Initial Experience With Single-Isocenter Radiosurgery to Target Multiple Brain Metastases Using an Automated Treatment Planning Software: Clinical Outcomes and Optimal Target Volume Margins Strategy

Abstract

Purpose Our purpose was to assess the clinical outcomes and target positioning accuracy of frameless linear accelerator single-isocenter multiple-target (SIMT) dynamic conformal arc (DCA) stereotactic radiosurgery (SRS) for multiple brain metastases (BM). Methods and Materials Between October 2016 and September 2018, 31 consecutive patients ≥18 years old with 204 BM <3 cm in maximum size receiving SIMT DCA SRS were retrospectively evaluated. All plans were created using a dedicated automated treatment planning software (Brainlab, Munich, Germany), and treatments were performed with a Truebeam STx or a Novalis Tx (Brainlab and Varian Medical Systems, CA). The accuracy of setup and interfraction patient repositioning was assessed by Brainlab ExacTrac radiograph 6-dimensional image system and the risk of compromised target dose coverage evaluated. Brain control and overall survival were estimated by Kaplan-Meier method calculated from the time of SRS. Results Fourteen patients were treated for 4 to 6 and 17 patients for 7 to 10 BM. The mean gross tumor volume (GTV) was 0.65 cm 3 and the mean planning target volume (PTV) was 0.89 cm 3 . Mean V95 (the volume of the PTV covered by 95% of the prescription dose) and D95 (the prescription dose covering 95% of the PTV) were 99.5% and 21.1 Gy, respectively. With a median clinical follow-up of 11 months (range, 4-26 months), the 1-year survival was 68% and local control was 89%. As a consequence of plan isocenter residual errors, a loss of target coverage, defined as V95 < 95%, occurred in 28 PTVs (10 patients); using a 1 mm GTV-to-PTV margin, adequate dose coverage was maintained for all lesions. Conclusions SIMT DCA SRS represents a fast and effective approach for patients with up to 10 BM. The dosimetric effects of residual set-up and intrafraction positioning errors are modest, although a GTV-to-PTV margin of 1 mm is recommended.

Predicting the effect of indirect cell kill in the treatment of multiple brain metastases via single‐isocenter/multitarget volumetric modulated arc therapy stereotactic radiosurgery

“…After an average of 12 months following up interval, very promising 1‐ and 2‐year tumor local control rates of 99 and 95% were observed. Other clinical studies have observed similar patient outcomes demonstrating SIMT‐VMAT SRS for m‐bm to be both safe and effective with high rates of tumor response 22–25 …”

“…41 Several recent clinical outcome studies have reported positive results of higher tumor local control rates of SIMT-VMAT treatment that do not align with the presence of these dosimetric disparities. [21][22][23][24][25] For instance Alongi et al used Varian single-isocenter VMAT in the treatment of 43 patients with m-bm and performed a clinical follow-up study within 6 months. They observed that 60% of the patients with partial or complete responses and 40% with stable disease control, though the medial overall survival had not yet been reported.…”

“…Other clinical studies have observed similar patient outcomes demonstrating SIMT‐VMAT SRS for m‐bm to be both safe and effective with high rates of tumor response. 22 , 23 , 24 , 25 …”

Investigating the impacts of intrafraction motion on dosimetric outcomes when treating small targets with virtual cones

“…In the past decade, irradiation of lesions <1 cc. using VMAT, or dynamic conformal arc therapy have appeared for Brain Metastases 26 , 27 and Trigeminal Neuralgia. 24 Popple et al .…”

“…However, Guckenberg showed that using a 0‐mm PTV margin on cranial lesions could result in a 40% reduction in the conformity index when intrafraction motion occurs. 25 There have been several bodies of work to investigate dosimetric impact of motion when treating larger targets (>0.52 cc) with MLC‐based VMAT, 22 , 26 , 27 but there remains a gap in the literature for investigating the dosimetric impact of treating with virtual cones. This study aims to investigate the impact of intrafraction motion when treating small cranial targets with a virtual cone.…”