Experimental determination of peripheral photon dose components for different IMRT techniques and linear accelerators

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Intensity Modulated Radiation Therapy (IMRT) is a sophisticated radiotherapy technique.
• Understanding peripheral photon doses (PD) is crucial for minimizing radiation exposure to healthy tissues outside the target volume.

Purpose of the Study:

• To quantify and compare relative peripheral photon doses (PD) from different IMRT technologies and linear accelerator (linac) head designs.
• To assess the impact of photon beam energy and delivery method on PD.

Main Methods:

• Measurements of PD were conducted on Elekta and Siemens linacs using TLD-700 detectors.
• IMRT beams were generated using segmental multileaf collimation (sMLC) and cerrobend compensators.
• PDs were measured at various depths and distances from the field edge, normalized to the mean dose.

Main Results:

• PD values were higher near the surface and decreased with depth.
• Segmental MLC techniques increased PD by 1.2-1.8 times compared to open fields, while compensators increased PD by approximately 2 times.
• Siemens linac exhibited 30-50% higher PD than Elekta linac at comparable energies and measurement conditions.

Conclusions:

• Linac treatment head design significantly influences peripheral photon doses in IMRT.
• Optimizing IMRT delivery methods and selecting appropriate photon beam energies are essential for minimizing PD.