Biomedical subjects
Publications and source records attributed to P Kohr.
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To evaluate a new therapy protocol for local dose escalation by high dose rate (HDR) brachytherapy for survival, morbidity and prognostic variables in men with localized prostate cancer. The prospectively recorded files of 189 men aged in median 69 years with a mean follow-up of 6 years (12-143 months) receiving curatively intended combined high dose rate (HDR) 192-iridium-brachytherapy (BT) and external beam radiation (EBR) for locally confined prostate cancer were analyzed. Mean age was 68.2 (range 44-84 years). Hundred and twenty-seven patients had T1-2 tumors, and 62 patients had T3-tumors. The total planned dose applied by external beam radiation was 50 Gy in the pelvis, and 40 Gy in the prostate by in-field-dose modification. The HDR-brachytherapy was delivered in two fractions. The dose per fraction amounted 15 Gy. Mean survival was 6 years (range 12-143 months), 76.7% of the patients survived and 86.3% were disease-free. The biochemical non-evidence of disease rate (BNED) was 78%. Univariate survival analysis revealed that low stage (T1-2), low grade (G1-2), normal PSA status after radiation therapy, and no adjuvant hormonal treatment were associated with long survival. However, the stratification for adjuvant hormonal treatment was not according to random. In multivariate analyses PSA status was an independent prognostic factor. The six year results confirm that local dose escalation by HDR-brachytherapy and external beam radiation is curative in men with locally confined prostate cancer. The results are especially in high risk patients encouraging.
PURPOSE: The combined external beam- and high-dose rate brachytherapy (HDR-BT) of localized prostate cancer was introduced at Kiel University in 1986. The aim of this intermediate analysis was to judge the Kiel method of localized prostate cancer radiation treatment after ten years experience. PATIENTS AND METHODS: In the past ten years 174 patients with histological proven localized prostate cancer were subjected to combined tele-/HDR-brachytherapy. Local staging in all of the cases by transrectal ultrasound, nodal staging in the majority of the cases by CT or MRI. Average age of the patients was 68.2 years (44-84). According to AJCC/UICC staging T1B, T2, T3 was found in 2, 113 and 59 cases, respectively. Highly differentiated tumors (G1) were found in 27, moderately differentiated (G2) in 87, poorly differentiated (G3) in 60 cases. The mean follow-up was 47.1 months with the median of 51.7 months. Total prescribed dose 50 Gy on the small pelvis and 70 Gy on the prostate capsule due to the integration of two, 15 Gy each, HDR-brachytherapy fractions in 6 weeks. RESULTS: Ten patients died of prostate cancer and 18 of intercurrent diseases resulting in a 5 years overall survival rate of 83% and tumor specific survival rate of 94%. Twenty-one patients showed a clinical progression, of these 14 systemic, 5 local and 2 both systemic and local. Additional 16 patients had PSA elevation only. The 5-years biochemical and/or clinical progression-free survival in the cohort was 79% and 73% for the T3 tumors. Side effects were 27 cases of proctitis/colitis and 20 cases of dysuria/cystitis. CONCLUSION: The integrated HDR-BT combined with external beam radiation treatment is a method with excellent tumor control rates at five years superior to those of external beam treatment alone or external beam combined with iodine-125 implants. This form of radiotherapy would appear to be particularly well-suited to treatment of advanced localized (T3) tumors.
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PURPOSE: Quality of a brachytherapy application depends on the choice of the target volume, on the dose distribution homogeneity and radiation injury on critical tissue, which should be postulated by advanced brachytherapy treatment planning systems. MATERIAL AND METHODS: Basic imaging method for conformal treatment planning is the cross-sectional imaging. The clinical applicability of a new type 3D planning system using CT and/or MRT-simulation or US-simulation for planning purposes was studied. The planning system developed at Kiel University differs from usual brachytherapy planning systems because of the obligatory use of cross-sectional imaging as basic imaging method for reconstruction of structures of interest. Dose distribution and normal anatomy can be visualized on each CT/MRT/US slice as well as coronal, sagittal, axial and free chosen reconstruction (3D), as well as dose-volume histogram curves and special colour-coded visualization of dose homogeneity in the target can be analyzed. RESULTS: Because of the experience in the clinical routine, as well as on the base of 30 simultaneous planning procedures on both 2D (semi-3D) and 3D planning systems we observed similar time consumption. Advantages of 3D planning were the better interpretation of target delineation, delineation of critical structures as well as dose distribution, causing more accurate volume optimisation of dose distribution. CONCLUSION: Conformal brachytherapy treatment planning for interstitial brachytherapy means significant advantages for the clinical routine compared to 2D or semi-3D methods.
In radiotherapy to an increasingly degree radiobiological aspects of the tumor behaviour during therapy are realized in daily routine. An example for this is the so called hyperfractionation of the total dose: that means multiple small fractions are applied. Doses of as low as circa 40 cGy per field are necessary. This investigation affects the constancy and the behaviour of the following beam parameters of various treatment units during the initial stage of operation (circa ten seconds): energy of bremsstrahlung, symmetry, flatness and proportionality of dose.
A method is presented for combined brachy-teletherapy by which the dose distribution of percutaneous irradiation is adapted to the distribution of short-distance irradiation with 192iridium by means of the so-called "field integrated dose modification". Insufficient or excessive doses within the area of superposition of both therapy modalities can so be avoided. Moreover, the therapist can define zones of deviation from the reference dose, if such a dose heterogeneity seems desirable in the individual case. The combined irradiation of prostata and cervix is given as an example to describe in detail the technical, clinical, and radiobiological aspects of this method.
In magna-field irradiation using high energy bremsstrahlung (photons), i.e. total body irradiation, it is desirable to achieve a homogeneous dose distribution or to realize a planned modification in dose deposition within the target volume. In the Department of Radiology, University of Kiel, for this purpose individually constructed compensators are in routine use for about three years. Some physical and dosimetric aspects of this irradiation technique are described briefly and the experimental test procedure for TBI-compensators is highlighted by several details, for example transmission measurements, radiographies of the compensators and determination of actual dose rates in the midplane of the patient.