Half-beam volumetric-modulated arc therapy in adjuvant radiotherapy for gynecological cancers

Purpose The purpose of this study is to introduce half‐beam volumetric‐modulated arc therapy (HVMAT), an innovative treatment planning technique from our work, for reducing dose to the organs at risk (OAR) during adjuvant radiotherapy for gynecological cancers. Methods and materials Seventy‐two treatment plans of 36 patients with gynecological cancers receiving adjuvant radiotherapy were assessed. Among them, 36 plans were designed using HVMAT and paired with the other 36 traditional volumetric‐modulated arc therapy (VMAT) plans for each patient. The main uniqueness of the HVMAT designs was that it consisted of two opposite‐shielded half‐beam fields rotated inversely in two coplanar arcs, collocating with the specially‐devised avoidance structures to enhance the control of the OAR doses. The dose distributions in HVMAT and VMAT were evaluated and compared using the random effects model. Results The ratios of OAR doses in HVMAT compared with VMAT showed a comprehensive OAR dose reduction when using HVMAT (V 20Gy: bladder, 0.92; rectum, 0.95; V 30Gy: bowel, 0.91; femoral heads, 0.66), except for the ilium (V 30Gy: 1.12). The overall mean difference for each OAR across V 40Gy, V 30Gy, V 20Gy, and bowel V 15Gy was statistically significant (almost all p