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Патент USA US3090561

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May 21, 1963
R. G. BAKER ETAL
3,090,551
AUTOMATIC DOSE COMPUTER
3 Sheets-Sheet 1
Filed Feb. 26, 1960
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May 21, 1963
3,090,551
R. G. BAKER ETAL
AUTOMATIC DOSE COMPUTER
3 Sheets-Sheet 2
Filed Feb. 26. 1960
FIG2C1.
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In v ew [5v-5
May 21, 1963
3,090,551
R. G. BAKER ETAL
AUTOMATIC DOSE COMPUTER
’ I5 Sheets-Sheet 5
Filed Feb. 26, 1960
FIGA.
FIGB.
l
à
40
United States Patent @ddee
Patented May 2l, 1963
l
2
3,090,551
It is a further object of the invention to provide a dose
computer which can be adjusted t-o take into account
AUTOMATÈC DÜSE CÜMPUTER
o
Robert G. Baker, 17 Notiert Road, Aginconrt, (interno,
Canada; Henry P. Webb, 37 Brightwood St., Downs Ul
view, Ontario, Canada; and Harold E. `lohns, 24 An
derson Ave., Toronto, Ontario, Canada
Filed Feb. 26, 196th Ser. No. 11,297
Claims priority, application Canada Mar. S, 1959
3 Claims. (Ci. ¿3i-61)
Radiotherapy involves the exposure of a patient to a
source of radiation in such manner that the radiation falls
upon a selected locality of the patient’s body. The dose
of radiation that the patient should absorb at this selected
locality is prescribed by the radiotherapist according to
the nature of the condition being treated.
1n most radiotherapy centres the required exposure
dose for a prescribed absorbed dose at the site of inter
est is first determined and then, `from the exposure dose
rate, the treatment time is calculated. Thus, the techni 20
cian is required to calculate the treatment time for each
given dose, set this time on a timer and switch on the
radiation machine lwhich is automatically switched ofî
at the expiry of the set time by switching means associated
with the timer.
rIhe calculation of the treatment time is carried out in
accordance with the characteristics of the radiation ma
changes in the intensity of the source of radiation.
The invention provides a dose computer comprising a
first rotatable tapered roller, a second rotatable tapered
roller, arranged in axially parallel side-by-side relation
ship with said first roller and tapering in- opposite direc
tion to said first roller, and coupling means for connect
ing said rollers, said coupling means being linearly dis
placeable between said rollers, said rollers being tapered
substantially in accordance with the equation
D
feo-1 +6-.,
wherein c is a constant, D is the distance between the axes
of the rollers less the separation between the rollers and
j'fx) is the radius of one of the rollers at an axial distance
x from an origin located at the center of that roller.
One embodiment of the invention is illustrated in the
accompanying drawings in which
FlG. l shows schematically a dose computer;
FIGS. 2 and 2a show the manner in which the tapered
rolls of the dose computer of FIG. l are mounted;
FIGS. 3 and 3a show means for coupling to each other
the tapered rolls of the dose computer of FIG. 1;
FÍG. 4 is a diagram showing the parameters used in
calculating an ideal shape for the rollers of the dose
computer of FlG. l, and
HG. 5 is a graph showing the maximum percentage
deviation
from logarithmic scale produced by the use of
30
the field oi radiation remains stationary, and rotation
linearly tapered rollers, as a function of speed range
techniques in which the source of radiation rotates around
ratio R.
the patient. In fixed field therapy the calculation of
The dose computer' comprises two hardened steel,
treatment time takes into account the intensity of the
tapered rollers 1 and 2 rotatably mounted in bearings 3
source, the tield size at the patient’s skin and the dis
chine and with the technique being employed. Radio
therapy techniques include ñxed field techniques, in which
tance between the source and the patient’s skin. In rota
tion therapy, the field size at the skin and the distance
and ól- on the sides 5' of a U-shaped frame 6. The frame
6 has been omitted from FIG. il tor the sake of clarity
and is shown in FlG. 2 which omits most of the details
of FiG. l. The roller 1 is driven at constant speed by a
lation is fundamentally more difiicult; however it may be
synchronous electric motor 7 through a gear box 8 and
simplified in practice -by using the concept of tumor-air
gear wheels Si and 10. The roller Z drives a digital
40
ratio and so Afar as the technician is concerned the calcu
counter' lil through gear wheels 12 and 13, the gear wheel
lation required for determining the treatment time in
13 being secured to a rotatable shaft 14 to which is also
rotation therapy is similar to that for fixed iield therapy
secured
a disc i5 carrying a pin 16. The pin 16 engages
except that he is concerned with tumor-air ratio instead
a slotted arm 17 connected to the counter 1:1 and rotation
of field size.
