathy (RION) after single-fraction stereotactic radiosurgery (SRS) or hypofractionated (2-5 fractions) radiosurgery (fSRS) were analyzed from pooled data that were extracted from published reports (PubMed indexed from 1990 to June 2015). This study was undertaken as part of the American Association of Physicists in Medicine Working Group on Stereotactic Body Radiotherapy, investigating normal tissue complication probability (NTCP) after hypofractionated radiation.Methods and materialsEligible studies described dose delivered to optic nerve/chiasm and provided crude or actuarial toxicity risks, with visual endpoints (ie, loss of visual acuity, alterations in visual fields, and/or blindness/complete vision loss). Studies of patients with optic nerve sheath tumors, optic nerve gliomas, or ocular/uveal melanoma were excluded to obviate direct tumor effects on visual outcomes, as were studies not specifying causes of vision loss (ie, tumor progression vs RION).ResultsThirty-four studies (1578 patients) were analyzed. Histologies included pituitary adenoma, cavernous sinus meningioma, craniopharyngioma, and malignant skull base tumors. Prior resection (76% of patients) did not correlate with RION risk (P = .66). Prior irradiation (6% of patients) was associated with a crude 10-fold increased RION risk versus no prior radiation therapy. In patients with no prior radiation therapy receiving SRS/fSRS in 1-5 fractions, optic apparatus maximum point doses resulting in

A literature review of more than 200 stereotactic body radiation therapy spine articles from the past 20 years found only a single article that provided dose-volume data and outcomes for each spinal cord of a clinical dataset: the Gibbs 2007 article (Gibbs et al, 2007(1)), which essentially contains the first 100 stereotactic body radiation therapy (SBRT) spine treatments from Stanford University Medical Center. The dataset is modeled and compared in detail to the rest of the literature review, which found 59 dose tolerance limits for the spinal cord in 1-5 fractions. We partitioned these limits into a unified format of high-risk and low-risk dose tolerance limits. To estimate the corresponding risk level of each limit we used the Gibbs 2007 clinical spinal cord dose-volume data for 102 spinal metastases in 74 patients treated by spinal radiosurgery. In all, 50 of the patients were previously irradiated to a median dose of 40Gy in 2-3Gy fractions and 3 patients developed treatment-related myelopathy. These dose-volume data were digitized into the dose-volume histogram (DVH) Evaluator software tool where parameters of the probit dose-response model were fitted using the maximum likelihood approach (Jackson et al, 1995(3)). Based on this limited dataset, for de novo cases the unified low-risk dose tolerance limits yielded an estimated risk of spinal cord injury of ≤1% in 1-5 fractions, and the high-risk limits yielded an estimated risk of ≤3%. The QUANTEC Dmax limits of 13Gy in a single fraction and 20Gy in 3 fractions had less than 1% risk estimated from this dataset, so we consider these among the low-risk limits. In the previously irradiated cohort, the estimated risk levels for 10 and 14Gy maximum cord dose limits in 5 fractions are 0.4% and 0.6%, respectively. Longer follow-up and more patients are required to improve the risk estimates and provide more complete validation.

Byline: Jinyu. Xue, Hesheng. Wang, David. Barbee, Matthew. Schmidt, Indra. Das Dosimetric accuracy of a volumetric modulated arc therapy (VMAT) plan is directly related to the beam model, particularly with [...]

Purpose: Treatment option of stereotactic radiosurgery versus whole brain radiotherapy for multiple brain metastases (>10) is an ongoing debate. Detailed dosimetric and biological information are presented in this study to investigate the possible clinical outcomes.Materials and Methods: Nine patients with multiple brain metastases (11-25) underwent stereotactic radiosurgery. Whole brain radiotherapy plans are retrospectively designed with the same MR image set and the same structure set for each patient using the standard opposing lateral beams and fractionation (3 Gy × 10).Physical doses and biologically effective doses are calculated for each lesion target and the CNS normal tissues and they are compared between whole brain radiotherapy and stereotactic radiosurgery in the context of clinical efficacy and published toxicities., Results: Tumor biologically effective dose is higher in radiosurgery than in whole brain radiotherapy by factors of 3.2-5.3 in maximum dose and of 2.4-3.1 in mean dose. Biologically effective mean dose in radiosurgery is 1.3-34.3% for normal brain, 0.7-31.6% for brainstem, 0.5-5.7% for chiasm, 0.2-5.7% for optic nerves and 0.6-18.1% for hippocampus of that in whole brain radiotherapy over nine cases presented here. We also presented the dose-volume relationship for normal brain to address the dosimetric concerns in radiosurgery., Conclusions: Dose-volume metrics presented in this study are essential to understanding the safety and efficacy of whole brain radiotherapy and/or radiosurgery for multiple brain metastases. Whole brain radiotherapy has resulted in higher incidence of radiation-related toxicities than radiosurgery. Even for patients with more than 10 brain metastases, the CNS normal tissues receive significantly lower doses in radiosurgery. Mean normal brain dose in SRS is found to correlate with the total volume of lesions rather than the number of lesions treated.

Purpose/objective: To determine clinically relevant SBRT/stereotactic ablative radiotherapy (SABR) dose tolerance limits for RP based on statistical analysis of outcomes data., Materials and Methods: Eighteen consecutive patients who were treated using volumetric modulated arc therapy (RapidArc) for lung tumors exceeding 80cc were assessed. Clinical outcomes have been published elsewhere, and here we present a normal tissue complication probability (NTCP) analysis. The dose volume histogram (DVH) reduction techniques of total lung V20Gy, V15Gy, V10Gy, V5Gy and mean lung dose (MLD) were each analyzed, as well as ipsilateral lung V5Gy and contralateral lung V5Gy, using the DVH Evaluator software tool. The framework of the Lyman Model was used except that each DVH reduction method was analyzed independently instead of using the power-law relationship for volume dependence. Model parameters were fitted using Maximum Likelihood., Results: RP was reported in 5 patients (CTC Grade 2 in 3, and Grade 3 in 2). Total lung V5Gy and contralateral lung V5Gy were the best predictors of RP (p < 0.0001 for both). For V5Gy, the 10% risk level for Grade 2-3 RP was 27.9% for total lung and 21.8% for contralateral lung. For V20Gy, the 25% risk level is 10.5% of total lung., Conclusions: Analysis of RP endpoints has identified total lung V5Gy and contralateral lung V5Gy as the best predictors of RP following SBRT when delivered with RapidArc. These findings are based on limited clinical data, and longer follow-up in larger patient cohorts is required in order to determine more accurate dose tolerance limits.