Although recent studies have shown the efficacy of using stereotactic body radiation therapy (SBRT) as a treatment modality for organ-confined prostate cancer, questions over urinary symptoms and sexual dysfunction have remained. According to findings presented at the 2015 Genitourinary Cancers Symposium, those questions have been answered: the SBRT approach demonstrates acceptable urinary and sexual toxicity.
“While an increase in IPSS [International Prostate Symptom Score] irritative score and a decrease in SHIM [Sexual Health Inventory for Men] score initially occurred, all symptoms return to baseline within 3 years,” said Zaker H. Rana, MD, Department of Radiation Oncology, Virginia Hospital Center, Arlington. “Age did not affect urinary or sexual dysfunction following radiotherapy, and patients with smaller prostate volumes had significantly better voiding and irritative outcomes when compared to larger volumes.”
As Rana explained, urinary symptoms and sexual dysfunction are the 2 most common complaints from patients following prostate radiotherapy, yet there are limited clinical data evaluating the effect of baseline patient characteristics on response to hypofractionated treatment.
“While higher doses result in a lower risk of biochemical failure, they also increase the risk of bladder, rectal, and small bowel toxicity,” said Rana. “This study sought to evaluate how patient age and prostate size affects voiding symptoms, irritative symptoms, and sexual function, following SBRT.”
The retrospective analysis included 102 nonmetastatic patients treated with SBRT between May 2008 and September 2014. All patients received treatment at a single institution. The course of radiotherapy consisted of 36.25 Gy (range 35-40) over 5 daily fractions. IPSS and SHIM were recorded at baseline and 1, 3, 6, 9, 12, 18, 24, and 36 months after treatment.
Median patient age was 72 years (range, 47-88). Median prostate volume was 43 cc (range, 18.7-170.7). Baseline IPSS irritative score, IPSS voiding score, and SHIM score were 5.21, 5.31, and 10.48, respectively.
“An increase in voiding (6.45), as well as a statistically significant increase in irritative symptoms (6.97), and significant decrease in SHIM score (11.95) were observed after 1 month (P<.05),” said Rana.
However, these changes proved to be transient.
“The IPSS irritative score and IPSS voiding scores returned to baseline in >75% of patients by 9 months and SHIM scores returned to baseline in >90% of patients by 2 years,” he reported.
Notably, prostate size ≤50 cc showed higher baseline IPSS voiding and irritative resolution rates after 3 months (P <.05).
“With smaller prostate volumes, you are hitting less surrounding structures, which may be leading to a reduction in toxicity,” hypothesized Rana. “Patients with larger prostates tend to have higher doses hitting their bladder, urethra, etc. We have no histological proof of this, but in theory it’s feasible.”
Rana also noted several limitations to this study.
“The use of androgen-deprivation therapy [ADT] results in reduction of prostate size and could explain improvement in urinary symptoms following SBRT,” he said, “but this effect should be minimal as only 8.9% of the patient population studied used ADT.… Carefully controlled prospective trials should be conducted to confirm the effectiveness of SBRT in the treatment of prostate cancer.”
Although Rana acknowledged the imprecision in comparing therapeutic strategies, he could not deny this study’s favorable results.
“Prostate cancer patients treated with SBRT exhibited minimal acute toxicity,” he concluded. “Three-year PSA response, reported toxicity, erectile function preservation, and urinary function improvement compare favorably to data presented following radical prostatectomy, brachytherapy, or conventional external beam radiation therapy.”
Rana ZH, Hong R, McRae D, et al. The impact of patient characteristics on voiding symptoms, irritative symptoms, and sexual function, following stereotactic body radiotherapy for prostate cancer. J Clin Oncol. 2015;33(suppl 7):abstract 245. Poster presented at: Genitourinary Cancers Symposium; February 26-28, 2015; Orlando, FL.