ESTRO 2020 Abstract Book

S1043 ESTRO 2020

identify the optimal photon radiotherapy technique for both pre-operative chemoradiotherapy and definitive treatment with dose escalation for distal esophageal cancer. Material and Methods 20 patients with distal esophageal cancer treated with 3D- CRT-plan to 41.4 Gy in 23 fractions were identified. A retrospective treatment planning study was preformed to compare IMRT and VMAT with the clinically delivered 3D- CRT plan. For definitive treatment we also investigated whether it was clinically acceptable to dose escalate to 50.4 Gy, and to the primary tumor simultaneously integrate a boost (SIB) to 56 Gy in 28 fractions. Six fields were used for IMRT/SIB-IMRT. For VMAT/SIB-VMAT we used two arcs with avoidance sectors over the lungs. All 100 treatment plans were evaluated with respect to PTV coverage, van’Riets Conformation Number (CN) and clinically relevant DVH metrics to the lungs and the heart. For statistical comparisons we used ANOVA for normally distributed variables, and Friedman ANOVA when the distribution was not normal. This QI project was approved by The Data Protection Officer in our hospital. Results PTV coverage (D 98 > 95% of prescribed dose) and dose homogeneity (D 2cc < 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

Abstract wirhdrawn

PO-1872 Dosimetric comparison of VMAT vs t-IMRT for patients with Aeroform Air Expanders undergoing PMRT M. Cokelek 1 , H. Ho 2 , T. Tran 2 , B. Subramanian 2 , R. Alinaghizadeh 3 , F. Foroudi 4 , J. Liew 5 , D. Neoh 5 , M. Law 6 , S. Jassal 6 , M. Chao 2 1 Radiation Oncology Victoria, Epping, Melbourne- Victoria, Australia ; 2 GenesisCare, Ringwood, Melbourne, Australia ; 3 Olivia Newton John Cancer Centre, Physics, Melbourne, Australia ; 4 Olivia Newton John Cancer Centre, Radiation Oncology, Melbourne, Australia ; 5 Olivia Newton John Cancer Centre, Heidleberg, Melbourne, Australia ; 6 Mitcham Breast and Endocrine Centre, Mitcham, Melbourne, Australia Purpose or Objective Many women who undergo an immediate breast reconstruction with implant (IBR-i) need an interim tissue expander. The Aeroform AirXpander is a novel tissue expander activated by remote control to release carbon dioxide (CO2) from an internal metallic reservoir to inflate the expander eliminating the need for the needle injections for saline expanders 1 . This provides the patient with control over the expansion process and makes the overall journey more convenient and more comfortable. However, the internal metallic reservoir is known to significantly impact dosimetry 2 . The aim of this study is to compare the PTV coverage and dose to organs at risk (OAR) with a subpectoral and prepectoral positioned AirXpander using a VMAT versus t-IMRT technique. Material and Methods