Authors: (including presenting author): :
Dr. Martin LAW
Affiliation: :
(1)Department of Radiology and nuclear medicine (2) Department of Clinical Oncology Tuen Mun Hospital
Keyword 1: :
breast cancer
Keyword 3: :
sentinel lymph node lymphoscintigraphy
Keyword 5: :
effective dose
Keyword 6: :
organ absorbed dose
Introduction: :
The technique of sentinel lymph node (SLN) biopsy in the clinical management of breast cancer has become a standard practice. In our previous study, organ absorbed radiation doses were measured both for internal emission dose due to injected 99mTc and for transmission dose due to the use of a 57Co flood source. Using the concept of cumulated activity, effective dose (ED) were calculated for patients undergoing different lymphoscintigraphy protocols (1-day and 2-day protocol) and surgical procedures whether the radiation containing tissues are excised or not. It has been an increasing trend to use hybrid imaging system SPECT/CT, SPECT imaging system in combination with a low dose CT scanner, for direct correlation of anatomic information and functional information resulting in better localization and definition of SLN imaging findings. From dosimetry point of view, patient receives radiation dose from 99mTc as internal emission source and from CT as transmission irradiating source, the patient ED of which has not yet been studied for SLN lymphoscintigraphy with a low dose CT component equipped with a tin filter in the latest model of a hybrid SPECT/CT system.
Objectives: :
To evaluate patient effective dose (ED) from sentinel lymph node (SLN) lymphoscintigraphy in breast cancer by using a low dose CT component of a hybrid SPECT/CT system and the 99mTc emission dose for different imaging protocols and to verify the 3D-image quality with a female humanoid phantom for potential SPECT/CT clinical application.
Methodology: :
Patient ED is an important factor to the SPECT/CT lymphoscintigraphy to directly correlate the lymphoscintigraphy and SLN locations in 3D, in that the lower CT dose will result in lower patient ED. Computer simulation to the organ absorbed doses and hence patient ED was performed with a CT component equipped with a tin filter. A female humanoid phantom was undergone SPECT/CT (Siemens Pro.specta X3) with clinical parameters to verify the image quality at CT tube voltage of 110 and 130 kV.
Result & Outcome: :
The patient ED per 100 mAs of the low dose CT has been computer-simulated as 0.9 mSv for 110 kV and 1.4 mSv for 130 kV. Since the patient ED, due to internal emission, has been measured as 0.4 mSv in the 2-day protocol, the total patient ED is about 2 mSv which is considered as much lower than previous results from early generation SPECT/CT systems. Cross-sectional humanoid 3D-images demonstrate the usefulness of hybrid SPECT/CT in SLN lymphoscintigraphy. The use of tin filter in the X-ray tube reduces the low energy CT dose and therefore lowers the total patient ED to the range of 2 mSv. The use of SPECT/CT in the SLN lymphoscintigraphy is more efficient without mounting a 57Co flood source onto the conjugate detector or using a 57Co pen for patient body contour outlining, hence eliminating radiation exposure to operators. Together with the 3D-images, a hybrid SPECT/CT system with a low energy CT component may be applicable for future SLN lymphoscintigraphy in breast cancer.
