Room: Exhibit Hall | Forum 7
Purpose: Quality assurance in radiotherapy does not include daily measures for each treatment field for each patient. This study explores the clinical use of an automated electronic portal imaging device (EPID) for measuring the exit dose for daily treatments in order to identify and characterize the magnitude and reason for dosimetric errors
Methods: The automated PerFRACTION system was used to collect daily integrated EPID exit dose images from each field from 60 treatment courses. In total, 4,079 daily field values (DFV) from 855 fractions were analyzed by the system using the Gamma index. The image from the first treatment day (reference) was compared to images from subsequent days (fraction N). Gamma tolerance values of 2%, 2mm and 3%, 3mm dose and distance to agreement were used to assess accuracy of treatment. Using 93% of pixels passing the Gamma test as the cutoff, pass-fail status was categorized by treatment modality and location. An attempt was made to identify the causes of all DFV failures.
Results: Overall, 20.5% of DFV failed at the 2%, 2mm tolerance level. However, 48% of fields experienced at least one DFV failure during the course of therapy. 3DCRT treatments failed at a higher rate than IMRT treatments. Chest, spine and head and neck treatments had the highest rates of failure. The most commonly identified reason for DFV failure was body position change, but this varied by location and modality, and the reason for approximately half of DFV failures could not be identified.
Conclusion: Analysis of EPID images revealed that dosimetric variations were present in a clinically relevant percentage of treatments. The reasons for failure were identifiable approximately half the time. Daily collection of EPID images using an automated system is a practical and effective way of monitoring dose delivery accuracy during radiotherapy and can provide actionable information.
Funding Support, Disclosures, and Conflict of Interest: Arthur Olch receives research funding from Sun Nuclear Corporation but was not funded for this work.
Not Applicable / None Entered.