PV QA 1 - Poster Viewing Q&A 1
Purpose/Objective(s): Multiple trials have established a survival benefit with the addition of ADT to standard dose external beam RT (EBRT) for patients (pts) with intermediate (IR) and high-risk (HR) prostate cancer (PC). The advent of DE RT in PC (total dose >75.59 Gy per NCCN guidelines) has prompted some to question whether more intense local therapy can obviate the need for micrometastasis-directed systemic therapy. Although subgroup analysis of EORTC 22991 demonstrated a progression-free survival benefit with ADT even in pts receiving DE-EBRT, the trial did not include pts who received DE RT via EBRT plus a brachytherapy boost (EBRT-BB). Given the ongoing debate of RT dose vs. ADT, we hypothesized that the proportion of pts receiving concurrent ADT would be lower among those receiving EBRT-BB vs. DE-EBRT.
Materials/Methods: Men with favorable/unfavorable IR (FIR/UIR) and HR PC treated with definitive RT from 2004-2015 were identified using the National Cancer Data Base. Pts who underwent extreme hypofractionation (i.e. SBRT) were excluded. DE-EBRT was defined as >75.59 Gy. An additional “favorable” HR subgroup (FHR, see table) was created to examine practice patterns for cases often considered resectable by urologists. Contingency tables and a logistic regression (LR) were created to measure associations and adjust for confounders (e.g. age, facility volume, comorbidities, year, etc).
Results: 120,277 men were included. The rate of ADT receipt in the UIR and FHR groups differed based on DE-EBRT vs. EBRT-BB. This difference held for both the older (UIR 8.4% absolute difference, FHR 12.1%) and more recent time periods (UIR 13.4% absolute difference, FHR 11.7%). In a multivariable LR, pts who underwent EBRT-BB were less likely to receive concurrent ADT compared to those who had DE-EBRT (odds ratio 0.76, 95% confidence interval 0.74 to 0.79). The interaction test between type of dose escalation (DE-EBRT vs. EBRT-BB) and risk group was significant at the p <0.0001 level.
Conclusion: Patients with unfavorable intermediate and favorable high risk PC are less likely to receive concurrent ADT if they are dose escalated with a brachytherapy boost compared to EBRT alone. We await the results of RTOG 0815 to guide whether it is clinically sound to omit ADT for patients receiving EBRT with a brachytherapy boost.
|Favorable Intermediate N=32,202||Unfavorable Intermediate N=34,457||“Favorable High” (Low volume GS8, T1c, PSA <=20) N=6,777||All Other High N=46,841|
|2004-2011 N=81,958||Not dose escalated||41.5||59.7||76.4||80.4|
|EBRT >75.59 Gy||35.1||56.6||77.7||81.3|
|EBRT with brachytherapy boost||38.1||48.2||65.6||74.0|
|2012-2015 N= 38,319||Not dose escalated||25.8||57.2||78.8||85.5|
|EBRT >75.59 Gy||30.3||56.1||82.3||87.3|
|EBRT with brachytherapy boost||24.3||42.7||70.6||84.0|
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