Biomedical subjects

P L Salmon

Publications and source records attributed to P L Salmon.

6 recordsLinked to original sources

PubMed1999

Alpha-particle doses to cells of the bone remodeling cycle from alpha-particle-emitting bone-seekers: indications of an antiresorptive effect of actinides.

There are indications that alpha-particle-emitting bone-seekers such as plutonium or americium could enhance bone mass by suppressing bone resorption. To assess this possibility, this study calculates doses from alpha-particle emitters to the cells involved in trabecular bone turnover. Alpha-particle energy deposition in tissue from a bone surface source was calculated by Monte Carlo modeling. This was combined with bone surface cellular geometry to yield dose rates to cells during the remodeling cycle. Bone-resorbing osteoclasts receive on average 50 times the dose rate that bone-forming osteoblasts receive. Newly formed bone shields osteoblasts from alpha particles emitted by the buried deposit of alpha-particle emitters. However, at alpha-particle bone-seeking radionuclide intakes known to cause changes in remodeling (about 3700 Bq/kg body weight), the alpha-particle dose to osteoclasts corresponds to an extremely low rate of cell traversals (0.07% per cycle). It is therefore unlikely that perturbation of bone remodeling by alpha-particle bone-seeking radionuclides is directly caused by alpha-particle traversals of remodeling cells; some other indirect mechanism might be involved.

Actinoid Series Elements↗

PubMed1998

Age and microdistribution of 210Pb at caribou bone surfaces measured by repeated alpha spectroscopy of 210Po.

PURPOSE: To measure microdistibution and age of 210Pb in Canadian caribou bone, and assess the accuracy of ICRP biokinetic and dosimetric models for 210Pb-supported 210Po at bone surfaces. MATERIALS AND METHODS: The previously described use of alpha spectroscopy to study 210Pb microdistribution at bone surfaces was expanded in a study of femora from 23 caribou. A new technique for measuring the age in vivo of Pb in bone, on the basis of the ratio of 210Po/210Pb activity, was carried out on eight caribou femora. RESULTS: The measured thickness p of the layer containing elevated concentration of 210Pb at femoral endosteal surfaces was 0.79 +/- 0.52 microm (SD). This thickness increased linearly with age in caribou aged 2-11 years. The surface/volume concentration ratio of 210Pb (As/Av) varied from 1 to 18, geometric mean 3.8. No trend in As/Av with caribou age was observed. In the upper 1 microm/210Pb was 17 +/- 22 days old, and at depths of 1-22 microm the age was 146 +/- 17 days. Thus Pb at the bone surface was about nine times younger than in underlying bone. CONCLUSIONS: Modifications to the ICRP 67 biokinetic model for Pb are proposed. The alpha dose to tissue above endosteal surfaces is reduced three times due to the low ingrowth ratio of 210Po.

Alpha Particles↗

PubMed1998

Monte Carlo/numerical treatment of alpha-particle spectra from sources buried in bone and resultant doses to surface cells.

PURPOSE: To calculate the depth distribution of radioactive decays in bone by fitting a calculated alpha-particle energy spectrum to a measured spectrum. The dose to bone surface cells is then calculated from the depth distribution. MATERIALS AND METHODS: The spectra are calculated using Monte Carlo methods and a numerical depth distribution obtained by trial and error. RESULTS: Alpha spectra for 210Po and 226Ra (plus decay products) in bone were calculated and fitted to experimental spectra. The dose to bone surface cells was calculated using the numerical technique and compared to previously published data. CONCLUSIONS: Alpha-particle spectra can be successful fitted using this method, which gives a more realistic distribution of decays with depth than simple surface and volume models.

Alpha Particles↗

PubMed1995

Distribution of 210Pb at endosteal surfaces of bone from Canadian Arctic caribou.

Alpha particle energy spectra were measured at femoral endosteal surfaces of Canadian Arctic caribou (Rangifer tarandus) to assess the profile of concentration with depth of 210Po supported by 210Pb. Femur samples from five caribou all showed a pronounced superficial concentration of 210Po, in a layer 1.9 - 6.4 microns thick. Within this layer 210Po was concentrated 1.5 - 10 times with respect to diffuse volume-distributed 210Po. This result is consistent with an earlier study of 210Po at human cranial bone surfaces, which showed 210Po to be concentrated about four times in a surface layer <3 microns thick. However, the present results have higher precision than the human bone data due to the much greater concentration of 210Pb and 210Po in caribou bone. The validity of using 210Po as a marker of 210Pb, and the in vivo 210Po/210Pb ratio are discussed. As a result of the measured endosteal superficial concentration of 210Po in caribou, the alpha particle dose was calculated to be enhanced by a factor of 1.06 - 1.96 (mean 1.48) for bone lining cells, and of 1.08 - 2.39 (mean 1.69) for soft tissue above the bone surface, assuming equilibrium between 210Pb and 210Po. It is suggested that an additional longer-lived compartment for bone surface lead could be incorporated into bio-kinetic models for lead.

Alpha Particles↗

PubMed1994

TASTRAK spectroscopy of polonium-210 alpha-particle activity at bone surfaces: evidence for a concentrated surface deposit less than 3 microns deep.

The technique of alpha-particle spectroscopy by CR-39 type TASTRAK plastic has been used to study the depth distribution of natural alpha-particle emitters at the surface of human bone. The predominant component of this alpha-particle activity was 210Po supported by 210Pb, although a smaller activity of 226Ra was also detected. Autopsy samples of human femur and cranium were obtained from subjects age 63 to 86. Both cortical and trabecular surfaces were analyzed. The results indicate that 210Pb-supported 210Po is concentrated at the surfaces of human bone from elderly subjects, in a narrow band 3 microns deep or less, by a factor of about four. As a result, the alpha-particle dose to the nuclei of cells lining bone surfaces is around 1.8 times greater than that calculated for a uniform volume distribution. Polonium-210 activity indicates the distribution of 210Pb, and of stable lead, received by continuous intake throughout life at a very low level. A persistent bone surface concentration of lead and other osteotropic metals may be associated with the hypermineralized layer about 1 micron thick which occurs at the surface of resting bone mineral.

Aged↗

PubMed1993

Viewing the client's world through drawings.

This article discusses the therapeutic use of drawings, outlines a specific drawing technique, and describes two case illustrations. Emphasis is placed on the healing quality of the drawing experience, a creative process in and of itself. These case illustrations were derived from an interpretive study in which life history and drawing methods were used to gather a holistic description about the experiences of women living with HIV disease. By making drawings depicting their illness, the ten women were offered another way to express and communicate their experiences, revealing rich descriptions that may not have been obtained by interviews alone. The drawings allowed the women to explore feelings that are often difficult to verbalize, offering additional insights about their worldview. For the practitioner, the use of drawings can therefore be a valuable tool to further understand a client, assess needs, and formulate a more inclusive approach to care.

Adult↗