Comparative assessment of doses to tumor, rectum, and bladder as evaluated by orthogonal radiographs vs. computer enhanced computed tomography-based intracavitary brachytherapy in cervical cancer

PURPOSE: To carry out a comparative assessment of intracavitary brachytherapy (ICBT) doses to tumor, bladder, and rectum based on orthogonal films and contrast enhanced computed tomography (CECT). METHODS AND MATERIALS: Fifty-five ICBT procedures with CT/MRI compatible applicator and CECT scans were evaluated. Doses to Point A, International Commission on Radiation Units and Measurement (ICRU) reference points for maximum bladder (B-max(ICRU)) and rectum (R-max(ICRU)) localized from orthogonal films were compared with CECT delineated tumor, bladder (B-max(CECT)), and rectum (R-max(CECT)) doses, respectively. The 95th and 90th percentile bladder (B-95(CECT) and B-90(CECT)) and rectal (R-95(CECT) and R-90(CECT)) doses based on CECT were also estimated. RESULTS: Mean percentage tumor volume encompassed within the prescribed dose of 600 cGy to Point A was 88.8%. Mean B-max(ICRU), B-max(CECT), R-max(ICRU), and R-max(CECT) were 631.3 cGy, 1221.4 cGy, 454.8 cGy, and 526.9 cGy, respectively. Paired mean differences were significant between B-max(ICRU) and B-max(CECT) or B-95(CECT) (both p<0.001); R-max(ICRU) and R-max(CECT) (p=0.005) or R-90(CECT) (p<0.001), whereas insignificant for B-max(ICRU) and B-90(CECT) (p = 0.281), and R-max(ICRU) and R-95(CECT) (p = 0.372). CONCLUSIONS: Prescription based on Point A ICBT doses could lead to uncertainty and under-dosage in tumor. ICRU 38 maximum bladder and rectal doses significantly underestimate the maximum doses to these organs and represent the 90th and 95th percentile of the maximum doses to these organs, respectively. (C) 2006 American Brachytherapy Society. All rights reserved.