PARENT SESSION
9:00 AM to 11:00 AM
Sunday, April 21, 2002
Symposium 6
Volume Effects in the Clinic
Room: Nevada 1-2
Chair: Marks, Lawrence²²Department of Radiation Oncology, Durham, NC
Speakers: Jackson, Andrew⁴; Flickinger, John⁵; Dawson, Laura⁶; Vujaskovic, Zeljko⁷⁴Memorial Slaon-Kettering Canter Center, New York, NY⁵Presbyterian University Hospital, Pittsburgh, PA⁶Unviersity of Michigan, Ann Arbor, MI⁷Department Radiation Oncology-Radiation Biology, Durham, NC

(S06-1) Volume effects in late rectal bleeding after external beam radiotherapy for prostate cancer.

Jackson, Andrew^*,1, ¹ Department of Medical Physics, New York, New York

ABSTRACT-
We will review evidence for volume effects in the incidence of late rectal bleeding after radiotherapy. Traditionally, dose delivered during external beam radiotherapy of prostate cancer has been limited by complications occurring in the rectal wall. Dose escalation protocols conducted in the past 10 years utilizing 3D conformal radiotherapy (3DCRT) have shown that rectal toxicity can be controlled by the careful use of conformal techniques. The most frequent gastrointestinal complications of conformal radiotherapy of prostate cancer are late rectal bleeding, and in severe cases, ulceration requiring cautery procedures and or transfusion. The benefits of (3DCRT) are technique dependent, with clear dose responses for single techniques for prescription doses over 70 Gy. Studies of rectal motion show that the anterior wall can move ~1cm during treatment, so portions of the anterior rectal wall may receive the full prescription dose if posterior margin sizes of 1cm are used in designing the PTV. Comparison of clinical data using different margins suggests that increased rectal shielding, and posterior PTV margin sizes ~0.6cm reduce rectal complication rates. Despite uncertainties due to rectal motion, studies of dose-volume histograms (DVHs) show that rectal toxicity is strongly influenced by the percent volumes of rectal wall exposed to doses ~70 Gy and higher. Recent analysis of data from Memorial Sloan Kettering Cancer Center suggests that percent volumes of rectal wall exposed doses between 40-50 Gy and the existence of a reserve of unexposed tissue may also play a role in determining rectal bleeding rates. Recent treatments with intensity modulated radiotherapy have resulted in a dramatic decrease in the incidence of rectal bleeding.

KEYWORDS: Volume Effects, Late Rectal Bleeding, 3D Conformal Radiotherapy