ESTRO 38 Abstract book

S1209 ESTRO 38

couch shift for superior-inferior (SI), anterior-posterior (AP), medial-lateral (ML) and yaw (rotation around the AP- axis) for all fractions were examined and the mean, minimum, maximum shift and standard deviation (SD) of each parameter in each treatment course was calculated. Results The mean couch shift following the 300 CBCT scans included (table 1) was 5.87 mm SI (Range: 0 – 30 mm, SD: 3.86), 3.96 mm AP (Range: 0 – 22 mm, SD 2.58), 6.51 mm ML (Range: 0 – 34 mm, SD 4.40) and 1.24° yaw (Range: 0 – 4,6°, SD .75). The greatest couch shifts and deviations were generally found in the ML direction. Table 1 Table 1 shows the mean, minimum, maximum shift and standard deviation of each parameter of the 30 patients’ treatment course. It should be noted that the couch corrections are not an expression of the direction the couch was moved, but an expression of the deviations corrected, regardless of direction.

Conclusion The CBCT based couch shifts showed, that IGRT is highly relevant and useful in ensuring correct treatment of patients with MSCC. EP-2192 A systematic approach aimed at reducing IGRT dose in paediatric patients S. Stead 1 1 Clatterbridge Cancer Centre NHS Trust, Radiotherapy, Wirral, United Kingdom Purpose or Objective Compared to adults, the higher survival rates and anticipated decades of longevity of paediatric patients heighten the concerns regarding late effects of radiotherapy and secondary malignancies. Much has changed in the way we plan and deliver radiotherapy and an understanding is required of the differences between adult and paediatric cancers and the consequences of treatment. With continual technological advances such as IMRT and VMAT the ability to optimise plans with sharp dose gradients has dramatically improved, reducing the amount of dose received by normal tissue. However, in order to minimise target volumes for these increasingly conformal techniques, there is a requirement for increased IGRT to ensure accurate tumour localisation and patient set up. Over-utilization of RT verification systems and procedures could inflict a large amount of excessive radiation