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Aim. The purpose of this planning report is to compare dosimetric results of deep inspiration breath hold (DIBH) and free breathing (FB) set up in patients with synchronous bilateral breast cancer (SBBC) treated with adjuvant radiotherapy. Material and methods. Fourteen patients with early stage bilateral breast cancer were treated with breast conservative surgery. Bilateral breast planning treatment volume (PTV) and organs at risk (OARs) were delineated for DIBH and FB datasets on the planning computed tomography (CT). Volumetric modulated arc therapy (VMAT/RapidArc ®) plans were generated in the two set up modalities. During plan optimization the objectives were to obtain comparable target coverage, dose conformity and homogeneity with an acceptable dose levels for OARs: both lungs, heart, left anterior descending coronary artery (LAD) and thyroid. Results. The maximum and the mean dose to the heart were reduced in DIBH modality with an average of 19.2 Gy and 6.5 Gy versus 25.9 Gy and 8 Gy in FB. The mean dose to the sum of lungs was 13.3 Gy in DIBH modality versus 14.3 Gy in FB. We observed a better sparing of LAD in DIBH with a maximum dose of 14.5 Gy versus 18 Gy in FB modality. Conclusions. DIBH allows a better sparing of heart and LAD compared to FB modality; it provides better results in term of mean dose to the sum of lungs. The clinical impact on acute and late toxicity is under investigation.

BackgroundThe aim of this work was to evaluate detection of low-contrast objects and image quality in computed tomography (CT) phantom images acquired at different tube loadings (i.e. mAs) and reconstructed with different algorithms, in order to find appropriate settings to reduce the dose to the patient without any image detriment.MethodsImages of supraslice low-contrast objects of a CT phantom were acquired using different mAs values. Images were reconstructed using filtered back projection (FBP), hybrid and iterative model-based methods. Image quality parameters were evaluated in terms of modulation transfer function; noise, and uniformity using two software resources. For the definition of low-contrast detectability, studies based on both human (i.e. four-alternative forced-choice test) and model observers were performed across the various images.ResultsCompared to FBP, image quality parameters were improved by using iterative reconstruction (IR) algorithms. In particular, IR model-based methods provided a 60% noise reduction and a 70% dose reduction, preserving image quality and low-contrast detectability for human radiological evaluation. According to the model observer, the diameters of the minimum detectable detail were around 2 mm (up to 100 mAs). Below 100 mAs, the model observer was unable to provide a result.ConclusionIR methods improve CT protocol quality, providing a potential dose reduction while maintaining a good image detectability. Model observer can in principle be useful to assist human performance in CT low-contrast detection tasks and in dose optimisation.