The accuracy and precision of Kilovoltage Intrafraction Monitoring (KIM) six degree-of-freedom prostate motion measurements during patient treatments

Background and purpose

To perform a quantitative analysis of the accuracy and precision of Kilovoltage Intrafraction Monitoring (KIM) six degree-of-freedom (6DoF) prostate motion measurements during treatments.

Material and methods

Real-time 6DoF prostate motion was acquired using KIM for 14 prostate cancer patients (377?fractions). KIM outputs the 6DoF prostate motion, combining 3D translation and 3D rotational motion information relative to its planning position. The corresponding groundtruth target motion was obtained post-treatment based on kV/MV triangulation. The accuracy and precision of the 6DoF KIM motion estimates were calculated as the mean and standard deviation differences compared with the ground-truth.

Results

The accuracy?±?precision of real-time 6DoF KIM?measured prostate motion were 0.2?±?1.3° for rotations and 0.1?±?0.5?mm for translations, respectively. The magnitude of KIM-measured motion was well-correlated with the magnitude of ground-truth motion resulting in Pearson correlation coefficients of? ≥0.88 in all DoF.

Conclusions

The results demonstrate that KIM is capable of providing the real-time 6DoF prostate target motion during patient treatments with an accuracy?±?precision of within 0.2?±?1.3° and 0.1?±?0.5?mm for rotation and translation, respectively. As KIM only requires a single X-ray imager, which is available on most modern cancer radiotherapy devices, there is potential for widespread adoption of this technology.