title: Changes in functional lung regions during the course of radiation therapy and their potential impact on lung dosimetry for non-small cell lung cancer.
abstract: OBJECTIVE
  To study changes in functional activity on ventilation (V)/perfusion (Q) single-photon emission computed tomography (SPECT) during radiation therapy (RT) and explore the impact of such changes on lung dosimetry in patients with non-small cell lung cancer (NSCLC).
  
  
  METHODS
  Fifteen NSCLC patients with centrally located tumors were enrolled. All patients were treated with definitive RT dose of ≥60 Gy. V/Q SPECT-CT scans were performed prior to and after delivery of 45 Gy of fractionated RT. SPECT images were used to define temporarily dysfunctional regions of lung caused by tumor or other potentially reversible conditions as B3. The functional lung (FL) was defined on SPECT by 2 separate approaches: FL1, a threshold of 30% of the maximum uptake of the patient's lung; and FL2, FL1 plus B3 region. The impact of changes in FL between initiation of RT and delivery of 45 Gy on lung dosimetry were analyzed.
  
  
  RESULTS
  Fourteen patients (93%) had larger FL2 volumes than FL1 pre-RT (P<.001). Dysfunctional lung became functional in 11 patients (73%) on V SPECT and in 10 patients (67%) on Q SPECT. The dosimetric parameters generated from CT-based anatomical lung had significantly lower values in FL1 than FL2, with a median reduction in the volume of lung receiving a dose of at least 20 Gy (V20) of 3%, 5.6%, and mean lung dose of 0.95 and 1.55 on V and Q SPECT respectively.
  
  
  CONCLUSIONS
  Regional ventilation and perfusion function improve significantly during RT in centrally located NSCLC. Lung dosimetry values vary notably between different definitions of functional lung.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan; Department of Radiation Oncology, Shandong Cancer Hospital, Shandong University, Jinan, China.
authors.forename: Xue
authors.initials: X
authors.lastname: Meng
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Kirk
authors.initials: K
authors.lastname: Frey
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Martha
authors.initials: M
authors.lastname: Matuszak
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Stanton
authors.initials: S
authors.lastname: Paul
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Randall
authors.initials: R
authors.lastname: Ten Haken
authors.affiliation: Department of Radiation Oncology, Shandong Cancer Hospital, Shandong University, Jinan, China.
authors.forename: Jinming
authors.initials: J
authors.lastname: Yu
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan; Department of Radiation Oncology, Georgia Regents University, Augusta, Georgia. Electronic address: fkong@gru.edu.
authors.forename: Feng-Ming Spring
authors.initials: FM
authors.lastname: Kong
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D012119:Respiration; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden
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