Matsumoto Kenji, Tamura Mikoto, Otsuka Masakazu, Wakabayashi Kazuki, Kijima Kenta, Monzen Hajime
Radiology Center, Kindai University Hospital.
Department of Medical Physics, Graduate School of Medical Sciences, Kindai University.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2020;76(12):1248-1255. doi: 10.6009/jjrt.2020_JSRT_76.12.1248.
This study investigated the dosimetric characteristics of electron beams shaped with a real-time shapeable tungsten-containing rubber (STR) collimator.
Circular irradiation fields of 40 mm diameter were shaped using STR or low melting-point alloy (LMA) placed on the electron applicator. The STR heated with approximately 70-degree warm water was molded into the template bottom of the applicator. Percent depth doses (PDDs) and lateral dose profiles of 6 and 12 MeV electron beams were measured and compared between STR and LMA. For the PDDs, the depths of maximum dose (d), 90% dose (d), and 80% dose (d) were evaluated. For the lateral dose profiles, penumbra as the width of the off-axis distance from 80% to 20% doses and treatment diameter covering over 90% dose were evaluated at the surface, d, d, and d. The transmission of the STR was also investigated at thicknesses fit to electron applicator for 6 and 12 MeV electron beams.
The STR was softened with 70-degree warm water. Therefore, it was easy to mold it and attach the applicator. The PDDs and penumbras at the surface, d, d, and d for the STR were almost equal to those for the LMA with 6 and 12 MeV electron beams. The treatment diameters covering over 90% dose for the irradiation fields with 40 mm diameter at d (LMA vs. STR) were 20.9 vs. 21.1 mm and 19.2 vs. 18.4 mm for 6 and 12 MeV electron beams, respectively. The transmission of the STR was almost same as that of LMA.
The dosimetric characteristics of the STR on the electron applicator were almost same as those of the LMA. The heated STR was shaped easily, flexibly, and immediately. The STR can be used as a substitute for LMA in electron radiotherapy.
本研究调查了使用实时可塑形含钨橡胶（STR）准直器塑形的电子束的剂量学特性。
使用放置在电子施源器上的STR或低熔点合金（LMA）对直径40 mm的圆形照射野进行塑形。用约70摄氏度的温水加热后的STR被模塑到施源器的模板底部。测量并比较了STR和LMA的6和12 MeV电子束的百分深度剂量（PDD）和侧向剂量分布。对于PDD，评估了最大剂量深度（d）、90%剂量深度（d）和80%剂量深度（d）。对于侧向剂量分布，在表面、d、d和d处评估了作为离轴距离从80%剂量到20%剂量的宽度的半值宽度以及覆盖超过90%剂量的治疗直径。还研究了6和12 MeV电子束在适合电子施源器的厚度下STR的透射率。
STR在70摄氏度的温水中变软。因此，很容易对其进行模塑并连接施源器。STR在表面、d、d和d处的PDD和半值宽度与6和12 MeV电子束的LMA几乎相等。对于直径40 mm的照射野，在d处（LMA与STR）覆盖超过90%剂量的治疗直径，6 MeV电子束分别为20.9对21.1 mm，12 MeV电子束为19.2对18.4 mm。STR的透射率与LMA几乎相同。
电子施源器上STR的剂量学特性与LMA几乎相同。加热后的STR易于塑形、灵活且即时。STR可在电子放射治疗中用作LMA的替代品。
