ESTRO 36 Abstract Book

S985 ESTRO 36 2017 _______________________________________________________________________________________________

Conclusion The reduction of the longitudinal margin from 4 cm to 3 cm can significantly reduce the dose to lungs, while the reduction to 2 cm can also reduce doses to the heart. Despite clinical benefit and oncologic outcome remain unclear, reduction of the longitudinal margins might provide the opportunity to reduce side effects of CRT for SCC in upcoming studies. EP-1824 Elective breast RT including level I & II lymph nodes: A planning study with the humeral head as PRV J. Van der Leer 1 , K. Surmann 1 , M. Van der Sangen 1 , M. Van Lieshout 1 , C.W. Hurkmans 1 1 Catharina Ziekenhuis, Radiotherapy, Eindhoven, The Netherlands Purpose or Objective The aim of this planning study was to determine a new technique for elective breast radiotherapy and level I and II lymph nodes following the new ESTRO delineation consensus guidelines. According to these guidelines the humeral head should be spared by introducing a planning risk volume (PRV) of the humeral head and connective tissue 10 mm around it. Material and Methods We included ten left sided breast cancer patients in our planning study in Pinnacle 3 v9.8. Each patient was planned with 16 x 2.66 Gy on the breast PTV (PTVp) and the elective level I and II lymph nodes (PTVn). We compared three treatment planning techniques: high tangential field (HTF), 6-field IMRT and VMAT. The HTF technique consisted of two open beams with extra segments and the cranial and posterior border was extended to include PTVn. Some of the leaves were closed to spare the humeral head + 10 mm around it (hh+10). For the IMRT technique we added four additional fields to the high tangential fields (gantry angle of 330, 30, 80 and 170 degrees) to ensure coverage of the cranial part of the breast and lymph nodes. The caudal border of these additional fields was set 1 cm below the attachment of the clavicle at the sternum. The third technique was a dual arc VMAT from 305 to 180 degrees. The plans were made by inverse planning, achieving a PTVp coverage of V95% ≥ 97% and a PTVn V90% ≥ 95%. Additionally, the dose to the lungs, heart and right breast (OARs) has been minimized. hh+10 was included with an objective of V40Gy < 1 cm 3 for all three techniques. Results HTF resulted in an average PTVp V95% of 97.2% and an average PTVn V90% of 90.4% (see Table 1 and Figure 1). With the additional fields of the IMRT technique the coverage of PTVn increased significantly to on average 98% (p=0.01) while PTVp did not vary significantly (p=0.92). The dose to the OAR was comparable between the HTF and IMRT techniques. When using VMAT the coverage of the PTVn was on average 99.5% (p<0.01 compared to the HTF and p=0.19 compared to IMRT). The dose to the OARs however increased as well. The mean dose to the contralateral breast increased significantly from 0.6 Gy with HTF and IMRT to 2.3 Gy with VMAT (p<0.01 for both).

Conclusion Both the 6-field IMRT and the VMAT technique can be used to spare the humeral head and surrounding tissues as aimed for in the ESTRO guidelines while still achieving proper target coverage. The IMRT technique discussed in our study resulted in a lower dose in the OARs and consequently this technique has been implemented in our institute. EP-1825 Evaluation for the usability of the Varian Standard Couch modeling using Treatment Planning System Y.M. Yang 1 , Y.M. Song 1 , J.M. Kim 1 , J.M. Choi 1 , B.K. Choi 1 1 Samsung Medical Center, Radiation Oncology, seoul, Korea Republic of Purpose or Objective When a radiation treatment, there is an attenuation by Carbon Fiber Couch. In this study, we tried to evaluate the usability of the