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Results for “Radiotherapy Planning, Computer-Assisted”

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PubMed1990

Improved dose homogeneity in the head and neck using computer controlled radiation therapy.

Computer-controlled radiation therapy techniques are demonstrated which improve dose homogeneity throughout the nasopharynx when compared to conventional treatment techniques. The typical approach using a heavily weighted anterior field and opposed wedged lateral fields results in a dose gradient from 95% to 110% or greater. All three of the computer-controlled techniques investigated improved the dose uniformity to a range from 95% to 105% or less. Multiple overlapping fields are used to compensate for patient anatomy and treatment beam characteristics. Treatment planning and monitor unit calculations are quite time-consuming at this stage of development. Actual treatment time is not unreasonably long and can be improved in future releases of the therapy machine control software.

Humans↗

PubMed1987

The utility of MR in planning the radiation therapy of oligodendroglioma.

Newer methods of radiation therapy for treating oligodendroglioma after surgical resection have produced promising results using high doses of radiation. However, these doses are close to those that cause necrosis of normal brain, making the accurate spatial localization of tissue at risk for containing tumor cells more important. Because MR imaging is superior to CT in detecting some types of intracranial disease, nine patients with oligodendroglioma were studied with both MR and CT. Results were compared with surgical findings. In six cases, MR identified some tumor volume found during surgery that was not detected by CT. In addition, the interface between abnormality (tumor plus edema) and normality was depicted much more clearly by MR than by CT in most cases. Such superior depiction of the margins of abnormality is important for radiation therapy planning because of the known tendency of oligodendroglioma to infiltrate adjacent edema, making all areas of abnormality potential tumor-bearing tissue. Finally, MR showed normal brain tissue in areas considered suspicious by CT, because they were not well seen on CT in several patients. In these cases of low-grade oligodendroglioma, MR was believed to be superior to CT in providing information needed for radiation therapy planning because of its ability to distinguish tumor and adjacent edema (considered tissue at risk for containing microscopic tumor) from contiguous normal brain.

Adult↗

PubMed1989

[Radiotherapy of the breast after conservative surgery for primary carcinoma. Irradiation technic with matched fields].

The authors report their technique for breast radiotherapy following conservative surgery (quadrantectomy + axillary dissection). The breast and chest wall are irradiated with photons from a 60Co unit through two fixed opposing tangential fields. The posterior field edges must be parallel and coplanar to the chest wall. A routine treatment plan using simulator, pantograph and computerized console is standardized by mathematical formulae elaborated from geometric breast measurement parameters. Gammagraphies acquired prior to and during therapy allow verification and control of treatment parameters. For 35 patients the therapy plan as described was compared with that obtained by CT images. Our procedure proved valid and an accurate treatment plan could be elaborated even without CT images. The use of wedges, half-field blocks and the dose scattered to the contralateral breast are also discussed.

Axilla↗

PubMed1988

Optimization of radiation therapy in prostatic cancer.

The results of a study on the optimization of external irradiation of prostatic cancer are discussed. The study was performed with the aid of an automatic water phantom, an automatic densitometer, and a computerized treatment planning system using an anthropometric phantom Alderson. The following parameters were studied: Dose gradient, the size of areas of selected isodoses, and the shape of the 90% isodose. At present, we consider that the twosector biaxial arc technique characterized by an arc angle of 120 degrees, a distance of the arc axes of 3 cm, employing a 20 MeV X-ray of a linear accelerator is the optimal technique for target irradiation of carcinomas of the prostate.

Humans↗

PubMed1992

Reduction of the dose to the lens in prophylactic cranial irradiation: a comparison of three different treatment techniques and two different beam qualities.

Three treatment techniques using two beam qualities have been compared on the basis of dose to the lens in prophylactic cranial irradiation. The dose to the lens and the globe was measured with thermoluminescent crystals in an anthropomorphic phantom and calculated by a computer-assisted planning system. A comparison was made of large field and small field techniques using 60Co and 8 MV photons. Modifications to the basic techniques studied included angulation of the gantry, angulation of the couch, and placement of an additional eye block close to the surface. The dose to the lens could be reduced to four percent of the midplane dose by applying the small-field technique combined with the use of 8 MV energy photons, by placing an additional block close to the surface, and by five degree occipitally angling the gantry, as well as rotating the treatment couch to account for the divergence of the beam. The use of 60Co produced an underdosage of the posterior segment of the globe in angled treatment techniques.

