title: A novel approach to postmastectomy radiation therapy using scanned proton beams.
abstract: OBJECTIVE
  Postmastectomy radiation therapy (PMRT), currently offered at Massachusetts General Hospital, uses proton pencil beam scanning (PBS) with intensity modulation, achieving complete target coverage of the chest wall and all nodal regions and reduced dose to the cardiac structures. This work presents the current methodology for such treatment and the ongoing effort for its improvements.
  
  
  METHODS
  A single PBS field is optimized to ensure appropriate target coverage and heart/lung sparing, using an in-house-developed proton planning system with the capability of multicriteria optimization. The dose to the chest wall skin is controlled as a separate objective in the optimization. Surface imaging is used for setup because it is a suitable surrogate for superficial target volumes. In order to minimize the effect of beam range uncertainties, the relative proton stopping power ratio of the material in breast implants was determined through separate measurements. Phantom measurements were also made to validate the accuracy of skin dose calculation in the treatment planning system. Additionally, the treatment planning robustness was evaluated relative to setup perturbations and patient breathing motion.
  
  
  RESULTS
  PBS PMRT planning resulted in appropriate target coverage and organ sparing, comparable to treatments by passive scattering (PS) beams but much improved in nodal coverage and cardiac sparing compared to conventional treatments by photon/electron beams. The overall treatment time was much shorter than PS and also shorter than conventional photon/electron treatment. The accuracy of the skin dose calculation by the planning system was within ±2%. The treatment was shown to be adequately robust relative to both setup uncertainties and patient breathing motion, resulting in clinically satisfying dose distributions.
  
  
  CONCLUSIONS
  More than 25 PMRT patients have been successfully treated at Massachusetts General Hospital by using single-PBS fields. The methodology and robustness of both the setup and the treatment have been discussed.
authors: Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts; Centre for Medical Radiation Physics, University of Wollongong, New South Wales, Australia. Electronic address: ndepauw@partners.org.
authors: Nicolas
authors: N
authors: Depauw
authors: Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts.
authors: Estelle
authors: E
authors: Batin
authors: Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts.
authors: Julianne
authors: J
authors: Daartz
authors: Centre for Medical Radiation Physics, University of Wollongong, New South Wales, Australia.
authors: Anatoly
authors: A
authors: Rosenfeld
authors: Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts.
authors: Judith
authors: J
authors: Adams
authors: Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts.
authors: Hanne
authors: H
authors: Kooy
authors: Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts.
authors: Shannon
authors: S
authors: MacDonald
authors: Francis H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts.
authors: Hsiao-Ming
authors: HM
authors: Lu
mesh_terms: D001943:Breast Neoplasms / Q000628:therapy*; D005260:Female; D006801:Humans; D008408:Mastectomy / Q000379:methods*; D059351:Organ Sparing Treatments / Q000379:methods*; D011182:Postoperative Care / Q000379:methods*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*; D016896:Treatment Outcome; D011522:Protons
chemical_list: D011522:Protons