ESTRO 2023 - Abstract Book

S2032

Digital Posters

ESTRO 2023

The significant changes in translational errors in Group A were in the X axis (P < 0 .03), while those in Group B were in the Z axis (P < 0 .036). As for in the 3D vector and rotational errors, there were no significant changes in either group. To compare between the groups, we found that the changes in errors in the Y axis (P < 0.048) and roll axis (P < 0.004) in Group A were significantly smaller than those in Group B. Conclusion During thermoplastic mask making, adjusting the patient’s cranial angle to ≤ 10° can provide better or similar treatment stability in translational and rotational axes compared to patients with a cranial angle >10°.

PO-2260 The effectiveness of SGRT and innovative pelvis positioning gadget for prone rectum RT patients

X. Chen 1 , A. Chen 1 , W. Cai 1 , X. He 1 , Y. Wang 1 , W. Diao 1 , L. Liu 1 , J. Zhu 1 , X. Jiang 1

1 Sun Yat-Sen University Cancer Center, Radiation Oncology, Guangzhou, China

Purpose or Objective Our institute has implemented SGRT as part of the positioning and treatment workflow for SRS/SRT, breast, thorax, and breast DIBH radiotherapy. Recently, we innovated a prone pelvis positioning gadget (PP) and would like to explore its effectiveness in combine with SGRT.

Materials and Methods Innovative Pelvis Positioning Gadget (PP)

The PP (Figure 1) was designed mainly to increase patient’s comfort and enhance the treatment reproducibility and stability. The chest area (yellow) was designed to better support the female breast contour. The hollow part (green) was shallower at the inferior part to push the small bowels superiorly. The height of this part was carefully considered to ensure patient’s abdominal region was not touching the couch top to avoid breathing-induced motion of the abdomen. The leg separator and indexing ankle support were designed to reproduce the leg positions. A vac-bag was usually placed on top of the PP in the pelvic region to increase the conformity and reproducibility.

12 rectum cancer radiotherapy patients were selected randomly. All patients were obliged to bladder and bowel protocols. The bowels are required to be emptied and bladder filling must fulfil the criteria of ±20% of the planned volume. Bladder scanner (Verathon, USA) was used before entering to the treatment room. Firstly, patient lied in prone position on PP and vac-bag. SGRT system (Vision RT, UK) was activated to provide the guidance for positioning. The region of interest ROI included the pelvic part only (Figure 2). The rotations of patient were adjusted by the therapists manually and ‘move couch’ function was applied to move the patient to the isocenter position automatically in 3D translational directions. CBCT was taken for the first 3 days and once a week subsequently. CBCT matching process included both auto- and manual- matching for the best outcome. All the CBCT 3D translational shifts were recorded and applied accordingly. A new reference surface was captured after every CBCT for monitoring. In the interest of investigating the positioning accuracy of SGRT, all CBCTs images were re-registered offline in 6D directions.