Absorbed dose to technicians due to induced activity in linear accelerators for radiation therapy

Almén, Anja; Ahlgren, Lars; Mattsson, Sören

doi:10.1088/0031-9155/36/6/009

Cited by 44 publications

(31 citation statements)

References 4 publications

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“…The results concurred with published estimates of the annual activation dose received by staff during routine procedures, which were in the range of 0.7-5 mSv/yr 27,40,41) . Even though estimated annual doses for all approaches were below maximum permissible dose values, i.e., 20 mSv/yr 20) , radiation therapists should remain alert to protect themselves from unnecessary radiation and limit the equivalent dose to as low as reasonably achievable, especially since the thermoluminescent dosimeter records for most staff at TMH tend to be approximately 2 mSv/yr.…”

Section: Dose Rates Versus Timesupporting

confidence: 89%

“…The half lives of activated tungsten, aluminium, magnesium and copper are 23.7 h, 2.3 min, 9.46 min and 9.7 min, respectively 4,23,24) . Also, particles in air can be activated, with the radiation intensity varying with beam energy [25][26][27] .…”

Section: Radioactivity Induced By Neutron Interactionmentioning

confidence: 99%

“…Gamma radiation from induced activity will give fairly uniform irradiation of radiation therapists who enter the treatment room, while beta radiation dominantly irradiates the hands when the radiation therapists come into direct contact with wedge filters or other activated accessories 13,[27][28][29] . As radiation therapists are associated with repetitive workflow, the damaging effects of radiation can be accumulated, and thus, radiation hazards should be minimized.…”

Section: Induced Activity As a Main Concern For Estimating Occupationmentioning

confidence: 99%

“…This may be due to ventilation that facilitated the air exchange rate in the treatment room, thus minimizing the doses from activation products in air 27) . One study has suggested that neutron capture leads to induced activity outside the treatment head, thus enhancing the contribution of the neutron-generated isotopes to staff dose, as these isotopes might be distributed throughout the treatment room.…”

Section: Neutron Production and Activationmentioning

confidence: 99%

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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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Section: Dose Rates Versus Timesupporting

confidence: 89%

Section: Radioactivity Induced By Neutron Interactionmentioning

confidence: 99%

Section: Induced Activity As a Main Concern For Estimating Occupationmentioning

confidence: 99%

Section: Neutron Production and Activationmentioning

confidence: 99%

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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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“…In figure 5 is shown the pulse height peak of the radioisotopes induced in the walls, where the main peaks are 125.95 KeV emitted by 55Fe (2.7 years half-life), 820 KeV emitted by 51Cr and 1099.24 and 1291.59 KeV that are emitted by 59Fe [8]. Figure 6 presents the simulation results inside the LinAc head.…”

Section: ) Activation Products Analysismentioning

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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Technical Note: Induced radioactivity in stereotactic body radiation therapy with a flattening‐filter‐free 10 MV beam model

et al. 2021

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The induced radioactivity in stereotactic body radiation therapy with a flattening-filter-free 10 MV beam model (10 FFF SBRT) was investigated for the risk to therapists. Methods: This study was performed on a Varian TrueBeam linac. The induced radioisotopes were identified by γ spectroscopy. The dose rate from the induced activity was measured for 12 treatment cycles in 4 h continuously. The impacts of the characteristic factors of 10 FFF SBRT on the dose rate were investigated, including monitor units (MU), beam rate, field size, and flattening filter. The dose rate was compared between the SBRT plans and conventional fractionation plans. A mathematical model was used to analyze the results and estimate the annual dose to therapists. Results: (a) The induced radioisotopes included 24 Na, 28 Al, 38 Cl, 56 Mn, 66 Cu, 187 W, and 196 Au. (b) In 4 h, the total dose contribution ratios were more than 70% for 28 Al, about 20% for 56 Mn, and 10% for all other long-lived radioisotopes, combining doses at the isocenter and end of the treatment couch. (c) The dose rate showed a nonlinear growth with increasing MU and beam rate. The variation of the dose rate was complicated with the jaw field and not sensitive to the MLC field. The removal of the flattening filter reduced the dose rate by about 40%. The dose level of SBRT was two to three times that of conventional fractionation. (d) The estimated annual dose to therapists was up to 0.20 mSv/y. Conclusions: The induced radioactivity in 10 FFF SBRT was higher compared with that in 10 MV conventional fractionation. More MU and higher beam rate were the primary factors that caused the increase. The therapists should wait longer after beam-off to reduce the occupational dose. In addition, aluminum and manganese should be less used in the treatment room.

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Absorbed dose to technicians due to induced activity in linear accelerators for radiation therapy

Cited by 44 publications

References 4 publications

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

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

Technical Note: Induced radioactivity in stereotactic body radiation therapy with a flattening‐filter‐free 10 MV beam model

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