Date Approved

8-7-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

School of Interdisciplinary Health

First Advisor

Vicente Ornelas, M.S., CMD, RT(T)*

Second Advisor

Kristen Vu, M.S., CMD, RT(T)

Third Advisor

Raj Mitra, PhD, DABR

Academic Year

2025/2026

Abstract

This study evaluated the dosimetric agreement between treatment plans calculated on Varian TrueBeam HyperSight iterative cone-beam computed tomography (iCBCT) and conventional computed tomography (CT) simulation for thoracic treatment planning. Using an anthropomorphic thorax phantom, 12 matched CT and HyperSight iCBCT treatment plans were evaluated across three photon energies and four treatment techniques. Plans were recalculated on the registered iCBCT using identical beam geometry, multileaf collimator apertures, dose calculation algorithm, and grid, without re-optimization. Seven dose-volume histogram endpoints were compared, including target coverage and organ-at-risk doses. Target dose metrics demonstrated strong agreement between CT and HyperSight iCBCT, with planning target volume (PTV) metrics differing by approximately 1% and PTV mean dose showing no statistically significant difference. Heart and spinal cord dose metrics also demonstrated agreement within a few percent. However, HyperSight systematically overestimated mean lung dose and lung V20 by approximately 19%, independent of treatment technique. These findings suggest that direct treatment planning on uncorrected HyperSight iCBCT may be feasible for target and serial-organ dose assessment; however, lung dose calculations require caution. Refinement of the cone-beam CT Hounsfield unit-to-density calibration is recommended before clinical implementation or use in adaptive treatment planning. Further investigation using optimized calibration and additional anatomical configurations is warranted.

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