Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
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Split dose experiments were carried out with two 2 Gy fractions per day at intervals ranging from 0.5 to 24 h, in order to investigate both the time to complete repair and the detailed kinetics of repair of sublethal damage in the cervical spine of rats. ⋯ Two components of repair (0.7 and 3.8 h) have been reported by Ang et al. (Ang, K.K., Jiang, G.L., Guttenberger, R., Thames, H.D., Stephens, L.C., Smith, C.D. and Feng, Y. Impact of spinal cord repair kinetics on the practice of altered fractionation schedules. Radiother. Oncol. 25: 287-294, 1992) in the spinal cord of Sprague-Dawley rats. Two components have also been reported by others more recently. The present results could, with its graphical interpretation, agree in principle, but with a shorter fast component and a longer slow component. A slow component of 5.5 h was reported by Ruifrok et al. (Ruifrok, A.C.C., Kleiboer, B.J. and van der Kogel, A.J. Fractionation sensitivity of rat cervical spinal cord during radiation retreatment. Radiother. Oncol. 25: 295-300, 1992) in a related strain of WAG/Rij rats. The possible presence of a slower component than Ang et al.'s 3.8 h might help to explain the four myelopathies observed in the pilot studies for the CHART clinical trial. The presence of the definite fast component (< 0.5 h) could have important consequences when pulsed brachytherapy is used to replace continuous low dose rate irradiation.
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Theoretical calculations suggest that pulsed dose-rate irradiation (PDR) should have approximately the same effectiveness as continuous low dose-rate (CLDR) when the same total dose is given in the same overall time, unless large doses per pulse (> 2 Gy) are used and/or non-exponential or very short half-times of repair (< 0.5 h) are present in the irradiated tissues. However, few animal experiments have been reported to test this theory, and some of them gave contradictory results. We have carried out experiments to determine whether PDR irradiation of 18 mm of cervical spinal cord in the rat was more or less effective than CLDR at 0.5-1 Gy/h, when the overall average dose rate during each day of PDR was close to the overall CLDR average dose rate. ⋯ Reasons for this absence of effect with CLDR in these experiments are discussed, the most likely explanation being that a substantial component of repair with very short T1/2 (< 0.5 h) was present in spinal cord of these rats. There is evidence from other experiments elsewhere and in our laboratory for such a fast component of repair.
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We reviewed our institution's experience in treating patients with clinically localized prostate cancer with external beam irradiation (RT) to determine if previously analyzed clinical and treatment related prognostic factors affected outcome when biochemical control was used as an end-point to evaluate results. ⋯ No significant effect of treatment time, overall time, pretreatment TURP, or boost technique was noted on outcome in patients treated with conventional external beam irradiation when biochemical control was used as the end-point to evaluate results.
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Clinical Trial
Kinetics of serum prostate-specific antigen after external beam radiation for clinically localized prostate cancer.
To determine the kinetics of serum prostate-specific antigen (PSA) after radiation therapy of localized prostate cancer and to evaluate whether such kinetics provide prognostic information. ⋯ Overall, the clinical utility of postradiation serum PSA kinetics was small. There were no discernible uses for PSA half-life. In patients with a rising PSA profile the faster the kinetics the more adverse the disease. Doubling times shorter than 8 months, especially if the rise begins in the first year, predict for metastatic relapse. However, in the absence of decisively useful treatment for metastatic prostate cancer the virtues of the early detection of metastases remain unclear.
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The authors review the main contributions of the international literature concerning the role of hyperfractionation (HF), accelerated fractionation (AF), and accelerated hyperfractionation (AHF) of the dose in radiation therapy (RT) of central nervous system tumors. Basic rationales, clinical results, acute/late toxicity, and current prospectives are summarized in three sections focusing on malignant gliomas, pediatric brainstem tumors, and brain metastases. In supratentorial malignant gliomas the superiority of AHF (0.89 Gy x 3 fractions/day; total dose 61.4 Gy) over conventional fractionation ((CF) total dose 58 Gy) was demonstrated by a randomized trial. ⋯ As late sequelae have been reported in the few long-term survivors, patients should be carefully selected. Regarding brain metastases AF RT and AHF RT, with their faster treatment course, may represent a convenient alternative to CF RT for the palliation of brain metastases. In carefully selected patients with solitary brain metastases non-CF RT may be part of aggressive treatment approaches.