The Effect of Treatment Position on Rectal and Bladder Dose-Volume Histograms for Prostate Radiotherapy Planned with 3-Dimensional Conformal Radiotherapy, Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy

Purpose: To compare target coverage and organ at risk (OAR) sparing in the supine and prone positions with 3-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in lowand high-risk prostate radiotherapy cases. Materials and Methods: Using magnetic resonance images of five healthy volunteers, six treatment plans (supine 3DCRT, prone 3DCRT, supine IMRT, prone IMRT, supine VMAT and prone VMAT) were generated. Planning target volume 1 (PTV1) was defined as the prostate gland plus the seminal vesicles with adequate margins in a high-risk setting, while PTV2 was defined as prostate only with margins in a low-risk setting. The mean dose for both PTV1 and PTV2 was set at 78 Gy. Plans generated by each of the 3 techniques were compared between the supine and prone positions using dose-volume histograms (DVHs). Results: For PTV1, prone 3DCRT provided a significantly higher D98% than did supine 3DCRT, and its homogeneity index (HI) was significantly better. IMRT and VMAT values did not differ significantly between the prone and supine positions. For PTV2, no values differed significantly between the supine and prone positions under any treatment plan. With respect to OAR, the rectal Dmean, D2%, V50, and V60 values of PTV1 were