Toxicity Outcomes at 18 Months for Cs-131 Low-Dose-Rate Prostate Brachytherapy Compared to I-125 and Pd-103

Abstract

<h3>Purpose/Objective(s)</h3> Low dose rate prostate brachytherapy is an established component of definitive radiotherapy options for localized prostate cancer. As the utility of LDR brachytherapy (LDRB) has evolved, the focus has shifted to improving the side effect profile while maintaining oncologic outcomes. Most prior efficacy and toxicity data were gathered using I-125 and Pd-103, but due to the shorter half-life and slightly higher average energy of Cs-131, several institutions have adopted its use in an attempt to improve outcomes and decrease toxicity. To report the toxicity outcomes up to 18 months after Cs-131 LDR brachytherapy at our institution, compared to our experience with I-125 and Pd-103. <h3>Materials/Methods</h3> A retrospective review was performed on the first 50 patients treated with Cs-131 LDRB for localized prostate cancer at our institution. Patients receiving either a full or partial implant were included. Prescription doses of 100Gy and 80Gy were utilized, respectively. Patients receiving partial implants generally received 45Gy external beam radiotherapy starting 6-8 weeks after implant. Data regarding AUA prostate symptom score, sexual health inventory for men (SHIM) score, and RTOG GI toxicity score were assessed pretreatment, at 1 month, and at each subsequent follow up. Demographic and clinical data were also collected. The data was compared to cohorts of the last 50 patients treated I-125 and the last 50 patients treated with Pd-103, to standard doses. Descriptive statistics were used to summarize variables. A linear mixed model was used to compare means and to identify variables as prognostic for toxicity (p≤0.05). <h3>Results</h3> The mean AUA scores prior to brachytherapy were similar for patients in all groups (p=1.00), while at 1-month post-treatment, mean AUA score was significantly higher for patients treated with Cs-131 and Pd-103 compared to I-125 (p<0.001). Mean AUA scores were not significantly different at longer follow-up (p>0.50). The need for a catheter post-brachytherapy occurred in 8% of patients and was not associated with type of isotope on multivariate analysis (MVA). Prostate volume, numbers of seeds, and prostate D90% were significant predictors for the need for a catheter on MVA. The use of ADT and the total activity were significant predictors on MVA for a decrease in SHIM score over time. The type of isotope used did not predict for erectile dysfunction (ED) as measured by SHIM score on MVA. Overall rates of GI toxicity were low with only 3 patients developing RTOG grade 2 toxicity or greater without any obvious difference between isotopes. <h3>Conclusion</h3> In patients treated with Cs-131 or Pd-103 LDRB, acute GU side effects peaked higher at 1 month than with I-125, but rapidly decreased to similar levels with longer follow-up. The type of source used did not predict for need for catheterization, ED, or GI toxicity at any time point.