ESTRO 2024 - Abstract Book

S4900

Physics - Quality assurance and auditing

ESTRO 2024

Justine Tyler 1 , Helen Baines 1 , Emma Hall 2 , Elizabeth Miles 3 , Hakan Nyström 4 , Petra Nyström 5 , Julian Phillips 3 , Rita Simoes 6 , David Thomson 7 1 The Royal Marsden NHS Foundation Trust, National Radiotherapy Trials Quality Assurance Group (RTTQA), London, United Kingdom. 2 The Institute of Cancer Research, Clinical Trials and Statistics Unit (ICR-CTSU), London, United Kingdom. 3 Mount Vernon Hospital, National Radiotherapy Trials Quality Assurance Group (RTTQA), Northwood, United Kingdom. 4 Oslo University Hospital, Medical Physics, Oslo, Norway. 5 Aalborg University Hospital, Oncology, Aalborg, Denmark. 6 University College London Hospital (UCLH) NHS Foundation Trust, National Radiotherapy Trials Quality Assurance Group (RTTQA), London, United Kingdom. 7 The Christie NHS Foundation Trust, Radiotherapy, Manchester, United Kingdom

Purpose/Objective:

The TORPEdO (TOxicity Reduction using Proton bEam therapy for Oropharyngeal cancer) trial is a phase III multicentre trial of intensity-modulated proton beam therapy (IMPT) versus intensity-modulated radiotherapy (IMRT) for multi toxicity reduction in oropharyngeal cancer 1 . Extensive OAR outlining with ambitious dose constraints were specified, to ensure plans were well optimised enabling valid comparisons between the treatment modalities. Centres were provided with a pre-trial benchmark case which was planned and submitted for radiotherapy trial QA (RTQA) review and feedback. Benchmark plans were evaluated, with an emphasis on the target coverage and dose sparing of OARs that were achieved. This study explores the variation in OAR doses achieved by the planning submissions.

Material/Methods:

CTVs and OARs were provided to the centres for the benchmark case. Centres applied their locally determined PTV and PRV margins for photon planning and uncertainty parameters for robust proton planning. Two proton and eight photon benchmark plans were submitted. Mandatory dose constraints were specified for critical OARs (spinal cord and brainstem), with optimal constraints provided for a total of 14 OARs, with pre-specified planning priorities. The RTQA team reviewed the plans and requested resubmission if any of the mandatory requirements of the trial were not achieved. The dose statistics for the final acceptable submissions were compared.

Results:

All plans had acceptable target coverage and achieved the mandatory constraints. The OAR doses acheived are displayed in table 1. Optimal constraints were achieved by all plans for the contralateral parotid, glottis, superior constrictor muscle, mandible and the contralateral cochlea. Table 1: Benchmark plan OAR doses achieved by centres, highlighting where optimal dose constraints were not achieved. Brachial plexus outlining was not required for photon plans. *Proton plan dose statistics are reported for the nominal plan only.