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.

Intraoperative Localisation of Impalpable Breast Lesions Utilising the ROLLIS Technique Following Peritumoral 99mTc-colloid Sentinel Node Lymphoscintigraphy.

BACKGROUND: Ultrasound or stereotactic guided hook-wire localisation has been the standard-of-care for the pre-surgical localisation of impalpable breast lesions, which account for approximately a third of all breast cancer. Radioguided occult lesion localisation using I-125 seeds (ROLLIS) is a relatively new technique for guiding surgical excision of impalpable breast lesions, and is a promising alternative to the traditional hook-wire method. When combined with Tc-99m labelled colloid for sentinel node mapping in clinically indicated cases, there has been uncertainty regarding whether the downscatter of Tc-99m into the I-125 energy spectrum could adversely affect the intra-operative detection of the I-125 seed, especially pertaining to a peritumoral injection. OBJECTIVE: To evaluate the percentage contribution of downscattered activity from Tc-99m into the I-125 energy spectrum in simulated intra-operative resections of an I-125 seed following different sentinel node injection techniques. METHOD: Two scenarios were simulated using breast phantoms with lean chicken breast. The first scenario, with a 2cm distance between the Tc-99m injection site and the I-125 seed, simulated a periareolar ipsiquadrant injection with the subdermal or intradermal technique. The second scenario simulated a peritumoral injection technique with the Tc-99m bolus and an I-125 seed at the same site. Count rates were acquired with a hand-held gamma probe, and the percentage contribution of downscattered Tc-99m gamma photons to the I-125 energy window was calculated. RESULTS: In scenarios one and two, downscattered Tc-99m activity contributed 0.5% and 33% respectively to the detected count rate in the I-125 energy window. In both scenarios, the I-125 seed was successfully localised and removed using the gamma probe. CONCLUSION: There is no significant contribution of downscattered activity associated with a peritumoral injection of Tc-99m to adversely affect the accurate intra-operative localisation of an I- 125 seed.

Radioguided occult lesion localisation using iodine-125 seeds ('ROLLIS') for removal of impalpable breast lesions: First Australian experience.

INTRODUCTION: Approximately one-third of breast cancers are impalpable and require pre-operative image-guided localisation. Hook-wire localisation (HWL) is commonly used but has several disadvantages. Use of a low-activity radioactive iodine-125 seed is a promising alternative technique used in the USA and the Netherlands. This pilot study describes the first use of this in Australia. METHODS: In this prospective pilot study, 21 participants with biopsy-proven breast cancer underwent radioguided occult lesion localisation using iodine-125 seed(s) (ROLLIS) with insertion of a hook-wire for back up. Sentinel node biopsy was performed where indicated. Ease of hook-wire and seed insertion, duration of the procedure, dependence on the seed versus hook-wire during surgery, lesion location within the specimen, histopathology including size of radial margins, the ease of seed retrieval in pathology, and safe return of seeds for disposal were documented. Radiation dosimetry of staff was performed. RESULTS: All seeds were placed within 3.5 mm of the lesion. All lesions and seeds were removed. One participant needed re-excision for involved margins. Radiologists and surgeons both preferred ROLLIS. Surgeons were able to depend on the seed for localisation in all but one case. Sentinel node biopsy was successfully performed when required. Pathologists found seed retrieval quick and easy, with no detrimental effect on tissue processing. No radiation doses measurably above background were received by staff. CONCLUSION: ROLLIS is an easily learnt, safe and effective alternative technique to standard HWL.

Scatter and transmission doses from several pediatric X-ray examinations in a nursery.

BACKGROUND: While several studies have investigated the dose from scattered radiation from X-ray procedures in a pediatric nursery, they examined scatter from chest procedures only, or the types of examination were not specified. OBJECTIVE: The aim of this study was to collect scatter and transmission data from several types of X-ray examinations. MATERIALS AND METHODS: Using a "newborn" anthropomorphic phantom and an ion chamber, a series of scatter and transmission dose measurements were performed using typical exposure factors for chest, chest and abdomen, skull, skeletal long bone and spine procedures. The phantom was inside a crib for all exposures. RESULTS: The maximum scatter dose measured at 1 m from the field center was about 0.05 micro Gy per exposure for lateral skulls. Transmission doses for lateral exams were around 0.1 micro Gy per exposure at 1 m from the isocenter. CONCLUSIONS: The study demonstrated that scatter dose to other patients in a neonatal unit is not significant, assuming the distance between adjacent cribs is in the order of 1 m. Transmission doses are also low provided the beam is fully intercepted by the cassette. For an average workload the dose received by imaging technologists would be small.