Note: Descriptions are shown in the official language in which they were submitted.
CA 02713375 2010-08-19
TITLE: FLUENCE MONITORING DEVICES WITH SCINTILLATING FIBERS
FOR X-RAY RADIOTHERAPY TREATMENT AND METHODS FOR
CALIBRATION AND VALIDATION OF SAME
FIELD
[0001] The embodiments described herein relate to the field of x-ray
radiation treatment, and in particular to fluence monitoring devices with
scintillating fibers, and validation methods for verification of the delivery
and
conformity of x-ray radiation dose patterns using such fluence monitoring
devices.
INTRODUCTION
[0002] Radiation therapy, or "radiotherapy", is the medical use of ionizing
radiation to control malignant cells in cancer treatments. Most frequently,
radiation therapy makes use of x-ray beams originating from outside the
patient
body (i.e. external x-ray radiotherapy). Many of the most advanced modes of
treatment in external x-ray radiotherapy make intensive use of multi-leaf
collimators (MLC) to adequately shape the x-ray beams used for a particular
treatment.
[0003] Each MLC may have a number of movable leaves (generally made
of a metal such as tungsten or another high atomic number material) that are
placed under the x-ray beam to block at least a part of the incident fluence
pattern and modulate the intensity profile of the x-ray beam. These advanced
modalities of treatment (such as intensity modulated radiation therapy (IMRT),
intensity modulated arc therapy (IMAT), or stereotactic body radiotherapy
(SBRT)) are inherently more complex in planning, delivery and
software/hardware communication than their static counterparts, and are often
subject to delivery and leaf positioning errors.
[0004] As these advanced treatment modalities use complex combinations
of often small and irregular field shapes to produce conformal radiation dose
distributions at a treatment region (e.g. a tumor site), a leaf positioning
error of
-1-
CA 02713375 2010-08-19
only a few millimeters can have dire repercussions on the actual dose
delivered,
greatly impacting the quality of the treatment. Large deviations from the
planned
treatment can lead to significant under-dosage or over-dosage, and may result
in
severe injury to a patient or even death.
[0005] Furthermore, the development of adaptive radiation therapy
procedures has resulted in an increased need for real-time quality control.
For
example, adaptive protocols may modify the MLC field shapes and dose
contribution in-use, or just before use (e.g. while treatment is underway or
about
to be delivered). Typical, off-line quality assurance protocols are currently
inadequate to assess the quality of such treatment procedures. As a result,
the
inventors have identified a need for improved verification and quality control
devices for x-ray radiation delivery systems.
SUMMARY
[0006] According to one aspect, there is provided a fluence monitoring
detector for use with a multileaf collimator on a radiotherapy machine having
an
x-ray radiation source, the fluence monitoring detector comprising a plurality
of
scintillating optical fibers, each scintillating optical fiber configured to
generate a
light output at each end thereof in response to incident radiation pattern
thereon
from the radiation source and multileaf collimator, a plurality of collection
optical
fibers coupled to the opposing ends of the scintillating optical fibers and
operable
to collect the light output coming from both ends of each scintillating
optical fiber,
and a photo-detector coupled to the collection optical fibers and operable to
converts optical energy transmitted by the collection optical fibers to
electric
signals for determining actual radiation pattern information. The
scintillating fibers
may be embedded in a phantom slab. The phantom slab may be made of a
material with properties relative to radiation that are similar to the
material used
in the scintillating optical fibers.
[0007] Each pair of leaves in the multileaf collimator may be associated
with a particular scintillating optical fiber. Each scintillating optical
fiber may be
-2-
CA 02713375 2010-08-19
arranged parallel to a direction of motion of the leaves of the multileaf
collimator.
Each scintillating optical fibers may be positioned underneath a pair of
leaves of
the multileaf collimator. Each scintillating optical fiber may have a length
selected
so as to span the maximum leaf span of a pair of leaves in the multileaf
collimator.
[0008] The scintillating optical fibers may be located on the opposite side
of the multileaf collimator from the radiation source.
[0009] The scintillating optical fibers may be located close enough to the
opposite side of the multileaf collimator from the radiation source as to keep
necessary clearance between the patient and the scintillating optical fibers.
[0010] The scintillating optical fibers may be thin enough so that one
scintillating optical fiber can monitor the fluence pattern associated with
one leaf
pair of the multileaf collimator.
[0011] In some embodiments, both the scintillating fiber length and the
phantom slab area are large enough to span the maximum leaf span of the
multileaf collimator.
