ArcCheck Hypothesis Testing: Is Dose Error in a Phantom Applicable to the Patient?
J Barbiere1*, A Ndlovu2, (1) ,,,(2) Hackensack Univ Medical Center, HACKENSACK, NJSU-E-T-175 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: The purpose of this work is to present a technique by which we are able to measure the error produced by computing the delivered dose to a patient based on the dose delivered to a uniform density cylindrical phantom.
Methods:ArcCHECK by Sun Nuclear (3DVH, Sun Nuclear Corp., Melbourne, FL) has the desirable ability to perform VMAT QA and configure the results in the form of a DVH similar to the original plan evaluation. In this work we examine the hypothesis that measured errors in a phantom translate very closely to those in a 3D patient.
It is possible to create Verification Plans (VP) whereby the treatment fields for a lung patient are applied to both the patient data set (VPpatient) and a predefined phantom data set (VPphantom). The VP 360 arcs are subdivided into 30 degree sectors. The most useful feature of the VP is that we now have the ability to make changes. Each of the individual sectors is essentially an independent control point with alterable treatment aperture and Monitor Units. We modified a control point in the phantom (VPphantomModified) to see the effect on the patient (VPpatientModified).
We tested the hypothesis in the two dimensional isocenter plane by exporting the four relevant dose matrices to MATLAB and performing the calculations as described by Sun Nuclear.
Results:The amount of error greater then the traditional acceptance vale of 3% can be significant. Most of this error is concentrated in the lung and rib regions as would be expected from their greatest deviation from the uniform density in the phantom.
Conclusion:This work shows a technique whereby the user of Sun Nuclear ArcCHECK can verify and quantify the hypothesis that measured dose error in a homogenous phantom is applicable to a heterogeneous patient.
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