Létourneau Daniel, Gulam Misbah, Yan Di, Oldham Mark, Wong John W
Department of Radiation Oncology, William Beaumont Hospital, 3601 W. Thirteen Mile Road, Royal Oak, MI 48073, USA.
Radiother Oncol. 2004 Feb;70(2):199-206. doi: 10.1016/j.radonc.2003.10.014.
The QA of intensity modulated radiotherapy (IMRT) dosimetry is a laborious task. The goal of this work is to evaluate the dosimetric characteristics of a new 2D diode array (MapCheck from Sun Nuclear Corporation, Melbourne, Florida) and assess the role it can play in routine IMRT QA.
Fundamental properties of the MapCheck such as reproducibility, linearity and temperature dependence are studied for high-energy photon beams. The accuracy of the correction for difference of diode sensitivity is also assessed. The diode array is benchmarked against film and ion chambers for conventional and IMRT treatments. The MapCheck sensitivity to multileaf collimator position errors is determined.
The diode array response is linear with dose up to 295 cGy. All diodes are calibrated to within +/-1% of each other, and mostly within +/-0.5%. The MapCheck readings are reproducible to within a maximum SD of +/-0.15%. A temperature dependence of 0.57%/ degrees C was noted and should be taken into account for absolute dosimetric measurement. Clinical performance of the MapCheck for relative and absolute dosimetry is demonstrated with seven beam (6 MV) head and neck IMRT plans, and compares well with film and ion chamber measurements. Comparison to calculated dose maps demonstrates that the planning system model underestimates the dose gradients in the penumbra region.
The MapCheck offers the dosimetric characteristics required for performing both relative and absolute dose measurements. Its use in the clinic can simplify and reduce the IMRT QA workload.
调强放射治疗（IMRT）剂量测定的质量保证是一项艰巨的任务。本研究的目的是评估一种新型二维二极管阵列（佛罗里达州墨尔本太阳核公司的MapCheck）的剂量学特性，并评估其在常规IMRT质量保证中所能发挥的作用。
研究了MapCheck对于高能光子束的基本特性，如可重复性、线性和温度依赖性。还评估了二极管灵敏度差异校正的准确性。将该二极管阵列与用于传统治疗和IMRT治疗的胶片及电离室进行了对比。确定了MapCheck对多叶准直器位置误差的敏感度。
二极管阵列的响应在剂量高达295 cGy时呈线性。所有二极管的校准误差在彼此的±1%以内，多数在±0.5%以内。MapCheck的读数可重复性极高，最大标准差在±0.15%以内。注意到温度依赖性为0.57%/℃，在进行绝对剂量测量时应予以考虑。通过七个射野（6 MV）的头颈部IMRT计划展示了MapCheck在相对和绝对剂量测定方面的临床性能，与胶片和电离室测量结果相比表现良好。与计算剂量图的比较表明，计划系统模型低估了半影区的剂量梯度。
MapCheck具备进行相对和绝对剂量测量所需的剂量学特性。其在临床中的应用可简化并减少IMRT质量保证的工作量。
