Abstract Book

S1250

ESTRO 37

EP-2388 Use of helical tomotherapy for local treatment in metastatic breast cancer: single center experience L. Thery 1 , M. Amessis 1 , C. Adrien 1 , A. Fourquet 1 , Y.M. Kirova 1 1 Institut Curie, Radiotherapy, Paris, France Purpose or Objective Helical tomotherapy (HT) improves target coverage and dose homogeneity and allows sparing of the organs at risk (OAR) compared to standard techniques. For patients with metastatic breast cancer (MBC) heavily pretreated, reduce the overall burden of radiotherapy is a major challenge. This study assesses the impact of HT in terms of acute and late toxicity and the survival in metastatic breast cancer. Material and Methods We retrospectively reviewed data of 57 patients (pts) with metastatic breast cancer who were treated by HT between 2008 and 2015. Irradiated volumes included breast+/- boost, or chest wall, axillary lymph nodes (LN) +/- internal mammary nodes (IMN) +/- mediastinum LN (in case of involvement). All patients received normo fractionated radiotherapy, with or without concurrent systemic treatment. The median survival outcomes were estimated with the Kaplan-Meier methods. All toxicities were described using the Common Toxicity Criteria for Adverse Events v4. Results Fifty-seven pts with stage IV have been studied. Median age was 60 years (range 28-77). The median follow-up was 41 months (range 10.8-95.8). Three (4,5%) pts presented with chronic respiratory disease, 19 (28,7%) pts were smokers. The coverage of target volumes (PTV) was as follows : breast 51,8 Gy ; simultaneous integrated boost 63 Gy ; chest wall 50 Gy ; PTV lymph nodes 50,4 Gy ; mediastinum 50 Gy. Systemic treatments were administered concurrently with HT in 95% of cases. Hormonal therapy (45%) was the most commonly used concurrent systemic agent followed by the association Trastuzumab and Pertuzumab (19.6%) and the oral chemotherapy Cyclophosphamide (10.5%). Most pts experienced grade 1 and 2 skin toxicity, as follows: grade grade 1=30 (52.6%), grade 2=11 (19.3%). Only 2 pts experienced grade 3 skin toxicity (concurrent 5 Fluorouracile and Vinorelbine-HT) and their irradiation was interrupted for local care. There were 42 pts (73.7%) with grade 0 esophagitis, 11 pts (19.3%) with grade 1 and 4 pts (7%) presented with grade 2 esophageal toxicity. One patient receiving concurrent treatment with Trastuzumab and Pertuzumab had a decreased left ventricular ejection fraction (by 14% compared to the initial value). There was no case with grade 1-2 pulmonary fibrosis. No cardiac or lung late toxicity was observed. On 9 pts with tumor involving skin, HT led to significant clinical improvement in almost 89%. The median survival was 37.5 months [95% CI, 32.6 to 42.3]. Conclusion This retrospective study suggests that the use of HT to irradiate complex volumes in patients with MBC is well tolerated and is feasible in association with systemic treatments, thus allowing to benefit from its more homogeneous volume coverage that standard irradiation. Its low side effects and its efficacy seem to be an asset for the future. Larger prospective studies with longer follow-up are needed to confirm these results.

EP-2389 Clinical comparison between OSMS data and CBCT matched values for brain metastasis with SRS W. Vingerhoed 1 1 iridium cancer network, radiotherapy, Antwerpen, Belgium Purpose or Objective To evaluate the accuracy of a video-based optical surface imaging system for motion monitoring during stereotactic treatment of brain metastasis. Precise patient positioning and thus of the PTV is a prerequisite for e ff ective treatment with SRS for brain mets. The intra fraction motion should at least be within the CTV-PTV margin used. Conventional imaging modalities used to ensure exact positioning for treatment typically involve additional radiation exposure of the patient. Patient alignment and monitoring during treatment, without additional exposure, is provided by optical 3D surface scanning and registration systems. Typical SRS brain treatments with multiple couch angels limits the ability of CBCT verification during treatment. This paper aims to correlate the data obtained by the OSMS system with the internal shifts observed by the offline CBCT matches pre- and post treatment. Material and Methods Patients treated with stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (FSRT) were immobilized with a thermoplastic double shell open face mask and a SRS immobilisation system (Encompass ™ Immobilisation System and Encompass ™ SRS Fiberplast Q- fix). During treatment a video-based three-dimensional optical surface monitoring system was used to monitor the motion of a region of interest. This motion monitoring was done in 6 dimensions. A tolerance of 0.2 cm for linear directions and 0.5 degrees for rotational directions was set. If the optical surface monitoring system detected an exceeding of the set tolerance, treatment stopped automatically. If necessary, the physician decided to take a new CBCT. A total of 26 patients were followed for SRS or FSRT treatment between June 2017 and October 2017 with a total of 31 fractions evaluated for intra fractional uncertainties. Both CBCT and snapshots obtained with the OSMS were acquired at the start and stop of every treatment to compare both methods. In addition the average motion and SD during treatment was monitored to investigate the validity of pre- and post measurements for assessing intra fractional motion. Results A mean intra fractional shift of 0.02 cm in vertical (stand dev of 0.01), 0.03 cm in longitudinal (stand dev of 0.03), 0.02 in lateral direction (stand dev of 0.04). Only in one patient, set tolerance was exceeded and a new CBCT was taken which showed a lateral shift of 0.19 cm. delta Vrt delta Lng delta Lat delta Pitch delta Roll delta Rot

0.01 0.20

0.10

0.20

median 0.01 0.02

mean 0.02 0.03

0.02 0.22

0.14

0.27

St Dev 0.01 0.03

0.04 0.20

0.16

0.29

Max

0.05 0.10

0.19 0.90

0.60

1.30

Conclusion The CBCT data clearly shows that the intra fractional offset of all brain metastasis patients treated with SRS or FSRT was below the institution’s predefined threshold. The OSMS data obtained during treatment still needs a more detailed evaluation. For further analysis the approach was changed and real time data during