Main Techniques of Sentinel Lymph Node Labeling 2

Two main technical principles are currently fol- lowed in labeling sentinel nodes: the two tech- niques can be used separately, but may also be combined.

·

Noncarcinogenic inert blue dye (patent blue) in- jection.

± The blue staining method with methylene blue or patent blue or other stains shows up the paths of the lymphatics from the pri- maries to the nodes. However, the disadvan- tages, especially in the areas surrounding the primary, are the general blue staining of all regional tissues (tumors, fibrous and fat tis- sue). This diffuse staining disturbs the over- view, especially for the pathologists (see also Bachter et al. 1996, 1998).

·

Radiocolloidal labeling (

Tc-nanocolloidals).

± A review of success rates as published by the Board of the New England Journal of Medi- cine showed that a combination of both methods provided best results (McMasters et al. 1998).

Tracers have been injected peritumorally, subcuta- neously or intradermally (in breast cancer) (Borg- stein et al. 1997, 1998; McIntosh et al. 1998).

The

Tc-nanocolloid method is a nuclear medicine procedure which involves exposure of the patient and, principally, of the staff in the depart- ment of nuclear medicine and the operating room and of the pathologist to radiation. The radioactive tracer is normally injected in the nuclear medicine department, where all suitable facilities exist for its administration and for the safe handling and disposal of the radioactive waste produced. Senti- nel node scintigraphy is a low-activity procedure for a regular nuclear medicine department. The patient's radiation exposure is about 0.32 mSv per examination.

Radiation doses arising from the sentinel node technique compare with a range of natural and man-made sources and statutory dose limits (data

obtained from the National Radiological Protection Board (NRPB) (International Commission on Ra- diological Protection 1990) (Table 1).

Good Practice for Radiation Protection in the Operating Room

The patient is usually scheduled for operation ap- proximately 24 h after tracer administration. When radioactive decay is taken into account, this results in retention of between 1 and 10 MBq activity at the injection site by the time the operation is per- formed. As detailed earlier, with the exception of the sentinel node and other axillary lymph nodes demonstrating a similar level of tracer uptake, there will be a negligible distribution of radioac- tivity outside the injection site. Specifically, there is an absence of detectable radioactivity both in the general circulation and in unrelated body tis- sues.

The possibility of radiation risk, however remote, must be considered: potentially, both internal and external radiation exposure may arise. Staff may be irradiated by virtue of their proximity to the radioactive patient and may also come into direct

Main Techniques of Sentinel Lymph Node Labeling 2

Table 1. Source of radiation exposure/relevant legislative limits

Radiation dose (mSv) Sentinel node technique

(breast carcinoma) 0.32

Return flight: London to New York

(dose from cosmic rays) 0.06

Return air flight: London to Sydney

(dose from cosmic rays) 0.20

One year's residence in Denver, Colorado, USA (additional radiation dose from cosmic radiation at higher altitude)

0.88

contact with the radioactive tracer in vivo, with any excised radioactive tissue specimen, or with con- taminated dressings, drapes or operating room equipment (Barres et al. 1992). The maximum activ- ity retained within the injection site at the time of operation will be approximately 10 MBq

Tc. Ex- posure to an unattenuated (i.e. unshielded) radioac- tive source containing this activity will effect a ra- diation dose rate of 0.17´ 10

Sv (0.17 lSv)/h at a distance of 1 m from the source, and of 1.8 lSv/h

at 30 cm [dose rate data obtained from the Institute of Physical Sciences in Medicine (IPSM, 1991)] („v- ril et al. 1996, 1997). For each surgical procedure, a typical total exposure time to the tissue containing the injection site of 1 h, at the lesser distance, will result in a maximum radiation dose to the sur- geon(s) involved of approximately 1.8 lSv per pa- tient procedure. In the UK, the maximum permitted annual radiation dose to a member of the public (which also means any member of staff not formally

