Preliminary study of in vivo dose measurement of intensity-modulated radiotherapy for cervical cancer / 中华放射肿瘤学杂志

ABSTRACT

Objective:To monitor and evaluate in vivo dose changes of intensity-modulated radiotherapy (IMRT) in patients with cervical cancer in a real-time manner. Methods:Twelve patients with cervical cancer admitted to our hospital were enrolled in this study. The in vivo doses were monitored by PerFRACTION?. Electronic portal imaging device (EPID) were collected in each treatment fraction for two-dimensional in vivo dose verification[γ index and dose difference (DD) index]. Log files were recorded for three-dimensional in vivo dose verification (γ index). The correlation between in vivo dose and treatment duration was analyzed by Pearson correlation analysis. Results:A total of 206 sets of EPID images and corresponding Log files were collected. The three-dimensional in vivo dose verification γ 1%/1mm of all patients was not correlated with treatment fraction ( P>0.05). Among them, the absolute difference of γ 1%/1mm of 94.66% fractions was< 1%. The mean DD 3% of two-dimensional in vivo dose verification of all patients was negatively correlated with treatment fraction ( P<0.05). Among which, the average γ 3%/3mm of 9 patients was>89% in the treatment fractions, and the average γ 3%/3mm of 98.57% fractions of these 9 patients was>93%. The other 3 patients had an average γ 3%/3mm ranged from 38% to 100%. CBCT images showed that the bladder volume of these 3 patients was significantly decreased with the relative changes by 82.08%, 84.41% and 73.59%, respectively, and the target area was retracted significantly with the relative changes by 38.12%, 59.79% and 24.46%, respectively. Conclusion:Combined with γ index and DD index, PerFRACTION? can monitor the mechanical stability of accelerator and MU delivery accuracy during treatment fractions, and monitor the changes of in vivo dose in patients with cervical cancer, which can improve the safety and quality assurance of IMRT for cervical cancer patients and provide guidance for patients with adaptive radiotherapy.