Transient dilutional acidosis but no lactic acidosis upon cardiopulmonary bypass in patients undergoing coronary artery bypass grafting.

INTRODUCTION: Dilutional acidosis may result from the introduction of a large fluid volume into the patients' systemic circulation, resulting in a considerable dilution of endogenous bicarbonate in the presence of a constant carbon dioxide partial pressure. Its significance or even existence, however, has been strongly questioned. Blood gas samples of patients operated on with standard cardiopulmonary bypass (CPB) were analyzed in order to provide further evidence for the existence of dilutional acidosis. MATERIAL AND METHODS: Between 07/2014 and 10/2014, a total of 25 consecutive patients scheduled for elective isolated coronary artery bypass grafting with CPB were enrolled in this prospective observational study. Blood gas samples taken regularly after CPB initiation were analyzed for dilutional effects and acid-base changes. RESULTS: After CPB initiation, hemoglobin concentration dropped from an average initial value of 12.8 g/dl to 8.8 g/dl. Before the beginning of CPB, the mean value of the patients' pH and base excess (BE) value averaged 7.41 and 0.5 mEq/l, respectively. After the onset of CPB, pH and BE values significantly dropped to a mean value of 7.33 (p < 0.0001) and -3.3 mEq/l (p < 0.0001), respectively, within the first 20 min. In the following period during CPB they recovered to 7.38 and -0.5 mEq/l, respectively, on average. Patients did not show overt lactic acidosis. CONCLUSIONS: The present data underline the general existence of dilutional acidosis, albeit very limited in its duration. In patients undergoing coronary artery bypass grafting it seems to be the only obvious disturbance in acid-base homeostasis during CPB.

Comparison of IMRT and VMAT plans with different energy levels using Monte-Carlo algorithm for prostate cancer.

PURPOSE: To make dosimetric comparisons of volumetric-modulated arc therapy (VMAT) and 7-field intensity-modulated radiotherapy (IMRT) with dynamic MLCs using the Monaco treatment planning system with Monte Carlo algorithm. MATERIALS AND METHODS: Single-arc VMAT and 7-field IMRT treatment plans were compared for 12 intermediate risk prostate cancer patients treated with prostate and seminal vesicle radiotherapy. For all patients, the prescribed dose was 78 Gy delivered in 39 fractions. The dosimetric data of IMRT and VMAT plans with 6, 10 and 15 MV energies were compared. The comparison was made for target volume, organs at risk (OAR) doses, and for monitor units (MU). RESULTS: The normal tissue surrounding the target were lower in VMAT plans compared to IMRT plans. VMAT plans achieved lower doses to all OARs for nearly all dosimetric endpoints. VMAT plans achieved 9.4, 9.0 and 7.0 % relative decrease in MUs required for RT delivery, for 6, 10 and 15 MV energy levels, respectively. The target volume and OAR dosimetric values did not differ significantly between 6, 10 and 15 MV photon energies. CONCLUSION: VMAT plans were found to be dosimetrically equivalent to IMRT plans for prostate cancer patients, with better rectum and bladder sparing and fewer MUs required.

CT- versus coregistered FDG-PET/CT-based radiation therapy plans for conformal radiotherapy in colorectal liver metastases: a dosimetric comparison.

PURPOSE: Our aim was to compare computed tomography (CT) and coregistered [(18)F]-fluorodeoxyglucose positron emission tomography CT-(FDG-PET/CT) based delineation of gross tumor volume (GTV) in unresectable colorectal liver metastasis (CRLM). MATERIALS AND METHODS: Fifty-four patients with unresectable CRLM were enrolled but 16 were excluded due to detection of additional hepatic metastases in ten on PET/CT scans, precluding radiotherapy because of transcendent critical organ doses beyond tolerable limits; and of extrahepatic metastases in six. For 38 eligible patients, both CT and PET/CT images were acquired, and two 3D conformal plans were made using the CT and FDG-PET/CT fusion data sets. Radiotherapy plans (RTP) and doses to critical organs were analyzed. RESULTS: Comparisons between two RTPs revealed need for change in GTV in 31 of 38 analyzable patients (81.6 %). In 25 (65.8 %) patients, GTV was significantly increased, with a median of 33.2 % (p < 0.001), whereas median 12.8 % decrease in six (15.8 %) (p < 0.001). There were no clinically meaningful differences in critical organ doses. CONCLUSION: Coregistered FDG-PET/CT may improve delineation of GTV and theoretically reduce the likelihood of geographic misses in unresectable CRLM. Additionally, integration of FDG-PET/CT in the initial assessments of CRLM may spare almost one third of patients from potentially futile radical interventions.

Evaluation of field-in-field technique for total body irradiation.

