Biomedical subjects

H M Kooy

Publications and source records attributed to H M Kooy.

10 recordsLinked to original sources

PubMed1992

Radiosurgery as part of the initial management of patients with malignant gliomas.

PURPOSE: Between May 1988 and May 1991, 41 patients with malignant gliomas were enrolled onto a prospective study designed to evaluate the role of radiosurgery as a component of initial management. PATIENTS AND METHODS: Thirty-seven patients underwent radiosurgery according to the protocol and were assessable for survival and complications of treatment. Diagnoses included glioblastoma multiforme (GBM) in 23 (62%) cases and anaplastic astrocytoma in 14 (38%) cases. In 20 (54%) cases, surgical resection was attempted initially, whereas 17 (46%) patients underwent biopsy only. Patients in the study group received external-beam radiotherapy that consisted of 5,940 cGy given in 33 fractions to partial brain fields that encompassed the primary tumor with a 3 to 4 cm margin. Radiosurgery, used as a technique for boosting the dose to any residual contrast-enhancing mass lesion, was given 2 to 4 weeks after the completion of conventional radiotherapy. Minimum radiosurgical doses ranged from 1,000 to 2,000 cGy (median, 1,200 cGy), whereas maximum doses ranged from 1,250 to 2,500 cGy (median, 1,500 cGy). The median tumor volume at the time of radiosurgery was 4.8 cm3 (range, 1.2 to 72 cm3). Adjuvant chemotherapy was not given. RESULTS: After a median follow-up of 19 months, only nine of 37 (24%) patients have died. Six patients (all glioblastoma multiforme) died of recurrent tumor, whereas death was attributable to complications of treatment in two cases and intercurrent disease in one case. Four patients with recurrent tumor failed at the margins of the radiosurgical treatment volume, whereas two patients progressed locally. One patient is alive with local and marginal failure. Seven (19%) patients underwent reoperation at a median time of 5 months (range, 1 to 14 months) after radiosurgery. CONCLUSION: We conclude that radiosurgery is a useful adjunct to other modalities in the initial management of patients with small, radiographically well-defined malignant gliomas.

Actuarial Analysis↗

PubMed1991

Treatment planning for stereotactic radiosurgery of intra-cranial lesions.

Stereotactic radiosurgery of intra-cranial lesions is a treatment modality where a well defined target volume receives a high radiation dose in a single treatment. Our technique delivers this dose using a set of non-coplanar arcs and small circular collimators. We use a standard linear accelerator in our treatments, and the adjustable treatment parameters are: isocenter location, gantry arc rotation interval, couch angle, collimator field size, and dose. The treatment planning phase of the treatment determines these parameters such that the target volume is sufficiently irradiated, and dose to surrounding healthy tissue and critical, dose-limiting structures is minimized. The attachment of a BRW localizing frame to the patient's cranium combined with CT imaging (and optionally MRI or angiography) provides the required accuracy for localizing individual structures in the treatment volume. The treatment is fundamentally 3-dimensional and requires a volumetric assessment of the treatment plan. The selection of treatment arcs relies primarily on geometric constraints and the beam's eye view concept to avoid irradiating critical structures. The assessment of a treatment plan involves isodose distributions throughout the volume and integral dose-volume histograms. We present the essential concepts of our treatment planning approach, and illustrate these in three clinical cases.

Adolescent↗

PubMed1990

Results of stereotactic brachytherapy used in the initial management of patients with glioblastoma.

Recent studies have shown a survival benefit for patients with recurrent glioblastomas treated with stereotactic brachytherapy. On the basis of these encouraging results, we began a prospective study in 1987 to evaluate the use of brachytherapy in patients with newly diagnosed glioblastoma. Patients were considered eligible for this study if they met the following criteria: Karnofsky performance status 70% or greater; tumor size not greater than 5 cm in any dimension; a radiographically well delineated, supratentorial lesion not involving the ependymal surfaces; and pathologically confirmed glioblastoma. We treated 35 such patients between 1987 and 1990 with stereotactic brachytherapy as part of their initial therapy. The treatment protocol involved surgery, partial brain external-beam radiotherapy (59.4 Gy in 33 fractions), and stereotactic brachytherapy with temporary high-activity iodine 125 sources giving an additional 50 Gy to the tumor bed. Chemotherapy was not used in the initial management of these 35 patients. To compare our results with those obtained in a matched control group, we identified 40 patients with glioblastoma treated with surgery and external radiotherapy, with or without chemotherapy, between 1977 and 1986 at our institution. These patients had clinical and radiographic characteristics that would have made them eligible for the brachytherapy protocol. Survival rates at 1 and 2 years after diagnosis were 87% and 57%, respectively, for patients receiving brachytherapy versus 40% and 12.5%, respectively, for the controls (P less than .001). We conclude that stereotactic brachytherapy improves the survival of patients with glioblastoma when it can be incorporated into the initial treatment approach. Unfortunately, only about one in four patients with glioblastoma are suitable candidates for brachytherapy at the time of initial presentation.

Adolescent↗

PubMed1990

The verification of an inverse problem in radiation therapy.

The inverse problem in radiation therapy presents a solution for a fluence distribution based on the specification of a region of dose in a patient. We show results for one such solution based on the inversion of an integral over a function of the fluence profile of a rotating beam. We use Monte Carlo methods and numerical integrations to evaluate dose distributions obtained with the inverse method and show the limitations of this theoretical approach. Our results show that dose to a single circular region at an arbitrary position in a 2-dimensional volume can be calculated. Uniform dose to arbitrarily shaped regions cannot be calculated with this formalism, although practical solutions can still be obtained.

