Clinical and dosimetric factors associated with acute rectal toxicity in patients treated with (131)Cs brachytherapy for prostate cancer.

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.