title: In vivo dosimetry with optically stimulated luminescent dosimeters for conformal and intensity-modulated radiation therapy: A 2-year multicenter cohort study.
abstract: OBJECTIVE
  Optically stimulated luminescent dosimeters (OSLDs) are utilized for in vivo dosimetry (IVD) of modern radiation therapy techniques such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). Dosimetric precision achieved with conventional techniques may not be attainable. In this work, we measured accuracy and precision for a large sample of clinical OSLD-based IVD measurements.
  
  
  METHODS
  Weekly IVD measurements were collected from 4 linear accelerators for 2 years and were expressed as percent differences from planned doses. After outlier analysis, 10,224 measurements were grouped in the following way: overall, modality (photons, electrons), treatment technique (3-dimensional [3D] conformal, field-in-field intensity modulation, inverse-planned IMRT, and VMAT), placement location (gantry angle, cardinality, and central axis positioning), and anatomical site (prostate, breast, head and neck, pelvis, lung, rectum and anus, brain, abdomen, esophagus, and bladder). Distributions were modeled via a Gaussian function. Fitting was performed with least squares, and goodness-of-fit was assessed with the coefficient of determination. Model means (μ) and standard deviations (σ) were calculated. Sample means and variances were compared for statistical significance by analysis of variance and the Levene tests (α = 0.05).
  
  
  RESULTS
  Overall, μ ± σ was 0.3 ± 10.3%. Precision for electron measurements (6.9%) was significantly better than for photons (10.5%). Precision varied significantly among treatment techniques (P < .0001) with field-in-field lowest (σ = 7.2%) and IMRT and VMAT highest (σ = 11.9% and 13.4%, respectively). Treatment site models with goodness-of-fit greater than 0.90 (6 of 10) yielded accuracy within ±3%, except for head and neck (μ = -3.7%). Precision varied with treatment site (range, 7.3%-13.0%), with breast and head and neck yielding the best and worst precision, respectively. Placement on the central axis of cardinal gantry angles yielded more precise results (σ = 8.5%) compared with other locations (range, 10.5%-11.4%).
  
  
  CONCLUSIONS
  Accuracy of ±3% was achievable. Precision ranged from 6.9% to 13.4% depending on modality, technique, and treatment site. Simple, standardized locations may improve IVD precision. These findings may aid development of patient-specific tolerances for OSLD-based IVD.
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York. Electronic address: ariegel@northwell.edu.
authors.forename: Adam C
authors.initials: AC
authors.lastname: Riegel
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York.
authors.forename: Yu
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York.
authors.forename: Ajay
authors.initials: A
authors.lastname: Kapur
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York.
authors.forename: Laura
authors.initials: L
authors.lastname: Apicello
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York.
authors.forename: Abraham
authors.initials: A
authors.lastname: Kuruvilla
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Rea
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York.
authors.forename: Abolghassem
authors.initials: A
authors.lastname: Jamshidi
authors.affiliation: Department of Radiation Medicine, Northwell Health, Lake Success, New York.
authors.forename: Louis
authors.initials: L
authors.lastname: Potters
mesh_terms: D000068598:Data Accuracy; D005260:Female; D006801:Humans; D000072231:In Vivo Dosimetry; D008297:Male; D008962:Models, Theoretical; D009369:Neoplasms / Q000532:radiotherapy*; D016011:Normal Distribution; D062791:Optically Stimulated Luminescence Dosimetry / Q000295:instrumentation*; D000072232:Radiation Dosimeters; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000295:instrumentation*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation; D012189:Retrospective Studies