Ingeniero Mecánico

SD0200005

Development of semi-empirical equations for In-water dose distribution using Co-60 beams By Siddig Abdalla Talha Abdalla

A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science in physics.

August, 2001 Department of physics Faculty of science University of Khartoum

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Contents List of Tables List of Figures Dedication Acknowledgement Arabic Abstract Abstract Chapter One Introduction Chapter two Concepts in radiation physics Radioactivity Cobalt-60 decay scheme lonization... Interaction ofradiation with matter Photoelectric effect Compton scattering Pair production Interaction coefficients 1 .Attenuation coefficient 2.Energy transfer coefficient(uu) 3.Energy absorption coefficient(uen) Radiation field quantities 1 .Photon flux(O) 2.Flux rate(0) 3.Energy fluence(vF) 4.Energy fluence rate ((p) 5.Effective energy : , .'.-.

page iv v vii viii ix x

1

4 4 5 6 6 6 7 7 8 8 8 9 9 9...9 10 10 10

6.Mean energy Radiation dosimetry 1 .Exposure(X) 2.Absorbed dose 3.Kerma(K) 4.Phantoms 5.Relation between kerma and absorbed dose Dose distribution and some radiological terms 1 .Dose distribution 2.Depth dose distribution 2-1 .Percentage depth dose 2-2.Peak absorbed dose 2-3.Build up 2-4.Radiation quality 2-5.Output 2-6.Geometrical field (beam) size 2-7.Source surface distance2-8.Back scatter factor(BSF) 2-9.Collimater sactter factor(Sc) 2-10.Phantom scatter factor (Sp). 2-11.Penumbra Isodose distribution General properties ofy ray dose distribution Parameters of isodose curves Beam quality Source size, SSD, and SSD the penumbra Coliimation Field size , .:

10 11 11 12 12 14 14 15 15 16 16 16 16 16 17 17 17 18 18 19 .....20 20 21 22 23 23 25 25

Chapter threeMaterials and experimental set up Machine specification Machine description Measuring assembly Experimental Set up 26 26 27 28

Chapter four Results and discussion 30

Chapter five Conclusion Recommendations References 61 62 63

List of Tables

List Table 4.1: Percentage depth dose for field size 4x4 cm2 Table 4.2: Percentage depth dose for field size 8x8 cm2 Table 4.3: Percentage depth dose forfield size 12x12 cm2 Table 4.4: Percentage depth dose for field size 25x25 cm2 Table 4.5: Percentage depth dose for field size 30x30 cm" Table 4.6: Ratio of PDD,CI./PDDC11| for field size 10x10 cm2 for depth (0.5 to 9) cm Table 4.7: Slope (jo.) and the constant A for selected fields Table 4.8: Field size 10x10 cm2 profiles Table 4.9: Field size 12x12 cm2 profiles

page 35 36 37 38 39

40 40 4142

Table 4.10: Fields and the corresponding parameters of the decrement line equation Table 4.11: Field size 6x6 cm2 selected isolines Table 4.12: Field size 10x10 cm selected isolines Table 4.13: Field size 18x18 cm2 selected isolines 43 43 44 45

IV

List of Figures

List Fig.2.1. Energy level diagram for the decay of Co-60 nucleus Fig.2.2.Plot of relative dose rate as inverse squarelaw function of distance from a point source fig.2.3. Output factor determination Fig.2.4. Depth dose profile Fig.2.5(a).Geometrical factors that lead to beam penumbra Fig.2.5(b).dose profile as measured in air Fig.3.1 .Block diagram for experimental set up Fig.4. l.Slopes(u,) of Ln(PDD) versus Ln(corresponding field size in cm) Fig.4.2.(PDDtex/PDDcal) versus Depth for field size 10x10 cm2 anddepths 0.5 to 9 cm Fig.4.3.Percentage depth dose (PDD) for field sizes 4x4, 10x10, 12x12 and 20x20 cm2 Fig.4.4.Field size 10x10 cm2 profiles Fig.4.5.Field size 12x12 cm2 profiles Fig.4.6.Field size 6x6 cm decrement lines Fig.4.7.Field size 8x8 cm decrement lines Fig.4.8.Field size 10x10 cm2 decrement lines Fig.4.9.Field size 12x12 cm decrement lines Fig.4.10. Comparison of calculated isodose curves...