Ablative Radiation Therapy to Restrain Everything Safely Treatable (ARREST): A Phase 1 Study of Stereotactic Ablative Radiation Therapy for Polymetastatic Disease.

PURPOSE: This phase 1 study aimed to assess the safety and feasibility of SABR therapy delivery to all sites of polymetastatic disease (>10 metastases). METHODS AND MATERIALS: A 3 + 3 study design was used with 5 dose levels from 6 Gy (6 Gy × 1) to 30 Gy (6 Gy weekly × 5). Dose-limiting toxicity (DLT) was defined as any grade 4 or 5 toxicity or more than 3 grade 3 toxicities within 6 weeks of treatment. The primary endpoint was the maximal tolerated dose, defined as the dose level where ≥2/6 of patients experienced DLT. Secondary endpoints included quality of life (Functional Assessment of Cancer Therapy - General and European Quality of Life 5 Dimension 5 Level) at 6 weeks posttreatment, progression-free survival, and overall survival. RESULTS: Thirteen patients were accrued: 12 Gy (n = 3), 18 Gy (n = 3), 24 Gy (n = 4), and 30 Gy (n = 3), and 207 lesions were treated. Nine patients (69%) had acute toxicity: grade 1 (n = 6, 46%), grade 2 (n = 2, 15%; n = 1 pneumonitis and n = 1 fatigue), and grade 3 (n = 1, 7.7% neutropenia). There were no grade 4 or 5 toxicities. Mean ± SD quality of life (Functional Assessment of Cancer Therapy - General and European Quality of Life 5 Dimension 5 Level health state) was 80.4 ± 21.9 and 77.4 ± 20.9 at baseline versus 76.4 ± 21.8 and 68.0 ± 24.2 at 6-week follow-up, respectively (p = .009 and p = .055, respectively). With a median follow-up of 8.7 months posttreatment (IQR, 2.4-24 months), 8 of 13 patients had disease progression (62%). The median and 12-month progression-free survival were 3.6 months and 11.3%, respectively. The median and 12-month overall survival were 13.8 months and 62%, respectively. CONCLUSIONS: In this phase 1 trial, SABR therapy for polymetastatic disease was technically feasible with acceptable acute toxicity at dose levels up to 30 Gy (6 Gy weekly × 5). DLT was not observed.

Salvage prostate brachytherapy in radiorecurrent prostate cancer: An international Delphi consensus study.

BACKGROUND AND PURPOSE: Local recurrences after previous radiotherapy (RT) are increasingly being identified in biochemically recurrent prostate cancer. Salvage prostate brachytherapy (BT) is an effective and well tolerated treatment option. We sought to generate international consensus statements on the use and preferred technical considerations for salvage prostate BT. MATERIALS AND METHODS: International experts in salvage prostate BT were invited (n = 34) to participate. A three-round modified Delphi technique was utilized, with questions focused on patient- and cancer-specific criteria, type and technique of BT, and follow-up. An a priori threshold for consensus of ≥ 75% was set, with a majority opinion being ≥ 50%. RESULTS: Thirty international experts agreed to participate. Consensus was achieved for 56% (18/32) of statements. Consensus was achieved in several areas of patient selection: 1) A minimum of 2-3 years from initial RT to salvage BT; 2) MRI and PSMA PET should be obtained; and 3) Both targeted and systematic biopsies should be performed. Several areas did not reach consensus: 1) Maximum T stage/PSA at time of salvage; 2) Utilization/duration of ADT; 3) Appropriateness of combining local salvage with SABR for oligometastatic disease and 4) Repeating a second course of salvage BT. A majority opinion preferred High Dose-Rate salvage BT, and indicated that both focal and whole gland techniques could be appropriate. There was no single preferred dose/fractionation. CONCLUSION: Areas of consensus within our Delphi study may serve as practical advice for salvage prostate BT. Future research in salvage BT should address areas of controversy identified in our study.

