Technique Of Intraoperative Gammaray Detection Probe Localization

The development of the hand-held, high-resolution gamma-ray detection probe, which provides real-time, rapid counting in the surgery room, has allowed the development of a much simpler technique for localizing bone lesions for biopsy. The gamma probe has been quite successfully used intraoperatively for ra-dioguided identification of sentinel lymph nodes in melanoma and breast cancer [13,14]. The gamma probe has been subsequently adapted for use at the H. Lee Moffitt Cancer Center for intraoperative localization of areas of increased uptake of a 99mTc-labeled tracer in ribs and the sternum to guide the surgeon in the open biopsy of suspicious bones [3].

The surgical technique using the gamma probe for intraoperative guidance is quite straightforward and has previously been described [3]. Three to 4 h before surgery the patient receives an intravenous injection of 99mTc-oxidronate in the standard dosage for a radioisotope bone scan (1036 MBq, 28 mCi). A 3-4 h interval from injection until surgery gives the best intraoperative discrimination. After induction of general anesthesia, preparing, and draping of the patient, the hand-held small pediatric size gamma probe (Neoprobe 1000, Neoprobe Corporation, Dublin, Ohio or Navigator, Model GGS, RMD Co., for U.S. Surgical Corporation, Watertown, Massachusetts) is packed in a sterile plastic sleeve. The device is used to localize the area of greatest tracer activity (measured in counts per sec) on the skin of the chest wall in the suspicious-looking area. A moderate amount of background activity from the tracer is found in all the nearby bones. The hot-spot target has a noticeably increased amount of tracer activity compared with the surrounding area.

A 3-4 cm incision is made over this area of increased radioactivity and the targeted rib or sternum is exposed. The probe in the sterile sleeve is then used to precisely localize in the surgical wound the area of increased tracer activity in comparison with background counts elsewhere on the same rib or on nearby ribs (Fig. 2). The point of greatest activity is then marked directly on the surface of the rib with the electrocautery device just prior to removal of that section. Although this is a small wound, the tissues can easily be moved around enough to obtain a count reading on the adjacent ribs immediately above and below the target rib, as well as further away from the hot spot on the same rib.

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Figure 2 Intraoperative view of the hand-held gamma probe (the smallest, pediatric size) in a sterile sleeve being used by the surgeon to measure counts directly on the left 8th rib laterally in patient number 23. The patient is in the right lateral decubitus position with the head superiorly to the right.

Figure 2 Intraoperative view of the hand-held gamma probe (the smallest, pediatric size) in a sterile sleeve being used by the surgeon to measure counts directly on the left 8th rib laterally in patient number 23. The patient is in the right lateral decubitus position with the head superiorly to the right.

In the initial few patients, an intraoperative cross-table lateral radiograph was obtained with a radio-opaque marker on the rib (a spinal needle imbedded in the periosteum is my preference) in the wound to verify that the correct numbered rib was being biopsied. Several radiographs were usually necessary to get the correct view so that the first or twelfth rib was included in the image to enable counting of the ribs from above or below. As the experience with the gamma probe grew, these time-consuming, costly radiographs were eliminated.

A 3 cm portion of the targeted rib or the outer table of the sternum is removed subperiosteally. The bone appears grossly normal in most patients with an abnormal bone scan and normal rib detail radiographs. The specimen of bone is placed in a decalcification solution and isolated 3 to 4 days to allow the 99mTc to decay. The decalcified bone subsequently undergoes histological study with particular attention paid to the area scored by the electrocautery.

The small wound is filled with saline to check for inadvertent entry into the pleura (bubbling in the wound with ventilation), which occurs about 10% of the time in our experience. If the parietal pleura has been entered, a 24 French chest tube is inserted through a separate stab wound into the pleural cavity. The tube is removed in the recovery room after a portable chest radiograph shows the absence of a pneumothorax or pleural effusion. The wound is closed in layers with absorbable sutures and a final subcuticular skin closure. Almost all patients are discharged the same day from the recovery room, with only the quite debili tated patients requiring observation overnight. The postsurgical chest radiograph also serves to document that the proper numbered rib was biopsied.

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