Pre-operative localization of impalpable breast lesions using iodine 125 seeds: Placement accuracy and multidisciplinary challenges.

INTRODUCTION: The number of impalpable breast lesions requiring pre-operative lesion localization (PLL) continues to increase. The use of Radio-guided Occult Lesion Localization with Iodine 125 Seeds (ROLLIS) offers multiple benefits for the multidisciplinary team (MDT), but is not without challenges. AIMS: The aims of this audit were to review our multidisciplinary team's experience following introduction of ROLLIS as standard of care for PLL, identify challenges and evaluate seed placement accuracy (SPA). RESULTS/OUTCOMES: Over a nineteen month period, 327 seeds were inserted: 96% of single seed localizations were within 10 mm, 91% within 5 mm and 42% within or in contact with the lesion (or marker clip surrogate) on post-insertion two view mammography. Each component of the MDT reported on benefits of the ROLLIS program and challenges faced. Examples included: an undetectable seed in the operating room, a seed damaged in pathology during specimen processing, suboptimal seed position requiring hook-wire localization (HWL) and delayed seed removal in a patient who initially refused to return for surgery. CONCLUSION: ROLLIS results in high seed placement accuracy. Despite clear advantages, use of ROLLIS presents some multidisciplinary challenges. Robust patient information, training of new staff and adherence to strict policies and protocols are required to ensure safe delivery of a ROLLIS program.

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

Radio-guided occult lesion localisation using iodine-125 seeds (ROLLIS) for surgical removal of impalpable breast lesions has been increasingly used as an alternative to hook-wire localisation. This technique involves implanting a low-level radioactive seed into the lesion, followed by excision of the lesion guided using a hand-held gamma probe. Although the level of radiation exposure from this procedure is low, there has not been an appropriate method to quantify the organ dose. 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 · h-1 · MBq-1 depending 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.

Humerus photon starvation streak artefact.

INTRODUCTION: The reduced (attenuated) number of photons passing through the arm can result in a combination of fine and thick streak artefacts, particularly with the use of thin CT slices and lower radiation dose parameters. This phenomenon is known as photon starvation. We noted an abnormal appearance of the humerus when imaged with certain arm position. This appearance was thought to be artefact due to photon starvation. METHODS: A human radius bone was imaged in different positions and the kV and mA were varied in an attempt to reproduce the artefact, which would support the hypothesis that the artefact may be caused by bone attenuation. RESULTS: Scanning the bone in a different angle and radiation dose parameters reproduced the artefactual appearance of the bone. CONCLUSION: Performing a chest CT scan with arms up can occasionally result in an abnormal appearance to the humerus due to photon starvation artefact. Familiarity with this artefact is essential to avoid misinterpretation.