WFU Physics PhD Thesis Presentation

TITLE: A SR-90 Irradiation Device for the Study of Cutaneous Radiation Injury from a Radiological Incident

SPEAKER: Jennifer E. Dorand,

TIME: Friday April 25, 2014 at 9:00 AM

PLACE: Room 107 Olin Physical Laboratory

In the event of a radiological accident or terrorist attack with fissionable materials, Strontium-90, a fission by-product, would likely be released. Due to the low energy and superficial penetration in tissue of β particles from Sr-90 radiation, cutaneous radiation injury (CRI) is a major concern. In the case of a radiation incident, the dose to the skin is unlikely to be known, but can be estimated with a thorough understanding of the surface dosimetry of Sr-90. The physics of Sr-90 is examined as part of a larger project to study Grade III CRI in a porcine animal model and examine the efficacy of KeraStat, a topical product with the potential to heal CRI.

To enable Sr-90 beta-induced CRI in vivo, a unique custom-built irradiation device has been designed, manufactured and investigated for its radiation dose characteristics. The irradiation device holds seven 100 mCi commercially-available Sr-90 sources in a combined circular symmetry to produce a 10 cm² circular irradiation area at the skin surface. A source cassette to hold the seven Sr-90 sources in a concentric configuration sits atop a manual shutter that has an opening to allow the beta radiation to pass through to the surface. A 2 cm tall, 1 cm thick Lucite applicator cone collimates the radiation and defines the 3.67 cm diameter field at the surface. Preliminary work allowed for the development of experimental techniques to ensure accurate skin dose measurement. The seven sources have been characterized individually using contact autoradiography as well as within the irradiator device. The surface dose rate and three-dimensional dose distribution, including in-plane and cross-plane dose profiles and the percent depth doses in tissue, have been characterized using Gafchromic. film, a Markus® parallel-plate ionization chamber, and an extrapolation ionization chamber. This device has been successfully implemented for in vivo irradiations to deliver doses of 18-48 Gy to porcine skin using an institutionally-approved animal irradiation protocol. In addition, the radiation safety aspects of this device have been studied to ensure personnel safety.

The individual sources were found to possess great inter- and intra-source inhomogeneities. However, with the sources placed in the mobile irradiation device with their regions of highest activity directed towards the outside of the applicator cone, at a source-to-irradiation plane distance of 2.95 cm, with a 1 cm thick Lucite applicator cone, individual source homogeneities were minimized and a uniform beta fluence at the surface was obtained. The mobile irradiation device is able to consistently deliver a homogeneous radiation field at the surface with a nominal dose rate of 3.4 Gy/min. Field symmetry is on the order of ± 3% and field flatness is within ± 5%. Bremsstrahlung radiation is readily detected outside the device, but is less than 1/1000 of the central axis beta dose rate. Despite great individual source inhomogeneity, a mobile irradiation device was developed that is able to produce a 40 mm diameter area of homogeneous skin dose with a dose rate that is useful for research purposes and clinically relevant for the induction of CRI.