3257 - Comparison of Urinary Toxicity in Prostate Cancer Patients Undergoing External Beam Radiation Therapy With High-Dose vs. Low-Dose Brachytherapy Boost
Presenter(s)
C. Drovetsky1, M. Guerrero1, J. Cammin1, N. Lamichhane2, J. Xu3, S. Mossahebi3, S. Kudryasheva2, B. Morris4, A. Foard4, Z. H. Rana3, M. Kim3, M. Naslund5, and J. K. Molitoris3; 1University of Maryland School of Medicine, Baltimore, MD, 2Department of Radiation Oncology, University of Maryland Medical Center, Baltimore, MD, 3Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 4University of Maryland Medical Center, Baltimore, MD, 5Division of Urology, University of Maryland Medical Center, Baltimore, MD
Purpose/Objective(s): External beam radiation therapy (EBRT) with brachytherapy boost significantly improves oncological outcomes for intermediate and high-risk prostate cancer. However, comparative urinary toxicity between high-dose-rate (HDR) and low-dose-rate (LDR) boost strategies remains uncertain. We hypothesized that HDR boost would be associated with improved urinary toxicity due to ability to modulate the dose more than LDR.
Materials/Methods: We performed a retrospective review of patients with unfavorable intermediate-risk or high-risk prostate cancer treated at one academic center with EBRT plus HDR or LDR brachytherapy boost. To minimize bias, consecutive patients treated after initiating our HDR program in 2020 were included. Urinary toxicity outcomes and clinical characteristics including risk group, baseline PSA, and androgen deprivation therapy (ADT) use were abstracted from electronic medical records. Severe treatment toxicity was defined as CTCAE (Common Terminology Criteria for Adverse Events) grade =3. Patient-reported urinary symptoms were assessed using the International Prostate Symptom Score (IPSS), with a clinically meaningful increase defined as >5 points from baseline. Categorical variables were compared using chi-square or Fisher’s exact tests; continuous variables were compared using a one-way ANOVA.
Results: Of 113 patients, 78 (69%) received LDR and 35 (31%) received HDR. Baseline ADT use was similar between groups (94.8% LDR vs. 100% HDR; p=0.176). A numerically higher proportion of HDR patients were high-risk (80% HDR vs. 59% LDR; p=0.087). Among the 75 patients for which severe urinary toxicity (CTCAE grade =3) data was available, severe toxicity events were rare and did not differ by modality (LDR 2/55 [3.6%] vs. HDR 1/20 [5.0%]; p=1.000). In contrast, patient-reported worsening of urinary symptoms occurred more frequently after treatment with LDR compared with HDR boost (LDR 32/40 [80.0%] vs. HDR 8/15 [53.3%]; p=0.048). With a median follow up of 29 months (range 3 – 55 months), no biochemical failures were observed.
Conclusion: In this retrospective cohort, EBRT plus LDR brachytherapy boost was associated with a higher likelihood of patient-reported worsening of urinary symptoms as compared with HDR. In contrast, severe CTCAE grade =3 urinary events were rare and similar for both treatment modality groups. These findings suggest that brachytherapy boost modality may impact patient-reported urinary symptom burden despite low rates of major complications. The divergence between patient-reported worsening of urinary symptoms and low rates of clinician graded severe toxicity suggests that reliance on CTCAE endpoints alone may underestimate urinary symptom burden relevant to patient experience. Ongoing dosimetry analyses will assess predictors of IPSS worsening across modalities.