title: Quantitative analysis of treatment process time and throughput capacity for spot scanning proton therapy.
abstract: OBJECTIVE
  To determine the patient throughput and the overall efficiency of the spot scanning system by analyzing treatment time, equipment availability, and maximum daily capacity for the current spot scanning port at Proton Therapy Center Houston and to assess the daily throughput capacity for a hypothetical spot scanning proton therapy center.
  
  
  METHODS
  At their proton therapy center, the authors have been recording in an electronic medical record system all treatment data, including disease site, number of fields, number of fractions, delivered dose, energy, range, number of spots, and number of layers for every treatment field. The authors analyzed delivery system downtimes that had been recorded for every equipment failure and associated incidents. These data were used to evaluate the patient census, patient distribution as a function of the number of fields and total target volume, and equipment clinical availability. The duration of each treatment session from patient walk-in to patient walk-out of the spot scanning treatment room was measured for 64 patients with head and neck, central nervous system, thoracic, and genitourinary cancers. The authors retrieved data for total target volume and the numbers of layers and spots for all fields from treatment plans for a total of 271 patients (including the above 64 patients). A sensitivity analysis of daily throughput capacity was performed by varying seven parameters in a throughput capacity model.
  
  
  RESULTS
  The mean monthly equipment clinical availability for the spot scanning port in April 2012-March 2015 was 98.5%. Approximately 1500 patients had received spot scanning proton therapy as of March 2015. The major disease sites treated in September 2012-August 2014 were the genitourinary system (34%), head and neck (30%), central nervous system (21%), and thorax (14%), with other sites accounting for the remaining 1%. Spot scanning beam delivery time increased with total target volume and accounted for approximately 30%-40% of total treatment time for the total target volumes exceeding 200 cm(3), which was the case for more than 80% of the patients in this study. When total treatment time was modeled as a function of the number of fields and total target volume, the model overestimated total treatment time by 12% on average, with a standard deviation of 32%. A sensitivity analysis of throughput capacity for a hypothetical four-room spot scanning proton therapy center identified several priority items for improvements in throughput capacity, including operation time, beam delivery time, and patient immobilization and setup time.
  
  
  CONCLUSIONS
  The spot scanning port at our proton therapy center has operated at a high performance level and has been used to treat a large number of complex cases. Further improvements in efficiency may be feasible in the areas of facility operation, beam delivery, patient immobilization and setup, and optimization of treatment scheduling.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Kazumichi
authors.initials: K
authors.lastname: Suzuki
authors.affiliation: The Proton Therapy Center Houston, Ltd., L.L.P., 1840 Old Spanish Trail, Houston, Texas 77054.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Palmer
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Narayan
authors.initials: N
authors.lastname: Sahoo
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Falk
authors.initials: F
authors.lastname: Poenisch
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Dennis S
authors.initials: DS
authors.lastname: Mackin
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Amy Y
authors.initials: AY
authors.lastname: Liu
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Richard
authors.initials: R
authors.lastname: Wu
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: X Ronald
authors.initials: XR
authors.lastname: Zhu
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Frank
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Gillin
authors.affiliation: Texas Center for Proton Therapy, 1501 W. Royal Lane, Irving, Texas 75063.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Lee
mesh_terms: D016543:Central Nervous System Neoplasms / Q000532:radiotherapy; D057286:Electronic Health Records; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D008962:Models, Theoretical; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D013899:Thoracic Neoplasms / Q000532:radiotherapy; D013997:Time Factors; D014565:Urogenital Neoplasms / Q000532:radiotherapy