ESTRO 36 Abstract Book

S874 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective To accurately perform voluntary moderately deep inspiration breath hold (vmDIBH) radiation therapy it is essential to determine the position of the chest wall at the start of treatment and to monitor deviations during treatment. An in-house developed real-time automated monitoring system of the respiratory motion is implemented to verify the reproducibility and stability of the vmDIBH during breast cancer treatments. Material and Methods Patients with left sided breast cancer are guided to perform vmDIBH assisted by verbal instructions and an additional aid called the ‘breathing stick’ [1]. A 3D Kinect v2 camera (Microsoft, USA) was mounted in the treatment room to visualize the patient on the treatment couch. Software was developed to track and visualize the anterior–posterior motion of a small area of the surface of the thoracic wall in real time, allowing RTTs in the treatment room to verify the reproducibility and stability of the breath holds during treatment. The data of ten patients was analysed for reproducibility and stability. The formulas for reproducibility and stability were derived from Cerviño et al. with minor adaptations [2]. For reproducibility the standard deviation of the mean of each DIBH level was used. For stability all breath holds were fitted by first order polynomials, the slopes were multiplied by their breath hold lengths to find a range and all these ranges were averaged. Results A typical example of reproducible and stable vmDIBHs during a treatment fraction of a patient is shown in Figure 1.

respectively. DIFGI is benchmarked against Varian’s RPM until final validation of the device, but it is compatible with all treatment units and CTs.

Fifteen left-sided breast cancer patients have been recruited until now. If heart constraints can’t be fulfilled in free-breathing (FB), then patients are trained and undergo a second CT scan in DIBH using the DIFGI. The stability, repeatability, reproducibility and reliability of the method are studied. Two radiopaque markers, one on the mediastinum tattoo and another along the back, serve as a reference to measure breath amplitude (Fig.2). The stability and repeatability are measured on the DIBH CT scan. The reproducibility mean value, systematic, and random errors are determined by using daily kV images and weekly CBCTs. The reliability of the device is calculated as the failure ratio compared to RPM.

Figure 1: Typical example of five reproducible and stable vmDIBHs for one treatment fraction The analysed reproducibility and stability of vmDIBH treatment for then patients using the breathing stick is shown in Figure 2. The median reproducibility and stability were 0.9 mm and 1.1 mm, respectively.

We also analyse Dmean, V30 (cm 3 ), and V25 (%) for the heart in both techniques. Results Stability and repeatibility are below 1.7 and 3.3 mm in all cases, respectively. Repoducibility mean value is 1.7 mm, systematic error is 0.5 mm, and random error is 0.9 mm. DIFGI reliability is 95%. All failures are human errors occurred during the learning period. Dosimetric benefits compared to FB for the heart are: 3.0 vs 6.7 Gy for mean dose, 14.9 vs 53.4 cm 3 for V30, and 2.8 vs 9.5% for V25. Conclusion DIFGI is a simple, friendly, low-priced external respiration-monitoring device compatible with all treatment units and CTs. The preliminary results of the stability, repeatability, reproducibility, and dosimetrical benefits are encouraging. The reliability of the device depends on human intervention so we plan to interlock it with the treatment unit. EP-1617 Reproducibility and stability of vmDIBHs during breast cancer treatment measured using a 3D camera M. Kusters 1 , F. Dankers 1 , R. Monshouwer 1 1 Radboud university medical center, Academic Department of Radiation Oncology, Nijmegen, The Netherlands

Figure 2: Clinical measurements of the reproducibility and stability of the vmDIBHs for ten patients Conclusion The reproducibility and stability of the chest wall can be accurately measured using the in- house developed monitoring system. vmDIBH in combination with the breathing stick shows good stability and reproducibility which are comparable to the results in the study of Cerviño et al. [2]. In this work the current results are limited to ten patients; we continue to, acquire more data for future analyses. The breathing stick is routinely used in our clinic; currently we use the breath hold monitoring system to test whether using this tool has an added value.