近距离治疗中放射源位置检验的数学形态学方法

Detection of brachytherapy source dwell positions based on mathematical morphology

利用数学形态学算法计算EBT3胶片拍摄的近距离治疗中放射源的位置准确性。目前验证192Ir放射源到位精度的方法主要包括胶片、Fricke放射量测定器、平板探测器、简单的直尺结合计量仪方法等,数学形态学算法自动计算曝光胶片放射源的位置未见报道。本研究用EBT3免冲洗胶片分别获得不同步进长度和已知驻留位置误差的影像。采用Contourlet变换对胶片图像进行去噪,求得放射源步进长度的误差小于±0.2 mm,源驻留位置的误差在±0.5 mm以内,符合临床要求。结果表明本方法简单,且结果可靠。

Background： Accuracy of brachytherapy source positions is an important part of radiotherapy quality assurance using two-dimension ion chamber array or film. It has already been confirmed that the mathematical morphology algorithm can be used for medical image processing. Purpose： This study aims to detect the dwell position of high-dose-rate brachytherapy source using EBT3 film based on mathematical morphology, Methods： EBT3 film was exposed for different step lengths of source and preset dwell position errors. The scanned digital images were denoised using contourlet transform. Black spots of 192Ir source were obtained on the basis of threshold selection and morphological operation. The positions of source were acquired by means of binary centroid algorithm. The calculated source position coordinates were compared with the reference data. Results： The error of source step length was less than ±0.2 mm, while the error of source dwell position was within ±0.5 mm. Conclusion： Mathematical morphology can be used in automatic detection ofbrachytherapy source positions. This method is simple and reliable.