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- Aad, G., et al.
(författare)
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- 2011
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swepub:Mat__t (refereegranskat)
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| 2. |
- Aad, G., et al.
(författare)
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- 2012
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swepub:Mat__t (refereegranskat)
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| 9. |
- Daşu, Alexandru, et al.
(författare)
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Should single or distributed parameters be used to explain the steepness of tumour control probability curves?
- 2003
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 48:3, s. 387-397
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Tidskriftsartikel (refereegranskat)abstract
- Linear quadratic (LQ) modelling allows easy comparison of different fractionation schedules in radiotherapy. However, estimating the radiation effect of a single fractionated treatment introduces many questions with respect to the parameters to be used in the modelling process. Several studies have used tumour control probability (TCP) curves in order to derive the values for the LQ parameters that may be used further for the analysis and ranking of treatment plans. Unfortunately, little attention has been paid to the biological relevance of these derived parameters, either for the initial number of cells or their intrinsic radiosensitivity, or both. This paper investigates the relationship between single values for the TCP parameters and the resulting dose-response curve. The results of this modelling study show how clinical observations for the position and steepness of the TCP curve can be explained only by the choice of extreme values for the parameters, if they are single values. These extreme values are in contradiction with experimental observations. This contradiction suggests that single values for the parameters are not likely to explain reasonably the clinical observations and that some distributions of input parameters should be taken into consideration.
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| 11. |
- Fowler, Jack F., et al.
(författare)
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Is the α/β ratio for prostate tumours really low and does it vary with the level of risk at diagnosis?
- 2013
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Ingår i: Anticancer Research. - : International Institute of Anticancer Research (IIAR). - 0250-7005 .- 1791-7530. ; 33:3, s. 1009-1011
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Tidskriftsartikel (refereegranskat)abstract
- Aim: To answer the questions: Is the α/β ratio (radiosensitivity to size of dose-per-fraction) really low enough to justify using a few large dose fractions instead of the traditional many small doses? Does this parameter vary with prognostic risk factors? Methods and Materials: Three large statistical overviews are critiqued, with results for 5,000, 6,000 and 14,000 patients with prostate carcinoma, respectively. Results: These major analyses agree in finding the average α/β ratio to be less than 2 Gy: 1.55, (95% confidence interval=0.46-4.52), 1.4 (0.9-2.2), and the third analysis 1.7 (1.4-2.2) by ASTRO and 1.6 (1.2-2.2) by Phoenix criteria. All agree that α/β values do not vary significantly with the low, intermediate, high and “all included” risk factors. Conclusion: The high sensitivity to dose-per-fraction is an intrinsic property of prostate carcinomas and this supports the use of hypofractionation to increase the therapeutic gain for these tumours with dose-volume modelling to reduce the risk of late complications in rectum and bladder.
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| 13. |
- Toma-Dasu, Iuliana, et al.
(författare)
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Theoretical simulation of oxygen tension measurement in the tissue using a microelectrode: II. Simulated measurements in tissues
- 2002
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 64:1, s. 109-118
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE: The objectives of this study were to make a computer simulation of tissues with different vascular structures and to simulate measurements of oxygen tension using an Eppendorf-like electrode in these tissues and to compare the response to radiation of the tissues with the real oxygen distributions (called input distribution) with the response to radiation of the tissues in which the oxygen distribution is given by the results of the simulated measurements (called output distribution).MATERIALS AND METHODS: The structure of various tissues and the measurements of oxygen tension using a microelectrode were simulated using a computer program. The mathematical model used combines the description of a gradient of tissue oxygenation and the electrode absorption process.RESULTS: We have compared the oxygen distributions resulting from diffusion (input) with those obtained from a simulation of measurements (output) for various tissues in the same points. Because the electrode measurement is an averaging process, the calculated oxygen distributions are different from the expected ones and the extreme high and low values are not detected. We have then calculated the survival curves describing the response to radiation if there is a small fraction of truly hypoxic cells (expected values) or a large fraction of cells at intermediate values (observed results) in order to determine the differences between them.CONCLUSIONS: The results of our study show that oxygen electrode measurements do not give the true distribution of pO(2) values in the tissue. However, our results do not contradict the numerous empirical correlations between the Eppendorf measurements of tumour oxygenation and the outcome of treatments. Measurement results will be misleading for modelling purposes since they do not reflect the actual distributions of oxygen tensions in the measured tissue. Decisions based on such modelling could be very dangerous, especially with respect to the clinical response of tumours to new treatments.
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