ESTRO 2023 - Abstract Book

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ESTRO 2023

Results Median age of presentation in our study is 47 years ( inter quartile range- 36-55 years). Median follow-up time is 4 years. Male to female ratio is 4:6. 66% patients presented with T3 lesions and 77% with N1b disease. There was no significant difference in overall survival (OS) in patients who received adjuvant RT following surgery in comparison to patients who underwent only surgery(92.9% vs 71.4% p value- 0.202). Similarly, there was no improvement in loco regional recurrence free survival( LRFS) (100% vs 85.7% , p value-0.157), Distant metastasis free survival (DMFS) (64.3% vs 71.4%, p value- 0.725) and Disease free survival (DFS) ( 64.3% vs 64.3%, p value- 0.91). Age, gender, nodal involvement, surgical resection status ( R0, R1, R2) didn’t have any effect on survival outcomes. DFS (100% vs 63.6% p value- 0.008), LRFS (100% vs 94.7% p value 0.002) and DMFS (100% vs 63.2% p value 0.006) were significantly better in T2 lesions compared to T3 lesions. Conclusion Adjuvant EBRT failed to show any significant improvement in survival outcomes and loco regional control in MTC. Further prospective randomised clinical trials are needed to validate the role of EBRT in MTC. Clinicians should proceed with caution before advising adjuvant radiotherapy in MTC and make an informed decision after weighting pros and cons of prescribing adjuvant EBRT. C. Zacharatou 1 , N. Bergin 2 , C. Fitzpatrick 3 , C. O’ Donovan 3 , O. McArdle 2 , S. Brennan 2 , S. Cain 1 , M. Dunne 4 , J. Armstrong 2 , B. McClean 1 1 St Luke's Radiation Oncology Network, Department of Medical Physics, Dublin, Ireland; 2 St Luke's Radiation Oncology Network, Department of Radiation Oncology, Dublin, Ireland; 3 St Luke's Radiation Oncology Network, Department of Radiation Therapy, Dublin, Ireland; 4 St Luke's Radiation Oncology Network, Department of Clinical Trials, Dublin, Ireland Purpose or Objective The two main intentions of proton therapy referral are iso-toxic increase of target dose or iso-effective toxicity reduction of OARs. According to the Dutch Health Council, referrals aiming at toxicity reduction make up for 85% of expected referrals. Considering the volume of these referrals and the limited availability of proton installations, a model-based method of patient selection (MBS) has been proposed by Dutch centres. In this retrospective study, we apply the Dutch model to determine (a) how many of our head&neck patients would qualify for proton treatment planning and (b) if the photon dose calculation approach would affect patient selection. Materials and Methods A patient sample was first obtained by searching the ARIA database for all H&N patients that began their treatment in the first quarter of 2022 in all three centres of SLRON. Patients were removed from the results of the ARIA query if they were treated with 3DCRT plans or palliative intent, had distant metastases or previous H&N irradiation, had a primary tumour not in the larynx, pharynx or oral cavity, had unidentified primary tumour site or failed to complete treatment because of poor overall condition. A total of 47 patients remained in the sample. Twelve plans were calculated in Eclipse (AAA v.15.6) and 35 plans were generated in Monaco (XVMC v.1.6). The Eclipse plans were recalculated with Acuros v.15.6 (dose to medium, same MUs) to assess the impact of dose calculation algorithm. Patient preselection was based on normal tissue complication probability (NTCP) for radiation induced xerostomia of Grade ≥ 2 six months post treatment. Baseline xerostomia was not systematically documented. NTCPs for dysphagia and tube-feeding dependence were not considered as swallowing subunits are not routinely contoured in our centre. We used the mean dose to the contralateral parotid to calculate NTCP for the photon plans, except in bilateral cases, where we used the lowest dose among the two parotids. Results We found that 34 out of 47 patients (72%) have a DNTCP=NTCP(photons)-NTCP(protons) for xerostomia above threshold (10%) and therefore qualify for proton treatment planning. Three patients had DNTCP between 10% and 20%, 14 patients between 20-30% and 17 patients above 30% (no parotid sparing in the photon plan). Mean parotid doses were reduced in the recalculated Acuros plans by 0.4 Gy-1 Gy, resulting in NTCP reductions between 0.5% and 1.7%, but none of these changes affected preselection. However, a recalculation with Acuros may be indicated for patients with NTCP values close to the selection threshold. Conclusion As NTCPs for dysphagia and tube-feeding dependence were not analysed in this study, our results are an underestimation of the number of H&N patients qualifying for proton planning. With 72% of our patients qualifying on xerostomia preselection alone, we concluded that a significant number of our patients currently not treated with protons would benefit from that treatment if it was more accessible in Ireland. PO-1180 Proton treatment planning: How many H&N patients qualify for proton plan calculation in Ireland?

PO-1181 Clinical outcomes after re-irradiation with dose painting of head and neck cancer

E. Dale 1 , M.E. Evensen 2 , C.D. Amdal 1 , T. Furre 3 , J.M. Moan 1 , A.M. Løndalen 4 , L.C. Heggebø 1 , E. Malinen 5

1 Oslo University Hospital, Department of Oncology, Oslo, Norway; 2 Drammen Hospital, Vestre Viken Hospital Trust, Section of Oncology, Drammen, Norway; 3 Oslo University Hospital, Department of Medical Physics, Oslo, Norway; 4 Oslo University Hospital, Department of Radiology and Nuclear Medicine, Oslo, Norway; 5 University of Oslo, Department of Physics, Oslo, Norway

Purpose or Objective