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B R Thomadsen

Publications and source records attributed to B R Thomadsen.

At least 19 recordsLinked to original sources
PubMed1998

A solid water pelvic and prostate phantom for imaging, volume rendering, treatment planning, and dosimetry for an RTOG multi-institutional, 3-D dose escalation study. Radiation Therapy Oncology Group.

PURPOSE: With increased interest in 3-D conformal radiation therapy and dose escalation, it is necessary to provide advanced techniques to assure quality in treatment delivery. Multi-institutional trials for these newer treatment techniques require methods of verifying the consistency of treatments between the participating institutions. For this reason, a phantom was designed to address the quality and consistency of Radiation Therapy Oncology Group (RTOG) 3-D prostate treatment protocol. METHODS AND MATERIALS: A solid water pelvic and prostate phantom for imaging, volume rendering, treatment planning, and dosimetry applications for performing comprehensive quality assurance has been designed and fabricated. Its configuration was based upon CT slices obtained from a patient study. Individual slices were machined with corresponding contours of the prostate, bladder, rectum, and the left and right femurs. Most of the phantom is made of solid water (Gammex/RMI, Middleton, WI), while the femurs are made of bone-equivalent material. The CT numbers from patient images were used to adjust the solid water composition within the organ volumes, providing image contrast from the remainder of the phantom. Cylindrical insertion grooves are machined in the phantom to allow placement of ionization chambers and thermal luminal dosimeters (TLDs) for dosimetry applications. During imaging, the cavities are filled with rods fabricated from solid water material. RESULTS: The phantom is being used to evaluate the consistency of a range of processes in radiation therapy simulation, planning, and delivery of 3-D-based treatments for prostate cancer. CONCLUSION: The ultimate study objective is to use the phantom to evaluate the accuracy and consistency of treatments delivered by institutions participating in national collaborative clinical trials involving 3-D conformal dose escalation.

Humans↗
PubMed1998

High dose-rate brachytherapy treatment delivery: report of the AAPM Radiation Therapy Committee Task Group No. 59.

The goals of this task group are to examine the current high dose-rate (HDR) treatment delivery practices and to prepare a document to assure safe delivery of HDR treatments. The document consists of detailed HDR procedures for design of an HDR brachytherapy program, staffing and training, treatment specific quality assurance, and emergency procedures. The document provides an extensive quality assurance (QA) check list. It reviews all aspects of HDR treatment delivery safety, including prescription, treatment plan, treatment delivery, and radiation safety.

Brachytherapy↗
PubMed1997

An investigation of tomotherapy beam delivery.

Experimental simulations for tomotherapy beam delivery were performed using a computer-controlled phantom positioner, a cylindrical phantom, and a 6 MV x-ray slit beam. Both continuous helical beam and sequential segmented tomotherapy (SST) beam deliveries were evaluated. Beam junctioning problem due to couch indexing error or field width errors presented severe dose uniformity perturbations for SST, while the problem was minimized for helical beam delivery. Longitudinal breathing motions were experimentally simulated for helical and SST beam delivery. While motions reduced the dose uniformity perturbations for SST, small artifacts in dose uniformity can be introduced for helical beam delivery. With typical breath frequency and magnitude, for a slit beam of 2.0 cm width at 4 rpm, the dose uniformity perturbation was not significant. A running start/stop technique was implemented with helical beam delivery to sharpen the 20%-80% longitudinal dose fall-off from 1.5 to 0.5 cm. The latter was comparable to the corresponding dose penumbra of a conventional 6 MV 10 x 10 cm2 field. All together, helical beam delivery showed advantages over SST for tomotherapy beam delivery under similar delivery conditions.

Biophysical Phenomena↗
PubMed1997

Innovations and advances in brachytherapy.

