Stereotactic body radiotherapy with a focal boost to the MRI-visible tumor as monotherapy for low- and intermediate-risk prostate cancer: early results

Abstract

BackgroundThere is growing evidence that prostate cancer (PC) cells are more sensitive to high fraction dose in hypofractionation schemes. High-dose-rate (HDR) brachytherapy as monotherapy is established to be a good treatment option for PC using extremely hypofractionated schemes. This hypofractionation can also be achieved with stereotactic body radiotherapy (SBRT). We report results on toxicity, PSA response, and quality of life (QOL) in patients treated with SBRT for favorable-risk PC.MethodsOver the last 4 years, 50 hormone-naïve patients with low- and intermediate-risk PC were treated with SBRT to a total dose of 38 Gy delivered in four daily fractions of 9.5 Gy. An integrated boost to 11 Gy per fraction was applied to the dominant lesion if visible on MRI. Toxicity and QoL was assessed prospectively using validated questionnaires.ResultsMedian follow-up was 23 months. The 2-year actuarial biochemical control rate was 100%. Median PSA nadir was 0.6 ng/ml. Median International Prostate Symptoms Score (IPSS) was 9/35 before treatment, with a median increase of 4 at 3 months and remaining stable at 13/35 thereafter. The EORTC/RTOG toxicity scales showed grade 2 and 3 gastrointestinal (GI) acute toxicity in 12% and 2%, respectively. The late grade 2 GI toxicity was 3% during 24 months FU. Genitourinary (GU) grade 2, 3 toxicity was seen in 15%, 8%, in the acute phase and 10%, 6% at 24 months, respectively. The urinary, bowel and sexual domains of the EORTC-PR25 scales recovered over time, showing no significant changes at 24 months post-treatment.ConclusionsSBRT to 38 Gy in 4 daily fractions for low- and intermediate-risk PC patients is feasible with low acute and late genitourinary and gastrointestinal toxicity. Longer follow-up preferably within randomized studies, is required to compare these results with standard fractionation schemes.

Continuous Monitoring and Intrafraction Target Position Correction During Treatment Improves Target Coverage for Patients Undergoing SBRT Prostate Therapy

“…To date, several centers have reported excellent clinical outcomes and tolerance profiles with ultrahypofractionated regiments, albeit without long-term follow-up (2)(3)(4)(5)(6)(7)(8). To establish the optimum dose for stereotactic body radiation therapy (SBRT), maximizing local control while minimizing normal tissue complications, our center conducted a phase 1 dose escalation study.…”

“…Additionally, bladder filling during the treatment could potentially push the trigone of the bladder into the high-dose region. In the studies referred to (2)(3)(4)(5)(6)(7), intrafractional monitoring of the target position, and intervention where necessary, was performed using either the Cyberknife robotic system (Accuray, Sunnyvale, CA), or the Calypso radiofrequency tracking system (Varian Medical Systems, Palo Alto, CA). Our clinic uses the Calypso system (Varian), which provides real-time locations of the centroids of 2 or 3 small transponders implanted transrectally into the patients' prostates.…”

Is robotic arm stereotactic body radiation therapy ‘virtual high-dose rate brachytherapy’ effective for prostate cancer? An analysis of comparative effectiveness using published data

“…MRI-transrectal ultrasound image fusion has been shown to guide prostate biopsies and identify the location and primary Gleason pattern of lesions in >90% of patients [46]. Currently, image-guided focal RT boost is still in preliminary stages using either SBRT [47,48] or HDR-BT [49,50]. If robotic arm SBRT is proven to be similar to HDR-BT in the coming years, then it too may be used as a boost, akin to how HDR-BT boost has been used to treat certain intermediateand high-risk tumors since 1980s [51].…”

Hypofractionated radiotherapy for organ-confined prostate cancer: is less more?

“…No definitive conclusions regarding the clinical benefits of extreme hypofractionation can be drawn yet, but evidence is accumulating that the results of these trials show excellent early biochemical outcomes and acceptably low toxicity rates [35][36][37][38][39][40][41][42][43][44][45] . Many of these trials employed fraction sizes of 6.7-10 Gy and were carried out with the aim of proving the feasibil ity of shortened schedules, predominantly in patients with lowrisk or intermediaterisk prostate cancer.…”

“…Using this technique, these functionally important anatomical structures can be selectively spared from highdose radiation with the intention to minimize genitourinary toxicity and, potentially, reduce the incidence of radiationinduced erectile dysfunction 59 . Furthermore, the integration of advanced molecularimaging techniques in the treat ment planning process enables enhancing the potential benefits of dosepainting, such as the ability to boost the dominant intraprostatic lesions 37,60 . This approach might result in improved clinical outcomes, as local recurrences occur predominantly at the primary lesion site 61,62 , even following doseescalated external beam radiotherapy.…”