Quality assurance analysis of a large multicenter practice: does increased complexity of intensity-modulated radiotherapy lead to increased error frequency?

PURPOSE: Error reduction is an important concern in clinical medicine. Intensity-modulated radiotherapy (IMRT) is an important advancement in radiation oncology that increases the complexity of treatment, potentially increasing the error risk. We studied the frequency and severity of errors in a large multicenter practice to ascertain the impact of quality improvement interventions over time, IMRT, and type of practice. METHODS AND MATERIALS: We analyzed prospective data from three academic and 16 community practice sites with 24,775 courses of radiotherapy (9,210 IMRT courses and 15,565 non-IMRT) between January 2006 and December 2009. All IMRT treatment was performed using one centralized dose planning center for all sites. RESULTS: We prospectively identified various errors or potential errors in 0.14 % vs. 0.40 % of the IMRT vs. non-IMRT courses (13/9,210 vs. 62/15,565, p = 0.0004) and excluding potential errors: 0.03 % for IMRT vs. 0.21% for non-IMRT. We developed the Clinical Radiotherapy Error Severity Scale (CRESS) to classify error severity from 1 to 10, with 1 to 3 for potential or completely correctable errors, 4 to 5 for dose variations <5%, and 6 to 10 for dose variations >5%. Multivariate analyses of CRESS values, severity >4, and any error (including potential) correlated significantly reduced errors with IMRT (p = 0.0001-0.0024) but found no significant difference between the academic and community practice sites and no change in error frequency over time despite implementation of 39 system-wide policy changes by the centralized quality improvement committee. CONCLUSIONS: Despite the increase in complexity with IMRT compared with conventional radiotherapy, it can be delivered with reduced error frequency.

Determination of CT-to-density conversion relationship for image-based treatment planning systems.

The implementation of tissue inhomogeneity correction in image-based treatment planning will improve the accuracy of radiation dose calculations for patients undergoing external-beam radiotherapy. Before the tissue inhomogeneity correction can be applied, the relationship between the computed tomography (CT) value and density must be established. This tissue characterization relationship allows the conversion of CT value in each voxel of the CT images into density for use in the dose calculations. This paper describes the proper procedure of establishing the CT value to density conversion relationship. A tissue characterization phantom with 17 inserts made of different materials was scanned using a GE Lightspeed Plus CT scanner (120 kVp). These images were then downloaded into the Eclipse and Pinnacle treatment planning systems. At the treatment planning workstation, the axial images were retrieved to determine the CT value of the inserts. A region of interest was drawn on the central portion of the insert and the mean CT value and its standard deviation were determined. The mean CT value was plotted against the density of the tissue inserts and fitted with bilinear equations. A new set of CT values vs. densities was generated from the bilinear equations and then entered into the treatment planning systems. The need to obtain CT values through the treatment planning system is very clear. The 2 treatment planning systems use different CT value ranges, one from -1024 to 3071 and the other from 0 to 4096. If the range is correct, it would result in inappropriate use of the conversion curve. In addition to the difference in the range of CT values, one treatment planning system uses physical density, while the other uses relative electron density.