Aluminum, copper, tin and lead as shielding materials in the treatment of cancer with high-energy electrons

• Published in: Radiation physics and chemistry (Oxford, England : 1993) Vol. 53; no. 4; pp. 361 - 366
• Main Authors: Prasad, S.Guru, Parthasaradhi, K, Bloomer, W.D, Al-Najjar, W.H, McMahon, J, Thomson, O
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.10.1998; Elsevier
• Subjects: Aluminum; Biological and medical sciences; Copper; Diseases; Electron beams; Electrons; Lead; Medical sciences; Oncology; Radiation shielding; Radiation therapy and radiosensitizing agent; Tin; Tissue; Treatment with physical agents; Treatment. General aspects; Tumors; Nuclear medicine; Materials; Transmission; Aluminium; Shielding; Radiotherapy; Radioprotection; Thickness; High energy; Tin; Lead; Copper; Biomedical engineering; Electrons
• ISSN: 0969-806X; 1879-0895
• DOI: 10.1016/S0969-806X(98)00130-3

During irradiation of lesions in cancer treatment with electrons, irregular field sizes are shaped by blocking off the areas to be protected usually with lead or Lepowitz metal of adequate thickness. Sometimes these blocks are placed directly on the skin. In such cases, the block should not only be of minimum weight (thickness), but also the residual dose received by the protected organs should be as small as possible. However, due to the production of bremsstrahlung, it is difficult to achieve a higher degree of attenuation unless a sufficient thickness of shielding material is used. Hence, a minimum or optimum thickness is needed to be measured. Transmission measurements are performed to determine suitable minimum thicknesses and to measure the transmission at this minimum thickness, for aluminum, copper, tin and lead for electron broad-beam field sizes 6×6, 10×10 and 20×20 cm 2 of energies 6, 12 and 20 MeV produced by a medical linear accelerator. The ratio of the measured ionization with and without the shielding material in percent is expressed as a measure of transmission. The minimum thickness is `knee' position of the transmission curves, where the dose received by the organs (residual dose) is mostly dominated by the bremsstrahlung component and any addition of shielding material is not of much advantage in achieving further appreciable shielding effect. It is noticed that at this minimum thickness the percentage dose received by the vital organs behind the shield varies from 1 to 14% of the original unshielded dose as the atomic number of the shielding material increases from 13 (aluminum) to 82 (lead) and as the electron energy of the beam increases from 6 to 20 MeV. In other words, the effectiveness of shielding decreases from 99 to 86% as the atomic number increases from 13 to 82. Depending on the treatment volume, its position and the clearance between the electron cone and the skin, the dose received by the vital organs surrounding the tumor can be minimized by choosing the optimum thickness of these elements.