Oare Courtney, Wilke Christopher, Ehler Eric, Mathew Damien, Sterling David, Ferreira Clara
University of Minnesota Medical School, 420 Delaware St SE, Minneapolis, MN 55414, USA.
3D Print Med. 2019 Feb 6;5(1):3. doi: 10.1186/s41205-019-0040-4.
3D printing technology has allowed the creation of custom applicators for high dose rate (HDR) brachytherapy, especially for complex anatomy. With conformal therapy comes the need for advanced dosimetric verification. It is important to demonstrate how dose to 3D printed materials can be related to dose to water. This study aimed to determine dose differences and uncertainties using 3D printed PLA and ABS plastics for Radiochromic film calibration in HDR brachytherapy.Gafchromic EBT3 film pieces were irradiated in water with an Ir-192 source at calculated dose levels ranging from 0 to 800 cGy, to create the control calibration curve. Similarly, film was placed below 3D printed PLA and ABS blocks and irradiated at the same dose levels calculated for water, ranging from 0 to 800 cGy. After a 72-h development time, film pieces were scanned on a flatbed scanner and the median pixel value was recorded in the region of highest dose. This value was converted to net optical density (NOD). A rational function was used to fit a calibration curve in water that relates NOD to dose for red, green, and blue color channels. Based on this fitted curve, ABS and PLA NOD values were used to estimate dose in 3D printed plastics.From the fitted calibration curve, mean residual error between measured and planned dose to water was less than 1% for each color channel at high dose levels. At high dose levels, ABS and PLA mean residual errors were about 6.9 and 7.8% in the red channel, while 5.2 and 5.7% in the green channel. Combined uncertainties measured to be about 6.9% at high dose levels. This study demonstrated dose differences and uncertainties using 3D printed applicators for HDR Ir-192 brachytherapy.
3D打印技术已能够制造用于高剂量率（HDR）近距离放射治疗的定制施源器，特别是针对复杂的解剖结构。随着适形治疗的出现，对先进剂量验证的需求也随之而来。证明3D打印材料的剂量与水的剂量之间的关系非常重要。本研究旨在确定在HDR近距离放射治疗中使用3D打印的聚乳酸（PLA）和丙烯腈-丁二烯-苯乙烯共聚物（ABS）塑料进行放射变色胶片校准时的剂量差异和不确定性。将Gafchromic EBT3胶片片在水中用铱-192源以0至800 cGy的计算剂量水平进行照射，以创建对照校准曲线。同样，将胶片放置在3D打印的PLA和ABS块下方，并以与水相同的计算剂量水平（0至800 cGy）进行照射。在72小时的显影时间后，将胶片片在平板扫描仪上进行扫描，并记录最高剂量区域的中位数像素值。该值转换为净光密度（NOD）。使用有理函数拟合水中的校准曲线，该曲线将红色、绿色和蓝色通道的NOD与剂量相关联。基于此拟合曲线，使用ABS和PLA的NOD值来估计3D打印塑料中的剂量。从拟合的校准曲线来看，在高剂量水平下，每个颜色通道测量剂量与计划水剂量之间的平均残余误差小于1%。在高剂量水平下，红色通道中ABS和PLA的平均残余误差分别约为6.9%和7.8%，而绿色通道中分别为5.2%和5.7%。在高剂量水平下测量的综合不确定性约为6.9%。本研究证明了在HDR铱-192近距离放射治疗中使用3D打印施源器时的剂量差异和不确定性。
