Potential benefits of adaptive intensity modulated proton therapy in nasopharyngeal carcinomas: a planning comparison study

Abstract Background To investigate potential advantages of adaptive intensity modulated proton beam therapy (A-IMPT) by comparing it to adaptive intensity modulated X-ray therapy (A-IMXT) for nasopharyngeal carcinomas (NPC). Methods Six patients with NPC treated with A-IMXT (step and shoot approach) and concomitant chemotherapy between 2015 and 2016 were selected. In the actual treatment, 46 Gy in 23fr fractions was prescribed using the initial plan and 24 Gy/12fr was prescribed using an adapted plan thereafter. New treatment planning of A-IMPT was made for the same patients using equivalent dose fractionation schedule and dose constraints. The dose volume statistics based on deformable images and dose accumulation was used in the comparison of A-IMXT with A-IMPT. Results The mean doses to the right parotid gland (p = 0.004), left parotid gland (p = 0.012), the oral cavity (p < 0.001), the thyroid gland (p = 0.047), the supraglottic larynx (p < 0.001), the glottic larynx (p = 0.001), the superior pharyngeal constrictor muscle (PCM) (p < 0.001), the middle PCM (p = 0.002), the inferior PCM (p < 0.001), and the cricopharyngeal muscle (p = 0.031) in A-IMPT are statistically significantly lower than those of A-IMRT with the statistical significance. The mean dose to the oral cavity, supraglottic larynx, and glottic larynx were all reduced by more than 20 GyE. Conclusion The adaptive approach is suggested to enhance the potential benefit of IMPT compared to IMXT to reduce adverse effects for patients with NPC.