A radiation safety survey on a Clinac-20 linear accelerator

Powell, N.; Newing, Angela; Bullen, M. A.; Sims, Christopher E.; Leaton, S F

doi:10.1088/0031-9155/32/6/004

Cited by 26 publications

(9 citation statements)

References 3 publications

(1 reference statement)

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“…Published estimates of the annual activation dose received by staff during typical operation are in the range 0.7-5 mSv/yr. [1][2][3][4] These numbers show that activation dose is not negligible and suggest that, at least in conservatively shielded facilities, the therapist receives a greater occupational dose from activation than from radiation transmitted through the shielding barriers.…”

Section: Introductionmentioning

confidence: 98%

Dose to radiation therapists from activation at high‐energy accelerators used for conventional and intensity‐modulated radiation therapy

2002

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The increased beam-on times which characterize intensity-modulated radiation therapy (IMRT) could lead to an increase in the dose received by radiation therapists due to induced activity. To examine this, gamma ray spectrometry was used to identify the major isotopes responsible for activation at a representative location in the treatment room of an 18 MV accelerator (Varian Clinac 21EX). These were found to be 28Al, 56Mn, and 24Na. The decay of the dose rate measured at this location following irradiation was analyzed in terms of the known half-lives to yield saturation dose rates of 9.6, 12.4, and 6.2 microSv/h, respectively. A formalism was developed to estimate activation dose (microSv/week) due to successive patient irradiation cycles, characterized by the number of 18 MV fractions per week, F, the number of MU per fraction, M, the in-room time between fractions, td (min), and the treatment delivery time t'r (min). The results are represented by the sum of two formulas, one for the dose from 28Al 1.8 x 10(-3) F M (1-e(-03t'(r))/t'r and one for the dose from the other isotopes approximately 1.1 x 10(-6) F(1.7) Mt(d). For conventional therapy doses are about 60 microSv/week for an 18 MV workload of 60,000 MU/week. Irradiation for QA purposes can significantly increase the dose. For IMRT as currently practiced, lengthy treatment delivery times limit the number of fractions that can be delivered per week and hence limit the dose to values similar to those in conventional therapy. However for an IMRT regime designed to maximize patient throughput, doses up to 330 microSv/week could be expected. To reduce dose it is recommended that IMRT treatments should be delivered at energies lower than 18 MV, that in multienergy IMRT, high-energy treatments should be scheduled in the latter part of the day, and that equipment manufacturers should strive to minimize activation in the design of high-energy accelerators.

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Section: Introductionmentioning

confidence: 98%

Dose to radiation therapists from activation at high‐energy accelerators used for conventional and intensity‐modulated radiation therapy

2002

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“…Therefore, radiation therapists should be alert and skilled in operational procedures to avoid accidental exposure. Wearing neutron dosimeters can help monitor the personal dose of radiation therapists who work in residual radiation fields 42) . Special arrangements could be made to concentrate high-energy treatments in the afternoon sessions or on Fridays.…”

Section: ) Good Working Habits and Proceduresmentioning

confidence: 99%

Evaluation of Optimum Room Entry Times for Radiation Therapists after High Energy Whole Pelvic Photon Treatments

