ESTRO 2023 - Abstract Book

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ESTRO 2023

life. While postoperative radiotherapy (PORT) is commonly used in these patients, literature concerning the effect of radiotherapy (RT) on the late loss of FFF reconstructions is limited. Materials and Methods From an existing cohort of patients treated with postoperative radiotherapy for OCC In the Erasmus MC, University Medical Center Rotterdam from 2010 to 2018, we included all patients (n=47) with resection of the mandible requiring FFF reconstruction. Patients had a minimum of one year disease free follow up. Dose-volume data were extracted from RT treatment plans. Cumulative incidence rates of loss of FFF reconstruction after RT (regardless of cause) were computed using the Kaplan Meier method (uncensored). Risk factors were evaluated with Cox regression models. Follow-up was censored at the first of the following: death, disease recurrence, or end of standard follow-up (5 years). Results Patients had a median age of 68 (range 40-85), 53% percent was male (N=25), and 21% had a second free flap because of an extensive composite defect (N=3 free radial forearm flap, N=6 anterolateral thigh flap). We observed eight patients (17%) with early complications requiring surgical intervention (N=1 total loss of FFF, N=2 loss of skin island). Frequently prescribed dose schedules were 30x2 Gy (21%) and 33x2 Gy (55%), with a median time between surgery and start of PORT of 41 days (range 27-82). The median follow up was 57 months (range 15-143 months). Nine patients (19%) developed complications after PORT leading to total (N=7) or partial (N=2) loss of the FFF, all involving the fibular bone. The median time between primary surgery and the loss of FFF was 21 months (range 9-59 months). Most (7 out of 9) of these complications were associated with infections, such as plate infections or abscesses. Ten patients had plate infections requiring removal, without the loss of FFF. The estimated cumulative incidence of FFF loss was 6.4% (SE 3.6%) at one year, 18.3% (SE 5.9%) at three years, and 22.8% (SE 7.1%) at five years (Figure 1). All patients with loss of FFF after PORT were irradiated with ≥ 60 Gy, with most (8 out of 9) receiving 66Gy. We found both mean dose to the fibula (Dmean) and the percentage of the fibula that received 65Gy (V65), to be significant risk factors for FFF loss in risk factor analysis (Table 1), with patients with FFF loss having a higher mean V65 (57.6%) and Dmean (64.9Gy) than patients without FFF loss (V65 25.9%, Dmean 61.9Gy).

Conclusion Patients treated with high dose postoperative radiotherapy are at a high risk of complications leading to late loss of FFF reconstruction, with a 5-year cumulative incidence as high as 22.8%. Higher mean doses and V65 to the reconstruction are significant risk factors for these complications.

PO-1193 Pattern of practice in elderly patients with HPV positive oropharyngeal cancer: a multicenter study

P. Bonomo 1 , A. Romei 1 , V. Salvestrini 2 , C. Doccioli 3 , L. Belgioia 4 , M. Maddalo 5 , G. Fanetti 6 , P. De Franco 7 , S. Bertocci 8 , F. De Felice 9 , S. Ursino 10 , A. Merlotti 11 , D. Alterio 12 , A.N. Iacovelli 13 , F. Miccichè 14 , E. D'Angelo 15 , C. Becherini 16 , I. Desideri 16 , S. Caini 17 , L. Livi 1