of the disc 15 causes a reciprocating movement of the
Whether a fixed ñeld or a rotation technique is used
arm 17 which serves to operate the counter 1l.
the task of the technician in making the necessary calcu~
The rollers 1 and 2 are coupled to each other by two
lation can be made fairly simple by the compilation of
hardened steel balls 18 and .12’ which are in contact with
suitable tables correlating the variables involved in such
the rollers 1 and 2 respectively and with each other.
manner that no great mathematical skill is demanded of
For the sake of clarity the manner in which the balls 18
the technician. However human error cannot be elimi
and 19 are mounted between the rollers 1 and 2 has not
nated. On the other hand it cannot be tolerated, for
been shown in FIG. 1 but appears from FIG. 3 which
obvious reasons. Therefore it is the practice in well-run
v is a partial sectional view of the dose computer of FIG.
hospitals to require that before treatment is commenced
1 along the line >III-Hl of FIG. l. The balls 18 and
all such calculations are checked by someone other than
19 are accommodated in a block 2th which is provided
the technician who makes the original calculation. This
with a cylindrical bore 21 having an annular insert 22
is often a great nuisance but the alternative is to risk a
of graphite-loaded nylon. The diameter of the insert 22
mistake which might have serious consequences and which
is only slightly greater than that of the balls 18 and 19
would in any event result in a wrong treatment being ad
so as to give a snug tit while penmitting free rotation of
ministered.
Apart from the difficulty arising from the need to 60 the balls. The length of the bore 12d. is somewhat less
than the sum of the diameters of the balls y18 and 19 so
avoid human errors the calculation tables with which
that each of these balls projects slightly above the face
the technician is provided must be periodically revised to
of the block Zit; thus the rollers 1 and 2 contact the balls
take into account the decay of the radioactive source or
1S and 19 respectively without contacting the block 20.
the change in exposure rate from the X-ray machine.
65 It may ybe mentioned at this point that the balls 18 and 19
It is an object of the present invention to provide a de
could v'be replaced by a single ball but that this is not de
vice for computing the time that a patient should be ex
sirable »because movement of the >block 20 relative to
posed to radiation from a given source of radiation, un
the rollers 1 and 2 would then involve sliding of one face
der a specified radiotherapie technique, in order that he
of the ball on the surface of one of the rollers instead of
will »receive the required exposure dose. For the sake of
the rolling action at both rollers which is obtained by us
brevity such a device is referred to hereafter as a dose
between source and skin are not constant so that the calcu~
computer.
ing two balls. Since sliding gives rise to greater frictional
acarrear
uw
forces than rolling the useful life of the rollers and balls
is diminished if only one ball is used. Experience has
shown that with two balls the extent of wearing is un
appreciable over a period equivalent to two years normal
use of the dose computer.
Fl YS. 2 and 2a illustrate the way in which the rollers
by slotted plate 36 which is secured to the scale 35 by
means of two screws 37 passing through the slot in the
plate 36 and engaging in threaded holes in the scale 35.
