Te-Jui Hung, John Burrage, Anita Bourke and Donna Taylor Pages 111 - 114 ( 4 )
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.
Downscatter, I-125, Tc-99m, Peritumoral, Sentinel lymph node, lymphoscintigraphy.
Department of Nuclear Medicine, Royal Perth Hospital, Perth, Department of Medical Engineering and Physics, Royal Perth Hospital, Perth, Western Australia, School of Surgery, University of Western Australia, Perth, Western Australia, School of Surgery, University of Western Australia, Perth, Western Australia