RESUMO
This note outlines an improved method of calculating dose per monitor unit values for small electron fields using Khan's lateral build-up ratio (LBR). This modified method obtains the LBR directly from the ratio of measured, surface normalized, electron beam percentage depth dose curves. The LBR calculated using this modified method more accurately accounts for the change in lateral scatter with decreasing field size. The LBR is used along with Khan's dose per monitor unit formula to calculate dose per monitor unit values for a set of small fields. These calculated dose per monitor unit values are compared to measured values to within 3.5% for all circular fields and electron energies examined. The modified method was further tested using a small triangular field. A maximum difference of 4.8% was found.
Assuntos
Algoritmos , Elétrons/uso terapêutico , Modelos Biológicos , Proteção Radiológica/métodos , Radiometria/métodos , Carga Corporal (Radioterapia) , Simulação por Computador , Relação Dose-Resposta à Radiação , Desenho de Equipamento , Análise de Falha de Equipamento , Humanos , Dosagem Radioterapêutica , Espalhamento de RadiaçãoRESUMO
Potassium deficiency decreased the total RNA per shoot in corn (Zea mays L.) seedlings due to the reduced sizes of the plant, but increased the ratio of RNA to dry matter as much as 40%. Total base composition of RNA was unaffected by K(+) deficiency. Thus K(+) deficiency does not appear to alter RNA metabolism to such an extent that a lack of RNA becomes a factor limiting growth. The RNA contents of leaves were followed as deficiency developed or as the plant recovered from deficiency. Such time-course studies, although extremely useful in microbial work, did not yield as much information with higher plants. The ratio of RNA to dry matter in younger leaves was much higher than that in older leaves. The ribonuclease level in corn shoots was increased as much as threefold by K(+) deficiency.