By a simple screwdriver adjustment the plate 36 and
therewith the pointer 28, may thus be displaced relative
l and 2 are mounted so as to be in resilient contact with
to the scale 35 so as to change the set distance between
the pointer 23 and the balls 18 and 19.
the balls i8 and lil. rThe frame 5 is divided into a mov
able upper `frame member 5l and a fixed lower trame
carried by the drum Sti being logarithmic. Suppose the
The operation of the device depends upon the scales
member 52 hingedly connected by hinge members 53. 10 output rate of rotation W0 is related to the input rate of
Coil springs 54 are secured to the sides 5 of the trame
rotation Wi by WozWieCX where x is the distance of the
6 and urge the upper frame member 5l towards the
«lower `frame member 52. The bearings 3 of the roller
l are mounted in the upper frame member 51 and the
bearings 4 of the roller 2 in the lower frame member
balls 18 and 19 from a reference point and c is a con
stant; then if one wishes to change the output speed by
a factor eey, one merely -moves the pointer 28 a distance
y relative to the balls i3 and 119 to yield
52 so the action of the springs Se urges the rollers l and
2 towards one another. Thereby the rollers l and 2 are
kept in rolling contact with the balls lâ and 19.
The block 20 has a threaded bore 23 at right angles
to the bore 2l.
Thus corrections `for decay or change in output may be
made with one simple adjustment. Any other type of
A coarse screw 24 passes in threaded 20 scale would require the construction of a new tield size
scale or tumor-air ratio scale every time the exposure
engagement through the bore 23 and is mounted in bear
ings 25 in the sides 5 of the frame 6. The screw 24 is
rotatable by means or" a knurled knob 216` fixed thereto
rate from the machine altered. Thus the rollers 1 and 2
of the dose computer should be designed so that
and upon rotation serves to move the block 20', with the
balls 1S and lié?, linearly between the rollers 1 and 2.
The Äblock 20 is prevented from rotating with the screw
23 by means of a lixed rod 27 extending between the
sides 5 of the frame 6 and fitting into a recess 27a lo
cated on the back -face or” the block so that the «block 20
Let the required shape of roller be represented by f(x)
as indicated in FIG. 4 with the origin at the centre and
the distance between the rollers axes D‘-l-A.
radii at distance x are f(x) and D-f(x) and
slides along the rod 27.
ÍV_0_ fte)
The block 20 carries a pointer 28 that moves over a
calibrated scale 29 which is one of tour scales carried
by a drum 30 rotatably mounted in bearings 30a in the
sides 5 of the trame ‘6. Each of these four scales corre
Wi_D-f(x)
lt is desired that this ratio be eCX.
tained
sponds to a given radiotherapy technique. The scale 29
Solving there is ob
D
is graduated in tield sizes ranging from 0 to 400` sq. cm.
ful-m
and is calibrated ñxed field therapy with a particular
radiation machine using a source to patient distance of
80 cm. The knob 3l by means of which the drum 30
Then the
(l)
It would `be very dillicult to machine rollers with a taper
given by Equation 1 so it was decided to investigate the
is rotated is marked at four points aligned with the four 40 possibility of a linear taper with f(x)=a-l~bx. The ratios
scales to indicate the nature of the technique to which
WO/Wi lfor the two expressions are
each scale corresponds. In the illustrated embodiment
the marking on the knob 3l adjacent the scale 29 indi
cates the source to patient distance of 80 cm. A diñerent
scale would be used for operation with a different source
to patient distance. Also, one or more of the scales on
the drum 30 may be calibrated in terms of tumor-air
ratios -for use in rotation therapy. Selection of one of
the four techniques corresponding to the four scales on
These may be made equal at x=0 and X=+x0 by the
proper choice of a and b. When this is done it is easily
seen that they match at x=-x0. The maximum devia
tion between the two expressions may be shown to occur
where x is approximately itlröxo. At this value of x
the drum 30 simultaneously selects, through a linkage 32,
the differences between the two expressions for W0/ W1
an appropriate gear of the gear box S.
It will be seen that the rollers 1 and 2 and the balls
1S and 19 constitu-te the essential parts of a continuously
variable speed drive between the gear box S and the
counter ll, the ratio of which can be changed by rota
tion of the knob 26. When using the computer the ra
of Equation 2 have been calculated and expressed as a
is plotted in FIG. 5 as a function of the overall range of
percentage of the exponential expression. This deviation
speeds, R, from end of the roller to the other. For speed
ratios less than 4:1 the maximum difference is less than
1 percent.
