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ABSORBED DOSE ASSESSMENTS IN DIAGNOSTIC RADIOLOGY NUCLEAR MEDICINE AND RADIOTHERAPY WITH RESPECT TO THE FEMALE BREAST.

Objective

THE OBJECTIVES OF THE PROJECT INCLUDE THE DETERMINATION OF ABSORBED DOSE DISTRIBUTIONS IN PMMA PHANTOMS OF VARIOUS THICKNESSES. THE DEPHT DOSE DATA OBTAINED AT DIFFERENT TUBE VOLTAGES WILL BE FITTED BY A THREE PARAMETER MODEL. THE PREVIOUSLY REPORTED DISCREPANCY BETWEEN THE DOSES VALUES OBTAINED FROM IONIZATION CHAMBERS AND THERMOLUMINESCENT DOSIMETERS (TLD) WILL BE INVESTIGATED BY STUDIES ON THE DISPLACEMENT CORRECTION FACTORS OF IONIZATION CHAMBERS AT LOW ENERGY X-RAYS AND BY STUDIES ON THE IRRADIATION GEOMETRY OF THE TL DOSIMETERS. ABSORBED DOSES IN THE BREAST DUE TO NUCLEAR MEDICINE INVESTIGATIONS AND DUE TO SEVERAL TYPES OF EXTERNAL RADIOTHERAPY (E.G., IN THE CASE OF SMALL CARCINOMA OF THE LUNG) WILL ALSO BE CONSIDERED FOR THE RADIOGENIC RISK OF BREAST CANCER INDUCTION.
THE ABSORBED DOSE DISTRIBUTIONS OBTAINED WITH PMMA PHANTOMS OF VARIOUS THICKNESSES WILL BE COMPARED WITH THE DOSE DISTRIBUTIONS IN BR-12 (BREAST SIMULATING MATERIAL) AND IN COMPRESSED BREASTS. INFORMATION WILL BE OBTAINED ON THE DISTRIBUTION OF THE THICKNESS OF COMPRESSED BREASTS IN A SCREENING PROGRAMME. A PROTOCOL WILL BE FORMULATED FOR QUALITY ASSURANCE IN MAMMOGRAPHY AND TESTED AT THE COMPREHENSIVE CANCER CENTER ROTTERDAM. IN ADDITION, INFORMATION WILL BE OBTAINED OF THE PHOTOGRAPHIC ASPECTS INCLUDING FILM DEVELOPMENT PROCESSING AS WELL AS DATA ON DOSES REQUIRED FOR NEW TYPES OF FILM/SCREEN COMBINATIONS ESPECIALLY WITH REGARD TO IMAGE QUALITY AT THICKER BREASTS.
A preliminary quality control protocol for technical and dosimetric aspects of mammography was investigated. Limiting values were derived for various relevant parameters.
The absorbed dose in the female breast due to radiotherapy of other organs is significant (ie about 0,16-0,34 mGy per woman (with an age in excess of 40 years) per year), compared to mammography. The absorbed dose in the breast due to nuclear medicine is marginal.
MAMMOGRAPHY IS GENERALLY ACCEPTED AS AN EFFECTIVE METHOD FOR THE EARLY DETECTION OF MALIGNANT LESIONS IN THE FEMALE BREAST. IN VIEW OF THE HIGH OCCURENCE OF BREAST CANCER IN THE NETHERLANDS (ANNUAL DIAGNOSIS OF BREAT CANCER IN APPROXIMATELY 7000 WOMEN OF AGES IN EXCESS OF 35 YEARS) A NATION WIDE SCREENING PROGRAMME EMPLOYING MAMMOGRAPHY IS CONSIDERED FOR THE NEAR FUTURE. THE EFFICACY OF SCREENING PROGRAMMES USING MAMMOGRAPHY AS DETECTION METHOD, HAS BEEN DEMONSTRATED AGAIN BY RECENT DUTCH AND SWEDISH STUDIES.
BEFORE SCREENING PROGRAMMES ARE IMPLEMENTED, A COST-BENEFIT ANALYSIS HAS TO BE CARRIED OUT. THE RISKS OF TUMOUR INDUCTION BY IONIZING RADIATION HAVE TO BE CONSIDERED WITH RESPECT TO THE ADVANTAGES OF EARLY DETECTION OF MALIGNANCIES. AN EVALUATION OF THE RISKS OF TUMOUR INDUCTION RESULTS IN MAXIMUM ACCEPTABLE DOSES IN MAMMOGRAPHY, WHEREAS THE IMAGE QUALITY OF THE MAMMOGRAMS HAS TO BE OF A SUFFICIENTLY HIGH LEVEL TO ALLOW FOR AN EFFICIENT DETECTION OF MALIGNANT LESIONS OF SMALL SIZES. A MAXIMUM VALUE OF 1 MGY (1 MSV) FOR THE AVERAGE ABSORBED DOSE (EQUIVALENT) IN THE BREAST HAS BEEN RECOMMENDED. ACCORDING TO THE ABOLUTE RISK MODEL THE INCIDENCE OF RADIATION-INDUCED TUMOURS AMOUNTS TO 20.10 TO THE POWER OF MINUS 6 MGY TO THE POWER OF MINUS 1 AND THE MORTALITY WILL BE 8.. IN ADDITION, A LATENCY PERIOD IN EXCESS OF 10 YEARS HAS TO BE EXPECTED. ON THIS BASIS, ANNUAL SCREENING OF 3.10-6 WOMEN EMPLOYING AN AVERAGE ABSORBED DOSE OF 1MGY PER INVESTIGATION WILL RESULT - AFTER THE LATENCY PERIOD - IN THE INDUCTION OF A NUMBER OF TUMOURS IN THE ORDER OF 60 PER YEAR, WITH A RELATED MORTALITY IN THE ORDER OF 25 WOMEN PER YEAR. THE LATTER NUMBER HAS TO BE COMPARED WITH THE ESTIMATED REDUCTION IN THE MORTALITY DUE TO YEARLY DETECTION OF MALIGNANCIES WHICH IS IN THE ORDER OF 1000 WOMEN EACH YEAR.
PREVIOUS STUDIES REVEALED LARGE VARIATIONS IN THE AVERAGE ABSORBED DOSE VALUES PER INVESTIGATION (OF AT MAXIMUM A FACTOR OF 7) AMONG THE PARTICIPATING INSTITUTES; THE LOWEST VALUE WAS 0.6 MGY EMPLOYING A 49 MM THICK POLYMETHYLMETHACRYLATE (PMMA) PHANTOM SIMULATING THE MEAN MAMMA. THE DIAGNOSTIC IMAGE QUALITY APPEARED NOT TO BE CORRELATED WITH THE AVERAGE ABSORBED DOSE VALUES AMONG THE DIFFERENT PARTICIPATING INSTITUTES. THIS CLEARLY INDICATES THE NEED FOR AN OPTIMIZATION OF MAMMOGRAPHY PROCEDURES RESULTING IN MINIMUM ABSORBED DOSES VERSUS MAXIMUM IMAGE QUALITY.

Coordinator

TNO RADIOBIOLOGISCH INSTITUUT
Address
Division For Health Research 151 Lange Kleiweg
2280 HV Rijswijk
Netherlands