What maximum volume (in cc's) of small bowel would you allow to receive 45 Gy in a patient with node positive squamous cell carcinoma of the anal canal receiving concurrent chemoradiation with 5-FU/MMC being treated with IMRT?  

This is a very good question because this comes up very commonly in female patients. The first thing to recognize is that the 45Gy microscopic dose is overtreatment for anal cancer. Your V35 is probably an effective microscopic dose. From the to 2D and 3D Era, 30.6 Gy in 17 fractions ...