The Hippocampus Sparing Volume Modulated Arc Therapy does not Influence Plan Quality on Locally Advanced Nasopharyngeal Carcinoma Patients

Wendong Gu,Ye Tian,Qilin Li,Honglei Pei,Juncong Mo,Dan Xi

doi:10.1038/s41598-017-03517-y

Abstract

Irradiation on hippocampus would lead to neuro-cognitive dysfunction in locally advanced nasopharyneal carcinoma (LA-NPC) patients accepting radiotherapy. Our study here aimed to investigate if undergoing hippocampus sparing (HS) volume modulated arc therapy (VMAT) would influence the plan quality in LA NPC patients. We designed three kinds of radiotherapeutic plans for 11 LA NPC patients: conventional VMAT (C-VMAT), HS-VMAT and HS intensity modulated radiation therapy with dynamic multileaf collimator (HS-dMLC). And the dose distribution on targets and surrounding organs at risk (OAR) were carefully evaluated. We found out that the expected doses on hippocampus were significantly lowered in HS-VMAT (899 ± 378 cGy) and HS-dMLC (896 ± 321 cGy) as compared to C-VMAT (1518 ± 337 cGy, p < 0.05), but meaningless difference was presented on plan quality of targets (p > 0.05). Moreover, lower radiation doses on brain stem were observed in HS-VMAT plan in comparison with C-VMAT plan (p < 0.05). However, there were no statistically meaningful diversities in the doses received by other OARs among all plans. Here we concluded that HS-VMAT presented promising advantages on protecting hipppcampus and brain stem as compared to C-VMAT and HS-dMLC, but enthusiastically had no effects on plan quality in LA-NPC patients.

Highlights

We designed three radiotherapeutic plans of conventional volume modulated arc therapy (VMAT) (C-VMAT), hippocampus sparing VMAT (HS-VMAT), and HS intensity modulated radiation therapy with dynamic multileaf collimator (HS-dMLC) for each LA NPC patient recruited into our study
HS-VMAT plan had no effect on the dose parameters for targets as compared to C-VMAT
No statistical significance was observed in the dose coverage of targets in all the 11 LA NPC patients in the two plans of C-VMAT and HS-VMAT (p > 0.05)

Summary

Methods and Meterials

All patients received computed tomography (CT) and magnetic resonance imaging (MRI), all the images were transferred to Monaco 5.10 TPS for further processing. According to The consensus on the target’s delineation for NPC among Chinese experts 201010 and RTOG 0615 protocol[11], targets and surrounding normal organs were contoured: (1) GTVnx: visible nasopharyngeal neoplasms in the images of MRI and planning CT; (2) GTVnd: cervical lymph node metastasis; the retropharyngeal lymph node metastasis was not defined separately; (3) CTV: adding 0.5 cm~1 cm margin to GTVnx and including the posterior nasal, posterior maxillary sinus, pterygopalatine fossa, part of ethmoid sinus, parapharyngeal gap, the base of the skull, part of the cervical vertebrae, the clivus and cervical lymph drainage zones; for simplifying the study, all cervical lymph drainage zones were seen as a part of CTV. We designed three radiotherapeutic plans of conventional VMAT (C-VMAT), hippocampus sparing VMAT (HS-VMAT), and HS intensity modulated radiation therapy with dynamic multileaf collimator (HS-dMLC) for each LA NPC patient recruited into our study. Data were analyzed by one-way analysis of variance (ANOVA One-Way) and the least-significant difference method (LSD), with p < 0.05 considered as statistical significance

Results

Discussion

Conclusion