Multiparametric MRI Results After Dose Escalated Radiotherapy Of Localized Prostate Cancer: 2 Year Follow-Up Of A Prospective Phase II Trial

Abstract

Dose escalation has been known to improve biochemical recurrence-free survival in patients with localized prostate cancer with intermediate-to-high risk features. Recently, the use of Prostate Imaging-Reporting and Data System (PI-RADS) with multiparametric MRI (mpMRI) has become an advanced tool in the detection of high-grade bulky prostate cancer (PCa), providing a reporting schema to classify each lesion based on the likelihood of clinically significant cancer. A phase II trial involving dose escalation to intra-prostatic PI-RADS III-V lesions via image-guided radiotherapy (IGRT) and SBRT/SIB boost was conducted. The aim of this study is to examine the PI-RADS lesions two years after completing protocol treatment. It is hypothesized that dose escalation would eliminate these intra-prostatic lesions to improve tumor control. Patients with localized prostate cancer and mpMRI PIRADS III-V lesions were recruited to receive a course of IGRT to the prostate and seminal vesicle +/- pelvic lymph nodes (PLN) to a dose of 45 Gy in 25 fractions followed by SBRT boost, 18 Gy in 3 fraction to the prostate with a simultaneous integrated boost 21 Gy in 3 fractions (EQD2 = 85.2 Gy using a/b 3 or 93.4 Gy using a/b 1.5) to the PI-RADS lesions. PI-RADS assessment using PI-RADS system 2.0 was evaluated by genitourinary radiologists. Patients were assessed every 3 months for the first 2 years and then every 6 months thereafter. Of a total of 50 patients recruited in the protocol, 14 patients repeated mpMRI approximately 2 years after initial pre-treatment mpMRI, which was subject for this analysis. Median age was 70 years (range: 59-83). All patients had PI-RADS lesions grade 3-5; 7 (50.0%), 6 (42.9%), and 1 (7.1%) patients having 1-3 lesions respectively. 4 (28.6%) patients, 8 (57.1%) patients, and 2 (14.3%) of patients had PI-RADS grade 3, 4, and 5 lesions respectively. Three (21.4%) patients had Gleason Score (GS) 8-10 and 11 (78.6%) had GS 7 disease. Median PSA was 6.06 ng/mL (range: 0.05-19.13). 10 (71.4%), 3 (21.4%), and 1 (7.1%) patients had stage T1, T2, and T3 tumor, respectively. 5 patients received treatment to the PLN and 9 received androgen deprivation therapy. Median follow up time was 28 months (range: 19-33). 14 (100%) patients had complete resolution of their PI-RADS lesions after dose escalated treatment. Two-year results of this prospective phase II trial suggested that high-dose radiotherapy (EQD2 = 85.2 Gy using a/b 3 or 93.4 Gy using a/b 1.5) via IGRT with SBRT boost might be sufficient to eliminate high grade intra-prostatic lesions. A large long-term study is needed to correlate the resolution of the high-grade PI-RADS lesions with clinical outcomes and to determine if follow-up mpMRI 2 years after radiation is a surrogate for radiotherapy outcomes.