[0012] In some embodiments, both the scintillating fiber and the phantom
slab assembly are thin enough as to minimize the attenuation of the incoming
radiation beam.
[0013] The total number of scintillating optical fibers may be equivalent to
the number of leaf pairs in the multi-leaf collimator.
[0014] The light collected by each end of each scintillating optical fiber
may be determined by the integration of the contribution of each infinitesimal
element along that fiber according to the following equation:
L
I,. = C* f K(x)=4), (x)-e*A(x)'dx
where K(x) represents the scintillation efficiency, P/(x) represents the
linear
fluence across the fiber (m"1), A(x) accounts for the differential light
attenuation
-3-
CA 02713375 2010-08-19
along the optical fiber, C represent the light losses due to the optical
coupling to
the photo-detector and L represent the fiber length.
[0015] The photo-detector may be further configured to determine actual
radiation pattern information, and compare this actual radiation pattern
information to the expected radiation pattern to determine how closely the
actual
radiation pattern matches the expected radiation pattern.
[0016] The detector may further comprise several solid slabs located
under the scintillating fiber array and the phantom slab.
[0017] According to another aspect there is provided a method of
calibrating a fluence monitoring detector that has scintillating optical
fibers for use
with a multileaf collimator on a radiotherapy machine having an x-ray
radiation
source, the method comprising using a narrow rectangular radiation field
incident
on the scintillating optical fibers, with the scintillating optical fibers set
perpendicular to the rectangular field and the radiation field is wide enough
to
enable simultaneous irradiation of all the fibers, and determining the light
collected by each end of the scintillating fibers according to the following
equation:
1=C=K(x0)'(Dint(x0)-e *'k (YO x0E[ xi_ a z,x.1+z
wherein d represents the effective rectangular field width (that is, the width
beyond which the radiation fluence is considered to be negligible) and x0
represents the effective point of measure, as defined by the integral mean
value
theorem, K(x) represents the scintillation efficiency, (h1(x) represents the
linear
fluence across the fiber (m"1), A(x) accounts for the differential light
attenuation
along the optical fiber, and C represent the light losses due to the optical
coupling to the photo-detector.
[0018] The method may further comprise determining the values of K(x)
and A(x) at the position xf on the fibers according to the following
equations:
-4-
CA 02713375 2010-08-19
1+`xr~ I_(O)
2 In I_ `xr \ I+ (0)
K\xt! /z+(xJ)I(xf)
K(0) I+(0) I-(o)
[0019] The method may further comprise applying the rectangular
radiation field over the entire scintillating optical fiber length in a
plurality of
irradiations in order to calculate N(x) and K(x) for all positions along the
fiber.
[0020] According to another aspect, there is provided a method of
validation of an incident radiation pattern on an array of scintillating
optical fibers
for use with a multileaf collimator on a radiotherapy machine having an x-ray
radiation source, comprising calculating the following field parameters:
central
position of the radiation interaction on the scintillation optical fiber (xe)
and the
integral of the fluence passing through the scintillating optical fiber
(0;,,t)
according to the following equations:
x~,= I In I+ =II-
2,u IN+ I-
I+ I
~,nt _ intN
wherein p is a constant that represents the mean attenuation coefficient of
the
scintillating optical fibers, and wherein l+ IN+ and IN_ are defined by the
following equation:
I = C* f x (x)' (D, (x)' eA(X) = dx
-L 1
2
-5-
CA 02713375 2010-08-19
where K(x) represents the scintillation efficiency, *P,(x) represents the
linear
fluence across the fiber (m"1), A(x) accounts for the differential light
attenuation
along the optical fiber, Ct represent the light losses due to the optical
coupling to
the photo-detector and L represent the fiber length.
[0021] In some embodiments of the method of validation, 1+ and L are for
the field under analysis and IN+ and IN_ are for the reference field, and the
method
further comprises comparing the calculated field parameters with those
measured during the treatment delivery.
[0022] In some embodiments of the method of validation, the reference
field used for calculation is rectangular, centered at the fiber center and
wide
enough to cover all the scintillating optical fibers.
[0023] In some embodiments of the method of validation, l+ and I. are from
the fluence pattern under verification, and IN+ and IN_ are from a previously
measured reference error-free field, and the method further comprises
comparing
the optical energy readings obtained during the treatment delivery with the
previously measured reference error-free field.
