Dosimetric Studies of VMAT for Prostate Cancer: Comparison of Single and Mixed Energy Techniques
PO-1853
Abstract
Dosimetric Studies of VMAT for Prostate Cancer: Comparison of Single and Mixed Energy Techniques
Authors: YUEN|, Adams Hei Long(1)*[yhladams@hotmail.com];
(1)The University of Hong Kong, Department of Diagnostic Radiology and Clinical Oncology- Li Ka Shing Faculty of Medicine, Hong Kong, Hong Kong SAR China;
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Purpose or Objective
Utilization of high energy photons with an optimal weight using a mixed energy technique is considered as a practical way to spare organs-at risk (OARs) while maintaining adequate target coverage in radiotherapy. The present study compared the dosimetric performance of single energy VMAT plans (SEP) using 6MV photon and 10MV photon, and a mixed energy VMAT plan (MEP) using both 6MV-10MV photon, in the treatment of stage IIIB prostate cancer.
Material and Methods
A cohort of 20 patients with stage IIIB prostate cancer were recruited in this retrospective study. All patients have undergone computed tomography simulation in supine position. SEP using 6MV photon and 10MV photon, and MEP using both 6MV-10MV photon, were generated for each patient. All VMAT plans comprised of 2 full arcs (181°-179° and 179°-181°). Collimator angle pair of 30° and 330° were used to reduce tongue-and-groove effect in multi-leaf collimators. Location of isocentre and field size at each angle were adjusted and defined according to the PTV in each case by the VMAT optimizer. Plan metrics from 3 techniques were compared using one-way repeated measures ANOVA. The magnitude and statistical significance of the observed dosimetric differences were quantified. The optimization objectives were not modified or individualized between patients to avoid introducing bias.
Results
Averaged results of planned target volume (PTV) and OARs were summarized in table 1. The typical iso-dose distribution of the 3 treatment techniques were demonstrated in figure 1. There were no significant difference in PTV coverage between 3 techniques (p>0.05). The results demonstrated that both 10MV SEP and 6MV-10MV MEP are capable to reduce radiation dose to the rectum and bladder (p<0.05), comparing with 6MV SEP. In addition, 10MV SEP was also compared favorably in PTV homogeneity and to reduce skin dose than 6MV SEP and 6MV-10MV MEP.
Conclusion
Superior rectum and bladder sparing ability were observed for 10MV SEP and 6MV-10MV MEPs. 10MV SEP have also exhibited the superior result in generating the least skin dose and PTV dose homogeneity. In conclusion, the present study serves as an initial reference of dosimetric performance between SEP and MEP for patient with stage IIIB prostate cancer.