Validation and comparison of intensity modulated radiation therapy patient plans with Octavius 4D Phantom using the Gamma Index analysis in 2D and 3D

Abstract

Author(s): Sanae Douama, Moulay Ali Youssoufi, Mohammed Bougtib, Youssef Bouzekraoui*, Mohamed Ait Erraisee, Fatima Zahra Abboud, Souad Oubelkacem, Khalid Hassouni, Khalid Hassouni, Drissi Lalla btissam and Farida Bentayeb

Purpose: The aim of this work is to investigate the dose verification of common conventional Intensity Modulated Radiation Therapy (IMRT) Quality Assurance (QA) performance metric using verisoft software. Based on Gamma index analysis we performed a comparison between 2D and 3D of the delivered and planed dose for complex geometry, Gamma index passing rate (GP%) is calculated using different criteria 3%/3 mm, 3%/2 mm and 2%/2mm dose difference/ distance-to-tolerance criteria (DD/DTA) to check the quality the plan before starting the treatment .

Materials and methods: Ten complex Intensity Modulated Radiation Therapy (IMRT) (80 beams) plans for two different pathologies are calculated using the Eclipse Treatment Planning System (TPS), Pre-treatment verifications were performed for all patients plans by acquiring planar dose distributions of each treatment field with 2D-diode array Octavius 4D cylindrical phantom that is matrix composed of 1500 ionisation chambers with a size of 4.4 × 4.4× 3 mm³, whose centres are separated two by two by 7.07 mm. Measured dose and calculated dose were compared by using Gamma index method, and pass/failed test were generated foe each pair of planar doses using the following acceptance criteria 3%/3 mm, 3%/2 mm and 2%/2mm. During the pre-treatment verification we acquired the dose distribution with DICOM RT plan, RT stricter set, and RT dose file from TPS, and then we loaded all plans into the verisoft softwar to analyse each individual plan.

Results: Overall, a good correlation was observed between the measured and calculated doses in most of the beams with success agreement of the Gamma index for 3D analysis being 99% compared to 2D which was 97.11% for the 3%/3mm criterion. The average difference in the percentage of passing pixels between the 2D and 3D analyses ranged from 0.9% to 2%.

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