title: Extrapolation of normal tissue complication probability for different fractionations in liver irradiation.
abstract: OBJECTIVE
  The ability to predict normal tissue complication probability (NTCP) is essential for NTCP-based treatment planning. The purpose of this work is to estimate the Lyman NTCP model parameters for liver irradiation from published clinical data of different fractionation regimens. A new expression of normalized total dose (NTD) is proposed to convert NTCP data between different treatment schemes.
  
  
  METHODS
  The NTCP data of radiation- induced liver disease (RILD) from external beam radiation therapy for primary liver cancer patients were selected for analysis. The data were collected from 4 institutions for tumor sizes in the range of of 8-10 cm. The dose per fraction ranged from 1.5 Gy to 6 Gy. A modified linear-quadratic model with two components corresponding to radiosensitive and radioresistant cells in the normal liver tissue was proposed to understand the new NTD formalism.
  
  
  RESULTS
  There are five parameters in the model: TD(50), m, n, alpha/beta and f. With two parameters n and alpha/beta fixed to be 1.0 and 2.0 Gy, respectively, the extracted parameters from the fitting are TD(50)(1) = 40.3 +/- 8.4Gy, m =0.36 +/- 0.09, f = 0.156 +/- 0.074 Gy and TD(50)(1) = 23.9 +/- 5.3Gy, m = 0.41 +/- 0.15, f = 0.0 +/- 0.04 Gy for patients with liver cirrhosis scores of Child-Pugh A and Child-Pugh B, respectively. The fitting results showed that the liver cirrhosis score significantly affects fractional dose dependence of NTD.
  
  
  CONCLUSIONS
  The Lyman parameters generated presently and the new form of NTD may be used to predict NTCP for treatment planning of innovative liver irradiation with different fractionations, such as hypofractioned stereotactic body radiation therapy.
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, USA.
authors.forename: An
authors.initials: A
authors.lastname: Tai
authors.forename: Beth
authors.initials: B
authors.lastname: Erickson
authors.forename: X Allen
authors.initials: XA
authors.lastname: Li
mesh_terms: D000465:Algorithms; D006528:Carcinoma, Hepatocellular / Q000473:pathology / Q000532:radiotherapy*; D016009:Chi-Square Distribution; D019583:Dose Fractionation, Radiation; D006801:Humans; D016014:Linear Models; D008099:Liver / Q000528:radiation effects*; D008113:Liver Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011336:Probability; D011832:Radiation Injuries / Q000209:etiology* / Q000517:prevention & control; D011836:Radiation Tolerance; D047368:Tumor Burden