Effect of Gantry Increment on Volumetric Modulated Intensity Arc
Therapy for Nasopharyngeal Carcinoma
LI Zhenghuan1, CHENG Yuan2, YUAN Wei3, WU Weiwei4
1. Department of Radiation Oncology, The Third Affiliated Hospital of Sun Yat-Sen University, Guangzhou Guangdong 510630, China;
2. Department of Radiotherapy, Fuzhou No.1 Hospital Affiliated with Fujian Medical University, Fuzhou Fujian 350009, China;
3. Department of Radiotherapy, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an Shaanxi 710061, China;
4. Department of Radiotherapy, Ganzhou Cancer Hospital, Ganzhou Jiangxi 341000, China
Abstract：Objective To explore the influence of gantry increment on volumetric modulated arc therapy (VMAT) for
nasopharyngeal carcinoma. Methods Fifteen patients with nasopharyngeal carcinoma were selected to design four VMAT plans
with gantry increment of 10°, 20°, 30° and 40°, and named as Inc10, Inc20, Inc30 and Inc40, respectively. The target dose, exposure
dose of organ at risk (OAR), segments, monitor unit and plan delivery time in different plans were compared. Results The dose
parameters of planning tumor volume (PTV) and OAR of Inc10 did not meet the clinical requirements. For PTVnx, there was no
statistically significant difference between D2 and homogeneity index (HI) in Inc20, Inc30 and Inc40 (P>0.05), there was significant
difference of the D50 between Inc20 and Inc40 (P<0.05), the difference between Inc20, Inc30 and Inc40 of CI was statistically
significant (P<0.05). For PTVnd, the difference between Inc20 and Inc40 of D2, HI and D50 was statistically significant (P<0.05), the
difference between Inc20, Inc30 and Inc40 of CI was statistically significant (P<0.05). For PTV1, the difference between Inc20 and
Inc40 of D2 was statistically significant (P<0.05), the difference between Inc20, Inc30 and Inc40 of D50 was statistically significant
(P<0.05), there was no statistically significant difference among Inc20, Inc30 and Inc40 of HI (P>0.05), the difference between
Inc20 and Inc40 of CI was statistically significant (P<0.05). For PTV2, the difference between Inc20 and Inc40 of D2, D50, HI and
CI was statistically significant (P<0.05), and there was no statistically significant difference of D2, D50, HI and CI between Inc30
and Inc40 (P>0.05). There was no significant difference in the dose parameters of temporomandibular joint, spinal cord, brainstem and parotid gland between Inc20 and Inc40 (P>0.05). The monitor unit (MU) and plan delivery time (PDT) decreased with the
increase of the gantry increment. The number of segments was the least in Inc30, and the plan delivery time (PDT) was the lowest in
Inc10, and the plan delivery time was the highest at Inc40. There was no significant difference in the PDT of Inc20, Inc30 and Inc40
plans. Conclusion When designing VMAT plan for nasopharyngeal carcinoma, the gantry increment of 40° can obtain better dose
distribution in target area and reduce the dose of OAR and normal tissues without reducing the execution efficiency of the plan.
