Use of a realistic breathing lung phantom to evaluate dose delivery errors

Area of Science:

• Radiation Oncology
• Medical Physics
• Biomedical Engineering

Background:

• Respiration-induced motion is a significant challenge in radiation therapy, potentially causing dose deviations.
• The interplay effect, where motion affects dose delivery, requires careful evaluation for different treatment techniques.
• Realistic phantoms and dosimetry measurements are crucial for assessing treatment accuracy.

Purpose of the Study:

• To compare the impact of respiration-induced motion on delivered radiation dose for various treatment techniques.
• To evaluate the interplay effect under clinically relevant conditions using a realistic phantom.
• To determine the dose deviations for different radiotherapy plans and their dependence on fractionation.

Main Methods:

• A 3D-printed tumor model was created from patient CT data and placed in an anthropomorphic breathing phantom.
• Micro-MOSFETs were used to measure dose distribution within the tumor model under simulated patient motion.
• Multiple treatment plans were generated using conformal, intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT) techniques.

Main Results:

• Most treatment plans showed dose deviations less than 2% after five fractions, except for complex dynamic IMRT, step-and-shoot IMRT (XiO), complex VMAT, and single-arc VMAT.
• Reducing the dose rate for complex IMRT plans significantly decreased dose deviations.
• Complex single-arc VMAT plans exhibited dose deviations exceeding 5% after five fractions.

Conclusions:

• Rapid prototyping enables creation of realistic tumor models for motion studies.
• Dose deviations due to motion generally average out with fractionation for most techniques.
• Complex treatment sequences increase dose deviations; reducing dose rate for IMRT and using double arcs for VMAT can improve accuracy.