ESTRO 38 Abstract book

S1208 ESTRO 38

Conclusion Both techniques provided good target coverage and good organs-at-risk sparing. However, IMRT resulted in lower dose to the bladder.

Electronic Poster: RTT track: Image guided radiotherapy and verification protocols

EP-2190 MVCT in pediatric craniospinal radiotherapy F. Ferraro 1 , A. Lastrucci 1 , Y. Wandael 2 , C. Galeotti 2 , M. Vernaleone 2 , D. Greto 2 , G. Simontacchi 2 , P. Bonomo 2 , L. Livi 1 1 University of Florence, Department of biomedical- experimental and clinical sciences "Mario Serio", Florence, Italy; 2 A.O.U. Careggi, Radiotherapy, Florence, Italy Purpose or Objective This work reports the analysis of MVCT, system based on the image-guided radiation therapy (IGRT) in the tomography treatment, used for the initial setup verification in pediatric patients treated with craniospinal irradiation. The duration of the MVCT scanning time on the entire craniospinal axis is high and anesthesia in pediatric patients is required during this period. For this reason, the reduction of the scanning time is a great interest. The final aim of this work is the comparison between the results obtained from the matching of MVCT and two different kind of patient centering on CT: one based on the scan of the entire craniospinal axis (case 1) and the other based on the acquisition average of the reduced volume at the end and at the beginning of the scanning (case 2). Material and Methods During this study 7 pediatric patients treated with craniospinal tomotherapy was investigated (total amount of 105 MVCT). Shifts (mm) along the three principal axes (X-lateral, Y-longitudinal and Z-vertical) were acquired for each single fraction associated to the different patients obtained during the matching. In the first case (matching between MVCT and CT scan of the entire craniospinal axis) the shifts were controlled by the operator and the results were acquired in the automatic mode; after the shifts were reset. In the second case (matching between MVCT and the average CT scans of the reduced volume at the end and at the beginning of the scanning) the matching of MVCT and CT on two different parts was acquired. The analyzed sections were, respectively, the region from frontal sinus to the first thoracic vertebra and the region from the eleventh thoracic vertebra to the first lumbar vertebra. In this case the average of the scans at different positions was considered. The results obtained in the two different cases were compared. During the matching was only considered shifts of translations. Results The analysis confirms that there is only a slight difference between the two different methods, in some cases less than 1 mm, as reported in the table 1.

Table1

Box plot representation of the average values obtained from the two different matching on three different planes. Conclusion The good accordance of these data confirms the quality of the entire procedure, but other studies are necessary before the implementation of this procedure in the clinical protocols. In order to fulfill this goal the evaluation of the following parameters is mandatory: Accordance between the results obtained by two different operators: evaluation of the matching of the data obtained by two different operators. Validation by third observator : evaluation of the differences between the two kinds of MVCT obtained from the entire craniospinal axis and from the average of two reduced volumes (frontal sinus/ D1 and D11/L1). EP-2191 Daily Image Guided Radiotherapy -the relevance for patients with metastatic spinal cord compression L. Johansen 1 , D. Gasic 1 , V. Gram 1 1 The Finsen Center - Rigshospitalet, Radiation Oncology, Copenhagen, Denmark Purpose or Objective There are wide differences in pre-treatment verification for patients with metastatic spinal cord compression (MSCC). At our clinic, daily Image Guided Radiotherapy (IGRT) with cone beam computed tomography (CBCT) and volumetric modulated arc therapy has been standard practice for MSCC patients for almost a decade. It is seen as a great safety precaution that the treatment is delivered correctly. These patients often suffer from neurological and cancer related pain in various degrees, which can make precise positioning according to setup tattoos alone difficult. This setup uncertainty is compensated by daily setup correction in the form of a couch shift based on the pre-treatment CBCT scan. For patients treated in the lumbar region of the vertebral column there are also added positional uncertainties as a result of the setup tattoos being placed on the side of the thorax wall, and therefore, far from the target. In addition, there are no fixations used for this anatomical site. Daily IGRT with couch corrections for MSCC patients is not standard procedure for many radiotherapy clinics and the relevance of it is often discussed. Advantages of IGRT and couch corrections include the ability of reducing target volumes, as well as an added security in correct positioning-ensuring irradiation of the affected vertebra(s). By looking at the setup corrections made for each fraction, it is possible to estimate the standard deviation and through this evaluate how far off mark a treatment would have been without the use of IGRT. Material and Methods A total of 30 consecutive patients from early 2018 with MSCC in the lumbar region (proximal thoracic vertebras were sometimes included in the lumbar target) treated with 3 Gy X 10, 5 F/W were included. The CBCT based