Photoneutron Dose Estimation in GRID Therapy Using an Anthropomorphic Phantom: A Monte Carlo Study

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• GRID therapy, historically used with orthovoltage beams, is now employed with megavoltage photons for palliative treatment of bulky tumors.
• GRID can attenuate and also produce photoneutrons in medical linear accelerator (LINAC) heads, necessitating radiation protection evaluation.

Purpose of the Study:

• To evaluate the effect of GRID therapy on photoneutron dose to patients undergoing radiotherapy.
• To assess the impact of GRID on neutron dose in various tissues/organs using a phantom model.

Main Methods:

• A full model of a LINAC was simulated using the Monte Carlo code MCNPX.
• Neutron source strength, flux, and ambient dose equivalent were calculated with and without GRID.
• Absorbed dose and dose equivalent of neutrons were computed in a MIRD phantom.

Main Results:

• GRID therapy increased photoneutron production in the LINAC head by only 0.3%.
• Neutron dose within GRID-covered organs was reduced by an average of 48% compared to conventional radiotherapy.
• Neutron dose in organs not covered by GRID was reduced by 25%.

Conclusions:

• GRID therapy significantly reduces neutron dose to patient tissues and organs compared to conventional radiotherapy.
• The use of GRID therapy does not raise concerns regarding increased unwanted neutron dose or secondary cancer risk.