1073 - Second-Line Radiation Therapy for Locally Recurrent Prostate Cancer after Focal Therapy: A Single Institution Matched-Pair Analysis

04:10pm - 04:15pm PT

Room 20/21

Presenter(s)

Nikitha Kalahasti, BS - Stanford University, San Jose, CA

N. V. Kalahasti¹, A. Ewongwo², K. Taparra³, H. P. Bagshaw³, and M. K. Buyyounouski³; ¹Stanford University, Palo Alto, CA, ²Department of Radiation Oncology, Stanford University, Stanford, CA, ³Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA

Purpose/Objective(s):

Focal therapy (FT) is an alternative to prostate radiation therapy (RT) that targets a single intraprostatic tumor. When it fails, second-line, whole-prostate radiation therapy (SRT) is considered but limited safety data is available. In this study, we test the hypothesis that prior FT does not significantly increase the toxicity of second-line RT.

Materials/Methods:

We performed a retrospective analysis of 5606 prostate cancer patients evaluated at our institution over 24 years. Patients who underwent FT followed by SRT for recurrence were compared to patients treated with RT alone. Propensity score matching (PSM) balanced patient baseline characteristics including NCCN risk group, grade group, PSA at diagnosis, and RT dose. Since pretreatment International Prostate Symptom Scores were not always available, benign prostatic hypertrophy was used as a matching characteristic. Acute and late CTCAE v5 toxicities were assessed and compared between treatment groups using Fisher’s exact or Chi-square test, as appropriate. Logistic regression was performed to evaluate associations between treatment groups and each toxicity outcomes.

Results:

Of the 5606 patients, 114 matched patients were analyzed (38 SRT, 76 RT alone). The median age at diagnosis was 69 years, with median follow-up of 5.7 years for SRT and 5.1 years for RT alone. Among SRT patients, 71% received HIFU, 18% cryoablation, 8% TULSA, and 3% focal laser ablation. The median time from FT to SRT was 3.3 years (IQR 2.0-5.1). SRT modalities included EBRT alone (82%), EBRT+BT (5.3%), and SBRT (13%). In RT alone group, 62% received EBRT alone, 34% EBRT+BT, and 4% SBRT. The only significantly different factor was RT modality (p<0.001), with higher use of EBRT alone (82% vs 62%) and SBRT (13% vs 4%) with SRT compared to the RT alone.

Acute toxicities ranged from 0% to 80% with urinary symptoms being the most common. Grade =2 urinary frequency (5.3% vs 14%, p=0.4) and urgency (5.3% vs 14%, p=0.8) were similar between groups. Late toxicities ranged from 0% to 26%, with hematuria and urinary symptoms being the most frequent. Hematuria trended higher with SRT (26%) than RT alone (13%, p=0.08), while grade =2 urinary incontinence was significantly higher with SRT (5.3%) vs RT alone (0%, p=0.01). Both groups had similar acute and late grade =2 GI or GU toxicities. Logistic regression showed no significant association between SRT and most toxicity outcomes, except SRT had a trend towards increased late hematuria risk. Anticoagulant use was not known or used as a matched variable in this preliminary analysis.

Conclusion:

To our knowledge, this is the largest retrospective comparative analysis of SRT after FT vs RT alone for locally recurrent prostate cancer. Acute and late GI and GU toxicities were largely comparable between groups. The rate of late grade =2 urinary incontinence was low but may be higher after SRT, which is important for patients considering FT. Overall, SRT after FT is a safe and acceptable practice standard.