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Biomedical subjects

J C Chu

Publications and source records attributed to J C Chu.

At least 19 recordsLinked to original sources
PubMed1996

Dose to contralateral breast: a comparison of four primary breast irradiation techniques.

PURPOSE: Contralateral breast dose from primary breast irradiation has been implicated in the risk of second breast malignancies. It has been previously shown that the use of half-beam blocking can increase the opposite breast dose by a factor of five. This study evaluates four different breast treatment techniques to compare the radiation dose to the contralateral breast. METHODS AND MATERIALS: Dose measurements were made using thermoluminescent dosimeters (TLD) capsules, which were placed in the Rando phantom in the following locations in the contralateral breast: seven along the central axis plane, on at 5 cm superior to, and one 5 cm inferior to the central axis plane. One TLD capsule was placed in the midcenter of the treated breast. The following radiation techniques were used: (a) half-beam with a custom block (HB+CB), (b) half-beam using asymmetric collimator jaw (HB/AJ), (c) half-beam using asymmetric collimator jaw with custom block (H/AJ+CB), and (d) isocentric technique with nondivergent posterior borders [Joint Center for Radiation Therapy (JCRT) techique]. For each technique, isodose distributions for the Rando phantom were optimized using (a) 15 degree medial and lateral compensating wedges, and (b) a single 30 degree lateral compensating wedge. The phantom was treated with 6 MV photons. Each technique was repeated six times, and the TLD readings were averaged. RESULTS: The custom cerrobend half-beam block technique gives the highest contralateral breast dose, regardless of wedge. The remaining techniques give results in a similar range, with the asymmetric jaw with no medial wedge technique giving the lowest total dose (p = not significant). The use of a medial wedge increases the opposite breast dose for all techniques. The asymmetric half-beam technique gives significantly less dose than the cerrobend half-beam technique, due to decreased transmission through the asymmetric collimators. The asymmetric jaw vs JCRT technique results in similar contralateral breast dose. CONCLUSIONS: As expected, dose to the contralateral breast increases with the use of a medial wedge. Cerrobend half-beam blocking gives the highest opposite breast dose. The lowest contralateral breast dose is with the asymmetric jaw with no medial wedge and no block. The asymmetric jaw technique with block yields equivalent contralateral breast doses to the JCRT technique.

Breast↗
PubMed1995

Using simulation data to predict lung geometry for inhomogeneity corrections in breast cancer treatments.

PURPOSE: To develop a statistical model based only on simulation measurement data, to predict the lung geometry in the central slice of the tangential radiation treatment fields for breast cancer. METHODS AND MATERIALS: A linear regression analysis was performed on 22 patients to determine the shape of lung in the central axis plane of the tangential radiation fields. Data collected include the greatest perpendicular distance (GPD) measured from the chest wall to the field border on computed tomography (CT) images, the central lung distance (CLD) measured from the posterior field border to the chest wall on the simulation portal images, and the lung contours digitized at 1 cm intervals. The lung contours of these patients were fitted to a parabolic curve through a polynomial regression model. A lung template based on the regression model is used to construct a "generic lung" contour on patients' external body contours for treatment planning. The accuracy of this technique was tested on another group of 15 patients for its ability to predict the shape of lung on the central axis plane and the accuracy of dose to the prescription point. RESULTS: The polynomial regression indicates that all the patients' lung contours in the tangential fields follow a parabolic curve: Y = -0.0808 X2 + 0.0096 X + 0.0326. The maximum lung involvement (GPD) can be determined from the value of CLD measured on the simulation film by the linear regression model with a determination coefficient of 0.712. The 15-patient test results indicate that our model predicts the lung separation on the central axis with an average deviation of 1.35 cm, and the average absolute dose deviation to the dose prescription point is 1.46%. CONCLUSION: The model presented in this article provides an efficient method to estimate the lung geometry for breast cancer treatment planning without the requirement of CT data. The lung contour predicted by our model is useful for calculating dose distributions with inhomogeneity correction and may potentially benefit patients at higher risk of pulmonary toxicity.

Breast Neoplasms↗
PubMed1995

Calculation of monitor units for a linear accelerator with asymmetric jaws.

A simple approach was developed that calculates the output factors and tissue maximum ratio of an asymmetric field at any point within the open field, and specifically both at the central axis (when the jaws do not shadow it) and at the effective center of the open field, using the existing tables for symmetric fields and the multidepth profile information for the largest available field size (either open or with a wedge present). Day's method was adapted to calculate the effective values of the usual field-size-dependent parameters. This approach makes these parameters also dependent on the location of the calculation point relative to the field edges in an asymmetric field. This algorithm was tested by comparing its predictions with measurements of asymmetric and half blocked fields, with and without wedges, in a water phantom at different depths and off-axis distances. The agreement between calculated and measured dose rate is within 1%-3% even in highly asymmetric fields for both 6- and 18-MV photons.

Models, Structural↗
PubMed1994

A single isocenter three-field breast irradiation technique using an empiric simulation and asymmetric collimator.

The treatment of abutting fields presents multiple difficulties, including problems of field overlaps or gaps, complexity of simulation, and the difficulties of daily setup and variation. Multiple techniques have been described for the treatment of the breast/chest wall and supraclavicular nodes using tangents and a matched supraclavicular field. The techniques described have used collimator angles, couch angles, and/or corner blocks in an attempt to match these fields with no overlap or gap. Some of these techniques required complex calculations or treatment devices to achieve a geometric match between fields. We describe a technique for treatment of breast and supraclavicular nodes that uses a single isocenter and requires asymmetric collimator jaws to give half-blocked fields. The simulation and setup are done empirically, with no complex calculations required. The daily setup and treatment can be done rapidly and reliably, with no extra equipment required. Custom blocks may be used to conform to the chest wall contour and decrease the amount of lung in the treatment fields.

Breast Neoplasms↗
PubMed1993

Streptolysin O-permeabilized cell system for studying trans-acting activities of exogenous nuclear proteins.

Efficient transfer of exogenous proteins into culture animal cells can be achieved by Streptolysin O (SLO) permeabilization of plasma membranes. We used this method to establish an in vitro transcription system for early response genes. The promoters of many early response genes contain an essential DNA motif known as the Serum Response Element (SRE). Recent data has shown that this DNA sequence is recognized by Serum Response Factor (SRF) and its associated proteins. Our initial experiments showed that HeLa nuclear extracts induced the transcription of the c-fos gene in serum-starved murine fibroblasts which were permeabilized by either physical method (glass beads) or cytolytic pore-forming protein (SLO). Plasma membrane permeabilization presumably permits passive diffusion of macromolecules into target cells and we showed that a truncated SRF expressed in bacteria was translocated into the nucleus within 30 minutes after SLO permeabilization. HeLa crude extracts were fractionated in order to identify the active nuclear factors. SRF was purified by binding to Wheat Germ Agglutinin (WGA)-agarose but the active factors remained in the WGA-unbound fractions. Our results demonstrate that this permeabilized cell in vitro transcription system is simple, efficient and can be used to test crude nuclear fractions as well as purified proteins expressed in bacteria; it will be an useful tool for the reproduction of transcriptional regulation on chromatin templates in vitro as well as the investigation of the biochemical functions of specific transcription factors or signal transduction effectors.

3T3 Cells↗
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↗