title: Scan path optimization with/without clustering for active beam delivery in charged particle therapy.
abstract: OBJECTIVE
  To compare different algorithms to optimize the scanning path in charged particle therapy with quasidiscrete scanning. We implemented a Hybrid Genetic Algorithm with Heuristics (HyGA) and combined it with clustering techniques. The performance was compared to Simulated Annealing (SA) and to commercially available treatment planning system (TPS).
  
  
  METHODS
  Performance and clinical implications were assessed using data from 10 patients treated at CNAO (Centro Nazionale di Adroterapia Oncologica). Clinical treatments are performed relying on beam deflection, avoiding irradiation for transitions between adjacent spots larger than 2 cm. A clustering method was implemented with HyGA (HyGA_Cl), which assumes beam deflection during transition between clusters. Clinical performance was determined as the total number of particles delivered during spot transitions and the number of particles wasted due to beam deflection. Results were compared to scan paths obtained with CNAO TPS.
  
  
  RESULTS
  SA and HyGA produced on average shorter paths compared to the currently available TPS. This did not result in a reduction of transit particles, due to the concomitant effect of beam deflection out of the extraction line. HyGA_Cl achieved 2% average reduction in transit particles when compared to CNAO TPS. As a drawback, wasted particles increased, due to more frequent use of beam deflection. Both the SA and HyGA algorithms reduced the number of wasted particles.
  
  
  CONCLUSIONS
  SA and HyGA proved to be the most cost-effective methods in reducing wasted particles, with benefits in terms of shorter scan paths. A decrease in transit particles delivered with beam deflection can be achieved using HyGA_Cl.
authors.affiliation: Department of Physics, Faculty of Sciences, University of Lisbon, Lisbon 1749, Portugal; Laboratório de Instrumentação e Física de Partículas, Lisbon 1749, Portugal; Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan 20133, Italy. Electronic address: marta.dias@mail.polimi.it.
authors.forename: Marta F
authors.initials: MF
authors.lastname: Dias
authors.affiliation: Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan 20133, Italy; Bioengineering Unit, Centro Nazionale di Adroterapia Oncologica, Pavia 27100, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Riboldi
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital - Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Joao
authors.initials: J
authors.lastname: Seco
authors.affiliation: Institute of Biophysics and Biomedical Engineering, Faculty of Sciences, University of Lisbon, Lisbon 1749, Portugal; Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan 20133, Italy.
authors.forename: Inês
authors.initials: I
authors.lastname: Castelhano
authors.affiliation: Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan 20133, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pella
authors.affiliation: Medical Physics, Centro Nazionale di Adroterapia Oncologica, Pavia 27100, Italy.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Mirandola
authors.affiliation: Department of Physics, Faculty of Sciences, University of Lisbon, Lisbon 1749, Portugal; Laboratório de Instrumentação e Física de Partículas, Lisbon 1749, Portugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Peralta
authors.affiliation: Medical Physics, Centro Nazionale di Adroterapia Oncologica, Pavia 27100, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Ciocca
authors.affiliation: Medical Department, Centro Nazionale di Adroterapia Oncologica, Pavia 27100, Italy; Advanced Radiotherapy Center - Radiotherapy Division, European Institute of Oncology, Milano 20141, Italy; Department of Science and Biomedical Technologies, Università degli Studi di Milano, Milano 20122, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Orecchia
authors.affiliation: Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan 20133, Italy; Bioengineering Unit, Centro Nazionale di Adroterapia Oncologica, Pavia 27100, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Baroni
mesh_terms: D000465:Algorithms; D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*
keywords: Optimization algorithms; Path length; Scan path; Transit particles; Wasted particles