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

Tianjun Ma,Lalith K Kumaraswamy,Matthew B Podgorsak

doi:10.1120/jacmp.v17i5.6344

Tianjun Ma, Lalith K Kumaraswamy + Show 1 more

Open Access

https://doi.org/10.1120/jacmp.v17i5.6344

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Abstract

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

Highlights

The delivery of an optimum dose distribution is made possible by the complex motions of the multileaf collimators (MLC) in intensity-modulated radiation therapy (IMRT)
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] 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
For 2D 3%/3 mm analysis, over half of the -3% and +3% monitor unit (MU) modified plans yielded passing rates less than 95%, due to fact that 3% is at the tolerance boundary

Summary

Introduction

The delivery of an optimum dose distribution is made possible by the complex motions of the multileaf collimators (MLC) in intensity-modulated radiation therapy (IMRT). The advent of volumetric-modulated arc therapy (VMAT) employing dynamic MLCs, variable dose rate, and variable gantry speed, further escalates the need for extensive quality assurance prior to treatment delivery. Analysis indicates how the measured dose to the phantom agrees with planned dose in the TPS. Even though GI and DTA are good indicators of deliverability of dynamic treatment plans, larger differences in a relative small volume might be overshadowed in the overall passing rate, resulting in clinically unacceptable doses to target structures and OARs.[4,5] new approaches based on measurement-reconstructed dose distributions are being investigated to predict clinically relevant results.[6]

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