medwireNews: One ultra-high dose of radiation may offer similar benefits and risks to those of an extreme hypofractionated stereotactic body radiotherapy (SBRT) regimen for men with organ-confined prostate cancer, indicate the results of a phase 2 proof-of-concept trial.
“The safety of 24 Gy SDRT [single-dose radiotherapy] encourages further studies to establish SDRT as a cost-effective and patient-friendly treatment in prostate cancer”, write Carlo Greco (Champalimaud Centre for the Unknown, Lisbon, Portugal) and co-workers in JAMA Oncology.
The PROSINT investigators randomly assigned 30 men to receive a single 24 Gy dose of radiation or five fractions of 9 Gy given over 5 consecutive days, a regimen that they say has “previously proven feasible and safe.”
All the patients had biopsy-confirmed prostate adenocarcinoma at stage T2a–T2C on magnetic resonance imaging and a prostate-specific antigen (PSA) level below 20 ng/mL and no nodal involvement. None of the men had been given androgen deprivation therapy.
“The present study shows that 24 Gy SDRT and 5 × 9 Gy SBRT match in each and every tumor toxic effect and PSA end [point],” Greco et al report.
Patients in both the SDRT and SBRT arms experienced peak acute grade 1 genitourinary symptoms 1 week after treatment, most commonly urinary frequency and dysuria, affecting 40% and 27% of the groups, respectively, with resolution occurring within 4 weeks.
There was no significant difference in cumulative late actuarial urinary toxicity of grade 1 or grade 2 and above between the groups, and there was “minimal” gastrointestinal toxicity of grade 1 and no events of grade 2 or more severe.
After 3 years, the median PSA was 0.40 ng/mL in the SDRT arm and 0.30 ng/mL in the SBRT arm, with 2-year actuarial biochemical recurrence-free survival (RFS) rates of 77.1% and 85.7%, respectively.
However, there were no PSA recurrences in the patients with favorable intermediate-risk prostate cancer in either group; the actuarial rates of biochemical RFS in the unfavorable intermediate-risk patients were a comparable 64% and 75% for the SDRT and SBRT arms, respectively.
Magnetic resonance imaging showed that 53% of SDRT and 71% of SBRT patients had a complete response at 12 months, rising to a corresponding 62% and 85% at 24 months. This was accompanied by “progressive glandular atrophy” resulting in 34% and 26% reductions in average prostate volume after 24 months, respectively.
“The glandular ablative effect defines SDRT akin to a virtual prostatectomy, with the entire therapeutic dose delivered in a single, short, noninvasive procedure,” the researchers remark.
Patient-reported quality of life was also comparable in the two groups according to Expanded Prostate Cancer Index Composite-26 score assessments, with a transient decrease in genitourinary and gastrointestinal scores at 1 month, followed by a return to baseline levels at 3 months.
None of the patients described experiencing “major [genitourinary] bother” at any point in the study, the PROSINT researchers say.
However, they note that the International Prostate Symptom Score measure revealed a transient flare of late urinary symptoms at 9–18 months in 20% of patients who received SDRT, whereas no such flare was identified in the SBRT patients.
“This study offers encouraging perspectives on the feasibility and safety of 24 Gy SDRT in organ-confined prostate cancer,” Greco et al conclude.
They add: “A phase 2 single-arm study designed to accrue 200 patients is currently underway (ClinicalTrials.gov identifier: NCT04035642) to further establish the efficacy, safety, and indications for SDRT for treatment of organ-confined primary prostate cancer.”
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JAMA Oncol 2021; doi:10.1001/jamaoncol.2021.0039