ESTRO 2021 Abstract Book

S579

ESTRO 2021

Conclusion The novel iCycle-Eclipse method for automated treatment planning was developed and validated on LA-NSCLC patients. A potential for sparing heart and esophagus dose for most patients compared to manual plans was revealed. The new method allows Eclipse to automatically generate plans that are close to Pareto-optimality. PD-0749 Tangential VMAT and IMRT for WBI compared using automated multi-criterial treatment planning L. redapi 1 , L. rossi 2 , L. marrazzo 3 , J. J.Penninkhof 4 , S. pallotta 5 , B. Heijmen 6 1 University of Florence, Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, Florence, Italy; 2 Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands; 3 University of Florence, Department of Experimental and Clinical Biomedical Sciences “Mario Serio”,, Florence, Italy; 4 Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands; 5 University of Florence, Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, Florence, Italy; 6 Erasmus MC Cancer Institute, Department of Radiation Oncology,, Rotterdam, The Netherlands Purpose or Objective A limitation of all published studies comparing VMAT and IMRT for whole-breast irradiation (WBI) is the use of manual planning, making results dependent on planner experience and allotted planning time. Moreover, sample sizes are always small, probably related to the manual planning workload. Comparisons for deep- inspiration breath-hold (DIBH) treatment were only performed in two small studies using manual planning and presenting diverging conclusions. The aim of this study was to use automated planning to systematically compare for a large cohort of left-sided breast cancer patients treated with DIBH two delivery techniques for WBI: 1) IMRT with two tangential fields, 2) VMAT with two small tangential arcs. Materials and Methods Forty-eight randomly selected left-sided breast cancer patients, treated with postoperative WBI in DIBH and daily CBCT setup correction, were included. Patients were clinically treated with a hybrid technique (tangential open and IMRT fields). Generation of autoIMRT and autoVMAT plans was performed with an in- house system for automated multi-criterial generation of deliverable IMRT and VMAT plans, which was configured for plan generation in line with clinical requirements. AutoIMRT and autoVMAT plans were compared in terms of dosimetric plan parameters, estimated excess relative risks (ERR) for toxicities, and delivery times, MUs, and delivery accuracy at a linac, the latter assessed with an Octavius phantom with a 2D- array729 (PTW Freiburg GmbH). Results Fig. 1 shows for most patients relatively large gains for autoVMAT compared to autoIMRT in PTV hot spots, heart and ipsilateral lung at the price of minor losses in contralateral breast and lung. Compared to autoIMRT , mean heart doses and mean ipsilateral lung doses in autoVMAT plans were on average reduced by 0.4 Gy (range: -0.2-1.6 Gy) and 2.0 Gy (range: -0.4-4.5 Gy), respectively with estimated average ERR reductions for major coronary events and ipsilateral lung tumors of 3% (range: -1%-12%) and 17% (range: -3%-38%), respectively. There were no statistically significant differences in ɤ passing rates, while a moderate increase in treatment time (68 vs 52 s) and an improvement in MUs (675 vs 273) for autoVMAT were observed. Fig. 2 presents for a selected patient autoVMAT and autoIMRT dose distributions, showing reduced ipsilateral lung and heart doses with autoVMAT and slightly enhanced contralateral breast dose. Conclusion For left-sided WBI in DIBH, autoVMAT with two tangential subarcs was overall favourable compared to autoIMRT with two tangential static fields . Although autoVMAT was favourable for most patients, for some patients, autoIMRT could have been a better choice because of a significantly lower contralateral breast dose. Automatic generation of an autoIMRT and an autoVMAT plan for each patient could be used for personalized