Radioguided occult lesion localization: better delineation of the injection site with a high-resolution collimator

Abstract

Aim: Radioguided Occult Lesion Localization (ROLL) is a method for guiding the excision of occult breast lesions. A radiotracer is injected preoperatively in the tumor. The surgeon can locate the lesion with a gamma probe. It has been recommended that the tissue is resected where the activity falls rapidly. But this cut-off level can fluctuate depending on the user. The aim of this study was to compare the accuracy of two different types of collimation.Materials and methods: To simulate the detection of a radioactive “lesion”, 0.2ml of a solution of 99mTc labeled colloids (4MBq) were deposited at 3cm depth in a chunk of cow muscle. Detection was performed with a gamma probe (GammaSup, Clerad, F) equipped either with a regular or with an additional high-resolution collimator. The response curve was drawn moving laterally the probe on the chunk of cow by 5mm steps. Edges of resection were determined with different cut-off levels (from 5 to 50% of maximum counts by 5% steps).Results: Without additional collimator, the mean distance between injection point and resection edge was 18mm, standard deviation 7.8mm with a range between 11 and 18mm. With additional collimator, the mean distance decreased to 10mm (−44%), standard deviation 4.2mm (−46%) with a range between 6 and 10mm.Conclusion: The results demonstrate that the additional collimator provides more precise and reproductive delineation of the injection site. It should be optimal for the ROLL technique.