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Biomedical subjects

J C Chu

Publications and source records attributed to J C Chu.

At least 37 records · Page 2Linked to original sources
PubMed1992

Quality assurance for intraoperative electron radiotherapy clinical trials: ionization chamber and mailable thermoluminescent dosimeter results.

Ionization chamber and thermoluminescent dosimeter measurements were made to verify the dosimetry data provided to the Radiation Therapy Chart Review office of interinstitutional electron intraoperative radiotherapy clinical trials. The ionization measurements included intraoperative radiotherapy applicator output and depth dose measurements made at the stated 80% and 50% depths at 14 different radiotherapy facilities. Mailable thermoluminescent dosimeter measurements, including output and depth dose measurements were made at 16 institutions. The mailable thermoluminescent dosimeter results show similar inter-institutional agreement, both for output and depth dose comparison, with the corresponding ion chamber results for intraoperative radiotherapy applicators. These results are compared to similar measurements made for conventional electron applicators.

Clinical Trials as Topic↗
PubMed1992

Use of computerized hot wire block cutter in radiation therapy.

The ability to define the target volume more accurately and to deliver the radiation therapy with better precision in modern radiation oncology has resulted in radiation treatments with tighter margins in order to spare additional normal tissues. This type of treatment requires that the radiation shielding blocks be produced with high accuracy. The computer-driven block cutter has the advantage of being able to accept block contours designed from digital simulation and portal images as well as beam's-eye-view patterns produced during treatment planning. A computerized hot wire block cutter installed in our department has shown the capability to produce accurate blocks and has reduced the number of blocks requiring modifications by about one-third. The use of templates plotted on the transparencies facilitates the accurate mounting of the blocks has resulted in further reduction of the number of block modifications.

Humans↗
PubMed1992

Three-dimensional dosimetric comparison of radiation therapy treatment planning of the pancreas.

Radiation therapy for carcinoma of the pancreas requires high doses for local control. Three-dimensional dose distributions are calculated for four patients with pancreatic cancer using two conventional (4-field box and 3-field techniques) and two noncoplanar (4 and 6 oblique fields) treatment field arrangements. Uniform dose distributions are obtained for all beam arrangements. The 4-field oblique beams show a potential advantage for lower dose to the kidneys when compared with 4-field box technique, and to the small bowel, when compared with 3-field beams. The data suggest that the noncoplanar beams may be useful alternative techniques for treating this disease with certain case presentations and should be considered during the treatment planning process.

Humans↗
PubMed1991

Numerical scoring of treatment plans.

This is a report on numerical scoring techniques developed for the evaluation of treatment plans as part of a four-institution study of the role of 3-D planning in high energy external beam photon therapy. A formal evaluation process was developed in which plans were assessed by a clinician who displayed dose distributions in transverse, sagittal, coronal, and arbitrary oblique planes, viewed dose-volume histograms which summarized dose distributions to target volumes and the normal tissues of interest, and reviewed dose statistics which characterized the volume dose distribution for each plan. In addition, tumor control probabilities were calculated for each biological target volume and normal tissue complication probabilities were calculated for each normal tissue defined in the agreed-upon protocols. To score a plan, the physician assigned a score for each normal tissue to reflect possible complications; for each target volume two separate scores were assigned, one representing the adequacy of tumor coverage, the second the likelihood of a complication. After scoring each target and normal tissue individually, two summary scores were given, one for target coverage, the second reflecting the impact on all normal tissues. Finally, each plan was given an overall rating (which could include a downgrading of the plan if the treatment was judged to be overly complex).

Humans↗
PubMed1991

Three-dimensional photon treatment planning of the intact breast.

Three-dimensional treatment planning for the intact breast was performed on two patients who had undergone CT scanning. A total of 38 treatment plans were evaluated. Multiple plans were evaluated for each patient including plans with and without inhomogeneity corrections, plans using varying photon energies of 60Co, 4 MV, 6 MV, 10 MV, and 15 MV, and three-dimensionally unconstrained plans. Increased hot spots were appreciated in the central axis plane when lung inhomogeneity corrections were used. Additional hot spots were appreciated in off-axis planes towards the cephalad and caudad aspects of the target volume because of lung inhomogeneity corrections and changes in the breast contour. The use of 60Co was associated with an increase in the magnitude and volume of hot spots, whereas the use of higher energy photons such as 10 MV and 15 MV was associated with an unacceptable target coverage at shallow depths. Therefore, for the two patients studied, the use of a medium energy photon beam (such as from a 6 MV linear accelerator) appeared to be the energy of choice for treatment of the intact breast. The three-dimensionally unconstrained plans were able to improve slightly upon the standard plans, particularly with relationship of dose to normal tissue structures. Areas for future research were identified, including the use of tissue compensators.

Adult↗
PubMed1991

Three-dimensional treatment planning for postoperative treatment of rectal carcinoma.

