Predicting rectal and bladder overdose during the course of prostate radiotherapy using dose-volume data from initial treatment fractions - Abstract

PURPOSE:To evaluate whether information from the initial fractions can determine which patients are likely to consistently exceed their planning dose-volume constraints during the course of radiotherapy for prostate cancer.

METHODS AND MATERIALS: Ten patients with high-risk prostate cancer were treated with helical tomotherapy to a dose of 60 Gy in 20 fractions. The prostate, rectum, and bladder were recontoured on their daily megavoltage computed tomography scans and the dose was recalculated. The bladder and rectal volumes (in mL) receiving ≥100% and ≥70% of the prescribed dose in each fraction and in the original plans were recorded. A fraction for which the difference between planned and delivered was more than 2 mL was considered a volume failure. Similarly if the difference in the planned and delivered maximum dose (Dmax) was ≥1% for the rectum and bladder, the fraction was considered a dose failure. Each patient's first 3 to 5 fractions were analyzed to determine if they correctly identified those patients who would consistently fail (i.e., ≥20% of fractions) during the course of their radiotherapy.

RESULTS: Six parameters were studied; the rectal volume (RV) and bladder volumes (BV) (in mL) received ≥100% and ≥70% of the prescribed dose and maximum dose to 2 mL of the rectum and bladder. This was given by RV100, RV70, BV100, BV70, RDmax, and BDmax, respectively. When more than 1 of the first 3 fractions exceed the planning constraint as defined, it accurately predicts consistent failures through the course of the treatment. This method is able to correctly identify the consistent failures about 80% (RV70, BV100, and RV100), 90% (BV70), and 100% (RDmax and BDmax) of the times.

CONCLUSIONS: This study demonstrates the feasibility of a method accurately identifying patients who are likely to consistently exceed the planning constraints during the course of their treatment, using information from the first 3 to 5 fractions.

Written by:
Murthy V, Shukla P, Adurkar P, Master Z, Mahantshetty U, Shrivastava S. Are you the author?
Department of Radiation Oncology and Medical Physics, Tata Memorial Hospital and Advanced Centre for Treatment, Research and Education in Cancer (ACTREC), Tata Memorial Centre, Mumbai.

Reference: Int J Radiat Oncol Biol Phys. 2012 Jan 31. Epub ahead of print.
doi: 10.1016/j.ijrobp.2011.11.001

PubMed Abstract
PMID: 22300567