Validation of the Octavius 4D Measuring System in Verifying Advanced External Beams Radiotherapy Techniques

Document Type : Original Article

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radiotherapy department ,faculty of medicine , Ain shams university , cairo , Egypt

Abstract

The development of advanced techniques as Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are characterized by their numerous steep dose gradient using the dynamic MLC modality and these requires specific quality assurance (QA) to meet this complexity. The conventional dosimetery techniques, such as ionization chamber, point dose measurements and film dosimetry, are gradually being replaced by detector arrays which can produce accurate results immediately. There are many commercial detector arrays one of them is 2D-ARRAY seven29 (PTW, Freiburg, Germany). We used the Octavius 4 D measuring system with its detector array, ionization chamber. The accuracy of the synchronizing motion of the phantom was validated. It was found that the detector array response is stable after warming up with 800 MU, the dose rate measurements and the dose response is linear with R2=0.929. The gamma index for the clinical IMRT plans were found to be 93.3%, 98.0 %, 95.5% and 96.2% for head and neck, prostate, breast and brain cases, and for VMAT plans are 96.3%, 99.4 %, 98.1% and 98.6% for head and neck, prostate, breast and brain, respectively, using gamma criteria 3%/3 mm. The aim of this work is to characterize and validate the Octavius 4D measuring system for 6MV beams. Also, to verify clinical IMRT and VMAT plans, the volumetric dose matrix of the clinical plans, dose line profiles and to study the factors affect the gamma index.

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