ESTRO 2022 - Abstract Book

S586

Abstract book

ESTRO 2022

Conclusion The dosimetric comparison carried out in this study suggests that MRgRT for partial irradiation of the uterine cervix is feasible and linked to dose reduction to all OARs. The observed dosimetric advantages could reduce toxicity rates and be advantageous especially in young patients. However, the real clinical impact of this approach must be investigated prospectively.

Poster Discussion: 15: Advances in patient care & treatment verifications

PD-0651 SGRT with Innovative Open-face Mask and Mouth Bite: Management of Patient Motion in SRS and SRT.

X. Jiang 1 , J. Liu 1 , X. Huang 1 , L. Liu 1 , L. Lin 1 , Y. Wang 1 , W. Diao 1 , W. Cai 1 , C. Lin 1

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

Purpose or Objective We would like to evaluate the inter- and intra-fractional motion of SG-SRS/SRT patients in combination of these immobilization devices. Materials and Methods Open-face mask (OM): We worked with local thermoplastic vendor (Klarity, China) to innovate an open-face mask which is compatible to our existing baseplate. In this process, we reviewed its shrinkage, rigidity, and the open area dimension. The open area needed to be sufficient for non-coplanar SGRT monitoring as well as maintaining its rigidity. Mouth bite (MB): 200 Chinese patients’ dental moulds were retrieved from department of dental and measured. The measurements were taken based on the curvatures of the upper and lower arches of the moulds. According to the collected data, 3D printing MB holders were made using ABS resin medical approved materials. Silagum-putty (DMG, Germany) was used for dental impression. 21 patients who were treated with SRS (4) or SRT (17) were included in this study. 4 to 5 non-coplanar fields of VMAT technique were applied to all patients. Before SGRT system (Vision RT, UK) was used to align the patient to the accuracy of less than 1mm and 1° in translational and rotational directions, the customised MB was inserted. Subsequently, the OM was put over patient’s head gently and locked. Fine tuning was done according to SGRT system to sub-millimeter accuracy. CBCT was acquired before each treatment session and shifts were applied. After that, a reference capture was taken on SGRT system. The patient was monitored by the SGRT system during the whole course of the treatment. Lastly, a CBCT was taken at the end of the treatment. All CBCT data in 6 degrees of freedom were recorded. The CBCT taken before the treatment (CBCTb) was considered as the inter-fractional positioning errors while the CBCT taken after the treatment (CBCTa) was considered as the intra-fractional motion. Results 40 CBCTb and CBCTa images were analysed. The average and standard deviations of both inter-fractional positioning errors(Table 1) and intra-fractional motion(Table 2) were 0.04±0.03cm, 0.07±0.05cm, 0.05± 0.04cm, 0.39±0.27°, 0.27±0.20°, 0.28±0.27° and 0.03±0.02cm, 0.03±0.03cm, 0.02±0.02cm, 0.12± 0.20°, 0.13±0.13°, 0.07±0.14° in lateral, longitudinal, vertical, pitch, roll and rotation directions. Both inter- and intra-fractional motion were all within 1mm and 0.5°. In all treatments, SGRT data also showed sub-millimeter movement which were in-line with the data analysis of CBCTa. However, the correlation between two datasets were not studied in this work.