Irrespective of the advantages of SPECT/CT imaging, the information obtained using dynamic lymphoscintigraphy remains essential [6.43, 6.44].
6.4. RADIOGUIDED SURGERY BASED ON POSITRON EMISSION
3-D volume rendering SPECT/CT images are ‘static’, and in some circumstances, SLN retrieval is complicated or even impossible.
Blue dye is less effective in areas of aberrant drainage that may be indicated pre-operatively by lymphoscintigraphy. It also has a limited value in deep nodal basins. However, it is well known in CM that, in particular, the SLN identification rate for melanomas located in the head and neck region is approximately 85%, which is considerably worse than the almost 100% success rate in other regions of the body. In this regard, the head and neck as the site of a primary CM has been found to be a predictive factor for a false negative SLNB, with false negative procedures in this region varying between 12% and 44% [6.51].
The recent introduction of a new generation of portable gamma cameras has stimulated interest for their intraoperative use also for SLNM and SLNB in patients with melanoma. The added value of this approach is expected particularly for melanomas located in the head or neck, and also for melanomas located in other regions of the body and in cases of SLNs located near the injection site, which are difficult to locate using the gamma probe alone. The portable gamma camera is also helpful to exclude a remaining hot spot after the hottest SLN has been harvested (Fig. 6.10). Another challenging condition is the retrieval of in-transit SLNs that, under some circumstances, appear in very rare locations.
In a recent study in this setting, the use of a portable gamma camera allowed retrieval of SLNs that, because of their anatomic location, had been missed by conventional gamma probe guidance [6.52]. Thus, the use of tomographic and fused images in the pre-operative setting provides the surgeon with valuable information for planning the most appropriate surgical approach. On the other hand, the use of a portable gamma camera for real time imaging in the operating theatre is expected to improve even further the SLN identification in patients with melanoma, as already demonstrated in other cancers, including head and neck, prostate and breast cancers [6.53–6.56].
The acquisition of additional real time scintigraphic images implies that surgical time may increase by various amounts, depending on the level of team coordination. On the other hand, if the portable gamma camera is not used, the surgeon may need to spend a significant amount of additional time seeking other SLNs or confirming complete SLN removal. Preliminary experience suggests that this extra time is worthwhile in this context for SLNs that are difficult to retrieve, as the use of the gamma camera might reduce the possibility of missing a metastatic SLN [6.52].
FIG. 6.10. The use of portable gamma cameras is expanding in some radioguided surgery scenarios. Upper left: Delayed right lateral static acquisition in a patient with a frontal melanoma draining to several LNs at different neck levels in the right cervical basin. Upper right: Image acquired using the portable gamma camera showing the same draining pattern.
Lower left: Intraoperative monitoring using the portable gamma camera of the lymphatic drainage area. Lower right: Image acquired using the portable gamma camera after resection of two SLNs, depicting one residual SLN to be resected. This example illustrates the added value of close monitoring of the surgical procedure using a portable gamma camera.
The freehand SPECT system mentioned in Chapter 4 of this publication combines acoustic signals with 3-D imaging for the localization of areas with focal radioactivity accumulation in the operating room. The system consists of a spatial localization system and two tracking targets that are fixed on the gamma probe and on the patient, respectively. The localization system consists of an optical camera and an infrared localization device. The 3-D images generated with this freehand SPECT probe are visualized on the screen. The images can be displayed in real time so that information on the depth of a node is available. The
feasibility of 3-D SLN localization using the freehand SPECT system is being tested in patients with melanoma, in addition to patients with breast cancer [6.57].
Additional radioguided surgery techniques have been adapted to this scenario, such as radioguided ultrasound lymph node localization (RULL) for melanoma patients presenting with US suspicious, non-palpable LNs.
Investigators from the European Institute of Oncology (Milan, Italy) adapted, for this purpose, the well known breast ROLL approach originally developed for non-palpable breast tumours. In particular, before surgery, approximately 12–15 MBq of 99mTc MAA in 0.2 mL of saline is injected into the suspicious LN under US guidance using a 25 G needle. A scintigraphic study is then performed to locate tracer activity and to ascertain that the hot spot has been placed in a well defined area. Testori et al. reported preliminary results obtained with this ‘new’
GOSTT technique in 12 patients with melanoma [6.58]. In all these patients, the hot spots were easily located using the gamma probe, and the radioactive area corresponded to the suspicious LNs. While four resected LNs did not contain metastasis, seven were positive for CM metastasis and one was positive for Hodgkin’s disease. These preliminary data suggest that RULL is simple, accurate and allows rapid removal of suspicious, non-palpable LNs compared with conventional techniques.
Another potential tool can ascertain the lymphatic drainage of certain cutaneous zones. Reynolds et al. [6.59] developed software specifically designed to yield a 3-D visualization of skin lymphatic drainage of the body, particularly in the head and neck region. They collected the data obtained from lymphoscintigraphies of 929 patients with head and neck CM performed at the Sydney Melanoma Unit. They then generated a 3-D computer model of the skin and LNs and created heat maps to visualize the relative likelihood that any skin region of the head and neck would drain to a specific LN basin. This model has educational and clinical utility, because when no lymphoscintigraphy is available, it could be used to predict possible SLN basins [6.59].