title: Is internal target volume accurate for dose evaluation in lung cancer stereotactic body radiotherapy?
abstract: OBJECTIVE
  4DCT delineated internal target volume (ITV) was applied to determine the tumor motion and used as planning target in treatment planning in lung cancer stereotactic body radiotherapy (SBRT). This work is to study the accuracy of using ITV to predict the real target dose in lung cancer SBRT.
  
  
  METHODS
  Both for phantom and patient cases, the ITV and gross tumor volumes (GTVs) were contoured on the maximum intensity projection (MIP) CT and ten CT phases, respectively. A SBRT plan was designed using ITV as the planning target on average projection (AVG) CT. This plan was copied to each CT phase and the dose distribution was recalculated. The GTV_4D dose was acquired through accumulating the GTV doses over all ten phases and regarded as the real target dose. To analyze the ITV dose error, the ITV dose was compared to the real target dose by endpoints of D99, D95, D1 (doses received by the 99%, 95% and 1% of the target volume), and dose coverage endpoint of V100(relative volume receiving at least the prescription dose).
  
  
  RESULTS
  The phantom study shows that the ITV underestimates the real target dose by 9.47%~19.8% in D99, 4.43%~15.99% in D95, and underestimates the dose coverage by 5% in V100. The patient cases show that the ITV underestimates the real target dose and dose coverage by 3.8%~10.7% in D99, 4.7%~7.2% in D95, and 3.96%~6.59% in V100 in motion target cases.
  
  
  CONCLUSIONS
  Cautions should be taken that ITV is not accurate enough to predict the real target dose in lung cancer SBRT with large tumor motions. Restricting the target motion or reducing the target dose heterogeneity could reduce the ITV dose underestimation effect in lung SBRT.
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China.|Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.
authors.forename: Jiayuan
authors.initials: J
authors.lastname: Peng
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China.|Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China.|Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.
authors.forename: Jiazhou
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China.|Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Xie
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China.|Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.
authors.forename: Weigang
authors.initials: W
authors.lastname: Hu
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*
keywords: 4DCT; ITV; SBRT; dose evaluation; lung cancer