DRAWINGS
[0024] The embodiments herein will now be described, by way of example
only, with reference to the following drawings, in which:
[0025] Figure 1 is a schematic view of a radiation fluence monitoring
detector according to one embodiment;
[0026] Figure 2 is a schematic view of the fluence monitoring detector of
Figure 1 in position with a radiation source and a multileaf collimator
according to
some embodiments;
[0027] Figure 3 is a schematic side view of the radiation source, multileaf
collimator and fluence monitoring detector of Figure 2;
-6-
CA 02713375 2010-08-19
[0028] Figure 4 is a schematic view of the multileaf collimator and fluence
monitoring detector of Figures 2 and 3, viewed from the perspective of the
radiation source;
[0029] Figure 5 is a schematic side view of a radiation fluence monitoring
detector irradiated with a radiation field for calibration according to one
embodiment;
[0030] Figure 6 is a schematic top view of the radiation fluence monitoring
detector of Figure 5;
[0031] Figure 7 is a schematic view of an embodiment wherein several
water-equivalent slabs are added under the radiation fluence monitoring
detector
of Figure 1 to facilitate fluence calculation;
[0032] Figure 8 is a schematic view of different multileaf collimator errors
that were analyzed and monitored using an exemplary embodiment; and
[0033] Figure 9 shows a table listing validation results according to some
embodiments.
DESCRIPTION OF VARIOUS EMBODIMENTS
[0034] It will be appreciated that numerous specific details are set forth in
order to provide a thorough understanding of the exemplary embodiments
described herein. However, it will be understood by those of ordinary skill in
the
art that the embodiments described herein may be practiced without these
specific details. In other instances, well-known methods, procedures and
components have not been described in detail so as not to obscure the
embodiments described herein. Furthermore, this description is not to be
considered as limiting the scope of the embodiments described herein in any
way, but rather as merely describing the implementation of various embodiments
as described herein.
[0035] While certain features have been illustrated and described herein,
many modifications, substitutions, changes, and equivalents will now occur to
-
7
CA 02713375 2010-08-19
those of ordinary skill in the art. It is, therefore, to be understood that
the
appended claims are intended to cover such modifications and changes as fall
within the true spirit of the invention.
[0036] According to some embodiments, a fluence monitoring device as
described herein includes a plurality of scintillating optical fibers sized
and
shaped to characterize an incident x-ray radiation pattern. Generally, at
least
some of the scintillating optical fibers are aligned along a direction of
motion of a
pair of leaves of a given multileaf collimator when the multileaf collimator
is
installed on a medical linear accelerator (also known as a "linac") operable
to
generate x-rays.
[0037] The scintillating optical fibers generate a light output at each end
thereof, with the light output dependant of the incident radiation pattern.
The
ends of the scintillating optical fibers are each coupled to an optical fiber
in order
to guide the light emitted by the scintillating fibers to a photo-detector
where it
can be processed to determine the actual pattern of the incident radiation.
[0038] In some embodiments, the fluence monitoring device includes a
phantom material (such as a thin slab of plastic or other material that is
equivalent to the composition of the scintillating optical fibers) located in
the
vicinity of an accessory tray of the medical linear accelerator, with the
scintillating
optical fibers embedded in the phantom material. In some embodiments, both the
scintillating fiber length and the phantom slab area are larger than the
maximal
cross-sectional area of the ionizing radiation beam at the height of the
accessory
tray of the medical linear accelerator (to accommodate beams of all sizes).
[0039] In some embodiments, the scintillating optical fibers are long
enough to span the maximum leaf span (e.g. the gap between opposing leaves)
of the multileaf collimator.
[0040] In some cases, each scintillating optical fibers may be arranged
parallel to the direction of motion of the leaves and positioned underneath a
pair
of leaves of the multileaf collimator.
-8-
CA 02713375 2010-08-19
[0041] In some embodiments, the total number of scintillating optical fibers
is equivalent to the number of leaf pairs in the multi-leaf collimator. In
other
embodiments, greater or lesser numbers of scintillating optical fibers may be
used.
[0042] Generally, the optical fibers are used to collect the light output
coming from both ends of each scintillating optical fiber. Thus two collection
optical fibers are generally used for each scintillating optical fiber.
[0043] In some embodiments, the fluence monitoring device has a photo-
detector that converts the optical energy transmitted by the optical fibers to
electric signals. These electrical signals may then be interpreted to
determine
actual x-ray radiation pattern information. This actual radiation pattern
information may then be compared to the expected radiation pattern to be
delivered by the medical linear accelerator to determine how closely the
actual
radiation pattern matches the expected radiation pattern.
