ESTRO 2024 - Abstract Book

S3248

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

A 10-phase 4D-CT was performed on a cubic phantom with pinpoint chamber insert (StereoPHAN ionisation chamber insert, Sun Nuclear) (fig. 1) and another one for the phantom with gafchromic film insert (StereoPHAN multifilm insert, Sun Nuclear) (fig. 1). The chamber volume was considered as target volume (CTV equivalent) and an ITV corresponding to 1, 2, 3, 4, 6 and 8 respiratory phases was generated. For the second gafchromic phantom only the 1-, 3- and 6 phase ITVs were generated and processed.

Figure 1: A. Cubic phantom with pinpoint chamber insert. B. Cubic phantom with film insert. C. Phased gating treatment in a TrueBeam HD 120 accelerator for only one phase (95% - 5%).

Firstly, the calculated treatment was delivered on a TrueBeam HD 120 accelerator (Varian, Palo Alto, USA) continuously and without movement of the phantom for each ITV. Afterwards, the same beams were delivered with the phantom moving and triggered with respiratory cycle control at the chosen phases. Depending on the phantom, the pinpoint chamber or EBT3 gafchromic films were introduced to obtain point dose or dose distribution respectively. The gafchromic films were analysed after 24 hours with an EPSON 10000XL scanner and OmniPro software (IBA, Schwarzenbruck, Bayern).

Results:

The table shows a comparison of the measurements made for the treatments generated with different numbers of phases. In all cases, the difference is less than 1%.