Ideal dose level in treatment planning optimization.
The biological response of the tumor is expressed in terms of tumor control probability (TCP) and its dependence on the inhomogeneous dose distribution throughout the tumor volume is studied. The ideal dose level to which the prescribed dose must be referred is derived, by employing a formula based on the linear quadratic model. To administer the prescribed dose to the ideal dose level renders the tumor control probability equal to that one corresponding to a uniform irradiation of the tumor. For the normal tissue irradiated a normal tissue complication probability index (NTCPI) is also defined and calculated. The comparison between NTCPIs of competing plans supports the optimization. In general the resulting ideal dose level is lower than the mean dose level, but not necessarily equal to the minimum in the tumor. This result shows the possibility of administering the prescribed dose to a dose level higher than the minimum, maintaining the tumor control probability at a good level and consequently lowering the complications to the normal tissue. The method offers a general support for the choice of the reference dose level and of the better technique. An example of application of the method is shown.
Begnozzi
L
L
Laboratorio Fisica Medica e Sistemi Esperti, C.R.S. Istituto Regina Elena, Roma, Italy.
Malaspina
F
F
Gentile
F P
FP
Chiatti
L
L
Carpino
S
S
Fragomeni
R
R
Benassi
M
M
D006801:Humans; D008433:Mathematics; D010347:Patient Care Planning; D011336:Probability; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage