Abstract
The dosimetric consequences of errors in patient setup or beam delivery and anatomical changes are not readily known. A new product, PerFRACTION (Sun Nuclear Corporation), is designed to identify these errors by comparing the exit dose image measured on an electronic portal imaging device (EPID) from each field of each fraction to those from baseline fraction images. This work investigates the sensitivity of PerFRACTION to detect the deviation caused by these errors in a variety of realistic scenarios. Integrated EPID images were acquired in clinical mode and saved in ARIA. PerFRACTION automatically pulled the images into its database and performed the user‐defined comparison. We induced errors of 1 mm and greater in jaw, multileaf collimator (MLC), and couch position, 1° and greater in collimation rotation (patient yaw), 0.5–1.5% in machine output, rail position, and setup errors of 1–2 mm shifts and 0.5–1° roll rotation. The planning techniques included static, intensity modulated radiation therapy (IMRT) and VMAT fields. Rectangular solid water phantom or anthropomorphic head phantom were used in the beam path in the delivery of some fields. PerFRACTION detected position errors of the jaws, MLC, and couch with an accuracy of better than 0.4 mm, and 0.5° for collimator rotation error and detected the machine output error within 0.2%. The rail position error resulted in PerFRACTION detected dose deviations up to 8% and 3% in open field and VMAT field delivery, respectively. PerFRACTION detected induced errors in IMRT fields within 2.2% of the gamma passing rate using an independent conventional analysis. Using an anthropomorphic phantom, setup errors as small as 1 mm and 0.5° were detected. Our work demonstrates that PerFRACTION, using integrated EPID image, is sensitive enough to identify positional, angular, and dosimetric errors.
Highlights
Medical physicists perform a wide array of quality assurance (QA) measures in support of all patient treatments as well as those that are patient-specific prior to the start of treatment
Patient-specific intensity modulated radiation therapy (IMRT) QA tests involving 2D Gamma passing rates commonly done prior to start of treatment have been found to be insufficient to verify the actual dose received by the patient.[1,2]
The smallest jaw position shift, which is 1.5 mm in the electronic portal imaging device (EPID) image, was apparent with the DTA tolerance set to 1.3 mm
Summary
Medical physicists perform a wide array of quality assurance (QA) measures in support of all patient treatments as well as those that are patient-specific prior to the start of treatment. Once treatment has started, other than weekly chart checks, there are few if any efforts to verify ongoing patient-specific treatment delivery accuracy. With the advent of complex treatments and tightening target volume margins, image guided treatments are being performed more frequently with the objective of assuring isocenter positional accuracy and reproducible body pose. These efforts, while necessary, are not sufficient to assure that the correct radiation dose is being delivered daily. Patient-specific intensity modulated radiation therapy (IMRT) QA tests involving 2D Gamma passing rates commonly done prior to start of treatment have been found to be insufficient to verify the actual dose received by the patient.[1,2]
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