ESTRO 2024 - Abstract Book

S3246

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Results:

The mean gamma value and the gamma passing rate of the ROI created has been evaluated for all plans delivered. The plans for motionless, free breath and for the 15 breath hold treatments have been measured and compared. In the case of the 15 breath hold measurements the average value of the mean gamma, and gamma passing rate have been calculated. The mean gamma values are: 0.22, 0.59 and 0.30 for the patient 1 and 0.28, 0.32 and 0.37 for the patient 2, for motionless, free breath and breath hold respectively. As regards the gamma passing rate the values are: 99.8%, 79.3% and 99.1% for patient 1, 98.9% 98.6% and 95.2% for patient 2, for motionless, free breath and breath hold respectively (Figure1).

The intra-patient repeatability of the 15 breath hold treatments was estimated by evaluating the variability of gamma passing rate values compared to the D4 motionless gamma passing rate value, used as reference (Figure 2).

For both patients the percentage CV (coefficient of variation) value is 0.62% and 3.8% for patient 1 and patient 2 respectively. For the patient 2, with greater difficulty to hold the breath, indeed the mean gamma values are turned out higher and the gamma passing rate presents values for five fractions lower than the tolerance threshold (87.7%, 94.9%,88.3%, 94.7%, 93.9%). However, the average of the gamma passing rate on all 15 fractions is above the tolerance threshold. As concern the comparison inter-patient the statistical analysis shows a p-value of 0.07 meaning that there is no statistically significant difference between the 15 breath hold treatments of the two patients.

Conclusion: