Robert Yoon Kim MD, FACRO, Presenter: Nothing to Disclose

Sui Shen, Abstract Co-Author: Nothing to Disclose

Jun Duan PhD, Abstract Co-Author: Nothing to Disclose

Purpose/Objective: Since publication of the ICRU 38, many institutions use this definition to calculate reference bladder and rectal doses for intracavitary brachytherapy (ICBT) of cervical cancer. Attention should also be given to doses to the sigmoid colon and small bowel around the uterus because they may pass close to the intrauterine sources. Doses to these organs have been mostly unknown for ICBT. With advances in imaging technology and 3-dimensional treatment planning systems, the DVH of the volume of interest can be obtained for the ICBT. However, DVHs for sigmoid colon and small intestine has not been reported. The aim of this study is to evaluate DVHs of bladder, rectum, as well as sigmoid colon and small bowel, and also to compare these with ICRU reference doses for the ICBT. Materials/Methods: Twenty-two patients with cancer of the cervix (1 IB1, 5 IB2, 11 IIB, 5 IIIB) were treated with CT-compatible HDR intracavitary applicators (Nucletron) and underwent post-implant pelvic CT scans with applicators in place. CT-images were transferred to the PLATO treatment planning system. The volumes of organs at risk (OAR) was digitized. Dwell positions were identified and registered both in the uterine tandem and colpostats for each patient. All patients were treated with 600 cGy per fraction to Point A using radiography-based planning. For the CT-based planning, the DVHs were computed for the bladder, rectum, sigmoid colon and small bowel. To compare doses of OARs, the minimum dose in 1.0 cm3, 2.0 cm3 and 5.0 cm3 volume receiving the highest dose (D1, D2, and D5, respectively) were calculated from DVHs. Results: The mean dose and dose range of D1, D2 and D5 for the OARs of interest are reported in Table I for the 22 patients. Within the GI tract, the sigmoid colon received the highest mean dose followed by rectum and small bowel. The most frequent organ receiving the highest dose was sigmoid colon in 9 of 22 patients (41%) followed by rectum in 7 of 22 patients (32%) and small bowel in 6 of 22 patients (27%). The mean ICRU bladder point dose (401 cGy) was underestimated compared to the mean doses of D1, D2 and D5 (533, 484 and 411 cGy, respectively). However, the mean ICRU rectal point dose (412 cGy) was underestimated to only D1 volume dose (419 cGy). Conclusions: Compared to the 3-D volume dose, the ICRU bladder point dose underestimated the dose more than the ICRU rectal point dose. Due to high sigmoid colon dose, special attention should be given to the sigmoid colon at the time of treatment planning.

Kim, R, Shen, S, Duan, J, Dose-Volume Histogram (DVH) Analysis of Organs at Risk for Intracavitary Brachytherapy of Cervical Cancer: Bladder, Rectum, Sigmoid, and Small Bowel.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4417808.html