ESTRO 2024 - Abstract Book

S2097

Clinical - Sarcoma, skin cancer, melanoma

ESTRO 2024

Patients with < 90% necrosis had higher loco-regional failure (12.5% vs 0%, p=0.037) and distant failure rates (24.0% vs 3.1%, p=0.009) compared to patients with ≥ 90% necrosis.

The 3-year loco-regional recurrence-free survival rate was 85.5% (95% CI, 77.3% - 92.3%) in patients with < 90% necrosis and 100% in those with ≥ 90% necrosis (p=0.051).

The 3-year distant disease-free survival rate was 74.6% (95% CI, 65.3% - 82.1%) for those with < 90% necrosis and 96.9% (CI, 78.4 - 99.7%) for ≥ 90% necrosis (p = 0.013). In univariate analysis, patients with ≥ 90% necrosis were 86.6% less likely to develop metastatic disease compared to patients with < 90% necrosis (HR 0.134, 95% CI 0.018 0.964, p = 0.049).

The 3-year overall survival rate was 80.0% (CI, 69.0% - 86.5%) % for patients with < 90% necrosis and 88.9% % (CI, 61.0% - 96.8%) for ≥ 90% necrosis (p = 0.161).

Conclusion:

Hypofractionated radiotherapy to a dose of 30Gy in 5 fractions was associated with higher rate of tumour necrosis compared to conventional fractionation radiotherapy using 50Gy in 25 fractions, especially in UPS, solitary fibrous tumour, and myxoinflammatory fibroblastic sarcoma. Necrosis ≥ 90% was strongly associated with reduced risk of developing distant metastasis with a trend for reduced risk of loco-regional failure as well, although this was not statistically significant. Overall survival was not influenced by tumour necrosis in this cohort, most likely explained by the short follow up time.

Keywords: Tumour necrosis, hypofractionated RT,low a/b ratio

1542

Mini-Oral

Changing patterns of care and increasing radiotherapy use in chordoma

Kendrick Koo 1,2 , Susie Bae 3 , Sam Ngan 2 , Julie Chu 3 , Jasmine Mar 2 , Katrina Woodford 2 , Iman Hussein 2 , Sarat Chander 2

1 Alfred Health, Radiation Oncology, Melbourne, Australia. 2 Peter MacCallum Cancer Centre, Radiation Oncology, Melbourne, Australia. 3 Peter MacCallum Cancer Centre, Medical Oncology, Melbourne, Australia

Purpose/Objective:

Chordomas are rare slow growing malignant tumours which occur in anatomically challenging axial skeletal sites, in particular the sacrum and skull base. Definitive radiotherapy is the preferred treatment modality if inoperable or where resection would result in unacceptable functional outcomes [1]. Chordomas have however been traditionally considered radioresistant - referral for particle therapy had been common to deliver higher doses in close proximity to critical structures [2], though in recent times, modern radiotherapy techniques, specifically volumetric arc therapy (VMAT) and stereotactic ablative radiotherapy (SABR)