Cataract↗

PubMedDate not supplied

The role of the CT scanner in RT planning.

Work has already been done showing the benefits and difficulties of CT planning. I have tried to discuss here the more practical aspects involved. Some 100 patients have now been planned using the CT scanner in conjunction with the planning computer. After a few initial problems (mainly concerning the transfer of data between the two computers), all the plans seem to fit well and set up on the treatment machines satisfactorily. Everything is verified using the simulator. In general, it takes only a little extra time on the CT scanner, and time is saved on the simulator. The benefits are:--1. More accurate dose distribution in the planning--tissue densities previously measured, for instance lung correction factors etc. 2. Bladder and prostate tumours--a cystogram can be avoided and also the possibilities of infection inherent in this invasive procedure. 3. Bladder tumours--a more realistic picture of the bladder as it will be when treated, that is, not fully drained (Figures 7a and 7b). 4. More accurate outline information over the whole length of the area to be treated. 5. More accurate information regarding the position of critical organs in relation to the tumour volume and the treatment volume.

Humans↗

PubMed1992

Various wedge isodose angles for treatment planning.

Various wedge isodose angles or simply wedge angles smaller than the nominal wedge angle were created by combining the isodose distributions generated from a single physical wedge with the isodose distributions of the open field for the 8-MV photon beam. The particular wedge angle generated depends on the weights imposed on these isodose distributions. The relationship between these weights and the wedge angle were examined and found to be nonlinear. The difference between the wedge angles defined at 10 cm depth and those defined using the 50% isodose curve is less 6 degrees. The present data was fitted using two proposed empirical equations.

Humans↗

PubMed1987

[Changes in the chest x-ray following postoperative irradiation of breast cancer].

The radiogenic modifications of the thorax radiography were evaluated in 100 patients irradiated postoperatively for mammary carcinoma between January, 1980 and March, 1983. No adjuvant chemotherapy was given. A telecobalt unit was used for the irradiations. A computer-assisted planning (Evados) was applied in order to obtain an individual optimization especially for the fields situated at the thoracic walls. The average focal doses to the thoracic wall and the regional lymph nodes were between 50 and 52 Gy. Taking into consideration all modifications visualized by radiography, 65% of patients had subacute radiogenic reactions in the lungs, especially in the apex fields. In general the modifications had no clinical importance. Only seven patients presented more severe forms of pneumonitis with clinical symptoms. Fibroses were developed only in the apex fields; infraclavicular infiltrations were seen only in exceptional cases. There were no costal necroses, essential pleural reactions, or radiogenic enlargements of the heart shadow. The rate of pulmonary reactions with clinical symptoms is reduced as compared with former techniques, e.g. opposing tangential fields. The knowledge of anamnesis and typical radiographic modifications should help to avoid problems of differentiation between apex reactions and tuberculosis.

Adult↗

PubMed1992

Optimization of a cord shielding technique for electrons.

Large anterior electron fields are sometimes used to irradiate the neck when treating head & neck tumors. To offer a degree of spinal cord shielding, wax bolus, approximately the width of the vertebral bodies, is placed on the immobilization shell. The thickness of the bolus is adjusted so that the radiological depth of the anterior edge of the vertebral bodies is equal to the R80 depth for the energy used. This approach ignores electron scattering. Using a CT study of a thyroid cancer patient, neck contours were generated at 0.5 cm intervals and entered into the Alberta Treatment Planning system. Internal contours for the trachea and vertebral bodies were added and CT information was used for treatment planning purposes. The bolus outline was added as described above, and the dose calculated using a 3D implementation of the M.D. Anderson (Hogstrom) algorithm. The calculation shows that the simple bolus technique described above is inappropriate. The spinal cord is adequately shielded, but the target volume is not covered by the 80% isodose line. Qualitatively, the results can be explained by the lateral scatter non-equilibrium introduced by the bolus. By iteratively adjusting the shape and thickness of the wax bolus and recalculating the dose distribution, we were able to better fulfill the dose prescription. Comparison with measured data shows reasonable, but not perfect agreement. In conclusion, electron beam treatments must be examined closely to ensure that the treatment goals are met. In some cases, treatment integrity may be compromised by incorrect assumptions regarding the nature of the electron transport and dose deposition.

Humans↗

PubMed1990

Treatment planning for internal radionuclide therapy: three-dimensional dosimetry for nonuniformly distributed radionuclides.

