Single detector non-imaging probes have been in use for some time to detect and locate the sentinel lymph node(s) during breast cancer surgery. These probes have proven to be useful to the surgeon in this regard. However, they are limited in use as they do not provide an image, just a crude count rate from a 1 cm2 area detector. Therefore, locating the sentinel node is not very accurate and it does not provide accurate information on the extent of the tumor. Therefore, an imaging probe with an adjustable spatial resolution by removing or exchanging the collimator will achieve significant improvement in sentinel node detecting and locating. It will also enable the imaging probe to be used for other applications such as detecting and locating primary and secondary tumors in the breast tissue and lymph nodes through scintimammography.
Recently breast imaging studies with 99mTc SestaMIBI and 201Tl have demonstrated uptake by sentinel lymph nodes and malignant breast tumors but not by benign masses (except some highly cellular adenomas). Most of the results give sensitivities and specificities of about 90%, and recently equally encouraging results have been reported for 99mTc Methylene Diphosphonate (MDP) with a sensitivity of 92% and a specificity of 95%, even though these studies were carried out with conventional full size gamma-ray cameras which have some inherent limitations for breast imaging especially during surgery:
1. The large size of the gamma camera makes it difficult to position optimally relative to the breast.
2. Not usable during surgery due to the large size, low sensitivity and low spatial resolution.
The reported small, compact, handheld solid-state imaging probe is expected to achieve much better performance in all of these categories. It will be especially useful before, during and after surgery to locate the sentinel lymph node(s) using the drainage of the radiopharmaceutical from the tumor site to the sentinel node(s). It may also be used in the scintimammography mode to locate a lesion and its metastatic components, completely remove the cancerous tissue and verify that no cancer is left behind. Also the cancers that are not detectable by conventional mammography such as fibrocystic change and dense breasts especially in young women (≈40% between 40 and 50 year old), lack of calcifications (about 50% of all preinvasive cancers) and mammographically occult breast cancers. These, in many cases, will be identifiable by the reported system, because the method of detection relies on isotope uptake in the tumor, not on subtle differences in its radiodensity.
The instruments described here are called SenProbe (FIG. 1) and MicroImager (FIG. 7). While the SenPROBE and MicroImager systems are not directly a therapeutic tool, They have the potential to become excellent tools in monitoring the progress of surgery. Before the surgery it can be used for detecting and locating the sentinel lymph node(s), searching for malignancy in the sentinel and axillary lymph nodes, the location, size and the distribution of the tumor. During surgery the accuracy of the position and the extent of the tumor can be determined, removal of the cancerous tissue can be monitored and for the metastatic tumors the lymph nodes and the surrounding tissue can be screened, decreasing the likelihood that the physician will leave cancerous tissue behind. After the surgery the surgeon can use the SenPROBE or the MicroImager to check that the tumor is completely removed, and no residual malignant tissue remains. SenPROBE or the MicroImager may also be used in some cases before, during and/or after chemotherapy. Monitoring the tumor size will confirm that the chemotherapy treatment is effective.