A Prospective Study of Magnetic Resonance Imaging-guided Focal Salvage High-dose-Rate Brachytherapy for Radiorecurrent Prostate Cancer: Updated Results of 30 Patients.

PURPOSE: Limited prospective data on focal salvage high-dose-rate (HDR) prostate brachytherapy is available. We sought to explore the toxicities, health-related quality of life (HRQoL), and efficacy of focal salvage HDR brachytherapy in a prospective clinical trial. This report presents the updated results of previously published data. METHODS AND MATERIALS: Patients with locally recurrent prostate cancer after previous external beam radiation therapy and/or brachytherapy were enrolled. Patients received magnetic resonance imaging (MRI)-guided, ultrasound-based focal HDR brachytherapy delivered over 2 fractions of 13.5 Gy delivered 1 to 2 weeks apart. Androgen deprivation therapy (ADT) was not used. RESULTS: Thirty patients were treated between 2012 and 2019. At a median follow-up time of 39 months, the 3-year biochemical failure-free rate was 61.8% (95% confidence interval, 44.0%-86.6%), and the 3-year ADT/salvage therapy-free rate was 86.0% (95% confidence interval, 74.1%-99.8%). Seventeen patients experienced subsequent biochemical failure, 9 received ADT and/or further local salvage, and no patients died of prostate cancer. Of the 28 patients who had posttreatment MRI, 26 had a local treatment response. No acute grade ≥3 genitourinary/gastrointestinal toxicity was observed. One temporary late grade 3 genitourinary toxicity event occurred, but no late grade ≥3 gastrointestinal toxicity was seen. No significant decline in urinary or bowel HRQoL was observed. CONCLUSIONS: Focal salvage HDR brachytherapy has a favorable side effect profile, no significant decline in HRQoL, and the 3-year biochemical control rates are in line with those of other salvage options. Early MRI response at the treated site is common, but does not preclude subsequent biochemical failure.

Radiation Oncologist Consultations Prior to Radical Prostatectomy: Disparities and Opportunities.

PURPOSE: In 2015, men undergoing radical prostatectomy in Ontario, Canada were recommended to undergo multidisciplinary care by seeing a radiation oncologist or discussion at multidisciplinary rounds before surgery. The a priori target rate was ≥76%. We used population-based data to explore factors associated with not receiving multidisciplinary care prior to radical prostatectomy. MATERIALS AND METHODS: Men who underwent radical prostatectomy for localized prostate cancer in Ontario between 2007 and 2017 were identified using administrative data. Physician billings identified patients who received multidisciplinary care. Multivariable logistic regression was used to predict receipt of multidisciplinary care. RESULTS: A total of 31,485 men underwent radical prostatectomy between 2007 and 2017. Of these patients 28.7% saw a radiation oncologist, 1.2% underwent multidisciplinary discussion and 1.9% had both before surgery. Multidisciplinary care receipt increased from 17.8% in 2007 to 47.8% in 2017 (p <0.001). The odds ratio between the highest and lowest geographic regions was 7.93 (95% CI 6.17-10.18, p <0.001). Lower odds of multidisciplinary care receipt were observed for men further from the nearest cancer center (OR 0.74 per 50 km, 95% CI 0.71-0.78, p <0.001) and higher odds for the highest versus lowest income quintile (OR 1.41, 95% CI 1.29-1.54, p <0.001). Of 128 urologists who performed ≥10 radical prostatectomies between 2016 and 2017, 29 (22.7%) met the target of having ≥76% of men seen for multidisciplinary care prior to surgery. CONCLUSIONS: Despite increasing utilization, many men do not receive multidisciplinary care prior to radical prostatectomy. While geography and the urologist appear to be the greatest factors predicting multidisciplinary care receipt, these factors are closely intertwined.

Can Polymetastatic Disease Be ARRESTed Using SABR? A Dosimetric Feasibility Study to Inform Development of a Phase 1 Trial.

