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Biomedical subjects

G Bruggmoser

Publications and source records attributed to G Bruggmoser.

At least 19 recordsLinked to original sources
PubMed2006

Determination of the recombination correction factor kS for some specific plane-parallel and cylindrical ionization chambers in pulsed photon and electron beams.

It has been shown from an evaluation of the inverse reading of the dosemeter (1/M) against the inverse of the polarizing voltage (1/V), obtained with a number of commercially available ionization chambers, using dose per pulse values between 0.16 and 5 mGy, that a linear relationship between the recombination correction factor kS and dose per pulse (DPP) can be found. At dose per pulse values above 1 mGy the method of a general equation with coefficients dependent on the chamber type gives more accurate results than the Boag method. This method was already proposed by Burns and McEwen (1998, Phys. Med. Biol. 43 2033) and avoids comprehensive and time-consuming measurements of Jaffé plots which are a prerequisite for the application of the multi-voltage analysis (MVA) or the two-voltage analysis (TVA). We evaluated and verified the response of ionization chambers on the recombination effect in pulsed accelerator beams for both photons and electrons. Our main conclusions are: (1) The correction factor k(S) depends only on the DPP and the chamber type. There is no influence of radiation type and energy. (2) For all the chambers investigated there is a linear relationship between kS and DPP up to 5 mGy/pulse, and for two chambers we could show linearity up to 40 mGy/pulse. (3) A general formalism, such as that of Boag, characterizes chambers exclusively by the distance of the electrodes and gives a trend for the correction factor, and therefore (4) a general formalism has to reflect the influence of the chamber construction on the recombination by the introduction of chamber-type dependent coefficients.

Biophysics↗
PubMed2002

The use of plane-parallel chambers in electron dosimetry without any cross-calibration.

Current dosimetry protocols from AAPM, DIN and IAEA recommend a cross-calibration for plane-parallel chambers against a calibrated thimble chamber for electron dosimetry. The rationale for this is the assumed chamber-to-chamber variation of plane-parallel chambers and the large uncertainty in the wall perturbation factor (p(wall)60Co)pp at 60Co for plane-parallel chambers. We have confirmed the results of other authors that chamber-to-chamber variation of the investigated chambers of types Roos, Markus, Advanced Markus and Farmer is less than 0.3%. Starting with a calibration factor for absorbed dose to water and on the basis of the three dosimetry protocols AAPM TG-51, DIN 6800-2 (slightly modified) and IAEA TRS-398, values for (p(wall)60Co)Roos of 1.024 +/- 0.005, (p(wall)60Co)Markus of 1.016 +/- 0.005 and (p(wall)60Co)Advanced Markus of 1.014 +/- 0.005 have been determined. In future this will permit electron dosimetry with the above-listed plane-parallel chambers having a calibration factor N(D, w)60Co without the necessity for cross-calibration against a thimble chamber.

Calibration↗
PubMed2001

Electron dosimetry based on the absorbed dose to water concept: a comparison of the AAPM TG-51 and DIN 6800-2 protocols.

The dosimetry protocols DIN 6800-2 and AAPM TG-51, both based on the absorbed dose to water concept, are compared in their theoretical background and in their application to electron dosimetry. The agreement and disagreement in correction factors and energy parameters used in both protocols will be shown and discussed. Measurements with three different types of ionization chambers were performed and evaluated according to both protocols. As a result the perturbation correction factor P(60Co)wall for the Roos chamber was determined to 1.024 +/- 0.5%.

Algorithms↗
PubMed1994

[Radiotherapy of malignant obstructive jaundice].

Brachytherapy using the afterloading technique with iridium 192 and percutaneous irradiation using 16 MV photons are used for the irradiation of malignant obstructive jaundice. Mostly, however, a combination of both methods can be used to advantage. In bile duct tumors and Klatskin tumors, the endoluminal part can be treated using brachytherapy. The extralumenal growth and, if necessary, all affected regional lymph node areas can be treated by a 3D planned, percutaneous, moving field technique. Intraoperative radiotherapy can be used in a few cases as booster irradiation of tumor conglomerates at the porta hepatis. The decision to use irradiation must be made very carefully since solid tumors are usually involved that require a high target dose, the application of which can lead to unacceptable side effects. The radio-oncological spectrum is therefore confined predominantly to palliative therapy.

Bile Duct Neoplasms↗
PubMed1993

[Radiation sensitivity of the normal bile duct during high dose rate afterloading irradiation with Iridium 192. Experimental studies in pigs].

