Focal Prostate Stereotactic Body Radiation Therapy With Correlative Pathological and Radiographic-Based Treatment Planning

Abstract

IntroductionAdvances in multiparametric MRI (mpMRI) combining anatomic and functional imaging can accurately identify foci of adenocarcinoma within the prostate, offering the possibility of partial gland therapy. We performed tandem prospective pilot trials to investigate the feasibility of focal prostate SBRT (f-SBRT) based on correlating diagnostic mpMRI and biopsies with confirmatory pathology in treatment planning.Materials and MethodsPatients with pathologic focal Gleason 6–7 disease and a corresponding PIRADS 4–5 lesion on mpMRI underwent targeted and comprehensive biopsies using MRI/ultrasound fusion under electromagnetic sensor navigation. After rigorous analysis for imaging biopsy concordance, five of 18 patients were eligible to proceed to f-SBRT. Chi-squared test was used for differences from expected outcomes, and concordance was estimated with binomial distribution theory and Wilson’s method.ResultsSix patients had Gleason 6 and 12 had Gleason 3 + 4 disease (mean PSA: 5.8 ng/ml, range: 2.2–8.4). Absolute concordance was 43.8% (95% CI: 0.20, 0.64). Patterns of discordance included additional sites of ipsilateral disease, bilateral disease, and negative target. Five were upstaged to a new NCCN risk category necessitating treatment escalation. The five patients with concordant pathology completed three-fraction f-SBRT with sparing of the surrounding normal structures (including contralateral neurovascular bundle), with no reported grade 2+ toxicities and favorable PSA responses (mean: 41% decrease).ConclusionsOn our pilot trials of f-SBRT planning using rigorous imaging and pathology concordance, image-guided confirmatory biopsies frequently revealed additional disease, suggesting the need for caution in partial-gland therapy. For truly focal disease, f-SBRT provided excellent dosimetry, minimal toxicity, and encouraging biochemical response. Clinical Trial Registration: www.clinicaltrials.gov, NCT02681614; NCT02163317.

Radiotherapy planning in a prostate cancer phantom model with intraprostatic dominant lesions using stereotactic body radiotherapy with volumetric modulated arcs and a simultaneous integrated boost

“…The precision of these advanced modalities allows for dose escalation as high as 75. 6 Gy in prostate cancer (PCa) (1). However, dose escalation is limited by the risk of toxicity to surrounding healthy tissues (2).…”

“…For ultrahypofractionated schemes, the recommended strategies are 35 Gy (five fractions of 7 Gy) or 36.25 Gy (5 fr x 7.25 Gy). Although higher doses (> 50 Gy in 5 fractions) to the entire prostate yield excellent 5-year biochemical control rates, there is an increased risk of high-grade toxicity (5,6).…”

“…Several different options are available to deliver the boost dose to the DIL. Some small studies have shown that the boost can be delivered using conventional fractionation or moderate hypofractionation to the whole prostate and the focal lesion (6,(12)(13)(14)(15)(16)(17)(18). An alternative approach is to deliver a simultaneous integrated boost (SIB) to the DIL using SBRT (SBRT-SIB).…”