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Biomedical subjects

F A Gibbs

Publications and source records attributed to F A Gibbs.

At least 19 recordsLinked to original sources
PubMed2001

Electron arc irradiation of the postmastectomy chest wall with CT treatment planning: 20-year experience.

PURPOSE: Since 1980, electron arc irradiation of the postmastectomy chest wall has been the preferred radiotherapy technique at the University of Utah for patients with advanced breast cancer. We report the results of this technique in 156 consecutive Stage IIA-IIIB patients treated from 1980 to 1998. METHODS: CT treatment planning was used in all patients to identify chest wall thickness and internal mammary lymph node depth. Computerized dosimetry was used to deliver total doses of 50 Gy in 5-1/2 weeks to the chest wall and the internal mammary lymph nodes with electron arc therapy. Patients were assessed for local, regional, and distant control of disease and for survival. Univariate and multivariate proportional hazards were modeled using a hierarchical nonproportional semiparametric model testing the following prognostic factors: age, stage, tumor size, number of positive lymph nodes, estrogen receptor status, and dose. End points evaluated included disease-free survival, cause-specific survival, and overall survival. RESULTS: Eighty-one percent of patients were at high risk for local-regional failure because of > T2 primary tumor or > 3 positive axillary lymph nodes. The median number of positive lymph nodes was 5, and the median tumor size was 3.5 cm. Actuarial 10-year local-regional control and overall survival were 95% and 52%, respectively. In multivariate analysis, the only factor prognostic for disease-free survival, cause-specific survival, and overall survival was the number of positive lymph nodes (p < 0.001). The 10-year rates of local-regional control for patients with 0, 1-3, 4-9, and > or = 10 involved lymph nodes were 100%, 98%, 93%, and 89%, respectively. The only rates of acute and chronic radiotherapy toxicity > or = 2 by RTOG/EORTC criteria were skin related and observed in 44% and 10% for acute and late reactions, respectively. CONCLUSION: These data demonstrate excellent local-regional control rates with electron arc therapy of the postmastectomy chest wall in patients with advanced breast cancer. Our 20-year experience with electron arc radiotherapy has demonstrated the safety and efficacy of this technique. The advantage of this technique is that the internal mammary lymph node chain can be easily encompassed while the dose to heart and lung is minimized; it also obviates match lines in areas of high risk.

Adult↗
PubMed2000

Dosimetric evaluation of a specialized radiotherapy treatment technique for scleredema.

Scleredema adultorum of Buschke is an unusual manifestation of diabetes mellitus that can result in painful indurations and thickening of the skin with associated limitation of motion, and has been previously reported to be responsive to radiotherapy. We report on the method employed to treat a severely affected patient by means of opposed photon fields and multiple electron fields encompassing his entire neck, arms, and thorax.

Humans↗
PubMed2000

Application of enhanced dynamic wedge to stereotactic radiotherapy.

Stereotactic radiotherapy has developed into a useful treatment technique in which conformal dose distributions can be delivered with precision and accuracy. In some cases, the position of the target volume relative to surrounding critical structures demands careful evaluation of fixed beam paths so that dose to these critical structures can be minimized. Micromultileaf collimators aid in conforming dose to the target volume but may not allow adjustment of an individual beam's intensity (intensity modulation) in an effort to achieve dose uniformity throughout the treatment volume. Enhanced dynamic wedge (EDW) is demonstrated to be a valuable tool in improving the dose distribution in stereotactic radiotherapy treatments in which these fixed, conformal fields must be used due to constraints in beam trajectories. Four cases are presented which show the potential for gain in dose uniformity with the addition of EDW. These cases represent typical applications of EDW to conformal stereotactic radiotherapy.

Humans↗
PubMed1999

Dosimetric advantages of enhanced dynamic wedge in small field irradiation for the treatment of macular degeneration.

