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Biomedical subjects

Bruce Thomadsen

Publications and source records attributed to Bruce Thomadsen.

10 recordsLinked to original sources
PubMed2006

Selective Internal Radiation Therapy (SIRT) for liver metastases secondary to colorectal adenocarcinoma.

INTRODUCTION: Selective internal radiation therapy (SIRT) is a relatively new commercially available microbrachytherapy technique for treatment of malignant hepatic lesions using (90)Y embedded in resin microspheres, which are infused directly into the hepatic arterial circulation. It is FDA approved for liver metastases secondary to colorectal carcinoma and is under investigation for treatment of other liver malignancies, such as hepatocellular carcinoma and neuroendocrine malignancies. MATERIALS/METHODS: A modest number of clinical trials, preclinical animal studies, and dosimetric studies have been reported. Here we review several of the more important results. RESULTS: High doses of beta radiation can be selectively delivered to tumors, resulting in impressive local control and survival rates. Ex vivo analyses have shown that microspheres preferentially cluster around the periphery of tumor nodules with a high tumor:normal tissue ratio of up to 200:1. Toxicity is usually mild, featuring fatigue, anorexia, nausea, abdominal discomfort, and slight elevations of liver function tests. CONCLUSIONS: Selective internal radiation therapy represents an effective means of controlling liver metastases from colorectal adenocarcinoma. Clinical trials have demonstrated improved local control of disease and survival with relatively low toxicity. Investigations of SIRT for other hepatic malignancies and in combination with newer chemotherapy agents and targeted biologic therapies are under way or in planning. A well-integrated team involving interventional radiology, nuclear medicine, medical oncology, surgical oncology, medical physics, and radiation oncology is essential for a successful program. Careful selection of patients through the combined expertise of the team can maximize therapeutic efficacy and reduce the potential for adverse effects.

Adenocarcinoma↗
PubMed2004

Proposed guidelines for image-based intracavitary brachytherapy for cervical carcinoma: report from Image-Guided Brachytherapy Working Group.

PURPOSE: To present issues to be considered in, and make proposals for, image-based brachytherapy for cervical cancer. METHODS AND MATERIALS: The Image-Guided Brachytherapy Working Group, consisting of representatives from the Gynecology Oncology Group (GOG), Radiologic Physics Center (RPC), American Brachytherapy Society (ABS), American College of Radiology (ACR), American College of Radiology Imaging Network (ACRIN), American Association of Physicists in Medicine (AAPM), Radiation Therapy Oncology Group (RTOG), and American Society for Therapeutic Radiology and Oncology (ASTRO), proposed guidelines for image-based brachytherapy for cervical cancer. This report was based on their aggregate clinical experience and a review of the literature. It reflects only the personal opinions of the authors and is not meant to be an endorsement from any of the above organizations. RESULTS: The Group recommended T(2)-weighted MRI using a pelvic surface coil with MRI-compatible brachytherapy applicators in place for image-based intracavitary brachytherapy for cervical cancer. Imaging must be performed with the patient in the treatment position, with all other treatment conditions duplicated as closely as possible. Future use of positron emission tomography or positron emission tomography/CT may obviate the need for special applicators. The group proposed the following terminology for image-based brachytherapy. The GTV((I)) is defined as the gross tumor volume as defined through imaging, GTV is defined as the GTV((I)) plus any clinically visualized or palpable tumor extensions, and GTV + cx is defined as the GTV plus the entire cervix. The dose-volume histograms (DVH) of the GTV, GTV((I)), GTV + cx should be performed, and the dose to 100%, 95%, or 90% of the GTV (D(100), D(95), and D(90), respectively) and the percentage of the GTV covered by Point A dose (V(100)) should be reported. Similarly, the DVH of the bladder and rectum wall should be performed, and the maximal dose at any point within the bladder and rectal wall should be reported, along with the maximal dose to a contiguous 1, 2, and 5 cm(3) volume of the bladder and rectum, respectively. In addition, the dose at the International Commission on Radiation Units and Measurements reference point for the bladder and rectum should be reported. The Group thought that the current dose prescription method in use for cervical cancer brachytherapy (i.e., to prescribe to Point A in most institutions) should not be changed as yet, because image-based dosimetry is not ready for routine practice. The Group proposes that for research purposes, individual centers and cooperative groups (e.g., GOG, RTOG, ACRIN) collect image-based dosimetry information and perform DVHs and correlate these data with the clinical outcome to determine which of the above parameters are relevant. The Group encourages external funding for image-based dosimetry and recommends that brachytherapy manufacturers develop image-compatible applicators. CONCLUSION: Although current institutional brachytherapy prescription for cervical cancer should continue, image-based data collection and analysis are needed to optimize cervical cancer brachytherapy. Proposals are made for research in image-based brachytherapy for cervical cancer.

