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ObjectThe objective of this study was to examine radiation dose distributions created by 2 competing radiosurgery modalities for treating multiple brain metastases: single-isocenter volumetric modulated arc radiosurgery (VMAS) and Gamma Knife Perfexion (GKP). In addition, the effectiveness of multiple radiosurgery quality metrics was evaluated and compared between these advanced treatment modalities.MethodsSeven anonymized MRI data sets, each showing 2–5 metastases, were used to create plans on each system. The GammaPlan (version 10.1) program was used for planning of GKP. A neurosurgeon contoured the volumes to be treated, and no planning target volume expansion was used. A prescription dose coverage of ≥ 99% was achieved for each tumor volume. The Philips Pinnacle (version 9.2) program was used for planning of VMAS, using the SmartArc optimization algorithm for delivery on a Varian iX linear accelerator. Contours were transferred from GammaPlan, and again no planning target volume expansion was used. Between 2 and 5 arcs with table angles of 90°–270° were used. Again, a V100% of ≥ 99% was achieved for each tumor volume. After planning, the MRI scans, tumor volumes, and dose information from each plan were exported according to the Digital Imaging and Communications in Medicine standard to the VelocityAI program for analysis. Brain dose-volume histograms (DVHs) for normal brain tissues were generated, and the volume of these tissues receiving 20%–90% of the prescription dose was tabulated. Finally, the prescription isodose to tumor volume ratio (PITV; Shaw et al., 1993), conformity index (CI; Paddick, 2000), gradient index (GI, Paddick and Lippitz, 2006), and conformity/gradient index (CGI, Wagner et al. 2003) were calculated for each plan. Both the PITV and CI have ideal values of 1, while the GI and CGI have ideal values of lowest and highest achievable, respectively.ResultsThe DVHs consistently showed that with VMAS a higher amount of normal brain tissues received each dose level than with GKP. These increases were largest for lower isodose levels, with the volumes of normal brain that received 20%–50% and 60%–90% of the prescription dose showing average increases of 403% and 227%, respectively. Prescription isodose conformality showed only minor differences between the 2 modalities. Radiosurgery quality metrics including measures of the dose gradient (GI and CGI) indicated that the GKP plan was superior in each case, with respective average GI and CGI values of 3.04 and 57.75 for GKP and of 10.22 and 10.85 for VMAS. Metrics evaluating prescription isodose conformality alone differed only slightly between the modalities. Average respective PITV and CI values were 2.13 and 0.53 for GKP and 2.27 and 0.51 for VMAS.ConclusionsStereotactic radiosurgery plans for the treatment of multiple metastases with VMAS delivered significantly more dose to the normal brain tissues than plans for GKP. Radiosurgery quality metrics including a measure of the dose gradient are better suited to providing contrast between modern radiosurgery treatment platforms.

Significant decrease in GTV volume based on daily CBCT was demonstrated during SBRT treatment. Adaptive SBRT has the potential to minimize integral dose to the surrounding normal tissues without compromising GTV coverage.

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Purpose/Objective(s): ASCENDE-RT, a recent randomized Phase III study comparing androgen suppression (AS) and external beam radiation therapy (EBRT) with either EBRT boost or low-dose rate brachytherapy (LDR-B) boost for men with intermediate and high-risk prostate cancer (PCa), reported improved biochemical failure for those undergoing LDR-B boost. Here we examine if there is a difference in overall survival (OS) between these treatment groups in the National Cancer Database (NCDB). Materials/Methods: We conducted a retrospective NCDB analysis between 2004 and 2012 of men with intermediate and high-risk PCa (Gleason 7-10, prostate specific antigen [PSA] 10 to <40 ng/mL, or T1c-T3a) treated with AS, defined as administration within 8 months of EBRT followed by LDR-B or EBRT boost (75.6-86.4 Gray [Gy]). Univariate, multivariate and subset survival analyses were completed using logistic regression, log-rank, Kaplan-Meier methods, and Cox-proportional hazards models. Multivariate model covariates were selected based on significance (P < 0.05) on univariate analyses. Propensity score match was completed using significant variables from logistic regression. Results: Among 25,164 patients treated with AS and EBRT, 20,624 (82%) were treated with EBRT boost and 4,540 (18%) with LDR-B boost. Mean follow up was 5 years (59.6 months, standard deviation [SD] Z 29.7). On univariate analysis, LDR boost was associated with improved OS (hazard ratio [HR] Z 0.6, 95% confidence interval [CI] Z 0.6-0.7, P < 0.001) when compared to EBRT boost. The 5 year OS for LDR-B and EBRT groups were 89.6% vs 83.7%, respectively, P < 0.001). On multivariate analysis, after controlling for age, race, insurance type, treatment location, facility type, Charlson comorbidity score, whole pelvis radiation, Gleason score, PSA and clinical T-stage, LDR-B boost remained independently associated with improved OS (HR Z 0.7, 95% CI Z 0.7-0.8, P < 0.001). Propensity score matching identified 6,860 patients and confirmed an OS associated with LDR boost (HR Z 0.6, 95% CI Z 0.5-0.7, P < 0.001). On subset analysis, the OS benefit of LDR-B boost persisted when stratified by favorable intermediate (HR Z 0.7, 95% CI Z 0.5-0.9, P Z 0.002), unfavorable intermediate (HR Z 0.7, 95% CI Z 0.6-0.8, P < 0.001), and high risk groups (HR Z 0.7, 95% CI Z 0.6-0.8, P < 0.001). Conclusion: For men with intermediate and high-risk PCa, treatment with AS and EBRT followed by LDR-B boost is independently associated with improved OS when compared to EBRT boost. These results show that the reported improvement in biochemical failure from the ASCENDE-RT trial may translate into improved OS outcomes.