Real-time guidance is important for radiotherapy, especially for areas with substantial motion (e.g. lungs). Calypso medical developed a very small transponder that can be located to sub-mm accuracy while implanted deep within the body.
In collaboration with Varian Medical Systems and Calypso Medical, I contributed to take this real-time position feedback and use it to tailor radiotherapy. In the first study, we ‘gated’ the treatment. This means we simply turned the beam off when the target left, and turned the beam back on when it returned. This system is currently treating patients in the clinic. Details of the initial implementation can be found here:
- Ryan L Smith, Kristen Lechleiter, Kathleen Malinowski. M. Shepard, D.J. Housley, M. Afghan, Jeff Newell, Jay Peterson, Brian Sargent, Parag Parikh. “Evaluation of Linac Gating With Real-Time Electromagnetic Tracking”, International Journal of Radiation Oncology*Biology*Physics, 74(3):920-927, July 2009.
In later studies, we combined the Dynamic Multi-Leaf Collimator (DMLC) tracking capabilities from Stanford University to move the treatment window in real-time to follow the target. MLCs are present on existing radiotherapy systems, and are essentially a stack of thin ‘leaves’ made from heavy metal to occlude the treatment beam. They are individually actuated to allow arbitrary beam shaping, along with Intensity Modulated Radiotherapy (IMRT). Here, we took the real-time signal from an implanted transponder, and followed it by moving the aperture created by the MLC:
- R. L. Smith, A. Sawant, L. Santanam, R. Venkat, J. Newell, B. Cho, P. Poulsen, H. Catell, P. Keall, P.J. Parikh. “Integration of Real-Time Internal Electromagnetic Position Monitoring Coupled with Dynamic Multileaf Collimator Tracking: An IMRT Feasibility Study”, International Journal of Radiation Oncol- ogy*Biology*Physics, 74(3):868-875, July 2009.
- Amit Sawant, Ryan Smith, Raghu Venkat, Lakshmi Santanam, Byung-chul Cho, Per Poulsen, Herbert Cattell, Laurence J Newell, Parag Parikh, Paul J. Keall. “Towards sub-mm accuracy in the management of intrafraction motion: The integration of real-time internal position monitoring and MLC target tracking”, International Journal of Radiation Oncol- ogy*Biology*Physics, 74(2):575-582, June 2009