title: Analytical anisotropic algorithm versus pencil beam convolution for treatment planning of breast cancer: implications for target coverage and radiation burden of normal tissue.
abstract: OBJECTIVE
  The present study aimed to investigate the implications of using the analytical anisotropic algorithm (AAA) for calculation of target coverage and radiation burden of normal tissues. Most model parameters, recommendations and planning guidelines associated with a certain outcome are from the era of pencil beam convolution (PBC) calculations on relatively simple assumptions of energy transport in media. Their relevance for AAA calculations that predict more realistic dose distributions needs to be evaluated.
  
  
  METHODS
  Forty patients with left-sided breast cancer receiving 3D conformal radiation therapy were planned using PBC with a standard protocol with 50 Gy in 25 fractions according to existing re-commendations. The plans were subsequently recalculated with the AAA and relevant dose parameters were determined and compared to their PBC equivalents.
  
  
  RESULTS
  The majority of the AAA-based plans had a significantly worse coverage of the planning target volume and also a higher maximum dose in hotspots near sensitive structures, suggesting that these criteria could be relaxed for AAA-calculated plans. Furthermore, the AAA predicts higher volumes of the ipsilateral lung will receive doses below 25 Gy and smaller volume doses above 25 Gy. These results indicate that lung tolerance criteria might also have to be relaxed for AAA planning in order to maintain the level of normal tissue toxicity. The AAA also predicts lower doses to the heart, thus indicating that this organ might be more sensitive to radiation than thought from PBC-based calculations.
  
  
  CONCLUSIONS
  The AAA should be preferred over the PBC algorithm for breast cancer radiotherapy as it gives more realistic dose distributions. Guidelines for plan acceptance might have to be re-evaluated to account for differences in dose predictions in order to maintain the current levels of control and complication rates. The results also suggest an increased radiosensitivity of the heart, thus indicating that a revision of the current models for cardiovascular complications may be needed.
authors.affiliation: Department of Oncology and Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden Anna.Maria.Flejmer@regionostergotland.se.
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Flejmer
authors.affiliation: Department of Radiation Physics and Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Frida
authors.initials: F
authors.lastname: Dohlmar
authors.affiliation: Futurum-Academy for Health and Care, County Council of Jönköping, Jönköping, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Nilsson
authors.affiliation: Futurum-Academy for Health and Care, County Council of Jönköping, Jönköping, Sweden.
authors.forename: Margaretha
authors.initials: M
authors.lastname: Stenmarker
authors.affiliation: Department of Radiation Physics and Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Dasu
mesh_terms: D000465:Algorithms; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal
keywords: Breast radiotherapy; analytical anisotropic algorithm; dose calculation algorithm; pencil beam convolution; planning guidelines