Influence of increment of gantry in volumetric modulated arc therapy plan on unilateral and bilateral target volumes of head and neck

doi:10.19438/j.cjoms.2024.06.011

Abstract

Abstract: PURPOSE: To investigate the effect of increment of gantry(INC) in the Monaco treatment planning system on VMAT plan, and provide reference for optimizing the parameters of radiotherapy plan. METHODS: A total of 15 patients with parotid gland cancer and 15 patients with tongue cancer requiring postoperative radiotherapy were selected from Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine from January to December 2022. Bilateral irradiation was used in tongue cancer group and unilateral irradiation in parotid gland cancer group. Except for changing the Inc parameters, the planning design parameters of the same case should not be changed, and the optimization results of planned dose should meet the requirements of clinical use. The optimization grouping angles of 20, 25, 30, 35, and 40 were compared, and the plan made from the optimization grouping angle of 30 was used as a reference plan. D_98%,D_5% and D_2%, as well as the conformity index(CI) and homogeneity index(HI) were calculated and compared. The organ at risk dose parameters and planned jumps caused by different Inc parameter plans were also compared. SPSS 22.0 software package was used for data analysis. RESULTS: The results of tongue cancer group with bilateral irradiation showed that when the Inc parameter was set to 30, the normalization of the target area was better. Compared with the control group, the target area HI of the other Inc parameter plans were significantly different. Except for the Inc35 plan, all other CI had significant differences. In terms of organ endangerment, except for the left parotid gland, the optimal angle of 30 for the right parotid gland and larynx was the best(P<0.05). There was no significant difference in the spinal cord, while 20 and 35 for the left parotid gland were the best(P<0.05). The results of the parotid gland cancer group plan with unilateral irradiation showed that the optimal angle of 30 had better performance and better normalization of the target area. There was significant difference (P<0.05) in the evaluation results of HI. The ipsilateral middle ear Inc was 20, and 25 performed better(P<0.05). The results were better when the distance between laryngeal tissue angles was 20, 25, and 40(P<0.05), and the best performance was when the distance between mandibular angles was 25(P<0.05). There was no significant difference in the spinal cord, brain stem, and contralateral parotid gland. The number of hops for all plans increased with the increment of Inc, and there was no significant difference in the monitor units for both unilateral and bilateral irradiation plans. CONCLUSIONS: The Inc selection of volumetric modulated arc therapy plan needs to be reasonable based on the irradiation range and tumor type. The default value of Inc is 30, which shows more advantages in the tongue cancer target area plan with bilateral irradiation. But for parotid gland tumors with unilateral irradiation, except for certain advantages in the target area, other advantages are not significant.

Key words: Head and neck tumor, Radiotherapy, Volumetric modulated arc therapy, Increment of gantry, Unilateral and bilateral target

CLC Number:

R739.8

SHI Hui-feng, TU Wen-yong, BI Fan. Influence of increment of gantry in volumetric modulated arc therapy plan on unilateral and bilateral target volumes of head and neck[J]. China Journal of Oral and Maxillofacial Surgery, 2024, 22(6): 584-589.

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