The treatment of cancer with radioactive sources using topical molds and intracavitary radium showed the efficacy of brachytherapy long before external radiation therapy became common practice. Brachytherapy is progressing in several clinical directions that reflect technological innovation as well as changes in medical care which combine to provide significant advances in the practice of brachytherapy today. A major change in brachytherapy, the development of high intensity sources, promoted clinical and technologic innovations in high dose-rate brachytherapy. Pulse dose-rate brachytherapy is the use of these sources to treat a target by using pulses of radiation for several minutes each hour with the same overall time and total dose as low dose-rate treatment. Recent novel approaches of using radiotherapy for prevention of restenosis in coronary and peripheral vessels has interested laboratory and clinical researchers. Most of the work toward new source material for brachytherapy centers around intravascular applications. Technology to support brachytherapy continues to advance rapidly. The interaction between images from diverse modalities and the various phases of the treatment planning is the basis of enhanced treatment planning procedures. Optimization in brachytherapy entails calculating the source strengths or source dwell times to satisfy a set of dose criteria to achieve the best dose distribution for a brachytherapy implant. Progress in computerization and calculation modeling has promoted this technical advance. Education and training in brachytherapy indications and techniques is mandatory to maintain high standards of brachytherapy practice.

Animals↗
PubMed1995

The adverse effect of treatment prolongation in cervical carcinoma.

PURPOSE: Proliferation of surviving tumor clonogens during a course of protracted radiation therapy may be a cause of local failure in cervical carcinoma. The effect of total treatment time was analyzed retrospectively in relation to pelvic control and overall survival for squamous cell carcinomas of the uterine cervix. METHODS AND MATERIALS: Two hundred and nine patients (Stage IB-IIIB) treated with a combination of external beam and low dose rate intracavitary irradiation were evaluable for study. Multivariate analysis and Kaplan-Meier statistical methods were used to determine the effect of treatment time on pelvic control and survival at 5 years. RESULTS: The median treatment duration was 55 days. For all stages combined, the 5-year survival and pelvic control rates were significantly different with treatment times < 55 days vs. > or = 55 days: 65 and 54% (p = 0.03), 87 and 72% (p = 0.006), respectively. By stage, a shorter treatment duration (i.e., < 55 days vs. > or = 55 days) was significant for 5-year overall survival and pelvic control for Stages IB/IIA and III, but not for Stage IIB: Stage IB/IIA (81 and 67%, 96 and 84%), Stage III disease (52 and 42%, 76 and 55%) and Stage IIB (43 and 50%, 74 and 80%, respectively). Survival decreased 0.6%/day and pelvic control decreased 0.7%/day for each additional day of treatment beyond 55 days for all stages of disease. Additionally, significant late complications were not influenced by treatment time. CONCLUSION: These results suggest that prolongation of treatment time is associated with decreased local control and survival in patients with cervical carcinoma. This is consistent with emerging data from other institutions. Therapeutic implications include avoidance of unnecessary treatment breaks, the design of fractionation schemes that decrease treatment duration, and possibly the use of tumor cytostatic drugs during conventional radiation.

Brachytherapy↗
PubMed1995

Postoperative vaginal cuff irradiation using high dose rate remote afterloading: a phase II clinical protocol.

PURPOSE: In September 1989, a postoperative Phase II high dose rate (HDR) brachytherapy protocol was started for International Federation of Gynecology and Obstetrics (FIGO) Stage I endometrial adenocarcinoma. This review reports the overall survival, local control, and complication rates for the initial 63 patients treated in this Phase II study. METHODS AND MATERIALS: High dose rate brachytherapy was delivered using an Iridium-192 HDR remote afterloader. Sixty-three patients were entered into the Phase II protocol, each receiving two vaginal cuff treatments 1 week apart (range 4-12 days) with vaginal ovoids (diameter 2.0-3.0 cm). No patient received adjuvant external beam radiation. A dose of 32.4 Gy in two fractions was prescribed to the ovoid surface in 63 patients. The first three patients treated at our institution received 15, 16.2, and 29 Gy, respectively, to determine acute effects. RESULTS: At a median follow-up of 1.6 years (range 0.75-4.3 years) no patient has developed a vaginal cuff recurrence. One regional recurrence (1.6%) occurred at 1.2 years at the pelvic side wall. This patient is alive and without evidence of disease 7 months after completion of salvage irradiation, which resulted in the only vaginal stenosis (1.6%). Fourteen patients (22%) experienced vaginal apex fibrosis by physical exam, which was clinically symptomatic in four patients. Two patients reported stress incontinence; however, these symptoms were noted prior to their HDR therapy. One patient died 2.4 years after HDR therapy due to cardiovascular disease without evidence of cancer at autopsy. CONCLUSION: Preliminary results of our phase II HDR vaginal cuff protocol for postoperative FIGO Stage IA, Grade 3 or Stage IB, Grade 1-2 patients demonstrate that 32.4 Gy in two fractions is well tolerated by the vaginal cuff mucosa. Local control appears comparable to our prior experience and others with low dose rate (LDR) brachytherapy. Additional patient accrual and further follow-up will better determine the late morbidity, local control, and overall survival of these patients.

