Method for determining a treatment plan including a dose distribution
The present invention provides a computer-implemented method for determining a treatment plan for a radiotherapy treatment including a dose distribution, the method comprising the steps of determining a transition region target thickness of a transition region comprised in a low dose target volume and adjacent to a high dose target volume. The method further comprises creating shells and determining, for each of the shells, a shell-specific upper dose constraint. The method further comprises generating, by means of an optimization algorithm, a treatment plan, the optimization algorithm constrained by a predetermined lower dose constraint in the high dose target volume, an upper dose constraint in the low dose target volume, and the respective shell-specific upper dose constraint.
1 . A computer-implemented method:
determining, based on a predetermined lower dose constraint C HL of a high dose target volume and an upper dose constraint C LU of a low dose target volume surrounding and adjacent to the high dose target volume, a transition region target thickness l t of a transition region comprised in the low dose target volume and adjacent to the high dose target volume;
determining, based on the thickness l t a number n of shells to be created so as to form the transition region;
creating n shells S i , where i=0 to n−1;
determining, for each of the shells, a shell-specific upper dose constraint C SU (i) based at least on the lower dose constraint C HL of the high dose target volume and the upper dose constraint C LU of the low dose target volume, wherein the upper dose constraint of at least one of the shells is higher than the upper dose constraint C LU of the low dose target volume and wherein the shell-specific upper dose constraint C SU (i) increases from the outermost shell S n-1 to the innermost shell S 0 ; and
generating, by an optimization algorithm, a treatment plan, the optimization algorithm constrained by the predetermined lower dose constraint C HL in the high dose target volume, the upper dose constraint C LU in the low dose target volume except for the transition region, and the respective shell-specific upper dose constraint C SU (i) for each of the shells in the transition region;
wherein the method further includes:
determining the transition region target thickness l t is performed based on a ratio C HL /C LU of the lower dose constraint C HL of the high dose target volume and the upper dose constraint C LU of the low dose target volume and optionally one or more parameters a j having been determined as yielding optimal dose distribution results for a given pair of values of a lower dose constraint C HL of the high dose target volume and a value of an upper dose constraint C LU of the low dose target volume.
2 . The method of claim 1 , wherein determining, for each of the shells, the shell-specific upper dose constraint C SU (i) comprises determining that
C SU (0)> C HL and C SU (0)≤ C HU ,
wherein C HU is an upper dose constraint of the high dose target volume, in particular, the upper dose constraint of the high dose target volume being predetermined or derived from another parameter, and
C SU ( i )= C HL −( i− 1)(( C HL −C LU )/( n− 1)) for i> 0.
3 . The method of claim 1 , wherein determining the transition region target thickness l t comprises that the transition region target thickness l t is determined to be 0 if the ratio C HL /C LU is smaller than 1 and that the transition region target thickness l t is determined to be l t =a 0 +a 1 (C HL /C LU −1), where a 0 >0 and a 1 >0.
4 . The method of claim 1 , wherein the predetermined shell thickness l s is determined so as to be larger than or equal to a dose grid resolution.
5 . The method of claim 1 , wherein the one or more parameters a 0 and a 1 , are parameters determined by solving a plurality of optimization problems for each of different sets of dose constraints and different sets of parameters a j , and by selecting, the one or more parameters a j yielding optimal dose distribution results for a given pair of values of a lower dose constraint C HL of the high dose target volume and a value of an upper dose constraint C LU of the low dose target volume, the selecting based on one or more criteria including at least one of homogeneity of the resulting dose distribution in the high dose target volume, constraint violation, steepness of a dose gradient from low dose target volume to high dose target volume, and stability of the resulting solution of the optimization problem.
6 . The method of claim 1 , further comprising, prior to the creating of the n shells, performing a 3D segmentation of the high dose target volume and the low dose target volume.
7 . The method of claim 1 , wherein the upper dose constraint C LU is a predetermined upper dose constraint received via a user input and/or retrieved from a data storage, or wherein the upper dose constraint is derived from C HL .
8 . The method of claim 1 , wherein the method further includes:
determining the number of shells n comprises dividing the transition region target thickness l t by a predetermined shell thickness l s and truncating the remainder.
9 . The method of claim 8 , wherein determining the number of shells n further comprises determining that n equals a number of shells n ini obtained by the steps of dividing the transition region target thickness l t by the predetermined shell thickness l s and truncating the remainder.
10 . The method of claim 8 , wherein determining the number of shells n further comprises determining whether a number of shells n ini obtained by the steps of dividing the transition region target thickness l t by the predetermined shell thickness l s and truncating the remainder exceeds a predetermined threshold n max and, if this is the case, determining that the number of shells n equals n max and otherwise determining that the number of shells n equals n ini .
11 . A non-transitory computer-readable medium comprising instructions which, when executed by a computer, cause the computer to
determine, based on a predetermined lower dose constraint C HL of a high dose target volume and a upper dose constraint C LU of a low dose target volume surrounding and adjacent to the high dose target volume, a transition region target thickness l t of a transition region comprised in the low dose target volume and adjacent to the high dose target volume;
determine, based on the thickness l t a number n of shells to be created so as to form the transition region;
create n shells S i , where i=0 to n−1;
determine, for each of the shells, a shell-specific upper dose constraint C SU (i) based at least on the lower dose constraint C HL of the high dose target volume and the upper dose constraint C LU of the low dose target volume, wherein the upper dose constraint of at least one of the shells is higher than the upper dose constraint C LU of the low dose target volume and wherein the shell-specific upper dose constraint C SU (i) increases from the outermost shell S n-1 to the innermost shell S 0 ; and
generate, by an optimization algorithm, a treatment plan, the optimization algorithm constrained by the predetermined lower dose constraint C HL in the high dose target volume, the upper dose constraint C LU in the low dose target volume except for the transition region, and the respective shell-specific upper dose constraint C SU (i) for each of the shells in the transition region;
wherein the instructions further cause the computer to:
determine the transition region target thickness l t is performed based on a ratio C HL /C LU of the lower dose constraint C HL of the high dose target volume and the upper dose constraint C LU of the low dose target volume and optionally one or more parameters a j having been determined as yielding optimal dose distribution results for a given pair of values of a lower dose constraint C HL of the high dose target volume and a value of an upper dose constraint C LU of the low dose target volume.