Prostate Cancer Outcomes Differ Widely Based on Radiation Therapy Choice

Patient outcomes differed widely based on which radiation therapy (RT) option was used to treat prostate cancer, according to a study published in Cancer Treatment Reviews.

Treatment for prostate cancer, a prevalent diagnosis in men, typically includes some combination of active surveillance, radical prostatectomy, and RT. Within RT, options can become even more complex, including external beam radiation therapy (EBRT), which may be conventionally fractionated with intensity modulated radiation therapy (IMRT) or protons, hypofractionated RT with IMRT or protons, or delivered as stereotactic body RT (SBRT); and brachytherapy (BT), at either high (HDR-BT) or low dose rates (LDR-BT). However, while there are many standard treatment options for prostate cancer, there have been few studies looking at the optimal therapy for patients with localized or locally advanced disease. 

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Researchers led by Nicholas G Zaorsky, MD, Fox Chase Cancer Center (Philadelphia, PA), conducted a systematic review in order to provide a better understanding about the definitive RT options available for prostate cancer care. 

To accomplish that, the researchers conducted a literature search of articles comparing different RT fractionation regimens, outcomes data related to those regimens, and future implications of RT care. Their primary outcome measure was freedom from biochemical failure (FFBF), defined by the Phoenix definition, because most randomized controlled trials of RT have historically utilized this endpoint. Overall survival (OS), prostate cancer specific mortality (CSM), and distant metastasis (DM) were also included as secondary endpoints. 

Results demonstrated wide variability in RT effectiveness. For EBRT, researchers found that FBFF improved. Five-year rates for low-, intermediate-, and high-risk groups were >90%, 60-85%, and 50-70%, respectively among patients in studies included in the review. Ten-year FFBF rates for these same groups were 45-90%, 40-60%, and 20-50%, respectively. No studies have yet compared EBRT with LDR-BT or HDR-BT. 

Additionally, no studies have yet been conducted comparing outcomes with LDR-BT to those with HDR-BT, though several single-arm studies have been conducted. In one study of 101 patients treated with LDR-BT and a median follow-up of 5.3 years, 5 patients had local failure, 1 patient had evidence of distant failure, and 6 had biochemical failures, all of which were comparable to other studies on BT and RT. 

Two studies with results on the efficacy and toxicity of HDR-BT as monotherapy were also included in the review. These demonstrated 5-year FFBF rates of >85%, 69-97%, and 63%-80% for low-, intermediate-, and high-risk patients, respectively. Five-year rates for CSM, OS, local recurrence, and DM, were 99-100%, 85-100%, 0-8%, and 2-12%, for these same patients, respectively. Further, one study comparing HDR-BT boost with EBRT found that 10-year FFBF rates were generally higher for those who received EBRT (60% vs. 100% for low risk patients; 62% vs. 89% for intermediate-risk patients; 70% vs. 80% for high-risk patients). 

In terms of toxicity IMRT was associated with decreased toxicity compared with other methods, while late toxicities were otherwise similar between conventionally fractionated RT and hypofractionated RT. However, differences in OS, DM, and CSM have not yet been well established in randomized clinical trials of dose escalation. 

“Long-term FFBF rates are roughly equivalent between conventionally fractionated RT and hypofractionated RT with IMRT (evidence level 1B) among all [National Comprehensive Cancer Network] risk groups,” researchers concluded. “Similarly, BT monotherapy is an acceptable treatment option for select low- and intermediate-risk patients. FFBF rates among SBRT studies appear promising. For certain intermediate- and high-risk patients, BT boost may have improved FFBF rates vs conventionally fractionated RT with IMRT alone.”—Sean McGuire

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Zaorsky NG, Shaikh T, Murphy CT, et al. Comparison of outcomes and toxicities among radiation therapy treatment options for prostate cancer [published online ahead of print June 17, 2016]. Cancer
Treat Rev
. doi: 10.1016/j.ctrv.2016.06.006.