Advanced Physics for Brachytherapy 2018

Example: random uncertainties for target + OAR

effect of random intra-/interfraction variation on D 90 , D 2cm³

and dose-response

OAR

target

18%

100%

98%

SD 10%

16%

96%

14%

SD 20%

94%

12%

SD 30%

92%

10%

model

90%

8% NTCP

TCP

SD 5%

88%

morbidity

local control

6%

SD 10%

86%

4%

SD 15%

84%

2%

82%

SD 20%

80%

0%

65

75

85

95

105

115

55

60

65

70

75

80

85

total treatment D 90

CTV HR

(EQD2

)

total treatment D 2cm³

(EQD2

)

a/b =10Gy

a/b =3Gy

Example: 75Gy, random variation of rectum D 2cm³ : • D D 2cm³ = ± 10%/fx -> observed NTCP 7.5 % (vs 7.3% model prediction) • D D 2cm³ = ± 20%/fx -> observed NTCP 8.9 % • D D 2cm³ = ± 30%/fx -> observed NTCP 10.5 % • Model predicts 10.5% morbidity NTCP @ 80Gy EQD2!

For target – differences in TCP < 0.5%