title: What is the appropriate size criterion for proton radiotherapy for hepatocellular carcinoma? A dosimetric comparison of spot-scanning proton therapy versus intensity-modulated radiation therapy.
abstract: BACKGROUND
  We performed a dosimetric comparison of spot-scanning proton therapy (SSPT) and intensity-modulated radiation therapy (IMRT) for hepatocellular carcinoma (HCC) to investigate the impact of tumor size on the risk of radiation induced liver disease (RILD).
  
  
  METHODS
  A number of alternative plans were generated for 10 patients with HCC. The gross tumor volumes (GTV) varied from 20.1 to 2194.5 cm3. Assuming all GTVs were spherical, the nominal diameter was calculated and ranged from 3.4 to 16.1 cm. The prescription dose was 60 Gy for IMRT or 60 cobalt Gy-equivalents for SSPT with 95% planning target volume (PTV) coverage. Using IMRT and SSPT techniques, extensive comparative planning was conducted. All plans were evaluated by the risk of RILD estimated using the Lyman-normal-tissue complication probability model.
  
  
  RESULTS
  For IMRT the risk of RILD increased drastically between 6.3-7.8 cm nominal diameter of GTV. When the nominal diameter of GTV was more than 6.3 cm, the average risk of RILD was 94.5% for IMRT and 6.2% for SSPT.
  
  
  CONCLUSIONS
  Regarding the risk of RILD, HCC can be more safely treated with SSPT, especially if its nominal diameter is more than 6.3 cm.
authors.affiliation: Department of Medical Physics, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Toramatsu
authors.forename: Norio
authors.initials: N
authors.lastname: Katoh
authors.forename: Shinichi
authors.initials: S
authors.lastname: Shimizu
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nihongi
authors.forename: Taeko
authors.initials: T
authors.lastname: Matsuura
authors.forename: Seishin
authors.initials: S
authors.lastname: Takao
authors.forename: Naoki
authors.initials: N
authors.lastname: Miyamoto
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Suzuki
authors.forename: Kenneth
authors.initials: K
authors.lastname: Sutherland
authors.forename: Rumiko
authors.initials: R
authors.lastname: Kinoshita
authors.forename: Rikiya
authors.initials: R
authors.lastname: Onimaru
authors.forename: Masayori
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Kikuo
authors.initials: K
authors.lastname: Umegaki
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000150:complications / Q000473:pathology / Q000532:radiotherapy*; D005500:Follow-Up Studies; D006801:Humans; D008107:Liver Diseases / Q000209:etiology*; D008113:Liver Neoplasms / Q000150:complications / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D011379:Prognosis; D061766:Proton Therapy / Q000009:adverse effects*; D011832:Radiation Injuries / Q000209:etiology*; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D012189:Retrospective Studies