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Biomedical subjects

D R Spelbring

Publications and source records attributed to D R Spelbring.

12 recordsLinked to original sources
PubMed1999

Matching photon and electron fields with dynamic intensity modulation.

A technique was developed to reduce the size and magnitude of the hot and cold spots in the abutting regions of photon and electron fields. The photon and electron fields were set up such that the photon field extended approximately 2 cm into the electron field in the abutting region. The region of the photon beam that overlapped the electron field was modulated using a multileaf collimator, effectively broadening the photon penumbra to make it complimentary to the electron penumbra. The computer calculations were verified using film measurements for abutting a 6 MV photon beam with a 9 MeV electron beam. A uniform dose was achieved at a prespecified depth of 2 cm, and dose uniformity was improved at the specified depth and beyond compared with unmodulated photon beams. A slight increase in dose inhomogeneity was seen at shallower depths. The overall areas of the hot and cold spots were significantly reduced. The technique also reduced the sensitivity of dose homogeneity to setup errors such that the magnitudes of the hot and cold spots were about half of those produced with unmodulated photon beam when an overlap or gap of 4 mm was introduced. The technique was applied to the treatment of a head and neck cancer and a lymphoma involving the right pleura with markedly reduced dose inhomogeneity in the abutting regions.

Computer Simulation↗
PubMed1997

Functional dose-volume histograms for functionally heterogeneous normal organs.

Functional dose-volume histograms are proposed as an extension of the conventional dose-volume histograms, for quantitative assessment of three-dimensional radiation dose coverage of functionally heterogeneous normal organs. Examples are given to illustrate possible applications of this approach to the treatment of a brain tumour or a lung tumour, in which cases the distribution of the normal organ function can be obtained from functional dose-volume modalities. It is shown that a significant difference exists between the functional dose-volume histograms and the conventional dose-volume histograms when the normal organ function is non-uniformly distributed within the organ. Utilization of functional dose-volume histograms as the input for the calculation of normal tissue complication probabilities is discussed for different normal tissue structures.

Humans↗
PubMed1995

A method of analyzing rectal surface area irradiated and rectal complications in prostate conformal radiotherapy.

PURPOSE: To develop a method of analyzing rectal surface area irradiated and rectal complications in prostate conformal radiotherapy. METHODS AND MATERIALS: Dose-surface histograms of the rectum, which state the rectal surface area irradiated to any given dose, were calculated for a group of 27 patients treated with a four-field box technique to a total (tumor minimum) dose ranging from 68 to 70 Gy. Occurrences of rectal toxicities as defined by the Radiation Therapy Oncology Group (RTOG) were recorded and examined in terms of dose and rectal surface area irradiated. For a specified end point of rectal complication, the complication probability was analyzed as a function of dose irradiated to a fixed rectal area, and as a function of area receiving a fixed dose. Lyman's model of normal tissue complication probability (NTCP) was used to fit the data. RESULTS: The observed occurrences of rectal complications appear to depend on the rectal surface area irradiated to a given dose level. The patient distribution of each toxicity grade exhibits a maximum as a function of percentage surface area irradiated, and the maximum moves to higher values of percentage surface area as the toxicity grade increases. The dependence of the NTCP for the specified end point on dose and percentage surface area irradiated was fitted to Lyman's NTCP model with a set of parameters. The curvature of the NTCP as a function of the surface area suggests that the rectum is a parallel structured organ. CONCLUSIONS: The described method of analyzing rectal surface area irradiated yields interesting insight into understanding rectal complications in prostate conformal radiotherapy. Application of the method to a larger patient data set has the potential to facilitate the construction of a full dose-surface-complication relationship, which would be most useful in guiding clinical practice.

Dose-Response Relationship, Radiation↗
PubMed1993

An analysis of image segmentation time in beam's-eye-view treatment planning.

