Randomized Trial of Conventional- vs Conventional plus Fluciclovine (18F) PET/CT-Guided Post-Prostatectomy Radiotherapy for Prostate Cancer: Volumetric and Patient-Reported Toxicity Analyses

Abstract

Purpose/Objective(s)

: Post-prostatectomy radiotherapy planning with fluciclovine (18F) PET/CT (PET) has demonstrated improved disease-free survival over conventional-only [CT or MRI-based] treatment planning. We hypothesized that incorporating PET would result in larger clinical target volumes (CTV's) without increasing patient-reported toxicities.

Materials/Methods

: From 2012-2019, 165 post-prostatectomy patients with detectable PSA were randomized (Arm 1 [no PET]: 82; Arm 2 [PET]: 83). Prostate bed target volumes with (CTV1 [45.0-50.4 Gy/1.8Gy]) or without (CTV2/CTV [64.8-70.2Gy/1.8Gy]) pelvic nodes, as well as organ-at-risk doses, were compared pre- v post-PET (Arm 2) using the paired t-test and between Arms using the t-test. Patient-reported outcomes (PRO's) utilized International Prostate Symptom Score (IPSS) & Expanded Prostate Cancer Index Composite for Clinical Practice (EPIC-CP). Univariate & multivariable analyses (MVA) were performed & linear mixed-models were fitted.

Results

: Median FU of the whole cohort was 3.52 years. All pts had baseline PRO's, 1 pt in Arm 1 & 3 pts in Arm 2 withdrew, & 4 Arm 2 pts had extra-pelvic uptake on PET with XRT aborted, leaving 81 [Arm 1] & 76 pts [Arm 2] for toxicity analysis. Mean CTV1 (427.6cc v 452.2cc [p=0.462], Arm 1 v Arm 2) and CTV2/CTV (137.18cc v 134.2cc [p=0.669]) were similar prior to PET incorporation. CTV1 (454.57cc v 461.33cc; p=0.003) and CTV2/CTV (134.14cc v 135.61cc; p<0.001) were modestly larger following PET incorporation. While V40Gy (p=0.402 & p=0.522 for rectum & bladder, respectively) & V65Gy (p=0.157 & p=0.182 for rectum & bladder, respectively) were not significantly different pre- v post-PET, penile bulb dose significantly increased post-PET (p<0.001 for both V40Gy & V65Gy). On MVA, Arm was not significant for any EPIC-CP subdomain. IPSS & EPIC-CP LMMs were not significantly different between Arms.

Conclusion

: Despite larger clinical target volumes after incorporation of fluciclovine (18F) PET, we found no significant difference in patient-reported toxicities with long-term follow-up.