3340 - Treatment Outcomes of Radiation Therapy with Androgen Deprivation Therapy in Patients with N1 Prostate Cancer

12:45pm - 02:00pm PT

Hall F

Screen: 24

POSTER

Presenter(s)

Kayeong Shin, MD - MD Anderson Cancer Center, Houston, TX

K. Shin¹, S. Choi¹, C. J. Hassanzadeh¹, K. E. Hoffman¹, S. E. McGuire¹, O. Mohamad¹, H. Mok¹, Q. N. Nguyen¹, R. J. H. Park¹, C. Tang¹, A. Zurita-Saavedra², B. Chapin³, and D. S. Surasi⁴; ¹Department of Genitourinary Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ²Department of Genitourinary Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ³Department of Urology, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁴Department of Nuclear Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s):

External beam radiation therapy (EBRT) combined with androgen deprivation therapy (ADT) often with androgen receptor signaling inhibitors (ARSI) has become the standard treatment for patients with node-positive prostate adenocarcinoma (PCa). This study examines efficacy, patterns of failure, and toxicity of EBRT in this patient group.

Materials/Methods:

Institutional databases were queried retrospectively to identify patients with cN1M0 PCa treated with either intensity-modulated radiation therapy (IMRT) or intensity-modulated proton therapy (IMPT) from 2017 to 2024. Patients with a follow-up of =24 months, or those who had recurrence or death, were included. Primary outcomes were nodal recurrence-free survival (NRFS). Secondary outcomes were metastasis-free survival (MFS), biochemical recurrence-free survival (bFS), overall survival (OS), distant metastasis (DM), pattern of progression, and genitourinary (GU) and gastrointestinal (GI) toxicities. Biochemical recurrence (BR) was defined using the Phoenix criteria. NR and DM were defined by imaging, most often by PSMA PET. GU and GI toxicities were graded using modified Radiation Therapy Oncology Group (RTOG) scale. Kaplan-Meier analysis was applied to assess survival, while descriptive statistics was applied to summarize the anatomical distribution of NR and DM, and toxicities.

Results:

Fifty-six patients were included, with a median follow-up of 39 months (IQR 32.3–57.8). IMRT was used in 37 patients and IMPT in 19. The median radiation dose was 78 Gy (range 70–78) to the prostate and 46 Gy (range 46–50.4) to the pelvis, with 52 patients receiving a nodal boost (median 60 Gy, range 48.3–70). All patients received ADT, 36 of whom also received ARSI (median duration: ADT 24 months, ARSI 22 months). NRFS at 3-/5-years were 94.4% and 74.5%, respectively. NRs were observed in 7 patients with 4 (57.1%) above the retroperitoneal (RP) nodes, 2 (28.6%) in the RP nodes, and 1 (14.3%) in the inguinal nodes. All NRs occurred outside the radiation field. MFS, bFS, and OS at 3-/5-years were 88.3%/61.1%, 88.4%/73.8%, and 91.0%/91.0%, respectively. DMs occurred in 11 patients, with the most frequent sites being bone (72.7%), liver (27.3%), and lung (18.2%). Notably, 4 out of 11 patients with NR and 3 out of 7 patients with DMs did not have BR. 85.7% of patients with NR had concurrent or subsequent DMs within 6 months, while 45.4% of those with DMs had no prior NR. Acute GU/GI toxicity seen were as follows: grade 1 (42.9%/44.6%), grade 2 (35.7%/16.1%), grade 3 (1.8%/1.8%). Late GU/GI toxicity were as follows: grade 1 (19.1%/14.9%), grade 2 (10.6%/4.3%), grade 3 (1.8%/0%).

Conclusion:

EBRT and ADT with or without ARSI showed favorable survival outcomes, with manageable toxicity. Absence of NR within the radiation field suggests that current boost doses are adequate for control. Patterns of failure indicate that NR or DM may occur without BR, which suggest imaging should be incorporated in addition to PSA in the follow-up of N1 patients.