Reduction in Doses to Organs at Risk and Normal Tissue During Breast Radiation Therapy With a Carbon-Fiber Adjustable Reusable Accessory.

PURPOSE: This pilot study (ClinicalTrials.gov NCT04543851) investigates a novel breast positioning device using a low density, high tensile carbon-fiber cradle to support the breast, remove the inframammary fold, and reduce dose to organs at risk for whole breast radiation therapy in the supine position. METHODS AND MATERIALS: Thirty patients with inframammary folds ≥1 cm or lateral ptosis in supine treatment position were planned with standard positioning and with a carbon-fiber Adjustable Reusable Accessory (CARA) breast support. Twenty patients received whole breast with or without regional nodal irradiation with 42.5 Gy in 16 fractions or 50 Gy in 25 fractions using CARA. Median body mass index was 32 in this study. RESULTS: CARA removed all inframammary folds and reduced V20Gyipsilateral lung, V105%breast, and V50% body, without compromising target coverage. Median (range) V20Gyipsilateral lung for whole breast radiation therapy was 12.3% (1.4%-28.7%) with standard of care versus 10.9% (1.2%-17.3%) with CARA (Wilcoxon P = .005). Median V105% breast was 8.0% (0.0%-29%) with standard of care versus 4.0% (0.0%-23%) with CARA (P = .006) and median V50% body was 3056 mL (1476-5285 mL) versus 2780 mL (1415-5123 mL) with CARA (P = .001). CARA was compatible with deep inspiration breath hold and achieved median V25Gyheart = 0.1% (range 0%-1.9%) for all patients with left breast cancer. Skin reactions with CARA were consistent with historical data and daily variation in treatment setup was consistent with standard supine positioning. CONCLUSIONS: CARA can reduce V105%breast, lung and normal tissue dose, and remove the inframammary fold for breast patients with large or pendulous breasts and high body mass index treated in the supine position, without compromising target coverage. CARA will undergo further study in a randomized controlled trial.

Ventilatory chemosensitivity in the chick embryo.

In the externally pipped chicken embryo, oxygen consumption through the chorioallantoic membrane (VO2CAM) ranged between 2 and 55% (mean approximately 24%) of that through the lungs (VO2lung). Hypercapnia (5'-10' of 2, 5, or 8% CO2) or mild hypoxia (15% O2) had minor effects on VO2, whereas moderate or severe hypoxia (10-5% O2) caused large drops of VO2. Hypoxia or hypercapnia delivered through the lungs increased pulmonary ventilation (VE), largely through increases in tidal volume (VT). Exposures of the whole embryo provoked VE responses either similar, or significantly higher, than with exposures of the lungs alone, because of greater increases in VT. The larger the VO2CAM, the smaller were the VE and VT responses when hypoxia or hypercapnia were delivered through the lungs. Hypoxic or hypercapnic exposures for longer periods of time (30'-40') gave qualitatively similar results. We conclude that in the externally pipped chick embryo (1) the increase in VT is the primary means of expressing the hypoxic or hypercapnic VE chemosensitivity, (2) hypometabolism contributes to the hypoxic hyperventilation, and (3) CAM gas exchange lowers the ventilatory effects of lung hypoxia or hypercapnia.

Effects of posture on the respiratory mechanics of the chick embryo.

In the chicken embryo, pulmonary ventilation and pulmonary gas exchange begin approximately one day before the completion of hatching. We asked to what extent the posture inside the egg, and the presence of the eggshell and membranes, may alter the mechanical behaviour of the respiratory system. The passive mechanical properties of the respiratory system were studied in chicken embryos during the internal pipping phase (rupture of the air cell) or the external pipping phase (hole in the eggshell). Tracheal pressure and changes in lung volume were recorded during mechanical ventilation, first, with the embryo curled up inside the egg, then again after exteriorization from the eggshell. In the internal pippers, respiratory system compliance increased and expiratory resistance decreased after exteriorization, whereas the mean inspiratory impedance did not change. In the external pippers, exteriorization had no significant effects on respiratory compliance, resistance, or impedance, and the values were similar to those of newly hatched chicks. We conclude that, in the chicken embryo, at a time when pulmonary ventilation becomes an important mechanism for gas exchange, the curled up posture inside the egg does not provide any significant mechanical constraint to breathing.

Metabolic control of pulmonary ventilation in the developing chick embryo.

In birds, during the period from the breaking of the air cell by the beak (internal pipping) to hatching, pulmonary ventilation (VE) begins and gas exchange is jointly provided by the lungs and the chorioallantoic membrane (CAM). We asked to what extent, during this phase of two concurrent gas exchange organs, changes in the embryo's metabolic needs were accompanied by changes in VE. The carbon dioxide and oxygen exchange rates (VCO2, VO2) through lungs and CAM were separately, but simultaneously, measured in chicken embryos at 20-21 days of incubation, while VE was calculated from the measurements of pressure oscillations in the air cell during breathing. During the last 24 h of incubation, lung VO2 and VCO2 gradually progressed as the corresponding CAM values declined. An increase in egg temperature (T) from 33 to 39 degrees C increased the embryo's total metabolic rate, especially when the lungs were the predominant gas exchange route. Whether metabolism increased because of the embryo's development or because of the increase in T, VE was linearly proportional to lung VO2 and VCO2, and not to the embryo's total metabolic rate. Hence, in the developing chick embryo, VE control mechanisms sense the peripheral tissue requirements via the gaseous component of cellular metabolism.