Proposed Topic (Most preferred): :
Clinical Safety and Quality Service II (Projects aiming to enhance clinical safety and outcomes, clinical governance / risk management)
Proposed Topic (Second preferred): :
Research and Innovations (new projects / technology / innovations / service models)
Authors (including presenting author) :
CHEUNG YC Joel(1)
Affiliation :
(1)Department of Oncology, Prince Margaret Hospital
Introduction :
Y90 treatment is a radiation therapy and embolization to treat cancer of the liver, also known as Selective Internal Radiation Therapy (SIRT). It involves injecting radioactive Y90 beads into the blood vessel that feeds the tumor. The beads emit radiation that kills the cancer cells while sparing the healthy liver tissue. Y90 is a pure beta emitting isotope with an average energy of 0.9 MeV. Bremsstrahlung x-rays from the Y90 beta is less than 0.01%. Beta is more ionizing than gamma and is therefore more hazardous and is a main concern in radiation protection while administration of Y90. The maximum penetration range of its beta in soft tissue is 1.1cm and therefore a transparent plastic box provided by the Y90 manufacturer together with a homemade Perspex shield seem traditionally good enough for radiation protection purpose. In reality, it is not the case. A significant high radiation level can still be measured after its beta is attenuated by a thick Perspex sheet.
Objectives :
1)To investigate the physics behind why does a high radiation level is still measured after all beta rays are attenuated by thick Perspex sheets. 2)To give a better and effective protection method based on this finding.
Methodology :
An EGSnrc software toolkit was employed to simulate the real administration setup. It performs Monte Carlo simulation of ionizing radiation transport through matter. A calculation input of Y90 beta ray spectrum was needed for our user Monte Carlo code. Scoring of exiting particles, such as Bremsstrahlung photons and its created secondary electrons, were made after the beta rays passed through a 1cm thick Perspex sheet.
Result & Outcome :
The Monte Carlo results showed that exiting Bremsstrahlung photons were created with an average energy of 194keV. These Bremsstrahlung photons further create negligible amounts of secondary electrons. Spectrum plots of the Bremsstrahlung photons was calculated. This spectrum plot obtained by physical measurement methods are impossible. These low energy photons are still hazardous and further shielding is in need. Radiation protection solely uses Perspex sheets is not enough. A simple lead glass shield is suggested for Y90 administration in a complete radiation protection point of view. Although Bremsstrahlung photons can be created through interaction of Y90 beta with the high atomic number material of lead glass, these Bremsstrahlung photons can be attenuated easily by the lead glass shield itself through photoelectric absorption.
