ESTRO 2024 - Abstract Book

S4789

Physics - Quality assurance and auditing

ESTRO 2024

Plan quality was assessed with the NTCP model for dysphagia grade 2+, used in the randomisation phase of the trial [2]. The model was based on the Dutch model selection [3,4].

Furthermore, treatment plan quality was evaluated using a new metric, the Normalised Toxicity Index (NTI), calculated as the normalised average of the mean dose to the OARs compared to the recommended mean dose thresholds outlined in the DAHANCA guidelines. An NTI > 1 indicated that, on average, the OARs received doses exceeding the recommended thresholds, while an NTI < 1 indicated that the OARs received doses below the thresholds. Hence, a lower NTI indicated better plan quality concerning OAR doses.

The mean dose delivered to 13 OARs relevant to head and neck cancer was analysed.

Results:

The NTCP was not significantly different for the photon plans, comparative proton plans, and clinical proton plans throughout the three consecutive intervals, as seen in Figure 1. The median NTCP for clinical proton plans was 9.1 % (interquartile range [6.1, 15.0]) in the Pilot phase, 11.1 % [8.6, 12.8] in Randomisation phase 1, and 10.4 % [6.5, 13.9] in Randomisation phase 2. There were no significant differences in NTI for the three time intervals for either of the treatment types, as depicted in Figure 2. For clinical proton plans, the median NTI values were 0.88 [0.70, 1.00] during the Pilot phase, 0.83 [0.75, 0.89] in Randomisation phase 1, and 0.79 [0.67, 0.98] in Randomisation phase 2.

Across the 13 OARs, the mean dose did not show a general time-dependent change, except for the right parotid gland in the clinical proton plans.