Dose Shadowing and Prosthesis Involvement for Megavoltage Photon In vivo Diode Dosimetry

Area of Science:

• Medical physics
• Radiation oncology
• Radiotherapy dosimetry

Background:

• Accurate dose delivery is critical in radiotherapy for effective tumor control.
• In vivo dosimetry devices, such as diodes, can introduce beam perturbations.
• The presence of medical implants, like titanium prostheses, can further complicate dose calculations.

Purpose of the Study:

• To investigate photon beam perturbations caused by an in vivo diode.
• To assess the combined effect of the diode and titanium prosthesis on dose distribution.
• To evaluate the impact on radiotherapy accuracy in a human-like phantom.

Main Methods:

• Utilized a water-equivalent pelvic phantom with bony structures and a Ti prosthesis.
• Measured dose distributions using Gafchromic EBT3 films with and without an EDP-203G in vivo diode.
• Examined 6 MV and 10 MV photon beams across various field sizes and treatment plans.

Main Results:

• Photon beam dose perturbations ranged from 2% to 7% for prosthetic fields and 5% to 12% for non-prosthetic fields.
• Relative differences in dose perturbations were between 2% and 4%.
• Depth dose measurements showed relative differences between 2% and 5%.

Conclusions:

• Diode-induced beam perturbations combined with prosthesis involvement can lead to a reduction in the prescribed target dose.
• This dose reduction may negatively affect tumor control probability.
• Accurate assessment of these perturbations is crucial for optimizing radiotherapy treatment plans.