Radiation therapy planning method and its system and apparatus

A plurality of axial images covering a region of interest in a subject to be treated are scanned and voxel data of the subject are produced from the axial images. The provisional location of an isocenter and the direction of radiation are determined over the axial images. A DRR of the subject viewed from the source of radiation is developed in accordance with the provisional isocenter location, the radiating direction, and the distance between the isocenter and the radiation source. The DRR is displayed together with three cross section images which represent an isocenter plane including the isocenter and arranged vertical to a line extending between the isocenter and the radiation source, a gantry rotation plane including the isocenter, and a plane including the isocenter and arranged vertical to both the isocenter plane and the gantry rotation plane. Each of the three cross section images indicates cross-hair ROI representing the other two planes and a cross-hair ROI representing the direction of radiation. The field of radiation is then determined over the three cross section images or the DRRs. The three cross section images and the DRRs can be updated in response to shift and rotation of the cross-hair ROIs.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a radiation therapy planning method and 
its system and apparatus, and more particularly to a radiation therapy 
planning method which accurately determines an isocenter and a radiation 
field with the use of a digitally reconstructed radiograph (DRR) or 
translucent image, a system and its apparatus. 
2. Description of the Related Art 
Such radiotherapy treatments for particular cancers are widely known using 
beams of X-ray or electron emitted from a linear accelerator (referred to 
as a linac hereinafter). Alternatively, microtron or betatron beams 
produced by the acceleration of electron different from the linac 
technique are used for the radiotherapy treatment. Recently, a variety of 
large-scale radiotherapy particle accelerators have been developed and 
available. 
An improved radiation therapy planning is then requested for providing the 
energy of radiation in a spatially and timely optimum profile so that a 
higher dose is directed to the target region to be treated while lower, 
acceptable doses fall on its surrounding normal organs causing no serious 
injury. 
In the radiotherapy treatment with external radiation of radioactive beams 
such as X-ray or electron over a patient, it is noted that the profile of 
the radiation is varied depending on the size and quality of the patient 
body and the shape and location of an affected part or organ. 
Accordingly, any radiation therapy planning has to be carefully designed in 
view of the clinical history and individuality of the patient. 
Conventional radiation therapy plannings employ a technique of X-ray 
simulation for defining the position of a patient relative to the X-ray 
source which is geometrically equivalent to the location of the patient 
relative to the radiation source in a radiation treatment apparatus. The 
X-ray simulation is realized by a mechanism (of an X-ray simulator) 
capable of controlling the geometrical parameters such as the distance 
between a radiation source and the rotation center of a clinical bed and 
the beam limiter aperture which are compatible with those of a radiation 
treatment apparatus shown in FIG. 6. For identifying the location, shape, 
and size of a part to be treated and determining the parameters for 
radiation such as the angle and field of radiation, X-ray images or 
radiographs are produced by the X-ray simulator. The part to be treated is 
projected and recorded together with a grating of wire collimator lines 
and a scale of simulation onto a the X-ray film. The data from the X-ray 
radiographs are then examined to locate and mark down the patient. 
The X-ray simulator of a known type is incapable of measuring a depth, as 
the result, it produces only two-dimensional images. This will decline the 
accuracy of tumor identification and fail to develop an advanced scheme 
for the radiation treatment. 
For compensation, there are introduced other types of simulation in which 
the three-dimensional data (voxel data) of a subject is produced with an 
X-ray CT apparatus and used for simulating a three-dimensional model. 
Among such types of simulation are a scano plan and an oblique plan for 
radiation therapy. 
The scano plan is relatively a simple method using both scano and axial 
images. The axial images and the scano image viewed from the direction of 
radiation are produced by an X-ray CT scanner and the field of radiation 
is directly determined over the scano image. The location of an isocenter 
which is a cross point between the gantry rotation axis e and the beam 
limiter rotation axis d of the radiation treatment apparatus and will be 
referred to as an I/C hereinafter is identified from a combination of the 
scano and axial images. The scano plan permits the axial images to be 
overlapped by a beam profile of radiation for estimating the radiation 
therapy planning. 
The oblique plan is for determining an object to be irradiated over the 
axial images. More specifically, each slice of the axial images produced 
by an X-ray CT scanner is examined to identify tumors to be treated and 
organs to be protected from radiation, and the I/C and the angle of 
radiation are determined to define the field of radiation automatically. 
The oblique plan allows multiple field irradiation in which beams of 
radiation are directed from different angles, arc therapy radiation in 
which radiation is made at a variable angle, and conformal therapy in 
which both the angle of radiation and the size of beam limiter aperture 
are varied. Through determining the radiation therapy planning with 
reference to the axial and oblique images, a translucent image 
geometrically equivalent to the radiograph viewed from the direction of 
radiation can be developed. This DRR is however a result of the planning 
and may be effective for reviewing the planning but not useful for 
estimating the planning because the planning is hardly modified while 
monitoring the DRR. 
