title: Volume changes with stereotactic body radiation therapy in early lung cancer: Time trends and outcomes.
abstract: BACKGROUND
  Tumour response during stereotactic body radiotherapy (SBRT) could be heterogeneous and the pattern of response may be used as an early predictor for outcome.
  
  
  METHODS
  Twenty-two consecutive patients with early lung cancer (ELC), treated with SBRT, were evaluated retrospectively for their gross tumour volume (GTV) changes during radiation therapy (RT). Kilo-voltage computed tomography scans (KVCTs) were acquired before every fraction and GTV was contoured manually on a total of 152 datasets. Tumour volume changes were noted with every fraction. The overall survival (OS), locoregional recurrence free survival (LRFS) and distant metastasis free survival (DMFS) were computed using the Kaplan-Meier method and comparisons were made using log-rank test.
  
  
  RESULTS
  Of the 22 patients, six had T1 tumours and 16 had T2 tumours. Median GTV was 40.6 cc (range 7.3-140.2 cc) on CT1 (KVCT at first fraction) and 33.3 cc (range 4.1-83.4 cc) on CTlast (KVCT at last fraction), suggesting a 17.9% median volume reduction at RT completion. Increase in tumour volume was noted in 18 (81.8%) patients at some point during RT. In the mid-treatment scan, 12 (54.5%) patients had higher tumour volumes than in CT1, however, only six (27.3%) patient's GTV remained larger compared to the baseline at the end of treatment. The median follow-up was 12.4 months. The OS, LRFS and DMFS rate at 12 and 18 months were 86.4%, 88.2%, 62% and 64.8%, 75.6% and 37.2% respectively. Tumours that regressed in volume by >17.9% (median volume reduction at RT completion) had significantly worse OS and LRFS compared to those that regressed <17.9% (P = 0.03 and 0.01 respectively).
  
  
  CONCLUSIONS
  Gross tumour volume undergoes significant changes during SBRT. Early regression in tumour volume may be used as a predictor of poor LRFS and OS.
authors.affiliation: Department of Radiation Oncology, Tata Memorial Centre, Mumbai, India.
authors.forename: Rima S
authors.initials: RS
authors.lastname: Pathak
authors.affiliation: Department of Radiation Oncology, Tata Memorial Centre, Mumbai, India.
authors.forename: Anil R
authors.initials: AR
authors.lastname: Tibdewal
authors.affiliation: Department of Radiation Oncology, Tata Memorial Centre, Mumbai, India.
authors.forename: Sarbani
authors.initials: S
authors.lastname: G Laskar
authors.affiliation: Department of Medical Physics, Tata Memorial Centre, Mumbai, India.
authors.forename: Suresh
authors.initials: S
authors.lastname: Chaudhari
authors.affiliation: Department of Radiation Oncology, Tata Memorial Centre, Mumbai, India. agarwaljp@tmc.gov.in.
authors.forename: Jai Prakash
authors.initials: JP
authors.lastname: Agarwal
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology* / Q000628:therapy*; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology* / Q000628:therapy*; D016634:Radiosurgery; D012189:Retrospective Studies; D016896:Treatment Outcome; D047368:Tumor Burden
keywords: early lung cancer; kilo-voltage computed tomography; stereotactic body radiotherapy; survival outcome; volume change