Dose distribution changes with shielding disc misalignments and wrong orientations in breast IOERT: a Monte Carlo -...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Simulation

Background:

• Intraoperative electron radiotherapy (IOERT) for breast cancer carries a risk of shielding disc malpositioning.
• Setup errors can cause non-uniform dose delivery in the target zone and irradiation of healthy tissues.
• Direct in vivo measurement of dose distribution during such errors is not feasible.

Purpose of the Study:

• To investigate the impact of shielding disc configuration errors on dose distribution in breast IOERT.
• To quantify the effects of lateral shifts and tilt angles of the shielding disc on radiation dose parameters.
• To provide a simulation-based method for estimating dose distribution in clinical scenarios.

Main Methods:

• Utilized the Geant4 Monte Carlo toolkit for simulating electron beam interactions.
• Investigated parameters including shielding factor (SF), backscattering factor (BSF), volume-dose histogram, and maximum leakage dose (MLD).
• Analyzed effects of varying lateral disc shifts and tilt angles on dose distribution.

Main Results:

• Lateral disc shifts significantly decrease the shielding factor (up to 40% for 40 mm misalignment).
• Tilt angles up to 10° showed no relevant dose variations, but larger tilts (30°) increased MLD.
• Maximum leakage dose increased to 3.45 Gy for 14 mm misalignment and 4.60 Gy for 30° tilt (prescribed dose 21 Gy).

Conclusions:

• Monte Carlo simulations accurately estimate dose distribution changes due to shielding disc errors in breast IOERT.
• Simulation results aid in understanding the consequences of setup errors and optimizing clinical procedures.
• This approach supports a posteriori assessment of treatment efficacy and patient safety.