Out-of-field scattering from the Integral Quality Monitor® in megavolt photon beams.

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate dose monitoring is crucial in radiation therapy.
• Understanding scattered radiation is essential for patient safety.
• The Integral Quality Monitor (IQM) is used for in-vivo dose verification.

Purpose of the Study:

• To quantify the out-of-field scattered radiation dose contribution from the Integral Quality Monitor (IQM).
• To investigate the impact of the IQM on surface dose profiles in megavoltage photon beams.

Main Methods:

• Out-of-field point doses were measured using Gafchromic EBT3 film strips.
• Measurements were performed on RW3 slabs at various distances from the central axis.
• Dose profiles were acquired with and without the IQM at different source-to-surface distances (SSD) and field sizes.

Main Results:

• Surface dose profiles were consistently higher with the IQM present.
• Out-of-field dose increased with higher photon energy, larger field sizes, and shorter SSDs.
• IQM-induced surface dose varied, for example, from 0.3% to 6.8% for 15 MV beams at 80 cm SSD.

Conclusions:

• The Integral Quality Monitor acts as an additional source of scattered radiation.
• The presence of the IQM significantly alters out-of-field dose distributions.
• These findings highlight the need to consider IQM scatter in treatment planning and verification.