Journal
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
Volume 53, Issue 2, Pages 434-442Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/S0360-3016(02)02750-5
Keywords
intensity-modulated radiation therapy (IMRT); photon energy; prostate cancer
Ask authors/readers for more resources
Purpose: To examine the influence of energy and number of beams on nontarget dose when using intensity-modulated radiation therapy (IMRT) to treat deep-seated targets. Methods and Materials: Ten patients with prostate cancer (36-226 cc) treated locally to 75.6 Gy were studied. IMRT plans were created for 6-, 10-, and 18-MV photons using 4, 6, 9, and 11 coplanar nonopposed fields. Plans, normalized to cover 95% of the target volume, were analyzed using: (a) conformity index (CI) at 105%, 100%, 95%, 90%, 80%, 70%, 50% of prescribed dose; (b) prescription isodose line (PI); (c) minimum dose to target (Tar in), (d) maximum dose to tissue (Tis(max)); (e) dose to rectum/bladder/penis bulb; (f) integral nontarget dose (ID). Because CI evaluates dose independent of location, tissue also was divided into near region (NR: 1-cm-thick shell surrounding target) and far region (FR: tissue minus NR) volumes that were evaluated at the same levels as CI. Results: The target and sensitive structure metrics were the same for all plans. However, although there was little difference in NR volume exposed to dose, regardless of energy or number of fields, there was a significant increase in FR volume exposed to dose, at all levels, for low energy/few field plans compared to high energy/many fields (e.g., > 50 cc greater than or equal to 65 Gy). This effect disappeared with greater than or equal to 9 fields regardless of energy. Conclusion: With IMRT, the use of 6 MV photons with less than 9 fields may result in an increase in dose in regions distant from the target volume (e.g., near the skin surface), even though the CI and sensitive structure metrics may indicate good conformance of high dose to the target volume itself. The clinical significance of this increased dose distant from the target, in terms of complications, remains to be determined. (C) 2002 Elsevier Science Inc.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available