Biomedical subjects

K Bratengeier

Publications and source records attributed to K Bratengeier.

16 recordsLinked to original sources

PubMed2001

Applications of two-step intensity modulated arc therapy.

PURPOSE: Organs at risk sometimes are surrounded by the target volume. At a first glance it seems to be impossible, to spare the organs at risk, i.e. the spinal cord, without underdosage of parts of the concave target volume. A fast method called "two-step intensity modulated arc therapy" (two-step IMAT) will be shown that avoids underdosage in the target volume near such organs at risk. MATERIALS AND METHODS: Simple rotational techniques reduce the dose to the surrounded organ, however, the blocking of the organ at risk spoils the homogeneity of dose in the target volume in the vicinity of the organ. A further narrow rotation field, tangential to the concave part of the target volume, increases the dose there and homogenizes the dose distribution without deteriorating the dose in the organ at risk significantly. RESULTS: Some cases show that the two-step IMAT and its modifications guarantee a sufficient dose homogeneity in the target volume surrounding an organ at risk. Besides basic theoretical considerations exemplary solutions for head and neck tumors, tumors adjacent to the spinal cord and mamma carcinoma of patients with extremely arched chest are demonstrated. CONCLUSION: Double rotation techniques can provide sufficient dose homogeneity for concave target volumes with excellent sparing of the surrounded organ at risk. They are not time consuming and can be used until IMRT will be applied routinely with adequate time load and effort.

Algorithms↗

PubMed2001

[A fast algorithm for homogeneous Ir-192--afterloading irradiation of cylindrical surfaces].

A fast algorithm was required to homogenise the dose on a cylinder mantle around a single straight applicator for Ir-192 afterloading. For linear applicators, an approximation formula for homogenisation of dose on one arbitrary cylinder mantle around the catheter is derived that predicts the required rise of dwell time tEnd at the end of the applicator. The other positions are loaded with a constant dwell time tMitte. The dwell time at the end tEnd appears to be independent of applicator length and can be described as a function of tMitte. In contrast to homogeneous loaded applicator, the dwell time in the central positions becomes also almost independent of catheter length, and is strictly proportional to the optimisation radius. TLD measurements and comparisons with a commercial planning system show the applicability of the procedure. This guarantees a homogeneous dose distribution even when modifications of the application length or optimisation distance become necessary. The algorithm can also be used to control the results of a planning system independently.

Algorithms↗

PubMed2001

[Conformal irradiation technique for the peri- and retrobulbar space in endocrine orbitopathy].

The clinical target volume (CTV) for the irradiation of the endocrine orbitopathy (Graves ophthalmopathy) includes the peri- und retrobulbar space with the extraocular muscles. We present here a conformal irradiation technique aimed at optimal coverage of the CTV. The irradiation technique consists of two rotation fields with a central lens block and two lateral fixed fields with dorsal blocking. In each Gantry position, the lenses are faded out through the central lens block. The isocenter of the two rotation fields is located in the lenses. For quality assurance of this irradiation technique, verification of the dose distribution was performed by film dosimetry using the humanoid Aldersone phantom. The use of this irradiation technique yielded a dose distribution with conformal CTV coverage of the peri- and retrobulbar space and of the extraocular muscles. The film dosimetry of the Aldersone phantom showed a maximal deviation of 5% between the measured and the calculated dose distribution. The radiation load to the eye lenses was 25% of the applied total dose.

Humans↗

PubMed2000

A new verification film system for routine quality control of radiation fields: Kodak EC-L.

BACKGROUND: The use of modern irradiation techniques requires better verification films for determining set-up deviations and patient movements during the course of radiation treatment. This is an investigation of the image quality and time requirement of a new verification film system compared to a conventional portal film system. MATERIAL AND METHODS: For conventional verifications we used Agfa Curix HT 1000 films which were compared to the new Kodak EC-L film system. 344 Agfa Curix HT 1000 and 381 Kodak EC-L portal films of different tumor sites (prostate, rectum, head and neck) were visually judged on a light box by 2 experienced physicians. Subjective judgement of image quality, masking of films and time requirement were checked. RESULTS: In this investigation 68% of 175 Kodak EC-L ap/pa-films were judged "good", only 18% were classified "moderate" or "poor" 14%, but only 22% of 173 conventional ap/pa verification films (Agfa Curix HT 1000) were judged to be "good". CONCLUSIONS: The image quality, detail perception and time required for film inspection of the new Kodak EC-L film system was significantly improved when compared with standard portal films. They could be read more accurately and the detection of set-up deviation was facilitated.

Humans↗

PubMed2000

Radiation techniques for head and neck tumors.

PURPOSE: A technique that combines some advantages of conforming techniques for advanced oro- and hypopharyngeal carcinomas is proposed. The aim is to increase the dose homogeneity in the target volume relative to lateral opposed fields. METHODS AND MATERIALS: This publication compares conforming radiation techniques based on standard equipment, standard linear accelerator setup and commercially available planning software with lateral opposed fields. More advanced conformal techniques reported in the literature are taken into account in a semi-quantitative manner. Our standard method uses an arc rotation, sparing the spinal cord. In contrast to earlier methods of this type, the resulting dose deficit in the vicinity of the spine is compensated by static lateral wedged fields. Dose distributions for 25 consecutive patients were planned. RESULTS: The conforming techniques were found to produce more homogeneous dose distributions than lateral opposed fields. In the planning target volume (PTV) (mean: 940 cm(3)) a standard deviation of dose of 4.6% was achieved. Ninety-five percent of the PTV were enclosed by the 90% isodose. The maximal spinal cord dose was limited to 45 Gy. The dose distributions of these techniques could compete with literature data on advanced techniques (the published dose-volume histogram (DVHs) of PTVs were evaluated). At the linear accelerator time for realization took 14 min on average. The planning time is 1-4 h (mean: less than 2 h). CONCLUSION: A rotational technique applicable with standard equipment is presented. Dose coverage of target volumes is improved, while the spinal cord is spared.

Female↗

PubMed1999

Carcinoma of the external auditory canal and middle ear.

PURPOSE: To evaluate therapeutic modalities used at our institutions regarding local control, disease-free survival and actuarial survival in carcinoma of the external auditory canal and middle ear, in an attempt to provide guidelines for therapy. METHODS AND MATERIALS: A series of 27 patients with carcinoma of the external auditory canal and middle ear treated between 1978 and 1997 in our institutions were analyzed with particular reference to tumor size and its relation to surrounding tissues, patterns of neck node involvement, surgical procedures, and radiation techniques employed. Clinical endpoints were freedom from local failure, overall survival, and disease-free survival. The median follow-up was 2.7 years (range 0.1-17.9 years). RESULTS: Treatment by surgery and radiotherapy resulted in an overall 5-year survival rate of 61%. According to the Pittsburgh classification, the actuarial 5-year survival rate for early disease (T1 and T2 tumors) was 86%, for T3 tumors 50%, and T4 stages 41%. Patients with tumors limited to the external auditory canal had a 5-year survival rate of 100%, patients with tumor invasion of the temporal bone 63%, and patients with tumor infiltration beyond the temporal bone 38%. The rate of freedom from local recurrence was 50% at 5 years. Unresectability by dural and cerebral infiltration, and treatment factors such as complete resection or resection with tumor beyond surgical margins are of prognostic relevance. All patients with dural invasion died within 2.2 years. The actuarial 5-year survival rate of patients with complete tumor resection was 100%, but 66% in patients with tumor beyond surgical margins. 192Iridium high-dose-rate (HDR) afterloading brachytherapy based on three-dimensional computed tomography (3D CT)-treatment planning was an effective tool in management of local recurrences following surgery and a full course of external beam radiotherapy. CONCLUSION: Surgical resection followed by radiotherapy adapted to stage of disease and grade of resection is the preferred treatment of cancer of the external auditory canal and middle ear.

Adult↗

PubMed1998

[3D-Ct-planned interstitial HDR brachytherapy + percutaneous irradiation and chemotherapy in inoperable pancreatic carcinoma. Methods and clinical outcome].

PURPOSE: Clinical experiences in interstitial 192-iridium HDR brachytherapy for the treatment of unresectable pancreatic carcinoma are presented. Brachytherapy has been used as boost irradiation in a multimodality treatment concept together with external radiotherapy and simultaneous chemotherapy. Practicability during clinical routine, tolerability and toxicity of treatment are investigated. PATIENTS AND METHODS: Nineteen patients (9 female, 10 male, median age 67 years) with unresectable carcinoma of the pancreas have been treated with interstitial brachytherapy. Distribution according to UICC stages showed 4, 10 and 5 patients in stage II to IV respectively. In all cases afterloading technique with 192-iridium in HDR-modus was used. A total dose of 10 to 34 Gy to the reference isodose was delivered (single dose 1.88 to 5 Gy, median 2.5 Gy). Brachytherapy was followed by external radiotherapy, delivering an additional dose of 40 to 58 Gy. Nine patients received simultaneous chemotherapy (5-fluorouracil, leucovorin). Treatment planning was performed based on CT scans, allowing spatial correlation of isodose curves to the patient's anatomy. RESULTS: Median survival time was 6 months. A trend of lower survival rates with advanced stage of disease (median survival stage IV 4 months, stage II and III 6.5 months) was seen. Local control rate was 70%. Brachytherapy treatment was well tolerated, severe acute side effects were not observed. One patient developed pancreatic fistulae 4 months and 1 patient a gastric ulcer 7 months after treatment. Pain release was achieved in all patients. CONCLUSIONS: 192-iridium HDR-brachytherapy is an effective tool in the treatment of unresectable pancreatic carcinoma with a high rate of local control and a low rate of side effects and is comparable IORT or seed implantation.

Adenocarcinoma↗

PubMed1997

[Intracavitary afterloading therapy as a new technique of boost irradiation in anal canal carcinoma].

PURPOSE: There are different techniques of boost irradiation in the treatment of patients with anal carcinoma. A new system of applicators is presented, which can be used for an intracavitary afterloading therapy. MATERIAL AND METHODS: Three different applicators are available, the first with a central catheter (K1), a second with 5 semicircular fixed catheters (K2) and an eccentric shield, a third with 8 circular fixed catheters and a central shield (K3). RESULTS: The adequate choice of applicator and catheters takes into consideration the individual localisation and extension of anal carcinoma in planning therapy. Thus, in circular growing tumors, an irradiation of the whole circumference of the anal canal is possible. In non-circular growing tumors, the dose applied in the non-affected part of the anal canal can be reduced to a quarter of the dose applied at the tumor. CONCLUSION: The new system of intracavitary afterloading therapy is a good alternative to previous techniques of boost irradiation in the treatment of anal carcinoma. By means of this technique, irradiation can be highly individualized, the tumor better included and non-affected sections of the anal canal saved.

Anus Neoplasms↗

PubMed1997

CT planning of boost irradiation in radiotherapy of breast cancer after conservative surgery.

BACKGROUND AND PURPOSE: A study was performed to compare the accuracy of clinical treatment set-up and CT planning of boost irradiation in radiotherapy of breast cancer. MATERIAL AND METHODS: Between September 1993 and October 1994, 45 women who underwent breast conserving surgery and irradiation containing a boost to the tumour bed were investigated. Prospective evaluation of CT planning of the boost was carried out. The target volume/boost field, electron energy and treatment set-up had been defined on the basis of clinical examination, initial and postsurgical mammograms by one radiotherapist. Next, a planning CT was performed in treatment position and a CT-based treatment plan was calculated according to a target volume defined by another radiotherapist. The clinical treatment set-up was imported into our computer planning system and the resulting isodose plots were compared with those from CT planning and reviewed critically. RESULTS: The clinically defined treatment set-up had to be modified in 80% of the patients. Most discrepancies observed were related to the size of the boost field itself and the chosen electron energy. Minor changes had to be made with respect to angle of table and gantry. CONCLUSIONS: Critical review of the isodose plots from both methods showed clear advantages for CT planning. Guidelines for target definition in CT planning of boost irradiation and subgroups of patients benefiting from this technique are described.

Breast Neoplasms↗

PubMed1997

Three dimensional variability in patient positioning using bite block immobilization in 3D-conformal radiation treatment for ENT-tumors.

BACKGROUND AND PURPOSE: The aim of this prospective study was to analyze the three-dimensional (3D) reproducibility of the isocenter position and of patient positioning with the use of bite block immobilization by means of a simple verification procedure for a complex beam arrangement applied for ENT-tumors. MATERIALS AND METHODS: We analyzed the positioning data of 29 consecutive patients treated for ENT-tumors at the Department of Radiotherapy and Oncology of the University of Wurzburg. A total of 136 treatment sessions were analyzed. Patients were positioned and immobilized using an individualized bite block system and a head and neck support. A complex beam arrangement was applied combining two offset rotational and two oblique wedge fields on a 5 MV linear accelerator. Orthogonal verification films were taken once weekly. Four to six film pairs per patient were obtained (during 4-6 weeks) with a mean number of 4.7 film pairs per patient. These were compared to the corresponding orthogonal simulator films taken during primary simulation. Deviations of the verified isocenter from the isocenter on the simulator film were measured and analyzed in three dimensions in terms of overall, systematic and random categories. A 3D-deviation vector was calculated from these 3D data as well as a 2D-deviation vector (for comparison with literature data) from the lateral verification films. RESULTS: The overall setup deviation showed standard deviations (SD) of 2.5, 2.7 and 3.1 mm along the cranio-caudal, anterior-posterior and medio-lateral axes, respectively. The random component ranged from SD 1.9 to 2.1 mm and the systematic component ranged from SD 1.8 to 2.2 mm. The mean length of the 3D-vector was 3.1 mm for the systematic as well as the random component. Ninety percent of 3D systematic and random deviations were less than 5 mm. The mean length of the 2D-vector was 2.4 mm for the random component and 2.2 mm for the systematic component. Ninety percent of 2D-random and systematic variations were less than 4 mm. CONCLUSIONS: The presented individualized bite block immobilization device provides an accurate and reproducible patient positioning for 3D-conformal radiation therapy in the head and neck. Random and systematic deviations in each of the three directions are in the range of +/-4 mm (2 SD, comprising 95% of the deviations) and are within the range or even less than deviations described for most thermoplastic or PVC-mask fixation devices. These deviations should be taken into account during definition of planning target volume in head and neck tumors.

Head and Neck Neoplasms↗

PubMed1997

CT simulation in stereotactic brain radiotherapy--analysis of isocenter reproducibility with mask fixation.

BACKGROUND AND PURPOSE: CT verification and measurement of isocenter deviation using repeated mask fixation in linac-based stereotactic high dose radiotherapy of brain metastases were performed in this study. MATERIALS AND METHODS: For stereotactic radiotherapy of brain metastases a commercial head mask fixation device based on thermoplastic materials (BrainLAB) was used. A two-step planning-treatment procedure was performed. Immediately before treatment the patient was relocated in the mask and a verification CT scan of the radiopaque marked isocenter was performed and if necessary its position was corrected. The verification procedure is described in detail. Twenty-two CT verifications in 16 patients were analyzed. Deviations were measured separately for each direction. A 3D-deviation vector was calculated. Additionally the average amount of deviation in each of the three dimensions was calculated. RESULTS: The mean deviation and standard deviation (SD) of the isocenter was 0.4 mm (SD 1.5 mm) in the longitudinal direction, -0.1 mm (SD 1.8 mm) in the lateral direction and 0.1 mm (SD 1.2 mm) in the anterior-posterior direction. The mean three-dimensional distance (3D-vector) between the verified and the corrected isocenter was 2.4 mm (SD 1.3 mm). The average deviation (without consideration of direction) was 1.1 mm (SD 1.1 mm), 1.3 mm (SD 1.3 mm) and 0.8 mm (SD 0.9 mm) in the longitudinal, lateral and sagittal directions, respectively. No correlation was found between 3D-deviation and the distance of the isocenter from the reference plane nor between deviation and the position of metastases in the brain (central versus peripheral or between different lobes), or the date of treatment. CONCLUSION: Reproducibility of the isocenter using the presented mask fixation is in the range of positioning reproducibility reported for other non-invasive fixation devices for stereotactic brain treatment. Our results underline the importance of CT verification as a quality assurance method in stereotactic radiotherapy. Under the condition of a preceding CT verification the mask can be used for single dose stereotactic radiotherapy. For fractionated stereotactic irradiation of small target volumes we recommend repeated CT verifications to assure reproducibility.

Brain Neoplasms↗

PubMed1993

[Interstitial HDR afterloading therapy with flexible catheters].

At the department of radiation therapy of the university of Würzburg flexible catheters are in use since 1989 for interstitial brachytherapy in high dose rate mode as the sole treatment modality or in combination with external beam therapy. The afterloading technique is applied in carcinoma of the oropharynx, of the oral cave, of the pancreas and in brain tumors. As flexible catheters are well tolerated, high radiation doses are given in fractions over several days up to two weeks. Localisation radiographs and CT scans are needed, in order to calculate exactly the dose distribution of target volume and adjacent healthy tissue. Doses up to 30 Gy for the target volume in 10 to 15 fractions are well tolerated. The patients daily activities are not restricted during the whole treatment time. Excellent palliations are achieved with minimal side effects.

Adolescent↗

PubMed1992

The use of isodose curves on radiographs and on CT scans in interstitial brachytherapy.

In brachytherapy an accurate dose distribution is usually not definable, and therefore not required. If flexible catheters are implanted, such as in head and neck cancer, resulting isodose curves only rarely fit exactly to radiographic films, and the target volume is not easily reconstructed. Usually no clear relationship exists between the three-dimensional (3D) dose distribution and target volume on the one hand and the two-dimensional (2D) radiographic films on the other. Dose distributions on radiographs are not sufficient to define the target absorbed dose and doses that critical areas will receive. A 3D imaging system, like computed tomographic (CT) scans, is needed in order to visualize underdosage inside the target volume and non-tolerable hot spots outside the tumour. Large-scale and expensive techniques exist to tackle these problems. Our inexpensive and verifiable approach to solve these problems combines localization radiographs with CT scans. Whereas tumour and critical areas are displayed on CT scans, flexible catheters loaded with dummy sources are best seen on radiographic films. With the help of a self-developed computer program, dose distributions are superimposed on CT scans. Doses to the target and critical organs are easily read and verified by external and internal detectors.

Brachytherapy↗

PubMed1992

Combined isodose curves of high-dose rate interstitial brachytherapy with external-beam radiation therapy in pancreatic carcinoma.

From September 1989 until March 1992 nine patients with unresectable, though localized carcinoma of the pancreas were treated by a multimodality therapy consisting of palliative surgery, interstitial conformal brachytherapy in high-dose rate mode (HDRBT) with iridium-192 up to 30 Gy and external-beam radiation therapy (EBRT) of about 52 Gy. Four patients simultaneously received two cycles of chemotherapy consisting of 5-FU and Leucovorin. Since high radiation doses are applied which are not tolerated in adjacent healthy tissues, doses to tumor and critical areas need to be known precisely and are to be adjusted before treatment. A three-dimensional imaging system is required. A self developed method combines the data of simulation radiographs and those of CT scans. The prescribed minimum target absorbed dose in HDRBT is adjusted to the target volume sparing organs at risk. The specialized quality assurance is adapted to this method. Differences between measured and calculated doses do not exceed 5%. The addition of isodoses of HDRBT and EBRT on CT scans is demonstrated. Due to patients' selection the treatment concept did not reveal any positive effects on survival. However, excellent palliative results were obtained without severe side-effects.

Adenocarcinoma↗

PubMed1991

[Assessment of radiotherapy plans: dose-volume histograms, integral effects and tumor control].

Suitable criteria are necessary for judgement and for comparison of treatment plans. These criteria must take into account radiobiological effects, i.e. tumor control and treatment complications. Quantitative evaluation of dose volume histograms gives helpful criteria for radiation treatment planning and for the choice between different treatment plans. For normal tissue and organs at risk it is shown, how to assign integral dose effect to inhomogeneous dose distribution. The evaluation algorithm is based on the assumption of a power law for volume dependence of dose effect. The algorithm is discussed for arbitrary form of dose effect function. Explicit evaluation is given in terms of the linear quadratic model. Hot spots influence integral dose effect much stronger than low dose level irradiation. For judgement of treatment plans, the significance of mean organ dose is only poor. Higher moments of dose distribution are more suitable. An effective tumor control probability is derived for judgement of tumor dose distribution. It is shown that tumor control is determined by mean dose and dose inhomogeneity in tumor volume. Control probability falls with increasing dose inhomogeneity in tumor region-in first order approximation characterized by variance of dose distribution. Using a clinical example, the evaluation rules for normal and tumor tissue are demonstrated. Two different treatment techniques are analyzed and discussed. Only numerical evaluation of dose volume histograms for lung region shows the better technique.

Algorithms↗

PubMed1991

[Quality assurance in dynamic radiotherapy techniques].

Compared with conventional radiation treatment techniques, quality assurance for dynamic techniques has to consider additionally the variability of the movement parameters of the treatment unit. In this context the exactness and the reliability of the computer control are of special interest. In this paper the results of quality assurance for dynamic treatment techniques are reported. At first investigations concerning the reproducibility are carried out. Another test is the simulation of conventional moving beam techniques by external computer control. Further the differences between measured dose distributions of dynamic techniques and the distributions resulting from the sequence of fixed fields approximating these techniques are determined. Finally we compared measured and calculated dose distributions. The results of the investigations justify the introduction of dynamic radiation treatment techniques into clinical use.

Humans↗