Yoon Myonggeun, Lee Doo-Hyun, Shin Dongho, Lee Se Byeong, Park Sung Yong, Cho Kwan Ho
Research Institute and Hospital, National Cancer Center, Ilsan-gu, Goyang, Korea.
Med Dosim. 2007 Spring;32(1):44-51. doi: 10.1016/j.meddos.2006.11.004.
We examined the degree of calculated-to-measured dose difference for nasopharyngeal target volume in intensity-modulated radiotherapy (IMRT) based on the observed/expected ratio using patient anatomy with humanoid head-and-neck phantom. The plans were designed with a clinical treatment planning system that uses a measurement-based pencil beam dose-calculation algorithm. Two kinds of IMRT plans, which give a direct indication of the error introduced in routine treatment planning, were categorized and evaluated. The experimental results show that when the beams pass through the oral cavity in anthropomorphic head-and-neck phantom, the average dose difference becomes significant, revealing about 10% dose difference to prescribed dose at isocenter. To investigate both the physical reasons of the dose discrepancy and the inhomogeneity effect, we performed the 10 cases of IMRT quality assurance (QA) with plastic and humanoid phantoms. Our result suggests that the transient electronic disequilibrium with the increased lateral electron range may cause the inaccuracy of dose calculation algorithm, and the effectiveness of the inhomogeneity corrections used in IMRT plans should be evaluated to ensure meaningful quality assurance and delivery.
我们使用具有类人头部和颈部模型的患者解剖结构，基于观察/预期比值，研究了调强放射治疗（IMRT）中鼻咽癌靶区计算剂量与测量剂量的差异程度。这些计划是使用基于测量的笔形束剂量计算算法的临床治疗计划系统设计的。对两种能直接表明常规治疗计划中引入误差的IMRT计划进行了分类和评估。实验结果表明，当射线束穿过类人头部和颈部模型中的口腔时，平均剂量差异变得显著，在等中心处显示出与处方剂量约10%的剂量差异。为了研究剂量差异的物理原因和不均匀性效应，我们用塑料和类人模型进行了10例IMRT质量保证（QA）。我们的结果表明，随着横向电子射程增加的瞬态电子不平衡可能导致剂量计算算法不准确，并且应评估IMRT计划中使用的不均匀性校正的有效性，以确保有意义的质量保证和治疗实施。
