title: Respiratory gating for proton beam scanning versus photon 3D-CRT for breast cancer radiotherapy.
abstract: Background Respiratory gating and proton therapy have both been proposed to reduce the cardiopulmonary burden in breast cancer radiotherapy. This study aims to investigate the additional benefit of proton radiotherapy for breast cancer with and without respiratory gating. Material and methods Twenty left-sided patients were planned on computed tomography (CT)-datasets acquired during enhanced inspiration gating (EIG) and free-breathing (FB), using photon three-dimensional conformal radiation therapy (3D-CRT) and scanned proton beams. Ten patients received treatment to the whole breast only (WBO) and 10 were treated to the breast and the regional lymph nodes (BRN). Dosimetric parameters characterizing the coverage of target volumes and the cardiopulmonary burden were compared using a paired, two-tailed Student's t-test. Results Protons ensured comparable or better target coverage than photons in all patients during both EIG and FB. The heterogeneity index decreased from 12% with photons to about 5% with protons. The mean dose to the ipsilateral lung was reduced in BRN patients from 12 Gy to 7 Gy  (RBE) in EIG and from 14 Gy to 6-7 Gy (RBE) in FB, while for WBO patients all values were about 5-6 Gy (RBE). The mean dose to heart decreased by a factor of four in WBO patients [from 1.1 Gy to 0.3 Gy (RBE) in EIG and from 2.1 Gy to 0.5 Gy (RBE) in FB] and 10 in BRN patients [from 2.1 Gy to 0.2 Gy (RBE) in EIG and from 3.4 Gy to 0.3 Gy (RBE) in FB]. Similarly, the mean and the near maximum dose to the left anterior descending artery (LAD) were significantly lower (p < 0.05) with protons in comparison with photons. Conclusion Proton spot scanning has a high potential to reduce the irradiation of organs at risk and other normal tissues for most patients, beyond what could be achieved with EIG and photon therapy. The largest dose sparing has been seen for BRN patients, both in terms of cardiopulmonary burden and integral dose.
authors.affiliation: a Department of Oncology and Department of Clinical and Experimental Medicine , Linköping University , Linköping , Sweden ;
authors.forename: Anna M
authors.initials: AM
authors.lastname: Flejmer
authors.affiliation: b Department of Medical Radiation Physics , Lund University , Lund , Sweden ;
authors.forename: Anneli
authors.initials: A
authors.lastname: Edvardsson
authors.affiliation: c 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: c Department of Radiation Physics and Department of Medical and Health Sciences , Linköping University , Linköping , Sweden ;
authors.forename: Dan
authors.initials: D
authors.lastname: Josefsson
authors.affiliation: d County Council of Jönköping, Futurum - Academy for Health and Care , Jönköping , Sweden ;
authors.forename: Mats
authors.initials: M
authors.lastname: Nilsson
authors.affiliation: e Department of Oncology , Uppsala University Hospital , Uppsala , Sweden.
authors.forename: Petra
authors.initials: P
authors.lastname: Witt Nyström
authors.affiliation: c 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: D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006321:Heart / Q000528:radiation effects; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000528:radiation effects; D008198:Lymph Nodes / Q000528:radiation effects; D058958:Organs at Risk / Q000528:radiation effects; D056888:Patient Positioning / Q000379:methods; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D012119:Respiration; D014057:Tomography, X-Ray Computed