Purpose: (131)Cs has been recently introduced for use in prostate brachytherapy. We wished to identify clinical and dosimetric factors associated with acute bowel/rectal toxicity in patients treated with (131)Cs.
Methods and materials: Patients treated with (131)Cs prostate brachytherapy at the University of Pittsburgh were asked to complete expanded prostate cancer index composite surveys preoperatively and at 2-4 weeks and 3 months postimplant. We identified patients who experienced acute and persistent acute bowel toxicity to determine if any factors could correlate with either situation.
Results: One hundred six patients were treated with (131)Cs from September 2006 to May 2008. Thirty-eight percent of patients met our criteria for patient-appreciated acute bowel symptoms. On multivariate analysis, the volume of rectum receiving 50% of the prescribed dose (R-V(50); 4.1 vs. 2.6cc, p=0.01), R-V(75) (1.3 vs. 0.62cc, p=0.01), the percentage of the prescribed dose received by 1cc of the rectum (R-D-1cc; 75% vs. 64%, p=0.02), and R-D-2cc (63% vs. 54%, p=0.003) were found to be factors associated with a greater risk of severe acute bowel toxicity. At 3-month followup, 28% of patients had persistent acute bowel toxicity. On multivariate analysis, no factors were identified that correlated with persistent acute bowel toxicity.
Conclusions: This study identifies R-V(50), R-V(75), R-D-1cc, and R-D-2cc as factors associated with patient-appreciated acute rectal toxicity. We are performing dosimetric analysis to determine the optimal distance for the posterior needles from the prostate-rectal interface to decrease rectal dose while still maintaining adequate coverage of prostate.
Copyright © 2010 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.