The Role of Image-guided Radiotherapy in the Treatment of Anorectal Cancer Using Prone Belly-board Positioning

• Published in: Anticancer research 2016-06, Vol.36 (6), p.3013-3017
• Main Authors: Miyamoto, Jaclyn, Michaud, Anthony L, Harandi, Nima K, Kim, Edward J, Semrad, Thomas, Khatri, Vijay, Mayadev, Jyoti, Perks, Julian, Monjazeb, Arta M
• Format: Article
• Language: English
• Subjects: Adult; Aged; Aged, 80 and over; Body Mass Index; Cone-Beam Computed Tomography - methods; Female; Humans; Male; Middle Aged; Patient Positioning; Radiotherapy, Image-Guided - methods; Rectal Neoplasms - radiotherapy; Retrospective Studies
• ISSN: 0250-7005; 1791-7530

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. 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. 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. 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.