Biological modelling of the radiation dose escalation effect of regional hyperthermia in cervical cancer.

BACKGROUND: Locoregional hyperthermia combined with radiotherapy significantly improves locoregional control and overall survival for cervical tumors compared to radiotherapy alone. In this study biological modelling is applied to quantify the effect of radiosensitization for three cervical cancer patients to evaluate the improvement in equivalent dose for the combination treatment with radiotherapy and hyperthermia. METHODS: The Linear-Quadratic (LQ) model extended with temperature-dependent LQ-parameters α and ß was used to model radiosensitization by hyperthermia and to calculate the conventional radiation dose that is equivalent in biological effect to the combined radiotherapy and hyperthermia treatment. External beam radiotherapy planning was performed based on a prescription dose of 46Gy in 23 fractions of 2Gy. Hyperthermia treatment using the AMC-4 system was simulated based on the actual optimized system settings used during treatment. RESULTS: The simulated hyperthermia treatments for the 3 patients yielded a T50 of 40.1 °C, 40.5 °C, 41.1 °C and a T90 of 39.2 °C, 39.7 °C, 40.4 °C, respectively. The combined radiotherapy and hyperthermia treatment resulted in a D95 of 52.5Gy, 55.5Gy, 56.9Gy in the GTV, a dose escalation of 7.3-11.9Gy compared to radiotherapy alone (D95 = 45.0-45.5Gy). CONCLUSIONS: This study applied biological modelling to evaluate radiosensitization by hyperthermia as a radiation-dose escalation for cervical cancer patients. This model is very useful to compare the effectiveness of different treatment schedules for combined radiotherapy and hyperthermia treatments and to guide the design of clinical studies on dose escalation using hyperthermia in a multi-modality setting.

Quantification of image distortions on the Utrecht interstitial CT/MR brachytherapy applicator at 3T MRI.

PURPOSE: To quantify distortions on MR images of the Utrecht interstitial CT/MR applicator at a field strength of 3T using an MRI-only method. MATERIALS AND METHODS: An MR-compatible phantom suspending the applicator in water was built and imaged on a Philips Ingenia 3T MRI scanner. A map of the magnetic field (B0) was calculated from multiecho images and used to quantify the field inhomogeneity. The expected displacements of the applicator could be quantified using the measured field inhomogeneity and sequence bandwidth. Additionally, two scans were acquired using opposing readout gradients. These scans were rigidly matched and their displacement was compared with the expected displacements from the B0 map. These same methods were applied in 4 patients. By rigid matching of the scans acquired with opposing readout direction the applicator displacement due to image distortion from B0 inhomogeneity as well as patient movement and organ deformation was determined. RESULTS: According to the B0 map, the displacement on the intrauterine device of the plastic brachytherapy applicator was <0.4 mm for both the phantom and patients. Displacements obtained by the opposing readout method were ≤0.8 mm for each patient with a mean ± SD over the patients of 0.3 ± 0.1 mm. CONCLUSION: The results of our study indicate that the B0 method agrees with the opposing readout method. Displacements caused by magnetic field inhomogeneity on 3T MRI were small compared with displacements due to patient movement and organ deformation.

Serum cholesterol and dietary data in middle-aged white males.

The mean daily dietary intake of normocholesterolaemic subjects (serum cholesterol less than 250 mg/100 ml) was compared with that of hypercholesterolaemic subjects (250 mg/100 ml or higher). Apart from a higher polyunsaturated fatty acid (PUFA) intake in the hypercholesterolaemic group, no other significant differences could be demonstrated between the two groups. Simple linear correlation coefficients (r) were calculated for the total sample, and the positive correlation (r = 0,29) between the serum cholesterol and the percentage of kilojoules derived from PUFA, was the only dietary variable to reach a statistically significant value (P less than 0,05). A stepwise regression analysis was used to calculate a multiple regression relationship (R2) between the dependent variable and the dietary variables. The results showed PUFA, total protein and saturated fatty acids (SFA) to have the highest cumulative influence on the serum cholesterol concentration. Only 29% of the variation in the serum cholesterol could be explained by the first 6 of 30 dietary variables tested in this survey. It was concluded that the small differences in the nutritional status among individuals from homogenous sample populations as well as the fact that non-linear relationships would not be reflected in the correlation coefficient, make it difficult to establish significant relationships between the dietary data and serum cholesterol concentration.