Dose-Volume Comparison of IMRT and PSPT Treatment Plans for Early-Stage Glottic Cancer.

Takahiro Kato,Nobukazu Fuwa,Masao Murakami

doi:10.14338/ijpt-20-00008.1

Abstract

PurposeTo clarify the dose distribution characteristics for early-stage glottic cancer by comparing the dose distribution between intensity-modulated radiation therapy (IMRT) and passive scattering proton therapy (PSPT) and to examine the usefulness of PSPT for early-stage glottic cancer.Materials and MethodsComputed tomography datasets of 8 patients with T1-2 glottic cancer who had been treated by PSPT were used to create an IMRT plan in Eclipse with 7 fields and a PSPT plan in XiO-M with 2 fields. Organs at risk (OARs) included the carotid arteries, arytenoids, inferior constrictor muscles, strap muscles, thyroid cartilage, cricoid cartilage, and spinal cord. The prescription dose was 66 GyRBE in 33 fractions to the planning target volume (PTV). All plans were optimized such that 95% of the PTV received 90% of the prescription dose considering that the skin was slightly spared.ResultsThe superiority of the PSPT was confirmed in all OARs. In the PSPT, the dose to the contralateral carotid artery and the spinal cord, which is slightly distant from the PTV, was dramatically reduced while maintaining the dose distribution uniformity of the PTV by comparison with IMRT.ConclusionPSPT for early-stage glottic cancer resulted in good target dose homogeneity and significantly spared the OARs as compared with the IMRT. PSPT is expected to be effective in reducing late effects and particularly useful for young people.

Highlights

Early-stage glottic cancer is highly curable with conventional parallel opposed radiation therapy (RT) and is expected to have a long survival
Dose distribution was very limited in the proton therapy (PT), while the middle- to low-dose range tended to spread with intensity-modulated radiation therapy (IMRT)
The volume receiving dose 35 GyRBE (V35) of both carotid arteries showed no significant difference between IMRT and PT, and both methods contributed to reduction of the carotid artery dose

Summary

Introduction

Early-stage glottic cancer is highly curable with conventional parallel opposed radiation therapy (RT) and is expected to have a long survival. Late side effects are not ignored especially in patients younger than 60 years [1]. Conventional RT preserves laryngeal function, but bilateral carotid arteries are usually injured from high radiation doses. It is hypothesized that the radiation disrupts the endothelial barrier of carotid vessels. Fokkema et al [2] examined histologic characteristics of carotid plaques from patients with prior RT and found more fibrous and less inflammatory plaques compared with those derived from non-RT patients. Radiation therapy is one of the risk factors accelerating carotid atherogenesis that may raise cerebrovascular events

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Discussion

Conclusion