Evaluation of base materials of TL slab dosimeter for heavy-ion radiotherapy
Evaluation of base materials of TL slab dosimeter for heavy-ion radiotherapy
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DOI：
10.1093/jrr/rrt186
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发表时间：
2014-03
影响因子：
2
通讯作者：
Wakabayashi G
中科院分区：
文献类型：
--
作者：
Koba Y;Shinsho K;Tamatsu S;Fukuda S;Wakabayashi G
为了测量x射线放疗中的三维剂量分布，我们采用Zeff = 7.42，密度为1.01 g/cm3的新型TL荧光粉Li3B7O12(Cu)，以合成树脂为粘结剂，研制了TL平板剂量计[]。使用该探测器可以方便、可靠地测量三维剂量分布。该探测器是一种很有前途的工具，用于高级x射线放射治疗，如IMRT等的QA/QC。在重离子放射治疗中，由于剂量分布非常陡，因此三维剂量分布的测量也很有必要。要在重离子剂量学中使用TL平板剂量计，必须充分测量其LET依赖性。对该剂量计对重离子的剂量水等效性进行评价是必要的。先前的研究表明，在碳290 MeV/u光束的bragg峰，该荧光体的相对辐射效率下降到~ 20%，该剂量计对碳离子的停止功率比为0.87[]。这些结果不利于重离子放射治疗的应用。一般tld（如LiF和BeO）的发光曲线形状与LET之间存在一定的关系。利用这种发光曲线与LET的关系，可以修正相对TL效率，并将TLDs应用于重离子放射治疗的剂量测量。TL平板剂量计基材的水当量比。在本研究中，为了研制出更好的用于重离子放疗的TL平板剂量计，使用具有上述特性的TL荧光粉，我们评估了几种用于TL平板剂量计的基材的剂量学水等效性。我们选用了几种耐热陶瓷作为基材；ISOPLATON E3, P1, M2， A98 S1和可加工陶瓷，TBS N64, N66, N1, N3 （ISOLITE Co. Ltd）。重点研究了这些材料对重离子的阻挡力、散射力和核截面。我们用Bethe公式，Gottschalk公式和Sihver公式计算了这些相互作用。图1为碳离子束的水当量比、停止功率比S/Sw、散射功率比T/Tw和核截面比σ/σw的理论计算结果。在这些陶瓷中，ISOPLANTON S1是碳离子束平板剂量计的最佳基材。在此基础上，我们将开发用于重离子放射治疗的TL平板剂量计。
In order to measure a three-dimensional dose distribution in X-ray radiotherapy, we developed TL slab dosimeter with new TL phosphor Li3B7O12(Cu), which has Zeff = 7.42 and a density of 1.01 g/cm3 and synthetic resin as binder [ ]. We can measure a three-dimensional dose distribution easily and reliably using this detector. This detector showed a promising tool for QA/QC in advanced X-ray radiotherapies such as IMRT, etc. In heavy-ion radiotherapies which shape precipitous dose distributions, it is also necessary to measure three-dimensional dose distribution easily. To use TL slab dosimeter in heavy-ion dosimetry, it is essential to measure its LET dependence sufficiently. And it is necessary to evaluate the dosimetric water equivalence of this dosimeter for heavy ions. Previous studies showed that the relative TL efficiency of this TL phosphor decreased to ∼20% at the Bragg-peak of carbon 290 MeV/u beams and the stopping-power ratio of this dosimeter to water for carbon ions was 0.87 [ ]. These results were not good for application in heavy-ion radiotherapy. It was often reported that there is a relationship between the glow curve shape of general TLDs (such as LiF and BeO) and LET. Using this relationship of glow curve and LET, the relative TL efficiency can be corrected and we could apply TLDs to dose measurement in heavy-ion radiotherapies. Water-equivalence ratio of the base materials for TL slab dosimeter. In this study, in order to develop better TL slab dosimeter for heavy-ion radiotherapy using TL phosphors with the above characteristics, we evaluated the dosimetric water equivalence of several base materials for TL slab dosimeter. We chose several kinds of ceramics with heating resistance as the base material; ISOPLATON E3, P1, M2, A98 S1 and Machinable Ceramics, TBS N64, N66, N1, N3 (ISOLITE Co., Ltd). We focused attention on stopping power, scattering power and nuclear cross-section of these materials for heavy ions. We calculated these interactions using the Bethe formula, the Gottschalk formula and the Sihver formula. Figure 1 shows the result of theoretical calculation of the water-equivalence ratio, stopping power ratio S/Sw, scattering power ratio T/Tw and nuclear cross-section ratio σ/σw for carbon-ion beam. In these ceramics, ISOPLANTON S1 was the best of base material for TL slab dosimeter for carbon-ion beam. On the basis of this evaluation, we will develop the TL slab dosimeter for heavy-ion radiotherapy.