Exudative macular degeneration is a process that affects the central retina and is the chief cause of blindness in people over 55 years old. Radiation appears to improve or stabilize visual acuity in some of these patients, although definitive clinical studies are ongoing. The delivery of radiation in patients with macular degeneration is unique and challenging because of the location of the surrounding structures, such as the lens and the opposite retina. The "standard" treatment technique has been an anterior oblique beam 20 degrees above lateral to limit dose to these structures. In preference to the undesirable hot spot caused by this single-beam technique, we have employed a superior and inferior oblique pair utilizing the Enhanced Dynamic Wedge (EDW). Couch rotation was used to establish the desired treatment angles. The anterior half of the fields were blocked with the asymmetric jaw (AJ). Studies were performed to determine the value of these methods in reducing lens dose. Although the peripheral dose measurements at Dmax using a 60 degrees metal wedge for > or = 10 cm square fields were higher than for an open field or the EDW, for the small retinal fields there was no lens-dose reduction attributable to the EDW. However, the steep wedge angles achievable with the EDW were useful for optimizing the dose distribution for the most desirable field angles. As expected, the independent collimator was more effective in reducing transmitted dose to the lens than a typical Cerrobend block. Measurements required to predict dose in and out of the field are discussed along with the dosimeters employed in evaluating small fields (less than 5 cm square) with the EDW. The technical challenges of positioning, immobilization, treatment planning and treatment delivery are presented.

Humans↗
PubMed1994

Mechanical assay of consequential and primary late radiation effects in murine small intestine: alpha/beta analysis.

A portion of jejunum in C3H/HeJ mice was irradiated in situ with 250 kV X rays, and the resulting elastic stiffness increase was used as an assay of chronic fibrotic injury. With data from this assay dose-response curves were evaluated with early- and late-appearing chronic intestinal injuries in two experiments. (1) After split-dose treatment with an interfraction interval of 0.0, 0.25, 0.5, 1.0, 2, 4 or 24 h, the asymptotic dose-recovery ratios in assays at 2-3 weeks and at 4 months were statistically similar, R = 1.34 (95% confidence limits: 1.29-1.39) with t1/2 = 0.75 h (0.48-1.17), and R = 1.36 (1.31-1.42) with t1/2 = 0.49 h (0.21-0.86), respectively, although the slopes of the dose-response curves for the early and late assays differed significantly. (2) Mice received 2, 3, 4, 5, 10 or 15 equal X-ray fractions in 5 days with interfraction intervals of at least 5.5-6 h. The data from the dose responses were used in either of two analyses of variance for calculating alpha/beta values. Using slopes in transformed Fe plots, alpha/beta was 8.5 Gy (6.1-12.5) for the assay at 2-3 weeks and 3.6 Gy (2.4-5.4) at 4 months. Using these and other data we argue that assay at the two times measured separate fibrotic responses to injuries to the small intestine, namely, a rapidly appearing consequential late effect that had the same alpha/beta value as for crypt microcolony assays because it was a sequela of acute inflammation after transient loss of mucosal epithelial integrity after crypt sterilization, and a lower-threshold primary or true late effect with a lower alpha/beta value, which progressively masked the consequential injury.

Analysis of Variance↗
PubMed1993

Measurement of mechanical accuracy of isocenter in conventional linear-accelerator-based radiosurgery.

PURPOSE: Five Varian linear accelerators were studied to determine whether their mechanical isocentric accuracies were sufficient for radiosurgery and, if not, if the observed errors were sufficiently consistent and predictable to be correctable by some form of secondary collimator steering device to maintain isocentric alignment. METHODS AND MATERIALS: A 0.3 mW 670 nm diode laser was mounted in the secondary collimator insert of a radiosurgery extended collimator assembly. A cylindrical lens was used to create a laser fan beam that passed through isocenter and could be oriented parallel or perpendicular to the plane of rotation. A position sensitive photo-diode having an electrical output that varied with the portion of its surface illuminated was mounted at isocenter in a rotational mount. This mount tracked the accelerator gantry such that the surface of the photo-diode remained perpendicular to the laser beam during gantry rotation. An X/Y recorder was connected to the gantry-angle potentiometer of the accelerator and to the photo-diode and plotted the positional variation from isocenter with gantry rotation. RESULTS: The root-mean-square error for the five machines was +/- 0.06 to +/- 0.08 mm in the plane of rotation and +/- 0.17 to +/- 0.35 mm out of (perpendicular to) the plane of rotation. The in-plane-of-rotation errors tended to be maximal near the diagonal gantry angles and the out-of-plane-of-rotation errors were maximal in the over and under vertical positions. CONCLUSIONS: Both types of errors were predictable but only the out-of-plane-of-rotation errors were considered large enough to warrant consideration of correction (although the need is debatable). On all the tested machines, the out-of-plane-of-rotation error curve was a relatively smooth bell-shaped function that would be readily amenable to correction. The diode laser/photo-detector system used should prove useful in accurately defining isocenter and facilitating the precise adjustment of the laser isocenter lights.

Humans↗
PubMed1991

Dynamic field shaping to optimize stereotactic radiosurgery.