In this work we tabulate and histogram the image segmentation time for beam's eye view (BEV) treatment planning in our center. The average time needed to generate contours on CT images delineating normal structures and treatment target volumes is calculated using a data base containing over 500 patients' BEV plans. The average number of contours and total image segmentation time needed for BEV plans in three common treatment sites, namely, head/neck, lung/chest, and prostate, were estimated.

Computer Peripherals↗
PubMed1992

The use of beam's eye view volumetrics in the selection of non-coplanar radiation portals.

In 3-dimensional treatment planning, beam's eye view (BEV) is used as an interactive tool to define portal entry angles that exclude critical structures while fully encompassing the target volume. With beam's eye view volumetrics (BEV volumetrics), the volume of intersected normal tissues is also calculated and is used as a quantitative tool to choose portal orientations that minimize normal tissue volumes irradiated. The axial beam entry angle and a polar angle (relative to the patient longitudinal axis) are specified to define the central axis orientation. Using BEV volumetrics, we have studied the quantities of normal tissues irradiated when treating tumors in the abdomen, thorax, and pelvis. The reduction of normal tissue irradiated is a strong function of site and patient-specific tumor size and location. Volumetrics combined with BEV is found to be useful in treatment planning because it (a) provides quantitative information needed in rationally choosing portal entry angles, (b) provides a near interactive speed approach to understanding the relative merits of different multiple field plans, and (c) compliments the information provided by the more time-consuming generation of dose volume histograms.

Humans↗
PubMed1992

Beam's eye view volumetrics: an aid in rapid treatment plan development and evaluation.

A well-designed treatment plan fully irradiates the target to the prescribed dose while minimizing radiation to adjacent critical structures. Beam's eye view is an important component of treatment planning systems because it provides the operator with tools needed to achieve this goal. Through interactive manipulation of displays, the planner uses beam's eye view to adequately cover the target volume while geometrically avoiding certain critical, normal structures. A factor not considered in current beam's eye view programs is the fractional volume of each structure irradiated given a specified beam direction. We have incorporated a rapid volume calculation capability in our beam's eye view program, and have applied it to provide a quantitative aid to treatment planning development and evaluation. Treatment planning of lung tumors has been studied using this tool. Volumes of lung and spinal cord treated as a function of portal angle may be calculated much more rapidly than dose volume histograms and yet provide quantitative indices which follow the trends of dose volume histograms as a function of field angle. Plots of normal tissue volume irradiated as a function of field angle identify the optimal angle to minimize irradiated volume of a structure at a glance. For multiple field plans, a bitmap approach identifies areas treated by various combinations of beams. Volumetrics combined with beam's eye view are useful in treatment planning because they (a) provide quantitative information needed in choosing and optimizing portal entry angle (b) provide an interactive approach to understanding the relative merits of different multiple field plans and (c) complement the information provided by the more time consuming generation of dose volume histograms. The clinical application of this tool in treatment planning is presented.

Computer Graphics↗
PubMed1992

Quantitation of treatment volumes from CT and MRI in high-grade gliomas: implications for radiotherapy.

Long-term survival of patients with high-grade gliomas remains extremely poor. The main reason for such an outcome is local failure, or recurrence, after surgery and/or radiotherapy. Higher doses of radiation may result in decreased local failure rates provided that the location (and extent) of gross tumor and microscopic disease can be defined accurately. The abnormalities appearing in images from diagnostic modalities, such as CT and MRI, are being used as a starting point and as a guide for the clinical definition of tumor and its extensions. However, some recent studies on two-dimensional specimens, correlating histopathological findings to CT and MRI images, showed that the resulting definition of tumor cell extensions was unsatisfactory, different, and in need of ample margins. We carried out a retrospective analysis to compare the target volumes that would have been defined by CT, T2-weighted MRI, and T1-weighted postgadolinium MRI images of the same individual and to explore the implications of the resulting volume definitions for radiotherapy. The results of our limited study, based on the margins used, indicate that the CT-defined target volume is consistently larger than that from either of the two MRI modalities and suggest that noncoplanar approaches for its treatment and other local approaches for tumor boost should be considered. We conclude that until more definitive histopathological guidelines correlated to image features have been formulated and agreed upon, one should try to make full use of all available diagnostic information in order to minimize the possibility of geographical miss of target extensions.

