Biomedical subjects

William V Prestwich

Publications and source records attributed to William V Prestwich.

3 recordsLinked to original sources

PubMed2006

A dose threshold for a medium transfer bystander effect for a human skin cell line.

The existence of radiation-induced bystander effects mediated by diffusible factors is now accepted, but the mechanisms and precise behavior at low doses remain unclear. We exposed cells to gamma-ray doses in the range 0.04 mGy-5 Gy, harvested the culture medium, and transferred it to unirradiated reporter cells. Calcium fluxes and clonogenic survival were measured in the recipients. We show evidence for a dose threshold around 2 mGy for the human skin cell line used with a suggestion of increased survival below that dose. Similar experiments using direct gamma irradiation showed no reduction in survival until the dose exceeded 7 mGy. Preliminary data for neutrons where the gamma-ray dose was kept below the bystander threshold do not show a significant bystander effect in the dose range 1-33 mGy. A lack of a bystander response with neutrons occurred at around 1 Gy, where significant cell killing from direct irradiation was observed. The result may have implications for understanding the role of bystander effects at low doses.

Bystander Effect↗

PubMed2002

Dosimetric properties of the new 125I BrachySeed model LS-1 source.

The BrachySeed model LS-1 is one of the latest in a series of new brachytherapy 125I seeds that have recently become available commercially for interstitial implants. The dosimetric properties of the seed were investigated analytically, experimentally, and by Monte Carlo simulation. Following the AAPM Task Group 43 formalism, the radial dose function, dose rate constant, and anisotropy parameters were determined. Experimental measurements were made in solid water-equivalent phantoms using GafChromic MD-55-2 films, with correction for the low energy film response. Analyses were carried out from absolute measurements, as well as relative measurements against the Nycomed Amersham OncoSeed Model 6711, which also served to validate our experimental methodology. A small, but systematic difference in the absolute measurements was observed depending on the duration of the irradiation. Monte Carlo simulation was performed using the Integrated Tiger Series CYLTRAN code. We benchmarked the code by comparing the dose parameters of Model 6702 with published values. The radial dose function, g(r), of the Model LS-1 seed was computed at distances from 0.25 to 10 cm by analytical and Monte Carlo calculations with reasonably good agreement. The suggested dose rate constant, A, based on the Monte Carlo simulation is 0.90+/-0.03 cGy h(-1) U(-1). This value is smaller than, but overlaps the experimental determination of 0.98+/-0.06 cGy h(-1) U(-1). The anisotropy function, F(r, theta), and anisotropy factor, phi(an)(r), compared favorably with those of the Model 6711.

Anisotropy↗

PubMed2002

Monte carlo investigation of the dosimetric properties of the new 103Pd BrachySeedPd-103 Model Pd-1 source.

Recently, 103Pd brachytherapy sources have been increasingly used for interstitial implants as an alternative to 125I sources. The BrachySeedPd-103 Model Pd-1 seed is one of the latest in a series of new brachytherapy sources that have become available commercially. The dosimetric properties of the seed were investigated by Monte Carlo simulation, which was performed using the Integrated Tiger Series CYLTRAN code. Following the AAPM Task Group 43 formalism, the dose rate constant, radial dose function, and anisotropy parameters were determined. The dose rate constant, A, was calculated to be 0.613 +/- 3% cGy h(-1) U(-1). This air kerma strength was derived from Monte Carlo simulation using the point extrapolation method. The radial dose function, g(r), was computed at distances from 0.15 to 10 cm. The anisotropy function, F(r,theta), and anisotropy factor, phi(an)(r), were calculated at distances from 0.5 to 7 cm. The anisotropy constant, phi(an), was determined to be 0.978, which is closer to unity than most other 103Pd seeds, indicating a high degree of uniformity in dose distribution. The dose rate constant and the radial dose function were also investigated by analytical modeling, which served as an independent evaluation of the Monte Carlo data, and found to be in good agreement with the Monte Carlo results.

Anisotropy↗