Eclipse treatment planning system

All IMRT plans were generated using the Eclipse Treatment Planning System (TPS) (v8.6; Varian Medical Systems, Palo Alto, CA, USA). Beam and collimator angles were chosen at the discretion of the radiation therapist and utilised five to seven coplanar static step-and-shoot fields.
Optimisation parameters were set according to departmental protocol and used physical/dose–volume-based objectives. OAR and non-target tissue (NTT) dose constraint objectives were used to reduce OAR maximum doses and hot spots outside the PTV respectively. Inhomogeneity corrections were applied and dose–volume histogram (DVH) data were generated. Final calculations were made using Eclipse AAA algorithm version 8.6 on an Elekta Synergy beam model using 1 centimetre (cm) multileaf collimators (MLC).

The Varian Eclipse treatment planning system (TPS) was used to prepare the two dynamic techniques (IMRT and VMAT) with an anisotropic analytical algorithm (AAA). The IMRT plans consisted of nine sliding window beams (0°, 40°, 80°, 120°, 160°, 200°, 240°, 280° and 320°). The VMAT plans had four partial arcs (235–125 collimator 30 and 330 clockwise arcs, 125–235 collimator 30 and 330 contraclockwise arcs). Both plans were calculated for 6 MV beam as it was only one output energy for CyberKnife. It was important to compare IMRT and VMAT under the most similar conditions to CK. Additional artificial structures were created to prepare a more suitable and conformal treatment plan.
Figure 1 shows the dose distributions for a patient on a transversal scan showing the IMRT (Figure 1A) and VMAT (Figure 1B) treatment plans. Figure 1C shows the CyberKnife plan for the same patient.

This retrospective study utilized thirty anonymized planning computed tomography (CT) datasets of early-stage female breast cancer patients previously treated with WBRT. To maintain diversity of breast sizes and shapes, 13 right-sided and 17 left-sided cases with various breast volumes and separations were selected (Table 1). Every identifiable patient data was replaced with unique numbers as part of de-identification step, according to the centre’s ethics protocol.
Planning CT datasets were acquired using Philips CT Big Bore (Philips Healthcare, Best, The Netherlands) with patients lying supine on a lift-up board and arms raised above the head. Each slice of acquired CT datasets was 3 mm in thickness. Image registration and delineation of gross tumour volume (GTV), PTV and OARs were performed using Eclipse Treatment Planning System (TPS) (version 13.6.23; Varian Medical Systems, Palo Alto, CA, USA). GTV and PTV were contoured by the radiation oncologist. Contoured OARs included contralateral breast (CB), heart, liver, left lung, right lung, and total bilateral lungs. Lung volumes were contoured using auto-threshold function of the planning system. Heart volume was contoured based the heart atlas guidelines. Both CB and liver were delineated based on the visible breast and liver tissues, respectively.