Clinical practice guideline for dedicated breast PET.

Dedicated breast positron-emission tomography (dedicated breast PET) is a diagnostic technique using a dedicated breast PET scanner. PET using 18F-2-deoxy-2-fluoro-d-glucose (hereafter, FDG) is a very useful diagnostic technique in medical examination. In 2002, FDG-PET was employed for health insurance checks on 12 diseases, mainly cancer. Since breast cancer has been covered under insurance from the beginning, the technique has played an important role, mainly in staging and recurrence screening [1]. According to a report of the National Cancer Center, as regards the probability of survival from breast cancer, there is a significant difference between T1b (from 0.5 to less than 1.0 cm) and T1c (from 1.0 cm to less than 2.0 cm) (P = 0.003), and it is, therefore, important to detect breast cancer of diameter less than 1.0 cm [2]. Although mammography is the standard technique for detecting breast cancer, its usefulness is limited in the high-density mammary gland of young people. On the other hand, although MRI is useful also to detect breast cancer in a high-density mammary gland, and there is a report that its sensitivity and degree of specificity are superior to those of mammography, it is necessary to perform the examination while taking the menstrual cycle into consideration, and there is a concern over the considerable side effects accompanying the use of contrast media. Although breast cancer is a disease for which health insurance covers diagnosis by FDG-PET, with conventional whole body PET equipment, sensitivity to a small primary tumor of diameter less than 1 cm is low. The reasons for this are that with whole-body PET, spatial resolution is limited; second, on the image obtained in the dorsal lying position, detectability falls due to respiratory movement; and third, a physiological FDG distribution is also obtained from a healthy mammary gland. Even if it is attempted to obtain an image in the prone lying position or a delayed image, detectability is still insufficient with whole-body PET. To overcome these problems, a dedicated breast contact PET scanner was developed. Since the breast is located in the body surface, the detector can be brought up close without limitation, and it may be expected that due to the close-up image, spatial resolution would be improved. If respiratory movement can be reduced by fixing the breast, or imaging with the patient in the prone position, it will also lead to an increase of detection sensitivity. It may be expected that by spending time to image only the breast, it will be possible to obtain a detailed image of the distribution of FDG in the mammary gland, and the contrast between healthy tissue and diseased tissue will become clear. The following 2 types of dedicated breast PET exist, including the scanner already approved also in Japan and those under development. We will refer to them temporarily as the opposite type and ring type, according to the placement of detectors. (1) Opposite type dedicated breast PET scanner In this type, the breast is interposed between two plate-like detectors to acquire an image, as in the case of a mammography. If the breast is directly fixed, the detector can be brought into close contact, and respiratory movement can be reduced. Tomographic images parallel to the two detectors on either side of the breast can thus be obtained [3–6]. In principle, two images, in the medio-lateral oblique direction and the cranial-caudal direction, are obtained for each of the left and right breasts, i.e., a total of 4 images.