ESTRO 2024 - Abstract Book

S5560

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

Results:

Fifteen patients CBCT’s were reviewed, 30 CBCT’s in total. Of the 30 CBCT’s acquired all were deemed clinically acceptable or above average regardless of the template used. Refer to Figure 2 for results summary.

Accurate CBCT interpretation can be negatively impacted by the effect of artefacts on the IQ4 and may require a change of CBCT template to ensure clinically acceptable IQ. One patient out of the 15 had an above average level of artefact, attributed to an implanted cardiac device. On evaluation this patient scored 3 on the Thorax_Standard template indicating that the IQ was clinically acceptable. This patient scored 4 on the Thorax_XLarge template (with a below threshold CTDIvol max of 12.9 mGy), only 1 of 2 patients to do so. This may indicate where an above average level of artefacts are present the Thorax_XLarge template could be beneficial. The CTDIvol max (mGy) range for the evaluated patients was 4.8–18.5. Of interest the patient with a CTDIvol max (mGy) of 18.5 scored 4 for Thorax_XLarge template but the IQ for Thorax_Standard was found to be acceptable for image matching purposes. When evaluating the patient with a CTDIvol max (mGy) at the lowest end of the range (4.8) an above average score was noted when using Thorax_Standard.

Conclusion:

Based on the evaluation of the 15 SABR patients CBCT’s it is appropriate to recommend that Thorax_Standard is used as standard for the acquisition of the pre and post treatment CBCT’s for Lung SABR. Local protocol provides reference threshold levels to indicate when it would be clinically useful to use Thorax_XLarge. All CBCT’s acquired using Thorax_Standard template were found to be acceptable for IGRT it would suggest that the CTDIvol max (mGy) threshold value at which Thorax_XLarge would be used is re-evaluated. The results for the patient with the lower CTDIvol max (mGy) suggest further optimisation by creating a lower dose template, if possible, may be beneficial. A number of limitations must be considered with this evaluation such as number of patients and experience of the radiographers performing image evaluation. It must also be noted that since the first local evaluation was undertaken in 2020, which established the CTDIvol max (mGy) threshold value, the radiographers’ image review experience will have improved due to increase departmental use of CBCT’s and therefore the IQ required for decision making could have changed.

Keywords: image, quality, dose

References:

1. HM Government. The Ionising Radiation (Medical Exposure) Regulations 2017. London: The Stationery Office, 2017