ESTRO 2022 - Abstract Book

S1474

Abstract book

ESTRO 2022

Results Absolute vertical setup deviations were ≤ 4 mm in 98 % and 97 % of the acquired MV images in DIBH and FB respectively (Figure 1). The setup deviations was found to be statistically significantly larger (p = 0.01) for patients treated in FB (median 2 mm) compared to DIBH (median 1 mm). The patient position correction based on the kV-kV setup led to yaw setup corrections within 1° and 2° in 56 % and 85 % of the treatment fractions, respectively (Figure 2). In 4 % of the treatment fractions the yaw setup corrections was above 3°, which would require patient repositioning.

Conclusion Setup of breast cancer patients based on planar kV-kV images was observed to be in good agreement with tangential MV images in both FB and DIBH. The setup deviation was statistical significantly larger for patients treated with FB compared to DIBH, however the difference in median was small (1 mm). With a kV-kV based setup it is possible to correct for yaw rotations, which based on the present study was above 2° in 15 % of the treatment fractions. Other advanatages using kV- kV for breast setup are visualization of surgical clips and heart.

PO-1675 Feasibility of robotic stereotactic body radiation therapy for palliative bile duct obstruction .

J. Seppälä 1 , J. Palmgren 1 , A. Pandey 2

1 Kuopio University Hospital, Radiotherapy Department, Kuopio, Finland; 2 University of Easter Finland, Department of Applied Physics, Kuopio, Finland Purpose or Objective It has been shown that high dose intraluminal high dose rate brachytherapy (BT) is superior to stent alone in terms of stent occlusion and mean survival in the palliative treatment of malignant bile duct obstruction [1, 2]. The most common complication associated with BT treatment has been duodenal ulceration, which could, in addition to high doses delivered, result from highly non-uniform dose distributions of BT treatments [2]. In this study, we evaluated the feasibility of CyberKnife (CK) radiosurgery system to deliver a single high dose to the stented area, allowing more flexibility in achieving high dose coverage and delivering accurate dose distribution in various treatment anatomies. Materials and Methods 3D printed phantoms along with dynamic motion CIRS phantom capable of resembling breathing motion were used for irradiating treatment plans created with Multiplan TPS and Oncentra Brachy TPS. Three different treatment geometries were simulated: A) straight, B) curved and C) branched stent (Fig 1). Four fiducial markers were attached around the metallic stents and the stents were inserted inside the phantoms. EBT3 radiochromic films were inserted in the middle of the split stents to measure the delivered 2D dose distributions. A 15 Gy single fraction dose irradiations were performed in static and moving conditions with the CK system and with the aid of Synchrony Respiratory Tracking System. With BT treatments, only a static phantom was used. All the irradiations were repeated twice and two films were irradiated simultaneously, thus four films in total for each scenario were irradiated and analysed. Results The global gamma index (±3mm / ±3%) was used to compare the agreement between measured and calculated 2D-dose distributions. The results are presented in Table 1. Overall, the agreement with CK irradiations was around 95%, with the exception of branched stationary phantom (84.3%). With BT the gamma agreement was also close to 95% with straight and branched geometries, but with the curved geometry the agreement was only 68.4%. This might be due the snaking effect of the source wire or catheter positioning inside the stent.