Adult↗
PubMed1995

Impact of "optimized" treatment planning for tandem and ring, and tandem and ovoids, using high dose rate brachytherapy for cervical cancer.

PURPOSE: Different treatment techniques are used in high dose rate (HDR) remote afterloading intracavitary brachytherapy for uterine cervical cancer. We have investigated the differences between "optimized" and "nonoptimized" therapy using both a tandem and ring (T/R) applicator, and a tandem and ovoids (T/O), applicator. METHODS AND MATERIALS: HDR afterloading brachytherapy using the Madison System for Stage IB cervical cancer was simulated for 10 different patients using both a T/R applicator and a T/O applicator. A treatment course consists of external beam irradiation and five insertions of HDR afterloading brachytherapy. Full dosimetry calculations were performed at the initial insertion for both applicators and used as a reference for the following four insertions of the appropriate applicator. Forty dosimetry calculations were performed to determine the dose delivered to Point M (similar to Point A), Point E (obturator lymph nodes), vaginal surface, bladder, and rectum. "Optimized" doses were specified to Point M and to the vaginal surface. "Nonoptimized" doses were specified to Point M only. Using the linear-quadratic equation, calculations have been performed to convert the delivered dose using HDR to the biologically equivalent doses at the conventional low dose rate (LDR) at 0.60 Gy/h. RESULTS: Major differences between "optimized" and "nonoptimized" LDR equivalent doses were found at the vaginal surface, bladder, and rectum. Overdoses at the vaginal surface, bladder, and rectum were calculated to be 208%, nil, and 42%, respectively, for the T/R applicator with "nonoptimization." However, for the T/O applicator, the overdoses were smaller, being nil, 32%, and 27%, respectively, with "nonoptimization." CONCLUSION: Doses given in high dose rate intracavitary brachytherapy border on tissue tolerance. "Optimization" of either applicator decreases the risk of a dose that may have potential for complications. Optimization of a tandem and ovoids best ensures that the doses are not diminished at the treatment sites, and that the potential for overdose is reduced.

Brachytherapy↗
PubMed1995

Quality assurance tool for high dose rate brachytherapy.

An insert for a well ionization chamber is described for quality assurance tests for high dose rate remote afterloaders. The use of this insert over time has shown its applicability for efficient QA tests for the high dose rate afterloader. The measurement results are six times greater than the uncertainties involved for the measurements. Checks on position can be made better than 1 mm and dwell times better than 1 s. The overall measurements can be done to better than 1.5%. QA checks can be accomplished in a shorter time period with as great or better accuracy than prior film techniques.

Brachytherapy↗
PubMed1995

Intercomparison of normalized head-scatter factor measurement techniques.

Normalized head-scatter factors were measured with cylindrical beam coaxial miniphantoms and high purity graphite buildup caps for 4-, 6-, 10-, and 24-MV photon beams at field sizes from 4 x 4 to 40 x 40 cm2. The normalized head-scatter factors determined by the two methods matched well for 4- and 6-MV photon beams. The miniphantom technique produced normalized head-scatter factors 1.5% and 4.8% lower than the buildup caps for the 10- and 24-MV beams for large field sizes, respectively. At small field sizes, the miniphantom technique produced larger normalized head-scatter factors than the buildup caps. Measurements made with an electromagnet indicate that a significant portion of the ionization measured in the buildup cap at 24 MV arises from contamination electrons. Measurements made with the miniphantom and magnet found no contamination electron contribution. The miniphantom technique may exclude such contamination electrons, potentially leading to inaccuracies in tissue-maximum ratios and phantom scatter factors, as well as inaccuracies in monitor unit calculations.

Humans↗
PubMed1994

A comparison of the efficacy and complication rates of low dose-rate versus high dose-rate brachytherapy in the treatment of uterine cervical carcinoma.

PURPOSE: To compare the outcome and complication rates for treatment of uterine cervical carcinoma with low dose-rate (LDR) vs. high dose-rate (HDR) brachytherapy at the University of Wisconsin Comprehensive Cancer Center (UWCCC). METHODS AND MATERIALS: One-hundred ninety-eight evaluable patients with cervical carcinoma, Stages IB to IIIB, treated with curative intent with a combination of megavoltage teletherapy and LDR brachytherapy from 1977 to 1988 were the subject of an initial review. In 1989, a HDR treatment program was initiated where all patients with cervical carcinoma were subsequently treated with a combination of HDR brachytherapy and teletherapy. Using the linear-quadratic model (LQ), the dose and schedule of HDR brachytherapy and teletherapy were designed to give similar tumor control and late effects as LDR therapy. Technically, the HDR schedule required meticulous attention to treatment geometry to limit severe late effects. Forty patients treated with the HDR program with 2-4 year follow-up were reviewed and compared to the previous LDR patient group. The LDR and HDR treatment groups were comparable with regards to age, weight, stage distribution, bulk of disease, and histology. RESULTS: No significant difference in survival was found between the LDR and HDR groups with 3-year actuarial overall survival being 66% and 77%, respectively. Three-year actuarial pelvic control rates were similar at 80% and 77% for the LDR and HDR groups, respectively. No significant difference in late treatment complications requiring hospitalization or surgery was found between the two treatment groups with a complication rate of 10% (20/198) for the LDR patients and 2.5% (1/40) for the HDR patients. CONCLUSION: As predicted by our LQ calculations, treatment results for LDR and HDR brachytherapy were similar with respect to survival, pelvic control and late complications in the treatment of cervical carcinoma. The HDR brachytherapy program at the UWCCC appears to be a safe and effective alternative to LDR therapy in the treatment of cervical carcinoma.

Adolescent↗
PubMed1994

A practical alternative to conventional five-field irradiation postmastectomy for locally advanced breast cancer.

A combination of electron and photon beams has been used as an alternative for the conventional five-field method to irradiate patients postmastectomy for locally advanced breast cancer. Anterior and posterior opposed photon beams treat in continuity the lateral chest wall, axilla, and supraclavicular lymph nodes. An adjacent anterior electron beam is used at an energy matched to the depth of the internal mammary nodes. It includes the anterior chest wall, but bolus is used in the lateral aspect to spare underlying lung. This electron beam eliminates the diverging junction between the internal mammary and medial tangential fields used in the conventional five-field technique. Overlaps along the junction between the photon and electron beams are minimized by placing the center of the photon field along its medial border. Measurements with an Alderson-Rando phantom show dose-distribution advantages for this technique over the conventional five-field approach. There is less chance of underdosing tumor cells or of overdosing normal tissue along beam junctions. Clinical studies on 29 patients treated by this technique between July 1985 and December 1989 show increased rates of acute skin reactions, but otherwise similar side effects compared with 57 breast cancer patients treated with the five-field technique over the same time period. Local recurrence rates and patient survival rates were similar for the two groups. Given the dose-distribution advantages of this technique and its simple adaptation to accommodate unusual surgical scars or cancer recurrences, its use should be considered for postmastectomy patients with locally advanced breast cancer in well-equipped cancer treatment centers.

Breast Neoplasms↗
PubMed1994

Technical exhibits.

Explore the source record for details and available documents.

Diagnostic Imaging↗
PubMed1993

The transit dose component of high dose rate brachytherapy: direct measurements and clinical implications.

