National practice patterns for lymph node irradiation in 197,000 men receiving external beam radiotherapy for localized prostate cancer.

Purpose: Controversy surrounds the benefit of pelvic lymph node irradiation (PLN-RT) in localized prostate cancer (CaP). Our objective was to determine the practice patterns and predictors of PLN-RT in a national cohort.
Materials and Methods: The National Cancer Data Base (2005-2015) was leveraged to obtain men diagnosed with nonmetastatic CaP treated with external beam radiotherapy (n = 197,378). Multivariable logistic regressions were used to assess temporal trends and factors associated with PLN-RT.
Results: PLN-RT occurred in 37% of patients overall, which increased to 41% by 2015. When stratified by risk group, there was no significant difference in PLN-RT over time in low, favorable intermediate, unfavorable intermediate, or high-risk CaP. PLN-RT increased for men with very high-risk disease (51%-60%; odds ratio per year 1.34, 95% confidence inrerval 1.06-1.70, P = 0.013). Increased odds of PLN-RT was associated with higher risk disease, addition of hormone therapy, treatment at community hospitals, and shorter patient travel distance to treatment facilities. Surprisingly, 26% and 34% of low and favorable intermediate risk CaP received PLN-RT, respectively. Predictors of PLN-RT among these patients included treatment at a community practice and use of brachytherapy or hormone therapy.
Conclusions: PLN-RT occurred in about one-third of men receiving external beam radiotherapy and increased over time, mostly in men with very high-risk CaP for unclear reasons. Of concern, over one-quarter of low-risk men receive PLN-RT. Further work is needed to understand the heterogeneity in PLN-RT use. We await the completion of RTO G 09-24 to better understand the role of PLN-RT for men with localized CaP.
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