Tumour hypoxia is a known microenvironmental culprit for treatment resistance, tumour recurrence and promotion of metastatic spread. Despite the long-known existence of this factor within the tumour milieu, hypoxia is still one of the greatest challenges in cancer management. The transition from invasive and less reliable detection methods to more accurate and non-invasive ways to identify and quantify hypoxia was a long process that eventually led to the promising results showed by functional imaging techniques. Hybrid imaging, such as PET-CT, has the great advantage of combining the structural or anatomical image (offered by CT) with the functional or metabolic one (offered by PET). However, in the context of hypoxia, it is only the PET image taken after appropriate radiotracer administration that would supply hypoxia-specific information. To overcome this limitation, the development of the latest hybrid imaging systems, such as PET-MRI, enables a synergistic approach towards hypoxia imaging, with both methods having the potential to provide functional information on the tumour microenvironment. This study is designed as a systematic review of the literature on the newest developments of PET-MRI for the imaging of hypoxic cells in breast cancer. The analysis includes the affinity of various PET-MRI tracers for hypoxia in this patient group as well as the correlations between PET-specific and MRI-specific parameters, to offer a broader view on the potential for the widespread clinical implementation of this hybrid imaging technique.

Background. A group of cardiopathies (ischemic, arrhythmic, and pericardial cardiac events) were shown to be associated with doses received by heart substructures following radiotherapy, alerting about the importance of dosimetric evaluation of cardiac structures besides the heart. The aim of this study was to assess the dosimetry of heart and heart substructures of left-sided breast cancer radiotherapy to evaluate possible radiation-induced complications. Methods and Materials. The study enrolled 20 patients treated with 3D-conformal radiotherapy (3DCRT), while intensity-modulated (IMRT) and volumetric-modulated arc radiotherapy (VMAT) plans were simulated for comparative purposes. The organs at risk (OARs) of interest were the heart, ascending aorta, descending aorta, left ventricle, left atrium, right ventricle, right atrium, superior vena cava, inferior vena cava, and pulmonary artery. Results. The percentage of left ventricle included in the radiation field was >5% for all plans (8.92% 3DCRT, 8.30% IMRT, and 6.84% VMAT). A strong correlation between mean heart dose and the percentage of left ventricle overlapping with the radiation fields was observed in 3DCRT (r = 0.784) and IMRT (r = 0.755) plans, and a moderate correlation was shown between tumor volume and the percentage of left ventricle included in the radiation field for all plans. A moderate correlation was observed between body mass index and cardiac structures for the mean dose to the right ventricle (r = 0.640) in conformal plans and of heart (r = 0.528) and left ventricle (r = 0.669) in volumetric-modulated plans. Additionally, moderate to strong correlations were found between maximum heart distance and heart dose in both conformal and modulated plans. Conclusions. Considering possible occurrences of cardiac events during or postradiotherapy, monitoring the heart and its substructures and setting dosimetric thresholds for healthy tissues must be a priority to achieve a personalized and effective treatment.

This study aims to assess setup errors for patients immobilized on different board inclinations and to evaluate the effect of body mass index (BMI) and breast size on positioning errors. Furthermore, the dosimetric impact of setup errors on target and organs at risk was measured using three different irradiation techniques (3D conformal radiotherapy, intensity modulated and volumetric modulated arc radiotherapy). A cohort of 40 breast cancer patients was split into two groups as a function of immobilization board inclination: 20 patients immobilized on 7.5° inclination (group A) and 20 on 0° (group B). Systematic and random errors were determined with weekly portal and tangential images. A strong correlation between BMI and both systematic (r = 0.720) and random errors (r = 0.752) was observed in posterior direction for group B, while the correlation between breast size and setup errors showed a moderate association under systematic errors for right (r = −0.507) and left (r = 0.503) directions. The dosimetric impact of setup errors on target volume showed higher contribution from systematic than from random errors. Suboptimal coverage of target volume was more prominent in group A for all planning techniques (46.65Gy 3DCRT, 46.95Gy IMRT, 46.90Gy VMAT). Patients with high BMI could benefit from the inclined immobilization board with a higher frequency of image position verification. When comparing 3DCRT versus modulated techniques the ipsilateral lung is better spared with the latter, while the contralateral lung is more efficiently protected with conformal technique.