Since national health insurance stipulates that whole-body PET must be used in conjunction, facilities must satisfy the following criteria regarding calculation of diagnosis and treatment remuneration:
At least 1 regular doctor who has 3 or more years’ experience in nuclear medicine diagnosis and has completed the prescribed training.
At least 1 radiological technologist who has specialized knowledge and experience regarding handling of PET pharmaceutical preparations.
A dedicated breast PET scanner is regarded as a single PET device as in the case of whole-body PET, and it is required that there be at least 1 radiological technologist per machine.
Also, because of the radiation that a radiological technologist working with a dedicated breast PET scanner may be exposed to, it is recommended that several radiological technologists work in rotation.
This is based on insurance coverage for breast cancer in PET and PET/CT.
(1) Insurance coverage criteria.
This coverage applies to patients in whom staging, metastasis, and recurrence could not be confirmed by other tests or imaging diagnosis.
(2) Selection criteria for insurance coverage.
(a) Patients in whom a malignant tumor has been confirmed histologically.
(b) Patients in whom, if a definitive diagnosis cannot be obtained histologically, there is clinically a high probability of diagnosing a malignant tumor from the clinical disease picture, bodily symptoms, image diagnostic observations apart from PET or PET/CT, tumor markers, and observations of the clinical course.
This is based on the guidelines for conventional whole-body PET.
A dedicated breast PET scan should be obtained quickly after the whole-body PET scan is complete. This is in order to reduce radiation exposure of the radiological technologist when positioning the breast scan, to set a suitable scan range based on the whole-body PET scan, and to achieve an increase of the tumor/background ratio due to passage of time.
In an opposite type scanner, the whole breast is mostly depicted, and images are taken in the medio-lateral oblique direction, and the cranial-caudal direction which complements it.
Determination and diagnosis
In a dedicated breast PET scan, accumulation sites higher than the background mammary gland are examined by visual evaluation. If possible, it is recommended to refer to a mammography and MRI and perform a comparative interpretation .
For a quantitative evaluation, it is first and foremost most desirable to use the SUV (standardized uptake value) which is a quantitative value common to whole-body PET. At the present time, however, it is difficult to interconvert SUV between a whole-body PET scanner and the dedicated breast PET scanner, and therefore a quantitative method specific to dedicated breast PET is now being considered. Methods proposed include the FDG accumulation ratio relative to dose per unit body weight, and the accumulation ratio between the lesion area and background mammary gland or mammary gland on the opposite side. In some dedicated breast PET scanners, no absorption correction is made, so it is necessary to take the characteristics of the machine into account.
In FDG-PET, it is difficult to detect malignant tumors with a low grape sugar metabolism, and false negatives sometimes occur. Also, immediately following biopsy, FDG becomes distributed due to inflammation which interferes with a precise diagnosis, so care must be taken. Dedicated breast PET has higher sensitivity and resolution than conventional whole-body PET, but in the case of very small breast cancers, sufficient FDG cannot be accumulated for a diagnosis, so they may be under-estimated.
Precautions in use
As with whole-body PET, FDG is administered when it is deemed that its diagnostic usefulness outweighs disadvantage due to radiation exposure. Also, the dosage is kept to the absolute minimum.
Radiation exposure amount
In general, there is no need to administer an additional dose of FDG in dedicated breast PET scans, so the radiation exposure is similar to that of a whole-body PET scan. In the present guideline, we give a figure based on the report of ICRP Publication 106 . The actual dosage if 185 MBq are administered to an adult is 3.5 mSv, and the radiation exposure in a regular transmission scan using 68Ge-68Ga sources is of the order of 0.25 mSv. On the other hand, the radiation in a CT scan done for correcting absorption in PET/CT, with a low radiation scan for generating a fused image, is said to be 1.4–3.5 mSv. If the CT in PET/CT uses a high radiation dose similarly to an ordinary it may be 10 mSv or more, so the need for this must be confirmed.
Precautions regarding dedicated breast PET
(1) Examination of patients with a pacemaker
For both the opposite type scanner and ring type scanner, lead wires may be broken due to compression of the body surface by the detectors, so due care is required.
(2) Patients who have had surgical implants of foreign materials
In the opposite type scanner, the breast is interposed between the detectors, and as the implant may be damaged by compression, care is required.
(3) Lactating patients
Since FDG accumulates more in the mammary gland tissue during lactation than when not lactating, these patients should not be subjected to a dedicated breast PET scan. In these patients, it is considered undesirable to use FDG, and advised to use it carefully only if it is deemed that the diagnostic benefit outweighs the risk due to radiation exposure.