Arnfield M R, Wu Q, Tong S, Mohan R
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
Med Dosim. 2001 Summer;26(2):179-88. doi: 10.1016/s0958-3947(01)00058-9.
The creation of intricate dose distributions produced by intensity-modulated radiotherapy (IMRT) depends on complex planning systems and specialized mechanical devices. The many possible sources of inaccuracy and the complexity of the dose maps themselves require that a substantial effort be made to ensure that calculated and delivered dose distributions agree. This review provides an overview of the current status of the validation of dose predictions of IMRT planning systems by comparisons with measurements. Emphasis is placed on multileaf collimator- (MLC) based IMRT. Discrepancies between calculations and measurements may be due to any of 3 causes: errors and uncertainties in the dose calculation algorithm, in measurements, or in beam delivery by the accelerator/MLC combination. Some of the factors affecting dosimetry include: the technique employed for modulating the fluence, the dose calculation algorithm and other aspects of the planning system, mechanical limitations of the MLC hardware, dosimetric characteristics of the MLC, such as MLC leakage and rounded leaf ends, the choice of dosimeter, and the measurement geometry and technique. The advantages and drawbacks of various dosimeters including film, ion chambers, thermoluminescent dosimetry, and electronic portal imaging devices are discussed. The steps involved in validating dosimetrically a planning system are outlined, including the various fields that need to be measured, the phantoms that may be used, and measurement techniques. The achievable accuracy of dosimetry for IMRT is discussed.
调强放射治疗（IMRT）所产生的复杂剂量分布的生成依赖于复杂的计划系统和专门的机械设备。剂量分布图本身存在诸多可能的误差来源且十分复杂，这就要求付出巨大努力来确保计算得出的剂量分布与实际交付的剂量分布一致。本综述通过与测量结果进行比较，概述了IMRT计划系统剂量预测验证的当前状况。重点在于基于多叶准直器（MLC）的IMRT。计算结果与测量结果之间的差异可能归因于以下3种原因中的任何一种：剂量计算算法、测量过程或加速器/MLC组合的射束输出过程中的误差和不确定性。影响剂量测定的一些因素包括：用于调制注量的技术、剂量计算算法以及计划系统的其他方面、MLC硬件的机械限制、MLC的剂量测定特性（如MLC泄漏和叶片端部圆钝）、剂量计的选择以及测量几何形状和技术。讨论了包括胶片、电离室、热释光剂量测定法和电子射野成像装置在内的各种剂量计的优缺点。概述了在剂量学上验证计划系统所涉及的步骤，包括需要测量的各个射野、可能使用的模体以及测量技术。还讨论了IMRT剂量测定可达到的精度。