[0044] Also generally described herein is a theoretical model for predicting
the optical energy produced by scintillating optical fibers and collected at
each
end thereof by collection optical fibers as a function of the incident x-ray
radiation
pattern.
[0045] Also generally described herein are methods of calibrating a
fluence monitoring detector that uses long scintillating optical fibers to
generate
optical energy in response to x-ray radiation patterns incident on the
scintillating
optical fibers.
[0046] Also generally described herein are two methods of validation of
the incident x-ray radiation pattern on scintillating optical fiber arrays.
The first
validation method compares the predicted optical energy readings with those
readings measured during the actual treatment delivery. The second validation
method compares the optical energy readings obtained during the treatment
delivery with previously measured optical energy readings obtained from an
error-free delivery.
-g-
CA 02713375 2010-08-19
[0047] Generally, some embodiments herein relate to a fluence monitoring
device that makes use of scintillating optical fibers. In some embodiments,
the
scintillating optical fibers can be made thin enough so that one long
scintillating
optical fiber can monitor the fluence pattern associated to one leaf pair of a
given
multileaf collimator.
[0048] Turning now to Figure 1, illustrated therein is a fluence monitoring
detector 9 according to one embodiment. As shown, the fluence monitoring
detector 9 includes a plurality of scintillating fibers 10 embedded in a
phantom
slab 14. Collection optical fibers 15 (e.g. clear or non-scintillating) are
coupled to
the ends of the scintillating fibers 10 in order for the emitted light 11+ and
11-
from both the opposing ends of the scintillating fibers 10 be collected by a
photo-
detector 21.
[0049] The phantom slab 14 can be made of a material (e.g. common
plastics) with properties relative to radiation that are similar to the
material used
in the scintillating optical fibers 10 (which may also be made of a plastic).
Accordingly, with the scintillating optical fibers 10 embedded in a phantom
slab
14 with similar material properties, the radiation beam perturbation tends to
be
minimized.
[0050] Figure 2 shows the fluence monitoring detector 9 of Figure 1
mounted in position relative to a multileaf collimator 17 and an x-ray
radiation
source (indicated schematically as 16) of a radiation delivery system. In
particular, as shown the multileaf collimator 17 is positioned between the x-
ray
radiation source 16 and the fluence monitoring detector 9 (e.g. the
scintillating
optical fibers 10 are located on the opposite side of the multileaf collimator
17
from the x-ray radiation source 16).
[0051] In-use (e.g. during treatment), the scintillating optical fibers 10 and
phantom slab 14 of the fluence monitoring detector 9 are irradiated by a
fluence
pattern 12 from the x-ray radiation source 16 (as modified by the multileaf
collimator 17). The actual size and shape of the fluence pattern 12 will
depend on
the position of the leaves of the multileaf collimator 17, as well as the
distance D1
-10- {
CA 02713375 2010-08-19
between the x-ray radiation source 16 and the multileaf collimator 17, and the
distance D2 between the x-ray radiation source 16 and the fluence monitoring
detector 9.
[0052] Figure 3 shows the same setup as in Figure 2, viewed from the
side. Those skilled in the art will recognize that the distance D2 between the
schematized x-ray radiation source 16 and the plane of the scintillating
optical
fibers 10 should be small enough so that any given patient can be treated with
radiation from the x-ray radiation source 16 while the fluence monitoring
detector
9 is in place (e.g. between the multileaf collimator 17 and the patient). In
particular, in some embodiments the fluence monitoring detector 9 and
multileaf
collimator 17 should be as close as possible.
[0053] Figure 4 shows the multileaf collimator 17 assembly and the
fluence monitoring detector 9, as viewed by the x-ray radiation source 16. As
a
matter of perspective, a visible portion 10a of the scintillating optical
fibers 10 is
visible from the x-ray radiation source 16 (represented by thick lines), while
a
masked portion 10b of the scintillating optical fibers 10 is masked by the
multileaf
collimator 17 (represented as dotted lines).
[0054] In order for the fluence pattern to be verified, each pair of leaves in
the multileaf collimator 17 may be associated with a particular scintillating
optical
fiber 10. Those skilled in the art will understand that the number of leaf
pairs in a
typical multileaf collimator assembly may be greater that the number shown in
the drawings. However, for clarity, the figures and embodiments herein show
and describe only a limited number of leaf pairs in the multileaf collimator
17, and
hence a limited number of scintillating optical fibers 10.
