X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1999-07-09
2001-04-24
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S064000
Reexamination Certificate
active
06222905
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an irradiation dose calculation unit and an irradiation dose calculation method for calculating from prescription data irradiation doses from one or more portals (directions) to a target, and to a recording medium for recording a program for implementing the irradiation dose calculation method.
2. Description of Related Art
FIG. 18
is a view illustrating proton beam radiation therapy described in M. Urie, “Treatment Planning for Proton Beams”, Ion Beams in Tumor Therapy published by CHAPMAN & HALL, pp. 279-289, 1995. In this figure, the reference numeral
1
designates a CT (Computed Tomography) of the head of a subject;
2
designates a target tumor for proton beam radiation;
3
designates a brain stem as a critical organ fragile to radiation;
4
designates a proton beam;
6
designates a bolus for varying the dose distribution in depth direction so as to focus a high dose portion on the location of the tumor
2
; and
7
a
and
7
b
designate a collimator for matching the lateral beam width to the width of the tumor
2
.
To apply the radiation therapy, the target is irradiated by the radiation beam while avoiding critical organs (the brain stem
3
, in this case) as shown in FIG.
18
. Although the proton bream radiation from a single portal is shown in
FIG. 18
, radiation from multiple portals (directions) is carried out in actual therapy, and doses from the portals are determined such that normal tissues and critical organs are protected from injury. Since the tolerable doses are known for normal tissues, the doses from the portals are empirically determined such that the doses absorbed by the normal tissues located in radiation paths do not exceed the tolerable doses.
Thus, the conventional irradiation dose calculation method empirically determines the doses from the portals such that the doses absorbed by the normal tissues located in the radiation paths become less than the tolerable doses. This method, however, presents a problem in that optimum doses to the target and critical organs are not always assured.
SUMMARY OF THE INVENTION
The present invention is implemented to solve the foregoing problem. It is therefore an object of the present invention to provide an irradiation dose calculation unit, an irradiation dose calculation method and a recording medium capable of setting appropriate doses in accordance with prescription data by calculating irradiation doses from the portals on the basis of a prescription of the doses for a target and critical organs prescribed by a physician.
According to a first aspect of the present invention, there is provided an irradiation dose calculating unit comprising: a prescription data input section for inputting prescription data which includes a prescription dose, minimum dose, maximum dose and underdose volume fraction for at least one target, and includes a limiting dose, maximum dose and overdose volume fraction for at least one critical organ; an absorbed dose distribution calculating section for calculating body absorbed dose distributions of radiation beams irradiated from a plurality of portals to the target; a first object function calculating means for calculating a first object function from the prescription data, irradiation dose ratios of the radiation beams irradiated from the portals to the target, and the body absorbed dose distributions calculated by the absorbed dose distribution calculating section, the first object function indicating a level of satisfaction of the prescription data for the critical organ; an irradiation dose ratio calculating section for calculating the irradiation dose ratios that optimize the first object function; a second object function calculating section for calculating a second object function from the prescription data and a product of a scaling parameter multiplied by a sum of products which are obtained by multiplying the body absorbed dose distributions for the portals by the irradiated dose ratios of the portals calculated by the irradiation dose ratio calculating section, a second object function indicating a level of satisfaction of the prescription data for the target and the critical organ; a scaling parameter calculating section for calculating the scaling parameter that optimizes the second object function; and an irradiation dose determining section for determining the irradiation doses of the portals from at least the scaling parameter calculated by the scaling parameter calculating section, the irradiation dose ratios of the portals calculated by the irradiation dose radio calculating section, and the body absorbed dose distribution for the portals.
Here, the body absorbed dose distributions may be normalized distributions obtained by dividing the body absorbed dose distributions of the radiation beams irradiated from the portals to the target by an absorbed dose at reference coordinates in the target.
The first object function calculating section may determine one of a first index and a second index as the first object function, the first index being calculated using a maximum value of the absorbed dose distributions in the critical organ, and the second index being calculated using a volume fraction of the critical organ, in which the absorbed dose is equal to or greater than a predetermined absorbeddose.
The irradiation dose ratio calculating section may determine the irradiation dose ratios of the portals by varying the irradiation dose ratios of the portals step by step from zero to one, by having the first object function calculating section calculate the first object function at each step, and by determining the irradiation dose ratios of the portals when the first object function is optimized.
The irradiation dose ratio calculating section may determine the irradiation dose ratios only for portals whose irradiation dose ratios are yet less than unity.
The irradiation dose ratio calculating section may calculate the irradiation dose ratios using an optimization method selected from a group consisting of an iterative search method, a simulated annealing method, a gradient method, and combinations of at least two of the iterative search method, the simulated annealing method and the gradient method.
The second object function calculating section may determine one of a first index, second index, third index, fourth index and fifth index as the second object function, the first index being calculated using a maximum value in the critical organ of the product of the scaling parameter multiplied by the sum of products which are obtained by multiplying the body absorbed dose distributions for the portals by the irradiated dose ratios of the portals calculated by the irradiation dose ratio calculating section, the second index being calculated using the overdose volume fraction of the critical organ in which the absorbed dose exceeds a predetermined absorbed dose, the third index being calculated using a minimum value in the target of the product of the scaling parameter and the sum of the products, the fourth index being calculated using a maximum value in the target of the product of the scaling parameter and the sum of the products, and the fifth index being calculated using the volume fraction of the target in which the absorbed dose is less than the predetermined absorbed dose.
The irradiation dose determining section may place a product of the scaling parameter and the prescription dose for the target as an absorbed dose at the reference coordinates in the target, and may determine the irradiation doses of the portals from the absorbed dose.
The irradiation dose determining section may place the product of the scaling parameter and the prescription dose for the target as the absorbed dose of the reference coordinates in the target, obtain a proportionality constant by dividing the absorbed dose by the absorbed dose at the reference coordinates obtained from the sum of products of the absorbed dose ratios of the portals and absorbed doses for the portals per unit irradiation dose
Kanematsu Nobuyuki
Yoda Kiyoshi
Bruce David V.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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