ESTRO 2021 Abstract Book

S1655

ESTRO 2021

Conclusion In our preliminary experience, the use of Bra improved simulation, planning and positioning. It reduced the amount of loose soft tissue lateral to the breast, improving daily reproducibility and cosmetic outcome. This device application also reduced dose to heart and ipsilateral lung. Further cases are needed to confirm its effectiveness in treatment reproducibility and dosimetric parameters improvement. PO-1942 Application of SGRT in Prone Cervix Positioning Z. Cui 1 , X. Li 1 , J. Xie 1 , J. Zhu 1,1 , C. Liu 1 , Z. Li 1 , P. Liu 1 , Y. Wang 1 , Y. Yin 1 1 Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Department of Radiation Oncology, Jinan, China Purpose or Objective Purpose: SGRT has been using widely for patient positioning in different anatomical regions in supine position. We would like to evaluate its application in prone cervix positioning. Materials and Methods We analyzed 452 CBCT images of 20 patients, who were treated from June 2020 to Jan 2021 retrospectively. Each patient was positioning based on skin marking (Group A) and SGRT (Group B) every alternate day. There was a total of 248 and 204 sessions for Group A and B positioning approach respectively. All patient had one anterior marking and two lateral markings on their pelvis region and a pre-treatment ROI drawn on SGRT system from the arch of the back to the start point of buttock crack and covered half body separation bilaterally. Both CBCT translational and rotational shifts were recorded. Results The average and standard deviations of translational (lateral, longitudinal and vertical) and rotational (pitch, roll and yaw) shifts between Group A and B were 0.24±0.21cm, 0.44±0.38cm, 0.44±0.33cm, 1.85±1.16˚, 0.98±0.78˚, 0.84±0.72˚ and 0.20±0.15cm, 0.25±0.18cm, 0.19±0.14cm, 1.05±0.86˚, 0.67±0.65˚, 0.99±0.73˚. All directions are statistically significant (p<0.05) except in yaw direction. Conclusion Positioning using SGRT is superior than skin marking in prone cervix cases. SGRT is an effective and accurate tool aiding in prone cervix positioning. PO-1943 Radiotherapy for the vulvar region in frog-leg position: improving reproducibility and comfort. W. De Vos 1 , L. Van den Berghe 1 , L. Paelinck 1 , S. Vansteenkiste 1 , B. Depaepe 1 , S. Lauwers 1 , J. Mortier 1 , E. De Rijcke 1 , A. Van Damme 1 , K. Vandecasteele 1 1 UZ Ghent, Radiotherapy, Ghent, Belgium Purpose or Objective Despite international guidelines advise the use of frog-leg position in vulvar irradiation, many centers still use supine position. The frog-leg position is often uncomfortable and difficult to reproduce. Online imaging and the decision of Radiotherapists (RTTs) whether or not to reposition is time-consuming. We aim to find out which positioning-accessories enable us to realize the fastest, highest reproducible and most comfortable frog-leg positioning technique for the (mostly elderly) vulvar cancer patients and compare this with the currently used supine positioning technique. Materials and Methods We performed an observational study using fieldwork and a structured observation. The used positioning techniques are illustrated in figure 1. For frog-leg positioning a blue knee cushion, a vacuum mattress and an immobilization mask (all ORFIT industries) were used. For supine position, we used a red knee cushion (CIVCO industries). Five voluntary RTTs (mean age: 35y) underwent all 4 positioning techniques. Five patients (mean age: 72y) being treated for vulvar cancer were positioned using the blue knee cushion or the vacuum mattress. Per individual positioning device, reproducibility, time (T) (rapid positioning is indicative for the reproducibility and important for patient comfort) and comfort was scored. Reproducibility was scored by the investigators using a score from 1 (very difficult) to 5 (very easy) T: was measured using 3 time-frames: -T1: from the moment that the patient/volunteer lies on the table until the moment of correct positioning. -T2: on-line imaging and treatment. -T3: time to get the patient/volunteer from the treatment table.