Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, Avd. Tres Cruces 2, 46014, Valencia, Spain.
Detection and Radiation Technologies (DART), Edificio Emprendia, 15782, Santiago de Compostela, Spain.
Med Phys. 2018 Apr;45(4):1771-1781. doi: 10.1002/mp.12816. Epub 2018 Mar 15.
The aim of this study was to present a novel 2041 liquid-filled ionization chamber array for high-resolution verification of radiotherapy treatments.
The prototype has 2041 ionization chambers of 2.5 × 2.5 mm area filled with isooctane. The detection elements are arranged in a central square grid of 43 × 43, totally covering an area of 107.5 × 107.5 mm . The central inline and cross-line are extended to 227 mm and the diagonals to 321 mm to be able to perform profile measurements of large fields. We have studied stability, pixel response uniformity, dose rate dependence, depth and field size dependence and anisotropy. We present results for output factors, tongue-and-groove, garden fence, small field profiles, irregular fields, and verification of dose planes of patient treatments.
Comparison with other detectors used for small field dosimetry (SFD, CC13, microDiamond) has shown good agreement. Output factors measured with the device for square fields ranging from 10 × 10 to 100 × 100 mm showed relative differences within 1%. The response of the detector shows a strong dependence on the angle of incident radiation that needs to be corrected for. On the other hand, inter-pixel relative response variations in the 0.95-1.08 range have been found and corrected for. The application of the device for the verification of dose planes of several treatments has shown gamma passing rates above 97% for tolerances of 2% and 2 mm. The verification of other clinical fields, like small fields and irregular fields used in the commissioning of the TPS, also showed large passing rates. The verification of garden fence and tongue-and-groove fields was affected by volume-averaging effects.
The results show that the liquid filled ionization chamber prototype here presented is appropriate for the verification of radiotherapy treatments with high spatial resolution. Recombination effects do not affect very much the verification of relative dose distributions. However, verification of absolute dose distributions may require normalization to a radiation field which is representative of the dose rate of the treatment delivered.
本研究旨在介绍一种新型的 2041 液体填充电离室阵列，用于高分辨率验证放射治疗。
该原型有 2041 个 2.5×2.5mm 面积的电离室，填充异辛烷。探测元件以中央 43×43 的正方形网格排列，完全覆盖 107.5×107.5mm 的区域。中央直线和十字线延伸至 227mm，对角线延伸至 321mm，以便能够对大野进行轮廓测量。我们研究了稳定性、像素响应均匀性、剂量率依赖性、深度和野大小依赖性以及各向异性。我们展示了输出因子、齿槽、花园围栏、小野轮廓、不规则野和患者治疗剂量平面验证的结果。
与用于小野剂量测量的其他探测器（SFD、CC13、microDiamond）的比较表明，具有良好的一致性。用该设备测量的 10×10 至 100×100mm 方形野的输出因子，相对差异在 1%以内。探测器的响应显示出对入射辐射角度的强烈依赖性，需要进行校正。另一方面，在 0.95-1.08 范围内发现并校正了像素间相对响应的变化。该设备在验证几个治疗计划的剂量平面中的应用表明，在 2%和 2mm 的容差下，伽马通过率超过 97%。对其他临床野的验证，如在 TPS 调试中使用的小野和不规则野，也显示出很高的通过率。花园围栏和齿槽野的验证受到体积平均效应的影响。
结果表明，这里介绍的液体填充电离室原型适用于高空间分辨率的放射治疗验证。复合效应不会对相对剂量分布的验证产生很大影响。然而，绝对剂量分布的验证可能需要归一化到与治疗中剂量率代表性的辐射场。
