Beam perturbation characteristics of a 2D transmission silicon diode array, Magic Plate

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Real-time quality assurance (QA) is crucial for modern radiotherapy.
• The Magic Plate (MP) system in transmission mode (MPTM) is a novel component for real-time QA during treatment delivery.
• Understanding the MPTM's impact on radiation beam characteristics is essential before clinical implementation.

Purpose of the Study:

• To evaluate the performance of the Magic Plate (MP) system in transmission mode (MPTM).
• To quantify the influence of the MPTM on radiation beam quality, including skin dose and percentage depth dose (PDD).
• To compare two MPTM operational setups for their suitability in real-time radiotherapy QA.

Main Methods:

• The MPTM was tested upstream of a phantom using a Varian linac at 6, 10, and 18 MV.
• Two setups were evaluated: MPTM alone and MPTM with an electron filter, compared against open field conditions.
• Ionization chambers (Markus, Attix, Farmer) and the Delta4 system measured surface doses, PDD, transmission factors, and 2D/3D dose distributions.

Main Results:

• Surface dose changes relative to dmax were less than 0.5% for all tested energies.
• Transmission factors for both MPTM setups were within 1.6% of open field values.
• Both MPTM configurations passed clinical gamma analysis criteria for 3D dose distribution.

Conclusions:

• Both tested MPTM operational setups are potentially suitable for real-time megavoltage photon treatment delivery QA.
• The bare MPTM configuration is slightly preferred as it minimally perturbs the radiation field.
• The MPTM does not significantly increase patient skin dose, supporting its clinical viability.