Kumar Sa Syam, Prabakar S, Sriram P, Vivekanandan N
Cancer Institute, Chennai, Tamilnadu.
Med Phys. 2012 Jun;39(6Part11):3734. doi: 10.1118/1.4735192.
To evaluate the Patient specific pre-treatment quality assurance for hundred RapidArc plans using semiflex (0.125cc) ionization chambers.
Absolute point dose were measured for head and neck, thorax and abdomen cases using semiflex (0.125 cc) ionization chamber. Verification plan was created for each treatment plan in eclipse 8.6 treatment planning system with the semiflex ionization chamber and the octavius phantom. Measurements were performed on a Varian Clinac2100C/D linear accelerator equipped with a millennium 120 leaf collimator. All the results were compared with the fluence measurements using 2D Seven29 ion chamber array combined with octavius phantom.
Positive absolute mean dose variation of 0.56 % was observed with thorax cases with a standard deviation (SD) of ± 1.13 between the plans with a range of -1.78% to 2.70%. Negative percentage dose errors were found with head and neck and abdomen cases, with a mean variation of -0.43 % (SD ± 1.50), (range -3.25 % to 2.85 %) and -0.35 % (SD ± 1.48), (range -3.10 % to 2.65 %) for head and neck and abdomen cases respectively. Relative dose measurements with 2D array agreed well with the TPS calculate for all the cases. The maximum percentage value failed in gamma analysis was found to be 4.95, 4.75, and 4.88 for head and neck, thorax, and abdomen cases respectively. In all the cases analysed the percentage dose points failed the gamma criteria was less than 5%.
On the basis of the studies performed it can be concluded that the semiflex ionization chamber having a volume of 0.125cc can be used efficiently for measuring the pre-treatment quality assurance of RapidArc plans for all the sites. The results provide an overall accuracy when compared to fluence measurement done using 2D array seven29.
使用半柔性（0.125cc）电离室评估100个容积调强弧形治疗（RapidArc）计划的患者个体化治疗前质量保证。
使用半柔性（0.125cc）电离室对头颈、胸部和腹部病例测量绝对点剂量。在Eclipse 8.6治疗计划系统中，使用半柔性电离室和Octavius体模为每个治疗计划创建验证计划。测量在配备有Millennium 120叶片准直器的Varian Clinac2100C/D直线加速器上进行。所有结果与使用二维Seven29电离室阵列结合Octavius体模的注量测量结果进行比较。
胸部病例观察到绝对平均剂量正变化为0.56%，计划间标准差（SD）为±1.13，范围为-1.78%至2.70%。头颈和腹部病例发现有负的剂量百分比误差，头颈和腹部病例的平均变化分别为-0.43%（SD±1.50），（范围-3.25%至2.85%）和-0.35%（SD±1.48），（范围-3.10%至2.65%）。二维阵列的相对剂量测量与所有病例的治疗计划系统（TPS）计算结果吻合良好。头颈、胸部和腹部病例在伽马分析中失败的最大百分比值分别为4.95、4.75和4.88。在所有分析的病例中，剂量百分比点不符合伽马标准的小于5%。
基于所进行的研究可以得出结论，体积为0.125cc的半柔性电离室可有效地用于测量所有部位的RapidArc计划的治疗前质量保证。与使用二维阵列Seven29进行的注量测量相比，结果提供了总体准确性。
