Date Approved


Graduate Degree Type


Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Kathryn J. Barnhart

Second Advisor

Beant Gill

Academic Year





For patients with prostate cancer receiving radiation, Radiation Technology Oncology Group (RTOG) consensus guidelines support contouring the rectum from the lowest border of the ischial tuberosities to the rectosigmoid junction. Anatomically, the rectum terminates at the level of the anorectal ring. Existing dosimetry constraints for rectum are based on the RTOG definition of rectum. If clinicians opt to contour the rectum true to anatomic definitions, it remains unclear whether there can be a method to readily and practically compare this to existing dosimetry goals based on RTOG contouring.


Successive, previously treated prostate cancer patients treated with definitive intensity-modulated radiation therapy were identified, either receiving 78-80 Gy in 2 Gy/fraction (Conventional Fractionation (CF)) or 70 Gy in 2.5 Gy/fx (Hypofractionation (HF)) based on institutional practice. Rectal dose-volume parameters were captured using the delivered plan: V75Gy, V70Gy and V50Gy for CF and V45Gy, V40Gy, V55Gy, V65Gy, D15%, D25%, D35%, and D55% for HF based on published constraints. Rectal contours were drawn to meet RTOG consensus definitions (R-RTOG) and anatomic definitions (R-A). Paired t-test was utilized to compare mean differences between rectum contours.


R-A volumes were expectedly smaller than R-RTOG for both subsets when contoured (CF -13.1 ± 1.1 cc, ppppConclusion

There was a consistent increase in rectal dosimetry and decrease in volume when comparing RTOG to anatomic rectal contouring. If contouring rectum anatomically for prostate cancer patients, clinicians should implement these corrective factors as a more rapid, practical way to apply accepted Nature Reviews Genetics (NRG)/RTOG constraints.

Key words: RTOG contouring, rectal toxicity, IMRT, prostate