6

Table 2.Calculations of radiation doses to the surgeon (Waddington et al. 2000) Dosage of nano-

colloid to breast Performance of SLN operation 24 h

after injection^a Performance of tumor and SLN operation 24 h after injection^a

15 MBq Whole body

0.21 lSv Finger

0.06 mSv Whole body

0.47 lSv Finger

0.12 mSv

aIncrease >4 lSv/h when the operation was performed 4 h after injection

Table 3. Values for radiation exposure of surgical staff evaluated by Institute of Physical Sciences in Medicine (1991) and Keshtgar et al. (1999)

Dosage At time of surgery Implication of 500

surgical SLN operations 10 MBq (unshielded) Whole body

0.21 lSv Finger

0.06 mSv 1 mSv

Table 4.Radiation dose to the breast referred to injected volume (modified from Eshima et al. 2000) Injection volume (ml) Dose (mGy/MBq)

0.48 160

0.96 87

1.92 44

3.85 23

5.77 15

Table 5.Radiation dose to staff (15 MBq, 24 h p.i.). (Modified from Waddington et al. 2000)

Procedure Organ Probe Dose

Immediate analysis

45' WB Primary SN 127 (6.33)

Processing 60' WB Primary SN 169 (8.44) 21.1 (1.05) 2.64 (0.13)

Close contact 15/5' Finger Primary SN 39.8 (6.64) 4.98 (83.0) 0.62 (10.4)

Microscope 15' Lens Primary SN 42.2 (2.11) 5.27 (0.26) 0.66 (0.03)

Treatment at 1 m distance Treatment at 30 cm distance

Op. (nSv) 18 h (nSv) 36 h (nSv)

designated a radiation worker) was reduced to 1 mSv (ICRP 60) (International Commission) in the year 2000, allowing approximately 500 sentinel node pro- cedures to be performed per year according to the protocol detailed in this text before the individuals exposed approach this annual dose limit. It is there- fore clear that there is a very low external radiation hazard to members of staff. One circumstance re- quiring extra consideration may be that of the preg- nant female surgeon or scrub nurse; when staff per- form or assist at this procedure regularly, specifically lower dose limits have to be observed for any who are pregnant in order to minimize the radiation dose, and especially that to the fetus. Thus, personal radiation badges issued to staff would be useful in resolving the exact significance of this issue, given the individual local circumstances of both workload and surgical protocols (Keshtgar et al. 1999).

Waddington et al. (2000) found that 95±99% of the tracer applied remained at the site of injection, with residual activity in the lymphatic basin even 24 h after the injection. In contrast, the systemic uptake calculated from blood measurements amounted to only 0.73% of the injected dose (Waddington et al. 2000).

When 15 MBq

Tc-nanocolloid was adminis- tered the effective dose equivalent was calculated to be 1´10

mSv/MBq overall to the patient and 7.2´10

mSv/MBq to the breast.

Eshima et al. (2000) investigated the significance of the injected volume for radiation exposure of the breast. Based on the assumption that the radio- activity is retained in a distinct area of the breast without diffusion to the other parts, they showed that breast radiation exposure can be reduced to one tenth by using a tenfold volume of tracer solu- tion.

Tables 2±5 give an exact overview of exposure of the patient's breast and of medical staff to ra- diation doses in relation to the volume adminis- tered and the duration of exposure at different times after injection.

Radioactivity Monitoring

Results of Measurements in Staff Members at the Royal Free University and Medical School, London The Royal Free Nuclear Medical Institute data re- sulting from control measurements have been pub- lished in a paper with Waddington (2000) as the main author, and their experience is as follows Minimal tracer

migration 95% (retention at the injection site) Dosage resulting for the

patient (mean dose at the breast)

2´ 1´10

mS/MBq 7´ 2´10

mGy/MBq Mean whole-body dose to

surgical staff per procedure 0.34 lSv

Mean finger dose 0.09 mSv (90 lSv) Pathology staff, predomi-

nantly below measurable levels

Relevant doses only when a large number of cases are analyzed promptly

Observed contamination of the floor in the operat- ing room (Waddington et al. 2000)

Upto 22% of the doses administered found in swabs!

Attempts to label cancer-infiltrated regional nodes by scintigraphy using monoclonal antibodies have had very little success, because it was not possible to detect micrometastases.

