Abstract

Vérane Achard¹, Reino Heikkilä², Piet Dirix^3,4, Shankar Siva⁵, Nick Liefhooghe⁶, Antonio Conde-Moreno⁷, Sabine Meersschout⁸, Paolo Muto⁹, Clara Eíto¹⁰, Marta Barrado¹¹, Paul Martin Putora¹², Daniel Zwhalen¹³, Marta Scorsetti^14,15, Almudena Zapatero¹⁶, Lien Van De Voorde ¹⁷, Fernando López Campos ¹⁸, Felipe Couñago^19,20, Frederik Vanhoutte²¹, Maud Jaccard¹, Giovanna Dipasquale¹, Piet Ost²¹, Thomas Zilli¹

¹Geneva University Hospitals, Radiation oncology, Geneva, Switzerland; ²Oslo University Hospital, Oncology, Oslo, Norway; ³Iridium Kankernetwerk, Radiation oncology, Antwerp, Belgium; ⁴University of Antwerp, Faculty of Medicine and Health Sciences, Antwerp, Belgium; ⁵Epworth Healthcare and Sir Peter MacCallum , Oncology, Melbourne, Australia; ⁶AZ Groeninge, Radiation oncology, Kortrijk, Belgium; ⁷Hospital Universitari i Politècnic la Fe, Radiation oncology, Valencia, Spain; ⁸AZ-St Jan-Brugge, Radiation oncology, Brugge, Belgium; ⁹Napoli Istituto Nazionale Tumori IRCCS Fondazione Pascale, Radiation oncology, Napoli, Italy; ¹⁰Instituto Oncólogico Clinica Universitaria IMQ, Radiation oncology, Bilbao, Spain; ¹¹Complejo Hospitalario de Navarra, Radiation oncology, Navarra, Spain; ¹²Kantonspital St. Gallen, Radiation oncology, St. Gallen, Switzerland; ¹³Kantonspital Winterthur, Radiation oncology, Winterthur, Switzerland; ¹⁴IRCCS Humanitas Research Hospital, Radiation oncology, Rozzano (Milan), Italy; ¹⁵Humanitas University, Biomedical Sciences, Pieve Emanuele (Milan), Italy; ¹⁶University Hospital La Princesa, Radiation oncology, Madrid, Spain; ¹⁷AZ St-Lucas, Radiation oncology, Ghent, Belgium; ¹⁸Hospital Universitario Ramón y Cajal, Radiation oncology, Madrid, Spain; ¹⁹University Hospital Quironsalud, Radiation oncology, Madrid, Spain; ²⁰Universidad Europea de Madrid, Medicine, Madrid, Spain; ²¹Ghent University Hospital, Radiation oncology and experimental cancer research, Ghent, Belgium

Optimal local treatment for nodal oligorecurrent prostate cancer (PCa) is unknown. In this setting, the ongoing prospective multicentre randomized phase II PEACE V-STORM trial is evaluating the impact of the addition of whole pelvic radiotherapy (WPRT) to metastasis-directed therapies (MDT: salvage lymph-node dissection or stereotactic body radiotherapy, SBRT) and short-term androgen deprivation therapy (ADT) on metastasis-free survival. The aim of the present study is to report the interim results of the radiation therapy quality assurance (RTQA) program. 

Patients diagnosed with PET-detected pelvic nodal oligorecurrence (≤5 nodes) following radical local treatment for PCa, are randomized in a 1:1 ratio between arm A: MDT and 6 months of ADT, or arm B: WPRT added to MDT and 6 months of ADT. A site-specific questionnaire and a dummy run (DR) consisting of a post-prostatectomy case with two ipsilateral iliac nodal recurrences were established for both SBRT (30 Gy/3 fx) and WPRT (45 Gy/25 fx with a nodal SIB to 65 Gy) treatments. Use of IMRT or VMAT techniques was mandatory. The uploaded plans were reviewed independently by two radiation oncologists for protocol compliance of delineation and treatment planning. Case reviews were categorized as: ‘Acceptable as per protocol’ (A), ‘Acceptable Variation’ (AV), or ‘Unacceptable Variations’ (UV). UV was assigned if there could be a material impact on clinical outcomes. 

DR of 18 centers among the 26 participating centers were analyzed in this interim analysis. The overall grading for delineation review of the 1^st submitted version of the DR was rated as ′UV′ or ′AV′ for 1 and 5 centers for arm A (33%) and 3 and 6 for arm B (50%), respectively. A lower upper limit of the WPRT CTV (n=2), an inappropriate (n=1) or missing delineation (n=1) of the prostate bed, and a missing nodal target volume (n=1 for arm A and B) constituted the observed ′UV′. With a 2^nd DR version, required for 8 centers, the overall delineation review showed 2 and 5 ′AV′ for arms A and B, respectively, with no ′UV′. For the dosimetric/plan quality review, arm B showed the largest protocol agreement, with only one AV consisting of a lower boost dose to a node. The largest variability in dosimetry was observed for SBRT plans, with PTV D_90% ranging from 22.9 Gy to 32.7 Gy for node 1 (close to a bowel loop) and from 26.8Gy to 34Gy for node 2 (close to sigmoid), respectively. Six SBRT plans were rated as ′A′, while 12 as ′AV′, mainly for exceeding the dose to the bowel-loop PRV. 

In this study, we observed up to 50% of protocol deviations in delineation of salvage radiotherapy treatments for nodal oligorecurrent PCa. While contouring of WPRT was more subject to variations, dosimetric variations were largest in the SBRT plans. Prospective RTQA programs should be implemented as critical component of future radiotherapy trials for oligometastatic disease.