Comparing Acute Toxicity Profiles for High Dose Rate Prostate Brachytherapy Patients Receiving Two Implants Separated by a One-Week Versus Two-Week Interval

Abstract

Multiple dose/fractionations and implant intervals have been used for patients undergoing definitive prostate high dose rate (HDR) brachytherapy (BT) as monotherapy, but limited data exist identifying the impact of interval duration on acute toxicity. We use 13.5 Gy x 2, given as one fraction per implant performed 1-2 weeks apart based on patient and OR availability at our institution. Our objective was to compare the acute toxicity profiles between patients receiving implants at a one-week or two-week interval. All patients were treated on a prospective institutional IRB-approved protocol by the same 2 brachytherapists. Patients completed IPSS and EPIC-26 questionnaires at their pre-treatment visit and at 1 and 3 months after BT. Physician-reported genitourinary (GU) and gastrointestinal (GI) CTCAE v4.03 toxicity grades at these same time points were recorded. IPSS and EPIC-26 values and physician-reported toxicity grades were compared for patients stratified into two interval duration groups, ≤10 days vs. >10 days between implants. Linear mixed effects models were used to estimate patients’ mean IPSS and EPIC-26 values over time based on their implant interval duration. Similarly, generalized linear mixed effects models were used to estimate the odds of higher physician-reported GU or GI toxicity grades over the same period for both groups. Median follow-up was 5 months (interquartile range [IQR]: 3 – 8 months). A total of 39 patients were analyzed, in which 21 had ≤10 days between implants and 18 had >10 days between implants with a median implant interval time of 7 (IQR: 7-7) and 14 (IQR: 12-14) days, respectively. There was no difference in IPSS and EPIC-26 values between the groups at pre-treatment, 1 month, and 3 months (Table). Similarly, when comparing the two interval duration groups, the physician-reported GI toxicity grades (p=.86) and GU toxicity grades (p=.30) were not meaningfully different at any time point. For patients with ≤10 days and >10 days between implants, 43% and 58% had grade ≥2 GU toxicity, respectively, and no patients had grade ≥2 GI toxicity. The interval duration between implants for patients undergoing HDR BT as monotherapy using a two implant regimen does not appear to be associated with patient-reported or physician-graded acute toxicity. Longer term follow-up is needed to assess for late toxicity and disease-control outcomes.Abstract 2595Mean IPSS (Standard Error [SE])p-valueMean EPIC GU (SE)p-valueMean EPIC GI (SE)p-value≤10 days>10 days≤10 days>10 days≤10 days>10 daysPre-treatment3.92 (1.29)5.79 (1.34).237.08 (1.10)7.11 (1.58).9916.67 (1.27)22.25 (2.10).481 Month13.15 (1.38)13.86 (1.52).699.06 (1.02)9.75 (1.49).7119.83 (1.18)18.96 (1.74).793 Months6.37 (1.48)8.70 (1.64).247.69 (1.09)7.09 (1.31).7317.81 (1.26)17.21 (1.52).77 Open table in a new tab