title: The influence of patient positioning uncertainties in proton radiotherapy on proton range and dose distributions.
abstract: OBJECTIVE
  Proton radiotherapy allows radiation treatment delivery with high dose gradients. The nature of such dose distributions increases the influence of patient positioning uncertainties on their fidelity when compared to photon radiotherapy. The present work quantitatively analyzes the influence of setup uncertainties on proton range and dose distributions.
  
  
  METHODS
  Thirty-eight clinical passive scattering treatment fields for small lesions in the head were studied. Dose distributions for shifted and rotated patient positions were Monte Carlo-simulated. Proton range uncertainties at the 50%- and 90%-dose falloff position were calculated considering 18 arbitrary combinations of maximal patient position shifts and rotations for two patient positioning methods. Normal tissue complication probabilities (NTCPs), equivalent uniform doses (EUDs), and tumor control probabilities (TCPs) were studied for organs at risk (OARs) and target volumes of eight patients.
  
  
  RESULTS
  The authors identified a median 1σ proton range uncertainty at the 50%-dose falloff of 2.8 mm for anatomy-based patient positioning and 1.6 mm for fiducial-based patient positioning as well as 7.2 and 5.8 mm for the 90%-dose falloff position, respectively. These range uncertainties were correlated to heterogeneity indices (HIs) calculated for each treatment field (38%<R2<50%). A NTCP increase of more than 10% (absolute) was observed for less than 2.9% (anatomy-based positioning) and 1.2% (fiducial-based positioning) of the studied OARs and patient shifts. For target volumes TCP decreases by more than 10% (absolute) occurred in less than 2.2% of the considered treatment scenarios for anatomy-based patient positioning and were nonexistent for fiducial-based patient positioning. EUD changes for target volumes were up to 35% (anatomy-based positioning) and 16% (fiducial-based positioning).
  
  
  CONCLUSIONS
  The influence of patient positioning uncertainties on proton range in therapy of small lesions in the human brain as well as target and OAR dosimetry were studied. Observed range uncertainties were correlated with HIs. The clinical practice of using multiple fields with smeared compensators while avoiding distal OAR sparing is considered to be safe.
authors.affiliation: EBG MedAustron GmbH, 2700 Wiener Neustadt, Austria; Francis H. Burr Proton Therapy Center, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114; and Department of Therapeutic Radiology and Oncology, Medical University of Graz, 8036 Graz, Austria.
authors.forename: Jakob
authors.initials: J
authors.lastname: Liebl
authors.affiliation: Francis H. Burr Proton Therapy Center, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Harald
authors.initials: H
authors.lastname: Paganetti
authors.affiliation: Francis H. Burr Proton Therapy Center, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Mingyao
authors.initials: M
authors.lastname: Zhu
authors.affiliation: Francis H. Burr Proton Therapy Center, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Winey
mesh_terms: D000328:Adult; D001932:Brain Neoplasms / Q000532:radiotherapy; D003198:Computer Simulation; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009010:Monte Carlo Method; D056888:Patient Positioning / Q000295:instrumentation / Q000379:methods*; D061766:Proton Therapy / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D012399:Rotation; D035501:Uncertainty; D011522:Protons
chemical_list: D011522:Protons