Iftimia I, Cirino E, Mower H, McKee A
Lahey Clinic, Burlington, MA.
Med Phys. 2012 Jun;39(6Part11):3735. doi: 10.1118/1.4735196.
To quantify the dwell position inaccuracy in Titanium ring applicators and develop a test to be performed quarterly, after source exchange.
All three rings from our Titanium kit (30, 45, 60 deg.) were used for this study. EDR2 film was placed on the Simulator table and a ring was taped to the film, with a solid water slab as buildup. A 1-cm spacing dummy wire was inserted into the ring. The film was exposed using 135 kV, 80 mA, 400 mAs. An HDR treatment was then delivered using the even source dwell positions from 2 to 16, with a 5 mm step size, nominal dwell time 0.4 sec/position. The procedure was repeated three times for each ring. The films were scanned and analyzed with the RIT software. The distance between the center of each source position to the adjacent dummy dots was measured for each ring on all three films. An average shift (AS) was obtained for each ring.New films were exposed with a treatment offset equal and in the opposite direction relative to the AS for the ring used. The films were visually inspected to assess if the source positions are centered in between two adjacent dummy dots, and also scanned and analyzed with the RIT software. This test will be performed quarterly to verify if the shifts remain stable.
The average shift was 2.5, 2.4, and 2.4 mm distally for the 30, 45, and 60 deg. rings, respectively. The offset for the quarterly test was set to 2 mm proximally, to take into account the 1 mm tolerance for the source position.
The dwell position inaccuracy in Titanium ring applicators was quantified and the quarterly test was successfully performed for two quarters. Work is started to assess the dosimetric implications of this shift.
量化钛环施源器中的驻留位置误差，并制定一项在源更换后每季度进行一次的测试。
本研究使用了我们钛环套件中的所有三个环（30度、45度、60度）。将EDR2胶片放置在模拟台上，用胶带将一个环固定在胶片上，并使用固体水模体作为建成材料。将一根1厘米间距的假导线插入环中。使用135 kV、80 mA、400 mAs的参数对胶片进行曝光。然后使用从2到16的均匀源驻留位置进行高剂量率（HDR）治疗，步长为5毫米，标称驻留时间为0.4秒/位置。每个环重复该过程三次。使用RIT软件对胶片进行扫描和分析。在所有三张胶片上，测量每个源位置中心到相邻假点之间的距离。计算每个环的平均偏移量（AS）。使用与所使用环的AS大小相等且方向相反的治疗偏移量对新胶片进行曝光。目视检查胶片，以评估源位置是否位于两个相邻假点之间的中心位置，同时也使用RIT软件进行扫描和分析。该测试将每季度进行一次，以验证偏移量是否保持稳定。
对于30度、45度和60度的环，平均偏移量分别为向远侧2.5毫米、2.4毫米和2.4毫米。考虑到源位置的1毫米公差，将季度测试的偏移量设置为向近侧2毫米。
量化了钛环施源器中的驻留位置误差，并成功进行了两个季度的季度测试。已开始评估这种偏移对剂量学的影响。
