Program Information
Challenges In The Clinical Implementation Of Dose Adaptive Radiation Therapy Using EPID Based Transit Dosimetry
A Sankar*, D Welsh , D Burns , F Henriquez , G Cooke , W Nailon , Edinburgh Cancer Centre, Edinburgh, Scotland
Presentations
SU-I-GPD-J-90 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To understand the constraints in the clinical implementation pathway of dose adaptive radiation therapy using EPID based transit dosimetry and address them to improve the reliability of the process.
Methods: EPID based transit dosimetry is routinely practiced in our centre using Dosimetry Check software (Math Resolutions Inc, USA) for treatments delivered from six Linear accelerators (Varian, USA). Integrated and Continuous data acquisition modes are used for conformal and Volumetric Modulated arc therapy (VMAT) respectively. Treatment plans for the conformal treatments were performed using Eclipse (Varian, USA) pencil beam algorithm and VMAT treatments were performed using Analytical Anisotropic Algorithm. Cone beam CTs acquired from head & neck VMAT treatments were used in the dose adaptive pathway to understand the constraints associated with the process flow. Mirada Medical Imaging software is used to register and deform the planning CT datasets with Cone beam CT datasets.
Results: The constancy check of EPIDs using the central pixel values acquired with 100MU delivery from 10x10 reference field varies within ±3.0% and ±5.0% for the True beam and C-series accelerators respectively. The accuracy of transit dosimetry calculation improved for VMAT deliveries if corrections are applied from integrated image. The detailed analysis of transit dosimetry results from 2953 conformal treatments and 842 VMAT treatments reliably linked the out-of-tolerance results with set-up errors, patient preparation differences and anatomy changes. The accuracy of transit dosimetry calculations using deformed planning CT datasets outweighs the calculations performed on cone beam CT datasets.
Conclusion: The accuracy of calculated transit dose supporting the dose adaptive pathway relies on the tighter quality control of the EPID’s, better understanding of the data acquisition modes and accuracy of algorithms employed in image processing and transit dosimetry calculation software. The technical improvements with amorphous silicon based EPIDs to address the dosimetry aspects will enhance the reliability of transit dosimetry and hence dose adaptive radiotherapy.
Contact Email: