title: A novel probabilistic approach to generating PTV with partial voxel contributions.
abstract: Radiotherapy treatment planning for use with high-energy photon beams currently employs a binary approach in defining the planning target volume (PTV). We propose a margin concept that takes the beam directions into account, generating beam-dependent PTVs (bdPTVs) on a beam-by-beam basis. The resulting degree of overlaps between the bdPTVs are used within the optimisation process; the optimiser effectively considers the same voxel to be both target and organ at risk (OAR) with fractional contributions. We investigate the impact of this novel approach when applied to prostate radiotherapy treatments, and compare treatment plans generated using beam dependent margins to conventional margins. Five prostate patients were used in this planning study, and plans using beam dependent margins improved the sparing of high doses to target-surrounding OARs, though a trade-off in delivering additional low dose to the OARs can be observed. Plans using beam dependent margins are observed to have a slightly reduced target coverage. Nevertheless, all plans are able to satisfy 90% population coverage with the target receiving at least 95% of the prescribed dose to [Formula: see text].
authors.affiliation: Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London SM2 5NG, United Kingdom.
authors.forename: H S
authors.initials: HS
authors.lastname: Tsang
authors.forename: C P
authors.initials: CP
authors.lastname: Kamerling
authors.forename: P
authors.initials: P
authors.lastname: Ziegenhein
authors.forename: S
authors.initials: S
authors.lastname: Nill
authors.forename: U
authors.initials: U
authors.lastname: Oelfke
mesh_terms: D006801:Humans; D008297:Male; D058958:Organs at Risk / Q000528:radiation effects; D017785:Photons / Q000009:adverse effects / Q000627:therapeutic use; D011336:Probability; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*