Evaluation of Hybrid Arc and Volumetric-Modulated Arc Therapy Treatment Plans for Fractionated Stereotactic Intracranial Radiotherapy

Purpose: The study was aimed to compare hybrid arc and volumetric-modulated arc therapy treatment plans for fractionated stereotactic radiotherapy of brain tumors. Methods: Treatment plans of 22 patients were studied. Hybrid arc and volumetric-modulated arc therapy plans were generated using Brainlab iPlanDose and Varian Eclipse treatment planning systems, respectively, with 6 MV photon beams on a Varian TrueBeam STx linear accelerator (Palo Alto, CA). Prescription dose was 54 Gy. The fractionation was 1.8 Gy per fraction and 30 fractions in total, or 2 Gy per fraction and 27 fractions in total. Planning target volume ranged from 2.4 to 28.6 cm(3). Dose conformity index, gradient index, homogeneity index, and maximum doses in organs at risk were compared. Wilcoxon signed rank test was used to determine statistical significance in paired comparison. Results: Conformity indexes of hybrid arc and volumetric-modulated arc therapy plans are 1.10 +/- 0.10 and 1.14 +/- 0.07, respectively (P = .4); gradient indexes are 5.02 +/- 1.20 and 5.64 +/- 1.28, respectively (P = .0001); homogeneity indexes are 1.02 +/- 0.01 and 1.05 +/- 0.01, respectively (P = .0001); brainstem maximum doses are 53.87 +/- 1.63 Gy and 54.06 +/- 3.17 Gy, respectively (P = .1); and optic chiasm maximum doses are 53.86 +/- 1.28 Gy and 53.95 +/- 1.81, respectively (P = .4). The monitor unit efficiencies of hybrid arc and volumetric-modulated arc therapy plans are 2.57 +/- 0.25 MU/cGy and 2.68 +/- 0.24 MU/cGy, respectively (P = .2). The differences of conformity index, gradient index, and homogeneity index between hybrid arc and volumetric-modulated arc therapy plans are small: 0.08 +/- 0.05, 0.65 +/- 0.46, and 0.02 +/- 0.01, respectively. The maximum doses in organs at risks are similar between hybrid arc and volumetric-modulated arc therapy plans. Hybrid arc and volumetric-modulated arc therapy plans, which have similar monitor unit efficiencies, present similar dosimetric results in the fractionated intracranial radiotherapy.