Medicina Nuclear e Radioterapia

By monitor breast cancer mass with ¹⁸F-fluorodeoxyglucose (FDG) and ⁹⁹mTc-HL91 positron emission tomography (PET) imaging, this study compares the efficacy of the two imaging methods in evaluation of the early response to neoadjuvant chemotherapy in stage II and III breast cancer patients. Images of region of interest were acquired with a hybrid PET/computed tomography scanner in forty patients after administration of ¹⁸F-FDG (4.44 MBq/kg) or ⁹⁹mTc-HL91 (12.3 MBq/kg) at baseline and after the third course of chemotherapy. And the values of tumor to non-tumor activity ratio (T/N) were compared between the two imaging methods and with the pathologic response. Surgery was performed after three courses of chemotherapy and pathological analysis revealed gross residual disease in 11 patients and minimal residual disease in 29 patients. When 20% reduction in T/N was set as the threshold for differentiation between responders and nonresponders by ¹⁸F-FDG imaging, 27 of 29 responders and 10 of 11 nonresponders were identified after three courses of chemotherapy. A linear correlation was observed between the T/N of ⁹⁹mTc-HL91 and the T/N of ¹⁸F-FDG (rs = 0.778, p<0.001), but almost lost after chemotherapy (rs = 0.518, p<0.001). In conclusion, we suggest that ¹⁸F-FDG imaging, but not ⁹⁹mTc–HL91 imaging with hybrid PET/CT provides a costeffective method, which could be well accepted for the low-income population in developing countries, to monitor early tumor response after three cycles of neoadjuvant chemotherapy in stage II and III breast cancer by using the reduction of N/T ratio as predictor.

Abstract Purpose: To investigate localization accuracy for frameless intracranial stereotactic-radiosurgery using 2D orthogonal planar imaging and 3D cone-beam CT (CBCT) in 6-degree-of-freedom (6-DOF).

Methods and Materials: In a phantom study, a target ball phantom was used to perform a Winston-Lutz test and to verify coincidence of imaging isocenter and radiation isocenter. A head phantom was placed with pre-defined positions and imaged with CBCT to test imaging accuracy. In a patient study, one hundred patients were included. Patients were initially positioned with a thermoplastic frameless mask system and then aligned with orthogonal planar imaging and CBCT. The setup discrepancies were quantitatively analyzed.

Results: Phantom experiments showed discrepancies in root-mean-square were 1.6mm translationally and 0.5° rotationally between CBCT 6-DOF image guidance and the known displacements after deviations from the radiation isocenter are considered. In the patient study, setup displacements between orthogonal planar imaging and CBCT 6-DOF image guidance were 3.2mm translationally and 0.9° rotationally. The positioning of twelve patients was corrected in 6-DOF using CBCT and a robotic couch to reduce translational and rotational discrepancies of 1.4mm and 1.3°, as compared with standard CBCT translational correction. Conclusion: CBCT 6-DOF image guidance offers an explicit view to verify patient positioning in translations and rotations.