Dosimetric comparison of vmat and rapidarc for nasopharyngeal carcinoma


Thesis Type: Postgraduate

Institution Of The Thesis: Uludağ Üniversitesi, Turkey

Approval Date: 2017

Thesis Language: Turkish

Student: ÖZCAN ÖZDEN

Supervisor: CANDAN DEMİRÖZ ABAKAY

Abstract:

The aim of this study is to evaluate target volume, conformity index (CI), homogeneity index (HI), risky organs and monitor unit (MU) by comparing two different Volumetric Modulated Arc Therapy (VMAT) techniques for nasopharyngeal cancers. Computer tomography images of 20 patients with advanced stage nasopharyngeal carcinoma were contoured on target volumes and locations of critical organs. Treatment plans were prepared for Elekta Synergy lineer accelerator which using Monaco TPS and Varian Trilogy lineer accelerator which using Eclipse TPS and treatment plans were prepared double arc (mutually overlapping) and collimator angles for each arc is 30-330 degrees. The target volume was calculated from 33 fractions (fx) by the simultaneous integrated boost (SIB) technique and the results were compared. In this study, volumetric arc therapy technique for Elekta was named "Elekta VMAT" and for Varian it was named "RapidArc". Although both tecniques are clinically acceptable, Elekta VMAT has succeeded in RapidArc technique in terms of wanted target dose. Elekta VMAT technique has kept the doses a little lower on critical organs such as brain stem, medulla spinalis than the wanted values for recurrence of the cancer or re-irradiation of the patient due to secondary cancers, although the risky organ doses can be accepted in both TPS plans. In addition, Elekta VMAT was superior in terms of CI and HI values. However, with the patient's lens, optic nerve doses and monıtor unit, the RapidArc technique yielded more successful results. As a result, although there are statistically significant differences between the treatment plans made in both techniques, the values are the acceptable limits. Depending on the condition of the patient one of the two techniques can be selected.