Volumetric and positional changes of planning target volumes and organs at risk using computed tomography imaging during intensity-modulated radiation therapy for head-neck cancer: an "old" adaptive radiation therapy approach.

Purpose: This study aimed to assess, in a department of radiation oncology not equipped with in-room imaging systems, volumetric and positional changes of planning target volumes (PTVs) and organs at risk in head and neck (H&N) cancer patients treated with intensity-modulated radiation therapy (IMRT), using consecutive off-board computed tomography (CT) imaging. Dosimetric aspects were not investigated.

Materials And Methods: Ten patients with H&N cancer underwent CT re-scanning at 3, 5, and 7 weeks. Positional changes of the PTVs and parotid glands as distances relative to the virtual isocentre were determined. The parotids glands (PGs) were re-delineated on each CT set and volume differences were computed. Anterior-posterior (AP) and latero-lateral (LL) displacements for the spinal cord at C1 and C6 level were calculated. Changes in patient body contours were evaluated by comparing the volumes within the external skin outline.

Results: Apart from two patients requiring re-planning due to substantial weight loss, our results evidenced no significant shifts of PTVs and PGs. PG volume decreased with a trend in volume reduction for the ipsilateral parotid. No significant shift of spinal cord at C1 and C6 level was detected, in either the AP or LL direction. The collected data demonstrated a trend in external skin contour volume loss.

Conclusions: Our preliminary results reflect the literature data and indicate that an off-line adaptive RT approach is appropriate in clinical practice.