Nodal recurrence patterns on PET/CT after RTOG-based nodal radiotherapy for prostate cancer

Area of Science:

• Radiation Oncology
• Prostate Cancer Research
• Medical Imaging

Background:

• Biochemical failure after radiotherapy for node-positive prostate cancer (PC_N+) frequently involves nodal recurrences, often outside the radiation field.
• Current Radiation Therapy Oncology Group (RTOG)-based elective nodal fields may not be optimal for PC_N+.
• Advances in imaging like PSMA PET/CT and choline PET/CT enable precise visualization of nodal recurrences.

Purpose of the Study:

• To evaluate recurrence patterns on PET/CT after external beam radiotherapy (EBRT) for PC_N+.
• To explore options for improved nodal target definition in radiation therapy for PC_N+.

Main Methods:

• Retrospective review of patients treated with curative intent EBRT for PC_N+ from 2008-2018.
• EBRT details: 70 Gy to prostate or prostate bed, 60 Gy to involved nodes, 52.5-56 Gy to RTOG-based elective nodal fields.
• Correlation of PET/CT recurrence locations with applied EBRT fields.

Main Results:

• 42 patients underwent PSMA (28) or choline (14) PET/CT at biochemical recurrence; 35 (83%) had positive scans.
• 17 patients showed nodal metastasis at first positive scan, with some also having local recurrence or distant disease.
• Out-field nodal recurrences (n=14) were more common than in-field (n=3), with most occurring just above elective fields.

Conclusions:

• Current RT with RTOG-based nodal fields offers good in-field control but frequent out-field recurrences suggest missed microscopic disease.
• Expanding elective fields to include the aortic bifurcation may improve recurrence-free survival for PC_N+.
• Further research is needed to balance the potential benefits of expanded fields against increased toxicity.