The Italian multicentre dosimetric study for lesion dosimetry in223Ra therapy of bone metastases: Calibration protocol of gamma cameras and patient eligibility criteria.
OBJECTIVE
The aims of this work were to explore patient eligibility criteria for dosimetric studies in223Ra therapy and evaluate the effects of differences in gamma camera calibration procedures into activity quantification.


METHODS
Calibrations with223Ra were performed with four gamma cameras (3/8-inch crystal) acquiring planar static images with double-peak (82 and 154keV, 20% wide) and MEGP collimator. The sensitivity was measured in air by varying activity, source-detector distance, and source diameter. Transmission curves were measured for attenuation/scatter correction with the pseudo-extrapolation number method, varying the experimental setup.223Ra images of twenty-five patients (69 lesions) were acquired to study the lesions visibility. Univariate ROC analysis was performed considering visible/non visible lesions on223Ra images as true positive/true negative group, and using as score value the lesion/soft tissue contrast ratio (CR) derived from99mTc-MDP WB scan.


RESULTS
Sensitivity was nearly constant varying activity and distance (maximum s.d.=2%). Partial volume effects were negligible for object area ⩾960mm2. Transmission curve measurements are affected by experimental setup and source size, leading to activity quantification errors up to 20%. The ROC analysis yielded an AUC of 0.972 and an optimal threshold of CR of 10, corresponding to an accuracy of 92%.


CONCLUSIONS
The minimum calibration protocol requires sensitivity and transmission curve measurements varying the object size, performing a careful procedure standardisation. Lesions with99mTc-MDP CR higher than 10, not overlapping the GI tract, are generally visible on223Ra images acquired at 24h after the administration, and possibly eligible for dosimetric studies.
Department of Medical Physics, Azienda Ospedaliera San Camillo Forlanini, Circonvallazione Gianicolense 87, 00152 Rome, Italy. Electronic address: mpacilio@scamilloforlanini.rm.it.
Massimiliano
M
Pacilio
Risk Management and Technology Assessment, Medical Physics Unit, Bambino Gesù Children's Hospital, IRCCS, P.zza S. Onofrio 4, 00165 Rome, Italy.
Bartolomeo
B
Cassano
Department of Nuclear Medicine, Istituto Nazionale Tumori IRCCS Foundation, Via Venezian 1, 20133 Milan, Italy.
Carlo
C
Chiesa
Department of Medical Physics, ASL Latina, Via Canova 3, 04100 Latina, Italy.
Stefano
S
Giancola
Department of Medical Physics, Istituto Europeo di Oncologia, Via Giuseppe Ripamonti 435, 20141 Milan, Italy.
Mahila
M
Ferrari
Department of Medical Physics, Policlinico S.Orsola-Malpighi, Via Pietro Albertoni 15, 40138 Bologna, Italy.
Cinzia
C
Pettinato
Section of Radiological Sciences, Department of Biomedical Sciences and of Morphologic and Functional Imaging, University of Messina, Via Consolare Valeria 1, 98125 Messina, Italy.
Ernesto
E
Amato
Department of Medical Physics, Azienda Ospedaliera S. Maria Nuova, IRCCS, Viale risorgimento 57, 42123 Reggio Emilia, Italy.
Federica
F
Fioroni
Postgraduate School of Medical Physics, "Sapienza" University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy.
Leda
L
Lorenzon
Department of Molecular Medicine, "Sapienza" University of Rome, Viale Regina Elena 291, 00161 Rome, Italy.
Rosanna
R
Pellegrini
Department of Radiological, Oncological and Anatomo Pathological Sciences, "Sapienza" University of Rome, Viale del Policlinico 155, 00161 Rome, Italy.
Elisabetta
E
Di Castro
Department of Medico-surgical Sciences and Biotechnologies, "Sapienza" University of Rome, Corso della Repubblica 79, 04100 Latina, Italy.
Roberto
R
Pani
Radiation Research Unit, Istituto Europeo di Oncologia, Via Giuseppe Ripamonti 435, 20141 Milan, Italy.
Marta
M
Cremonesi
D001859:Bone Neoplasms / Q000532:radiotherapy* / Q000556:secondary*; D002138:Calibration; D015902:Gamma Cameras; D006801:Humans; D007558:Italy; D018579:Patient Selection; D012372:ROC Curve; D011874:Radiometry / Q000295:instrumentation*; D011883:Radium / Q000627:therapeutic use*
D011883:Radium
(223)Ra-dichloride; Bone metastases; Dosimetry; Radionuclide therapy