The role of three-dimensional (3-D) treatment planning for postoperative radiation therapy was evaluated for rectal carcinoma as part of an NCI contract awarded to four institutions. It was found that the most important contribution of 3-D planning for this site was the ability to plan and localize target and normal tissues at all levels of the treatment volume, rather than using the traditional method of planning with only a single central transverse slice and simulation films. There was also a slight additional improvement when there were no constraints on the types of plans (i.e., when noncoplanar beams were used). Inhomogeneity considerations were not important at this site under the conditions of planning, i.e., with energies greater than 4 MV and multiple fields. Higher beam energies (15-25 MV) were preferred by a small margin over lower energies (down to 4 MV). The beam's eye view and dose-volume histograms were found quite useful as planning tools, but it was clear that work should continue on better 3-D displays and improved means of translating such plans to the treatment area.

Combined Modality Therapy↗
PubMed1991

Digital imaging in the radiation oncology environment: a personal computer local area network solution.

Personal computer (PC) driven digital imaging devices are now becoming available in the market place for use in radiation oncology to produce what are known as real time portal images. These limited contrast images are used to verify the patient anatomy under treatment by megavoltage x-rays and are a vital part of the patient treatment. The current generation of devices can produce both single and movie loop images in real time for physician review and approval. To disseminate these images and other digital images used in the planning and delivery of radiation therapy, a PC-based picture archiving and communications system has been developed that is tailored to the special needs of radiation oncology.

Humans↗
PubMed1991

Conformal static field therapy for low volume low grade prostate cancer with rigid immobilization.

The ability to improve existing standards of treating prostate cancer was investigated. To deliver a homogenous dose to the prostate with as little normal tissue margin as practical, seven patients with low volume carcinoma of the prostate were immobilized with alpha cradle body casts prior to using a CT-based 3D treatment planning system and beam's eye view (BEV) template. All patients had clinical Stage B-1 prostate cancer of favorable histologic differentiation (Gleason Score 2-5). A four field box technique was used, each beam having a single customized cerrobend block cut-out conforming to the exact contour of the prostate. To assess the accuracy of this process, daily port films were taken for 5 consecutive days and compared to a matched control group who were treated in a similar fashion, but were not casted. Dose volume histograms illustrate an average of 14% of bladder dose and 14% of rectal dose that can be eliminated using this technique when compared to field sizes and block placement in our previous technique. Daily setup variation was markedly improved using the cast, with a median daily variation of 1 mm as compared to 3 mm without the cast. The average range of movement for each of the seven casted patients was 3.3 mm as compared to 8 mm for the seven uncasted patients. Immobilization eliminated the worst 10% of all daily positioning errors. Using CT treatment planning with the patient casted and BEV allows for precise block placement with the prostate gland in its proper orientation during daily treatment. With improved immobilization and precise localization of the prostate gland, margins around the target can be made significantly smaller, and this may translate into a decrease in acute and/or late complications.

Humans↗
PubMed1991

Significance of prone positioning in planning treatment for esophageal cancer.

The treatment of esophageal cancer is made difficult by the close proximity of the esophagus to the spinal cord and the requirement to treat the esophageal target volume to doses greater than or equal to 60 Gy while limiting the spinal cord dose to less than or equal to 46 Gy. By placing the patient in the prone position, the esophagus can be displaced away from the spinal cord. We explored the results of this commonly used technique on 16 patients who have undergone simulation in both supine and prone positions. Both AP and lateral orthogonal radiographs were obtained in both positions. The distance between contrast material in the esophagus and spinal cord was noted in at least four transverse planes through the thoracic esophagus on each of the 16 patients. These four transverse planes were located at 3 cm above the carina, at the carina, 3 cm below the carina and 6 cm below the carina. The mean displacement (+/- 1 SD) of the esophagus away from the spinal cord when the patient was in the prone position compared to supine at each of these levels was 1.3 (+/- 0.8) cm, 1.8 (+/- 0.9) cm, 1.8 (+/- 1.0) cm, and 1.9 (+/- 1.1) cm. The range of displacement for all 64 displacement determinations was 0 to 4.2 cm with a mean of 1.7 cm. To evaluate further the consequences of prone positioning on treatment planning and doses received to target volumes and critical structures, we performed 3-dimensional treatment planning with a patient in both prone and supine positions. The requirements were to achieve a tumor volume dose of 60 Gy while keeping the spinal cord dose below 46 Gy. Two types of conventional treatment plans were examined in prone and supine positions. A 6-field plan consisted of delivery of 40 Gy through a large 3-field beam arrangement followed by delivery of 20 Gy through a similar 3-field cone down. An 8-field plan involved the delivery of 30 Gy through AP/PA beams followed by a 3-field beam arrangement to 40 Gy and a subsequent 3-field cone-down for the final 20 Gy. Comparison of dose volume histograms revealed that the 6-field plan spared relatively more heart whereas the 8-field plan spared relatively more lung. Regarding the primary consideration of coverage of target volume with avoidance of spinal cord, prone positioning was superior to supine positioning whether 6- or 8-field arrangements were used.