[0055] Also described herein is a model that predicts the optical energy
produced by the scintillating optical fibers 10. From this model and following
the
irradiation of a long scintillating fiber 10, as shown schematically in Figure
3, the
light collected by each end (+/-) of the fiber (i.e. I+ and L) is determined
by the
integration of the contribution of each infinitesimal element 13 on the
scintillating
optical fibers 10:
-11-
CA 02713375 2010-08-19
1I* =C+' f K(x) ,(x)=et"(X)=dx (1)
_t
2
[0056] where K(x) represents the scintillation efficiency (i.e. the number of
scintillation photons emitted per incident fluence particles), Oj(x)
represents the
linear fluence across the fiber (m"1), A(x) accounts for the differential
light
attenuation along the optical fiber, Ct represent the light losses due to the
optical
coupling to the photo-detector and L represent the fiber length. As shown, the
position "x = 0" has been defined as the center of the fibers 10 with respect
to the
radiation source 16.
[0057] Also described herein is a method of calibrating a fluence
monitoring detector (e.g. the fluence monitoring detector 9) that includes
long
scintillating optical fibers (e.g. optical fibers 10) that generate optical
energy in
response to the incident radiation pattern. As used herein, "calibrating"
generally
refers to the determination of a scintillation efficiency (K(x)) and a
differential light
attenuation (A(x)) for all positions on a particular scintillating optical
fiber or array
of scintillating optical fibers.
[0058] As seen in Figure 5 (side view) and Figure 6 (top view), the
calibration may be done using a narrow rectangular x-ray radiation field 18
incident on the array of scintillating optical fibers 10. The scintillating
optical fibers
are set perpendicular to the rectangular x-ray field 18 and the x-ray
radiation
field 18 is wide enough (e.g. 30 to 40 cm) to enable simultaneous irradiation
of all
the fibers 10.
[0059] It may be assumed that the irradiated portion 19 of each scintillating
optical fiber 10 has a length d and is defined around its central position xf.
The
integral mean value theorem of Equation (1) above can then be used to find:
I: = C~ ' K (x0 (D ,c (x0 etxO E [xf - 2 , x f + 2 (2)
-12-
CA 02713375 2010-08-19
[0060] where d represents the effective rectangular field width (that is, the
width beyond which the radiation fluence is considered to be negligible) and
xo
represents the effective point of measure, as defined by the integral mean
value
theorem; Ct, K, O;,,t and A are defined as before. As d is small, we can
consider
that x0 will be equivalent to xf. This assumption is corroborated by the fact
that 1)
K is approximately constant along the interval, 2) 'Pf is symmetrical with
respect to
xf and 3) the variation attributable to A is small along the interval. Having
deduced
that x0 = xf, the value of K(x) and A(x) can be computed at the position xf on
the
fiber:
Y (x'. = 1 In I - (0) (3)
2 I_ (x,.) 1+ (0)
K(x11)^ /J~(xf)I(xf) (4)
K(0) 1+(0) 1_(0)
[0061] To complete the calibration, one can apply the abovementioned
rectangular x-ray radiation field over the entire scintillating optical fiber
length
(e.g. in a plurality of irradiations) in order to calculate N(x) and K(x) for
all
positions along the fiber.
[0062] Also provided herein are two exemplary methods of validation of
the incident radiation pattern on an array of scintillating optical fibers
(e.g.
scintillating optical fibers 10). These validation methods use comparison and
calculation of field parameters, namely the central position of the radiation
interaction on the scintillation optical fiber (xe) and the integral of the
fluence
passing through the scintillating optical fiber (0;,,f). These field
parameters are
calculated as follow :
XC = In I IN - (5)
2 IN+ I-
-13-
CA 02713375 2010-08-19
I+ I- (6)
(Dint = ~'intN I I
N'-
[0063] where l+ , L , IN+ and IN_ are defined by Equation 1, both l+ and L for
the field under analysis and both IN+ and IN_ for the reference field. The
constant N
represents the mean attenuation coefficient of the scintillating optical
fibers.
[0064] The first validation method compares the calculated field
parameters (using Equations 5 and 6) with those measured during the treatment
delivery. The reference field used for calculation is usually rectangular,
centered
at the fiber center (e.g. x=0) and wide enough to cover all the scintillating
optical
fibers.
