Stereotactic body radiation therapy (SBRT) in previously irradiated patients “appears clinically feasible”, and provides good disease control out to five years for men with locally recurrent prostate cancer. This is the conclusion of a recent prospective study from Donald Fuller (Genesis Health Care Partners, San Diego, USA), published in the International Journal of Radiation Oncology Biology Physics.
The investigators set out to evaluate the use of SBRT retreatment for biopsy-proven local persistence in prostate postradiation therapy, evaluating efficacy and toxicity. For this patient cohort, the authors explain how a number of local salvage methods have been described, but say that none have been widely used, “primarily owing to elevated toxicity concerns”.
Analysing outcomes in the 50 patients enrolled in the study from February 2009 to March 2018 from two community-based radiation oncology centres, Fuller et al assessed toxicities before and after SBRT salvage using CTCAE v.3 criteria and International Prostate Symptom Score (I-IPSS). SBRT was performed with the CyberKnife system from Accuray.
The authors report that 69% of the patients required no androgen deprivation therapy (ADT) treatment within the first five years following CyberKnife prostate SBRT. There were also low overall rates of toxicity among the patients, all of whom had undergone radiation therapy treatment prior to SBRT.
“Most men, if treated, receive only ADT, which has the potential for long-lasting whole-body side effects while rarely eradicating the tumour completely,” Fuller comments. “Without effective local retreatment, it is likely that most, if not all of them [the patients treated in this study], would have needed ADT treatment at a far earlier point in their history. Because ADT has many long-lasting detrimental ‘whole body’ symptoms, effective SBRT local salvage thus preserves better quality of life, greatly delaying or avoiding ADT systemic effects for most patients.”
Furthermore, at five years, the disease-free survival rate was 60%, indicating patients experienced no signs or symptoms of their cancer during that time. The authors write: “In spite of the relatively high-risk patient population described herein, the five-year biochemical relapse-free survival rate of 60% confirms extended disease-free survival in the majority of SBRT salvage cases.”
Comparing SBRT favourably to radical prostatectomy, Fuller and colleagues say: “We also report a biochemical relapse-free efficacy rate that appears at least comparable to that reported with salvage radical prostatectomy; 60% five-year biochemical relapse-free survival in the present series versus 57% three-year biochemical relapse-free survival in a contemporary salvage radical prostatectomy series of similar size and similar median follow-up. This suggests a definite role for salvage SBRT, particularly well-suited for those who either do not desire to or are not physically able to withstand the rigors and potential complications of a salvage radical prostatectomy procedure.”
The median prostate-specific antigen decreased to 0.16ng/mL at five years, similar to initial treatment with brachytherapy and lower than typical conventional fractionation, based on results from other studies.
No grade two or higher gastrointestinal events were reported. Genitourinary toxicity also was lower than reported rates for salvage radical prostatectomy and seems less frequent after prior standard external radiation treatment.
“Our results suggest that efficacious salvage of locally recurrent prostate cancer with SBRT is possible, with an acceptable toxicity risk, in appropriately selected patients,” Fuller et al conclude.