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

Abstract

Background 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). 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. Methods The 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. Results Comparisons 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. Conclusion We 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.

A Novel Approach for Position Verification and Dose Calculation through Local MVCT Reconstruction

“…During the treatment process, the EPID transmission images are collected. Based on our previously developed EPID dose verification algorithm [ 27 ], after scatter correction, attenuation correction, and grayscale-intensity conversion, the EPID transmission images can be utilized to calculate the primary fluence values of the accelerator, as shown in Equation (12): where represents the primary fluence of the accelerator’s rays. Because the unit of the EPID image is a grayscale value, which is different from the unit of accelerator fluence value, it needs to be converted through a conversion coefficient , which signifies the linear conversion parameter of the EPID image’s grayscale value to the accelerator’s intensity value.…”

“…During the treatment process, the EPID transmission images are collected. Based on our previously developed EPID dose verification algorithm [27], after scatter correction, attenuation correction, and grayscale-intensity conversion, the EPID transmission images can be utilized to calculate the primary fluence values of the accelerator, as shown in Equation ( 12):…”