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

C P Liskamp; M L Donswijk; H G van der Poel; E E Schaake; W V Vogel

doi:10.1016/j.ctro.2020.02.006

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

Clin Transl Radiat Oncol. 2020 Feb 26:22:9-14. doi: 10.1016/j.ctro.2020.02.006. eCollection 2020 May.

Authors

C P Liskamp¹, M L Donswijk², H G van der Poel³, E E Schaake¹, W V Vogel^{1

2}

Affiliations

¹ Department of Radiation Oncology, NKI-AVL, Amsterdam, The Netherlands.
² Department of Nuclear Medicine, NKI-AVL, Amsterdam, The Netherlands.
³ Department of Urology, NKI-AVL, Amsterdam, The Netherlands.

Abstract

Purpose: Biochemical failure after external beam radiotherapy (RT) for node-positive prostate cancer (PC_N+) frequently involves nodal recurrences, in most cases out of field. This raises the question if current RTOG-based elective nodal fields can still be considered optimal. Modern diagnostic tools like PSMA PET/CT and choline PET/CT can visualize nodal recurrences with unprecedented accuracy. We evaluated recurrence patterns on PET/CT after RT for PC_N+, with the aim to explore options for improved nodal target definition.

Methods and materials: Data of all patients treated with curative intent EBRT for PC_N+ in NKI-AVL from 2008 to 2018 were retrospectively reviewed. EBRT comprised 70 Gy to the prostate or 66-70 Gy to the prostate bed, 60 Gy to involved nodes, and 52,5-56 Gy (46 Gy EQD2) to RTOG-based elective nodal fields, in 35 fractions. Locations of recurrences on PET/CT were noted, and nodal locations were correlated with the applied EBRT fields.

Results: 42 patients received PSMA (28) or choline (14) PET/CT at biochemical recurrence. 35 patients (83%) had a positive scan. At their first positive scan 17 patients had nodal metastasis, in some cases together with a local recurrence or distant disease. In-field nodal recurrences were uncommon (n = 3). Out-field nodal recurrences occurred more frequently (n = 14), with the majority (n = 12) just above the elective nodal field. These nodes were the single area of detectable failure in 6 patients (14%).

Conclusions: Current RT with RTOG-based nodal fields for PC_N+ provides good in-field tumour control, but frequent out-field nodal recurrences suggest missed microscopic locations. Expanding elective fields to include the aorta bifurcation may prolong recurrence-free survival. Future research must address whether the potential benefits of this strategy outbalance additional toxicity.

Keywords: BCR, biochemical recurrence; Choline PET/CT; GS, Gleason Score; IMRT, Intensity-Modulated Radiation Therapy; IRB, Institutional Review Board; LND, Lymph Node Dissection; NKI-AVL, Nederlands Kanker Instituut Antoni van Leeuwenhoek; PCN+, node-positive prostate cancer; PET/CT, positron emission tomography / computed tomography; PSMA PET/CT; PSMA, Prostate-Specific Membrane Antigen; Prostate cancer; RP, radical prostatectomy; RT, external beam radiotherapy; RTOG, Radiation Therapy Oncology Group; Radiotherapy; Recurrence patterns; SNB, Sentinel Node Biopsy; SNP, Sentinel Node Procedure; Target definition; VMAT, Volumetric Arc Therapy; ePLND, extended pelvic lymph node dissection; rLND, retroperitoneal lymph node dissection (rLND); sRT, Salvage Radiotherapy.