The Spatial Pattern of Recurrence in Oral Cavity Cancer Treated With Definitive (chemo)radiotherapy: A Tertiary...

The aim of this study was to determine the outcome and spatial dosimetric pattern of recurrence in oral cavity squamous cell cancer (OCSCC) patients treated with definitive (chemo)intensity-modulated radiotherapy (IMRT).

OCSCC patients treated with IMRT between 2018 and 2021 were assessed for locoregional and overall survival (OS). The recurrent gross tumour volume (rGTV) disease was contoured on the recurrence scan which was deformably coregistered with the original planning computed tomography (CT). The cumulative delivered dose was calculated by summating all deformed weekly cone beam CTs. Mapped rGTVs were analysed according to the delivered dosimetry: Type A (central 95%-isodose) or B (peripheral 95%-isodose) failure.

Forty patients were assessed, including 25 (63%) stage IVa and 8 (20%) stage IVb patients. Five (13%) had unintended treatment prolongation, and one stopped IMRT early. Of the 14 concomitant cisplatin patients, only 3 (21%) received a cumulative dose ≥200 mg/m². The 3-year OS for stage IVa patients was 36%, and 1-year OS for stage IVb was 22%. Twenty-one patients (53%), all treated with 65Gy/30f over 6 weeks, subsequently developed locoregional recurrences. Fourteen (67%) recurrences occurred within 6 months of IMRT. There were 28 individual rGTVs: 20 (71%) type A and 6 (21%) type B failures. In terms of volume receiving 100% isodose, there was a median -23.7% reduction (range=-61-34%) than planned within the rGTVs (p = 0.01). The median aggregate-match error from 621 onboard images was 3 mm (range=0-12 mm), with 199 (32%) fractions delivered at >3 mm.

Definitive IMRT did not demonstrate satisfactory disease control in OCSCC. Careful treatment selection and delivery is essential if definitive IMRT is to be considered as a radical approach.