title: The investigation on the location effect of external markers in respiratory-gated radiotherapy.
abstract: OBJECTIVE
  To investigate the effect of the marker placement on the correlation relationship between the motions of external markers and the internal target under different breathing patterns for several lung cancer patients.
  
  
  METHODS
  To monitor and record simultaneous motions of internal target and associated surrogate markers during respiratory gated radiotherapy, an infrared camera system synchronized with a medical simulator was installed in our institute. Multiple external markers were placed on the patients' chest wall with proper geometrical arrangement in closely monitoring the motion of skin near tumor. The motion signals of three breathing sessions (free breathing, breath-holding, and free breathing after breath-holding) were recorded and the quality of correlation between them was analyzed. For a single marker motion, its correlation with the internal target was analyzed using cross-covariance function. For the multiple markers, their correlation with the internal target was analyzed based on additive model.
  
  
  RESULTS
  Seven patients undergoing radiotherapy with right upper or middle lobe lesions were enrolled in this study. Statistic analysis based on the internal-external motion signals shows that the effect of marker location on the quality of its correlation with the internal target is varied from patient to patient. There was no specific marker location where consistently demonstrated superior quality of correlation with the internal target motion over three breathing sessions for all patients. As the composite surrogate signal which was generated from the motions of multiple external markers was used to correlate the internal target motion, significant improvement of the quality of correlation was achieved.
  
  
  CONCLUSIONS
  The correlation of external marker to the internal target could be influenced by several factors such as patient population, marker locations, and breathing patterns, considerably. The quality of correlation and predictability to the internal target furnished by a single external marker is inferior to that of the composite signal generated from multiple external markers. The use of composite signal shows great potential in improving the predictability of internal target motion and presents an effective way to track tumor more accurately.
authors: Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, U.S.A.
authors: Hui
authors: H
authors: Yan
authors: Department of Radiation Oncology, Henry Ford Hospital, Detroit, Michigan, U.S.A.|Department of Radiation Oncology, Cancer Hospital of Fudan University, Shanghai, China.
authors: Guopei
authors: G
authors: Zhu
authors: Department of Biostatistics, Henry Ford Hospital, Detroit, Michigan, U.S.A.
authors: James
authors: J
authors: Yang
authors: Department of Biostatistics, Henry Ford Hospital, Detroit, Michigan, U.S.A.
authors: Mei
authors: M
authors: Lu
authors: Department of Radiation Oncology, Henry Ford Hospital, Detroit, Michigan, U.S.A.
authors: Munther
authors: M
authors: Ajlouni
authors: Department of Radiation Oncology, Henry Ford Hospital, Detroit, Michigan, U.S.A.
authors: Jae Ho
authors: JH
authors: Kim
authors: Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, U.S.A.
authors: Fang-Fang
authors: FF
authors: Yin
mesh_terms: D000230:Adenocarcinoma / Q000532:radiotherapy; D000368:Aged; D001943:Breast Neoplasms / Q000532:radiotherapy*; D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration