Semester of Graduation

Summer 2023

Degree

Master of Science (MS)

Department

Department of Physics & Astronomy

Document Type

Thesis

Abstract

Purpose: Irregular surfaces in bolus electron conformal therapy (BECT) create target volume dose inhomogeneity, which off-axis intensity modulation (IM) can reduce. This research developed and tested a patient-specific clinical quality assurance (QA) procedure for fabricated Passive Radiotherapy Intensity Modulation for Electrons (PRIME) devices used for IM-BECT delivery.

Methods: To evaluate MapCheck3 (MC3) diode array accuracy, electron dose measurements beneath PRIME devices were compared with scanned measurements in a water phantom. Lateral dose profile comparisons were made for 35 combinations of five beam energies (7-20MeV) and seven PRIME devices - converging and diverging island blocks (pins) having 100-68.8% intensities. To evaluate for QA, MC3 dose measurements beneath PRIME devices were compared with dose calculated in water by .decimal’s ElectronRT (eRT) planning system. Comparisons were made for combinations (70) of seven energies (7-20MeV) and ten PRIME devices having 100-68.8% intensities with small random, large random, and large systematic fabrication errors. Dose distributions were compared using γ-test analysis, with dose difference/distance-to-agreement of 3%/2mm, as recommended by AAPM TG-218. Similarly, nine PRIME devices were designed within an IM-BECT eRT plan using patient data. Underlying MC3-measured and eRT-calculated dose distributions in water were compared.

Results: MC3 doses agreed well with lateral profiles measured by a scanning diode, with maximum dose difference

Conclusions: The MC3 diode array was shown suitable for QA of PRIME devices. Although paralleling TG-218 x-ray IMRT QA procedure for a single IM field produced acceptable ϒ-test passing rates for properly constructed test PRIME devices, it did not produce failing rates for some constructed with significant random or systematic errors. Further investigation could improve analysis criteria for QA of PRIME devices. Lastly, MC3 QA measurements for nine patient-specific IM-BECT PRIME devices begin populating a database for testing future QA analysis criteria.

Date

7-10-2023

Committee Chair

Pitcher, Garrett

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