ESTRO 2020 Abstract book

S1096 ESTRO 2020

PTV coverage (D 98 homogeneity (D 2cc

GTV and lungs-PTV contours were generated for dosimetric comparison using the following minor to major toxicity in house dose constraints: 35%

> 95% of prescribed dose) and dose

< 107% of prescribed dose) were similar for all techniques. The highest PTV conformity, represented by the CN, was obtained with IMRT/SIB-IMRT and VMAT/SIB-VMAT. IMRT plans reduced the lung volume receiving 10 Gy (lung V10 ), 20 Gy (lung V20 ) and mean lung dose (lung mean ), p ≤ 0.05, compared to both 3D-CRT and VMAT. VMAT had the lowest mean heart dose (heart mean ), p < 0.05, and both IMRT and VMAT showed less heart volume receiving 30 Gy (heart V30 ), p < 0.00 compared to 3D-CRT (Table I). For definitive treatment with dose escalation, SIB-IMRT and SIB-VMAT had significantly lower heart V30 , p < 0.00, but similar heart mean , p = 1.00/0.058, compared to the clinically treated 3D-CRT delivered to 41.4 Gy. Lung V10 was similar for SIB-IMRT and 3D-CRT, p = 0.75. For the other lung parameters, 3D-CRT was superior to both SIB-IMRT and SIB-VMAT, p < 0.00. SIB-IMRT was superior to SIB-VMAT for the parameter lung V10, lung V20 and lung mean, p < 0.00 (Table II). Clinically acceptable dose-constraints were achieved for 14 out of 20 patients.

Conclusion IMRT is the optimal radiation technique for pre-operative chemoradiotherapy for distal esophageal cancer in our clinic. For definitive treatment with dose escalation, SIB- IMRT is the preferred technique, and makes dose escalation within the clinically accepted dose-constraints feasible. PO‐1871 Introducing proton therapy for thoracic cancer; an RTT perspective P. Klinker 1 , E. Blokzijl 1 , H.P. Van der Laan 1 , E. Korevaar 1 , R. Wijsman 1 Purpose or Objective The purpose was to report on the challenges encountered and solutions found during the implementation of intensity modulated proton therapy (IMPT) for thoracic cancer in our institution. As protons are more sensitive to inter- and intrafractional uncertainties and adequate target 1 UMCG University Medical Center Groningen, Radiotherapy, Groningen, The Netherlands