Proton Beam Ocular Treatment in Eyes with Intraocular Silicone Oil: Effects on Physical Beam Parameters and Clinical Relevance of Silicone Oil in EYEPLAN Dose-Volume Histograms

• 作者: Bertil E. Damato Inder K. Daftari Kavita K. Mishra Michael Seider
• 来源期刊: 医学物理学、临床工程、放射肿瘤学(英文)
• 学科: 医学
• 关键词: Proton Beam Therapy UVEAL MELANOMA Depth Dose and SILICONE Oil
• 年，卷（期）: 2018,（3）
• 页码范围: 347-362
• 页数: 16页
• 分类号: R73

摘要

Proton beam therapy (PBRT) is an essential tool in the treatment of certain ocular tumors due to its characteristic fall-off and sharp beam parameters at critical structures. Review of clinical cases in our ocular PBRT program identified patients with silicone oil used as an intraocular tamponade following pars plana vitrectomy for repair of retinal detachment. Patient’s eye may be filled with silicone oil prior to PBRT for an ocular tumor. The objective of this study was to extend our knowledge of the physical characteristics of proton beams in silicone oil by measuring dose within a silicone tank itself, hence better representing the surgical eye, as well as applying the range changes to EYEPLAN software to estimate clinical impact. The relevant proton beam physical parameters in silicone oil were studied using a 67.5 MeV un-modulated proton beam. The beam parameters being defined included: 1) residual range;2) peak/plateau ratio;3) full width at half maximum (FWHM) of the Bragg peak;and 4) distal penumbra. Initially, the dose uniformity of the proton beam was confirmed at 10 mm and 28 mm depth, corresponding to plateau and peak region of the Bragg peak using Gefchromic film. Once the beam was established as expected, three sets of measurements of the beam parameters were taken in: a) water (control);b) silicone-1000 oil and water;and c) silicone-1000 oil only. Central-axis depth-ionization measurements were performed in a tank (“main tank”) with a 0.1cc ionization chamber (Model IC-18, Far west) having walls made of Shonka A150 plastic. The tank was 92 mm (length) × 40 mm (height) × 40 mm (depth). The tank had a 0.13 mm thick kapton entrance window through which the proton beam was incident. The ionization chamber was always positioned in the center of the circular field of diameter 30 mm with the phantom surface at isocenter. The ionization chamber measurements were taken at defined depths in increments of 2 mm, from 0 to 35 mm. To define the effect of silicone oil on the physical characteristics of p