ESTRO 2024 - Abstract Book

S6022

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

2970

Mini-Oral

Ongoing protocol compliance of radiotherapy planning within the ATNEC trial (NCT04109079)

Zohal nabi 1 , Patricia Diez 1 , Roeum Butt 1 , Gareth Jackson 1 , Duncan Wheatley 2 , Carmel Anandadas 3 , Andrea Marshall 4 , Sophie Nicholls 4 , Natalie Hammonds 4 , Amit Goyal 5 1 National Radiotherapy Trials Quality Assurance Group, Mount Vernon Cancer Centre, Northwood, United Kingdom. 2 Royal Cornwall Hospitals NHS Trust, Clinical Oncology, Cornwall, United Kingdom. 3 The Christie NHS Foundation trust, Clinical Oncology, Manchester, United Kingdom. 4 University of Warwick, Warwick Clinical Trials Unit, Coventry, United Kingdom. 5 Royal Derby Hospital, Oncoplastic Breast Surgery, Derby, United Kingdom

Purpose/Objective:

Axillary Management in Breast Cancer Patients With Needle Biopsy Proven Nodal Metastases After Neoadjuvant Chemotherapy, ATNEC, is a randomised phase III trial investigating whether axillary treatment can be avoided in patients with no residual lymph node disease after neoadjuvant chemotherapy. All centres participated in a pre-trial RT QA program before opening to recruitment. As part of the on-trial QA, the first patient at each centre underwent prospective review and the remainder were submitted for retrospective review to monitor ongoing protocol compliance. With 250 patients now randomised, an interim assessment of protocol compliance is warranted to ensure there has been no drift in the quality of RT plans treated within ATNEC.

Material/Methods:

Retrospective reviews were carried out for 1 in 3 of recruited patients at each centre, and assessed on Velocity v4.1 (Varian Medical Systems, Inc.). Plans were evaluated for protocol compliance including dose prescription, technique, primary and nodal PTV coverage and organ at risk (OAR) dose-volume constraints.

Results:

Currently, 31/45 centres open to recruitment have entered patients into the trial, of which 18 have moved to the retrospective review stage and submitted 61 plans for assessment. Fractionation schedule and planning technique are summarised in Figure 1. The majority of breast only patients were treated with 26Gy in 5 fractions and breast plus lymph node (LN) chain with 40.05Gy in 15 fractions, all according to trial protocol. Treatment technique was variable, with most patients being treated with 3D conformal radiotherapy (3DCRT) or forward planned IMRT. Centres treating internal mammary nodes (IMN) generally used VMAT. Fifty-nine plans (96.7%) met all mandatory dose-volume constraints and 28 of these also met all optimal constraints. Of the non-compliant plans, one was due to the sub optimal technique used for IMN treatment and the other was a clinical decision favouring OAR sparing over PTV coverage. Results are summarised in Figure 2.