Main Session
Sep
29
PQA 06 - Genitourinary Cancer, Gynecological Cancer, and Health Care Access and Engagement
3398 - Prospective Phase 1 Clinical Trial of CBCT-Guided Adaptive SBRT to the Prostate and Pelvic Nodes with Simultaneous Integrated Boost to the MR-Detected Nodule for Patients with High-Risk and Unfavorable Intermediate-Risk Prostate Cancer
Presenter(s)
Vladislav Sviderskiy, MD, PhD - Washington University School of Medicine in St. Louis, St. Louis, MO
A. Willett1, W. Liu1, D. Hong1, V. Sviderskiy1, T. Zimmerman1, M. Mahmood1, M. R. Waters1, J. P. Schiff2, D. Sievert1, D. Caruthers1, L. E. Henke3, E. Laugeman1, R. Beckert1, J. W. Randall1, B. C. Baumann4, J. M. Michalski1, P. Samson1, C. G. Robinson1, H. A. Gay1, and A. K. Bhatt1; 1WashU Medicine, Department of Radiation Oncology, St. Louis, MO, 2Department of Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles, CA, 3Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH, 4Hopewell Oncology, St. Louis, MO
Purpose/Objective(s):
Online adaptation can improve the therapeutic ratio in stereotactic body radiotherapy (SBRT) with elective nodal irradiation for high-risk prostate cancer. This prospective study evaluated the safety and efficacy of cone beam CT (CBCT)-guided online adaptive SBRT with a simultaneous integrated boost (SIB).Materials/Methods:
A CBCT-guided online adaptive approach was used to treat patients with unfavorable intermediate-risk or high-risk prostate adenocarcinoma: 25Gy to the elective pelvic lymph nodes, 36.25Gy to the prostate and proximal seminal vesicles, 40Gy CTV to the prostate, and SIB 50Gy to an MR-detected lesions. Reasons for adaptation and comparisons of target coverage between the initial plan (PI) and adapted plan (PA) were recorded prospectively and compared with a paired t-test. Acute (within 90 days of SBRT) and late (90 days post SBRT) toxicities were assessed using CTCAE v5. Patient-reported quality of life (QoL) metrics were collected at baseline, end of treatment, and 3, 6, 9,12, 15, and 18 months post-treatment via the EPIC-26 and EQ-5D-5L.Results:
From 2/2023 to 5/2025, 25 patients with median age of 70 years (range, 56 –79) were enrolled. At median follow up of 11 months (range, 5 – 26), biochemical recurrence free survival, failure free survival, and metastasis free survival were 100%. Overall survival was 96%; one patient died from an unrelated event. 93% of fractions were adapted. Adaptation occurred to improve target coverage alone (19%), resolve organs at risk (OAR) dose constraint violation alone (5%), or both 73%. Violations to rectum (54%) and urethra (35%) constraints were most common followed by bladder, femur, and bowel. Adaptation improved planning target volume coverage to the V3625 cGy (7% improvement, p<0.01), V4000(8% improvement, p<0.01) and gross tumor coverage to V5000 (29% improvement , p<0.01). There were no acute Grade 3 or higher GU or GI toxicities. Two late Grade 3 GI toxicities occurred: one anal fissure and one anal fistula possibly related to treatment. Acute and chronic Grade 2 GU toxicities were 24% and 8%, respectively. There were 0 acute and 12% late Grade 2 GI toxicities. QoL EPIC26 urinary obstruction scores declined (worsening of symptoms) by 26 points from screening to end of treatment (p<0.01) then recovered by 31 points by 18 months (p<0.01). Urinary incontinence scores declined from screening to 15 months by 22 points (p=0.02).Conclusion:
Online adaptive SBRT with SIB resulted in no acute Grade 3 toxicities and a low incidence of late Grade 3 GI toxicity possibly related to treatment. Adaptation improved dosimetry, and short-term outcomes were excellent.