Dose monitoring-guided replanning timing in adaptive radiotherapy for laryngeal cancer.

This study aimed to determine the optimal timing for adaptive replanning in patients with locally advanced laryngeal cancer undergoing radiotherapy and to investigate how this timing varies based on anatomical and dosimetric threshold values. Volumetric modulated arc therapy planning was performed for twenty patients with locally advanced laryngeal cancer. All treatments were delivered with daily two dimensional kilovoltage imaging and weekly three dimensional cone beam computed tomography (CBCT) imaging for patient setup verification. The six weekly CBCT datasets obtained during the treatment course were used for dose accumulation analysis. Weekly dose variations in the target volumes and organs at risk were evaluated according to predefined dosimetric thresholds. Neck diameters and parotid gland volumes were measured on the synthetic computed tomography images generated from CBCTs using deformable image registration and assessed according to anatomical thresholds. An average reduction of - 1.18 ± 0.67 cm in neck diameter was observed throughout the treatment course. When the initial plan was compared with the weekly accumulated doses, a D98% dose deviation of - 1.92 Gy was detected for PTV54, while the mean dose deviations for the ipsilateral and contralateral parotid glands were calculated as 2.10 Gy and 1.46 Gy, respectively. By the end of treatment, approximately 65% of patients had exceeded at least one anatomical or dosimetric threshold. The third week, when these thresholds first began to be exceeded, appears to represent a potential standard reference point for replanning evaluation. In patients with locally advanced laryngeal cancer, the third week of treatment, when anatomical and dosimetric thresholds are generally beginning to be exceeded, may serve as a standard reference point for re-planning assessment in radiotherapy. However, it should be noted that anatomical and dosimetric thresholds are not always exceeded simultaneously, and relying solely on anatomical changes may be insufficient for making accurate replanning decisions.