Search PubMed⌕ Search

Biomedical subjects

M Urie

Publications and source records attributed to M Urie.

30 records · Page 2Linked to original sources
PubMed1986

Visual outcome after proton beam irradiation of uveal melanoma.

Prognostic factors for visual loss following proton irradiation of uveal melanoma were evaluated for 440 eyes treated from 1975 to 1984, with visual acuity 20/200 or better before treatment. Analysis involved Kaplan-Meier survival curves and Cox proportional hazards analysis with visual outcome defined as worse than 20/200. Prognostic factors were tumor height: rate ratio (ratio of rate of visual loss for one category of the variable relative to the rate of visual loss for a reference category of that variable) of 5.26 (95% confidence interval, 2.66-10.39) for tumors greater than 5 mm compared to tumors 3.0 mm or less in height; distance of tumor from the optic disc and fovea: rate ratio 2.59 (1.63-4.11) for tumors 2DD or less from both the optic disc and fovea compared to those greater than 2 DD from these structures. Also predictive of visual loss were tumor location close to disc only, or close to fovea only, macular detachment, worse pretreatment vision, and higher radiation doses delivered to both the disc and fovea, and lens. Regression analysis using a visual acuity scale gave similar results.

Adolescent↗
PubMed1986

Degradation of the Bragg peak due to inhomogeneities.

The rapid fall-off of dose at the end of range of heavy charged particle beams has the potential in therapeutic applications of sparing critical structures just distal to the target volume. Here we explored the effects of highly inhomogeneous regions on this desirable depth-dose characteristic. The proton depth-dose distribution behind a lucite-air interface parallel to the beam was bimodal, indicating the presence of two groups of protons with different residual ranges, creating a step-like depth-dose distribution at the end of range. The residual ranges became more spread out as the interface was angled at 3 degrees, and still more at 6 degrees, to the direction of the beam. A second experiment showed little significant effect on the distal depth-dose of protons having passed through a mosaic of teflon and lucite. Anatomic studies demonstrated significant effects of complex fine inhomogeneities on the end of range characteristics. Monoenergetic protons passing through the petrous ridges and mastoid air cells in the base of skull showed a dramatic degradation of the distal Bragg peak. In beams with spread out Bragg peaks passing through regions of the base of skull, the distal fall-off from 90 to 20% dose was increased from its nominal 6 to well over 32 mm. Heavy ions showed a corresponding degradation in their ends of range. In the worst case in the base of skull region, a monoenergetic neon beam showed a broadening of the full width at half maximum of the Bragg peak to over 15 mm (compared with 4 mm in a homogeneous unit density medium). A similar effect was found with carbon ions in the abdomen, where the full width at half maximum of the Bragg peak (nominally 5.5 mm) was found to be greater than 25 mm behind gas-soft-tissue interfaces. We address the implications of these data for dose computation with heavy charged particles.

Humans↗
PubMed1985

Current results of proton beam irradiation of uveal melanomas.

Proton beam irradiation has been used for the treatment of 241 uveal melanomas over the past 7 1/2 years. Twelve melanomas (5%) were small, 99 (41%) medium, 103 (43%) large and 27 (1%) extra-large melanomas. The mean length of follow-up was 21 months and the median 15 months. Ninety-four percent of the treated lesions with a follow-up more than two years and 65% of tumors with shorter follow-up showed regression. The most recent visual acuity was 20/40 or better in 47% and 20/100 or better in 66%. Ten eyes were enucleated because of complications (9) or continued tumor growth (1). Thirteen patients developed metastases from 4 to 50 months of treatment. Our data indicate that proton irradiation can be used to treat melanomas of various sizes and in a variety of locations, and preliminary results suggest that proton therapy has no deleterious effect on the likelihood of the development of metastases.

Adolescent↗
PubMed1984

Compensating for heterogeneities in proton radiation therapy.

