title: Quantification of tumor volume changes during radiotherapy for non-small-cell lung cancer.
abstract: OBJECTIVE
  Dose escalation for lung cancer is limited by normal tissue toxicity. We evaluated sequential computed tomography (CT) scans to assess the possibility of adaptively reducing treatment volumes by quantifying the tumor volume reduction occurring during a course of radiotherapy (RT).
  
  
  METHODS
  A total of 22 patients underwent RT for Stage I-III non-small-cell lung cancer with conventional fractionation; 15 received concurrent chemotherapy. Two repeat CT scans were performed at a nominal dose of 30 Gy and 50 Gy. Respiration-correlated four-dimensional CT scans were used for evaluation of respiratory effects in 17 patients. The gross tumor volume (GTV) was delineated on simulation and all individual phases of the repeat CT scans. Parenchymal tumor was evaluated unless the nodal volume was larger or was the primary. Subsequent image sets were spatially co-registered with the simulation data for evaluation.
  
  
  RESULTS
  The median GTV reduction was 24.7% (range, -0.3% to 61.7%; p < 0.001, two-tailed t test) at the first repeat scan and 44.3% (range, 0.2-81.6%, p < 0.001) at the second repeat scan. The volume reduction was not significantly different between patients receiving chemoradiotherapy vs. RT alone, a GTV >100 cm(3) vs. <100 cm(3), and hilar and/or mediastinal involvement vs. purely parenchymal or pleural lesions. A tendency toward a greater volume reduction with increasing dose was seen, although this did not reach statistical significance.
  
  
  CONCLUSIONS
  The results of this study have demonstrated significant alterations in the GTV seen on repeat CT scans during RT. These observations raise the possibility of using an adaptive approach toward RT of non-small-cell lung cancer to minimize the dose to normal structures and more safely increase the dose directed at the target tissues.
authors.affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Jana
authors.initials: J
authors.lastname: Fox
authors.forename: Eric
authors.initials: E
authors.lastname: Ford
authors.forename: Kristin
authors.initials: K
authors.lastname: Redmond
authors.forename: Jessica
authors.initials: J
authors.lastname: Zhou
authors.forename: John
authors.initials: J
authors.lastname: Wong
authors.forename: Danny Y
authors.initials: DY
authors.lastname: Song
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D003131:Combined Modality Therapy / Q000379:methods; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden / Q000528:radiation effects*