PURPOSE: To evaluate the clinical use of a field-in-field (FIF) technique for total body irradiation (TBI) using a treatment-planning system (TPS) and to verify TPS results with in vivo dose measurements using metal-oxide-semiconductor field-effect transistor (MOSFET) detectors. METHODS AND MATERIALS: Clinical and dosimetric data of 10 patients treated with TBI were assessed. Certain radiation parameters were measured using homogenous and regular phantoms at an extended distance of 380 cm, and the results were compared with data from a conventional standard distance of 100 cm. Additionally, dosimetric validation of TPS doses was performed with a Rando phantom using manual calculations. A three-dimensional computed tomography plan was generated involving 18-MV photon beams with a TPS for both open-field and FIF techniques. The midline doses were measured at the head, neck, lung, umbilicus, and pelvis for both open-field and FIF techniques. RESULTS: All patients received planned TBI using the FIF technique with 18-MV photon energies and 2 Gy b.i.d. on 3 consecutive days. The difference in tissue maximum ratios between the extended and conventional distances was <2%. The mean deviation of manual calculations compared with TPS data was +1.6% (range, 0.1-2.4%). A homogenous dose distribution was obtained with 18-MV photon beams using the FIF technique. The mean lung dose for the FIF technique was 79.2% (9.2 Gy; range, 8.8-9.7 Gy) of the prescribed dose. The MOSFET readings and TPS doses in the body were similar (percentage difference range, -0.5% to 2.5%) and slightly higher in the shoulder and lung (percentage difference range, 4.0-5.5%). CONCLUSION: The FIF technique used for TBI provides homogenous dose distribution and is feasible, simple, and spares time compared with more-complex techniques. The TPS doses were similar to the midline doses obtained from MOSFET readings.

Dosimetric comparison of the field-in-field technique and tangential wedged beams for breast irradiation.

PURPOSE: To analyze tangential wedged beam and field-in-field (FIF) technique doses using dose-volume histograms and conformality indices for target volume and healthy tissues within the irradiated volume. MATERIALS AND METHODS: Thirty patients treated with breast-conserving surgery and postoperative whole breast radiotherapy were enrolled. Three plans were generated: a standard tangential plan with either one outer field wedge or bilateral wedges, and an FIF plan. Three indices were used: the dose homogeneity index (DHI), PTV dose improvement index (PDI(index)) and geometric conformity index (g). Also ipsilateral lung, heart and contralateral breast doses were compared for each plan. RESULTS: Dose homogeneity index was significantly lower for the FIF (0.117 ± 0.021) than for the single wedge (0.131 ± 0.025, p = 0.02) and double wedged plan (0.128 ± 0.025, p = 0.04), respectively. The g was significantly less in the FIF (0.70 ± 0.14) compared to the wedge plans (0.80 ± 0.17, p = 0.02 and 0.83 ± 0.16, p = 0.003). Contralateral breast doses were significantly lower in the FIF plan. The FIF plan significantly lowered MU compared to both the single wedge and bilateral wedge plans. CONCLUSION: The dose distribution within the target was more homogenous, and the doses for healthy tissue were less in the FIF plan compared to the tangential wedge plans.

Radiation dose distribution in the external auditory canal with different prosthetic materials: a clinical report.

Radiotherapy (RT) is an essential component of cancer treatment and aims to deliver higher doses at target volumes and lower doses to surrounding organs to achieve higher tumor control with fewer side effects. Significant dose heterogeneities can occur during treatment of irregular surfaces with electron beams, especially in head, neck, and breast tissue. The external ear and external auditory canal have irregular surfaces, which may cause dose heterogeneity, primarily resulting in excessive doses in the normal tissues lining and adjacent to the ear canal. The purpose of this clinical report is to describe the use of an acrylic resin and an elastomeric material to fill the air cavities of the external auditory canal and compare the dosimetric parameters. The complications that occur after electron-beam therapy of the ear canal can be significantly reduced by filling the ear cavity with acrylic resin, which is a simple, feasible, and cost-effective method.

Comparison of rectal volume definition techniques and their influence on rectal toxicity in patients with prostate cancer treated with 3D conformal radiotherapy: a dose-volume analysis.

BACKGROUND: To evaluate the impact of four different rectum contouring techniques and rectal toxicities in patients with treated with 3D conformal radiotherapy (3DCRT). METHODS: Clinical and dosimetric data were evaluated for 94 patients who received a total dose 3DCRT of 70 Gy, and rectal doses were compared in four different rectal contouring techniques: the prostate-containing CT sections (method 1); 1 cm above and below the planning target volume (PTV) (method 2); 110 mm starting from the anal verge (method 3); and from the anal verge to the sigmoid flexure (method 4). The percentage of rectal volume receiving RT doses (30-70 Gy) and minimum, mean rectal doses were assessed. RESULTS: Median age was 69 years. Percentage of rectal volume receiving high doses (>or= 70 Gy) were higher with the techniques that contoured smaller rectal volumes. In methods 2 and 3, the percentage of rectal volume receiving >or= 70 Gy was significantly higher in patients with than without rectal bleeding (method 2: 30.8% vs. 22.5%, respectively (p = 0.03); method 3: 26.9% vs. 18.1%, respectively (p = 0.006)). Mean rectal dose was significant predictor of rectal bleeding only in method 3 (48.8 Gy in patients with bleeding vs. 44.4 Gy in patients without bleeding; p = 0.02). CONCLUSION: Different techniques of rectal contouring significantly influence the calculation of radiation doses to the rectum and the prediction of rectal toxicity. Rectal volume receiving higher doses (>or= 70 Gy) and mean rectal doses may significantly predict rectal bleeding for techniques contouring larger rectal volumes, as was in method 3.