Dosimetric comparison of intensity modulated radiosurgery with dynamic conformal arc radiosurgery for small cranial lesions

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: