A multimodality localization technique for radio-guided surgery
© Gulec et al; licensee BioMed Central Ltd. 2007
Received: 01 February 2007
Accepted: 25 April 2007
Published: 25 April 2007
Intraoperative localization of image or endoscopy-detected lesions occasionally pose surgical challenges due to the small lesion size and/or difficult anatomic exposure. Identification of such lesions can be facilitated using a hand-held gamma probe with utilization of Tc-99m macroaggregate albumen (MAA) localization technique. The radiopharmaceutical injection can be performed using ultrasound (US) or endoscopy guidance.
The clinical use of the Tc-99m MAA protocol gamma probe-guided surgery was discussed in three representative cases. Surgical indication was diagnostic exploration in two patients with suspicious lymphadenopathy, and determination of extent of surgical resection in a patient with polyposis. Lesion localization with 100 microcurie (3.7 MBq) Tc-99m MAA prior to surgical exploration resulted in definitive localization of lesions intraoperatively.
The use Tc-99m MAA deposition technique at the site of surgical target is a highly efficient radio-guided surgery technique with definitive impact on the success of surgical exploration in selected indications.
The role of gamma probes in surgical oncology practice has been well established [1–9]. Surgical performance with intraoperative gamma probe detection is critically dependent on target to surrounding background ratio (TBR). This ratio, for localization techniques that involve systemic administration of radiopharmaceuticals, is a function of radiopharmaceutical uptake and clearance kinetics. Probe's ability to discern the target signal also is a major technical factor in the clinical success. A minimum TBR of 1.5:1 is needed in the operative field for the operating surgeon to be comfortable that the differences between the target tissue and normal adjacent tissue are real . Obtaining a satisfactory TBR is always a significant technical challenge with localization techniques using systemic administration of radiopharmaceuticals. Administration of a locally-entrapped radiopharmaceutical in or around the target tissue results in an ideal TBR.
Gamma probe-guided surgery protocol
Gamma probe-guided surgery protocol for Tc-99m MAA
Tc-99m MAA Lesion Localization with image/endoscopy guidance
• Tc-99m MAA
• 0.1 mCi (.0037 MBq)/direct injection
Standard Imaging Protocol
• No nuclear medicine imaging needed
Timing of Surgical Exploration
• Within 6 h post-injection
• Not required
• Standard medium-energy gamma probe
• Analyzer Settings: Photopeak: 140 keV, Window: 20%, Threshold: 136 keV (In commercial systems this is a default setting)
• Verify calibration and settings of the system
• Cover the probe with sterile plastic sleeve
• Probe survey at counts- per-second mode (Dynamic pitch range feed-back helpful)
• Hot-spot confirmation with TBR>1.5 at 10-second count mode (TBR ratio feed-back helpful)
Avoid simultaneous electrocautery use
The use Tc-99m MAA deposition technique at the site of surgical target is a highly efficient radio-guided surgery technique with definitive impact on the success of surgical exploration in selected indications. Administration of the locally-entrapped Tc-99m MAA in or around the target tissue results in an ideal TBR. Tc-99m MAA, when injected into the tissues, remains almost stationary with a minimal local diffusion. Particle degradation, slow lymphatic absorption and phagocytosis constitute the principal mechanisms for MAA clearance. The biologic half life of MAA is approximately 6 hours. The effective half life of Tc-99m MAA is calculated at approximately 3 hours when the 6-hour physical half life of Tc-99m is factored in (1/2 TEff = 1/2 TBiol + 1/2 TPhys). A 0.1 mCi Tc-99m provides satisfactory signal intensity for gamma probe detection within a wide range of time frame. Surgical procedure can be scheduled any time after injection up to 6 hours. (Suggestion: Surgical procedures can be scheduled any time during the 6 hours post injection.) Tc-99m MAA injection can be given under CT, US or endoscopic guidance. Lymphazurin blue (blue dye) can be added to the injectate to facilitate dissection by providing a visual aid.
Major applications of the technique include localization of lymph nodes and colonic polyps. The technique may also be used in localization of non-palpable breast lesions as an adjunct to needle/wire localization techniques.
The information in this document was obtained in accordance with HIPAA regulations and with the approval of our Institutional Review Board. Patients consent was obtained for publication of their case records
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