Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Med Phys. 2010 Aug;37(8):3919-26. doi: 10.1118/1.3457328.
To investigate the dosimetric effect of the air inside the SAVI partial breast irradiation device.
The authors have investigated how the air inside the SAVI partial breast irradiation device changes the delivered dose from the homogeneously calculated dose. Measurements were made with the device filled with air and water to allow comparison to a homogenous dose calculation done by the treatment planning system. Measurements were made with an ion chamber, TLDs, and film. Monte Carlo (MC) simulations of the experiment were done using the EGSnrc suite. The MC model was validated by comparing the water-filled calculations to those from a commercial treatment planning system.
The magnitude of the dosimetric effect depends on the size of the cavity, the arrangement of sources, and the relative dwell times. For a simple case using only the central catheter of the largest device, MC results indicate that the dose at the prescription point 1 cm away from the air-water boundary is about 9% higher than the homogeneous calculation. Independent measurements in a water phantom with a similar air cavity gave comparable results. MC simulation of a realistic multidwell position plan showed discrepancies of about 5% on average at the prescription point for the largest device.
The dosimetric effect of the air cavity is in the range of 3%-9%. Unless a heterogeneous dose calculation algorithm is used, users should be aware of the possibility of small treatment planning dose errors for this device and make modifications to the treatment delivery, if necessary.
研究 SAVI 部分乳房照射设备内空气对剂量的影响。
作者研究了 SAVI 部分乳房照射设备内的空气如何改变由均匀计算剂量所给出的剂量。通过设备充满空气和水的测量来允许与治疗计划系统进行的均匀剂量计算进行比较。使用电离室、TLD 和胶片进行测量。使用 EGSnrc 套件对实验进行了蒙特卡罗（MC）模拟。通过将充满水的计算结果与商业治疗计划系统的计算结果进行比较，验证了 MC 模型。
剂量学效应的大小取决于空腔的大小、源的排列以及相对驻留时间。对于仅使用最大设备的中央导管的简单情况，MC 结果表明，离空气-水边界 1 厘米处的处方点的剂量比均匀计算高约 9%。在具有类似空气腔的水模体中的独立测量给出了类似的结果。对最大设备的多个实际驻留点计划的 MC 模拟显示，在处方点的平均差异约为 5%。
空气腔的剂量学效应在 3%-9%的范围内。除非使用不均匀剂量计算算法，否则用户应该意识到该设备治疗计划剂量可能存在小误差，并在必要时对治疗输送进行修改。
