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


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.


CONCLUSIONS
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.
Department of Radiation Oncology, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Jaclyn
J
Miyamoto
Department of Radiation Oncology, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Anthony L
AL
Michaud
Department of Radiation Oncology, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Nima K
NK
Harandi
Division of Hematology Oncology, Department of Internal Medicine, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Edward J
EJ
Kim
Division of Hematology Oncology, Department of Internal Medicine, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Thomas
T
Semrad
Division of Surgical Oncology, Department of Surgery, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Vijay
V
Khatri
Department of Radiation Oncology, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Jyoti
J
Mayadev
Department of Radiation Oncology, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A.
Julian
J
Perks
Department of Radiation Oncology, UC Davis Comprehensive Cancer Center, Sacramento, CA, U.S.A. ammonjazeb@ucdavis.edu.
Arta M
AM
Monjazeb
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012004:Rectal Neoplasms / Q000532:radiotherapy*; D012189:Retrospective Studies
Belly board; anorectal cancer; planning target volume