title: The impact of microscopic disease on the tumor control probability in non-small-cell lung cancer.
abstract: OBJECTIVE
  To indicate which clinical target volume (CTV) margin (if any) is needed for an adequate treatment of non-small-cell lung cancer (NSCLC) using either 3D conformal or stereotactic radiotherapy, taking the distribution of the microscopic disease extension (MDE) into account.
  
  
  METHODS
  On the basis of the linear-quadratic biological model, a Monte-Carlo simulation was used to study the impact of MDE and setup deviations on the tumor control probability (TCP) after typical 3D conformal and stereotactic irradiation techniques. Setup deviations were properly accounted for in the planning target volume (PTV) margin. Previously measured distributions of MDE outside the macroscopic tumor in NSCLC patients were used. The dependence of the TCP on the CTV margins was quantified.
  
  
  RESULTS
  The presence of MDE had a demonstratable influence on the TCP in both the 3D conformal and the stereotactic technique when no CTV margins were employed. The impact of MDE on the TCP values was greater in the 3D conformal scenario (67% TCP with MDE; 84% TCP without MDE) than for stereotactic radiotherapy (91% TCP with MDE; 100% TCP without MDE). Accordingly, an increase of the CTV margin had the greatest impact for the 3D conformal technique. Larger setup errors, with appropriate PTV margins, lead to an increase in TCP for both techniques, showing the interdependence of CTV and PTV margins.
  
  
  CONCLUSIONS
  MDE may not always be eradicated by the beam penumbra or existing PTV margins using either 3D conformal or stereotactic radiotherapy. Nonetheless, TCP modeling indicates an overall local control rate above 90% for the stereotactic technique, while a non-zero CTV margin is recommended for better local control of MDE when using the 3D conformal technique.
authors.affiliation: The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Department of Radiotherapy, Amsterdam, The Netherlands.
authors.forename: Christian
authors.initials: C
authors.lastname: Siedschlag
authors.forename: Liesbeth
authors.initials: L
authors.lastname: Boersma
authors.forename: Judith
authors.initials: J
authors.lastname: van Loon
authors.forename: Maddalena
authors.initials: M
authors.lastname: Rossi
authors.forename: Angela
authors.initials: A
authors.lastname: van Baardwijk
authors.forename: Kenneth
authors.initials: K
authors.lastname: Gilhuijs
authors.forename: Joep
authors.initials: J
authors.lastname: Stroom
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D003198:Computer Simulation; D019583:Dose Fractionation, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D009010:Monte Carlo Method; D011336:Probability; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*