title: Prototype development of an electrical impedance based simultaneous respiratory and cardiac monitoring system for gated radiotherapy.
abstract: BACKGROUND
  In radiotherapy, temporary translocations of the internal organs and tumor induced by respiratory and cardiac activities can undesirably lead to significantly lower radiation dose on the targeted tumor but more harmful radiation on surrounding healthy tissues. Respiratory and cardiac gated radiotherapy offers a potential solution for the treatment of tumors located in the upper thorax. The present study focuses on the design and development of simultaneous acquisition of respiratory and cardiac signal using electrical impedance technology for use in dual gated radiotherapy.
  
  
  METHODS
  An electronic circuitry was developed for monitoring the bio-impedance change due to respiratory and cardiac motions and extracting the cardiogenic ECG signal. The system was analyzed in terms of reliability of signal acquisition, time delay, and functionality in a high energy radiation environment. The resulting signal of the system developed was also compared with the output of the commercially available Real-time Position Management™ (RPM) system in both time and frequency domains.
  
  
  RESULTS
  The results demonstrate that the bioimpedance-based method can potentially provide reliable tracking of respiratory and cardiac motion in humans, alternative to currently available methods. When compared with the RPM system, the impedance-based system developed in the present study shows similar output pattern but different sensitivities in monitoring different respiratory rates. The tracking of cardiac motion was more susceptible to interference from other sources than respiratory motion but also provided synchronous output compared with the ECG signal extracted. The proposed hardware-based implementation was observed to have a worst-case time delay of approximately 33 ms for respiratory monitoring and 45 ms for cardiac monitoring. No significant effect on the functionality of the system was observed when it was tested in a radiation environment with the electrode lead wires directly exposed to high-energy X-Rays.
  
  
  CONCLUSIONS
  The developed system capable of rendering quality signals for tracking both respiratory and cardiac motions can potentially provide a solution for simultaneous dual-gated radiotherapy.
authors.affiliation: Department of Medical Physics, Fraser Valley Center, BC Cancer Agency, 13750 96th Avenue, Surrey V3V 1Z2, BC, Canada. kkohli@bccancer.bc.ca.
authors.forename: Kirpal
authors.initials: K
authors.lastname: Kohli
authors.forename: Jeff
authors.initials: J
authors.lastname: Liu
authors.forename: Devin
authors.initials: D
authors.lastname: Schellenberg
authors.forename: Anand
authors.initials: A
authors.lastname: Karvat
authors.forename: Ash
authors.initials: A
authors.lastname: Parameswaran
authors.forename: Parvind
authors.initials: P
authors.lastname: Grewal
authors.forename: Steven
authors.initials: S
authors.lastname: Thomas
mesh_terms: D018281:Cholangiocarcinoma / Q000188:drug therapy*; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D016503:Drug Delivery Systems; D054855:Drug-Eluting Stents; D017097:Electric Impedance; D006415:Hematoporphyrins / Q000008:administration & dosage*; D006801:Humans; D008567:Membranes, Artificial; D008855:Microscopy, Electron, Scanning; D008991:Monitoring, Physiologic; D009068:Movement; D010778:Photochemotherapy / Q000379:methods; D011091:Polyesters / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011878:Radiotherapy / Q000379:methods*; D012995:Solubility; D013997:Time Factors; D000093542:Gemcitabine
chemical_list: D006415:Hematoporphyrins; D008567:Membranes, Artificial; D011091:Polyesters; D011108:Polymers; D003841:Deoxycytidine; C016240:polycaprolactone; D011092:Polyethylene Glycols; D000093542:Gemcitabine