Dosimetric Benefit Analysis And Prognostic Study Of Helical Tomotherapy For Early-stage Nasopharyngeal Carcinoma

Objective: To explore the dosimetric advantages and disadvantages of helical tomotherapy(HT)compared with volumetric modulated arc therapy(VMAT)and intensity-modulated radiation therapy(IMRT)for early-stage nasopharyngeal carcinoma(NPC)patients.Methods: Forty-four early-stage NPC patients underwent HT between January 2016 to December 2019 in Hunan Cancer Hospital were included.Twenty patients were randomly selected and re-planned by VMAT(three-arcs)and IMRT(nine-fields)for dosimetric comparison.The dosimetric factors of the planning target volumes(PTVs)and organs at risk(OARs)were compared among the three techniques.The survival conditions and all acute and late toxicities of the enrolled patients were counted and analyzed.Results: With the prescribed target coverage,the conformity index(CI)and homogeneity index(HI)obtained for PGTVnx in HT highlight a significant difference(all P ≤0.001)when compared with that for IMRT and VMAT.Regarding dose comparison of OARs,both the maximum and average doses to the spinal cord and brain stem with HT were significantly lower than those with IMRT and VMAT(all P <0.05).HT also achieved the lowest dose to the parotid gland,though the mean dose and V35 were not statistically different from the VMAT plans(P=0.151,P=0.057,respectively).However,HT delivered significantly the highest doses to the optic apparatus and cochlea.In addition,HT was inferior to protect the skin and low-dose volume in the body compared to the other two techniques.During the treatment,all patients suffered varying degrees of radiation oral mucositis and dermatitis,radiation induced ototoxicity(59%)and xerostomia(52%)are the most common chronic toxicities in patients we followed up.Conclusions: Our results indicate that compared to IMRT and VMAT,HT provided the best conformity and homogeneity.For the sparing of OARs,HT showed a strong ability to protect the spinal cord,brain stem and parotid gland while weak in sparing the visual apparatus,cochlea and low-dose radiation volumes.Acute skin and mucosal lesions and chronic ototoxicity and parotid toxicity were the most prominent radiation side effects in patients treated with HT.