ESTRO meets Asia 2024 - Abstract Book

S309

Physics – Detectors, dose measurement and phantoms

ESTRO meets Asia 2024

Results:

The result of this evaluation is shown in Figure 1. Evidently, even without applying any stopping-power corrections the Octavius 729 array results are already well matched to the water-tank-measured PDD profiles. This result suggests that there is some aspect of the design and scatter conditions of the Octavius 729 array that counteracts the depth dependence of electron beam energy (expected to decrease by approximately 2 MeV per 10 mm) and produces a result that is more similar to the behaviour of an array of diodes than an array of vented, air-filled ionisation chambers.

Figure 1: PDI profiles measured in water tank (dashed lines), PDD profiles derived from PDI measurements in water tank (solid lines) and relative central axis dose readings from Octavius 729 array under Virtual Water (crosses). All data sets are normalised to their maximum values for each electron beam. No corrections or conversions have been applied to the Octavius array results.

Conclusion:

This result opens the door to using the Octavius 729 ionisation chamber array, with an appropriate calibration, to measure electron radiotherapy dose downstream of phantoms with variable thicknesses or containing variable materials without the need to generate corresponding two-dimensional arrays of stopping-power corrections. Clearly, it would be desirable to investigate which aspects of the design of the array are leading to the observed energy-independence, potentially via comparison with other types of ionisation chamber arrays that have different internal compositions and geometries.

Keywords: electron radiotherapy, dosimetry

References:

1. Webb L. K., Crowe S. B., Heseltine L., Charles P. H., Kairn T. (2022) "3D printed tissue & bone equivalent anthropomorphic head phantom for electron beam validation", Physical and Engineering Sciences in Medicine 45(1): 356-357

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