Feasibility Study of Pharyngeal Constrictor Muscle Sparing In Proton Radiotherapy for Nasopharyngeal Carcinoma Based on MRI/CT Fusion Image
Abstract
Purpose
To contour the PCMs utilizing MRI/CT image fusion technology and to evaluate the feasibility of PCM-sparing in proton therapy for NPC.
Methods
Simulated MR and CT images from 30 NPC patients were retrospectively reviewed in this study. The PCM together with its structures: superior PCM (sPCM), middle PCM (m PCM), and inferior PCM (iPCM) was contoured on fused MRI/CT images based on anatomical landmarks. Four treatment plans were designed for each patient: photon intensity-modulated radiation therapy (IMRT); IMRT with PCM sparing (IMRT-S); intensity-modulated proton therapy (IMPT); IMPT with PCM sparing (IMPT-S). Related dosimetric parameters between the four plans were compared.
Results
The four plans met the prescribed target coverage rate criteria. A statistically significant difference was observed in both conformity index (CI) and homogeneity index (HI) between IMRT-S vs IMPT-S and IMRT vs IMPT (p 0.05). However, compared with IMRT-S, IMPT-S can reduce PCM dose including the mean dose (Dmean), maximum dose (Dmax), V40, V50, V60, V65 by 7.8 Gy, 2.5Gy, 9.4%, 34.6%, 16.8%, 13.1% respectively. Dmean, Dmax, V50, V60, and V65 of mPCM and iPCM from IMPT-S were also lower than those of IMRT-S (p<0.05).
Conclusion
IMRT-S for NPC can reduce most of the dose parameters of PCM while contouring PCM as an organ-at-risk (OAR) during treatment planning optimization. Moreover, this study also demonstrates more dosimetric advantages for IMPT-S in NPC RT.