White

Chan

et al. 2012

Journal of Occupational Health

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High energy photon beams (greater than 10 MV) are routinely employed in clinical use for treatment of deep-seated tumors 1,2) . However, they induce undesirable photonuclear and electronuclear reactions 3) that produce neutrons and radioisotopes. Neutron production increases with photon energy, and the induced radioactivity depends on the neutron radiation level 3,4) . This phenomenon induces potential exposure for radiation therapists due to neutron, gamma and beta radiations emitted from decay of activation products 1, 3) . As occupational doses are of concern, undesirable photoneutrons should be minimized and actions taken to reduce unnecessary exposure. Neutron productionThe minimum energy required to remove a neutron from a nucleus decreases with increase in target atomic number 5) and lies between 6 to 16 MeV for nuclei heavier than carbon 6) . Linear accelerators generate high energy photon beams by accelerating electrons to 6-25 MV and then converting them to therapeutic X-rays. For photon energies below 10 MV, minimal photonuclear reaction occurs, and neutron production is negligible 5) . Neutrons are also produced by photodisintegration processes. However, since these have fewer interactions with the nuclei of the accelerator head components 7) , photonuclear reactions are considered to be the main cause of neutron contamination in external beam radiotherapy.Neutron production takes place inside machinery components of the linear accelerator head and the bodies of patients, as well as in the walls of the treatment room [1][2][3][4][8][9][10][11] . The target, beam collimation systems and multi-leaf collimators (MLCs) are the major sources of neutron production where the photon This study estimated gamma dose contributions to radiation therapists during high energy, whole pelvic, photon beam treatments and determined the optimum room entry times, in terms of safety of radiation therapists. Methods: Two types of technique (anteriorposterior opposing and 3-field technique) were studied. An Elekta Precise treatment system, operating up to 18 MV, was investigated. Measurements with an area monitoring device (a Mini 900R radiation monitor) were performed, to calculate gamma dose rates around the radiotherapy facility. Measurements inside the treatment room were performed when the linear accelerator was in use. The doses received by radiation therapists were estimated, and optimum room entry times were determined. Results: The highest gamma dose rates were approximately 7 μSv/h inside the treatment room, while the doses in the control room were close to background (~0 μSv/h) for all techniques. The highest personal dose received by radiation therapists was estimated at 5 mSv/yr. To optimize protection, radiation therapists should wait for up to11 min after beam-off prior to room entry. Conclusions: The potential risks to radiation therapists with standard safety procedures were well below internationally recommended values, but risks could be further decreased by delaying room entry times. Dependent on the te...

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“…Several authors have centered their studies in this field for different installations and machine types over the past 20 years [2], [3], [4] concluding that patients receive an expected additional dose around 0.5-5 mSv/yr. There is no data for the Elekta Precise linear accelerator and its bunker, therefore this work studies the induced dose by a 15 MV photon beam inside the bunker including the adjacent control room around that LinAc head.…”

Section: Introductionmentioning

confidence: 99%

MCNP6 unstructured mesh application to estimate the photoneutron distribution and induced activity inside a linac bunker

Juste

Morató

Miró

et al. 2017

Radiation Physics and Chemistry

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Unwanted neutrons in radiation therapy treatments are typically generated by photonuclear reactions. High energy beams emitted by medical linear accelerators (LinAcs) interact with high atomic number materials situated in the accelerator head and release neutrons.As photoneutrons scatter easily, they can leave the planned radiation field and be spread throughout the treatment bunker, contributing patients to receive a low (but non-negligible) dose, which is not estimated by treatment planning systems. Moreover, since neutrons have a high relative biological effectiveness, even low neutron doses may imply significant exposure of patients. It is also important to study activated radioisotopes for radiation protection purposes, as persons not present during irradiation (e.g. medical staff) may be exposed to them even when the accelerator is not operating.The Monte Carlo code MCNP6 has been used in this work for quantifying the neutron contamination inside the treatment room. Walls and LinAc head activation processes by these neutrons have also been estimated by simulation. To that, a detailed model of particles transport inside the bunker has been carried out using a meshed geometry model. The LinAc studied is an Elekta Precise electron accelerator with a treatment photon energy of 15 MeV.

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A radiation safety survey on a Clinac-20 linear accelerator

Cited by 26 publications

References 3 publications

Dose to radiation therapists from activation at high‐energy accelerators used for conventional and intensity‐modulated radiation therapy

Dose to radiation therapists from activation at high‐energy accelerators used for conventional and intensity‐modulated radiation therapy

Evaluation of Optimum Room Entry Times for Radiation Therapists after High Energy Whole Pelvic Photon Treatments

MCNP6 unstructured mesh application to estimate the photoneutron distribution and induced activity inside a linac bunker

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