PURPOSE: Phase 2 randomized trials suggest that stereotactic ablative radiation therapy improves progression-free and overall survival in patients with oligometastatic cancer, with phase 3 trials currently testing stereotactic ablative radiation therapy in up to 10 metastases. Whether stereotactic radiation therapy could provide similar benefits in polymetastatic disease (>10 metastases) is unknown. We sought to evaluate the dosimetric feasibility of using stereotactic radiation therapy in polymetastatic disease in preparation for a phase 1 trial. METHODS AND MATERIALS: Five craniospinal computed tomography simulations were used to simulate 24 metastatic targets (n = 2 patients), 30 targets (n = 2 patients), and 50 targets (n = 1 patient) that were not present on the initial scan. Creation of radiation therapy plans was attempted for doses up to 30 Gy in 5 fractions, with de-escalation to 24 Gy/4, 18 Gy/3, 12 Gy/2, or 6 Gy/1 if not feasible based on standardized dose constraints. Plans were created using Raystation for delivery on linear accelerators using volumetric modulated arc therapy and validated using Mobius 3D. RESULTS: A stereotactic radiation therapy treatment plan was generated for each simulated patient. Dose constraints were met to a dose of 30 Gy in 5 fractions for the patients with 24 and 30 lesions. For the patient with 50 targets, dose de-escalation to 12 Gy in 2 fractions was required to meet lung constraints. Estimated beam-on time varied between 18 and 29 minutes per fraction of 6 Gy. Median D95 planning target volume dosimetry ranged from 96.6% to 97.7% of the prescription dose. The conformity index (R100) range was 0.89 to 0.95, and R50 range was 6.84 to 8.72. CONCLUSIONS: Stereotactic radiation therapy treatment plans meeting standardized dose constraints could be created in the setting of 24 to 50 metastatic lesions using volumetric modulated arc therapy. This safety of this approach is being evaluated in a phase 1 trial (NCT04530513).

Organ at Risk Dose Constraints in SABR: A Systematic Review of Active Clinical Trials.

PURPOSE: Organ at risk (OAR) dose constraints are a critical aspect of SABR treatment planning. There is limited evidence supporting preferred dose constraints for many OARs. We sought to evaluate OAR dose constraints used in ongoing clinical trials of SABR for oligometastatic disease. METHODS AND MATERIALS: Clinicaltrials.gov was searched from inception to February 2020 to capture actively accruing clinical trials using SABR in oligometastatic disease. Dose constraints were obtained by contacting principal investigators and abstracted by 2 authors. Variability of constraints was assessed by comparing the width of the interquartile range and difference between the maximum and minimum dose to a volume. RESULTS: Fifty-three of 85 eligible clinical trials contributed OAR constraints used in analysis. Dose constraints for 1 to 8 fractions of SABR were collected for 33 OARs. Variability was found in the absolute allowable OAR doses, use of planning OAR volumes, and whether constraints were optional versus mandatory. For many OARs, modal dose constraints often matched a pre-existing publication, but no single pre-existing publication matched the modes of all OAR dose constraints. Organs displaying the most variability were the rectum, penile bulb, and chest wall and ribs. The esophagus, stomach, duodenum, and small bowel also indicated high variability for at least 1 constraint. OARs previously evaluated by HyTEC appeared to have less variability among study protocols. CONCLUSIONS: We found substantial variability in OAR dose constraints used in current clinical trials evaluating SABR in oligometastatic disease. We are unable to comment on toxicity rates or acceptability of dose constraints used. Future research and recommendations for standardized OAR dose constraints, as well as consistency in implementing planning OAR volume margins, should be priorities for the field of radiation oncology.

Ablative radiation therapy to restrain everything safely treatable (ARREST): study protocol for a phase I trial treating polymetastatic cancer with stereotactic radiotherapy.

