ESTRO 2020 Abstract book

S1120 ESTRO 2020

DIBH using the SHRMD could demonstrate comparable dosimetric outcome and treatment efficiency as using the ABC system. The ABC system was superior in keeping low intrafractional and interfractional variabilities, and smaller random error. Further improvements are required to make the SHRMD become an alternative to the ABC system in treating left breast cancer patients. PO-1912 Clinical experience of using stereotactic ablative body radiotherapy on inoperable pancreatic cancer J. Duong 1 , Y.M. Tsang 1 , M. Harrison 2 1 Mount Vernon Cancer Centre, Radiotherapy, Northwood Middlesex, United Kingdom ; 2 Mount Vernon Cancer Centre, Clinical Oncology, Northwood Middlesex, United Kingdom Purpose or Objective Survival rates of patients with inoperable pancreatic cancer are very low in relation to other cancers and the length of time between diagnosis and death is typically short, usually less than 6 months. Conventional fractionated chemo-radiotherapy is protracted and associated with a poor toxicity profile. Stereotactic Ablative Body Radiotherapy (SABR) is being used with increasing frequency and has shown favourable clinical results. This study looks at the efficacy of SABR within this patient cohort in terms of overall survival (OS) and post- radiotherapy (RT) toxicity. Material and Methods A retrospective review of all patients with pancreatic cancer (T1-3N0M0) who were treated with a dedicated robotic stereotactic RT machine at our institution was conducted. All patients were treated under free breathing with real time motion tracking image-guided RT. The OS was calculated using Kaplan-Meier method and the post RT toxicity data was scored following the CTCAE v4.0 protocol. Assuming a/ß=10 for tumour control, the biological equivalent doses (BED) of prescribed treatment were calculated. For subgroup analysis of prognostic factors, medians were used to categorise patients into 2 groups: £median and > median. A Mantel-Cox log-rank analysis was used to assess OS between these groups. Results In between July 2011 to July 2018, 20 patients with inoperable pancreatic cancer who received SABR (either 3 or 5 fractions) at our institution were included in this study. The median follow-up was 9.6 months (range 1.0- 34.2). 60% of the patients received chemotherapy prior SABR and none of them were treated with concurrent chemotherapy during SABR. The median OS was 9.2 months (95%CI 5.9-12.5) and the OS at 12months was 35%. Acute and late side effects from stereotactic treatment include fatigue, nausea and bowel disturbance. 50% of patients reported grade 1 and grade 2 fatigue within 12 months post completion of RT. No greater than grade 3 post RT toxicity has been reported in this cohort. No statistically significant differences in OS were found when comparing the median groups of patients’ ages, the number of fractions, chemotherapy prior SABR status, BED, gross tumour volume (GTV) and planning target volume (PTV) sizes (p>0.05 of all factors).

evaluated to compare the treatment efficiency between the two techniques.

Results No statistically significant difference was found between the two techniques in terms of OAR sparing (all p>0.05). The intrafractional variabilities of using the SHRMD and the ABC system were 0.55±0.31mm and 0.23±0.14mm respectively (p<0.01), while the interfractional variabilities of using the SHRMD and the ABC system were 2.18±0.60mm and 1.35±0.37mm respectively (p<0.01). DIBH using the SHRMD demonstrated significantly larger intrafractional and interfractional variabilities. Using the SHRMD, the group systematic error M was -0.96mm, with the standard deviation (SD) of the systematic error Σ and random error σ to be 1.84mm and 2.25mm respectively. Using the ABC system, the group systematic error M was - 1.01mm, with the SD of the systematic error Σ and random error σ to be 2.04mm and 1.39mm respectively. There were no significant differences in the group systematic error and the SD of the systematic error between the two techniques (all p>0.05), but the SD of the random error of using the SHRMD was significantly larger (p<0.01). Treatment setup time and treatment delivery time were similar for both techniques (all p>0.05).

Conclusion The use of SABR in our cohort of patients with inoperable pancreatic cancer has shown promising OS rates irrespective of patients’ ages, the number of fractions,

Conclusion