The purpose of the study is to measure anatomical and dosimetric changes experienced by patients with head and neck cancer undergoing intensity-modulated radiation therapy and evaluate the need for adaptive radiotherapy using predefined relative thresholds as benchmarks.

This study involved 31 consecutive patients. Two computed tomography (CT) scans were utilized for initial treatment planning and a midpoint assessment. The study employed rigid registration and contour transfer techniques to apply primary dose calculation to midpoint CT, generating a hybrid plan, and an adaptive plan was generated on the midpoint CT.

The results revealed statistically significant volume reductions mainly in PTV70, PTV60 and PTV54 volumes. The volume of the parotid glands exhibited volumetric reductions in most of the patients. Hybrid plans demonstrated inferior dose coverage of the tumour regions, and comparisons between hybrid and adaptive plans showed significant variations in the maximum doses.

Anatomical deviations necessitating a repeat CT scan, along with the application of a new immobilization mask, emerged as a primary rationale for replanning. Indicators that could potentially encompass a breach of 95% dose coverage for 95% of the tumour volume, maximum doses surpassing 50 Gy in the spinal cord and 59 Gy in the brainstem<>, as well as lateral neck displacement exceeding 1cm from the initial position act as benchmarks before implementing a replan.