Brachytherapy↗
PubMed2004

CT-based analysis of dose homogeneity in total body irradiation using lateral beam.

A computed tomography (CT) based treatment planning system for total body irradiation (TBI) is presented and compared with the commonly practiced lateral treatment delivery. The TBI regimen has been proved to be an essential conditional regimen for patients undergoing bone marrow transplantation. The advantage of the TBI regimen with bone marrow transplantation (BMT) in hematological malignancies can be offset by toxicities arising from TBI in posttransplant complications. With the increasing survival rates, the evaluation of long-term side effects and quality of life has become an important area of research interest. There have been several treatment techniques developed over the decades designed to achieve accurate dose delivery and dose homogeneity. This paper reports on the verification of the dose delivery for a basic lateral technique using thermoluminescent dosimeters (TLDs) placed in an anthropomorphic phantom and its correlation with CT-based treatment planning. CT-based treatment plans on several patients were used to evaluate the doses delivered to the whole body and critical organs. A large variation in doses delivered to the whole body was demonstrated, with some parts of the bone marrow failing to receive the prescribed dose and some critical organs, such as the lungs, receiving excessive doses. Placing the arms at the sides only partially compensates for the increased transmission of the lungs because the arms only shadow part of the lung. This study shows that CT-based treatment planning for TBI provides precise and accurate dose calculations and allows for the correlation of clinical outcomes with the doses actually delivered to various organs.

Body Burden↗
PubMed2003

Analysis of treatment delivery errors in brachytherapy using formal risk analysis techniques.

PURPOSE: To identify hazardous situations in treatments, analyze the nature of errors committed, and assess the value of several analysis techniques. MATERIALS AND METHODS: The study applied several risk analysis techniques to brachytherapy events (misadministrations) reported to the U.S. Nuclear Regulatory Commission and the International Atomic Energy Agency. RESULTS: (1) Events usually have multiple causes. (2) Failure to consider human performance in the design of equipment led to a large fraction of the events. (3) Verification procedures often were ineffectual. (4) Many events followed the failure of persons involved to detect that the situation was abnormal, often even though many indications pointed to that fact. Once the event was identified, the response often included actions appropriate for normal conditions, but inappropriate for the conditions of the event. (5) Events tended to happen most with actions having the least time available. (6) Lack of training and procedures covering unusual conditions frequently contributed to events. (7) New procedures or new persons joining a case in the middle present increased hazards. CONCLUSIONS: Risk analysis tools common in industry provide useful information for error reduction in medical settings, although not as effectively, and modification of such techniques could improve their efficacy.

Algorithms↗
PubMed2003

Craniospinal treatment with the patient supine.

Radiotherapy of the craniospinal axis in young children is frequently complicated by the need for access to the patient's airway for sedation and anesthesia delivery or by frequent, unanticipated movement. Positioning the patient supine, instead of in the conventional prone position, allows the use of immobilization facemasks with body molds and more positive patient fixation, and improved airway access. The procedure for establishing the various fields differs from the prone approach. In this paper, we describe the methodology to achieve successful supine positioning.

Age Factors↗
PubMed2003

Inter-society standards for the performance of brachytherapy: a joint report from ABS, ACMP and ACRO.

PURPOSE: The proliferation of various brachytherapy modalities for different anatomical sites necessitates the creation of standards for brachytherapy. METHODS: A panel consisting of members of The American Brachytherapy Society (ABS), The American College of Medical Physics (ACMP) and The American College of Radiation Oncology (ACRO) developed standards for the clinical practice and quality assurance (QA) of brachytherapy. These were based upon their clinical experience and a review of the literature. RESULTS: Recommended practice standards are presented for clinical processes, treatment planning, equipment, facilities, QA, dose evaluation, dose specification, dose reporting, the training, and credentialing of personnel, and radiation control/safety/protection. Safe and efficacious performance of brachytherapy requires a highly structured QA program and carefully designed treatment delivery processes, as well as a coordinated effort amongst the team members. CONCLUSION: Standards for clinical brachytherapy are proposed. Practitioners are encouraged to use these standards to design and implement a consistent and efficacious brachytherapy program.

Brachytherapy↗
PubMed2002

The American Brachytherapy Society recommendations for low-dose-rate brachytherapy for carcinoma of the cervix.

