ESTRO 2024 - Abstract Book

S1429

Clinical - Head & neck

ESTRO 2024

exact location of recurrences in head-and-neck cancer patients after (chemo)radiotherapy treatment in order to find their possible cause.

Material/Methods:

From 2016 to 2022, recurrence locations were systematically recorded and analyzed at University Medical Center Utrecht. For this purpose, radiotherapy masks were stored and patients with recurrences were imaged in radiotherapy position using a dedicated 3.0 T MR follow-up protocol. The acquired images of the recurrences were co-registered with the initial images and treatment plan. Recurrences were delineated and classified as local, regional or distant and the center-of-mass (COM) was assumed to be the origin of the recurrence. The distances from the COM of the recurrences to the target volumes and the dose at the COM of the recurrences were determined.

Results:

A total of 150 recurrences were recorded, 114 were loco-regional and were further analyzed. Local and regional recurrences with positive nodes mainly originated from the high-dose GTV-P/N and CTV-P1/N1 (80%). No local recurrences were observed in the low-dose CTV-P2 (i.e. the second 5mm according to Gregoire et al.)1 (Figure 1). Similar patterns were observed for regional recurrences of patients with positive nodes, with only 2% originating from the low-dose CTV-P2 volume (i.e. elective treated lymph node levels).

Conclusion:

Local and regional recurrences analyzed in this study indicate that the patients received (chemo)radiotherapy with adequate treatment margins and no indications for delineation or positioning errors were observed. Most recurrences originated from within the high dose region. Results indicate that CTV-P2 should be reconsidered.