Evaluation of the introduction of a 'traffic light protocol' for dose-volume histogram constraints of organs at risk in definitive radiotherapy at Liverpool and Macarthur Cancer Therapy Centres.

INTRODUCTION: Protocols have been developed in our department with recommended dose constraints for organs at risk (OAR) for each tumour site receiving definitive radiotherapy. We have developed a colour coding system to indicate when constraints are meeting objectives (green), have minor variation from planning objectives (yellow) and have major variation from planning objectives (red). We performed a quality audit to assess adherence to the protocol and to determine the rate of acute and subacute toxicities. METHODS: All definitive radiotherapy dose-volume histogram (DVH) reports generated in the first 6 months of 2017 at Liverpool and Macarthur cancer therapy centres were collected. For each radiotherapy group, the overridden dose constraints were evaluated and categorized to red and yellow. For all patients in our data set, follow-up documents/assessments were searched for grade 3 or higher acute or subacute radiotherapy toxicity and compared with those who had overridden dose constraints. RESULTS: There were 210 (34%) plans accepted with at least one major variation and 161 (26%) plans with minor variation. Head and neck group had the most rate of major variations (77%). The best groups in adherence to protocol were lymphoma and breast groups. In general, grade 3 toxicity was observed in 1%, 4% and 9% of patients who were in green, yellow and red categories. Overall, we noted a correlation with grade 3 toxicities between acceptable plans (green) and ones with a minor or major variation (yellow or red) (1% vs. 7% P = 0.0001). CONCLUSION: In conclusion this study showed an increased risk of higher grade toxicities when DVHs were beyond our departmental constraints using a 'Traffic Light System'. With this new colour coding system, we can facilitate auditing of the dose constraints in order to improve the quality of radiotherapy plans and potentially provide benchmarking for reducing toxicities in radiotherapy treatments.

Comparison of digitally reconstructed radiographs generated from axial and helical CT scanning modes: a phantom study.

Digitally reconstructed radiographs (DRRs) play a vital role for verifying patient position for many radiotherapy treatments. As DRRs are generated from CT scans, image quality may be affected by the scanning mode (axial or helical). The aim of this study was to investigate the high and low contrast resolution and the spatial linearity in DRRs as a function of CT scanning mode and to highlight the significance of this variation, if any. A commercial CT phantom (Fluke Biomedical Model 76-417) was scanned with a Siemens Somatom Sensation 4 CT scanner using six variations of field of view, scanning mode and helical pitch. The image quality of the DRR's produced from the scans was evaluated in terms of high contrast resolution using the modulation transfer function, low contrast resolution using Image Quality Score method and spatial linearity. The results indicated that the high contrast resolution for the axial mode was comparable to that for the helical modes. The low contrast resolution with axial scanning was comparable to scans performed with a helical pitch of 1 but deteriorated at pitches greater than 1. The field of view was not found to impact the low contrast resolution. When changing scanning parameters the impact on DRR quality should be considered. For DRRs, particularly where visualisation of low contrast structures is desired, a helical scan with a pitch of 1 is recommended.