ESTRO 2024 - Abstract Book

S2236

Clinical - Upper GI

ESTRO 2024

unadapted plan (p=0.001). In patients adapted because of MHD increases, an average reduction of 1.2Gy (p<0.001) was achieved, while other adaptation reasons resulted in an MHD reduction of 0.4Gy (p=0.3) (Figure 1).

CTV coverage because of adaptation decreased on average by 0.4% (p=0.6), with a decrease of 0.6% (p=0.8) in patients with adaptations because of CTV under-dosage (Figure 2). In 3 of 13 patients, adaptation managed to undo an under-dosage. In 5 patients, the initial plan would not have resulted in under-dosage, and in 5 patients, adaptation was unsuccessful in preventing CTV under-dosage. Adaptation reduced NTCP for two-year mortality by 0.8% on average (p=0.002). In patients adapted because of MHD, NTCP reduction was 1.4% on average (p<0.001), while other adaptation reasons resulted in a NTCP reduction of 0.4% (p=0.3)

Conclusion:

A dose-based adaptation protocol, focusing on CTV coverage and MHD is effective in reducing MHD and related NTCP. CTV coverage effects of adaptation were only minor in a majority of patients, suggesting that coverage-based adaptation could be omitted in future.

Figure 1: Mean heart dose (MHD) from original plan vs summed dose all repeat CTs. In blue the patients adapted because of MHD increase during treatment. In red the patients adapted because of decrease in target coverage. In