Biomedical Physics Seminars - Feb 6

Event Date/Time: 
Mon, 02/06/2017 - 12:00pm
KHE 225

Please join us for the Biomedical Physics Seminar Series.

Student: Daniel Dicenzo
Supervisors: Dr. Claire McCann & Dr. Carl Kumaradas

ABSTRACT: Low dose rate (LDR) brachytherapy is a common radiation treatment and has been used to treat breast cancer. LDR brachytherapy uses radioisotopes permanently inserted into the breast to deliver a prescribed radiation dose over a long period of time (months). Radioisotopes used in this treatment include Iodine-125 and Palladium-103 (Pd-103). These isotopes release photons at average energies of 28 keV and 21 keV respectively. An advantage of LDR brachytherapy to conventional external beam radiation therapy is that LDR brachytherapy can provide a localised radiation dose to the target volume without the need to pass through as much healthy tissue. This treatment also requires a single surgery allowing for one continuous radiation treatment deposited over a period of months. A drawback to the conventional use of brachytherapy sources is the inhomogeneity of dose deposition. This can result in underdosing to certain areas, allowing for the possibility of cancer recurrence. To ensure a more homogeneous dose distribution, more effective techniques need to be investigated.
Currently, a popular method being investigated to improve radiotherapy is the use of gold nanoparticles (GNP) in conjunction with radiation. GNPs have been widely shown to enhance radiation dose due to the greater number of charged particles produced when radiation interacts with the gold. The small size and biocompatibility allow for GNPs to be delivered to a tumor to enhance the delivered dose. By producing radioisotopes inside gold nanoparticles and placing them in a dissolvable seed (to be injected into the breast), it is possible that the controlled diffusion of the nanoparticles can provide a more homogeneous dose distribution than with conventional LDR seeds. Furthermore, the ability for the nanoparticles to enter cells may allow for greater cell death due to the close proximity of the nanoparticles to the cell’s nucleus.

This study will investigate dose deposition in breast cancer cells using Pd-103 nanoparticles coated in gold. Monte Carlo code will be used to simulate the radiation emitted from a Pd-103 GNP. This will allow us to calculate the dose absorbed in a cell when exposed to the nanoparticles. Furthermore one can determine the dose absorbed in a group of cells and evaluate cell survival. The future plan of this study is to evaluate GNP distribution and dose to a tumor when the nanoparticles are placed in a dissolvable brachytherapy seed.

Student: Daniel Cardenas
Supervisors: Dr. Ana Pejovic-Milic

ABSTRACT: Osteoporosis is a debilitating disease that leads to the loss of bone mass, which is a very prevalent health problem in the northern countries such as Canada. Strontium based medications, such as strontium ranelate (Protelos R ), have been indicated to treat and alleviate the condition. On the other hand, strontium salts that are available o -shelf in stores in Canada, have been assumed to provide similar e ffects to the strontium medication. The objective of this study was to compare the distribution of strontium in animal bones following administration of strontium ranelate and
strontium citrate.
Sprague-Dawley female rats were dosed with the two strontium salts; six animals received strontium ranelate, seven received strontium citrate, and six were left as the control group. Rats were dosed daily over ten weeks; the strontium ranelate and strontium citrate group received 174.3 mg/kg/day and 235.7 mg/kg/day of elemental Sr, respectively; the strontium citrate group received 35% more elemental Sr. A right humerus was collected from all animals and measured for strontium distribution using 2D XRF in Atominstitut, Institute for Atomic and Subatomic Physics, Vienna, Austria and 3D Dual Energy K-edge Subtraction Imaging available at the Canada Light Source, Saskatoon, Saskatchewan. Fresh bones were submerged in 70% ethanol and shipped to Vienna for a sample preparation. Three thin (10 - 20 m) slices from each of the groups were analyzed by 2D scanning diff erent regions of interest containing trabecular and cortical bone using a Rh anode tube (Microfocus Oxford "Apogee", 20 W maximum power). The scanning parameters used were a step-size of 50  50 m2 acquisition time of 100 s per point, the x-ray tube was set to a current of 0.4 mA and a voltage of 50 kV. The measurements yielded maps for Ca, Sr, P, S, and Zn. The Ca maps between the two Sr-treated groups showed similar intensities, which would suggest similar levels of calci cation. Sr signals were detected in the Sr-treated groups; while no detectable signal was observed in the control sample. The accumulation of strontium can be seen primarily in the
trabecular or inner region of the bones in both groups.

Samples measured at Canadian Light Source were also defatted in ethanol solution for two weeks and air dried for one week, prior to the measurement. The samples were cut down into 2 - 3 mm thick slices using a diamond wafering blade in order to allow the flux of photons to penetrate adequately. Eight samples from the strontium citrate, strontium ranelate, and control groups were scanned using the BioMedical Imaging and Therapy (BMIT-BM) beamline, the source-to-sample
distance was 25 m while the sample-to-detector distance was 0.2 m. Two sets of data were obtained for each bone using computed tomography (CT) imaging every 0.1 over 180 at two energies, one below and the second one above the K-edge of strontium of 16.105 keV. The resultant images were co-registered and subtracted in order to obtain the Sr maps. These maps provided a spatial distribution as well as concentration (mg/cm3) of elemental Sr in the calci ed tissue of the rat bones. Sr was observed to be largely present in the trabecular regions near the epiphyseal plate in both the Sr-treated groups, while the level of Sr in the control bones was below or close to the detection limit.

Our work will present the 2D spatial distribution of Sr and other elements from XRF, as well as the 3D spatial distribution with quanti cation of Sr from dual energy K-edge subtraction imaging in the bones of rats treated with Sr ranelate and citrate in comparison to the control.