ESTRO 38 Abstract book

S715 ESTRO 38

The mean movement of the left lung between FB and DIBH was 1.5 ±2.4 mm to the left, 16.0 ± 4.0 mm in anterior, 12.2 ± 4.6 mm in caudal direction with a mean 3D movement of 20.8 ± 4.1 mm (Fig 1). Depending on the individual patients, the ratio between movements in anterior and caudal varied from 89% to -54%, but that had no effect on the resulting dose. Increased lung movement correlated only with an increase in irradiated lung volume.

are in line with historical data (Bartelink JCO 2007, Lancet Oncol 2015: moderate/severe fibrosis 28.1/30.4% at 10/20y). Local recurrence rate was 1.7/2.0/6.6/10.1% at 3/5/10/15y, second breast cancer rate was 3.8/6/10.4% at 5/10/15y, axillary recurrence rate was 0.5/1.5% at 5/8- 15y, metastasis rate was 4.1/6.7/14% at 3/5/10-15y and overall survival was 95.7/92.1/81.8/80.7% at 3/5/10/15y, which compares favorably to historical data (Bartelink JCO 2007, Lancet Oncol 2015: Local recurrence as first event 6.4/12/15% at 10/12/15y, metastasis 26% at 20y, overall survival 82/~73/59.7% at 10/15/20y). Conclusion IORT boost with low kV x-rays is a safe boost method for (high risk) breast cancer patients with a good local and distant control and acceptable toxicity rates during long- term follow-up. EP-1306 Gated treatment of left-sided breast cancer: evaluation of lung movement, irradiated volume and mass M. Oechsner 1 , M. Duesberg 1 , K. Borm 1 , J.J. Wilkens 1 , S.E. Combs 1,2,3 , M.N. Duma 1,2,3 1 Klinikum rechts der Isar- TU München, Department of Radiation Oncology, Munich, Germany ; 2 Deutsches Konsortium für Translationale Krebsforschung DKTK, Partner Site Munich, Munich, Germany ; 3 Institute of Innovative Radiotherapy, Department of Radiation Sciences- Helmholtz Zentrum München, Munich, Germany Purpose or Objective Treatment of left-sided breast cancer in deep inspiration breath-hold (DIBH), compared to free breathing (FB), was proved to reduce the dose to the heart and mostly also to the lung. For the evaluation of lung dose the dose mass histogram (DMH) seems to be more adequate than the dose volume histogram (DVH). The aim of this study was to compare DVH and DMH parameters for the left lung between treatment in FB and DIBH. Additionally, lung motion between FB and DIBH was analyzed. Material and Methods 31 left-sided breast cancer patients were retrospectively selected. Treatment plans were optimized on CT datasets in FB and DIBH with the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA). The CT datasets, structures and dose were transfered to the Matlab software (The MathWorks, Natick, MA) and DVH and DMH were calculated using self-written programms. Mean doses (Dmean) and volumes and masses receiving a certain dose (V5-45 and M5-45) were evaluated. Using deformable image registration of the open source software plastimatch we calculated deformation vector fields to analyze the movement of the left lung between FB and DIBH. Mean values for the movement in left-right, anterio-posterior and crasnio-caudal direction and a 3D vector were calculated and correlated to dose parameters. Data were statistically analysed using the wilcoxon test. Results The mean lung volume was 1432 ± 290 ml (mean ± standard deviation) in FB and 2581 ± 321 ml in DIBH. The mean lung density changed between FB and DIBH from 0.31 ± 0.05 g/cm 3 to 0.17 ± 0.03 g/cm 3 . Irradiation in DIBH resulted in a significantly reduced Dmean of the left lung: 10.0 ± 1.7 Gy in FB and 8.3 ± 1.5 Gy in DIBH (p<0.01). Relative volumes V5-45 were always smaller in DIBH than in FB (- 12% to -51%, Table 1). In contrast to that, absolute volumes V5-45 were larger in DIBH (29% to 63%), except for V45 (-11%). For the irradiated lung mass the mean M5- 45 were always larger in DIBH than in FB for both relative and absolute mass. However, some patients had an increased irradiated lung mass in DIBH (e.g. 4 patients for M20) or a decreased absolute irradiated lung volume in DIBH (e.g. 3 for V20).

Conclusion Treatment oft left-sided breast cancer in DIBH resulted mostly in lower doses to the lung. Despite an increase in absolute irradiated lung volume in DIBH the irradiated lung mass is reduced. But for some patients there can also be a reverse effect. The amount of lung movement depends on the individual patient and correlated only to the absolute irradiated lung volume. EP-1307 Deep inspiration breath-hold technique versus free breathing in RT treatment of left-sided breast N. Jankarashvili 1 , I. Sikharulidze 2 , R. Sreseli 3 , N. Kartvelishvili 4 , M. Topeshashvili 1 1 Academician F. Todua Medical Center-Research Institute of Clinical Medicine, Radiation Oncology, Tbilisi, Georgia ; 2 Tbilisi Cancer Center, Oncological Surgery, Tbilisi, Georgia ; 3 S. Khechinashvili University Hospital, Chemotherapy Department, Tbilisi, Georgia ; 4 S. Khechinashvili University Hospital, Oncological Surgery, Tbilisi, Georgia Purpose or Objective This study evaluates heart dose for deep inspiration breath hold (DIBH) versus free breathing (FB) technique in patients with left-sided breast cancer. For left-sided breast cancer patients, the heart, major coronary arteries, and left lung tend to be co-irradiated due to their proximity to the anterior chest wall. Therefore, radiotherapy can result in severe complications, and many