1987 Douglas Lea memorial lecture. Particle dosimetry in bone and the toxicity of bone-seeking radionuclides.

Consideration is given to the tissues at risk in bone and a Monte Carlo method is described which determines the absorbed dose to endosteal tissues and marrow in trabecular bone. The method synthesizes random tracks through the trabecular structures that deposit energy along a path through any given trabecular cavity. The path lengths through the trabeculae and marrow cavities are measured with a bone-scanning microscope and other bone data, such as trabecular surface areas, can also be derived.

Photoelectron enhancement of the absorbed dose from X rays to human bone marrow: experimental and theoretical studies.

A technique is described by which lithium fluoride powder is introduced into the marrow cavities in specimens of human trabecular bone to determine the excess photoelectron dose to marrow, when bone is irradiated by X rays of energies between 20 keV and 140 keV. Three specimens of trabecular bone, containing respectively 10, 15 and 25% bone by volume, were investigated and the results compared with those derived on the basis of earlier calculations for mono-energetic electrons by Whitwell. Reasonable agreement was found between the experimental and theoretical results, although there was some indication that scatter influenced the practical measurements at the higher photon energies.

Leukaemia incidence in the U.S. dial workers.

Late biological effects of radium deposited in the human skeleton have manifested themselves unequivocally as osteogenic sarcomas or carcinomas of the mastoid air cells or paranasal sinuses. On the basis of current estimated risk factors, it might be expected that an excess of certain other malignancies could occur in a population of the size of the group exposed to radium (some 3500 cases located, which more than 2000 have measured 226Ra and 228Ra burdens), compared with the incidence in the population at large. An increased incidence of breast cancer has already been reported in female dial workers and it was related to the initial radium intake.

Sites of incidence of osteosarcoma in the long bones of man and the beagle.

Information has been assembled on the frequency of occurrence of osteosarcomas in the long bones of groups of beagles irradiated by alpha particles from bone-seeking radionuclides. These data are compared with measured trabecular surface areas in the long bones of a beagle, determined at the Bone Dosimetry Research Laboratory, Cookridge Hospital, Leeds. It is shown that, as in the human case, the percentage tumour occurrence in a long bone (or in separate thirds of a long bone) was linearly related to the corresponding trabecular surface area with a high value of the correlation coefficient.

Mean skeletal dose factors for beta-particle emitters in human bone. Part II: surface-seeking radionuclides.

Mean skeletal dose factors for surface-seeking beta-emitting radionuclides have been derived on the basis of the beta-particle dose factors calculated for human bones by Spiers et al. (1978b), or from empirical formulae representing these calculations given by Beddoe and Spiers (1979). The dose factors are derived for the same tissues as in Part I (Spiers et al.

Attenuation factors for certain tissues when the body is irradiated omnidirectionally.

Experimental values of mean attenuation factors are reported for certain tissues in an anthropomorphic phantom irradiated omnidirectionally with gamma rays from sodium-24, radium-226, iodine-131 and xenon-133. The data are used to relate the mean absorbed dose to the whole body, bone marrow, gonads and skin to (a) the absorbed dose in air and (b) the exposure in air. Correlations are made for the degradation of the radiation by scatter and the photoelectron enhancement effect.

Mean skeletal dose factors for beta-particle emitters in human bone. Part I: volume-seeking radionuclides.

Based on calculations by Whitwell and Spiers, mean skeletal dose factors for beta-particle emitters have been derived for application to dosimetry in nuclear medicine, radiobiology and radiation protection. The dose factors apply to bone-seeking radionuclides that are depostited more or less uniformly throughout the human mineralized skeleton and are defined as: (1) vDM/DB, the mean dose to the haemopoietic marrow in trabecular bone as a fraction of the "dose to bone", DB; (2) vDs/DB, the mean dose to endosteal (osteogenic) tissue lying in a zone 0--10 micron from trabecular surfaces, also as a fraction of the dose DB. Dose factors are given for three ages, 1.

Calculated dose factors for the radiosensitive tissues in bone irradiated by surface-deposited radionuclides.

The method of calculating dose factors for the haemopoitic marrow and endosteal tissues in human trabecular bone, used by Whitwell and Spiers for volume-seeking radionuclides, has been developed for the case of radionuclides which are deposited as very thin layers on bone surfaces. The Monte Carlo method is again used, but modifications to the computer program are made to allow for a surface rather than a volume source of particle emission. The principal change is the introduction of a surface-orientation factor which is shown to have a value of approximately 2, varying slightly with bone structure.

Measurements of endosteal surface areas in human long bones: relationship to sites of occurrence of osteosarcoma.

Using techniques of bone scanning and ashing, the areas of the endosteal surfaces in cortical and trabecular bone have been determined for the proximal, mid and distal thirds of each of the six long bones of an adult human subject. The relative frequency of occurrence of bone sarcomas, scored as to site, has been analysed in relation to these measured areas. Data on tumour occurrence have been drawn from three sources: radium-case data from Rowland and Keane (33 cases), naturally-occurring cases from series by Sissons (139 cases) and by Dahlin (473 cases).

'Radial' scanning of trabecular bone: consideration of the probability distributions of path lengths through cavities and trabeculae.

Previous methods of dosimetry for radionuclides deposited in trabecular bone have been based on probability distributions of random path lengths through the trabeculae and marrow cavities. These distributions have been measured by a technique in which thin bone sections are effectively scanned along sets of parallel grid lines. A new technique is described in this paper, in which all scan lines pass through a selected point in the section scanned, so that they effectively radiate from the point (or focus) in the manner in which particles emerge isotropically from a radioactive atom.

Measurements of trabecular bone structure in man.

A quantitative analysis of trabecular bone structure is presented, based on omnidirectional distributions of paths across (a) trabeculation and (b) marrow cavities. The omnidirectional distributions, which take into account structural anisotropy, are generated from measured distributions of paths. Representative examples are given, together with values of two commonly quoted structural parameters, the ratio of endosteal surface to bone volume and percentage bone volume.

Hazards of plutonium with special reference to the skeleton.

In the past attempts have been made to deduce plutonium toxicity in man from studies based on animal experimentation. An alternative method is to use the comparative dosimetry of plutonium and radium in man, with results broadly in agreement with maximum permissible levels set by the International Commission of Radiological Protection.

The absorbed dose to bone marrow in the treatment of polycythaemia by 32P.

This paper reports the determination of absorbed dose to bone marrow in the treatment of polycythaemia by 32P, based on the measurement of activities in bone and marrow biopsies taken at various times from 1 to 27 days after injection of the radionuclide. Activities were measured in the cortex, trabeculation and marrow of biopsies taken from the iliac crest, and slso in sternal marrow. The biological half-life of 32P in marrow from the iliac crest was found to be nine days; that derived for sternal marrow was lower, but the difference was not statistically significant; the value for trabecular bone was 27 days.

Calculated beta-ray dose factors for trabecular bone.

Mean dose factors have been calculated for those tissues in bone that are relevant to the induction of late irradiation effects; namely, red bone marrow and endosteal tissues lining trabecular bone surfaces. The calculations are based on a Monte Carlo computer method for beta-emitting radionuclides which are distributed uniformly throughout the volume of mineralized bone. Results are given for the radionuclides 14C, 45Ca, 22Na, 18F, 32P, 90Y and 90Sr+90Y (all considered for this purpose as volume-seekers) for seven bones from the adult human skeleton and calculations are also presented of average skeletal dose factors.