Electronic Portal Imaging Device

State-of-the art techniques in photon radiation therapy, such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), are rapidly increasing in clinical routine. These advanced technologies can provide considerably improved dose conformity to the tumor and better sparing of organs at risk. However, the complexity of these techniques adds more dosimetric uncertainties in treatment delivery. Hence, more robust Quality Assurance (QA) tests are advisable to ensure that the dose is correctly delivered as planned. To this end, an Electronic Portal Imaging Device (EPID) rigidly attached to the linear accelerator is an attractive tool showing interesting dosimetric characteristics. Although the primary use of this device is imaging, several groups, including our collaborators from the Maastro Clinic, developed calibration methodologies facilitating its application to dosimetric QA procedures. Yet, the development and improvement of the methods is an ongoing process.

In our research activities, an EPID-based 3D dose reconstruction algorithm was developed for plan-specific pretreatment QA (see figure 1) at the collaborating LMU University Hospital. In parallel, in collaboration with the Universitätsklinikum Mannheim, a linac-specific Geant4 Monte Carlo (MC) model has been developed (figure 2) and is under validation for accurate dose distribution simulations of IMRT and VMAT procedures.
Both dose reconstruction and simulation are part of an envisioned comprehensive QA scheme including patient-specific pre-treatment and in-vivo dosimetry.

Contact:

Dr. Chiara Gianoli
Prof. Dr. Katia Parodi

References:

Alhazmi, Abdulaziz, et al. "A novel approach to EPID-based 3D volumetric dosimetry for IMRT and VMAT QA." Physics in medicine and biology(2018).

Martins, Juliana Cristina, et al. "An equipment-specific Geant4 model for the Elekta Agility collimator." Physica Medica: European Journal of Medical Physics 42 (2017): 30-31.