Gamma Locator for the Sentinel Lymph Nodes Localization
- Anastasia BERDNIKOVA
- Anastasia BERDNIKOVA (National Research Nuclear University "MEPhI")
Gamma locator is a handheld lightweight and compact gamma probe based on a scintillation crystal LaBr3:Ce and SensL MicroFB-30035-SMT silicone photomultiplier to be used for detection of gamma-radiation emitted by radionuclides such as Tc-99m, I-125, In-111, F-18. There are two main applications of gamma locator: intraoperative detection of sentinel lymph nodes and non-invasive scanning the surface of the body. In the first case, a radiotracer is injected into the patient preoperatively and surgeon checks the presence of metastasis in the lymph nodes after the removal of the tumor. In the second case, the gamma locator can detect tumors located superficially, and accurately determine their boundaries. When selecting the scintillator the following requirements should be considered: high relative light yield compared to NaI(Tl), the high value of the effective atomic number. The lanthanum cerium bromine has demonstrated the best features: the light yield higher than that of NaI(Tl) (130%), high density, high atomic number provide high efficiency of photoelectric absorption of gamma rays, and the decay time of the order of tens of nanoseconds provides high temporal resolution of the detector. Silicon photomultiplier is a device for detection of low intensive and very fast (several hundred nanosecond duration) light flashes. SiPM is used due to its high detection efficiency, low bias voltage, compact dimensions and high gain of signals. The scintillation crystal of 5 mm diameter and 10 mm length is optically connected with the SensL MicroFB-30035-SMT SiPM of 3x3 mm2 sensitive area. Experimental studies have shown that a scintillator packaged separately from the photodetector provides only 10.7% energy resolution at 662 keV (Cs-137) while being packed in a single enclosure with the SiPM it provides 6.9% FWHM energy resolution. Gamma probe can be constructed in corded or cordless configuration and equipped with a lithium-ion battery. Indication is performed by an acoustic signal and LED. Adjusting of the bias voltage of the photodetector and the thresholds of the discriminator is carried out by changing the resistance of the trimmers. The main technical characteristics of the prototype gamma locator were determined in the laboratory of NRNU MEPhI. Spatial resolution of gamma locator is the minimum distance between two point sources on which they can be resolved separately, or FWHM of the dependence of counting rate of the transverse distance between the detector and the source, and is measured to be 18 mm in the air and 20 mm in the scatter medium. Spatial selectivity is the polar angle, at which the count rate drops twice and it is measured to be 17 degrees in the air and 26 degrees in the scatter medium. Sensitivity is 191 cps/MBq in the air and 112 cps/MBq in the scatter medium. This work was supported in part by the Ministry of Education of the Russian Federation (State Contract with the NRNU MEPhI no. 11.G34.31.0049 of Oct. 19, 2011) and the Skolkovo Institute of Science and Technology (a part of the Skoltech/MIT Initiative project).
National Research Nuclear University “MEPhI”, Moscow, Russia