Yaparpalvi Ravindra, Hong Linda, Mah Dennis, Shen Jin, Mutyala Subhakar, Spierer Marnee, Garg Madhur, Guha Chandan, Kalnicki Shalom
Department of Radiation Oncology, Montefiore Medical Center and The Albert Einstein College of Medicine, NY 10467, USA.
Radiother Oncol. 2008 Dec;89(3):347-52. doi: 10.1016/j.radonc.2008.07.025. Epub 2008 Aug 31.
IMRT clinical trials lack dose prescription and specification standards similar to ICRU standards for two- and three-dimensional external beam planning. In this study, we analyzed dose distributions for patients whose treatment plans incorporated IMRT, and compared the dose determined at the ICRU reference point to the PTV doses determined from dose-volume histograms. Additionally, we evaluated if ICRU reference type single-point dose prescriptions are suitable for IMRT dose prescriptions.
For this study, IMRT plans of 117 patients treated at our institution were randomly selected and analyzed. The treatment plans were clinically applied to the following disease sites: abdominal (11), anal (10), brain (11), gynecological (15), head and neck (25), lung (15), male pelvis (10) and prostate (20). The ICRU reference point was located in each treatment plan following ICRU Report 50 guidelines. The reference point was placed in the central part of the PTV and at or near the isocenter. In each case, the dose was calculated and recorded to this point. For each patient--volume and dose (PTV, PTV mean, median and modal) information was extracted from the planned dose-volume histogram.
The ICRU reference dose vs PTV mean dose relationship in IMRT exhibited a weak positive association (Pearson correlation coefficient 0.63). In approximately 65% of the cases studied, dose at the ICRU reference point was greater than the corresponding PTV mean dose. The dose difference between ICRU reference and PTV mean doses was 2% in approximately 79% of the cases studied (average 1.21% (+/-1.55), range -4% to +4%). Paired t-test analyses showed that the ICRU reference doses and PTV median doses were statistically similar (p=0.42). The magnitude of PTV did not influence the difference between ICRU reference and PTV mean doses.
The general relationship between ICRU reference and PTV mean doses in IMRT is similar to that in 3D CRT distributions. Point doses in IMRT are influenced by the degree of intensity modulation as well as calculation grid size utilized. Although the ICRU reference point type prescriptions conceptually may be extended for IMRT dose prescriptions and used as a representative of tumor dose, new universally acceptable dose prescription and specification standards for IMRT based on RTOG IMRT prescription model incorporating dose-volume specification would likely lead to greater consistency among treatment centers.
调强放射治疗（IMRT）临床试验缺乏类似于国际辐射单位与测量委员会（ICRU）针对二维和三维外照射放疗计划所制定的剂量处方和规范标准。在本研究中，我们分析了治疗计划采用IMRT的患者的剂量分布情况，并将在ICRU参考点确定的剂量与从剂量体积直方图中确定的计划靶体积（PTV）剂量进行了比较。此外，我们评估了ICRU参考类型的单点剂量处方是否适用于IMRT剂量处方。
在本研究中，随机选取并分析了在我们机构接受治疗的117例患者的IMRT计划。这些治疗计划临床应用于以下疾病部位：腹部（11例）、肛门（10例）、脑部（11例）、妇科（15例）、头颈部（25例）、肺部（15例）、男性盆腔（10例）和前列腺（20例）。按照ICRU第50号报告的指南，在每个治疗计划中确定ICRU参考点。参考点置于PTV的中心部位以及等中心处或其附近。在每种情况下，计算并记录该点的剂量。对于每位患者，从计划剂量体积直方图中提取体积和剂量（PTV、PTV均值、中位数和众数）信息。
IMRT中ICRU参考剂量与PTV平均剂量之间的关系呈现出较弱的正相关性（皮尔逊相关系数为0.63）。在大约65%的研究病例中，ICRU参考点处的剂量大于相应的PTV平均剂量。在大约79%的研究病例中，ICRU参考剂量与PTV平均剂量之间的剂量差异为2%（平均1.21%（±1.55），范围为 -4%至 +4%）。配对t检验分析表明，ICRU参考剂量与PTV中位数剂量在统计学上相似（p = 0.42）。PTV的大小并未影响ICRU参考剂量与PTV平均剂量之间的差异。
IMRT中ICRU参考剂量与PTV平均剂量之间的总体关系与三维适形放疗（3D CRT）分布中的情况相似。IMRT中的点剂量受强度调制程度以及所使用的计算网格大小的影响。尽管ICRU参考点类型的处方在概念上可能扩展用于IMRT剂量处方并用作肿瘤剂量的代表，但基于美国放射肿瘤学会（RTOG）IMRT处方模型并纳入剂量体积规范的新的普遍可接受的IMRT剂量处方和规范标准可能会使各治疗中心之间的一致性更高。
