Main Session
Sep 29
PQA 06 - Genitourinary Cancer, Gynecological Cancer, and Health Care Access and Engagement

3301 - A Phase II Trial of MRI-Mapped Dose-Escalated Salvage Radiotherapy Post-Prostatectomy: The Miami MAPS Trial

02:15pm - 03:30pm ET
Poster Hall - Exhibit Hall A
Screen: 12
POSTER

Presenter(s)

David Lee, MD - Sylvester Comprehensive Cancer Center, University of Miami, Miami, FL

D. J. Lee1, S. Han2, R. Stoyanova3, N. Dogan4, S. Punnen5, B. Spieler4, L. M. Freedman6, B. A. Mahal7, A. Dal Pra4, A. Pollack4, and M. C. Abramowitz4; 1Department of Radiation Oncology, University of Miami Sylvester Comprehensive Cancer Center, Miami, FL, 2Biostatistics and Bioinformatics Shared Resources, Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL, 3Department of Radiation Oncology, Sylvester Comprehensive Cancer Center, Miller School of Medicine, University of Miami, Miami, FL, 4Department of Radiation Oncology, University of Miami/Sylvester Comprehensive Cancer Center, Miami, FL, 5Department of Urology, University of Miami/Sylvester Comprehensive Cancer Center, Miami, FL, 6Department of Radiation Oncology, Sylvester Comprehensive Cancer Center, University of Miami Leonard M. Miller School of Medicine, Miami, FL, 7Dana-Farber Cancer Institute and Brigham and Women’s Hospital, Department of Radiation Oncology, Boston, MA

Purpose/Objective(s):

Biochemical failure occurs in up to 1/3 of patients within 5 years of salvage radiotherapy (SRT). We hypothesized that suspicious lesions on dynamic contrast–enhanced MRI (DCE–MRI) predispose to early failures and that lesion targeted dose SRT would significantly reduce such failures. The MAPS phase II trial evaluated whether MRI-mapped dose-escalated post-prostatectomy SRT (MTSRT) improves early complete biochemical response (CBR) without increasing toxicity.

Materials/Methods:

Patients with post-prostatectomy PSA =0.1 ng/mL, no distant metastases, no ADT within 6 months, and a 0.4–6 cc DCE–MRI-detected lesion in the PB or regional lymph nodes were eligible. Patients were initially randomized to MTSRT or standard-dose SRT (SSRT) without a boost. This trial was designed prior to widespread PSMA-PET adoption; evolving imaging standards raised concerns regarding potential undertreatment in the SSRT arm. Along with slow accrual, this prompted conversion to a single-arm design after 15 SSRT randomizations. The original planned sample size was 80 patients.

All patients received PB SRT to 68 Gy in 2-Gy fractions using IMRT/IGRT. The MTSRT arm received a simultaneous integrated boost to 76.5 Gy (EQD2=80 Gy, a/ß=3). CBR was defined as a PSA <0.1 ng/mL at 21 months post-RT. Genitourinary (GU) and gastrointestinal (GI) toxicities were graded per CTCAE v4.0. Between-arm comparisons were made using Fisher’s exact test.

Results:

37 participants (n=22 MTSRT, n=15 SSRT) completed RT per protocol. Median follow-up was 64.5 months (IQR 64.1–66). Accrual spanned 9.5 years and ended early due to slow enrollment. Median PSA was 4.8 ng/mL (IQR 0.5–8.7). The CBR rate was 35.1% and numerically higher with MTSRT (45.5%) than SSRT (20.0%) (p=0.087). Post-RT attrition occurred in 13.6% (MTSRT) and 6.7% (SSRT). Overall grade =2 GU and GI toxicity rates were similar between arms (GU: 50.0% MTSRT vs. 46.7% SSRT, p=1.000; GI: 20.0% vs. 18.2%, p=1.000). No grade 3 GI toxicities were observed in either arm. Grade 3 GU events occurred in 14 MTSRT and 7 SSRT patients, with most being urinary urgency, frequency, and incontinence.

Conclusion:

MTSRT demonstrated numerically higher early CBR rates than SSRT, although this difference was not statistically significant, likely related to limited power. Grade =2 GU and GI toxicity rates were similar between arms. Grade 3 GU toxicity events were numerically higher in the MTSRT cohort and occurred in both arms. These findings are directionally consistent with imaging-guided dose-escalation data from EMPIRE-2. A multi-institutional phase III trial incorporating PSMA-PET is warranted to better define efficacy and safety.

CBR

 Total (N=37)

 SSRT (N=15)

 MTSRT (N=22)

 P
No

 20 (54.1%)

 11 (73.3%)

 9 (40.9%)

 0.087
Yes

 13 (35.1%)

 3 (20.0%)

 10 (45.5%)
Data Missing

 4 (10.8%)

 1 (6.7%)

 3 (13.6%)
Table 1. Achievement of CBR, by arm.
Toxicity

 Total

 SSRT

 MTSRT

 P
GU

 18 (48.6%)

 7 (46.7%)

 11 (50.0%)

 1.000
GI

 7 (18.9%)

 3 (20.0%)

 4 (18.2%)

 1.000
Table 2. Overall CTCAE grade =2 GU and GI toxicity rates, by arm.