A dynamic field shaping collimation system is evaluated for use in stereotactic radiosurgery of non-spherical lesions. The concept is as follows: (a) use the existing circular collimators to define a cone which encompasses the maximum dimensions of the target volume; (b) position two sets of independent rectangular photon collimators immediately upstream from the circular aperture and allow each collimator to have independent translational and rotational motion in order to define, for each increment of arc, a polygonal field shape having up to four straight and four curved edges which enscribe the beam's eye projection of the target; (c) modify the translational and rotational position of each independent collimator with each change in arc angle to continuously shape the instantaneous field to the target shape. A prototype device has been constructed and uses vane control technology developed in a related research project in electron arc therapy. The efficacy of this device is illustrated by dose calculations and measurement based on actual clinical data. Dose volume histograms are used to compare the dose received by three techniques: single isocenter treatment using a single circular aperture, dual isocenter treatment, and single isocenter treatment using dynamically shaped fields. Doses were calculated throughout the brain using a volume grid of 3 mm spacing. Dose volume histograms comparing dose within the target volume and brain volume excluding target volume, as well as computed isodose distributions, demonstrate the possible reduction in normal tissue dose burden while simultaneously preserving dose uniformity throughout the prescribed target volume. This simple four-vane collimation system may provide a viable alternate treatment technique for non-spherical lesions.

Humans↗
PubMed1990

Thermochemotherapy in inoperable head and neck cancer.

A combined hyperthermia and chemotherapy approach was used to treat five patients with locally advanced or recurrent squamous cell carcinoma of the head and neck whose tumors had failed to respond to chemotherapy. In two patients, tumor had recurred after initial combined modality therapy (surgery/radiation) and had failed to respond to one course of cisplatin/5-fluorouracil (cisplatin/5-FU) chemotherapy. The three remaining patients were enrolled onto a phase II evaluation of induction chemotherapy with cisplatin/fluorouracil for advanced head and neck carcinomas and had failed to achieve a partial remission after one treatment cycle. Palpable cervical tumors were heated to 40 degrees to 42 degrees C for 30 to 40 minutes, during which time cisplatin (100 mg/m2) was infused intravenously. A 5-day infusion of 5-fluorouracil (1000 mg/m2/d) followed. Despite less than a partial response to previous cisplatin/fluorouracil chemotherapy alone, two patients had complete clinical resolution of the heated tumor volume with two cycles of the combined thermochemotherapy approach. One patient achieved a partial remission with this approach. The remaining two patients died shortly after the initial thermochemotherapy treatment, as a result of progressive tumor growth. The two complete responders were subsequently treated with radiation (1 patient) and radical neck dissection (1 patient) and remained without evidence of disease 2 and 26 months after the completion of therapy, respectively. The toxicity of this combined modality approach was acceptable and appeared to be no greater than had been experienced during earlier treatment with chemotherapy alone. Further studies using a combination of these treatment modalities for locally advanced head and neck carcinomas are warranted.

Aged↗
PubMed1989

Prognostic indicators in head and neck cancer patients receiving combined therapy.

In 1983 we initiated a prospective nonrandomized study of the value of preoperative chemotherapy in previously untreated patients with stages III and IV squamous cell carcinoma of the head and neck. In 1983 and 1984, 50 patients were entered in the study. Prior to therapy all patients were evaluated by a representative from the Medical Oncology, Radiation Therapy, and Head and Neck Surgery Divisions, University of Utah School of Medicine, Salt Lake City. In addition to the standard preoperative evaluation, pretreatment computed tomographic scans were performed on all patients. Follow-up computed tomographic scans were performed after the second cycle of chemotherapy and at the completion of treatment. Initial therapy in all patients consisted of induction chemotherapy with cisplatin (day 1, 100 mg/m2) and fluorouracil (days 1 through 5, 1000 mg/m2). Several factors were examined for their utility in predicting response to therapy and survival. Factors evaluated included: (1) extent and timing of chemotherapeutic response; (2) computed tomographic quantitated primary tumor size; (3) size of computed tomographic quantitated regional (neck) metastases; (4) performance status; (5) cancer stage; (6) total lymphocyte count; and (7) serum liver function tests. The factor found to be most useful in predicting improved survival was the extent of response to chemotherapy. The remaining factors, performance status, regional lymph node status, serum gamma-glutamyltransferase levels, and cancer stage, were also found to correlate with length of survival but were much less important than the response to chemotherapy.

Antineoplastic Combined Chemotherapy Protocols↗