Doses to patients from photoneutrons emitted in a medical linear accelerator

Saeed, M.K.; Moustafa, O.; Yasin, OEzkanca; Tuniz, Claudio; Habbani, F.

doi:10.1093/rpd/ncp029

Cited by 20 publications

(11 citation statements)

References 19 publications

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“…Saeed et al .,[27] calculated the neutron dose equivalent of the 18 MV Varian 2100C by the Geant4 code about 4.4 mSv.Gy −1 at the isocenter; whereas, the values found by Fernández et al .,[6] were 6 mSv.Gy −1 using activation gold foils. These results show a reasonable agreement with what we found in this study (6.07 mSv.Gy −1 ).…”

Section: Discussionmentioning

confidence: 99%

Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations

et al. 2014

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High-energy linacs produce secondary particles such as neutrons (photoneutron production). The neutrons have the important role during treatment with high energy photons in terms of protection and dose escalation. In this work, neutron dose equivalents of 18 MV Varian and Elekta accelerators are measured by thermoluminescent dosimeter (TLD) 600 and TLD700 detectors and compared with the Monte Carlo calculations. For neutron and photon dose discrimination, first TLDs were calibrated separately by gamma and neutron doses. Gamma calibration was carried out in two procedures; by standard 60Co source and by 18 MV linac photon beam. For neutron calibration by 241Am-Be source, irradiations were performed in several different time intervals. The Varian and Elekta linac heads and the phantom were simulated by the MCNPX code (v. 2.5). Neutron dose equivalent was calculated in the central axis, on the phantom surface and depths of 1, 2, 3.3, 4, 5, and 6 cm. The maximum photoneutron dose equivalents which calculated by the MCNPX code were 7.06 and 2.37 mSv.Gy-1 for Varian and Elekta accelerators, respectively, in comparison with 50 and 44 mSv.Gy-1 achieved by TLDs. All the results showed more photoneutron production in Varian accelerator compared to Elekta. According to the results, it seems that TLD600 and TLD700 pairs are not suitable dosimeters for neutron dosimetry inside the linac field due to high photon flux, while MCNPX code is an appropriate alternative for studying photoneutron production.

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Section: Discussionmentioning

confidence: 99%

Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations

et al. 2014

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“…The absorbed dose and dose equivalent due to the secondary neutron evaluated from the LET spectrum of recoiled tracks produced in CR-39 are compared with the previous results carried out in the other works [6,[51][52][53][54] as summarized in Table 2. The quite large differences in the dose value, ranging from 0.05 to 1.4 mSv/Gy, are found in the similar experiments.…”

Section: Discussionmentioning

confidence: 99%

Measurement of the secondary neutron dose distribution from the LET spectrum of recoils using the CR-39 plastic nuclear track detector in 10 MV X-ray medical radiation fields

Kodaira¹,

Sawaguchi

Abe

et al. 2015

Nuclear Instruments and Methods in Physics Research Section B:

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“…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%

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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Doses to patients from photoneutrons emitted in a medical linear accelerator

Cited by 20 publications

References 19 publications

Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations

Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations

Measurement of the secondary neutron dose distribution from the LET spectrum of recoils using the CR-39 plastic nuclear track detector in 10 MV X-ray medical radiation fields

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

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