ESTRO 2023 - Abstract Book

S364

Sunday 14 May 2023

ESTRO 2023

Conclusion These results once again demonstrated the ability of BT to drastically spare healthy tissue surrounding the tumor. Proton therapy is an encouraging alternative for many of the locations analyzed. This exhaustive study in the techniques implemented provides quantitative arguments as to the clinical options to be considered. The database will be continued in order to increase its completeness.

OC-0460 HDR-IBT liver for oligometastatic disease from NPC S. Abdul Shukor 1 , G.K. Appalanaido 2 , M.Y. Musa 3 , E. Seng Ch'ng 4

1 National University Cancer Institute, Singapore, Radiation Oncology, Singapore, Singapore; 2 Advanced Medical & Dental Institute, Universiti Sains Malaysia, Radiotherapy & Oncology, Penang, Malaysia; 3 Advanced Medical & Dental Institute, Universiti Sains Malaysia, Head & Neck Surgery, Penang, Malaysia; 4 Advanced Medical & Dental Institute, Universiti Sains Malaysia, Pathology, Penang, Malaysia Purpose or Objective Liver metastasis (LM) in nasopharyngeal carcinoma (NPC) carry a poor prognosis. The role of local liver directed therapy (LLDT) in oligometastatic liver disease from NPC (OLM- NPC) is poorly defined. Liver HDR-IBT is one of the LLDT used mostly in primary liver tumours and colorectal liver metastasis. This is the first study in the literature to report on the outcome of liver HDR-IBT in OLM-NPC. Materials and Methods Between Feb 2019 till January 2022, 6 patients with 15 OLM-NPC lesions who underwent CT-guided HDRIBT were prospectively followed up with 3 monthly radiological imaging that consist of either CT-Scan, MRI or PET-CT and analysed for local control (LC) rate of the treated lesions, local progression free interval (PFI) in the liver and OS. LC is defined as either no increase in the largest tumour diameter (LTD) of contrast enhancing lesion in CT/MRI (stable disease, SD) or no increase in SUV uptake on PET-CT compared to baseline. Metabolic complete response (mCR) is defined as no significant SUV uptake of the treated lesion in PET-CT. Results Median age is 50.5 years and follow-up range from 152 to 986 days. Two patients had prior treatment to liver with surgery, RFA and/or SBRT. The mean of LTD and volume is 2.4cm (range 0.5 to 4.2 cm) and 3.49cc (range 0.95 to 10.1cc) respectively. The peripheral prescribed dose range from 20Gy to 25Gy in single fraction with mean (range) D99%, D95% and D90% of 31.45Gy (18.7 – 51.56Gy), 36.5Gy (21.2 – 60.4Gy) and 27.16Gy (23.69 – 69.11Gy) respectively. Out of 15 lesions treated, 1 lesion had PD. Two-year LC rate is 80% (95% CI: 52%, 100%). Eight lesions had PET-CT assessment with 7 showing mCR and median time to attain mCR is 185days (95% CI: 161 days, NA). One-year cumulative mCR rate is 69% (95% CI: 27%, 90%). Four out of 6 patients developed new liver lesion/s and 2 attained local progression free interval (PFI) in liver after the first HDR-IBT. One-year local PFI at the liver is 50% (95% CI: 22%, 100%). Two-year OS is 83% (95% CI: 58%, 100%) and 2 patients died during follow up due to progressive distant metastasis. Most common acute toxicity is fever, nausea and vomiting and pain which was well controlled with medications. No grade 4 toxicity seen in this study. In one lesion that had PD, the D99%, D95% and D90% was 20.11Gy, 23.02Gy and 25.23Gy respectively. This patient had systemic chemotherapy prior to the liver HDR-IBT and it was a marginal recurrence. Conclusion In this study, the OS and PFS is better than published results of OLM-NPC. The excellent LC rate with HDRIBT is likely due to the inherent radiosensitivity of NPC. Minimum peripheral dose of 16Gy is able to control 80% of the tumours. HDRIBT in OLM-NPC is a low morbidity procedure and larger study is needed to ascertain if this excellent LC rate prevent visceral crisis and translates into improved OS.

Proffered Papers: Advancements in RTT practice

OC-0461 The four pillars of advanced practice: perspectives from key radiotherapy stakeholders across Europe C. Oliveira 1 , B. Barbosa 2 , J.G. Couto 3 , I. Bravo 2 , C. Hughes 4 , S. McFadden 5 , R. Khine 6 , H.A. McNair 7 1 Instituto Português de Oncologia do Porto (IPO Porto), Radiotherapy, Porto, Portugal; 2 Instituto Português de Oncologia do Porto (IPO Porto), Medical Physics, Radiobiology Group and Radiation Protection Group, IPO Porto Research Centre (CI IPOP), Porto, Portugal; 3 Faculty of Health Sciences, University of Malta, Msida, Malta., Radiography , Msida, Malta; 4 Ulster University , School of Health Sciences, Belfast, Portugal; 5 Ulster University, School of Health Sciences, Belfast, United