A radiation safety survey on a Clinac-20 linear accelerator

Area of Science:

• Medical Physics
• Radiation Protection
• Radiological Physics

Background:

• Linear accelerators (LINACs) operating at high energies (e.g., 20 MV) are associated with significant radiation protection concerns.
• The 18 MV photon beam in particular generates substantial neutron production, necessitating careful consideration of associated risks.

Purpose of the Study:

• To discuss radiation protection issues linked to 20 MV LINACs, focusing on neutron production.
• To evaluate patient neutron dose, shielding needs, and neutron activation of the LINAC and its environment.
• To validate predictive methods for neutron dose equivalent and assess measurement techniques.

Main Methods:

• Structural protection surveys were conducted.
• National Council on Radiation Protection and Measurements (NCRP) methods for predicting neutron dose equivalent at maze ends were assessed.
• Dose rates from neutron activation were measured in the treatment room and on the LINAC.
• Neutron dose equivalents were measured in the patient plane using standard neutron badges and CR-39 dosimeters.

Main Results:

• NCRP methods for predicting neutron dose equivalent were found to be reliable.
• Measurements confirmed neutron activation of the treatment room and LINAC components.
• Assessment of potential staff doses was performed.
• CR-39 dosimeters provided sensible results for neutron dose equivalent measurements.

Conclusions:

• Radiation protection strategies for 20 MV LINACs must account for neutron production.
• NCRP guidelines offer reliable predictions for neutron shielding.
• CR-39 dosimetry presents a viable method for neutron dose assessment in LINAC facilities.