SU-E-T-391: Modelling Peripheral Photon Dose in TomoTherapy Treatments

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Photon radiotherapy delivers therapeutic doses but also imparts peripheral dose to organs, increasing secondary cancer risk.
• Helical TomoTherapy (HT) is a complex technique requiring accurate peripheral dose estimation.
• Previous studies compared TLD measurements with Monte Carlo modeling for peripheral dose estimation.

Purpose of the Study:

• To develop experimental models for predicting equivalent photon dose as a function of distance from the isocenter in HT treatments.
• To present a specific model for prostate cancer treatment using HT.
• To differentiate scatter and leakage dose contributions.

Main Methods:

• A Helical TomoTherapy (HT) prostate plan was delivered to an anthropomorphic phantom.
• Thermoluminescence dosimeter (TLD) measurements were taken at 16 points within the phantom.
• A polyethylene sheet was used to measure the off-axis dose profile at midplane depth.

Main Results:

• A two-exponential curve fitting model was developed to describe scatter and leakage dose components.
• Scatter dose was predominant proximally (10-14cm), while leakage dose dominated distally (x>14cm).
• The model demonstrated good agreement with experimental data, with a 13% mean deviation.

Conclusions:

• Peripheral photon dose profiles in HT treatments can be effectively modeled using a two-exponential function.
• The model successfully separates scatter and leakage dose contributions.
• This modeling is essential for optimizing radiation delivery and reducing risks associated with peripheral dose.