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

Rawlinson, J. A.; Islam, Mohammad K.; Galbraith, D. M.

doi:10.1118/1.1463063

Cited by 62 publications

(53 citation statements)

References 11 publications

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“…MLC-based IMRT techniques have shown several drawbacks in clinical application. (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) For instance, the total monitor units (MUs) required for a segmental MLC-IMRT treatment are often much higher than that of the corresponding nonintensity modulated treatment. As a result, the treatment delivery time is often considerably extended, and concerns about radiation contamination of the prolonged beam-on time are also raised.…”

Section: Introductionmentioning

confidence: 99%

“…As a result, the treatment delivery time is often considerably extended, and concerns about radiation contamination of the prolonged beam-on time are also raised. (9) The often highly irregularly shaped MLC segment fields pose challenges to dose and MU calculation. (14) The dynamics of intensity map production by the MLC-IMRT techniques might also interfere with the dynamics of patient organ motion when it is considered for treatment planning.…”

Section: Introductionmentioning

confidence: 99%

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Compensators: An alternative IMRT delivery technique

Chang

Cullip

Deschesne

et al. 2004

J. Appl. Clin. Med. Phys.

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Seven years of experience in compensator intensity-modulated radiotherapy (IMRT) clinical implementation are presented. An inverse planning dose optimization algorithm was used to generate intensity modulation maps, which were delivered via either the compensator or segmental multileaf collimator (MLC) IMRT techniques. The in-house developed compensator-IMRT technique is presented with the focus on several design issues. The dosimetry of the delivery techniques was analyzed for several clinical cases. The treatment time for both delivery techniques on Siemens accelerators was retrospectively analyzed based on the electronic treatment record in LANTIS for 95 patients. We found that the compensator technique consistently took noticeably less time for treatment of equal numbers of fields compared to the segmental technique. The typical time needed to fabricate a compensator was 13 min, 3 min of which was manual processing. More than 80% of the approximately 700 compensators evaluated had a maximum deviation of less than 5% from the calculation in intensity profile. Seventy-two percent of the patient treatment dosimetry measurements for 340 patients have an error of no more than 5%. The pros and cons of different IMRT compensator materials are also discussed. Our experience shows that the compensator-IMRT technique offers robustness, excellent intensity modulation resolution, high treatment delivery efficiency, simple fabrication and quality assurance (QA) procedures, and the flexibility to be used in any teletherapy unit.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Compensators: An alternative IMRT delivery technique

Chang

Cullip

Deschesne

et al. 2004

J. Appl. Clin. Med. Phys.

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“…To attenuate the high-energy photons, the walls of the LinAc bunker are made of thick concrete, (density ρ=2.43 g/cm 3 ), with the exception of some extra shields, whose material are Ledite XN-288 (ρ=4.8 g/cm 3 ) and Ledite XN-240 (ρ=3.8 g/cm 3 ). Ledite is a concrete and steel mixture that combines excellent structural strength with a high level of resistance to radiation.…”

Section: ) Elekta Modelmentioning

confidence: 99%

“…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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“…Annual occupational doses of radiation therapists from induced activity may be reduced through time delay before entry into the treatment room after high energy photon beam treatments 22,28,30) . With a view to achieve the "As Low As Reasonably Achievable" (ALARA) principle, a compromise should be made between patient throughput and occupational radiation safety.…”

Section: Current Practice In Hong Kongmentioning

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

Cited by 62 publications

References 11 publications

Compensators: An alternative IMRT delivery technique

Compensators: An alternative IMRT delivery technique

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

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

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