Feasibility of dose escalating [18F]fluciclovine positron emission tomography positive pelvic lymph nodes during moderately hypofractionated radiation therapy for high-risk prostate cancer

Abstract Purpose To report the treatment planning feasibility of dose escalation to suspicious lymph nodes (LNs) for a series of men who underwent pretreatment [ 18 F]fluciclovine-PET/MRI. Methods and Materials Cases of men with prostate cancer who enrolled in a clinical trial of pretreatment [ 18 F]fluciclovine PET who had suspicious LNs were selected. Pelvic LNs 18 F]fluciclovine-PET if their SUV max was 1.3-fold or greater above the reference blood pool SUV mean , and LNs ≥1cm were defined as positive if the SUV was greater than the reference SUV bone marrow reference. For each case, a radiation treatment plan was generated to deliver 70 Gy to the prostate and proximal seminal vesicles, 60.2 Gy to the PET positive LNs, and 50.4 Gy to the elective nodal regions, simultaneously in 28 fractions of 2.5 Gy, 2.15 Gy, and 1.8 Gy, respectively. Treatment planning goals were defined a priori . The resulting target volume and organ-at-risk dosimetry was compared to the original treatment plan. Results Four cases were identified, with between 1 and 5 [ 18 F]fluciclovine PET positive LNs each. Goals for the prostate and elective nodal target volumes were successfully met in all cases. The goal of covering more than 90% of the positive LN planning target volume by the prescription dose of 60.2 Gy was met in 3 of the 4 cases. This goal was not met in 1 case, but 100% of clinical target volume was covered by 60.2 Gy. The primary organ-at-risk tradeoff was that a small volume (0.5cc – 8.2cc) of small bowel would receive ≥54 Gy in each case. Conclusion These preliminary results suggest that [ 18 F]fluciclovine-PET/MRI directed dose escalation of suspicious pelvic LNs is likely feasible in the setting of definitive radiotherapy. The potential clinical benefit of dose escalating [ 18 F]fluciclovine-PET positive LNs should be investigated in a prospective clinical trial.