ESTRO 2024 - Abstract Book

S6009

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

IMPT and IMRT replanning rates for the TORPEdO (CRUK/18/010) trial: dosimetric review for trial QA

Julian Phillips 1 , Justine Tyler 2 , Elizabeth Miles 1 , Lee Harrison-Carey 3 , Mat Lowe 4 , Alison Hand 4 , Callum Gillies 5 , Matthew Tyler 6 , Emma Hall 6 , James Price 4 , David Thomson 4 1 Mount Vernon Hospital, National Radiotherapy Trials Quality Assurance (RTTQA) Group, Northwood, United Kingdom. 2 The Royal Marsden NHS Foundation Trust, National Radiotherapy Trials Quality Assurance (RTTQA) Group, London, United Kingdom. 3 University College Hospitals London, National Radiotherapy Trials Quality Assurance (RTTQA) Group, London, United Kingdom. 4 The Christie NHS Foundation Trust, Radiotherapy, Manchester, United Kingdom. 5 University College Hospitals London, Radiotherapy, London, United Kingdom. 6 The Institute of Cancer Research, Clinical Trials and Statistics Unit (ICR-CTSU), London, United Kingdom

Purpose/Objective:

The TORPEdO (TOxicity Reduction using Proton bEam therapy for Oropharyngeal cancer) IMRT versus IMPT randomised trial 1 is the first proton trial in the UK. Patients with head and neck cancer (HNC) can require replanning during treatment. As IMPT plans are less robust to anatomical changes, more replans are anticipated. As part of the trial QA programme, we compared IMRT and IMPT replanning rates, timing during treatment and the most common reasons for replans. The implications for additional QA workload were evaluated.

Material/Methods:

Patients were randomised to IMPT or IMRT with a 2:1 allocation ratio, CBCT was acquired according to local practice. The trial mandated rescanning and dosimetric review for all patients treated with IMPT or IMRT during week 3 of treatment. Replans were also permitted at any point during the treatment course if indicated by changes seen in verification CBCT.

Three criteria were pre-defined in the RT guidelines to determine the need for a replan:

1. The target coverage doesn’t meet the D99% and D95% protocol criteria and on visual review target coverage is deemed not to be clinically acceptable.

2. The cumulative maximum dose to critical structures is >2% over tolerance or less as per local centre protocol.

3. The mean dose to parotids/oral cavity/submandibular glands has increased by >3 Gy (RBE) assuming the entire treatment will be delivered as per the verification scan.

Rescan and replan information along with reasons for replanning at dosimetric review against the pre-defined criteria were recorded on the radiotherapy case report form (CRF). All rescan and replan data were collected and underwent external independent QA review.

Results: