Strahlentherapie最新文献

Intracavitary brachytherapy will continue to play an important role in primary radiotherapy of gynecologic tumors. However, afterloading methods with remote control will more and more replace the classical radium therapy. The authors discuss the radiophysical and radiobiological differences between radium therapy and afterloading therapy with remote control and present a comparison of both methods based on their own clinical results.

From 1978 to 1982, 45 postoperative cases of breast cancer with lymphatic spread received radiation to the chestwall and axillary, supra- and infraclavicular lymph nodes up to 40 Gy. In addition, we gave 600 mg cyclophosphamide, 50 mg methotrexate and 750 mg 5-fluorouracil intravenously on day 1 of altogether nine 21-day cycles. The median follow-up is 37 months, and we calculate a 5-year over-all actuarial survival-rate which was 83% in the premenopausal and 77% in the postmenopausal patients. The disease-free 5-year survival-rate was 74% for the premenopausal and 61% for the postmenopausal women. There were twice as many patients with stage N2 in the postmenopausal group. No severe side-effects were observed. These promising preliminary results and the good tolerance of the above-mentioned combined therapy recommend it for future randomized studies.

The dependence of chronic radiation damage of the rectosigmoid on dose, dose rate and irradiated volume after intracavitary irradiation with an oscillating iridium source was studied in rats. The incidence of large bowel stenosis increased with increasing dose, dose rate and volume. The nominal dose leading to 50% incidence of stenosis was 27 Gy at 2 Gy/min, 32.5 Gy at 0.2 Gy/min and 51 Gy at 0.05 Gy/min.

Since April 1983 patients with gynecologic tumors have been irradiated with the HDR afterloading method at the University Hospital of Cologne. The therapy scheme for the carcinoma of the cervix consists of a combination of intracavitary contact irradiation and external radiotherapy. Brachytherapy is preponderant in an early stage of tumor extension, whereas teletherapy contributes more to the total dose in advanced stages. At first, the pelvis is totally exposed to a homogenous irradiation, so the shrunken tumor can more easily be arrived by curietherapy. The therapy scheme is described for the different tumor stages with its dosages, fractionations, and treatment pauses. Besides the use of special multiple-way applicators, the risk organs are protected by collimating with a block the middle part of the external irradiation field as soon as the maximum permissible dose is reached. A special block shape minimizes the dose irregularities at the field borders. The total physical dose at point A is about 60 Gy. The high dose rate of HDR afterloading has to be considered when calculating the biologic efficient dose. Here the dose rate factor furnishes a rough relation to the established radium dosage.

During combined treatment of Chinese hamster cells with cisplatinum and irradiation under aerobic conditions, there appear interactions between the two treatment modalities depending on the treatment sequence and the time interval. Treatment with cisplatinum followed by irradiation leads to a reduction of the shoulder of the survival curve with increasing time interval. Simultaneous treatment with cisplatinum and irradiation under aerobic or hypoxic conditions does not change the survival curve. Treatment with cisplatinum under aerobic conditions followed by irradiation in hypoxia does not lead to any interaction of both modalities independent of the time interval in contrast to subsequent irradiation under aerobic conditions. The specific sensitization of hypoxic cells by cisplatinum towards irradiation described in the literature could not be demonstrated with our cell line.

Thanks to computed tomography the diagnostics of Hodgkin's disease has improved for both the nodal and the extranodal affection. CT is of special importance to determine an extension along the thoracic wall and to assess a pericardial and vascular invasion. All lymph node groups are visualized by computed tomography, but the structure of the lymph nodes cannot be assessed. In a series of 68 patients suffering from Hodgkin's and non Hodgkin's lymphomas, a retroperitoneal lesion was found by CT in 77% and by lymphography in 90% of cases. Sonography is considered as a complementary method. CT is not very sensitive in case of a spleen and liver lesion. Percutaneous biopsy is recommended for the diagnosis of recurrences and for the assessment of residual tumor tissue.

Physical optimization in brachytherapy refers to the process of determining the radioactive-source configuration which yields a desired dose distribution. In manually afterloaded intracavitary therapy for cervix cancer, discrete source strengths are selected iteratively to minimize the sum of squares of differences between trial and target doses. For remote afterloading with a stepping-source device, optimized (continuously variable) dwell times are obtained, either iteratively or analytically, to give least squares approximations to dose at an arbitrary number of points; in vaginal irradiation for endometrial cancer, the objective has included dose uniformity at applicator surface points in addition to a tapered contour of target dose at depth. For template-guided interstitial implants, seed placement at rectangular-grid mesh points may be least squares optimized within target volumes defined by computerized tomography; effective optimization is possible only for (uniform) seed strength high enough that the desired average peripheral dose is achieved with a significant fraction of empty seed locations.

In radium therapy, the spatial and temporal dose distribution have never been identical in the different hospitals. However, the healing results did not vary correspondingly despite the partly great methodical differences between German and foreign hospitals. Furthermore, the spatial and temporal dose distribution in radium therapy did not conform to theoretic considerations but were a result of the low specific activity of radium as well as of the technical standard of X-ray therapy units until the sixties. It is shown that all requirements valid for radium therapy are also fulfilled by the afterloading method using a linear ray emitter, if an adequate dosage and fractionation is chosen. Taking into account the radiation risk, we think that the radium must be replaced by an afterloading method using a less dangerous nuclide. In our opinion the high dose rate technique is the most favorable method.

Intrauterine ultrasonography has proved to be an adequate method to represent the normal myometrium as well as its pathologic modifications, especially for the assessment of localization and extent of malignant processes. So for the first time, intracavitary radiotherapy of the carcinoma of the body, especially the afterloading technique, can work by means of the produced crossections with a precisely defined target volume, because the sonographic probe and the afterloading probe have identical geometric configurations. A method is presented which allows a computer-assisted determination of the tumor volume by means of the segmentation of organ sections and a pseudo-threedimensional projection in combination with the energy dose distribution of the radioactive source.

Compared to the other chemotherapeutic preparations discussed today, cyclophosphamide in combination with radiotherapy is a relatively unproblematic substance. Despite the great number of experimental and clinical data, the evaluation does not prove an advantage of the combined therapy with cyclophosphamide and irradiation as against radiotherapy alone in local tumor treatment. This should give occasion to further experimental investigations in adequate models. On the other hand, the practice of combined treatment with irradiation and preparations containing cyclophosphamide should be reconsidered for those cases where local control of a tumor is the principal therapeutic aim.