BACKGROUND: Patients with polymetastatic cancer are most often treated with systemic therapy to improve overall survival and/or delay progression, with palliative radiotherapy reserved for sites of symptomatic disease. Stereotactic ablative radiotherapy (SABR) has shown promise in the treatment of oligometastatic disease, but the utility of SABR in treating all sites of polymetastatic disease has yet to be evaluated. This study aims to evaluate the maximally tolerated dose (MTD) of SABR in patients with polymetastatic disease. METHODS: Up to 48 patients with polymetastatic cancer (> 10 sites) will be enrolled on this phase I, modified 3 + 3 design trial. Eligible patients will have exhausted (or refused) standard systemic therapy options. SABR will be delivered as an escalating number of weekly fractions of 6 Gy, starting at 6 Gy × 2 weekly fractions (dose level 1). The highest dose level (dose level 4) will be 6 Gy × 5 weekly fractions. Feasibility and safety of SABR will be evaluated 6 weeks following treatment using a composite endpoint of successfully completing treatment as well as toxicity outcomes. DISCUSSION: This study will be the first to explore delivering SABR in patients with polymetastatic disease. SABR will be planned using the guiding principles of: strict adherence to dose constraints, minimization of treatment burden, and minimization of toxicity. As this represents a novel use of radiotherapy, our phase I study will allow for careful selection of the MTD for exploration in future studies. TRIAL REGISTRATION: This trial was prospectively registered in ClinicalTrials.gov as NCT04530513 on August 28, 2020.

A Novel Salvage Option for Local Failure in Prostate Cancer, Reirradiation Using External Beam or Stereotactic Radiation Therapy: Systematic Review and Meta-Analysis.

PURPOSE: Reirradiation (re-RT) using external beam radiation therapy (EBRT) is a novel salvage strategy for local failure in prostate cancer. We performed a systematic review describing oncologic and toxicity outcomes for salvage EBRT/stereotactic radiation therapy (SBRT) re-RT. METHODS AND MATERIALS: A International Prospective Register of Systematic Reviews registered (#141466) systematic review, meta-analysis, and meta-regression was conducted using preferred reporting items for systematic reviews and meta-analyses guidelines. PubMed and EMBASE were searched from inception through September 2019. Outcome measures included local control (LC), biochemical relapse free survival (BRFS), and ≥grade 3 genitourinary (GU)/gastrointestinal (GI) toxicity. EBRT and SBRT data were collected separately. Meta-regression explored disease and toxicity outcomes as a function of equivalent dose in 2 Gy fractions (EQD2), length of follow-up, and partial versus whole prostate reirradiation. RESULTS: Nineteen studies representing 13 cohorts were included (428 patients). Weighted mean follow-up was 26.1 months. Median re-RT EQD2 was 77.1 Gy (α/ß = 1.5), with 92% of patients receiving SBRT, 52.1% of patients receiving partial prostate re-RT, and 30.1% of patients receiving androgen deprivation therapy with re-RT. LC was 83.2% (95% confidence interval [CI], 75.5%-90.9%) and BRFS was 59.3% (47.9%-70.7%). Reported late toxicity ≥grade 3 was 3.4% (95% CI, 1.0%-5.8%) for GU and 2.0% (95% CI, 0.1%-4.0%) for GI. Meta-regression found higher LC, BRFS, and reported GU/GI toxicity with increasing EQD2, with partial prostate re-RT associated with less reported GU/GI toxicity and no detriment to LC and BRFS. CONCLUSIONS: Salvage re-RT using EBRT, particularly with SBRT, is an emerging technique to treat isolated local failure of prostate cancer. With short-term follow-up, LC, BRFS, and reported toxicities appear reasonable, although further follow-up is required before definitive statements on late toxicities can be made. Our review is limited by incomplete reporting of androgen deprivation therapy use in the primary literature. Further prospective studies and longer follow-up are needed before considering re-RT as standard practice.