Our method for predicting, and compensating for, the effects of surface irregularities and tissue heterogeneities in proton radiation therapy was evaluated by comparing the predicted and measured dose distributions. Two heterogeneity configurations in a D-shaped water-filled phantom were handled in exactly the same way as patients. Target volumes were designated on thin-section CT scans, a single en face portal was defined, compensating boli were designed and made, and the dose distribution behind the phantom measured and compared with that intended. The compensation was accurate to within 1 mm for the phantom with a single air heterogeneity and to within 2.5 mm for the phantom with multiple bone and air heterogeneities. The bolus and phantom were misaligned by 3 mm and the dramatic change in the dose distribution demonstrated the need to address the problems of patient motion and imperfect immobilisation through compensator design. A philosophy of 'expanding' the bolus is described, and dose distributions measured with the 'expanded' boli indicate that target volume treatment can be assured within prespecified repositioning and motion uncertainties. The uncertainty in the alignment of bolus and heterogeneities leads to corresponding uncertainty in the penetration of the protons. Ranges within which they will stop are calculated and shown to encompass adequately the measured distributions in both the aligned and misaligned cases.

Humans↗
PubMed1984

Preliminary results of proton beam irradiation of macular and paramacular melanomas.

Proton beam irradiation has been used for the treatment of 60 eyes with choroidal melanomas located 3 mm or less from the fovea. The average follow-up period was 18 months. 86% of the treated lesions showed regression at the time of this analysis, and the 14% that did not were followed up for less than a year. Visual acuity remained the same in 47% of the treated eyes, improved in 20%, and deteriorated in 33%. 58% of the treated eyes had visual acuity of 20/100 or better at the last follow-up examination. Radiation vasculopathy with macular oedema was the most common complication, and it was observed in 22% of the treated eyes. These preliminary observations suggest that proton beam irradiation may be a reasonable alternative to enucleation even for this group of choroidal melanomas, which is considered unfavourable in respect of the preservation of visual function.

Adolescent↗
PubMed1982

Proton beam irradiation of uveal melanomas. Results of 5 1/2-year study.

Proton beam irradiation was used in the treatment of 76 uveal melanomas from July 1975 to December 1980. Five (7%) were small, 32 (42%) were medium, and 39 (51%) were large melanomas. The follow-up period ranged from two months to 5 1/2 years; 19 patients were followed up for more than two years and 39 were observed for more than a year. Tumor regression has been achieved in all eyes with more than 12 months of follow-up except one, which was enucleated because of secondary complications. Three patients in whom metastatic disease developed died. Our data indicate that proton irradiation can be used for the treatment of relatively large lesions that previously were considered untreatable and reduces the high ocular morbidity experienced with other methods in the treatment of medium and small melanomas.

Adult↗
PubMed1982

Evaluation of the clinical applicability of proton beams in definitive fractionated radiation therapy.

We report on the treatment of 317 patients treated either wholly or in part with proton beams at the Harvard Cyclotron Laboratory. These include: 130 patients treated for definitive radiation therapy of choroidal melanoma; 17 patients treated for tumors of the base of skull, cervical spine and cranium, which abut structures of the central nervous system (CNS); 23 patients treated for sarcomas of soft tissue and bone; 65 patients treated for carcinoma of the prostate; 14 patients treated for carcinoma of the rectum and anus; and 23 patients treated for squamous carcinoma of the oral cavity and oro-pharynx. Data on causes of failure and morbidity of treatment are presented. Overall the results are judged to be extremely encouraging. In particular, the treatment of the choroidal melanomas and sarcomas abutting CNS structures have clear clinical value, and the treatment of prostatic tumors and tumors of the head and neck are thought to be promising.

Bone Neoplasms↗
PubMed1979

The vacuum cassette for improved linear accelerator portal films.

The use of a commercially available vacuum cassette with lead screens for linear accelerator portal films is described. The vacuum cassette technique provides improved quality with no increase in patient discomfort or cost and avoids gemoetric distortion, compared to other currently available methods.

Humans↗
PubMed1979

Routine fluoroscopy using minispot cameras.

Routine fluoroscopy was performed using 100- and 105-mm spot film cameras. Radiation dose was reduced to between 30% and 43%, and cameras were acceptably reliable. Cost for film and holders was high.

Fluoroscopy↗
PubMed1978

A device for insuring the congruency of opposed irregularly blocked fields.

A device for insuring the congruency of opposed irregularly blocked fields has been developed which permits the treatment of both fields of a parallel opposed pair without the realignment of any field-shaping standard non-divergent blocks. The device is an adaptor which attaches directly to the shadow tray or wedge holder and provides 2 channels for 1 Lucite shadow tray. A mirrow-image field is obtained without disturbing the position of the blocking array. Set-up times are decreased.

Radiotherapy↗