Fast regional readout CMOS Image Sensor for advanced radiotherapy treatment verification
Hafiz ZIN1,2, Emma HARRIS2, John OSMOND3, Phil EVANS2,4
1Advanced Medical and Dental Institute, Universiti Sains Malaysia, 13200, Kepala Batas, Penang, Malaysia
2Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey, SM2 5PT, United Kingdom
3Elekta Limited Crawley, Linac House, Flemming Way, RH10 9RR, Crawley, United Kingdom
4Centre for Vision, Speech and Signal Processing, University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom
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Purpose: Advanced radiotherapy techniques such as volumetric modulated arc therapy (VMAT) require verification of the complex beam delivery including tracking of multileaf collimators (MLC) and monitoring the dose rate. This work explores the feasibility of a prototype Complementary metal-oxide semiconductor Image Sensor (CIS) for verifying and tracking these complex treatments by utilising fast, region of interest (ROI) readout functionality.
Methods: Performance of the ROI read out of the CISis characterised using a novel method, to investigate the accuracy of the resulted fast read out rate. The ROI readout was then used to image the radiotherapy beamat various linac dose rates and dynamic MLC positions.An automatic edge tracking algorithm was used to locate the MLC leaves edges moving at various speeds (from a moving triangle field shape), imaged with a combination of linac dose rates and sensor frame rates.
Results:The CIS with proper calibration to the frame rate shows a linear sensor response with increasing dose rate and successful edge detection of the dynamic MLC motion. This demonstrates the feasibility of the APS to verify VMAT treatment delivery (monitoring the dose rate as well as tracking the MLC shape) up to 400 samples per second, which is equivalent to the linac pulse rate. This is superior to current techniques using electronic portal imaging devices (EPID) and fluoroscopic based imaging.
Conclusions: CIS provides the basis to an essential real-time verification tool, useful in accessing accurate delivery of complex high energy radiation to the tumour and ultimately to achieve better cure rates for cancer patients.
Acknowledgement: This work is supported by EPSRC grant MI-3 plus (EP/G037671). Research at The Institute of Cancer Research is also supported by Cancer Research UK under Programme C46/A10588 and NIHR funding to the Biomedical Research Centre. The authors would like to acknowledge Professor Nigel Allinson who led the MI-3 consortium and Rutherford Appleton Laboratory, specifically Renato Turchetta and Andy T. Clark, for the design of the detector and useful discussion.HZ was funded by a PhD studentship from the Malaysian Government and University Sains Malaysia.