Answer to Question #11015 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
We are operating an 18 MV linear accelerator (LINAC). The maximum instantaneous neutron dose at the door is about 150 µSv h-1. The maximum instantaneous photon dose on the door is about 50 µSv h-1. The patient load is 50 patients per day (on average). We only have TLD (thermoluminescent dosimeter) badges for our workers which are good for photon dosimetry. Could you suggest how we can assess whether the door shielding is sufficient? Are there any publications on this matter?
There are three independent steps that need to be followed to ensure that the door shielding is adequate:
- Perform shielding calculations for the total (photon and neutron) weekly and hourly doses at the door for the site specific workload and usage factors. Compare these doses to the applicable regulatory limits.
- Perform careful photon and neutron radiation surveys outside the door. Calculate total weekly and hourly doses using site specific workload and usage factors.
- Install passive radiation monitoring devices (e.g., TLDs for photons, track-etch dosimeters for neutrons, etc.) outside the door. Process these at some preestablished frequency.
Please refer to National Council on Radiation Protection and Measurements Report No. 151, Structural Shielding Design and Evaluation for Megavoltage X and Gamma-ray Radiotherapy Facilities, which provides recommendations on shielding calculations, radiation surveys, and neutron monitoring equipment.
Nisy Ipe, PhD, CHP