Measurement of the Shrinkage of Thermoplastic Mask in Radiation Therapy
ZHANG Yin, LI Minghui, LUO Jingwei
Department of Radiotherapy, National Cancer Center/National Clinical Research Center for Cancer/Chinese Academy
of Medical Sciences, Beijing Union Medical College Hospital Cancer, Beijing 100021, China
Abstract：Objective Radiotherapy thermoplastic mask has been widely used in tumor radiotherapy localization. This study
analyzed the impact of the shrinkage of thermoplastic mask on target positioning accuracy. Methods The shrinkage of
radiotherapy thermoplastic mask in free state was measured as following. Firstly, the thermoplastic mask with the specification
of 100 mm×100 mm×3.2 mm was heated and stretched in a straight direction at a certain tensile ratio. Then the length of
thermoplastic mask was measured at different time after stretching, and the shrinkage amplitude of thermoplastic film was analyzed
with time. The relationship between different tensile ratios and contraction amplitude was analyzed according to different tensile
ratios. Results The shrinkage amplitude of thermoplastic mask after thermal stretching increased approximately linearly in the first
20 minutes, and reached the maximum at the first 20 minutes. The length of thermoplastic mask remained stable after half an hour.
The shrinkage of thermoplastic mask was constant within the range of 1.5-3.0, which was commonly used in clinical practice. The
average shrinkage rate was 1.5%±0.1%. Conclusion The shrinkage of thermoplastic mask changed the most within 20 minutes after
the stereotyping, indicating that the cooling time should not be less than 20 minutes when radiotherapy thermoplastic mask is made
for patients. The shrinkage extent of thermoplastic mask is related to the tensile degree of the film, which indicates that it should be
uniformly stretched to avoid excessive or too small tensile ratio.
张寅，李明辉，罗京伟. 肿瘤放疗热塑膜伸缩特性的测试[J]. 中国医疗设备, 2018, 33(7): 30-32.
ZHANG Yin, LI Minghui, LUO Jingwei. Measurement of the Shrinkage of Thermoplastic Mask in Radiation Therapy. China Medical Devices, 2018, 33(7): 30-32.