Esophageal Neoplasms↗
PubMed1990

A nondivergent three field matching technique for breast irradiation.

Effective radiation therapy to intact breasts requires the delivery of adequate dose to a large target volume using complex beam arrangements. A semi-empirical method is described to determine the correct gantry, collimator, and couch positions for a geometrically accurate field match among adjoining radiation beams. The technique uses a metal rod and chain combination to aid determination of the proper couch setting under remote fluoroscopy control. A couch position error of more than half a degree is easily detectable by this technique.

Breast Neoplasms↗
PubMed1990

Misadministration of prescribed radiation dose.

During a course of radiation therapy treatments, an incident involving machine malfunction or human error can result in delivering a dose other than the prescribed daily dose of radiation. The process of correcting and documenting the misadministration of prescribed radiation dose led to the creation of a department policy that has proved to be a useful quality assurance tool. Explanation of the policy and the information form is given. Incidents involving misadministration of prescribed dose during 1988 and 1989 have been reviewed and the results are presented. This paper describes the specific categories used to classify misadministrations, the frequency of occurrence for certain types of errors, and constructive quality control measures implemented to avoid recurrence of such incidents.

Equipment Failure↗
PubMed1989

Patterns of change in the physics and technical support of radiation therapy in the USA 1975-1986.

Information on the patterns of personnel and related equipment support and availability at various types of radiation oncology facilities are included in the Facilities Master List surveys conducted by the American College of Radiology. This paper summarizes the surveyed data obtained during 1975-1986. The data presented include the use of equipment and the degree of personnel support at government owned, hospital or university based, and freestanding facilities. There is increasing use of linear accelerators, simulators, and treatment planning computers among all types of facilities. The use of 60Co units has been progressively decreasing. Almost all types of facilities show inadequate, but slowly improving, numbers of physicians, physicists, dosimetrists, and technologists when compared with the level recommended by the Blue Book.

Health Facilities↗
PubMed1989

Equipment and manpower needs in radiation oncology dosimetry and treatment delivery.

Information on the patterns of personnel and equipment support at various radiation oncology facilities are included in the Facilities Master List surveys conducted by the American College of Radiology. This paper summarizes the surveyed data on equipment and dosimetrist and technologist support obtained during 1975-1986. There is increasing use of linear accelerators, simulators, and treatment planning computers but the use of 60Co units has been progressively decreasing. There are inadequate but slowly improving numbers of dosimetrists and technologists when compared with the level recommended by the Blue Book.

Hospital Departments↗
PubMed1988

Construction of three-dimensional compensators using a simplified moiré camera.

We describe a simple technique for fabrication of tissue compensators using a simplified moiré contouring camera mounted on a commercial simulator. It is shown that high-quality optical enlargement of moiré photographs can be employed to make tissue compensators quickly using 0.4 mm lead sheets. Phantom measurement shows that this technique accurately compensates an irregularly shaped surface.

Humans↗
PubMed1987

Determination of depth for electron breast boosts.

A technique has been developed to determine the depth for the electron boost treatments for patients undergoing definitive irradiation for early stage breast cancer. A series of parallel link chains are placed on the breast over the clinically determined site of the boost. Using fluoroscopy, the physician confirms that the chains overlie the tumor bed which is outlined by radiopaque surgical clips placed at the time of the breast biopsy. A pair of orthogonal films and/or rotational stereo shift films are obtained with a standard simulator unit. Using the image of the chains to define the surface contour, the depth of each surgical clip is measured directly from the orthogonal films or calculated from the rotational stereo shift films. With this information, the physician can determine the appropriate electron energy to cover the target volume. This method was tested by comparison with depths measured from CT scan, and close agreement was demonstrated.

Breast Neoplasms↗
PubMed1987

Practice of 3-dimensional treatment planning at the Fox Chase Cancer Center, University of Pennsylvania.

The use of 3-dimensional (3-D) dose distributions and dose-volume histograms in radiation therapy treatment planning is illustrated on a patient with a head and neck tumor. The patient was immobilized in a rectangular tissue compensation bolus box. The treatment was planned with a 14 MeV D-T derived fast neutron therapy beam. The isodose distributions and the dose-volume histograms at multiple adjacent levels are used to evaluate the adequacy of coverage of target volumes and the doses to the normal tissues. Such dose-volume histograms are useful and practical in summarizing the dose distribution throughout the irradiated volume, assessing the degree of uniformity of the dose distribution within the target volume, quantifying the amount of normal tissue irradiated, and evaluating rival treatment plans for both particle and nonparticle beams.

Fast Neutrons↗