This animal study was designed to assess the tolerance of the normal bile duct to a single intraluminal high-dose-rate afterloading irradiation. This information is essential for treatment recommendations in irradiation therapy of malignant bile duct stenoses. In 16 pigs bile duct catheters were inserted surgically. Over these devices single intraductal doses of 7.5 Gy and 15 Gy were applied using an iridium-192 source. After a period of two to three months the bile ducts and the surrounding structures were investigated by means of cholangiography, angiography, and macropathological and histological investigations. A single intraductal dose of 7.5 Gy leads to a slightly scarred shrinkage of the bile duct with sclerosis and obliteration of the capillary vessels. Vasculitis and necrosis of the bile duct wall are still evident three months after irradiation. A single dose of 15 Gy leads to severe lesions with widespread necroses of the bile duct wall which tend to bleed, and result in a high degree of shrinkage of the bile duct. The radiation damage is most prevalent near the papilla and in the narrow segments near the liver. Single intraluminal high-dose-rate afterloading doses of 7.5 and 15 Gy cause significant lesions and complications at the bile ducts. As the intact bile duct is the Achilles heel of intraductal therapy, considerably lower single doses are recommended for a fractioned treatment.

Animals↗
PubMed1991

Three-dimensional treatment planning for conformation therapy of a bronchial carcinoma.

Three-dimensional (3-D) radiotherapy planning is applied for the conformation therapy of a bronchial carcinoma. The treatment technique, using dynamically controlled shielding blocks, and the treatment planning procedure are described. The method has now been in clinical routine since 4 years; problems with the patient's positioning are discussed.

Bronchial Neoplasms↗
PubMed1989

[Intracavitary high-dose-rate-afterloading-radiotherapy in the esophagus of the pig].

The tolerance of sound esophageal mucosa to intracavitary high dose rate afterloading contact therapy with unique doses of 6 Gy and 12 Gy, respectively, was investigated in 15 pigs. Whereas no macroscopic or microscopic alterations of the mucosa are found after 6 Gy, a unique application of 12 Gy produces most severe side effects such as vascular occlusion due to fibrosis of the intima, formation of fistulas, and perforations of the esophagus wall. Future investigations will have to aim at the elaboration of schemes for dosage and fractionation.

Animals↗
PubMed1988

[Implantation of 125 iodine seeds in the dog vocal cord. An experimental morphologic study].

Following the first positive therapeutic results of T1a vocal chord cancer with 125iodine seeds in man (brachytherapy), we were concerned with the effects of this low-energy photon source on healthy laryngeal tissue. In the larynx, changes in the area of the vocal chord and the cartilaginous laryngeal structures were investigated in particular. These experimental studies were performed on the larynx of the dog. Through direct laryngoscopy, two 125iodine seeds were implanted in the anterior third of each vocal chord in 8 dogs; the resulting prick canals were sealed with fibrin glue. During survival the correct position of the seeds was radiologically monitored. After survival periods of 1, 3, 6, and 12 months the larynges were fixed by perfusion, removed, imbedded in paraplast, and stained with H. E., Azan, and E. v. G. After this protracted irradiation with 125iodine seeds only slight and for the most part reversible pathological changes had occurred. One month after implantation, only a perivascular infection was found in the vocal chord. After three months an inhibition of the fibrin organization around the seeds was observed as well as a localized dyschylia with broadening of the gland ducts. Additionally, a circumscribed dysplasia of the squamous epithelium, swelling of the capillary endothelium, atrophy of muscular fibres around the seeds, and telangiectasia of blood vessels were discernable. 6 and 12 months after implantation, only the muscular atrophy and the telangiectasia of the blood vessels remained detectable, in addition to a reduced inhibition of the fibrin organisation by connective tissue.

Animals↗
PubMed1988

[Determinants of local tumor control in interstitial radiotherapy of prostatic cancer].

Clinical followup of 52 patients treated with I-125 implants for localized prostatic cancer demonstrated local control in 85% and failure in 15%. Determining factors for local control or failure were analyzed and underline that homogeneous dose distribution is the most important factor for local control in interstitial radiotherapy. With the use of I-125 seeds this can only be achieved in small-volume (T2) stages with refined technique. For larger tumor volumes (T3) an external boost or the use of other radionuclides is preferable.

Aged↗
PubMed1987

[Combined intraductal and percutaneous radiotherapy of malignant bile duct obstruction with subsequent prosthetic management].

Radiotherapy of the inoperable malignant bile duct obstruction is performed to prolong the survival time in comparison to the palliative drainage. The preferable method is a combination of intracavitary irradiation via a percutaneous transhepatic drainage (30-40 Gy at a distance of 1 cm) and a moving field technique (30-40 Gy). This combination allows a high local tumor dose and a relatively large treatment volume. After radiotherapy, the PTD is being exchanged by a large-bore biliodigestive prosthesis.

Adenocarcinoma↗
PubMed1987

[Individual field shaping in rotational irradiation].

At the Radiotherapy Department of the University Hospital of Freiburg i.Br., an additional diaphragm controlled by an electronic system in dependence on the angles was developed for the optimization of irradiation planning, i.e. administration of the therapeutically necessary dose to the target volume and, at the same time, sparing of risk organs.

Esophageal Neoplasms↗