Zifodya Jackson M, Challens Cameron H C, Hsieh Wen-Long
North West Cancer Centre, Tamworth Rural Referral Hospital, Tamworth, NSW, 2340, Australia.
Australas Phys Eng Sci Med. 2016 Jun;39(2):431-9. doi: 10.1007/s13246-016-0436-z. Epub 2016 Mar 23.
When implementing Acuros XB (AXB) as a substitute for anisotropic analytic algorithm (AAA) in the Eclipse Treatment Planning System, one is faced with a dilemma of reporting either dose to medium, AXB-Dm or dose to water, AXB-Dw. To assist with decision making on selecting either AXB-Dm or AXB-Dw for dose reporting, a retrospective study of treated patients for head & neck (H&N), prostate, breast and lung is presented. Ten patients, previously treated using AAA plans, were selected for each site and re-planned with AXB-Dm and AXB-Dw. Re-planning was done with fixed monitor units (MU) as well as non-fixed MUs. Dose volume histograms (DVH) of targets and organs at risk (OAR), were analyzed in conjunction with ICRU-83 recommended dose reporting metrics. Additionally, comparisons of plan homogeneity indices (HI) and MUs were done to further highlight the differences between the algorithms. Results showed that, on average AAA overestimated dose to the target volume and OARs by less than 2.0 %. Comparisons between AXB-Dw and AXB-Dm, for all sites, also showed overall dose differences to be small (<1.5 %). However, in non-water biological media, dose differences between AXB-Dw and AXB-Dm, as large as 4.6 % were observed. AXB-Dw also tended to have unexpectedly high 3D maximum dose values (>135 % of prescription dose) for target volumes with high density materials. Homogeneity indices showed that AAA planning and optimization templates would need to be adjusted only for the H&N and Lung sites. MU comparison showed insignificant differences between AXB-Dw relative to AAA and between AXB-Dw relative to AXB-Dm. However AXB-Dm MUs relative to AAA, showed an average difference of about 1.3 % signifying an underdosage by AAA. In conclusion, when dose is reported as AXB-Dw, the effect that high density structures in the PTV has on the dose distribution should be carefully considered. As the results show overall small dose differences between the algorithms, when transitioning from AAA to AXB, no significant change to existing prescription protocols is expected. As most of the clinical experience is dose-to-water based and calibration protocols and clinical trials are also dose-to-water based and there still exists uncertainties in converting CT number to medium, selecting AXB-Dw is strongly recommended.
在Eclipse治疗计划系统中使用Acuros XB（AXB）替代各向异性解析算法（AAA）时，面临着报告介质剂量（AXB-Dm）还是水剂量（AXB-Dw）的两难选择。为了协助决定选择AXB-Dm还是AXB-Dw进行剂量报告，本文对接受头颈部（H&N）、前列腺、乳腺和肺部治疗的患者进行了回顾性研究。每个部位选择10名先前使用AAA计划治疗的患者，并用AXB-Dm和AXB-Dw重新计划。重新计划采用固定监测单位（MU）和非固定MU进行。结合ICRU-83推荐的剂量报告指标，分析了靶区和危及器官（OAR）的剂量体积直方图（DVH）。此外，还对计划均匀性指数（HI）和MU进行了比较，以进一步突出算法之间的差异。结果表明，平均而言，AAA对靶区体积和OAR的剂量高估不到2.0%。所有部位AXB-Dw和AXB-Dm之间的比较也表明总体剂量差异很小（<1.5%）。然而，在非水生物介质中，观察到AXB-Dw和AXB-Dm之间的剂量差异高达4.6%。对于含有高密度材料的靶区体积，AXB-Dw还往往具有意外高的三维最大剂量值（>处方剂量的135%）。均匀性指数表明，AAA计划和优化模板仅需对头颈部和肺部部位进行调整。MU比较表明，AXB-Dw相对于AAA以及AXB-Dw相对于AXB-Dm之间差异不显著。然而，AXB-Dm的MU相对于AAA，平均差异约为1.3%，表明AAA存在剂量不足。总之，当报告剂量为AXB-Dw时，应仔细考虑PTV中高密度结构对剂量分布的影响。由于结果表明算法之间的总体剂量差异较小，从AAA过渡到AXB时，预计现有处方方案不会有显著变化。由于大多数临床经验基于水剂量，校准方案和临床试验也基于水剂量，并且将CT值转换为介质仍存在不确定性，强烈建议选择AXB-Dw。