In the scano plan type of conventional radiation therapy planning, the 
scano image are produced with the use of a parallel beam and geometrically 
different from the DRR of a subject produced by a fan beam from the source 
of radiation and may have a degree of distortion. This will impair the 
accuracy of simulation and prevent the planning from having a desired 
angle of radiation and being executed with ease. 
The oblique plan type of conventional radiation therapy planning requires 
entry of target data over a considerable number of the axial images, hence 
giving complications of the target setting and an increased length of the 
operating time. 
SUMMARY OF THE INVENTION 
It is an object of the present invention, in view of the above aspects, to 
provide a radiation therapy planning method capable of determining a 
desired angle of radiation within a shorter period of time, and a system 
and its apparatus employing the method. 
It is another object of the present invention to provide a radiation 
therapy planning method capable of determining the location of an I/C and 
the angle of radiation by a manner similar to a common X-ray simulation 
technique without holding the patient to an X-ray simulator for a longer, 
painful duration, and a system and its apparatus employing the method. 
It is a further object of the present invention to provide a radiation 
therapy planning method capable of minimizing entry operation and reducing 
labor of the operator, and a system and its apparatus employing the 
method. 
For achievement of the above object, there is provided a radiation therapy 
planning method of estimating the direction of radiation and/or the field 
of radiation prior to actual radiation treatment, comprising the steps of: 
producing voxel data of a region of interest in a subject to be treated; 
constructing a translucent image of the subject from the voxel data which 
is viewed from a desired location or direction; and determining the field 
of radiation over the translucent image. 
Also, there is provided a radiation therapy planning method of estimating 
the direction of radiation and/or the field of radiation prior to actual 
radiation treatment, comprising the steps of: shooting a plurality of 
axial images covering a region of interest in a subject to be treated; 
producing voxel data of the subject from the axial images; determining the 
provisional location of an isocenter and the direction of radiation over 
the axial images; developing a translucent image of the subject, which is 
viewed from the source of radiation, in accordance with the provisional 
location of the isocenter, the direction of radiation, and the distance 
between the isocenter and the radiation source over the axial images; 
displaying the translucent image together with three images which 
represent an isocenter plane including the isocenter and arranged vertical 
to a line between the isocenter and the radiation source, a gantry 
rotation plane including the isocenter, and a plane including the 
isocenter and arranged vertical to both the isocenter plane and the gantry 
rotation plane; indicating in each of the three plane images a cross-hair 
ROI representing the location of the other two planes and a cross-hair ROI 
representing the direction of radiation; determining the field of 
radiation over the three plane images or the translucent image; shifting 
and/or rotating the ROIs; and updating at real time the three plane images 
and the translucent image in response to the shift and rotation of the 
ROIs. 
Furthermore, there is provided a radiation therapy planning method of 
estimating the direction of radiation and/or the field of radiation prior 
to actual radiation treatment, comprising the steps of: shooting a 
plurality of axial images covering a region of interest in a subject to be 
treated; producing voxel data of the subject from the axial images; 
determining the provisional location of an isocenter and the direction of 
radiation over the axial images; developing a translucent of the subject, 
which is viewed from the source of radiation, in accordance with the 
provisional location of the isocenter, the direction of radiation, and the 
distance between the isocenter and the radiation source over the axial 
images; displaying the translucent image together with three images which 
represent a gantry rotation plane, a coronal plane, and a sagittal plane 
all including the isocenter; indicating in each of the three plane images 
a cross-hair ROI representing the location of the other two planes and a 
cross-hair ROI representing the direction of radiation; determining the 
field of radiation over the three plane images or the translucent image; 
shifting and/or rotating the ROIs; and updating at real time the three 
plane images and the translucent image in response to the shift and 
rotation of the ROIs. 
For achievement of the above object, there is provided a radiation therapy 
planning apparatus comprising: a voxel data producing means for producing 
voxel data of a region of interest in a subject to be treated from a 
plurality of axial images received; a cross section image reconstructing 
means for reconstructing a group of selected cross section images from the 
voxel data; and a translucent image developing means for developing a 
translucent image of the subject viewed from the direction of radiation 
which is predetermined. 
