title: Benchmarking dosimetric quality assessment of prostate intensity-modulated radiotherapy.
abstract: OBJECTIVE
  To benchmark the dosimetric quality assessment of prostate intensity-modulated radiotherapy and determine whether the quality is influenced by disease or treatment factors.
  
  
  METHODS
  We retrospectively analyzed the data from 155 consecutive men treated radically for prostate cancer using intensity-modulated radiotherapy to 78 Gy between January 2007 and March 2009 across six radiotherapy treatment centers. The plan quality was determined by the measures of coverage, homogeneity, and conformity. Tumor coverage was measured using the planning target volume (PTV) receiving 95% and 100% of the prescribed dose (V(95%) and V(100%), respectively) and the clinical target volume (CTV) receiving 95% and 100% of the prescribed dose. Homogeneity was measured using the sigma index of the PTV and CTV. Conformity was measured using the lesion coverage factor, healthy tissue conformity index, and the conformity number. Multivariate regression models were created to determine the relationship between these and T stage, risk status, androgen deprivation therapy use, treatment center, planning system, and treatment date.
  
  
  RESULTS
  The largest discriminatory measurements of coverage, homogeneity, and conformity were the PTV V(95%), PTV sigma index, and conformity number. The mean PTV V(95%) was 92.5% (95% confidence interval, 91.3-93.7%). The mean PTV sigma index was 2.10 Gy (95% confidence interval, 1.90-2.20). The mean conformity number was 0.78 (95% confidence interval, 0.76-0.79). The treatment center independently influenced the coverage, homogeneity, and conformity (all p < .0001). The planning system independently influenced homogeneity (p = .038) and conformity (p = .021). The treatment date independently influenced the PTV V(95%) only, with it being better at the start (p = .013). Risk status, T stage, and the use of androgen deprivation therapy did not influence any aspect of plan quality.
  
  
  CONCLUSIONS
  Our study has benchmarked measures of coverage, homogeneity, and conformity for the treatment of prostate cancer using IMRT. The differences seen between centers and planning systems and the coverage deterioration over time highlight the need for every center to determine their own benchmarks and apply clinical vigilance with respect to maintaining these through quality assurance.
authors.affiliation: Division of Radiation Oncology, Peter MacCallum Cancer Center, East Melbourne, VIC, Australia. sasha.senthi@petermac.org
authors.forename: Sashendra
authors.initials: S
authors.lastname: Senthi
authors.forename: Suki S
authors.initials: SS
authors.lastname: Gill
authors.forename: Annette
authors.initials: A
authors.lastname: Haworth
authors.forename: Tomas
authors.initials: T
authors.lastname: Kron
authors.forename: Jim
authors.initials: J
authors.lastname: Cramb
authors.forename: Aldo
authors.initials: A
authors.lastname: Rolfo
authors.forename: Jessica
authors.initials: J
authors.lastname: Thomas
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Duchesne
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Hamilton
authors.forename: Daryl Lim
authors.initials: DL
authors.lastname: Joon
authors.forename: Patrick
authors.initials: P
authors.lastname: Bowden
authors.forename: Farshad
authors.initials: F
authors.lastname: Foroudi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000726:Androgen Antagonists / Q000627:therapeutic use; D019985:Benchmarking / Q000379:methods / Q000592:standards*; D016001:Confidence Intervals; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D058958:Organs at Risk; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods / Q000592:standards*; D012044:Regression Analysis; D012189:Retrospective Studies; D047368:Tumor Burden; D014739:Victoria
chemical_list: D000726:Androgen Antagonists