Bawazeer Omemh, Herath Sisira, Sarasanandarajah Sivananthan, Kron Tomas, Dunn Leon, Deb Pradip
Discipline of Medical Radiations, RMIT University, Melbourne, Australia.
Discipline of Sciences, Umm Al-Qura University, Mecca, Saudi Arabia.
Australas Phys Eng Sci Med. 2019 Dec;42(4):1183-1189. doi: 10.1007/s13246-019-00789-8. Epub 2019 Aug 26.
We propose a simple and efficient method to measure beam attenuation in one or two dimensions using an amorphous silicon electronic portal imaging device (a-Si EPID). The proposed method was validated against ionization chamber measurements. Beam attenuation through treatment couches (Varian Medical Systems) and immobilization devices (CIVCO Radiotherapy, USA) was examined. The dependency of beam attenuation on field size, photon energy, thickness of the couch, and the presence of a phantom were studied. Attenuation images were derived by computing the percentage difference between images obtained without and with a couch or immobilization devices determining the percentage of attenuation at the center and the mean attenuation. The beam attenuation measurements obtained with an a-Si EPID and an ionization chamber agreed to within ± 0.10 to 1.80%. No difference was noted between the center and mean of an attenuated image for a small field size of 5 × 5 cm, whereas a large field size of 15 × 15 cm exhibited differences of up to 1.13%. For an 18 MV beam, the a-Si EPID required additional build-up material for accurate assessment of beam attenuation. The a-Si EPID could measure differences in beam attenuation through an image guided radiotherapy (IGRT) couch regardless of the variabilities in couch thickness. Interestingly, the addition of a phantom reduced the magnitude of attenuation by approximately 1.20% for a field size of 15 × 15 cm. A simple method is proposed that provides the user with beam attenuation data in either 2D or 1D within a few minutes.
我们提出了一种简单有效的方法，使用非晶硅电子射野影像装置（a-Si EPID）来测量一维或二维的射束衰减。所提出的方法通过与电离室测量结果进行了验证。研究了射束通过治疗床（瓦里安医疗系统公司）和固定装置（美国CIVCO放射治疗公司）的衰减情况。研究了射束衰减对射野大小、光子能量、治疗床厚度以及模体存在与否的依赖性。通过计算在有和没有治疗床或固定装置的情况下获得的图像之间的百分比差异来得出衰减图像，从而确定中心处的衰减百分比和平均衰减。使用a-Si EPID和电离室获得的射束衰减测量结果在±0.10%至1.80%的范围内一致。对于5×5 cm的小射野尺寸，衰减图像的中心值和平均值之间没有差异，而对于15×15 cm的大射野尺寸，差异高达1.13%。对于18 MV的射束，a-Si EPID需要额外的建成材料来准确评估射束衰减。a-Si EPID可以测量通过图像引导放射治疗（IGRT）治疗床的射束衰减差异，而不考虑治疗床厚度的变化。有趣的是，对于15×15 cm的射野尺寸，添加模体可使衰减幅度降低约1.20%。本文提出了一种简单的方法，可在几分钟内为用户提供二维或一维的射束衰减数据。
