Abstract:

Objective To investigate the dosimetric characteristics of intensity modulated proton therapy （IMPT） and photon volumetric modulated arc therapy （VMAT） in typical head and neck malignant tumors. Methods Three types of typical head and neck tumors （nasopharyngeal carcinoma， parotid gland carcinoma， laryngeal carcinoma） treated at Shandong Cancer Hospital and Institute from December 2023 to December 2024 were taken as research subjects. IMPT and VMAT radiotherapy plans were created according to clinical prescription requirements of target and organs at risk limits respectively. The conformity index （CI）， homogeneity index （HI） and gradient index （GI） for target coverage of two radiotherapy plans were evaluated for 3 patients， as well as the dosimetric indicators of organs at risk. Results The CI of IMPT for nasopharyngeal carcinoma， parotid gland carcinoma and laryngeal carcinoma were 0.70， 0.72 and 0.67， respectively. The HI were 0.11， 0.08 and 0.08， respectively. The GI were 3.08， 2.49 and 3.75， respectively. The CI of VMAT plans were 0.77， 0.82 and 0.91， respectively. The HI were 0.12， 0.10 and 0.04， respectively. The GI were 3.67， 2.63 and 3.45， respectively. The results showed that CI of IMPT plan was slightly lower than that of VMAT plan， and HI of IMPT plan was comparable to that of VMAT plan， the GI of the IMPT plan for patients with nasopharyngeal carcinoma and parotid gland carcinoma was lower than that of the VMAT plan， and the GI of the IMPT plan for patient with laryngeal carcinoma was higher than that of the VMAT plan， and all were within the clinically acceptable range. The IMPT plan has demonstrated significant dose advantages in the treatment of nasopharyngeal carcinoma， parotid gland carcinoma and laryngeal carcinoma. For patient with nasopharyngeal carcinoma， the IMPT plan reduced the D_max of the left and right crystals by 54.1% and 50.4%， respectively， compared to VMAT plan， and reduced the D_mean of the oral and laryngeal tissues by 40.5% and 49.6%， respectively. For patient with parotid gland carcinoma， IMPT plan reduced the D_max of the brainstem and spinal cord by 66.2% and 40.5%， respectively， compared to VMAT plan. For patient with laryngeal carcinoma， IMPT reduced spinal cord D_max by 77.0%， while thyroid cartilage D_mean increased by 8.0% compared to VMAT plan. For the additional dose in the patients' body， taking the absolute volumes occupied by the prescribed dose areas of 10%， 30%， and 50% in the patients' body as examples， IMPT plan of nasopharyngeal carcinoma patient decreased by 29.7%， 29.6%， and 34.9% compared to VMAT plan， respectively. IMPT plan of parotid gland carcinoma patient decreased by 61.0%， 39.7%， and 17.4% compared to VMAT plan， respectively. IMPT plan of laryngeal carcinoma patient decreased by 63.9%， 31.7%， and 4.1% compared to VMAT plan， respectively. Conclusions Compared with VMAT plan， IMPT plan can effectively reduce the irradiation dose of most organs at risk near the target of head and neck tumors， but the dose of string organs close to the target area may be higher， which needs attention.

Key words: Head and neck neoplasms, Radiotherapy, Proton therapy, Dosimetry