ESTRO 2020 Abstract book

S1079 ESTRO 2020

Longitudinal axis 0.02 cm (range ‐0.3 to 0.2 cm), Lateral ‐ 0.01 cm (range ‐0.1 to 0.1 cm), Vertical 0.03 cm (range ‐ 0.2 to 0.5 cm), Roll 0.17° (range ‐2.7 to 2.1°), Pitch 0.59° (range ‐1.8 to 5°) and yaw 0.04° (range ‐1.7 to 2.5°). Conclusion This experience is showing that this immobilization device is a feasible and efficient for patients treated with radiotherapy for Central Nervous system disease. Additionally, patient comfort and preparation time from RTT are considered acceptable. Future application with surface guided radiotherapy is going to confirm our data. PO‐1842 Set‐up accuracy of BrainLab immobilization mask for intracranial stereotactic radiotherapy C. Di Carlo 1 , M. Valenti 2 , S. Costantini 1 , F. Cucciarelli 1 , F. Fenu 1 , L. Vicenzi 1 , S. Di Biase 1 , S. Maggi 2 , G. Mantello 1 1 Ospedali Riuniti Ancona, Radiotherapy Department, Ancona, Italy ; 2 Ospedali Riuniti Ancona, Medical Physics, Ancona, Italy Purpose or Objective The purpose of this study was to evaluate inter and intrafraction setup accuracy of the BrainLAB stereotactic immobilization mask for intracranial stereotactic radiotherapy (SR) and to calculate a margin from Gross Tumor Volume (GTV) to Planning Target Volume (PTV) to compensate the residual set up error. Material and Methods We report data of 10 patients underwent intracranial stereotactic radiotherapy for secondary brain lesions. Radiotherapy treatment workflow included: 1)BrainLab mask preparation for patient immobilization; 2) Planning CT; 3) Diagnostic contrast‐enhanced magnetic resonance imaging (MRI) acquired with 1 mm slice thickness;4) Target volume definition: GTV was defined on diagnostic MRI fused with planning‐CT. GTV was expanded to 1 or 2 mm to generate PTV. Before treatment delivery CBCT was acquired and automatically co‐ registrated with planning‐CT to correct set up errors (translations and rotations). After set‐up correction, ExacTrac X‐ray 6D imaging were obtained and registered with the corresponding DRRs to evaluate residual set‐up errors. Bone matching algorithm was used to all registrations. According to our protocol the 6D ExacTrac tolerance was set to rotation < 1° and translational shift < 1 mm. During treatment ExacTrac X‐ray images were taken at each couch position. Mean and standard deviation of translational and rotational errors were calculated to obtain systematic and random errors. Results RESULTS: The interfraction systematic error registered with CBCT was 0.9 mm both for vertical and longitudinal shifts and 0.5 mm for lateral direction. About rotational, systematic errors was 0.72°, 0.46° and 0.61° for rotation, roll and pitch respectively. The random error was 0.6 mm, 0.8 mm and 0.3 mm for vertical, longitudinal and lateral shifts and 0.35°, 0.31°, 0.51° for rotation, roll and pitch.The intrafraction systematic error measured with ExacTrac X‐ray imaging was 0.14 mm, 0.16 mm, 0.32 mm in the vertical, longitudinal and lateral directions, respectively. The systematic error in the rotation, roll and pitch was 0.25°, 0.08°, 0.23°. The random error was 0.24 mm, 0.40 mm, 0.32 mm for vertical, longitudinal and lateral shifts, and 0.25°, 0.21° and 0.28° for rotation, roll and pitch respectively. Applying Van Herk formula we calculated the set up margin which was inferior to 1 mm in all directions. Rotations were considered negligible assuming lesions with spherical shape and little volume. Conclusion Our CBCT data confirm the accuracy of BrainLab sterotactic mask in the interfraction error evaluation. Considering intrafraction errors evaluated with Exac Trac, we can assert that 1 mm GTV‐PTV margin is adequate for treatment.

CT emphasised. Bladder preparation was followed and an ultrasound performed. If the volume was <200ml it was reiterated that if this happened at CT they would not be scanned and their treatment delayed. Results 28 patients were included in the retrospective audit from 08/05/2017 to 16/06/2017. 21% had <200ml in their bladder at their CT scan. 12 patients were included in the pilot study between 16/10/17 and 01/12/17. After hydration advice, 8% of patients had bladder volumes of <200ml during the Pre‐Radiotherapy consultation. This evaluation was repeated from 29/01/18 to 09/02/18. 10 patients were included and after hydration advice, 0% had bladder volumes of <200ml. Conclusion A Pre‐Radiotherapy consultation appointment proved beneficial for prostate patients and is now standard practice. The reduction in lost CT scan appointments increased efficiency of the pre‐treatment service and prevented delays in patients starting treatment. PO‐1841 Efficacy of a new dedicated immobilization device for treatment of Central Nervous disease N. Giaj Levra 1 , V. Figlia 1 , R. Mazzola 1 , L. Nicosia 1 , F. Ricchetti 1 , M. Rigo 1 , D. Tomasini 2 , F. Cuccia 1 , L. Agostinelli 1 , R. Ruggieri 1 , F. Alongi 1,3 1 IRCCS Ospedale Sacro Cuore-Don Calabria, Radiation Oncology, Negrar, Italy ; 2 Spedali Civili, Radiation Oncology, Brescia, Italy ; 3 University of Brescia, University of Brescia, Brescia, Italy Purpose or Objective Immobilization devices are crucial to minimize patient uncertainty and positioning errors. Recently, a new has been developed in order to specifically treated patients with Central Nervous oncological disease (Solstice TM , CIVCO®). To date, few data are available on the efficacy and tolerability of this device in daily clinical practice. Aim of this prospective data collection is to report the intra and interfraction variations, patient and RTT comfort. Material and Methods The patient selection criteria for the use of this immobilization device were: age >18 years, diagnosis of primary brain tumor or intracranial metastatic lesions. Stereotactic intracranial radiotherapy was considered an exclusion criteria. In all patients, the immobilization device was assembled during CT simulation. A short questionnaire to the patient about conform of the device was completed at the end of the procedure. Additionally simulation setup time and RTT procedures have been evaluated. During the radiation treatment a pre‐ radiotherapy cone beam CT (CBCT) was performed to verify the correct position of the patients. After the end of the session, an additional CBCT was done in order to verify any possible variation in patient position. At least two pre and post treatment CBCT were done for each patient during the radiation treatment. Results Between October 2018 and October 2019, 35 patients (19 men and 16 women) with a diagnosis of intracranial oncological disease tumor were treated. Twenty (57%) patients had a diagnosis of brain metastases, while fifteen (43%) reported a primary central nervous systemic tumor. Median target volume was 97 cc (range 1.5‐1628 cc), while median dose prescription and number of fraction were 30 Gy (range 27 Gy‐60 Gy) and 10 (range 3‐10), respectively. A good comfort was reported excellent in 25 patients and good in 10 cases. Median time request to RTT to perform with Solstice TM was 8 minutes (range 6‐12 minutes). Total number of CBCT pre and post treatment were 360. Interfraction mean values were: Longitudinal axis 0.10 cm (range ‐0.37 to 0.8 cm), Lateral 0.01 cm (range ‐1.1 to 1.09 cm), Vertical ‐0.01 cm (range ‐1.4 to 0.5 cm), Roll 0.04° (range ‐1.6 to 2.2°), Pitch 0.25° (range ‐1.6 to 3°) and yaw 0.19° (range ‐3.4 to 4.2°). Intrafraction mean values were: