Catching errors with in vivo EPID dosimetry

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.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sensitivity study of an automated system for daily patient QA using EPID exit dose images

Zhuang

Olch

2018

“…Nonetheless, there are many arguments in favor of in vivo dosimetry (IVD), that is, a method to measure the dose deposited in the patient during treatment, as an auxiliary optimization and safety procedure. IVD can identify errors in dose calculation, data transfer, patient setup, and dose delivery, and may be used as a trigger for adaptive radiotherapy in cases of changing patient anatomy 1 , 2 , 3 . More importantly, most RT errors which have led to serious patient injury or death 4 , 5 , 6 could have been avoided or reduced with IVD.…”

Section: Introductionmentioning

confidence: 99%

“…Another tool for in vivo dosimetry, which has been largely investigated but used clinically only in few select sites, (1) is the electronic portal imaging device, or EPID. The intensity of the transit portal image (acquired through the patient during treatment) can be related to the dose absorbed by the patient.…”

Section: Introductionmentioning

confidence: 99%

Two‐dimensional in vivo dose verification using portal imaging and correlation ratios

Peca

Brown

2014

The electronic portal imaging device (EPID) has the potential to be used for in vivo dosimetry during radiation therapy as an additional dose delivery check. In this study we have extended a method developed by A. Piermattei and colleagues in 2006 that made use of EPID transit images (acquired during treatment) to calculate dose in the isocenter point. The extension allows calculation of two‐dimensional dose maps of the entire radiation field at the depth of isocenter. We quantified the variability of the ratio of EPID signal to dose in the isocenter plane in Solid Water phantoms of various thicknesses and with various field sizes, and designed a field edge dose calculation correction. To validate the method, we designed three realistic conventional radiation therapy treatment plans on a thorax and head anthropomorphic phantom (whole brain, brain primary, lung tumor). Using CT data, EPID transit images, EPID signal‐to‐dose correlation, and our edge correction, we calculated dose in the isocenter plane and compared it with the treatment planning system's prediction. Gamma evaluation (3%, 3 mm) showed good agreement (Pγ<1 ≥ 96.5%) for all fields of the whole brain and brain primary plans. In the presence of lung, however, our algorithm overestimated dose by 7%–9%. This 2D EPID‐based in vivo dosimetry method can be used for posttreatment dose verification, thereby improving the safety and quality of patient treatments. With future work, it may be extended to measure dose in real time and to prevent harmful delivery errors.PACS numbers: 87.55.km, 87.55.Qr, 87.55.T‐

“…This error was designed to test the sensitivity of the 3DVH system in detecting dose deviations due to changes in MU. For CP deletion study, three, five, and eight control points were deleted from each arc of the error‐free plans so as to simulate the potential data loss resulting from transferring plans via the network (18) . Finally, uniform gantry angle deviations were introduced to six of the plans to test the magnitude of dose fluctuation that could potentially be introduced from gantry angle variation.…”

Section: Methodsmentioning

confidence: 99%

Accuracy of one algorithm used to modify a planned DVH with data from actual dose delivery

Podgorsak

Kumaraswamy

2016

Detection and accurate quantification of treatment delivery errors is important in radiation therapy. This study aims to evaluate the accuracy of DVH based QA in quantifying delivery errors. Eighteen previously treated VMAT plans (prostate, H&N, and brain) were randomly chosen for this study. Conventional IMRT delivery QA was done with the ArcCHECK diode detector for error‐free plans and plans with the following modifications: 1) induced monitor unit differences up to ±3.0%,2) control point deletion (3, 5, and 8 control points were deleted for each arc), and 3) gantry angle shift (2° uniform shift clockwise and counterclockwise). 2D and 3D distance‐to‐agreement (DTA) analyses were performed for all plans with SNC Patient software and 3DVH software, respectively. Subsequently, accuracy of the reconstructed DVH curves and DVH parameters in 3DVH software were analyzed for all selected cases using the plans in the Eclipse treatment planning system as standard. 3D DTA analysis for error‐induced plans generally gave high pass rates, whereas the 2D evaluation seemed to be more sensitive to detecting delivery errors. The average differences for DVH parameters between each pair of Eclipse recalculation and 3DVH prediction were within 2% for all three types of error‐induced treatment plans. This illustrates that 3DVH accurately quantifies delivery errors in terms of actual dose delivered to the patients. 2D DTA analysis should be routinely used for clinical evaluation. Any concerns or dose discrepancies should be further analyzed through DVH‐based QA for clinically relevant results and confirmation of a conventional passing‐rate‐based QA.PACS number(s): 87.56.Fc, 87.55.Qr, 87.55.dk, 87.55.km