Aims: To dosimetrically compare the fixed gantry intensity modulated radiosurgery (IMRS) with dynamic conformal arc radiosurgery (DCARS) for cranial lesions. This study investigates whether IMRS can be an adequate dosimetric alternative to DCARS for cranial stereotactic radiosurgery (SRS).
Subjects and methods: Forty-five SRS procedures for solitary brain metastasis (range: 0.44-29.18 cm 3) performed at our institution were selected for this study. Two plans were generated per patient: One IMRS plan using a multileaf collimation (MLC) of 5 mm, and one DCARS plan designed with a 3 mm micro-MLC. Dosimetric comparison metrics include the target coverage (Cov), conformity index (CI), homogeneity index (HI), gradient index (GI), and volume of the normal brain tissue receiving ≥12 Gy (V12). In addition, maximum doses to organs at risk (OAR) (brainstem, optic apparatus and cochlea) were compared for both techniques.
Results: Compared to DCARS, IMRS improved mean CI (IMRS: 0.81 vs.
Dcars: 0.63, P < 0.001), with no significant difference in target Cov (IMRS: 0.99 vs.
Dcars: 0.99, P > 0.05), HI (IMRS: 1.22 vs.
Dcars: 1.24, P > 0.05), GI (IMRS: 5.44 vs.
Dacrs: 5.44, P > 0.05). A weak significant difference in V12 (IMRS: 4.6 cm 3 vs. 5.2 cm 3, P = 0.033) was obtained. Subgroup analysis per target volume (small: <1 cm 3, intermediate: ≤1 cm 3 and <5 cm 3 and large: ≥5 cm 3) only revealed the statistically difference for CI metric (P < 0.001). No significant differences were found for maximum dose to the OAR.
Conclusions: We have shown that IMRS provides the dosimetric advantages compared with DCARS. Based on the dosimetric findings in this study, fixed gantry IMRS technique can be adopted as a standard procedure for cranial SRS when micro-MLC technology is not available on the linear accelerator.