title: Comparison of doses and NTCP to risk organs with enhanced inspiration gating and free breathing for left-sided breast cancer radiotherapy using the AAA algorithm.
abstract: BACKGROUND
  The purpose of this study was to investigate the potential dose reduction to the heart, left anterior descending (LAD) coronary artery and the ipsilateral lung for patients treated with tangential and locoregional radiotherapy for left-sided breast cancer with enhanced inspiration gating (EIG) compared to free breathing (FB) using the AAA algorithm. The radiobiological implication of such dose sparing was also investigated.
  
  
  METHODS
  Thirty-two patients, who received tangential or locoregional adjuvant radiotherapy with EIG for left-sided breast cancer, were retrospectively enrolled in this study. Each patient was CT-scanned during FB and EIG. Similar treatment plans, with comparable target coverage, were created in the two CT-sets using the AAA algorithm. Further, the probability of radiation induced cardiac mortality and pneumonitis were calculated using NTCP models.
  
  
  RESULTS
  For tangential treatment, the median V25Gy for the heart and LAD was decreased for EIG from 2.2% to 0.2% and 40.2% to 0.1% (p < 0.001), respectively, whereas there was no significant difference in V20Gy for the ipsilateral lung (p = 0.109). For locoregional treatment, the median V25Gy for the heart and LAD was decreased for EIG from 3.3% to 0.2% and 51.4% to 5.1% (p < 0.001), respectively, and the median ipsilateral lung V20Gy decreased from 27.0% for FB to 21.5% (p = 0.020) for EIG. The median excess cardiac mortality probability decreased from 0.49% for FB to 0.02% for EIG (p < 0.001) for tangential treatment and from 0.75% to 0.02% (p < 0.001) for locoregional treatment. There was no significant difference in risk of radiation pneumonitis for tangential treatment (p = 0.179) whereas it decreased for locoregional treatment from 6.82% for FB to 3.17% for EIG (p = 0.004).
  
  
  CONCLUSIONS
  In this study the AAA algorithm was used for dose calculation to the heart, LAD and left lung when comparing the EIG and FB techniques for tangential and locoregional radiotherapy of breast cancer patients. The results support the dose and NTCP reductions reported in previous studies where dose calculations were performed using the pencil beam algorithm.
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden. anneli.edvardsson@med.lu.se.
authors.forename: Anneli
authors.initials: A
authors.lastname: Edvardsson
authors.affiliation: Department of Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden. martin.nilsson@med.lu.se.
authors.forename: Martin P
authors.initials: MP
authors.lastname: Nilsson
authors.affiliation: Department of Oncology and Radiation Physics, Skåne University Hospital, Malmö, Sweden. sousana.amptoulach@skane.se.
authors.forename: Sousana
authors.initials: S
authors.lastname: Amptoulach
authors.affiliation: Department of Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden. sofie.ceberg@med.lu.se.
authors.forename: Sofie
authors.initials: S
authors.lastname: Ceberg
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D016477:Artifacts; D003131:Combined Modality Therapy; D003331:Coronary Vessels / Q000528:radiation effects; D005260:Female; D006321:Heart / Q000528:radiation effects; D006331:Heart Diseases / Q000209:etiology / Q000401:mortality / Q000517:prevention & control; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000528:radiation effects; D008408:Mastectomy; D015412:Mastectomy, Segmental; D008875:Middle Aged; D009038:Motion; D058958:Organs at Risk; D011336:Probability; D011832:Radiation Injuries / Q000517:prevention & control; D017564:Radiation Pneumonitis / Q000517:prevention & control; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D000069584:Unilateral Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery