title: Clinical implications in the use of the PBC algorithm versus the AAA by comparison of different NTCP models/parameters.
abstract: OBJECTIVE
  Retrospective analysis of 3D clinical treatment plans to investigate qualitative, possible, clinical consequences of the use of PBC versus AAA.
  
  
  METHODS
  The 3D dose distributions of 80 treatment plans at four different tumour sites, produced using PBC algorithm, were recalculated using AAA and the same number of monitor units provided by PBC and clinically delivered to each patient; the consequences of the difference on the dose-effect relations for normal tissue injury were studied by comparing different NTCP model/parameters extracted from a review of published studies. In this study the AAA dose calculation is considered as benchmark data. The paired Student t-test was used for statistical comparison of all results obtained from the use of the two algorithms.
  
  
  RESULTS
  In the prostate plans, the AAA predicted lower NTCP value (NTCPAAA) for the risk of late rectal bleeding for each of the seven combinations of NTCP parameters, the maximum mean decrease was 2.2%. In the head-and-neck treatments, each combination of parameters used for the risk of xerostemia from irradiation of the parotid glands involved lower NTCPAAA, that varied from 12.8% (sd=3.0%) to 57.5% (sd=4.0%), while when the PBC algorithm was used the NTCPPBC's ranging was from 15.2% (sd=2.7%) to 63.8% (sd=3.8%), according the combination of parameters used; the differences were statistically significant. Also NTCPAAA regarding the risk of radiation pneumonitis in the lung treatments was found to be lower than NTCPPBC for each of the eight sets of NTCP parameters; the maximum mean decrease was 4.5%. A mean increase of 4.3% was found when the NTCPAAA was calculated by the parameters evaluated from dose distribution calculated by a convolution-superposition (CS) algorithm. A markedly different pattern was observed for the risk relating to the development of pneumonitis following breast treatments: the AAA predicted higher NTCP value. The mean NTCPAAA varied from 0.2% (sd = 0.1%) to 2.1% (sd = 0.3%), while the mean NTCPPBC varied from 0.1% (sd = 0.0%) to 1.8% (sd = 0.2%) depending on the chosen parameters set.
  
  
  CONCLUSIONS
  When the original PBC treatment plans were recalculated using AAA with the same number of monitor units provided by PBC, the NTCPAAA was lower than the NTCPPBC, except for the breast treatments. The NTCP is strongly affected by the wide-ranging values of radiobiological parameters.
authors.affiliation: Medical Physics, PioXI Clinic and UOC Medical Physics, S Giovanni Calibita Fatebenefratelli Hospital, Rome, Italy. ant.buf@tiscali.it
authors.forename: Antonella
authors.initials: A
authors.lastname: Bufacchi
authors.forename: Barbara
authors.initials: B
authors.lastname: Nardiello
authors.forename: Roberto
authors.initials: R
authors.lastname: Capparella
authors.forename: Luisa
authors.initials: L
authors.lastname: Begnozzi
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D001943:Breast Neoplasms / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D010306:Parotid Gland / Q000528:radiation effects; D011336:Probability; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D012189:Retrospective Studies; D012306:Risk