Dose equivalent consideration from neutron contamination in modified radiotherapy vault: a Monte Carlo study

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Engineering

Background:

• Space-restricted radiotherapy centers require effective radiation shielding.
• Multilayer barriers with metal sheets are proposed for shielding in smaller vaults.
• Photoneutron contamination is a concern in high-energy photon radiotherapy.

Purpose of the Study:

• To assess photoneutron contamination in radiotherapy vaults with laminated barriers.
• To evaluate the impact of different metal sheets (lead, steel) and borated polyethylene (BPE) on neutron dose.
• To determine the associated cancer risks for patients and personnel.

Main Methods:

• Monte Carlo simulations were used to model an 18 MV linear accelerator (LINAC) and a Medical Internal Radiation Dose (MIRD) phantom.
• Simulations reconstructed vaults with various combinations of metal sheets and BPE during pelvic radiotherapy.
• Ambient neutron dose (Hn*(10)) and neutron equivalent doses in organs were calculated.

Main Results:

• Lead and steel sheets increased ambient neutron dose by 3.27 and 2.91 times, respectively, compared to concrete.
• Neutron doses outside the treatment room remained within permissible limits (20 μSv/week).
• No significant differences in organ dose, fatal cancer risk, or cancer mortality were observed across barrier compositions.

Conclusions:

• Laminated barriers with metal sheets and BPE are effective for space-restricted radiotherapy vaults.
• While metal increases neutron dose, BPE addition mitigates risks to acceptable levels.
• Cancer risk variations due to photoneutrons are minimal with these barrier designs.