The National Council on Radiation Protection and Measurements (NCRP) Report No. 151 is an essential document for bunker design commonly applied for radiotherapy treatment rooms. This document is used as a reference by several countries, including Brazil. The objective of this study is to evaluate the shielding dimensioning methodology recommended by NCRP 151, and compare it with the one adopted by the Brazilian regulatory authority. Radiotherapy rooms and respective doors were designed to use linear accelerators operating at 6, 10, 15, and 18 MeV under two different ways: (a) applying exclusively the methodology recommended by the NCRP 151, and (b) taking into consideration the complementary recommendations from the Brazilian authorities. The results suggest that designers in Brazil can count on at least 4 and 11% safety margin for dimensioning primary barriers in controlled and free areas respectively. Also 8% for secondary barriers in controlled areas, 9.7% for secondary barriers adjacent to the primary belt of free areas, and 6.6% for the lead of the doors.

No abstract

Within a radiotherapy room, in addition to the primary beam, there is also secondary radiation that leaks from the accelerator head and scattering caused by surrounding objects, the patient’s body and even the walls of the shielded room itself, designed to protect the external individuals, disregarding effects on the patient. The aim of this work is to study the radiation effect on the patient’s healthy tissues caused by scattering from a concrete shield expressed as equivalent and effective doses. MCNPX simulations of the linear accelerator Varian 2100/2300C/D were performed for a MAX phantom of a patient in a typical radiotherapy room. In addition, calculations were made with and without shielding. It was concluded that the concrete shielding affects in 5% the effective dose absorbed by the patient.

O objetivo deste trabalho é determinar os fatores de transmissão (FT) para fótons em blindagens multilaminadas usando 4 materiais diferentes, através de métodos de cálculo analítico. As espessuras e materiais considerados são os seguintes: 1,00cm de concreto comum, 1,00cm de alumínio, 1,00cm de ferro e 1,00cm de chumbo. As camadas foram permutadas em 24 arranjos sequenciais diferentes. Considerou-se uma fonte pontual isotrópica emitindo fótons monoenergéticos de energia 0,661657 MeV para interações com a matéria. Analiticamente, a atenuação exponencial e os fatores de buildup de Taylor (BT) foram calculados para o meio infinito, também foi usada a Equação de Broder (BB) e, em seguida, o Microsoft Excel para calcular os FT para os diferentes arranjos. Sendo a intensidade de radiação (I) e a intensidade de radiação inicial (I0), a razão I / I0 é denominada como FT. Os FT das 24 permutações possíveis mostraram boa concordância entre a metodologia analítica e a esperada. Em relação à atenuação, a ordem mais apropriada de materiais na direção da fonte-detector é a seguinte: concreto ordinário, alumínio, ferro e chumbo.