PURPOSE: This report presents guidelines for using low-dose-rate (LDR) brachytherapy in the management of patients with cervical cancer. METHODS: Members of the American Brachytherapy Society (ABS) with expertise in LDR brachytherapy for cervical cancer performed a literature review, supplemented by their clinical experience, to formulate guidelines for LDR brachytherapy of cervical cancer. RESULTS: The ABS strongly recommends that radiation treatment for cervical carcinoma (with or without chemotherapy) should include brachytherapy as a component. Precise applicator placement is essential for improved local control and reduced morbidity. The outcome of brachytherapy depends, in part, on the skill of the brachytherapist. Doses given by external beam radiotherapy and brachytherapy depend upon the initial volume of disease, the ability to displace the bladder and rectum, the degree of tumor regression during pelvic irradiation, and institutional practice. The ABS recognizes that intracavitary brachytherapy is the standard technique for brachytherapy for cervical carcinoma. Interstitial brachytherapy should be considered for patients with disease that cannot be optimally encompassed by intracavitary brachytherapy. The ABS recommends completion of treatment within 8 weeks, when possible. Prolonging total treatment duration can adversely affect local control and survival. Recommendations are made for definitive and postoperative therapy after hysterectomy. Although recognizing that many efficacious LDR dose schedules exist, the ABS presents suggested dose and fractionation schemes for combining external beam radiotherapy with LDR brachytherapy for each stage of disease. The dose prescription point (point A) is defined for intracavitary insertions. Dose rates of 0.50 to 0.65 Gy/h are suggested for intracavitary brachytherapy. Dose rates of 0.50 to 0.70 Gy/h to the periphery of the implant are suggested for interstitial implant. Use of differential source activity or loading minimizes excessive central dose rates. These recommendations are intended only as guidelines. The responsibility for medical decisions ultimately rests with the treating radiation oncologist. CONCLUSION: Guidelines are suggested for LDR brachytherapy for cervical cancer. Practitioners and cooperative groups are encouraged to use these guidelines to formulate their treatment and dose-reporting policies.

Brachytherapy↗
PubMed2002

Measurements of the dosimetric constants for a new 103Pd brachytherapy source.

PURPOSE: This report provides dosimetry information for a new brachytherapy 103Pd source (Model 2335) manufactured by Best Medical International and, through comparisons with data from another published report for the same source, presents a suggested hybrid dataset for clinical applications. METHODS AND MATERIALS: Dose measurements were made using thermoluminescent dosimeters (TLD), with the 103Pd source in the center of a Virtual Water phantom on a rotating insert, allowing for a number of different possible angles, and 12 TLD cubes (1.0 x 1.0 x 1.0 mm) and 16 TLD rods (1.0 x 1.0 x 3.0 mm) arranged in an outward spiral pattern at distances ranging from 0.5 to 5.0 cm. All measurements are based on the 2000 correction of the National Institute of Standards and Technology 1999 standard. RESULTS: From these measurements, tables are presented for the radial dose function and the anisotropy function. The dose rate constant=0.71 +/- 0.07 cGy h(-1) U(-1) and the anisotropy constant=0.96 +/- 0.03. CONCLUSIONS: The dose rate constant for the hybrid=0.70 and the anisotropy constant for the hybrid=0.92, Hybrid tables are presented.

Anisotropy↗
PubMed2002

A quality management program in intravascular brachytherapy.

While simple, intravascular brachytherapy (IVB) presents a considerable potential for harm to the patient. The medical physicist maintains the responsibility to minimize the likelihood of operational problems or dosimetric errors. The principals for safe operation remain the same as with any radiotherapy treatment: to deliver the correct dose, to the correct location, safety. To develop an effective and comprehensive quality management (QM) program for IVB, a physicist should utilize proven risk assessment techniques rather than simply thinking of things to check, and follow guidances such as ISO9001:2000. The proposed QM program includes the following: Procedures designed to assure the safety of the patient. Identification of the patient; tests of the integrity and patency for the delivery catheter, operation of the source train, and patency of the catheter in the treatment position; a check for recovery preparations; and verification of source recovery. Procedures to assure positional accuracy of the treatment: Verification of the positioning the catheter in the artery and of the sources in the catheter. Procedures to assure dosimetry accuracy: Acceptance testing of the device, including verification of the source strength and uniformity, and of the treatment duration tables; verification of the treatment prescription and duration for each patient; and control measures that minimize the likelihood of errors removing the source at the correct time.

Brachytherapy↗