Département d'Ingénierie et de Physique médicale, Institut Claudius Regaud (ICR), Institut Universitaire du Cancer de Toulouse-Oncopole (IUCT-O), Toulouse, France.
SIMAD LU50, Université Paul Sabatier Toulouse III, Castres, Toulouse, France.
PLoS One. 2020 May 4;15(5):e0232315. doi: 10.1371/journal.pone.0232315. eCollection 2020.
The INTRABEAM Carl Zeiss Surgical system (Oberkochen, Germany) is a miniature accelerator producing low energy photons (50 keV maximum). The published dosimetric characterization of the INTRABEAM was based on detectors (radiochromic films or ionization chambers) not allowing measuring the absorbed dose in the first millimeters of the irradiated medium, where the dose is actually prescribed. This study aims at determining with Magnetic Resonance Imaging (MRI) the sensitivity of a paramagnetic gel in order to measure the dose deposit produced with the INTRABEAM from 0 to 20 mm. Although spherical applicators are mostly used with the INTRABEAM system for breast applications, this study focuses on surface applicators that are of interest for cutaneous carcinomas. The irradiations at 12 different dose levels (between 2 Gy and 50 Gy at the gel surface) were performed with the INTRABEAM and a 4 cm surface applicator. The gel used in this study is a new « sensitive » material. In order to compare gel sensitivity at low energy with high energy, gels were irradiated by an 18 MV photon beam produced by a Varian Clinac 2100 CD. T2 weighted multi echo MRI sequences were performed with 16 echo times. The T2 signal versus echo times was fitted with a mono-exponential function with 95% confidence interval. The calibration curve determined at low energy is a linear function (r2 = 0.9893) with a sensitivity of 0.0381 s-1.Gy-1, a similar linear function was obtained at high energy (0.0372 s-1.Gy-1 with r2 = 0.9662). The calibration curve at low energy was used to draw isodose maps from the MR images. The PDD (Percent Depth Dose) determined in the gel is within 5%-1mm of the ionization chamber PDD except for one point. The dosimetric sensitivity of this new paramagnetic ferrous gel was determined with MRI measurements. It allowed measuring the dose distribution specifically in the first millimeters for an irradiation with the INTRABEAM miniature accelerator equipped with a surface applicator.
INTRABEAM 卡尔蔡司手术系统（德国奥伯科亨）是一种产生低能量光子（最大 50keV）的微型加速器。INTRABEAM 的已发表剂量学特性是基于不能在照射介质的最初几毫米内测量吸收剂量的探测器（辐射变色胶片或电离室），而这正是剂量实际规定的位置。本研究旨在通过磁共振成像（MRI）确定顺磁凝胶的灵敏度，以便测量 INTRABEAM 在 0 至 20mm 范围内产生的剂量沉积。虽然 INTRABEAM 系统主要用于乳房应用的球形施源器，但本研究侧重于对于皮肤癌更有意义的表面施源器。在凝胶表面的 12 个不同剂量水平（2Gy 至 50Gy）下进行了 INTRABEAM 和 4cm 表面施源器的照射。本研究中使用的凝胶是一种新的“敏感”材料。为了比较低能和高能下的凝胶灵敏度，使用瓦里安 Clinac 2100CD 产生的 18MV 光子束对凝胶进行了照射。使用 16 个回波时间进行 T2 加权多回波 MRI 序列。T2 信号与回波时间的关系用 95%置信区间的单指数函数拟合。在低能下确定的校准曲线是一条线性函数（r2=0.9893），灵敏度为 0.0381s-1.Gy-1，在高能下也得到了类似的线性函数（r2=0.9662，灵敏度为 0.0372s-1.Gy-1）。在低能下的校准曲线用于从 MR 图像中绘制等剂量图。在凝胶中确定的 PDD（百分深度剂量）除了一个点之外，与电离室 PDD 的差值在 5%至 1mm 范围内。通过 MRI 测量确定了这种新型顺磁亚铁凝胶的剂量学灵敏度。它允许使用配备表面施源器的 INTRABEAM 微型加速器进行照射，专门测量最初几毫米内的剂量分布。
