title: Proton pencil beam scanning for mediastinal lymphoma: treatment planning and robustness assessment.
abstract: BACKGROUND
  Modern radiotherapy (RT) for lymphoma is highly personalized. While advanced imaging is largely employed to define limited treatment volumes, the use of proton pencil beam scanning (PBS) for highly conformal lymphoma RT is still in its infancy. Here, we assess the dosimetric benefits and feasibility of PBS for mediastinal lymphoma (ML).
  
  
  METHODS
  Ten patients were planned using PBS for involved-site RT. The initial plans were calculated on the average four-dimensional computed tomography (4D-CT). PBS plans were compared with 3D conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and proton double scattering (DS). In order to evaluate the feasibility of PBS and the plan robustness against inter- and intra-fractional uncertainties, the 4D dose was calculated on initial and verification CTs. The deviation of planned dose from delivered dose was measured. The same proton beamline was used for all patients, while another beamline with larger spots was employed for patients with large motion perpendicular to the beam.
  
  
  RESULTS
  PBS provided the lowest mean lung dose (MLD) and mean heart dose (MHD) for all patients in comparison with 3D-CRT, IMRT, and DS. For eight patients, internal target volume (ITV) D98%was degraded by <3%; and the MLD and MHD deviated by <10% of prescription over the course of treatment when the PBS field was painted twice in each session. For one patient with target motion perpendicular to the beam (>5 mm), the degradation of ITV D98%was 9%, which was effectively mitigated by employing large spots. One patient exhibited large dose degradation due to pericardial effusion, which required replanning across all modalities.
  
  
  CONCLUSIONS
  This study demonstrates that PBS plans significantly reduce MLD and MHD relative to 3D-CRT, IMRT, and DS and identifies requirements for robust free-breathing ML PBS treatments, showing that PBS plan robustness can be maintained with repainting and/or large spots.
authors.affiliation: a Department of Radiation Oncology , University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Chuan
authors.initials: C
authors.lastname: Zeng
authors.affiliation: a Department of Radiation Oncology , University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Plastaras
authors.affiliation: a Department of Radiation Oncology , University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Paul
authors.initials: P
authors.lastname: James
authors.affiliation: a Department of Radiation Oncology , University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Zelig A
authors.initials: ZA
authors.lastname: Tochner
authors.affiliation: a Department of Radiation Oncology , University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Hill-Kayser
authors.affiliation: a Department of Radiation Oncology , University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.|b Division of Radiation Oncology , University of Texas MD Anderson Cancer Center , Houston , TX , USA.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Hahn
authors.affiliation: a Department of Radiation Oncology , University of Pennsylvania Perelman School of Medicine , Philadelphia , PA , USA.
authors.forename: Stefan
authors.initials: S
authors.lastname: Both
mesh_terms: D005240:Feasibility Studies; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008223:Lymphoma / Q000532:radiotherapy*; D008297:Male; D008479:Mediastinal Neoplasms / Q000532:radiotherapy*; D018579:Patient Selection; D057285:Precision Medicine / Q000379:methods*; D061766:Proton Therapy / Q000295:instrumentation / Q000379:methods*; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal; D050397:Radiotherapy, Intensity-Modulated; D012542:Scattering, Radiation