Development and application of a simple method for calculating breast dose from radio-guided occult lesion localisation using iodine-125 seeds (ROLLIS).

This study aims to provide a simple technique to estimate the mean absorbed dose to the breast in patients undergoing the ROLLIS procedure.
 The transverse plane dose rates as a function of distance for the I-125 seed were used to calculate the dose rate to voxels in a breast modelled as a hemisphere. The dose rate to each voxel was assumed to arise from an isotropic point source, and calculated using a linear interpolation of the dose rate data and the radial distance of each voxel from the seed position. Two scenarios were simulated: (i) One seed at the centre of the lesion; and (ii) Two seeds bracketing the lesion. The mean absorbed dose was calculated by excluding the volume of lesion and surgical margin which are modelled as a sphere with its centre at the centre of the lesion. Mean absorbed doses were calculated for a range of breast and lesion sizes.
 The calculated dose rate factors from the ROLLIS procedure ranged from 0.0097 to 0.0477 mGy∙hr-1∙MBq-1depending on many factors including breast size, lesion size, seed number, seed activity and the time in situ. Lookup tables were compiled to allow a convenient way to calculate the mean absorbed dose for future ROLLIS patients. Based on clinical data collected at our institution, the mean absorbed dose to the breast for a typical ROLLIS patient would be approximately 0.50 mGy.
PMID: 30673651 [PubMed - as supplied by publisher]

Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Reed AJ, Kim JH, Burrage JW Tags: Phys Med Biol Source Type: research