PURPOSE: To measure the transit dose produced by a moving high dose rate brachytherapy source and assess its clinical significance. METHODS AND MATERIALS: The doses produced from source movement during Ir-192 HDR afterloading were measured using calibrated thermoluminescent dosimeter rods. Transit doses at distances of 0.5-4.0 cm from an endobronchial applicator were measured using a Lucite phantom accommodating 1 x 1 x 6 mm thermoluminescent rods. Surface transit dose measurements were made using esophageal and endobronchial catheters, a gynecologic tandem, and an interstitial needle. RESULTS: No difference was detected in thermoluminescent dosimeter rod responses to 4 MV and Ir-192 spectra (427 nC/Gy) in a range of dose between 2 and 300 cGy. The transit dose at 0.5 cm from an endobronchial catheter was 0.31 cGy/(Curie-fraction) and followed an inverse square fall-off with increasing distance. Surface transit doses ranged from 0.38 cGy/(Curie-fraction) for an esophageal catheter to 1.03 cGy/(Curie-fraction) for an endobronchial catheter. Source velocity is dependent on the interdwell distance and varies between 220-452 mm/sec. A numeric algorithm was developed to calculate total transit dose, and was based on a dynamic point approximation for the moving high dose rate source. This algorithm reliably predicted the empirical transit doses and demonstrated that total transit dose is dependent on source velocity, number of fractions, and source activity. Surface transit doses are dependent on applicator diameter and wall material and thickness. Total transit doses within or outside the desired treatment volume are typically < 100 cGy, but may exceed 200 cGy when using a large number of fractions with a high activity source. CONCLUSION: Current high dose rate brachytherapy treatment planning systems calculate dose only from source dwell positions and assume a negligible transit dose. Under certain clinical circumstances, however, the transit dose can exceed 200 cGy to tissues within and outside the prescribed treatment volume. These additional, unrecognized doses could increase potential late tissue complications, as predicted by the linear quadratic model. To enhance the clinical safety and accuracy of high dose rate brachytherapy, total transit dose should be included in calculated isodose distributions. Significant transit doses to tissues outside the treatment volume should be documented.

Algorithms↗
PubMed1993

Radiographic visualization of vaginal cylinders in gynecologic high dose rate brachytherapy.

PURPOSE: To develop a marker system allowing an accurate determination of vaginal applicator dimensions and geometry from a radiograph. METHODS AND MATERIALS: The markers consist of two sets of gold seeds embedded into each cylinder identifying the cylinder diameter, and a thin stainless steel disk interposed between adjacent cylinders identifying their interface. An evaluation of the dosimetric properties of the markers was undertaken. An applicator was assembled using four cylinders (4 cm diameter) surrounding a stainless steel uterine tandem with a stainless steel disk 0.05 mm thick and 3.6 cm in diameter interposed between each consecutive pair of cylinders. The assembly was placed on a film and an Ir-192 high dose rate source was programmed to a single dwell position within the applicator. The markers were removed and a second film was exposed with the same dwell position and time. This procedure was repeated with various dwell positions along the applicator. A scanning densitometer was used to measure the density profiles and isodensity distributions of each film. RESULTS: The optical density profiles and isodensity distributions with and without the markers in place were identical for all source dwell positions except when the source was centered in the plane of one of the stainless steel disks, where a maximum decrease of less than 2% in the dose rate was measured. The disks had no effect on the profiles measured along axes more than 2 cm from the projection of the applicator central axis on the film. CONCLUSION: The markers provide geometrical information about the position of the applicator relative to the anatomy necessary for optimized treatment planning. Slight dose perturbations resulting from the markers do occur, but only for dwell positions that center the source in the plane of a disk, and even then only at points very close to the disk. The markers can therefore be ignored from a dosimetric point of view.

Administration, Intravaginal↗
PubMed1992

High dose rate intracavitary brachytherapy for carcinoma of the cervix: the Madison system: I. Clinical and radiobiological considerations.

