2.3 - ALARA For Linacs

What processes and equipment are in place to assist the ALARA principle of radiation protection for staff, patients and the public at the treatment machine?

The three tenets of ALARA are time, distance and shielding.

Protection of Staff

Linear accelerators generate no radiation when idle, making time a less important consideration for staff. Older teletherapy machines (eg. 60Co) contained a radioactive source and therefore there was always a very low rate of dose within the room. For older machines, staff should be adept in performing procedures quickly to prevent excessive exposure over time. One of the numerous benefits of modern machines is the reduced dose received by staff over time.
During treatment, staff exit the bunker to the control room, increasing the distance between them and the radiation source. Distance is limited by practicality - if the control room is too far away from the bunker then treatment will be inefficient. Shielding allows the bunker and control room to be located closer together, protecting staff from harmful levels of ionising radiation.

Protection of Patients

Patients have similar protection issues to staff; ideally receiving a high dose of radiation to the treated area and minimal dose elsewhere.
Patients should not remain in the bunker of teletherapy machines for longer than necessary. Distance is not possible for patients during treatment; however waiting rooms should generally be located at some distance or behind sufficient shielding.

Protection of the General Public

The general public is is protected in several ways:

  • Ensuring that rooms near the linear accelerator are infrequently used or inhabited; this limits the time the public is exposed to radiation.
  • Frequently frequented areas are located at a distance from the machine
  • Shielding is used to reduce exposure rates in both infrequently and frequently used areas.