ESTRO 36 Abstract Book

S545 ESTRO 36 2017 _______________________________________________________________________________________________

Orfit Industries: Efficast® Push Pin)/Wedges 5 0 & 7 0 (Cablon Medical)/Head supports (2014/2015: CIVCO Medical solutions: Posifix® Supine Headrests, 2016 Orfit Industries: Raycast® Head supports regular density with lateral neck flaps). For each year, 10 patients with head-and-neck cancer were selected randomly. All patients had daily CBCT imaging (Varian Medical Systems). The position of both shoulders on the CBCT relative to the mask was quantified in inferior direction in Offline Review (Varian Medical Systems). Measurements were performed on the coronal plane, 1.5cm dorsal of the isocenter (Figure 1).

Purpose or Objective To further test the positioning accuracy of an optical surface monitoring device called Align RT for the treatment of breast cancer patients. The data will then be analyzed to determine if the daily positioning with Align RT is accurate enough to allow for fewer weekly MV imaging of breast radiotherapy patients. Material and Methods 16 breast cancer patients were treated using 3D tangential fields. Patients were positioned supine on the breast board using an optical surface detector (Align RT). After positioning, MV imaging and bone match on the chest wall was done to verify the patients position, and corrected accordingly. All shifted values were recorded. The Align RT system consists of 6 cameras, which acquire the patients’ position in 2D, and a computer vision algorithm, which reconstructs the image into 3D. The patients’ reference surface was imported from the CT scan and the region of interest of the treated area was selected. The patient was positioned by using the Monitoring mode in Align RT and driving couch values until pre-shift Align RT deltas were as close to zero as possible. The Vertical (VRT), Lateral (LAT), Longitudinal (LNG) shift values generated from the MV images equal to or less than 5mm were marked as falling within our accepted tolerance for breast patients. This data was further analyzed to conclude if it would be acceptably accurate enough to reduce daily imaging. Results Out of the 16 patients involved in the study, a total of 213 fractions were treated using Align RT. Of these fractions, 201 (94.4%) had MV shift values, in all directions, within our 5mm tolerance. 209 of 213 fractions (98%) were within a 6mm tolerance or less. The largest shift observed was 9.5mm in the lateral direction, however the most frequent axis that fell out of tolerance were VRT and LNG. The most failed fractions (fractions with shift greater than 5mm) observed from an individual patient was 3 out of her 25 recorded fractions. 9 of the 16 patients were treated with all fractions within tolerance. Conclusion The data was found to be very consistent across all patients, with 9 from 16 patients having all MV shifts equal to or less than 5mm in all directions after using Align RT for positioning and the remaining having minimal fractions outside this tolerance. This data suggests a strong argument for reducing daily imaging with breast patients being positioned with Align RT. Reducing daily imaging to 2-3 times per week in combination with daily positioning using Align RT would then be valuable in reduction of both excess dose to the patient and treatment time on the Linear accelerator. PO-0997 Improving shoulder positioning in a 5-points mask. L. Mesch 1 , S. Hol 1 , G. D'Olieslager 2 , C. Buijs 1 , D. Washington 1 1 Dr. Bernard Verbeeten Instituut, Department of Radiation Oncology, Tilburg, The Netherlands 2 Dr. Bernard Verbeeten Instituut, Department of medical Physics & Engineering, Tilburg, The Netherlands Purpose or Objective Immobilization and positioning are necessary in radiation therapy of head-and-neck patients. A 5-points mask offers stability, although large shifts of the shoulder (>1cm) routinely can occur. A wrong positioned shoulder can cause coverage loss or an increased critical structure dose. The purpose of this study was to decrease the shouldershifts by increasing the awareness of the RTT’s. Material and Methods In the period January 2014 till June 2016 head-and-neck patients were immobilized daily with a 5-points mask (2014/2015: CIVCO Medical solutions: Posicast®, 2016:

Results Three hundred CBCT scans (600 shoulder positions) were examined. Table 1 shows the shoulder shifts in inferior direction. In 2014 23% of the shoulders was positioned ≥15mm inferior relative to the mask. At the end of 2014 the results were presented at our institute. Extra awareness of the RTT’s resulted in a decrease of the shouldershifts ≥15mm (7%). After a second presentation in December 2015, the percentage of shifts ≥15mm decreased (3.5% vs. 7%) in 2016. The percentage of shifts 5mm ≤ x < 10mm increased relative to 2015 (34.5% vs. 24.5%). This might be due to lack of experience with the new type of masks.

Conclusion A presentation and discussion session is a simple and efficient way to create more awareness. Extra awareness of the RTT’s improved the setup of the shoulders in a 5- points mask, but the immobilization of the shoulders demands attention. The reason for the increase in shifts 5mm ≤ x < 10mm will be further investigated. PO-0998 Comparison of the accuracy of different pillow for radiation therapy of head and neck cancer C.Y. Lin 1 , W.H. Yu 1 , C.Y. Lin 1 , J.T.C. Chang 1 1 Chang Gung Memorial Hospital, Department of Radiation Oncology, Taoyuan, Taiwan Purpose or Objective Random error occurring in daily treatment is always a serious concern in fractionated radiotherapy (RT). Image guided radiotherapy can partially solve some of these problems. However, the curvature of the cervical spine is still a problem. Change of spine curvature can easily result in a deviation of more than 3mm. Therefore, we initiate this study to evaluate the accuracy of different pillow