ESTRO 2024 - Abstract Book

S4810

Physics - Quality assurance and auditing

ESTRO 2024

The plans with gantry angle +5°were not delivereable, because the end angle was past the final angle achievable by the linac.

Two of the plans with the known errors in the original plan were not picked up by Prosoma Core. They were delivered consecutively, without allowing sufficient time between the end of one delivery and the beginning of the following. A minimum of 10 minutes was required between deliveries, and this was followed for the deliveries of the PTV3 plan. The log-file analysis picked up all the plans for PTV3. The errors were appearing as cold streaks on the difference of plan-to-log-file fluence map and the % relative movement errors for the MLC, when these had been altered, were progressively worse with each increasing displacement. Plans with errors as small as 1 mm on some MLCs have a measurable impact on the PSQA results. However, the magnitude depends on the plan. In the Original plan, where the MLCs displaced were not all directly affecting the PTV, the PSQA results with a 1mm displacement, showed a decrease in the gamma, but still passed the 95% threshold. On the contrary, for PTV3, where the MLCs displaced where directly affecting the dose delivered, the impact on the result was larger. The failures were very clear on the film.

Conversely, a change in the collimator angle impacts different plans differently. When the target is spherical and on axis (PTV3), the impact is not measurable. For the original plan (off-axis), the results show a drop of 30% in the gamma.

Conclusion:

Errors as small as 1mm were picked up both by the PSQA and Prosoma Core. The errors that were not picked up by Prosoma Core, showed no effect in the PSQA results. This is heavily dependant on the shape of the tumour and its location with respect to the isocentre. Overall, the results of the testing were reassuring. Both our PSQA process as well as Prosoma Core show high reliability for picking up clinically significant errors. Prosoma Core will need further testing with clinical cases prior to its full clinical implementation in replacing SRS PSQA in our centre.

Keywords: Prosoma Core, SRS