Eldib A, Li J, Jin L, Ma C
Fox Chase Cancer Center, Philadelphia, PA.
AlAZhar University, Department of physics, Cairo, Egypt.
Med Phys. 2012 Jun;39(6Part17):3806. doi: 10.1118/1.4735530.
Fabrication of electron beam cutouts not only is a time consuming process but also involves the handling of cerrobend which is a toxic material. Hospital workers involved in cutout construction can actually be exposed to toxic fumes that are usually generated during the process. The aim of this work is to study the feasibility of replacing electron cutouts with our prototype motorized electron multileaf collimator (eMLC).
Electron beams collimated by an eMLC have very similar penumbra to those collimated by applicators and cutouts as we already demonstrated in a previous study. However undulation of the isodose curves is expected due to the finite size of the eMLC. This may be a problem when the field edge is close to critical structure. Thus ten different breast cases that were previously treated with an electron boost were selected from our database. An inhouse Monte Carlo based treatment planning system were used for dose calculation using the patients CTs. For each patient two plans were generated one with electron beams collimated using the applicator/cutout combination and the other plan with beams collimated only by the eMLC. Treatment plan quality was compared for each patient based on dose distribution and dose volume histogram. In order to determine the optimal position of the leaves, the impact of the different leaf positioning strategies were investigated.
Results have shown that target coverage and critical structure sparing can be effectively achieved by electron beams collimated by eMLC. Preliminary results have shown that the out-of-field strategy is most conservative and would be the recommended method to define the actual leaf position for the eMLC defined field.
The eMLC represents an effective time saving and pollution free device that can completely eliminate the need for patient specific cutouts. This work has been supported by a UICC American Cancer Society Beginning Investigators Fellowship funded by the American Cancer Society.
制作电子束限光筒不仅耗时，而且涉及到对有毒材料——铈镧合金的处理。参与限光筒制作的医院工作人员实际上可能会接触到该过程中通常产生的有毒烟雾。这项工作的目的是研究用我们的原型电动电子多叶准直器（eMLC）替代电子限光筒的可行性。
正如我们在之前的一项研究中已经证明的那样，由eMLC准直的电子束与由施源器和限光筒准直的电子束具有非常相似的半值层。然而，由于eMLC的尺寸有限，预计等剂量曲线会有起伏。当射野边缘靠近关键结构时，这可能会成为一个问题。因此，从我们的数据库中选择了10例先前接受过电子增量治疗的不同乳腺病例。使用基于蒙特卡罗的内部治疗计划系统，利用患者的CT进行剂量计算。对于每位患者，生成两个计划，一个计划使用施源器/限光筒组合准直电子束，另一个计划仅使用eMLC准直电子束。根据剂量分布和剂量体积直方图，比较每位患者的治疗计划质量。为了确定叶片的最佳位置，研究了不同叶片定位策略的影响。
结果表明，通过eMLC准直的电子束可以有效地实现靶区覆盖和关键结构保护。初步结果表明，场外策略最为保守，将是为eMLC定义的射野确定实际叶片位置的推荐方法。
eMLC是一种有效的省时且无污染的设备，可完全消除对患者专用限光筒的需求。这项工作得到了国际抗癌联盟美国癌症协会初出茅庐研究者奖学金的支持，该奖学金由美国癌症协会资助。