Also, there is provided a radiation therapy planning system comprising: an 
X-ray CT scanner for producing a plurality of axial images covering a 
region of interest in a subject to be treated; a radiation therapy 
planning apparatus for producing voxel data of the subject from the axial 
images, reconstructing a selected number of cross section images according 
to the location of an isocenter and the angle of radiation entered, and 
developing a translucent image of the subject viewed from the source of 
radiation in accordance with the isocenter location, the radiation angle, 
and the distance between the isocenter and the radiation source; a display 
means for displaying the axial images as well as the cross section images 
and the translucent image produced by the radiation therapy planning 
apparatus; an entry means for determining the isocenter location and the 
radiation angle over the axial images displayed on the display means and 
the radiation field over the translucent image displayed on the display 
means, and if it is desired to modify the translucent image, changing the 
isocenter location and the radiation angle over the cross section images 
displayed on the display means; and a projector means responsive to data 
of the isocenter location from the radiation therapy planning apparatus 
for projecting a laser marking of the isocenter onto the body surface of 
the subject. 
A preferred embodiment of the present invention may further comprises an 
external memory means for saving the relevant data for radiation therapy 
planning. 
In another preferred embodiment of the present invention, the cross section 
images represent three planes: an isocenter plane including the isocenter 
and arranged vertical to a line extending between the isocenter and the 
radiation source, a gantry rotation plane including the isocenter, and a 
plane including the isocenter and arranged vertical to both the isocenter 
plane and the gantry rotation plane. 
In a further preferred embodiment of the present invention, the image of 
each of the three planes indicates the other two planes with a cross-hair 
ROI. 
In a still further preferred embodiment of the present invention, the 
cross-hair ROI is shifted or rotated by the entry means to change the 
isocenter location and the radiation angle. 
In a still further preferred embodiment of the present invention, the cross 
section images and the translucent image displayed on the display means 
are updated at real time in response to the shift and rotation of the 
cross-hair ROI. 
In a sill further preferred embodiment of the present invention, the 
display means indicates overlapping of a beam profile of radiation with 
the axial images and both BE and BP planes after the isocenter location, 
radiation angle, and radiation field are determined. 
In a still further preferred embodiment of the present invention, the cross 
section images represent three planes: a gantry rotation plane, a coronal 
plane, and a sagittal plane all including the isocenter. 
The nature, principle and utility of the invention will become more 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described in more details 
referring to the accompanying drawings. 
A radiation therapy planning system according to the present invention is 
explained as shown in FIG. 2. The radiation therapy planning system 1 
comprises an X-ray CT unit 2, a projector unit 3, a display unit 4, an 
entry unit 5, an external memory unit 6, a radiation therapy planning 
apparatus 7, and a bus 8 connecting the units to each other. 
The X-ray CT unit 2 is well known as provided for shooting a succession of 
axial images of slices to gain the voxel data b of a subject to be 
treated. A gantry 21 of the X-ray CT unit 2 contains an X-ray tube and an 
X-ray detector located opposite to each other and on both sides of a 
center opening and is driven for rotation about the opening by a gantry 
controller 22. A tabletop 24 of a diagnostic table 23 on which the subject 
to be scanned is positioned is moved in and from the opening of the gantry 
21. 
The diagnostic table 23 includes a drive mechanism for moving the tabletop 
24 longitudinally. A combination of the rotation of the gantry 21 and the 
longitudinal movement of the tabletop 24 permits the X-ray CT unit 2 to 
helically scan the subject on the tabletop 24 and produce a succession of 
axial images within a short duration of time. 
The projector unit 3 projects a profile of the I/C and defines the field of 
radiation over the surface of the subject positioned on the tabletop 24. 
The display unit 4 displays the axial images of the subject; images on the 
I/C plane, images on the gantry rotation plane, images perpendicular to 
both the I/C and gantry rotation planes, X-ray images, etc. 
The entry unit 5 includes a pointing device such as a mouse or a tracking 
ball for entry of relevant parameters such as the location of the I/C and 
the angle of radiation by pointing locations on a display of the display 
unit 4. 
The radiation therapy planning apparatus 7 comprises a voxel data b 
generating unit 71 for producing the voxel data b of the subject from a 
succession of the axial sliced images taken by the X-ray CT unit 2, a 
cross section image reconstructing unit 72 for reconstructing images of 
selected cross sections from the voxel data b, a DRR developing unit 73 
for developing DRR of the subject viewed from a predetermined direction of 
radiation. The radiation therapy planning apparatus 7 is adapted for 
displaying a given number of reconstructed images on the display unit 4 
and transmitting desired data to and from the external memory unit 6. 
A procedure of the radiation therapy planning method of the present 
invention will now be explained referring to a flowchart of FIG. 1. The 
procedure starts with the X-ray CT unit 2 producing a succession of the 
axial images representing a region of interest on the subject (Step S10). 
The voxel data b or three-dimensional volume data is then constructed from 
the axial images by a common interpolation technique (Step S15). 
This is followed by viewing selected ones of the axial images saved and 
displayed in an order of the sliced locations, identifying the location of 
tumors, and determining the provisional location of the I/C and the angle 
of radiation (Step S20). It is also a good idea for ease of the setting to 
display the I/C location and the radiation angle in combination with a 
beam profile which is variable in divergence. In general, the I/C may be 
located either on the axis of the subject body or on the center of a part 
to be treated. 