diographer merely has to select the appropriate technique
In the embodiment described it was found convenient
by rotation of the knob 3l, bring the pointer 2S to the
to have a speed ratio of about 2:1 from one end of the
spot on the scale 29 corresponding to the field size or
roller to the other. The actual ratio is indicated on the
tumor-air ratio involved, set the prescribed dose on the 60 auxiliary scale 3S which ranges from 1.0 to 0.60. When
counter 1l by means of the knob 33 and then switch on
R=2 the maximum difference is 0.13 percent which is
the »motor 7, simultaneously switching on the radiation
entirely satisfactory `for practical operations.
machine. When the counter has been «driven tor such
a length of the time that the prescribed dose has been
were intended for use in connection with only one radio
It will be appreciated that if the embodiment described
administered, i.e., the reading on the counter has been
therapy technique the gear box 8 and the drum 30 could
reduced to Zero, a switch 34, such as is shown in U.S.
be dispensed with.
Patent No. 1,992,841, to O. C. Roesen, associated with
the counter is opened and breaks the circuit of the motor
’7, simultaneously shutting off the radiation machine.
The dose computer of the invention is calibrated for
siderable length of time the whole of the decay adjust
use with a particular radiation machine but it is clear
that provision has to be made to take into account the
decay of the radioactive source or a change in output
of the machine. For this purpose there is provided a
scale 3S vfixed to the block 20. The pointer 23 is carried
When the dose computer has been in use for a con
ment provided by the scale 3S will eventually become
used up. However it is then only necessary to change
the ratio of the gear wheels 12 and 13 in order to make
it possible to return the pointer 2S to its initial position
with respect to the scale 35.
We claim:
1. A dose computer for a radiation machine com
3,090,551
5
6
of said rollers, said block also having a threaded bore at
right angles to said first-mentioned bore, and a rotatable
coarse screw passing in threaded engagement through
said threaded bore whereby rotation of said coarse screw
effects linear displacement of said block between said
rollers.
3. A dose computer according to claim 1 which fur
prising a first rotatable tapered roller, a constant speed
motor for driving said iirst roller through a gear box
at one of a plurality of constant speeds, a second rotat
able tapered roller arranged in axially parallel side-by
side relationship with said ñrst roller and complementary
thereto, a counter driven by said second roller, coupling
means for connecting said rollers, said coupling means
ther comprises a first frame member and a second frame
being linearly displaceable between said rollers and commember pivotally connected to said ûrst `frame member
prising a pair of balls in rolling contact with each other
and in rolling contact with said rollers, means for setting 10 and wherein one of said rollers is mounted in said ñrst
frame member and the other of said rollers is mounted
said coupling means at a desired distance from the ends
in said second frame member and means are provided
ot said rollers, an indicator carried Áby said coupling
for resiliently urging said second frame member towards
means, a logarithmic scale calibrated in accordance with
said ñrst frame member whereby said rollers are held
the characteristics of said radiation machine and a chosen
radiotherapy technique, said indicator being movable over 15 in contact with said balls.
said logarithmic scale, the radii of each of said rollers
References Cited in the iile of this patent
being determined by the equation
UNITED STATES PATENTS
558,315
Shaw ______________ ..._ Apr. 14, 1896
wherein c is a constant, D is the distance between the
755,084
Vermehren __________ __ Mar. 22, 1904
axes of the rollers less the separation between the periph
eral faces of the rollers and f(x) is the radius of one
825,363
1,992,841
2,159,882
2,206,252
20
of the rollers at an axial distance x from an origin
located at the centre of that roller.
25
2. A dose computer according to claim 1 wherein said
coupling means comprises a block secured against rota
tion and having a bore of such diameter as to accom
modate said pair of balls with each of the balls project
ing slightly beyond a face of the block to contact one 30
2,602,338
2,731,831
2,801,795
2,872,814
2,979,256
Vermehren __________ __ July 10,
Roesen _____________ -_ Feb. 26,
Borden ____________ __ May 23,
Gould _______________ __ July 2,
Opocensky ___________ __ July 8,
Schaefer ____________ __ Jan. 24,
Williams ____________ __ Aug. 6,
1906
1935
1939
1940
1952
1956
1957
Brown _____________ __ Feb. 10, 1959
Cushman ____________ __ Apr. 11, 1961
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