A method for in vivo treatment verification of IMRT and VMAT based on electronic portal imaging device

Jun Zhang,Junhai Wen,Miaomiao Lu,Maria F Chan,Ruijie Yang,Xiuqing Li,Xile Zhang,Qilin Zhang

doi:10.1186/s13014-021-01953-9

Abstract

BackgroundIntensity-modulated radiation therapy (IMRT) and volume-modulated arc therapy (VMAT) are rather complex treatment techniques and require patient-specific quality assurance procedures. Electronic portal imaging devices (EPID) are increasingly used in the verification of radiation therapy (RT). This work aims to develop a novel model to predict the EPID transmission image (TI) with fluence maps from the RT plan. The predicted TI is compared with the measured TI for in vivo treatment verification.MethodsThe fluence map was extracted from the RT plan and corrections of penumbra, response, global field output, attenuation, and scatter were applied before the TI was calculated. The parameters used in the model were calculated separately for central axis and off-axis points using a series of EPID measurement data. Our model was evaluated using a CIRS thorax phantom and 20 clinical plans (10 IMRT and 10 VMAT) optimized for head and neck, breast, and rectum treatments.ResultsComparisons of the predicted and measured images were carried out using a global gamma analysis of 3%/2 mm (10% threshold) to validate the accuracy of the model. The gamma pass rates for IMRT and VMAT were greater than 97.2% and 94.5% at 3%/2 mm, respectively.ConclusionWe have developed an accurate and straightforward EPID-based quality assurance model that can potentially be used for in vivo treatment verification of the IMRT and VMAT delivery.

Highlights

Radiotherapy is an effective method for tumor treatment
Compared with the method using only central axis measurement data, our method improves the calculation accuracy of off-axis points and simplifies the calculation process compared with the Monte Carlo (MC) method
The fluence map of a 10 × 10 cm2 field is converted into the open portal image after penumbra correction, response correction, and horn correction

Summary

Introduction

Radiotherapy is an effective method for tumor treatment. Intensity-modulated radiation therapy (IMRT) and volume-modulated arc therapy (VMAT) have become increasingly common in radiation therapy, as they can control the irradiation area more accurately and enable the target area to receive a higher and more conformal dose. Dose verification with EPID is mainly divided into pre-treatment dose verification [5,6,7] and in vivo dose verification [3, 4, 8,9,10,11,12,13,14,15,16]. There is a strong need for in vivo patient-specific quality assurance procedure (QA). Intensity-modulated radiation therapy (IMRT) and volume-modulated arc therapy (VMAT) are rather complex treatment techniques and require patient-specific quality assurance procedures. Electronic portal imaging devices (EPID) are increasingly used in the verification of radiation therapy (RT). The predicted TI is compared with the measured TI for in vivo treatment verification

Objectives

Methods

Results

Discussion

Conclusion