Plan quality and delivery time comparisons between volumetric modulated arc therapy and intensity modulated radiation therapy for scalp angiosarcoma: A planning study

Introduction: Due to its spherical surface, scalp angiosarcoma requires careful consideration for radiation therapy planning and dose delivery. Herein, we investigated whether volumetric modulated arc therapy (VMAT) is superior to intensity modulated radiation therapy (IMRT) in terms of the plan quality and delivery time. Methods: Three different coplanar treatment plans were created for four patients, comprising a two-arc VMAT plan as well as 5-field and 9-field IMRT plans with 6 MV beams. The X-ray Voxel Monte Carlo algorithm was employed for dose calculation. A radiation therapy dose of 60 Gy was prescribed to the planning target volume (PTV) in 30 fractions. The homogeneity indexes (HIs) and conformity indexes (CIs) of the PTV, organs at risk (OARs) doses and delivery times were calculated and compared. Results: For the VMAT, 5-field and 9-field IMRT plans, the mean HIs were 0.14, 0.16 and 0.15; CIs(100%) were 0.63, 0.61 and 0.64; CIs(98%) were 0.72, 0.66 and 0.70 and CIs(95%) were 0.74, 0.67 and 0.71 respectively. All mean dose parameters of the VMAT and 9-field IMRT plans for the brain were equal to or lower than those of the 5-field IMRT plan. For the 5-field IMRT plan, the dose constraints for the left lens were not satisfied in two patients. The mean delivery times were 3.3, 11.1 and 14.7 min for the VMAT, 5-field and 9-field IMRT plans respectively. Conclusion: The VMAT plan quality is comparable to that of 9-field IMRT, with a reduced delivery time. Therefore, VMAT represents a valuable, sophisticated irradiation technique for treating scalp angiosarcoma.