In vivo dosimetry with optically-stimulated luminescent dosimeters for conformal and intensity-modulated radiation therapy: A two year multi-center cohort study

Publication date: Available online 7 September 2016
Source:Practical Radiation Oncology
Author(s): Adam C. Riegel, Yu Chen, Ajay Kapur, Laura Apicello, Abraham Kuruvilla, Anthony J. Rea, Abolghassem Jamshidi, Louis Potters
PurposeOptically-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 and MaterialsWeekly IVD measurements were collected from 4 linear accelerators for 2years and were expressed as percent differences from planned doses. After outlier analysis, 10,224 measurements were grouped thusly: Overall, modality (photons, electrons), treatment technique (3D conformal, field-in-field [FIF] intensity modulation, inverse-planned IMRT, VMAT), placement location (gantry angle, cardinality, and central axis positioning), and anatomical site (prostate, breast, head-and-neck, pelvis, lung, rectum and anus, brain, abdominal, esophagus, and bladder). Distributions were modeled using 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 using ANOVA and Levene's tests (α=0.05).ResultsOverall, μ±σ was 0.3±10.3%. Precision for electron measurements (6.9%) was significantly better than photons (10.5%). Precision varied significantly among treatment techniques (p<0.0001) with FIF lowest (σ=7.2%) and IMRT and VMAT highest (σ=11.9% and 13.4%). 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 (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 to other locations (10.5–11.4%).ConclusionsAccuracy 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.



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