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Spiral volumetric modulated arc therapy for whole-brain radiotherapy with simultaneous integrated boost to multiple
Yuan Xu1, Junjie Miao2, Jianrong Dai3
1Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100021, China.
Purpose:
Spiral volumetric modulated arc therapy (SVMAT) is an integrated radiation therapy technique with longitudinal couch movement to generate a spiral/helical trajectory. This approach combines the merits of volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT). This study aimed to investigate the treatment planning of SVMAT for whole-brain radiotherapy (WBRT) with simultaneous integrated boost (SIB) for a large number (> 40) of metastases.
Materials And Methods:
Ten patients with multiple brain metastases (40-120 metastases) were retrospectively enrolled. These patients had previously received treatment with HT using the WBRT + SIB technique. Prescribed doses of 40 Gy for the whole brain and 60 Gy for the metastases were delivered in 20 fractions. In this study, SVMAT plans were designed using DeepPlan (version 1.3, Wisdom Tech., Hefei, Anhui, China) as the treatment planning system for the radiotherapy machine NeuRT Aurora (Neusoft IntelliRay Technology, Shenyang, Liaoning, China). In all SVMAT plans, the patient couch was set to move out after specified multiple gantry rotations and then move in within a single treatment fraction. The number of gantry rotations ranged between 6 and 16. These SVMAT plans were compared with HT and piecewise VMAT (previously proposed PVMAT) based on a plan quality metric (PQM) comprising 20 metrics.
Results:
For target coverage and conformity index (CI) of whole brain and metastases, no significant differences were observed between the SVMAT&HT or between SVMAT&PVMAT plans (p > 0.05). The sparing of right hippocampus, optic nerves and optic chiasm were improved using the SVMAT plan compared to the HT plan (p < 0.05). However, no significant difference was observed between the SVMAT and PVMAT plans for OAR sparing (p > 0.05). The mean total scores of PQM were 51.70 ± 8.14 (mean ± standard deviation), 53.24 ± 5.84, 53.64 ± 7.16, 54.24 ± 7.06, 54.60 ± 6.30, and 55.05 ± 6.18 points for SVMAT plans with gantry rotations of 6 8, 10, 12, 14, and 16, respectively. The average score for HT was 38.18 ± 5.48 points, which was significantly lower than that for the SVMAT plans (p < 0.05). Furthermore, the mean score for PVMAT was 54.34 ± 6.48 points, and no significant differences were observed between SVMAT and PVMAT (p > 0.05). The beam delivery time was shorter for SVMAT with 6 (271.5 ± 53.7 s), 8(310.3 ± 42.9 s), and 10(359.6 ± 34.4 s) rotations compared to HT (393.0 ± 25.0 s) (p < 0.05) and also shorter for SVMAT with six rotations compared to PVMAT (312.6 ± 53.7 s) (p < 0.05).
Conclusions:
For WBRT + SIB, SVMAT achieved improved plan quality and higher delivery efficiency compared with HT and had similar plan quality compared with PVMAT.
