Neutron Measurements Around High Energy X-Ray Radiotherapy Machines

Nath, Ravinder; Boyer, Arthur L.; Riviere, Philip D. La; McCall, R.C.; Price, Kenneth W.

doi:10.37206/18

Cited by 27 publications

(17 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Zabihzadeh et al [ 4 ] reported the equivalent neutron dose of 4.1 mSv/Gy at the isocenter for the 40 × 40-cm 2 field size calculated by Monte Carlo simulation. Chibani et al [ 2 ] reported the equivalent neutron dose of 13.3 mSv/Gy for the 10 × 10-cm 2 field size calculated by the MCNPX code in Varian machine. The equivalent neutron dose was also investigated for different SSDs.…”

Section: Discussionmentioning

confidence: 99%

“…However, the high-energy photons can also produce unwanted neutrons from the photoneutron [γ,n] interaction [ 1 ]. Neutrons are emitted from the interactions between photons and the nuclei of a high-atomic-number (high-Z) material when the photon energy is higher than the binding energy (5–15 MeV) of the nucleons [ 2 ]. The linear accelerator head components such as the target, primary collimators, flattening filter, secondary collimator, and multileaf collimators (MLCs) are made of high Z materials.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Evaluation of equivalent dose from neutrons and activation products from a 15-MV X-ray LINAC

Israngkul-Na-Ayuthaya

Suriyapee

Pengvanich

2015

J Radiat Res

View full text Add to dashboard Cite

A high-energy photon beam that is more than 10 MV can produce neutron contamination. Neutrons are generated by the [γ,n] reactions with a high-Z target material. The equivalent neutron dose and gamma dose from activation products have been estimated in a LINAC equipped with a 15-MV photon beam. A Monte Carlo simulation code was employed for neutron and photon dosimetry due to mixed beam. The neutron dose was also experimentally measured using the Optically Stimulated Luminescence (OSL) under various conditions to compare with the simulation. The activation products were measured by gamma spectrometer system. The average neutron energy was calculated to be 0.25 MeV. The equivalent neutron dose at the isocenter obtained from OSL measurement and MC calculation was 5.39 and 3.44 mSv/Gy, respectively. A gamma dose rate of 4.14 µSv/h was observed as a result of activations by neutron inside the treatment machine. The gamma spectrum analysis showed 28Al, 24Na, 54Mn and 60Co. The results confirm that neutrons and gamma rays are generated, and gamma rays remain inside the treatment room after the termination of X-ray irradiation. The source of neutrons is the product of the [γ,n] reactions in the machine head, whereas gamma rays are produced from the [n,γ] reactions (i.e. neutron activation) with materials inside the treatment room. The most activated nuclide is 28Al, which has a half life of 2.245 min. In practice, it is recommended that staff should wait for a few minutes (several 28Al half-lives) before entering the treatment room after the treatment finishes to minimize the dose received.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evaluation of equivalent dose from neutrons and activation products from a 15-MV X-ray LINAC

Israngkul-Na-Ayuthaya

Suriyapee

Pengvanich

2015

J Radiat Res

View full text Add to dashboard Cite

show abstract

“…Accurate dosimetry in mixed photon–neutron fields is very challenging 34–36 . Neutron detectors can suffer from pulse pileup, which can lower the linearity of their response when the neutron dose per burst is high.…”

Section: Methodsmentioning

confidence: 99%

Radiation shielding and safety implications following linac conversion to an electron FLASH‐RT unit