A calculational approach is described that provides the spatially varying radiation absorbed dose, presented as isodose contours superimposed on CT images, from nonuniform and/or irregular cumulated activity distributions. CT images are read from magnetic tape and are displayed on a high-resolution color graphics display monitor. Source tissue geometries are defined on a series of contiguous CT images automatically (by an edge detection algorithm) or manually (using a trackball), thereby obtaining a three-dimensional representation of the various source volumes of activity. Dose calculations are performed using a radionuclide-specific absorbed dose point kernel in the form of a lookup table. The method described yields the spatially varying dose delivered to tumor and normal tissue volumes from a patient-specific cumulated activity distribution in a clinically implementable manner. This level of accuracy in determining normal tissue and tumor doses may prove valuable in the evaluation and implementation of radionuclides and radiolabeled compounds for therapeutic purposes.

Algorithms↗

PubMed1988

Multimodality image display: desirable frame buffer characteristics.

The intent of this paper is to understand the characteristics of those frame buffers currently used to display images, versus more ideal frame buffers for medical image display purposes. This study is based on current needs and what characteristics might be desirable. Two case examples are presented: (1) a system developed for high quality computer graphics and (2) a system developed for nuclear medicine and radiation therapy treatment planning. Our study considers: (1) defining a pixel depth sufficient to hold data, (2) the desirability of multiple color look-up tables, (3) how cine loops are managed, and (4) display memory size.

Computer Graphics↗

PubMed1989

Minimizing and measuring lens dose when giving cranial irradiation.

Three different techniques of administering cranial irradiation were used to determine the dose to the lens as measured in the Rando phantom. The techniques employed were as follows: (1) the central axis of the radiation beam was placed at the thickest portion of the cranium; (2) the central axis of the radiation beam was placed at the lateral orbital rim (bony canthus); (3) the central axis of the radiation beam was placed at the thickest portion of the cranium but with the beam angled 5 degrees posteriorly away from the eye. Thermal luminescent dosimeters (TLD) were placed in a phantom, at a point determined from a life-sized anatomical section of the plane through the midsection of the eye, to be at the location of the posterior capsule of the lens. In addition, TLDs were placed on the outer surface of the phantom head, directly lateral to the location determined to be where the lens would lie. With equally weighted lateral opposed beams, delivering a midplane dose of 200 cGy, the TLDs at the point of the lens measured 21, 9.9 and 10.6% of the midplane doses from the three techniques respectively. TLDs placed directly lateral to the lens on the surface of the phantom head gave an approximation of the lens dose, particularly when techniques 2 and 3 were used. Isodose curve generated by a General Electric treatment planning computer gave lens doses similar to those of the phantom data for each of the three different radiotherapy techniques. Cranial irradiation should be carried out by either technique 2 or technique 3 to minimize radiation dose to the lens.

Brain Neoplasms↗

PubMed1989

Manual reconstruction of tumor volumes from CT scans for radiotherapy planning.

Using a computed tomographic scan to construct a tumor volume on a simulation film has become an important part of radiation therapy treatment planning. Techniques for reconstruction of brain tumor volumes from computed tomographic scans onto simulation films are discussed. A technique for reconstructing by hand the tumor volume projection at a different angle from the plane of the computed tomographic scan is outlined. Ignoring beam divergence simplifies reconstruction, allowing it to be done by hand but introduces an additional error of at most 0.06, 0.15, 0.26 and 0.42 cm for tumors with maximum diameters of 5, 7.5, 10 and 12.5 cm, respectively. This technique provides the capability for limited 3-dimensional volume reconstruction of small tumors without the use of the computer.

Brain↗

PubMed1991

Application of the LQ model to the interpretation of absorbed dose distribution in the daily practice of radiotherapy.

In 1991, the vast majority of radiotherapy centers are implemented with computer treatment planning systems (TPS), and it has become routine practice to compute full absorbed dose distribution (ADD) in almost all treatment situations. Usually the target is covered by the 100% isodose and the surrounding normal tissues receive a lesser dose than the tumor. It implies, that, as the dose per fraction of, say, 2 Gy is prescribed at the 100%, normal tissues receive a daily dose different than 2 Gy. The absorbed doses delivered at different organs have therefore not the same biological effectiveness and must be corrected according to the actual dose per fraction for a proper interpretation of the treatment planning. This is of great importance since most of the "tolerance levels" used in the practice have been determined for doses per fraction around 1.8-2 Gy. The linear-quadratic (LQ) model provides a simple method for establishing biological equivalencies and has been used throughout this article to establish the difference between the absorbed dose computed by the TPS and its biological equivalent. It is shown that normal tissues receiving less than 100% of the daily dose are relatively more protected than suggested by the ADD, and, inversely, that normal structures overdosed and thus receiving more than the 100% daily dose are relatively more at risk for complications than suggested from the ADD.

Bronchial Neoplasms↗

PubMed1992

Radiation oncology residents' computer workstation.

We are investigating the feasibility of using the Macintosh computer as a workstation platform for radiation oncology residents because of its ease of use, graphics capability, and low cost. Hypercard was chosen as the programming environment because it easily mixes graphics, text, and control functions in an integrated screen display. Furthermore, it results in a system that can be relatively easily extended and customized by individual users with varying degrees of computer skills. We have developed several software modules in order to test the ability of this environment to support the demands of such a workstation. Modules created thus far include various clinical physics aids and tutorials, treatment planning guides, oncology databases, and others. The software runs on all Macintosh configurations, but calculation speeds are improved when a 68020 or greater processor is used. In general, we have been pleased with the implementation thus far. Graphics display capability is good, but design and entry of graphics have proved labor-intensive. Searching is fast and text is easily entered and manipulated. Finished modules can be customized with minimal computer training, but implementing complex new functions requires familiarity with Hypercard's programming language. New modules, once developed, are easily integrated into the workstation universe, suggesting that cooperative development of the workstation by multiple contributors is realistically achievable.

Computer Graphics↗

PubMed1991

The use of T2 distribution to study tumor extent and heterogeneity in head and neck cancer.

Demarcation of the extent of malignant tissue is essential for planning a course of radiotherapy. MR images may provide additional information for delineating the target volume because of the large difference in the proton magnetic resonance relaxation times between normal and malignant tissues. In 13 patients with head and neck tumors the distribution of the proton spin-spin relaxation times, T2, at 1.5 Tesla were evaluated throughout the physician designated target volume and normal surrounding tissue. The T2 values within the tumor were always elevated compared with normal tissue, the highest values being in the nominal center of the tumor and decreasing toward the periphery. The regional distribution of T2 values within the tumor is a measure of the tissue heterogeneity within the tumor volume. In addition, the large differences in T2 relaxation times between normal and disease tissues were used in a computer algorithm to automatically demarcate the boundary of abnormal tissue in each axial MRI section. This potentially could significantly expedite the time required to identify the target volume on multiple sections and thus remove one of the major time constraints for 3D treatment planning.

Head and Neck Neoplasms↗

PubMedDate not supplied

Computer applications to radioactive-seed: brain-tumor implants.

Malignant brain tumors, in general, and anaplastic astrocytoma and glioblastoma multiforme in particular, have been highly refractory to conventional treatments including surgery, chemotherapy and external-beam irradiation. Although better local control can be achieved with high-dose, external beam irradiation, necrosis of normal brain tissue reduces the quality of life and survival. In order to localize the radiation dose given to brain tumors, the temporary implantation of 125I and 192Ir seeds is undergoing clinical trials at several medical centers. Computers play a key role in this treatment modality: in addition to being essential for image reconstruction of CT scans, a computer is used to reconstruct a tumor volume from outlined regions on individual cuts; a programable calculator is used in conjunction with a stereotaxic head holder to obtain the coordinates of the radioactive seeds; a radiation-therapy, treatment-planning computer is used to optimize the radioactive-seed positions and strengths, and to generate the corresponding dose distribution.

Astrocytoma↗

PubMedDate not supplied

Acquisition and display of radiation dose distributions using microcomputer technology.

In the commissioning or quality assurance of a medical linear accelerator or a computerized radiotherapy planning system, the traditional approach usually consists of acquiring and comparing one-dimensional dose profiles. This methodology is tedious and incomplete since only a portion of the radiation field can realistically be sampled. We have developed an automated measurement system which allows efficient measurement and display of complete two-dimensional dose distributions. The general purpose microcomputer used (IBM PC/XT compatible) can be interfaced economically to any water phantom dosimetry system equipped with a three axis scan controller, and can also communicate data to the treatment planning system. This allows for direct comparison of measured with computed dose distributions, thus revealing discrepancies in the dose computation algorithms used. In this paper, we describe the interface between the microcomputer, a conventional water dosimetry system (Therados RFA-3), and a treatment planning computer. We report our early experience with acquiring dose distributions and show sample comparisons with computed results for megavoltage electron beams incident on homogeneous and heterogeneous systems.

Humans↗