Evaluation of neutron spectra and dose equivalent from a Varian 2100C/D Medical Linear Accelerator: Monte Carlo simulation and a literature review

Razghandi, S.; Karimi-Shahri, Keyhandokht; Firoozabadi, Mohammad Mehdi

doi:10.1051/radiopro/2021002

Cited by 5 publications

(3 citation statements)

References 37 publications

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“…It happens that the LNT model has been largely based on those Japanese bomb survivors, who therefore received an irradiation very different from what is received by radiotherapy patients. -The type of radiotherapy beams needs to be considered, knowing in particular the role played by particles with high relative biological effectiveness (RBE) such as neutrons in the Japanese survivors, while neutrons are not used any more in radiotherapy (Razghandi et al, 2021). -The shape of the risk curve at high doses is obviously the most important point to be considered when trying to evaluate the risk of the "very high" doses of radiotherapy.…”

Section: Reasons Of the Discrepancy Between Lnt Model Predictions And...mentioning

confidence: 99%

Is the linear no-threshold (LNT) model relevant for radiotherapy?

Cosset

2022

Radioprotection

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Initially considered as a kind of radiobiological law, the linear no-threshold (LNT) model, which by definition supports the absence of any threshold for cancer risk induction after irradiation, is nowadays more reasonably described as a pragmatic and prudent approach by the International Organizations. However, it remains today a dogma in radiological protection. Actually, this model had been essentially developed for the radiological protection of a general population against low, and sometimes very low, doses of irradiation. Radiation oncologists are dealing with a totally different situation since they deliver, on purpose, high doses of radiations in more or less limited volumes of the body of cancer patients, patients for whom no other alternatives do exist to get rid of their malignant tumors. Simultaneously, the radiation oncologists inevitably give low and even very low doses at distance from the so-called target volumes. In such a specific situation, what is the carcinogenicity of these low doses and the relevance of the LNT model in radiotherapy? Thus, this paper addresses three critical questions: 1) what is the risk acceptability of the radiation doses delivered by radiotherapy of malignant tumors? 2) what is the real carcinogenic risk of (very) low doses delivered at distance from the target volume? 3) are the clinical radiotherapy data, i.e., the number of second primary cancers, accumulated since more than a century, consistent with the LNT model? In conclusion, the LNT model appears to be poorly adapted to the high doses locally delivered to cancer patients and dramatically overestimates, in most cases, the risk of secondary radio-induced cancers. In fine, the real risk of the LNT model in radiotherapy would be to promote radiophobia in cancer patients and to see some of them turning away from a life-saving treatment.

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Section: Reasons Of the Discrepancy Between Lnt Model Predictions And...mentioning

confidence: 99%

Is the linear no-threshold (LNT) model relevant for radiotherapy?

Cosset

2022

Radioprotection

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“…Fast neutrons emitting from the accelerator head can directly reach the patient's bed or slow down by interaction with the components of the treatment room, including walls, tables, and the like, and eventually, be converted into thermal neutrons [18]. Therefore, a spectrum of neutron energy is expected anywhere on the patient's bed [19,20].…”

Section: Introductionmentioning

confidence: 99%

Semi-experimental assessment of neutron equivalent dose and secondary cancer risk for off-field organs in glioma patients undergoing 18-MV radiotherapy

et al. 2022

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Neutron contamination as a source of out-of-field dose in radiotherapy is still of concern. High-energy treatment photons have the potential to overcome the binding energy of neutrons inside the nuclei. Fast neutrons emitting from the accelerator head can directly reach the patient’s bed. Considering that modern radiotherapy techniques can increase patient survival, concerns about unwanted doses and the lifetime risk of fatal cancer remain strong or even more prominent, especially in young adult patients. The current study addressed these concerns by quantifying the dose and risk of fatal cancer due to photo-neutrons for glioma patients undergoing 18-MV radiotherapy. In this study, an NRD model rem-meter detector was used to measure neutron ambient dose equivalent, H*(10), at the patient table. Then, the neutron equivalent dose received by each organ was estimated concerning the depth of each organ and by applying depth dose corrections to the measured H*(10). Finally, the effective dose and risk of secondary cancer were determined using NCRP 116 coefficients. Evidence revealed that among all organs, the breast (0.62 mSv/Gy) and gonads (0.58 mSv/Gy) are at risk of photoneutrons more than the other organs in such treatments. The neutron effective dose in the 18-MV conventional radiotherapy of the brain was 13.36 mSv. Among all organs, gonads (6.96 mSv), thyroid (1.86 mSv), and breasts (1.86 mSv) had more contribution to the effective dose, respectively. The total secondary cancer risk was estimated as 281.4 cases (per 1 million persons). The highest risk was related to the breast and gonads with 74.4 and, 34.8 cases per 1 million persons, respectively. Therefore, it is recommended that to prevent late complications (secondary cancer and genetic effects), these organs should be shielded from photoneutrons. This procedure not only improves the quality of the patient’s personal life but also the healthy childbearing in the community.

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“…High-energy linac, i.e. 18 MV linac, generates high photoneutron contamination, with its amount varied between various field sizes [18,19]. Some studies confirm that photoneutrons generated inside the linac head are primarily in a fast neutron energy range.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the linac neutron dose profile for various depths and field sizes: a Monte Carlo study

Prasada¹,

Ciamaudi²,

Fadli³

et al. 2021

Biomed. Phys. Eng. Express

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High-energy medical linear accelerator (Linac) has been widely used for treating cancer patients. However, with its effectiveness, high-energy linac yields an undesirable amount of neutron contamination. An MCNPX code version 2.6.0 was used for calculating photoneutron contamination from Varian Clinac iX 15 MV linac heads in this study. The fast neutrons were dominantly produced inside the linac head. The neutron fluence, absorbed dose, and dose equivalent calculations occurred inside a linac head and a water phantom model. The fast neutrons begin to be moderated after 1 cm inside the water phantom by calculating the energy spectra. Variations in the field sizes from 2×2, 5×5, 10×10, and 15×15 cm 2 show that the neutron production yield would increase for larger field sizes. The maximum neutron dose equivalents are 3.745; 7.687; 11.794 and 14.197 μSv/MU for 2×2, 5×5, 10×10 and 15×15 cm 2 field sizes, respectively. These calculations predict the photoneutron characteristics with more detail inside a treated patient during radiation therapy procedures.

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Evaluation of neutron spectra and dose equivalent from a Varian 2100C/D Medical Linear Accelerator: Monte Carlo simulation and a literature review

Cited by 5 publications

References 37 publications

Is the linear no-threshold (LNT) model relevant for radiotherapy?

Is the linear no-threshold (LNT) model relevant for radiotherapy?

Semi-experimental assessment of neutron equivalent dose and secondary cancer risk for off-field organs in glioma patients undergoing 18-MV radiotherapy

Evaluation of the linac neutron dose profile for various depths and field sizes: a Monte Carlo study

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