Bentefour El Hassane, Both Stefan, Tang Shikui, Lu Hsiao-Ming
Ion Beam Applications s.a.
J Appl Clin Med Phys. 2015 Nov 8;16(6):472–483. doi: 10.1120/jacmp.v16i6.5212.
This study explores the potential of cone-beam computed tomography (CBCT) for monitoring relative beam range variations due to daily changes in patient anatomy for prostate treatment by anterior proton beams. CBCT was used to image an anthropomorphic pelvic phantom, in eight sessions on eight different days. In each session, the phantom was scanned twice, first at a standard position as determined by the room lasers, and then after it was shifted by 10 mm translation randomly along one of the X, Y, or Z directions. The filling of the phantom bladder with water was not refreshed from day to day, inducing gradual change of the water-equivalent path length (WEPL) across the bladder. MIMvista (MIM) software was used to perform image registration and re-alignment of all the scans with the scan from the first session. The XiO treatment planning system was used to perform data analysis. It was found that, although the Hounsfield unit numbers in CBCT have substantially larger fluctuations than those in diagnostic CT, CBCT datasets taken for daily patient positioning could potentially be used to monitor changes in patient anatomy. The reproducibility of the WEPL, computed using CBCT along anterior-posterior (AP) paths across and around the phantom prostate, over a volume of 360 cc, is sufficient for detecting daily WEPL variations that are equal to or larger than 3 mm. This result also applies to CBCT scans of the phantom after it is randomly shifted from the treatment position by 10 mm. limiting the interest to WEPL variation over a specific path within the same CBCT slice, one can detect WEPL variation smaller than 1 mm. That is the case when using CBCT for tracking daily change of the WEPL across the phantom bladder that was induced by spontaneous change in the bladder filling due to evaporation. In summary, the phantom study suggests that CBCT can be used for monitoring day to day WEPL variations in a patient. The method can detect WEPL variation equal to or greater than 3 mm. The study calls for further investigation using the CBCT data from real patients. If confirmed with real patients' data, CBCT could become, in addition to patient setup, a standard tool for proton therapy pretreatment beam range check.
本研究探讨了锥形束计算机断层扫描（CBCT）在监测因前列腺癌患者每日解剖结构变化而导致的前向质子束治疗中相对束流射程变化方面的潜力。使用CBCT对一个人体骨盆模型进行成像，在八个不同的日子里进行了八次扫描。在每次扫描中，模型被扫描两次，第一次在由机房激光确定的标准位置，然后在沿X、Y或Z方向之一随机平移10毫米后再次扫描。模型膀胱中的水填充并非每天更新，导致膀胱内水等效路径长度（WEPL）逐渐变化。使用MIMvista（MIM）软件对所有扫描图像与第一次扫描图像进行图像配准和重新对齐。使用XiO治疗计划系统进行数据分析。结果发现，尽管CBCT中的亨氏单位数波动比诊断CT中的波动大得多，但用于每日患者定位的CBCT数据集有可能用于监测患者解剖结构的变化。在360立方厘米的体积内，沿模型前列腺前后（AP）路径使用CBCT计算的WEPL的再现性足以检测等于或大于3毫米的每日WEPL变化。该结果也适用于模型从治疗位置随机平移10毫米后的CBCT扫描。如果将兴趣限制在同一CBCT切片内特定路径上的WEPL变化，则可以检测到小于1毫米的WEPL变化。当使用CBCT跟踪因膀胱蒸发导致的膀胱自发充盈变化而引起的模型膀胱内WEPL的每日变化时就是这种情况。总之，模型研究表明CBCT可用于监测患者每日的WEPL变化。该方法可以检测到等于或大于3毫米的WEPL变化。该研究呼吁使用真实患者的CBCT数据进行进一步调查。如果得到真实患者数据的证实，CBCT除了可用于患者摆位外，还可能成为质子治疗预处理束流射程检查的标准工具。