The decision to use five high dose rate intracavitary (HDR-ICR) insertions at weekly intervals for invasive carcinoma of the cervix treated at the University of Wisconsin Comprehensive Cancer Center (UWCCC) was made clinically. It was based on practical considerations and on previous clinical experience worldwide which showed that between 2 and 16 insertions have been used with apparently acceptable results. Although radiobiological considerations favor a large number of small doses, such a large number of HDR-ICR insertions is not clinically practical. Our strategy was to keep the biological effects of external beam and intracavitary insertions in the same ratio as used on a large series of patients treated here with low dose rate (LDR) therapy. This means keeping the same external beam treatment scheme and finding high dose rate (HDR) doses that are biologically equivalent to the previous LDR therapy, as far as possible. External beam and HDR intracavitary dose schedules for the Madison System of treating cervical carcinoma are described in detail. Because there is more repairable damage in late-reacting normal tissues, there is a bigger loss of sparing in these tissues than in tumors when changing from LDR to HDR, so total doses should be reduced more for equal late complications than for equal tumor control. The clinical decision was made to aim at equal tumor control. The possible increase in late complications has to be avoided by reducing the doses to critical normal tissues using extremely careful anatomic positioning of the HDR sources. Critical normal tissues must be kept further away from the radiation sources so that their doses are about 20% lower than with LDR geometry. This requires an extra separation of some millimeters depending on the anatomy and geometry of the individual insertion. The strategy is that the unfavourable radiobiological effects of a few large fractions must be counteracted by better physical dose distributions with HDR-ICR than with the previous LDR insertions. These good distributions are obtainable with the short exposures at HDR.

Brachytherapy↗
PubMed1992

High dose rate intracavitary brachytherapy for carcinoma of the cervix: the Madison system: II. Procedural and physical considerations.

The loss in therapeutic ratio accompanying a conversion from low dose-rate (LDR) to high dose-rate (HDR) intracavitary brachytherapy (ICR) requires increased attention to the precision and accuracy of dose distribution calculations and treatment delivery. While the HDR-ICR treatment unit allows better custom-tailored dose distributions compared to LDR, it also requires more attention to detail to achieve the distribution desired. Because the relative biological effectiveness of different isodose levels in a dose distribution varies with the absolute dose (as described in Part 1 of this article), the relative dose distribution used with LDR must be modified for HDR to produce the same expected biological effect. Because of the difference in the radiobiology and physical positioning, simply duplicating applications as performed with LDR misses opportunities for dose distribution improvement as well as opens possibilities for significant complications. Due to differences in positioning the applicator (e.g., retraction of the cervix low in the pelvis instead of packing the applicator high), traditional definitions of points of interest (such as point A) apply poorly with HDR-ICR, compelling new systems of dose specification. With HDR-ICR, irreparable mistakes can happen very quickly, and quality assurance for the treatment plan and calculated dwell times prove much more important than with LDR. Key features of the dose distribution and constant relationships involving doses and dwell times help screen planned treatments for mistakes. This paper details the procedural and physical consideration of the Madison system for HDR-ICR brachytherapy for carcinoma of the cervix.

Brachytherapy↗
PubMed1992

A new re-entrant ionization chamber for the calibration of iridium-192 high dose rate sources.

A re-entrant (well-type) ionization chamber has been designed and fabricated at the University of Wisconsin for use with iridium-192 high dose-rate (HDR) remote after-loading brachytherapy devices. The chamber was designed to provide an ionization current of about 10(-8) ampere with a nominal 10 curie iridium-192 source. A narrow opening is provided into the sensitive volume of the chamber to insert a Nucletron MicroSelectron catheter, or catheters with similar diameters from other HDR manufacturers. The chamber exhibits a flat response (+/- 0.1%) for any source position within +/-4 mm of the chamber center. A 300 volt chamber bias yields a 99.96% ion collection efficiency. The chamber is capable of being calibrated directly with an iridium-192 source which has in turn been calibrated with thimble-type ion chambers. Reproducibility for readings in the current mode for 10 consecutive insertions of the MicroSelectron iridium-192 HDR source is within 0.02% or less. Two thimble chambers calibrated by the U.S. National Institute of Standards and Technology provide calibration traceability of iridium-192 HDR sources and re-entrant chambers to a primary national standards laboratory. Results of activity measurements of 6 commercial iridium-192 HDR sources are reported.

Calibration↗