Date Approved

8-1-2024

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Lee Culp

Second Advisor

Kristen Vu

Academic Year

2023/2024

Abstract

This study examines the effect of Hounsfield Unit (HU) correction of air in rectal tissue on dose distribution during prostate cancer radiation therapy planning. Ten patients treated between 2023 and 2024, of which received 70 Gray (Gy) in 28 fractions, were retrospectively analyzed. Inclusion criteria included the presence of rectal gas during simulation and noncompliance with pre-simulation preparation instructions. Statistical tests, including a standard t-test and a sign test, were used to compare dose planning without HU correction to planning with HU-corrected rectal gas to tissue, focusing on differences in rectal doses and planned target volume doses. Radiation therapy plans for the ten patients, all treated and planned with rectal gas and a density override, were analyzed. Differences in rectal volume and the amount of rectal gas during simulation were noted. Each plan per patient used the Volumetric Modulated Arc Therapy (VMAT) technique. Dosimetry parameters, such as maximum, minimum, and mean doses for prostate and rectal structures, were collected with and without density override. These data points were then statistically analyzed to compare the means of the two samples. Advancements in prostate radiation treatments, including Image Guided Radiation Therapy (IGRT) and VMAT, have significantly improved outcomes and reduced radiation toxicity to critical structures near the prostate. However, managing rectal dose during simulation, planning, and treatment delivery remains challenging due to variations in rectal volume caused by rectal gas. Patient compliance with protocols, such as maintaining an empty rectum and a full bladder, is crucial.

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