et al. 2021

View full text Add to dashboard Cite

Purpose Due to their finite range, electrons are typically ignored when calculating shielding requirements in megavoltage energy linear accelerator vaults. However, the assumption that 16 MeV electrons need not be considered does not hold when operated at FLASH‐RT dose rates (~200× clinical dose rate), where dose rate from bremsstrahlung photons is an order of magnitude higher than that from an 18 MV beam for which shielding was designed. We investigate the shielding and radiation protection impact of converting a Varian 21EX linac to FLASH‐RT dose rates. Methods We performed a radiation survey in all occupied areas using a Fluke Biomedical Inovision 451P survey meter and a Wide Energy Neutron Detection Instrument (Wendi)‐2 FHT 762 neutron detector. The dose rate from activated linac components following a 1.8‐min FLASH‐RT delivery was also measured. Results When operated at a gantry angle of 180° such as during biology experiments, the 16 MeV FLASH‐RT electrons deliver ~10 µSv/h in the controlled areas and 780 µSv/h in the uncontrolled areas, which is above the 20 µSv in any 1‐h USNRC limit. However, to exceed 20 µSv, the unit must be operated continuously for 92 s, which corresponds in this bunker and FLASH‐RT beam to a 3180 Gy workload at isocenter, which would be unfeasible to deliver within that timeframe due to experimental logistics. While beam steering and dosimetry activities can require workloads of that magnitude, during these activities, the gantry is positioned at 0° and the dose rate in the uncontrolled area becomes undetectable. Likewise, neutron activation of linac components can reach 25 µSv/h near the isocenter following FLASH‐RT delivery, but dissipates within minutes, and total doses within an hour are below 20 µSv. Conclusion Bremsstrahlung photons created by a 16 MeV FLASH‐RT electron beam resulted in consequential dose rates in controlled and uncontrolled areas, and from activated linac components in the vault. While our linac vault shielding proved sufficient, other investigators would be prudent to confirm the adequacy of their radiation safety program, particularly if operating in vaults designed for 6 MV.

show abstract

“…These were calculated from Eq. 3involving the average neutron energy (E avg ), adopted from AAPM Report 19 [15], separately for slow and fast components of neutron fl ux. Based on the analysis of neutron spectra given in the literature, [16][17][18] the average neutron energy were taken as 0.2 eV and 0.5 MeV for slow and fast components, respectively.…”

Section: Neutron Measurementsmentioning

confidence: 99%

Measurements of doses from photon beam irradiation and scattered neutrons in an anthropomorphic phantom model of prostate cancer: a comparison between 3DCRT, IMRT and tomotherapy

et al. 2017

View full text Add to dashboard Cite

Introduction. The rapid development of new radiotherapy technologies, such as intensity modulated radiotherapy (IMRT) or tomotherapy, has resulted in the capacity to deliver a more homogenous dose in the target. However, the higher doses associated with these techniques are a reason for concern because they may increase the dose outside the target. In the present study, we compared 3DCRT, IMRT and tomotherapy to assess the doses to organs at risk (OARs) resulting from photon beam irradiation and scattered neutrons. Material and methods. The doses to OARs outside the target were measured in an anthropomorphic Alderson phantom using thermoluminescence detectors (TLD 100) 6Li (7.5%) and 7Li (92.5%). The neutron fluence rate [cm−2·s−1] at chosen points inside the phantom was measured with gold foils (0.5 cm diameter, mean surface density of 0.108 g/cm3). Results. The doses [Gy] delivered to the OARs for 3DCRT, IMRT and tomotherapy respectively, were as follows: thyroid gland (0.62 ± 0.001 vs. 2.88 ± 0.004 vs. 0.58 ± 0.003); lung (0.99 ± 0.003 vs. 4.78 ± 0.006 vs. 0.67 ± 0.003); bladder (80.61 ± 0.054 vs. 53.75 ± 0.070 vs. 34.71 ± 0.059); and testes (4.38 ± 0.017 vs. 6.48 ± 0.013 vs. 4.39 ± 0.020). The neutron dose from 20 MV X-ray beam accounted for 0.5% of the therapeutic dose prescribed in the PTV. The further from the field edge the higher the contribution of this secondary radiation dose (from 8% to ~45%). Conclusion. For tomotherapy, all OARs outside the therapeutic field are well-spared. In contrast, IMRT achieved better sparing than 3DCRT only in the bladder. The photoneutron dose from the use of high-energy X-ray beam constituted a notable portion (0.5%) of the therapeutic dose prescribed to the PTV.

show abstract

Neutron Measurements Around High Energy X-Ray Radiotherapy Machines

Cited by 27 publications

References 0 publications

Evaluation of equivalent dose from neutrons and activation products from a 15-MV X-ray LINAC

Evaluation of equivalent dose from neutrons and activation products from a 15-MV X-ray LINAC

Radiation shielding and safety implications following linac conversion to an electron FLASH‐RT unit

Measurements of doses from photon beam irradiation and scattered neutrons in an anthropomorphic phantom model of prostate cancer: a comparison between 3DCRT, IMRT and tomotherapy

Contact Info

Product

Resources

About