Stereotactic body radiation therapy with simultaneous integrated boost for prostate cancer: does MRI-targeted biopsy alter the boost field?

INTRODUCTION

We aim to investigate if the addition of MRI-US fusion biopsy (FB) can aid in radiation planning and alter the boost field in cases of stereotactic body radiation therapy (SBRT) for prostate cancer with a simultaneous integrated boost (SIB) to a magnetic resonance imaging (MRI)-defined intraprostatic lesion.

MATERIALS AND METHODS

Patients undergoing SBRT with SIB for biopsy-proven prostatic adenocarcinoma and a pre-radiation MRI were retrospectively reviewed. 36.25 Gy in 5 fractions was delivered to entire prostate along with SIB of 40 Gy to an MRI-defined intraprostatic lesion. Demographic, radiation planning details, and post-procedural outcomes were compared between patients undergoing systematic transrectal ultrasound (TRUS) biopsy followed by MRI to those undergoing an MRI followed by a FB prior to radiation planning.

RESULTS

Forty-three patients underwent systematic TRUS biopsy followed by MRI and 46 patients underwent FB prior to radiation planning. Patients undergoing systematic TRUS biopsy had a smaller prostate volume when compared to the FB cohort (37.58 ± 13.78 versus 50.28 ± 26.76 cc, p = 0.007). No differences in prostate planning target volume (PTVprostate) and boost volume (PTVboost) were noted, but those undergoing TRUS biopsy prior to MRI had a higher integrated boost volume density (IBVD = PTVboost/total prostate volume) (0.16 ± 0.09 versus 0.13 ± 0.06, p = 0.045). No differences were observed in genitourinary or gastrointestinal toxicity rates.

CONCLUSIONS

Compared to systematic TRUS biopsy, implementation of prebiopsy prostate MRI and FB allows for safe and feasible SBRT in patients with significantly larger prostate volumes without increasing SIB cancer-directed treatment volumes, oncologic outcomes, quality of life measures, or treatment-related toxicities.