ESTRO 2024 - Abstract Book

S1424

Clinical - Head & neck

ESTRO 2024

2713

Digital Poster

Optimal time for adaptive radiotherapy planning in head and neck cancer patients

Jamuna Angel Joy 1 , Jomon Raphael C 1 , Paul Gopu G 2 , Mathew Varghese K 1 , Vidhu M Joshy 3 , Febin Antony 1

1 Amala Institute of Medical Sciences, Radiation Oncology, Thrissur, India. 2 Swansea Bay University Health Board, Clinical Oncology, Swansea, United Kingdom. 3 Andaman & Nicobar Islands Institute of Medical Sciences, Bio statistics, Andaman & Nicobar Islands, India

Purpose/Objective:

Though adaptive radiotherapy (ART) has been found to be beneficial in improving the dose distribution to tumor volume and organs at risk (OAR), literature is scant regarding the optimal time for rescanning and replanning in head and neck radiotherapy (RT). In this single institutional study, we aimed to identify the optimal timing for ART in head and neck squamous cell carcinoma (HNSCC) using easily measurable anatomical parameters.

Material/Methods:

In this prospective study, patients with stage III and stage IV HNSCC planned for definitive RT from 2018-2020 were enrolled. Anatomical parameters like body mass index (BMI) and skin to skin separation (SSS) of neck were monitored weekly and all patients underwent a repeat computed tomography (CT) imaging at 18th (CT18) and 25th (CT25) fraction of treatment. These images were registered with the initial planning CT images and dose-volumetric changes in contra-lateral parotid gland (PG) were analysed by fusing the initial approved RT plan on to it. Primary end point was increase in contralateral PG dose from baseline by 10% in CT18 and CT25. Summary statistics were used to describe cohort and anatomical parameters. Fischer’s exact test was used to study the relation between mean BMI loss, mean SSS loss and change in dose to contralateral PG.

Results:

Of the 25 patients enrolled, 20 were males and 5 were females. In CT18, 14 patients and 11 patients had ‹10% increase and ›10% increase in dose to contralateral PG, respectively. In CT25, 10 patients and 15 patients had ‹10% increase and ›10% increase in dose to contralateral PG, respectively. Mean BMI loss was 4.57% ± 2.91 and mean SSS loss was 3.15% ± 2.21. Among 50% (8/16) patients who had BMI loss ‹4% and SSS loss ‹3%, none of them had ›10% increase in contralateral PG dose in both CT18 and CT25. Among 50% (8/16) patients who had BMI loss ›4% and SSS loss ›3%, 25% (2/8) had ‹10% increase in PG dose and 75% (6/8) had ›10% increase in PG dose (p = 0.001).

Conclusion:

BMI loss ›4% from baseline and SSS loss ›3% from baseline showed an increase in contralateral PG dose by ›10%. As these parameters are easily measurable, we recommend a replanning for ART at this juncture.