Advanced Physics for Brachytherapy 2018

Example: influence of the number of BT Fx Random uncertainties and dose response for different fractionation schemes

OAR

target

20%

1

0,99

1Fx 2Fx 3Fx 4Fx 5Fx model

0,98

15%

0,97

0,96

1Fx

10%

0,95

2Fx

3Fx

morbidity N TCP

0,94 probability TCP

4Fx

0,93

5%

5Fx

0,92

model

0,91

0%

0,9

55

60

65

70

75

80

85

75

85

95

105

115

total treatment D2cm³ rectum (EQD2

)

a/b =3Gy

total treatment dose (EQD2

)

a/b =10Gy

= ± 20%/fx :

Example: random uncertainty D D

For target: using 1 fx vs 2-5 fx results in ~0.5% lower response probability than predicted by model

2cm³

• nFx=5 => observed morbidity @75Gy 8.5% • nFx=4 => observed morbidity @75Gy 8.9% • nFx=3 => observed morbidity @75Gy 9.4% • nFx=2 => observed morbidity @75Gy 10.3% • nFx=1 => observed morbidity @75Gy 12.3%