3216 - Safety and Early Outcomes of External Beam Radiation Therapy with Low Dose Brachytherapy Boost in Patients with Prostate Cancer

12:45pm - 02:00pm PT

Hall F

Screen: 10

POSTER

Presenter(s)

Zakaria El Kouzi, MD - MD Anderson Cancer Center, Houston, TX

Z. El Kouzi¹, R. Kouzy², S. Choi³, H. Mok³, K. E. Hoffman¹, Q. N. Nguyen⁴, C. J. Hassanzadeh³, C. Tang³, S. J. Shah⁵, S. E. McGuire³, L. L. Mayo¹, Y. Kim⁶, S. Prajapati⁶, S. Vijayan², R. Kudchadker⁵, T. Bruno⁵, S. J. Frank³, and O. Mohamad³; ¹Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ²MD Anderson Cancer Center, Houston, TX, ³Department of Genitourinary Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁴The University of Texas MD Anderson Cancer Center, Houston, TX, ⁵Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁶Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s): Randomized trials showed that brachytherapy boost improves biochemical control when combined with external beam radiation therapy (EBRT) in patients with unfavorable intermediate- and high-risk prostate cancer. Here, we retrospectively report the safety and early efficacy of using EBRT and low-dose-rate (LDR) brachytherapy boost with or without androgen deprivation therapy (ADT) at the University of Texas MD Anderson Cancer Center.

Materials/Methods: Patient demographics, initial disease characteristics, treatment details, gastrointestinal (GI) or genitourinary (GU) toxicity, and oncologic outcomes were documented. Risk stratification was done as per the National Comprehensive Cancer Network (NCCN) guidelines. Biochemical failure was defined according to the Phoenix criteria as PSA nadir + 2 ng/mL or starting treatment with a rising PSA. Late GI and GU toxicities were defined as any toxicities occurring >90 days from the radiation start date and were assessed according to the Common Terminology Criteria for Adverse Events (CTCAE), version 5.

Results:

Between 1999 and 2024, 307 patients received EBRT and LDR. Of the 307 patients, 117 patients (38%) had NCCN intermediate-risk prostate cancer with 88 (28.7%) having unfavorable intermediate risk, 137 patients (45%) had high-risk, and 53 patients (17%) had very high-risk disease. The median age at diagnosis was 66 (IQR 61-72). 279 (91%) patients received ADT, with a median of 11 (IQR 6-12) months. 208 (68%) patients received photon EBRT while 99 (32%) received proton therapy. Lymph node irradiation was prescribed in 108 (35%) patients. Median EBRT dose was 44 Gy/CGE and median

brachytherapy dose was 90 Gy. Pd-103 was used in 249 (81%) patients, I-125 in 58 (19%) patients, and 233 (76%) patients had MRI-guided brachytherapy. Rectal spacer was used in 47 (15%) patients.

With a median follow up of 4 years, 23 patients developed biochemical recurrence for a 5-year biochemical recurrence-free survival of 98% in intermediate-risk patients and 90% in high- or very high-risk patients. Five patients had acute urinary retention. Late grade =2 GU or GI toxicity was found in 30 patients and 12 patients, respectively. Seven patients had grade 3 or higher adverse events.

Conclusion: Acknowledging the intermediate follow-up duration, EBRT and LDR boost with and without ADT can achieve high control rates and acceptable toxicity for prostate cancer patients with intermediate and high-risk prostate cancer.