ESTRO 2024 - Abstract Book

S4944

Physics - Quality assurance and auditing

ESTRO 2024

Additionally, detailed instructions were provided to the planning team on the technique, help structures, and optimization objectives to achieve these goals.

A query to the ARIA database was set up to assess the quality of our plans. We searched for all patients treated with SBRT in the lung and mediastinum between January 2015 to January 2023. The following dosimetric parameters were extracted: For the PTV: the volume that receives 100% of the dose (V100%), the mean dose, the maximum dose, the volume, and the conformity index, for the ITV the volume that receives 135% of the dose (V135%), the mean dose, the maximum dose and the volume. Some post-processing was performed to exclude patients with central lung tumors. Central lung tumors were treated with a smaller dose inhomogeneity using a different protocol.

Results:

We identified in total 1077 target volumes treated with 939 plans for 602 patients. The number of treated target volumes was increasing over time, with 80 patients treated in 2015 and 155 patients treated in 2022. For 152 target volumes (86%) only dose to the PTV and not to the ITV could be evaluated due to inconsistencies in the structure naming. After an institution-wide standardization of structure naming beginning of 2018 this issue was significantly reduced (39% before, 5% after standardization). Compliance with the protocol was 90%, there was a learning phase in the first year with only 72% compliance, whereas in the following years, there were no significant changes (figure 1).

The most challenging objective to be achieved was the ITV coverage (compliance 92%), whereas the maximum dose and the conformity index were nearly never a problem (compliance 99.6% and 99%). The most common reasons for non-compliant plans were: HU of the lung tissue around the tumor of less than 900HU, air bubbles inside the tumor, treatment of multiple tumors very close to each other, and serial organs at risk abutting the PTV, HUs of the tumor very small and volume of the tumor less than 0.5cc.

The average of the mean ITV dose was 146% (+/-3%) (of the prescribed dose) for all plans, and 147% (+/-2%) (of the prescribed dose) for the protocol-compliant plans. There was no dependence on the ITV or PTV volume.

Conclusion:

Multi-criteria optimization has demonstrated its feasibility in the context of lung SBRT when employing a standardized protocol. This approach has proven effective in achieving a high degree of consistency in dose distribution within both the ITV and the PTV. It is important to emphasize that consistent nomenclature is paramount in facilitating the