RT Journal Article SR Electronic T1 The Role of Image-guided Radiotherapy in the Treatment of Anorectal Cancer Using Prone Belly-board Positioning JF Anticancer Research JO Anticancer Res FD International Institute of Anticancer Research SP 3013 OP 3017 VO 36 IS 6 A1 JACLYN MIYAMOTO A1 ANTHONY L. MICHAUD A1 NIMA K. HARANDI A1 EDWARD J. KIM A1 THOMAS SEMRAD A1 VIJAY KHATRI A1 JYOTI MAYADEV A1 JULIAN PERKS A1 ARTA M. MONJAZEB YR 2016 UL http://ar.iiarjournals.org/content/36/6/3013.abstract AB Aim: To evaluate Radiation Therapy Oncology Group planning target volume margins of 7-10 mm for radiation therapy in anorectal cancer using prone belly-board positioning without image guidance. Patients and Methods: 375 kV cone beam computed tomography image-guided radiotherapy (IGRT) images from 20 patients treated for anorectal cancer were retrospectively analyzed for setup shifts. We calculated the total translational shift for each patient and the frequency with which setup shifts exceeded 7 mm and 10 mm. Results: A total of 42.7% of treatments required shifts >7 mm and 20.8% >10 mm. The mean translational shift was 7.1 mm. 70% of patients experienced shifts ≥7 mm in 20% or more of their treatments and 25% of ≥10 mm in 20% or more of their treatments; 15% experienced shifts ≥10 mm in over half of their treatments. van Herk calculations suggest margins of 12.8 mm are necessary for accuracy without IGRT. Conclusion: IGRT using a prone belly board and 7-10 mm margins requires daily image-guidance to prevent planning target volume misses and ensure optimal dose delivery.