Radiation Dosimetry in Brachytherapy, Introducing A Spherical Diode Dosimeter

Abstract

Brachytherapy is a cancer treatment modality in which a radiation source is inserted into the tumor. It is done in one of two ways: Low Dose Rate (LDR) treatment where seeds are permanently implanted, or High Dose Rate (HDR), a short time exposure. The isotopes mostly used for LDR treatment are I-125 and Pd-103 of activity about 18.5 MBq per seed. HDR treatment is generally done with Ir-192 sources of activity 370 GBq. We introduce a new source for both HDR and LDR treatment, namely Tm-170. Safety considerations for the medical staff, the patient and people around him include: well shielded sources, shortest handling time and keeping uninvolved people at a safe distance. HDR sources are kept in a lead container and applied by a remote controlled delivery system. Radiation dosimetry and source calibration is done before the sources are applied to the patient. The methods used for dose measurement are: TLD, diode or ion chamber. We introduced a new diode for dosimetry, micro-spherical diode. This tiny diode causes very little perturbation and provides spherically symmetrical dose measurements. Monte Carlo calculations are used to verify the measurements. Source parameters are calculated for source quality comparison.