Evaluation of three gamma detectors for intraoperative detection of tumors using 111In-labeled radiopharmaceuticals.
Attempts to detect tumors with intraoperative scintillation using tumor-binding radiopharmaceuticals have intensified recently. In some cases previously unknown lesions were found, but in most cases no additional lesions were detected. In this study the physical characteristics of three detector systems and their ability to detect tumors through accumulation of an 111In-labeled radiopharmaceutical were investigated. The first was a sodium iodide (NaI[TI]) detector; the second, a cesium iodide (CsI[TI]) detector; and the third, a cadmium telluride (CdTe) detector.


METHODS
A body phantom and tumor phantoms (diameter 5-20 mm) made of water, agarose gel or epoxy with a density and attenuation coefficient similar to those of soft tissue were used to simulate a clinical situation. The activity concentration in the body phantom was based on reported values of 111In-octreotide in normal tissue in humans. The 111In activity concentration in the tumor phantoms varied from 3 to 80 times the 111In activity concentration in the body phantom. Data were processed to determine tumor detection levels.


RESULTS
The NaI(TI) detector showed the lowest values for full width at half maximum because this detector had the best collimation, leading to a high ratio between counts from tumor and counts from background, i.e., small tumors could be detected. Because of high efficiency, the CsI(TI) detector sometimes required a somewhat shorter acquisition time to produce a statistically significant difference between tumor phantom and background. For deep-lying tumors the NaI(TI) detector was superior, whereas the CdTe detector was best suited for superficial tumors with a high activity concentration in the underlying tissue.


CONCLUSIONS
At a maximum acquisition time of 30 s, almost all superficial tumors with a diameter of 10 mm or larger were detected if the ratio between the 111In concentration in the tumor and the 111In concentration in the background exceeded 3. However, in clinical situations, biologic variations in the uptake of 111In-octreotide in tumors and in normal tissue makes difficult the determination of a distinct detection level. For such clinical conditions, the NaI(TI) detector is the best choice because it has good resolution despite a lower efficiency. Documentation of detector characteristics is important so that clinicians can make an adequate device in relation to tumor location and receptor expression.
Benjegård
S A
SA
Department of Radiation Physics, Sahlgrenska University Hospital, Göteborg University, Sweden.
Sauret
V
V
Bernhardt
P
P
Wängberg
B
B
Ahlman
H
H
Forssell-Aronsson
E
E
D019187:Cadmium Compounds; D002586:Cesium; D005069:Evaluation Studies as Topic; D005720:Gamma Rays; D006801:Humans; D007205:Indium Radioisotopes; D007432:Intraoperative Period; D007454:Iodides; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery; D015282:Octreotide / Q000031:analogs & derivatives; D004369:Pentetic Acid / Q000031:analogs & derivatives; D019047:Phantoms, Imaging; D011877:Radionuclide Imaging / Q000295:instrumentation*; D019275:Radiopharmaceuticals; D012974:Sodium Iodide; D013691:Tellurium
D019187:Cadmium Compounds; D007205:Indium Radioisotopes; D007454:Iodides; D019275:Radiopharmaceuticals; C071632:SDZ 215-811; D002586:Cesium; D004369:Pentetic Acid; D012974:Sodium Iodide; D013691:Tellurium; D015282:Octreotide; C028337:cadmium telluride; C040050:cesium iodide