ESTRO 2020 Abstract Book

S1066 ESTRO 2020

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).

Poster: RTT track: Motion management and adaptive strategies

PO-1911 Comparison of in-house self-held respiratory monitoring device and ABC system in DIBH left breast RT W.K. Chow 1 , V.W. Wu 2 , G. Chiu 1 , P.S.W. Kong 1 1 Hong Kong Sanatorium & Hospital, Department of Radiotherapy, Hong Kong, Hong Kong SAR China ; 2 The Hong Kong Polytechnic University, Department of Health Technology and Informatics, Hong Kong, Hong Kong SAR China Purpose or Objective To find out whether left breast radiotherapy in DIBH using an in-house self-held respiratory monitoring device (SHRMD) is at least as good as the commercially available Active Breathing Coordinator™ (ABC) system in terms of normal tissue sparing, intrafractional and interfractional position reproducibility, setup accuracy and treatment efficiency. Material and Methods Thirty-two early-stage left breast cancer patients who previously received radiotherapy treatment on the left breast or left chest wall only were retrospectively recruited. Half of them were treated with SHRMD and the other half by ABC system (n=16). Forward-planned IMRT plans of DIBH using SHRMD and ABC system were re- generated. Dosimetric comparison was carried out on dosimetric parameters of OARs including the heart, LAD and left lung between the two DIBH techniques. Daily electronic portal images were acquired in cine loop for measurement of the central lung distance (CLD), which was used to compare the intrafractional and interfractional variabilities between using the two DIBH techniques. The differences between the average CLD measured in the portal images and the CLD measured on DRRs were also evaluated to compare the systematic and random errors between the two techniques. Finally, the treatment setup time and treatment delivery time were evaluated to compare the treatment efficiency between the two techniques.

Conclusion 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

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