https://eprints.ncl.ac.uk/file_store/production/187503/F3CBDFF1-CE60-43F7-AF30-EA88A642F2F4.pdf

Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study

Numerical Initial Value Problems in Ordinary Differential Equations

Sources, Effects and Risks of Ionizing Radiation

Age-dependent doses to members of the public from intake of radionuclides Part 4: Inhalation dose coefficients

The internal dosimetry schema of the Medical Internal Radiation Dose (MIRD) Committee of the Society of Nuclear Medicine has provided a broad framework for assessment of the absorbed dose to whole organs, tissue subregions, voxelized tissue structures, and individual cellular compartments for use in both diagnostic and therapeutic nuclear medicine. The schema was originally published in 1968, revised in 1976, and republished in didactic form with comprehensive examples as the MIRD primer in 1988 and 1991. The International Commission on Radiological Protection (ICRP) is an organization that also supplies dosimetric models and technical data, for use in providing recommendations for limits on ionizing radiation exposure to workers and members of the general public. The ICRP has developed a dosimetry schema similar to that of the MIRD Committee but has used different terminology and symbols for fundamental quantities such as the absorbed fraction, specific absorbed fraction, and various dose coefficients. The MIRD Committee objectives for this pamphlet are 3-fold: to restate its schema for assessment of absorbed dose in a manner consistent with the needs of both the nuclear medicine and the radiation protection communities, with the goal of standardizing nomenclature; to formally adopt the dosimetry quantities equivalent dose and effective dose for use in comparative evaluations of potential risks of radiation-induced stochastic effects to patients after nuclear medicine procedures; and to discuss the need to identify dosimetry quantities based on absorbed dose that address deterministic effects relevant to targeted radionuclide therapy.

https://jnm.snmjournals.org/content/jnumed/50/3/477.full.pdf

MIRD Pamphlet No. 21: A Generalized Schema for Radiopharmaceutical Dosimetry—Standardization of Nomenclature

The microdistributions of the alpha-particle-emitting bone surface-seeking radionuclides (239)Pu, (241)Am and (233)U in the mouse femoral shaft have been studied using computer-based image analysis of neutron-induced and alpha-particle track autoradiographs, prepared from femora of CBA/H mice which had been injected with 40 kBq kg(-1) of radionuclide (as citrate solution) at times from 1 to 448 days previously. Employing dosimetric methods, radiation dose rates and cumulative radiation doses to regions of the bone marrow thought to contain hemopoietic and stromal progenitor cells susceptible to neoplastic transformation to leukemia and osteosarcomas have been calculated. It has been shown that the three radionuclides differ in their relative deposition on the bone surfaces, and that patterns of changing redistribution with time are also varied. For stromal progenitor cells, which are thought to be targets for induction of osteosarcoma and are found in proximity to the bone surfaces, cumulative doses showed the trend (239)Pu > (241)Am > (233)U, correlating well with incidences of osteosarcoma observed in mice. Cumulative doses to the primitive hemopoietic stem cells, concentrated in the central marrow and thought to be susceptible to neoplastic transformation to myeloid leukemia, were considerably lower and also showed the trend plutonium > americium > uranium.

Temporal change in microdosimetry to bone marrow and stromal progenitor cells from alpha-particle-emitting radionuclides incorporated in bone.

Major current efforts within Committee 2 of the International Commission on Radiological Protection (ICRP) involve the development of dose coefficients for inhalation and ingestion of radionuclides...

https://journals.sagepub.com/doi/pdf/10.1177/0146645316636010

ICRP dose coefficients: computational development and current status:

Gut transfer and doses from environmental plutonium and americium.

Publication 100 of the International Commission on Radiological Protection (ICRP) provides a Human Alimentary Tract Model (HATM) to replace the gastrointestinal (GI) model described in Publication 30. The HATM will be used for future calculations of dose coefficients and bioassay predictions, first in a series of publications on occupational intakes of radionuclides, and subsequently in revision of dose coefficients for public exposures. This paper compares dose coefficients calculated using the new model with current values calculated using the GI model for a range of radionuclides. Colon doses are lower using the HATM in all cases considered, in some cases by significant factors. Stomach doses tend to be lower, but are in some cases higher under HATM. The extent to which these changes in doses to gut tissues impacts upon the effective dose varies among nuclides, but there is a tendency for lower effective doses. Special-case applications of the HATM are also described, considering retention on teeth or in the walls of the small intestine. Although the effect of such retention on the regional tissue dose can be large, the effective dose is not greatly changed.

Dose coefficients calculated using the new ICRP model for the human alimentary tract.

Two books with very similar titles have been published recently: Radiation and the Gastrointestinal Tract (edited by A Dubois et al) and Radiation and Gut. Despite their rather similar titles, their content is very different. The former is concerned with acute radiation effects and their avoidance or control in the context of radiation therapy and the possible irradiation of military personnel. It consists essentially of extended papers from the proceedings of a symposium. The latter, while also having chapters contributed by different authors, seeks to cover the field from the basic structure and cell replacement processes in the gut to its response to radiation in terms of cancer induction and tissue injury in experimental animals and human beings. The gut is a remarkable organ. As is commonly understood, it forms a tube from mouth to anus, but less well known is the rate of cell renewal in its epithelial lining, particularly in the small intestine. It is estimated that, for example, a mouse replaces about cells in its small intestine during a 3 year life-span. In human beings, this number of cells may be produced each day, corresponding to a mass of tissue produced and shed during a 70 year life-span of about ten times adult body weight. People have puzzled over the apparent paradox that the small intestine is the most sensitive region of the gut to radiation-induced cell killing and reproductive failure, consistent with its high rate of cell turnover, but has a low susceptibility to cancer induction. Thus, about 40% of the excess cancers among the A-bomb survivors in Japan are attributable to those arising in the gut but with significant increases confined to the stomach and colon. One emerging explanation, based on studies using mice, is that the small intestine may have an efficient mechanism for recognising and removing damaged stem cells. This is thought to involve a process of programmed cell death, termed apoptosis, in which cells commit suicide. Comparisons of apoptotic response to radiation in the small and large intestine show correspondence with the position thought to be occupied by the stem cells in the small intestine but not the large intestine. It may be, therefore, that stem cells in the large intestine are substantially more prone to the accumulation of genetic errors that might ultimately lead to malignant change. Populations differ considerably in their incidence of gut cancer. They account for 15 - 16% of total cancer deaths in England and Wales and in the USA and about 30% in Japan. Colorectal cancer accounts for about 80% of deaths from gut cancer in the USA whereas stomach cancer predominates in Japan. An important uncertainty in current risk estimates for radiation-induced gut cancer, based largely on incidence in Japan, is the lack of knowledge of how risks should be transferred from one population to another. Radiation and Gut provides very readable and detailed accounts of these issues and generally of the effects of radiation on the gut in experimental animals and human beings. Prominent among the contributors for individual chapters are the editors, Chris Potten and Jolyon Hendry, drawing extensively from their own work at the Paterson Institute for Cancer Research. It will be a pity if the high price of the book limits its availability.

http://iopscience.iop.org/0952-4746/17/2/021/pdf/0952-4746_17_2_021.pdf

John Harrison

Papers

Temporal change in microdosimetry to bone marrow and stromal progenitor cells from alpha-particle-emitting radionuclides incorporated in bone.

ICRP dose coefficients: computational development and current status:

Gut transfer and doses from environmental plutonium and americium.

Dose coefficients calculated using the new ICRP model for the human alimentary tract.

Radiation and Gut