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

Abstract

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.

Radioactive seed localization is a safe and effective tool for breast cancer surgery: an evaluation of over 25,000 cases

“…While the less precise MIRD methodology gave a higher dose estimate, it is important to note that even these larger values represent very low overall radiation exposures to breast tissue. These findings also reinforce the need for continued research in developing, selecting and implementing dose calculation methodologies in RSL procedures [35].…”

Multimodal soft tissue markers for bridging high-resolution diagnostic imaging with therapeutic intervention

“…This allows all radionuclide handling to be performed according to institutional and national radioisotope guidelines, which is highly attractive from a production, distribution, storage, and regulatory point of view. The radioactivity levels included in this study have already been reported as safe for patients and medical personnel in breast surgery (40). The use of radio guidance must, however, be evaluated in terms of acceptable radiation dose for each indication and adhere to applicable guidelines.…”

ROLLIS roll‐out: Pitfalls, errors, lessons learned and recommendations from Australian and New Zealand experience during the randomised controlled trial, implementing a novel localisation method for impalpable malignant breast lesions, radio‐guided occult lesion localisation with iodine‐125 (125I) seed (ROLLIS)

“…As an example, a person would need to sit 30 cm from a 3.7 MBq 125 I seed for 2.7 h per day, 5 days a week, 52 weeks a year (or 140 h @ 1 m from seed for a week) to reach the public radiation limit (1 mSv/year). A method for calculating the radiation dose from an in‐situ seed is available 24 . A lack of knowledge of the radiation dose can cause confusion.…”

“…A method for calculating the radiation dose from an in‐situ seed is available. 24 A lack of knowledge of the radiation dose can cause confusion.…”