I've heard of a similar 20MBq limit here, but frankly, if you want to image a faint node, it isn't enough too frequently to be of use. I like to use 37 MBq. Frankly, I don't know where the 20 MBq idea came from, using radioactive antimony I suspect in the old days. But, for Tc99m it is a silly idea. The nodes have a wait and see if you can see me attitude toward physicians. Some show up in 5 minutes, some take 40 minutes, and some don't show that easily. I find that if you cannot see them on planar imaging, do a SPECT, and they will show up. But, in that case, one cannot do skin marking to aid in localization. But having a CT-SPECT fusion certainly does localization that well enough for anyone. BTW, the CT dose probably is larger than the 20 MBq Tc99m dose. Just guessing, on that, but 20 MBq? We give heart patients 1000 MBq for their stress images alone, so what is the deal with 20 MBq? Absence of thought perhaps? Lots of that to go around.
20 MBq Tc is such a small amount of activity for a cancer patient, who will get a radiotherapy later on, that I cannot understand this minimized value. It´s far more important to really find the storing nodes even under OP situations where you take a simple counter to find them.
Thats why I agree with Carls response.
@Farshid,
you are right, in Germany we also have the ALARA principle, which requests the minimalisation of radiation doses. But this principle doesn´t mean, that you can risk some serious faults when treating a patient, for example by missing a positive lymph node because of to low activity. Therefore the physician is demanded to weight his methods.
Thank you for the interesting comments with amazing discussion on different applicated activities! Hope to get more response from different centers and different countries pro and con low and high SLN activity to emphasise the purport of this issue for breast cancer patients!!
Accordingly, EANM and SNMMI practice guideline for lymphoscintigraphy and sentinel node localization in breast cancer 2013, support this deiscrepancy and report no consensus on the activity to be administered in a SLN procedure. The investigated and suggested activities vary considerably, as discussed in this forum. Activities as low as 3.7 MBq (1) and as high as 370 MBq (2) have been used in different studies.
According to this guidline, a total injected dose of 5 to 30 MBq is generally considered sufficient for surgery planned for the same day.
Howerver, I believe, more data are needed to clarify this issue!
1. McCarter MD, et al. Ann Surg Oncol. 2001
2. van der Ent FW, et al. Eur J Surg Oncol. 1999
Usually for sentinel node biopsy with surgery to be done same day, 20 MBq is adequate and should be injected at least 2 hours before the surgery. If surgery is planned the next day , then 37-100 MBq is recommended.
It depends on center to center on type of injection, usually we prefer peri-areolar as peritumoral lymphatics may be heavily laden with tumoral cells so that lymphatics might not flow leading to failure of technique. Peri-areolar injection concept has come up because of unique nature of superficial lymphatics of breast (Sappy plexus).
Imaging before the surgery, again varies between various centers depending on the time at your disposal. In many busy centers, they do not do imaging and send the patient directly for surgery, but in my opinion, we should do planar imaging and in doubt SPECT- CT for confirmation.
During surgery, with the use of gamma probe, the injection site is marked and any node having more than 10% of injection site count is considered as positive. This should be taken out for frozen section. Again whole axilla should be surveyed for activity and same principle of 10% should be followed till we do not find anything more than background.
Hope this would help...Best of luck