Humans↗

PubMed1990

The treatment of recurrent brain metastases with stereotactic radiosurgery.

Between May 1986 and August 1989, we treated 18 patients with 21 recurrent or persistent brain metastases with stereotactic radiosurgery using a modified linear accelerator. To be eligible for radiosurgery, patients had to have a performance status of greater than or equal to 70% and have no evidence of (or stable) systemic disease. All but one patient had received prior radiotherapy, and were treated with stereotactic radiosurgery at the time of recurrence. Polar lesions were treated only if the patient had undergone and failed previous complete surgical resection (10 patients). Single doses of radiation (900 to 2,500 cGy) were delivered to limited volumes (less than 27 cm3) using a modified 6MV linear accelerator. The most common histology of the metastatic lesion was carcinoma of the lung (seven patients), followed by carcinoma of the breast (four patients), and melanoma (four patients). With median follow-up of 9 months (range, 1 to 39), all tumors have been controlled in the radiosurgery field. Two patients failed in the immediate margin of the treated volume and were subsequently treated with surgery and implantation of 125I to control the disease. Radiographic response was dramatic and rapid in the patients with adenocarcinoma, while slight reduction and stabilization occurred in those patients with melanoma, renal cell carcinoma, and sarcoma. The majority of patients improved neurologically following treatment, and were able to be withdrawn from corticosteroid therapy. Complications were limited and transient in nature and no cases of symptomatic radiation necrosis occurred in any patient despite previous exposure to radiotherapy. Stereotactic radiosurgery is an effective and relatively safe treatment for recurrent solitary metastases and is an appealing technique for the initial management of deep-seated lesions as a boost to whole brain radiotherapy.

Adenocarcinoma↗

PubMed1989

A three-dimensional electron pencil-beam algorithm.

We describe the implementation of a three-dimensional electron-dose algorithm based on a Gaussian pencil-beam model. The algorithm calculates dose to an arbitrarily distributed set of points in a heterogeneous volume. Multiple non-coplanar beams can be positioned relative to the volume. The algorithm consists of three basic components: (i) the transport of a pencil-beam through a heterogeneous volume, (ii) the evaluation of the pencil-beam fluence at a given depth in the volume in the presence of irregular fields, and (iii) the matching of points in the volume receiving a significant fluence contribution from a pencil-beam at a given depth in the volume and the calculation of dose to those points. An efficient point-matching algorithm reduces the computation time to the level of conventional two-dimensional implementations. The algorithm uses an optimised subdivision for irregular fields, and accurately predicts output factors for irregular fields placed between the final collimators and the patient. We show comparisons between the new algorithm and conventional two-dimensional calculations using measurements and calculations for finite heterogeneities, irregular fields and output factors.

Algorithms↗

PubMed1988

Quadtrees as a representation for irregularly shaped fields in radiotherapy applications.

The choice of data representations in treatment planning software impacts on the accuracy of the treatment plan and the total computation time. We present the quadtree data structure as one such representation for irregularly shaped fields in a three-dimensional electron pencil-beam algorithm. The quadtree subdivides the irregular field into pencil-beams of unequal size and considerably reduces the number of pencil-beams needed in the dose calculation while preserving the calculational accuracy. Small pencil-beams are concentrated around the field edges to provide optimal resolution and computational accuracy in penumbra regions. The quadtree simplifies the evaluation of the pencil-beam fluence at a given depth, and removes systematic errors present in alternative implementations. The quadtree algorithm results in a ten-fold performance improvement when compared to alternative implementations for the irregular field.

Algorithms↗

PubMedDate not supplied

Parallel-plate ionization chamber response in cobalt-60 irradiated transition zones.

The authors study the acceptance of a Capintec parallel-plate ionization chamber. The Capintec chamber is used for dose measurements in a lead and polystyrene slab phantom irradiated with cobalt-60 gamma rays. The authors define an enhancement ratio to quantify the dose measurements. The enhancement ratio equals the ratio of dose measured with the lead slab present to dose measured under equilibrium conditions in polystyrene at equal primary beam attenuation. The measured enhancement ratio at the exit side of the lead/polystyrene interface is 25% lower than the Monte Carlo predicted enhancement ratio. The authors propose that geometric acceptance limitations of the Capintec chamber to large-angle, low-energy electrons are the cause for this difference. A Monte Carlo simulation of the Capintec chamber acceptance confirms the hypothesis.

Cobalt Radioisotopes↗

PubMedDate not supplied

Spherical harmonic expansion of cranial surfaces.

A three-dimensional analytical technique for the representation of the cranial surface based on a spherical harmonic expansion is presented. The analytical surface representation is used in conjunction with a sample iterative ray-intersection algorithm to compute the dose calculation depth. The technique is compared to other conventional techniques and it is determined that the spherical harmonic approach of approximating the cranial surface decreases the depth calculation time by approximately a factor of 60.

Algorithms↗

PubMedDate not supplied

A geometric algorithm for medical image correlations.

An automatic image correlation algorithm is discussed for the cranial region which is based on the geometric properties of the second moment tensor associated with a volume. The second moment tensor of two identical volumes represented in two different coordinate frames is evaluated to obtain the set of translations, rotations, and anisotropic scaling operators which relate the two coordinate frames. The theory is presented along with a discussion of quantitative error analysis to measure the usefulness of such an algorithm in the clinical setting.

Algorithms↗