Adult↗
PubMed1990

Radiation therapy in the treatment of cervical cancer: the University of Chicago/Michael Reese Hospital experience.

A retrospective analysis was conducted on 307 patients referred for radiation therapy at The University of Chicago and Michael Reese Hospital between 1971 and 1986. Median follow-up was 6.4 years. Treatment techniques varied during the time of the study. Actuarial disease-free survivals were 78%, 64%, 55%, 33%, 41%, and 60% for stage IB, IIA, IIB, IIIA, IIIB, and IVA, respectively. Stage, size of the cervical lesion, and hemoglobin level during treatment were prognostic factors. Treatment technique as well as time dose factors were analyzed with respect to survival, failures, and complications.

Adult↗
PubMed1990

Beam's eye view based prostate treatment planning: is it useful?

Prostate cancer is a common malignancy often treated with radiation therapy. Treatment optimization may improve local control while reducing acute and long-term complications. We routinely obtained CT scans on prostate cancer patients in treatment position after simulation. We analyzed the impact and implications of using our 3-D Beam's Eye View (BEV) capability on field definition and blocking for 12 consecutive patients. Conclusions include: (a) it is necessary to use multiple bony landmarks to align BEV images with simulator films; (b) it is difficult to enter volumes precisely, that is, the exact inferior extent of prostate; (c) Beam's Eye View-based plans show more individual variability in field size and position than are allowed for by recommendations in the literature; and (d) in this small series we found no significant correlation between prostate volume and clinical staging. In addition, computerized Beam's Eye View capability enables us to do normal tissue dosimetry. We have used Dose Volume Histograms (DVH) to study the impact of Beam's Eye View on optimization of dose to the bladder and rectum while adequately treating the prostate, with or without the seminal vesicles. Dose Volume Histograms using Beam's Eye View are compared with Dose Volume Histograms using target volumes from the literature. The results will be discussed, as well as the relative advantages of using Beam's Eye View for prostate cancer on a routine basis.

Evaluation Studies as Topic↗
PubMed1989

Breast conserving surgery and definitive irradiation for early stage breast cancer.

Breast conserving surgery and postoperative breast radiotherapy were used to treat 219 cases of AJCC Stage I and II breast carcinoma at the Michael Reese and University of Chicago Hospitals. Most patients were treated with lumpectomy and axillary sampling followed by breast irradiation to a dose of 46 Gy followed by a boost dose of 14-16 Gy to the surgical bed. The 5-year actuarial local control is 92%. Follow-up is 1 to 10 years and the median follow-up is 36 months. Of the seven patients who recurred in the breast, three failed in the boost site and three failed adjacent to the boost site. The seventh patient recurred diffusely in the breast and skin. Four of the seven recurrences were in patients with positive surgical margins. The 5-year actuarial relapse-free survival is 80%. Factors which had an adverse affect on the cosmetic results were a scar length greater than 8 cm and a volume of resected breast tissue greater than 100 cm3. Treatment related complications were minor and infrequent. Breast conserving surgery followed by radiation therapy is effective in achieving local control with good to excellent cosmetic results.

Adult↗
PubMedDate not supplied

Accurate three-dimensional registration of CT, PET, and/or MR images of the brain.

A surface matching technique has been developed to register multiple imaging scans of the brain in three dimensions, with accuracy on the order of the image pixel sizes. Anatomic information visualized in X-ray CT and magnetic resonance images may be integrated with each other and with functional information from positron emission tomography. Anatomical structures and other volumes of interest may be mapped from one scan to another, and corresponding sections through multiple scans may be directly compared. This capability provides a novel quantitative method to address the fundamental problem of relating structure to function in the brain. Applications include basic and clinical problems in the neurosciences and delivery and assessment of brain tumor therapy.

Brain↗