Antibodies against tumor-specific antigens (SM3, mAb 170 H.82 or

Tc-labeled anti-CEA Fab fragment) demonstrated sensitivity amounting to upto 80% in detection of cancer-infiltrated lymph nodes (Dessureault et al. 1997; Limouris et al. 1997; Britton et al. 2000; Goldenberg et al.

2000). In contrast to these results, however,

F-

FDG-PET and scintigraphy with such nonspecific

tracers as

Tc-sestamibi or tetrofosmin showed

promising results in advanced tumor stages, with

upto 95% sensitivity, but failed to yield accurate

lymph node status evaluation in pT1 stages („vril

et al. 1996; Adler et al. 2000; Yutani et al. 2000).

Good Radiation Protection Practice in the Pathology Laboratory

Histopathology staff members can also potentially be exposed to both internal and external radiation by virtue of their work practices. However, the ini- tial sample preparation is typically very rapidly executed and should therefore present little scope for any measurable radiation exposure. Subsequent to this initial stage, preparatory fixing of the speci- men in formalin for a period of not less than 48 h will lead to a reduction in the radioactive content of the specimen by a factor of approximately 250.

Thus, normal histological analysis of multiple tis- sue samples entails negligible further exposure to radiation. After a total of 1 week's storage, all tis- sue specimens will have decayed so that they will now contain less than 1 Bq activity and may safely be disposed of as nonradioactive waste.

New approaches to MR lymphography are in progress (Anzai et al. 1994; Vassalo et al. 1994;

Bengele et al. 1994; Harika et al. 1995; Palmacci and Josephson 1996; Mussurakis et al. 1997). The new element in radiologic diagnosis is the use of Sinerem (Guerbet, France), a tissue-specific con- trast agent used in MRI. This new agent, which is currently in phase III of clinical development, con- tains iron oxide nanoparticles surrounded by low- molecular-weight dextran. A smaller particle size than that of the established liver-specific contrast agent Endorem (Guerbet, France), which is taken upby reticuloendothelial cells of the liver (Kupffer cells), enables Sinerem to cross the capillary wall and ultimately to be taken upby the mononuclear phagocytic system (MPS) of lymph nodes (see long-term work carried out by Weissleder's group (Weissleder et al. 1988, 1989a,b, 1990 a,b, 1994, 1996; Jung et al. 1996). Preliminary work was also performed by Brady and Ferrucci (1987).

Apart from the development of X-ray lymphan- giography in the late 1970s, the new generation of MRI contrast agents targeting the MPS represents the primary approach by radiologists to examine lymph nodes in a functional, and no longer in a purely morphologic, manner. Several clinical stud- ies have shown a significant signal increase in nor- mal or inflammatory lymph nodes, whereas meta- static lymph nodes have shown no significant up- take of the contrast agent. Sinerem has to be admi- nistered by i.v. infusion outside of the MRI scan- ner after a non-contrast-enhanced baseline exami-

nation. The postcontrast images can be obtained in a time-window of 6±24 h. It must be stressed that the method of i.v. lymph node contrasting does not allow specific visualization of sentinel lymph nodes (SLN); the SLN can only be identified by staff with adequate anatomical knowledge.

Trials to identify SLN and lymphatic drainage by means of the s.c. administration of ultrasmall iron oxide particles (USPIO) have been reported, but mostly in animal studies (Rogers et al. 1998).

However, some clinical study programs are already in progress (see chapter 19).

F-18-FDG-PET has advantages: besides the imaging of the primary tumor, PET allows localiza- tion of metastases in an acceptable proportion of cases. Small lesions, even those with a diameter of 3±5 mm, can be detected with F-18-FDG-PET.

However, when lesions are smaller it gives false- negative results. Thus, sentinel node detection and a pathological work-up are always necessary in tu- mors that are negative according to PET. In cases positive for FDG uptake the diagnostic accuracy is very high (see also chapter 5).

Several points still require discussion with re- spect to the different techniques. First of all, it must be pointed out that attempts at interdisciplin- ary management can only be successful with opti- mal performance of all disciplines involved in such evaluation programs (surgeons, specialists in nu- clear medicine and/or radiodiagnosis, and pathol- ogists), because the initial locoregional operative work and the histological evaluation of lymph node material must be optimal.

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