Multiparametric Magnetic Resonance Imaging- Guided Dose-Escalated Radiation Therapy for Localized Prostate Cancer: A Prospective Phase 2 Trial

PURPOSE

This trial's purpose was to determine the late toxicity associated with dose escalation to Prostate Imaging Reporting and Data System (PI-RADS) III-V lesions on multiparametric magnetic resonance imaging (MRI) with an image guided combined IMRT-stereotactic body radiation therapy (SBRT) approach in men with localized prostate cancer.

METHODS AND MATERIALS

In this phase 2 trial patients with localized prostate cancer with clinical tumor stage T1-T3bN0 and at least one PIRADS III-V lesion were recruited to receive 45 Gy in 25 fractions to the prostate and seminal vesicles followed by a boost of 18 Gy in 3 fractions to the prostate with a simultaneous integrated boost 21 Gy in 3 fractions to the PI-RADS lesion(s). The primary endpoint was the cumulative incidence of late grade ≥3 genitourinary and gastrointestinal toxicity by 18 months (National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.0).

RESULTS

Overall, 50 patients were enrolled in this study, and 43 patients completed at least 18 months of follow-up. The cumulative incidence of grade 1, 2, and 3 late genitourinary toxicity at 18 months was 18%, 53%, and 2%. One patient was noted to have grade 3 hematuria and needed cystoscopy-guided cauterization. No acute grade 3 gastrointestinal or genitourinary toxicities were observed. The cumulative incidence of grade 1, 2, and 3 late gastrointestinal toxicity at 18 months was 31%, 4%, and 0%, respectively. At a median follow-up of 43.5 months, 3 patients developed biochemical recurrence, each with distant bone metastases without local or nodal recurrence. At 3 years, freedom from biochemical failure rate was 95.3% (95% CI, 89.2%-100%).

CONCLUSIONS

Multiparametric MRI-guided dose escalation to PI-RADS III-V lesions using a combined image guided IMRT-SBRT approach is associated with an acceptable risk of late gastrointestinal and genitourinary toxicity. The results should be interpreted with caution considering their single institutional nature, small sample size, and short follow-up and should be validated in a larger study.

Multi-parametric MRI guided dose escalated radiotherapy for treatment of localized prostate cancer (PCa): Initial toxicity results of a prospective phase II trial

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Background: Multi-parametric MRI (mpMRI) of PCa uses advanced sequences to detect aggressive, high grade and bulky lesions. Given known advantages of hypofractionated radiotherapy (RT) to treat PCa (low a/b ratio), we conducted a phase II trial to escalate a high dose to mpMRI lesion(s) via Image-Guided (IG)-RT/Volumetric Arc Therapy (VMAT)/Stereotactic Body Radiotherapy (SBRT) technology. We present the acute toxicity results of this novel approach. Methods: 22 pts with mpMRI lesion(s) were prospectively treated to a course of IGRT/VMAT to the prostate & 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 mpMRI prostatic lesion(s). Placement of 3 polymer based fiducial markers visible in both CT and MRI for image co-registration and treatment guidance was performed. Genitourinary (GU) and gastrointestinal (GI) adverse events (AE) were scored using CTCAE v4. DSMC approved reporting of acute AE results prior to completion of trial accrual as an interim safety assessment prior to final trial accrual. Results: Median age was 66.5 years (range: 57-80). All patients had PI-RADS grade 3-5 mpMRI lesion(s); 41.0%, 45.4% and 13.6% having 1, 2 and 3 lesions respectively. Ten (45%) pts had Gleason Score (GS) 8-10 and 12 had GS 7 disease. Median PSA was 8.97 (range: 4.0-77.9). Eleven (50%), 10 (46%), and 1 (5%) pts had stage T1, T2, and T3 tumor, respectively. Nine pts received treatment to the PLN and 15 received androgen deprivation therapy. All patients completed the protocol treatment without reporting acute GI or GU AEs grade ≥3 during treatment or at follow up. Grade 2 GI (diarrhea) and GU toxicity (frequency) was seen in 2 (9%) and 9 (41%) pts, respectively, during treatment. Of the 16 pts (71%) with least 3 months follow-up all grade 2 GI and 55.5% GU toxicities had resolved. Conclusions: Early results of this prospective Phase II study suggest that high-dose RT for localized PCa via mpMRI-guided RT/VMAT and SBRT boost is tolerable with a favorable acute toxicity profile.

Central zone lesions on magnetic resonance imaging: Should we be concerned?

INTRODUCTION AND OBJECTIVE

The Prostate Imaging Reporting and Data System (PI-RADS) score was developed to evaluate lesions in the peripheral and transition zone on multiparametric magnetic resonance imaging (mpMRI) of the prostate. We aim to determine if the PI-RADS scoring system can be used to evaluate central zone lesions on mpMRI.

MATERIALS AND METHODS

A retrospective review of 73 patients who underwent mpMRI/ultrasound (US) fusion-guided biopsy of 143 suspicious lesions between February 2014 and October 2015 was performed. All patients underwent a 3T mpMRI. Indications for mpMRI included an abnormal digital rectal examination, PSA velocity >0.75ng/dl/y, and patients on active surveillance. The mpMRI sequence involved T2-weighted imaging, diffusion-weighted imaging, and dynamic contrast enhancement. Using 3-dimensional model software (Invivo Corporation, Gainesville, FL, USA), a minimum of 3 magnetic resonance imaging (MRI)/US fusion-guided biopsy samples were taken from each prostate lesion seen on mpMRI irrespective of PI-RADS score, using local anesthesia in an outpatient clinic setting.

RESULTS

A total of 73 patients underwent MRI/US fusion-guided biopsy of 85 peripheral zone lesions, 31 transitional zone lesions, and 27 central zone lesions. Only 2 (7%) of central zone lesions were positive for prostate cancer. Both patients had lesions which were graded as PI-RADS 3. Both the patients had multifocal lesions that encompassed≥50% of the central and transition zones on the sagittal view MRI images. Both patients previously had transrectal US-guided biopsy of the prostate which was negative for cancer. Both patients underwent a robotic-assisted laparoscopic prostatectomy, each revealing high-grade cancer.

CONCLUSIONS

Lesions involving only the central gland/zone seen on MRI are less concerning for malignancy and should not be given equal weight as peripheral zone lesions. In this series, no lesions involving solely the central gland/zone, regardless of PI-RADS score, was positive for malignancy on MRI/US fusion-guided biopsy. Consideration of a modified PI-RADS scoring system should be given to help identify central zone lesions with malignant potential.