Advanced Physics for Brachytherapy 2018

Brachy dosimetry is challenging … for an Ir-192 HDR source K S zyD ) , ( .

Dose rate varies from ~20 Gy/s @ (0.5cm,90 0 ) from an Ir-192 HDR source to ~2 μGy/s @ (5cm,90 0 ) from an I-125 LDR source Sensitivity high for low uncertainty, dose range high, (preferably) with k l =k dr =1 Spatial dose gradient is high (i.e. ~25%/mm in the radial direction @ (0.5cm,90 0 ) from an Ir-192 HDR source) Volume must be small, positional accuracy is very important (1% rel. uncert. in D(1cm,90 0 ) requires 0.05mm uncertainty in r, assuming 1/r 2 dose dependence since: ) If solid phantoms are used to increase positional accuracy a correction is required from D w,phant to D w,w at each meas. position r D r D   2 =

Figure from: Taylor, Yegin, Rogers, Med. Phys. 34(2) 445 (2007)