Dosimetry of lesions in radioiodine therapy of metastatic throid cancer: SPECT-TC calibration, verification and preliminary patient results. (September 2016)

• Record Type: Journal Article
• Authors: Richetta, E.; Radici, L.; Cutaia, C.; Valzano, S.; Moro, G. Lo; Pasquino, M.; Pellerito, R.E.; Stasi, M.
• Is Part Of: Physica medica. Volume 32(2016)Supplement 3
• Page Start: 200
• Publication Date: 2016-09
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2016.07.678
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Introduction: 131 I is used in treatment of metastatic thyroid cancer. Higher activity seems to improve the outcome compared to multiple lower treatments. Patient-specific dosimetry avoids adverse effects and allows appropriate metastasis irradiation. SPECT-TC is more accurate to estimate activity than planar methods. Purpose: To define quantitative SPECT-TC lesion dosimetry protocol. Materials and methods: Three hollow spheres (11.5, 5.6 and 1.1 ml) and a cylinder (130 ml), filled with liquid 131 I (13 MBq/ml) and placed into a water phantom, were acquired (SPECT-TC SiemensIntevo, 64views, 20s/view, circular-orbit, 128 × 128 and 256 × 256) on successive days (dead time 26 ÷ 0.5%). Images were Iterative (Flash3D) scatter-attenuation corrected. Detectors counts-rates and dead-time were noted. Counts/activity were evaluated on volumes segmented with TC and threshold-method. Partial volume effects, radius dependence (25-33cm) and dead-time were evaluated; calibration's verification and a first patient dosimetry was also reported. Results: Calibration factors (cylinder:25.4, smallest sphere:1.4 kcts/MBq) confirmed partial volume effects. Volume recovery coefficients (130 ml–100%, 11 ml–75%, 5.5ml-58%, 1.1 ml–6%) showed radius dependence (within 4.5 % for cylinder; up to 43% for the smallest sphere). The dead-time versus cts/MBq showed a linear dependence (r 2 = 0.99) that allowed the relative correction. According to literature (MIRD24), calibration's verification showed an accuracy within ± 11 % (except for the smallest volume up to 36 %). Similar results were found for all segmentation methods but the CT-based was the most accurate one. This calibration was applied to a patient lung lesion (56 Gy). Conclusion: SPECT-TC represents the more reliable system for lesion dosimetry, allowing accurate volumes and dead-time correction.