title: Impact of fraction size on lung radiation toxicity: hypofractionation may be beneficial in dose escalation of radiotherapy for lung cancers.
abstract: OBJECTIVE
  To assess how fraction size impacts lung radiation toxicity and therapeutic ratio in treatment of lung cancers.
  
  
  METHODS
  The relative damaged volume (RDV) of lung was used as the endpoint in the comparison of various fractionation schemes with the same normalized total dose (NTD) to the tumor. The RDV was computed from the biologically corrected lung dose-volume histogram (DVH), with an alpha/beta ratio of 3 and 10 for lung and tumor, respectively. Two different (linear and S-shaped) local dose-effect models that incorporated the concept of a threshold dose effect with a single parameter D(L50) (dose at 50% local dose effect) were used to convert the DVH into the RDV. The comparison was conducted using four representative DVHs at different NTD and D(L50) values.
  
  
  RESULTS
  The RDV decreased with increasing dose/fraction when the NTD was larger than a critical dose (D(CR)) and increased when the NTD was less than D(CR). The D(CR) was 32-50 Gy and 58-87 Gy for a small tumor (11 cm(3)) for the linear and S-shaped local dose-effect models, respectively, when D(L50) was 20-30 Gy. The D(CR) was 66-97 Gy and 66-99 Gy, respectively, for a large tumor (266 cm(3)). Hypofractionation was preferred for small tumors and higher NTDs, and conventional fractionation was better for large tumors and lower NTDs. Hypofractionation might be beneficial for intermediate-sized tumors when NTD = 80-90 Gy, especially if the D(L50) is small (20 Gy).
  
  
  CONCLUSIONS
  This computational study demonstrated that hypofractionated stereotactic body radiotherapy is a better regimen than conventional fractionation in lung cancer patients with small tumors and high doses, because it generates lower RDV when the tumor NTD is kept unchanged.
authors: Department of Radiation Oncology, Henry Ford Hospital, Detroit, MI 48202, USA. jjin1@hfhs.org
authors: Jin-Yue
authors: JY
authors: Jin
authors: Feng-Ming
authors: FM
authors: Kong
authors: Indrin J
authors: IJ
authors: Chetty
authors: Munther
authors: M
authors: Ajlouni
authors: Samuel
authors: S
authors: Ryu
authors: Randall
authors: R
authors: Ten Haken
authors: Benjamin
authors: B
authors: Movsas
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D008297:Male; D008954:Models, Biological; D011832:Radiation Injuries / Q000473:pathology* / Q000517:prevention & control; D016634:Radiosurgery; D047368:Tumor Burden