As the provisional location of the I/C and the angle of radiation have been 
determined to locate the subject relative to the source of radiation, the 
images of three cross sections of the subject taken along the I/C plane, 
the gantry rotation plane, and the plane perpendicular to the two previous 
planes all including the I/C are reconstructed from their voxel data b and 
displayed together on the display unit 4 (Step S25). Each of the three 
images includes a cross-hair ROI representing the other two planes. 
The I/C plane is a plane vertical to a line between the I/C and the 
radiation source 100 as shown in FIG. 3A. When the I/C is present on the 
axis of the subject body, the image on the I/C plane is a coronal image 
but otherwise, a common oblique image. 
The location of the radiation source 100 is then calculated from the I/C 
location, the radiation angle, and the distance between the I/C and the 
radiation source 100 predetermined and saved, and the DRR of the voxel 
data b is determined with the view point aligned to the radiation source 
100 (Step S30). As shown in FIG. 3B, the DRR is calculated using a maximum 
and a sum average of CT values of the voxel data b fallen on a plurality 
of beam paths a extending from the radiation source 100 to the DRR 
developing plane. 
This is followed by displaying the DRR on the display unit 4 and 
determining the field of radiation with the entry unit 5 (Step S35). 
Simultaneously, the cross sections of the subject produced in relation to 
the prescribed three planes at Step S25 are displayed together with the 
DRR on the display unit 4, as shown in FIG. 4. 
When it is desired to modify the DRR (as judged "yes" at Step S40), desired 
parameters of the I/C location and the radiation angle are entered through 
the entry unit 5. More particularly, the I/C location and the radiation 
angle are changed by shifting and rotating the cross-hair ROI. In response 
to the shift and rotation of the cross-hair ROI, the radiation therapy 
planning apparatus 7 updates the DRR and the three cross section images at 
real time and indicates them on the display unit 4 (Step S45). 
In updating the DRR and the three cross section images, the duration from 
commanding the shift and rotation of the cross-hair ROI to the display of 
the updated images is minimized by increasing the pixel pitch of the 
images to be reconstructed and thus decreasing the size of calculation. If 
required, the images with a higher resolution are calculated and 
displayed. This will improve the efficiency of operation. 
When the I/C location and the radiation angle have been determined and the 
DRR is produced, the field of radiation may be modified. 
In particular, after the I/C location, the radiation angle, and the 
radiation field are determined, any of the axial images, the beam profile 
configuration across BE (beam's eyes) plane or BP (beam path) plane, or 
the radiation field may be reviewed and readjusted as desired as shown in 
FIGS. 5A and 5B (Step S50). The BE plane is an oblique plane extending in 
parallel with the I/C plane and the radiation field is enlarged or reduced 
in size depending on the distance between the radiation source 100 and the 
oblique plane. 
The BP plane is an oblique plane including the radiation source 100 and 
thus determining a beam profile c for the radiation treatment. In case of 
a multi-division aperture control such as a multi-leaf collimator 101, the 
BP plane is utilized for finely adjusting the beam profile c with a cross 
section defined thereon by a combination of the radiation source 100 and 
the aperture control. 
Upon the review and adjustment of the beam profile c being completed, the 
data of the I/C location is transmitted from the radiation therapy 
planning apparatus 7 to the projector unit 3 where it is used as a 
reference for the positioning in the radiation treatment. More 
specifically, the I/C is projected in the form of a laser mark by the 
projector unit 3 on the surface of the subject body. The laser mark is 
then traced with a marking pen or the like for I/C marking (Step S55). The 
data may be recorded on a film or transferred directly to a radiation 
treatment apparatus for controlling the radiation (Step S60). 
Although the prescribed embodiment permits a group of the I/C plane, the 
gantry rotation plane including the I/C, the plane arranged perpendicular 
to the I/C plane and the gantry rotation plane and including the I/C to be 
displayed on the display unit 4, the gantry rotation plane including the 
I/C will be displayed in combination with a coronal plane and a sagittal 
plane both including the I/C. 
As set forth above, the present invention is advantaged by planning the 
radiation treatment with a desired angle of radiation within a shorter 
period of time. 
Also, the present invention allows the I/C location and the radiation angle 
to be determined by a sophisticated manner similar to a known technique of 
X-ray simulation, hence minimizing the involving time of a patient and 
easing the pain of binding. 
Furthermore, the present invention permits the operator to enter a far less 
number of parameters for the radiotherapy planning with a minimum of 
complications. 
It should be understood that many modifications and adaptations of the 
invention will become apparent to those skilled in the art and it is 
intended to encompass such obvious modifications and changes in the scope 
of the claims appended hereto.