Pacilio Massimiliano, Cassano Bartolomeo, Pellegrini Rosanna, Di Castro Elisabetta, Zorz Alessandra, De Vincentis Giuseppe, Ventroni Guido, Mango Lucio, Giancola Stefano, Ferrari Mahila, Cremonesi Marta, Bianchi Claudia, Virotta Giorgio, Carbonini Claudia, Cesana Patrizia, Fulcheri Cristian, Reggioli Valentina, Ricci Alessandra, Trevisiol Edoardo, Anglesio Silvia, Pani Roberto
Department of Medical Physics, Azienda Ospedaliera Universitaria Policlinico Umberto I, Viale del Policlinico 155, 00161 Rome, Italy.
Postgraduate School of Medical Physics, "Sapienza" University of Rome, Piazzale Aldo Moro no. 5, 00185 Rome, Italy.
Phys Med. 2017 Sep;41:117-123. doi: 10.1016/j.ejmp.2017.04.019. Epub 2017 Apr 28.
The aim was to calibrate gamma cameras in the framework of the Italian multicentre study for lesion dosimetry in Ra therapy of bone metastases. Equipments of several manufacturers and different models were used.
Eleven gamma cameras (3/8- and 5/8-inch crystal) were used, acquiring planar static images with double-peak (82 and 154keV, 20% wide) and MEGP collimator. The sensitivity was measured in air, varying source-detector distance and source size. Transmission curves were measured, calculating the parameters used for attenuation/scatter correction with the pseudo-extrapolation number method, and assessing their variations with the source size.
Values of the calibration factor (geometric mean of both detector sensitivities) ranged from 41.1 to 113.9cps/MBq. For the smallest source (diameter of 3.5cm), the calibration factor decrease ranged from -30% to -4%, highlighting the importance of partial volume effects according to the equipment involved. The sensitivity variation with the source-detector distance, with respect to the 15cm-value, reached 10% (in absolute value) in the range 5-30cm, but fixing the distance between the two heads, the calibration factor variation with the distance from the midline was within 3.6%. Appreciable variation of the transmission curves with the source size were observed, examining the results obtained with six gamma cameras.
Assessments of sensitivity and transmission curve variations with source size should be regularly implemented in calibration procedures. The results of this study represent a useful compendium to check the obtained calibrations for dosimetric purposes.
在意大利多中心骨转移瘤镭治疗中病变剂量测定研究框架内对γ相机进行校准。使用了多家制造商的不同型号设备。
使用了11台γ相机（3/8英寸和5/8英寸晶体），采用双峰（82和154keV，20%带宽）和MEGP准直器采集平面静态图像。在空气中测量灵敏度，改变源 - 探测器距离和源尺寸。测量传输曲线，用伪外推数法计算用于衰减/散射校正的参数，并评估其随源尺寸的变化。
校准因子（两个探测器灵敏度的几何平均值）的值范围为41.1至113.9cps/MBq。对于最小的源（直径3.5cm），校准因子下降范围为 -30%至 -4%，突出了根据所涉及设备部分容积效应的重要性。源 - 探测器距离的灵敏度变化，相对于15cm的值，在5 - 30cm范围内达到10%（绝对值），但固定两个探头之间的距离时，校准因子随与中线距离的变化在3.6%以内。在用六台γ相机获得的结果中观察到传输曲线随源尺寸有明显变化。
在校准程序中应定期评估灵敏度和传输曲线随源尺寸的变化。本研究结果是用于剂量测定目的检查所获得校准的有用汇总。
