ESTRO 2024 - Abstract Book

S4829

Physics - Quality assurance and auditing

ESTRO 2024

Python script extracted the required DICOM tags of each RTPLAN. Similarly, data were extracted from a backup copy of the OMS, and both sets of data were uploaded to an SQL server. The data were compared between the OMS and RTPLAN to highlight any discrepancies. In addition to the initial risk identified, the script compared other data imported into the OMS from the RTPLAN. The automated audit included all external beam treatment plans between October 2012 and September 2023, where the monitor units (MUs) were calculated within the TPS. Over 52,206 RTPLANs, representing 44,547 patients, were compared. Once completed, the results from the automated audit were manually reviewed to determine the underlying cause of any differences.

Results:

The audit identified 368 treatment plans with differences in MU across 628 beams, one plan with a difference in gantry angle and one plan with a difference in FFF status for a single beam. Differences were found in 0.55% of all beams. The gantry angle difference was to avoid contralateral breast splash. Of the 628 beams with MU differences: • 355 (56% of identified beams, 0.29% of total beams) were corrections for couch density which couldn’t be modelled in the TPS • 171 (27% of identified beams, 0.15% of total beams) were intentional treatment changes documented in the OMS • 50 (8% of identified beams, 0.04% of total beams) were due to the complexity of the craniospinal pathway (not including couch corrections) • 27 (4% of identified beams, 0.02% of total beams) were due to documented miscellaneous reasons unrelated to the treatment, for example the OMS having a maximum MU per beam • 26 (4% of identified beams, 0.02% of total beams) were false positives

The difference in FFF status was a genuine error. The OMS delivered 6 MV instead of 6 MV FFF for a 40 Gy in 15 fractions IMRT breast treatment. This resulted in a 25% increase in delivered dose to the target volume [1].

The overall trend in manual updates in the OMS has decreased since 2013 (Figure 1). Improvements in the TPS and process changes have reduced the need for manual updates to the treatment plan within the OMS.