Radiation interaction parameters of dosimetric importance for some commonly used compensators in IMRT using Monte...

Area of Science:

• Medical Physics
• Radiation Oncology
• Materials Science

Background:

• Radiotherapy, a cornerstone of cancer treatment, utilizes intensity modulated radiotherapy (IMRT) for precise dose delivery.
• Compensators in IMRT are crucial for managing dose uniformity by accounting for anatomical irregularities.
• Selecting appropriate compensator materials is vital for optimizing therapeutic outcomes and minimizing radiation exposure.

Purpose of the Study:

• To investigate and compare the radiation shielding characteristics of different compensator materials used in IMRT.
• To analyze key dosimetric parameters, including mass attenuation coefficients, effective atomic numbers, and buildup factors.
• To understand the influence of photon energy, material composition, and penetration depth on these parameters.

Main Methods:

• Computed mass attenuation coefficients using the XCOM program and the Monte Carlo N-particle-5 (MCNP5) code for cerrobend, brass, steel, and lucite.
• Calculated linear attenuation coefficients, mass energy absorption coefficients, effective atomic numbers, electron densities, and energy absorption/exposure buildup factors.
• Studied parameter variations across a wide energy range (0.015–15.0 MeV) and penetration depths.

Main Results:

• High agreement was found between XCOM and MCNP5 computed mass attenuation coefficients.
• A notable trend reversal in buildup factors was observed around 3 MeV and 14 mean free paths (mfp).
• Compensators with lower effective atomic numbers exhibited higher buildup factors below 3 MeV (e.g., Cerrobend near 100 keV) and lower buildup factors above 3 MeV.

Conclusions:

• The study highlights the energy-dependent radiation shielding behavior of IMRT compensator materials.
• Effective atomic number and photon interaction processes significantly influence radiation buildup factors.
• Material selection and energy considerations are critical for optimizing IMRT dose distribution and patient safety.