[0065] The theoretical fluence pattern can be calculated using
independent fluence calculation software (e.g. treatment planning software) or
measured with a dosimeter for both the treatment field and the reference
field.
From this fluence pattern, the value obtained for the scintillation efficiency
(K(x)),
and the differential light attenuation (A(x)) from the calibration of the
detector, the
theoretical field parameters can be calculated. These calculated field
parameters
can then be compared during the treatment delivery of a particular patient to
the
value measured by the fluence monitoring detector 9 for x, and (:Pit.
[0066] The second validation method compares the optical energy
readings obtained during the treatment delivery with the previously measured
optical energy readings obtained from a reference delivery. This reference
fluence pattern may be asserted error-free by an alternate validation method,
for
example, using the first validation method described herein or a quality
assurance test performed experimentally on the treatment plan.
[0067] To apply this second validation method for a given fluence pattern,
one may compute the field parameters (xc and 0;t) with Equations 5 and 6,
using
both l+ and L from the fluence pattern under verification, and both IN+ and
IN_ from
the reference error-free field. If the field under examination is free of
delivery
-14-
I
CA 02713375 2010-08-19
errors, the value measured for x, should be 0 and the value measured for c;,,r
should be 1, according to Equations 5 and 6.
[0068] Also described generally herein are performance measurements of
an exemplary embodiment of the fluence monitoring detector 9. In this
embodiment (as shown in Figure 7), the an array of scintillating optical
fibers 10
is located at the isocenter of a treatment linear accelerator (e.g. 100 cm
from the
x-ray radiation source 16), with a phantom slab 14 made of a material
equivalent
to solid water and which is 2 cm thick. Also included are several solid water
slabs
20 located under the scintillating fiber array 10 phantom slab 14.
[0069] These additional slabs 20 are added to enable consistent
calculation of the incident fluence pattern by the treatment planning software
used (in this embodiment, Pinnacle3 8.0m, a radiation therapy planning system
offered by Philips, was used).
[0070] To evaluate the performance of the embodiment shown in Figure 7,
randomly generated errors where included in fourteen step-and-shoot IMRT
fields extracted from an oropharyngeal head and neck cancer case. Those
random errors were classified as two types: 1) single leaf errors (SLE), in
which
only an individual leaf in the multileaf collimator 17 is moved from its
original
position by a certain amount and 2) pair translation errors (PTE), in which
two
associated leaves forming a pair in the multileaf collimator 17 are moved in
the
same direction, to preserve the opening length (e.g. the gap) between the two.
[0071] SLE is expected to modify the radiation output more significantly
than PTE. However PTE would produce a systematic shift of position of the
radiation field.
[0072] The impact of leaf bank errors were also explored. A field in which
all the leaves in one of the leaf bank underwent a SLE were classified as leaf
bank error (LBE), while a field in which the two leaf banks underwent the same
parallel displacement (similar to a PTE) were classified as field translation
error
(FTE). All described errors are illustrated generally in Figure B.
-15-
CA 02713375 2010-08-19
[0073] These erroneous fields (in which a random leaf error was included)
were verified using the second validation method described above. The correct
field (with no random error included) was used as normalization field. The
results
of this validation are presented in table 1 as shown in Figure 9. The
deviation
between the measured and expected value of x, was quantified as a number of
standard deviations (SD) attributable to statistical variation (following a
Poissonnian model). The deviation between the measured and expected value of
O it was quantified in percent of the total expected integral fluence. As one
can
see, the deviation observed for unmodified (error-free) leaves is
representative of
the intrinsic variation of the field parameters.
[0074] Generally, some embodiments as described herein cannot detect
leaf errors inferior to these intrinsic statistical variations. Setting the
detection
threshold (above which an error can be detected) to 3 standard deviations for
x,
and 0.5% for o t, one can see that any SLE, LBE or FTE of 1 mm or more or any
PTE of 2mm or more can be identified by the embodiments as described herein.
[0075] The embodiments herein generally enables in-use (e.g. during
treatment) verification of any radiotherapy treatment that makes use of
multileaf
collimators. The embodiments as described herein also make use of the
significant attenuation of scintillating optical fibers to provide monitoring
of the
incident fluence using two independent field parameters.
[0076] Real-time validation of the incident fluence can be made by
comparing the calculated field parameters (using an independent fluence
calculator and fiber calibration) to the measured ones. This real-time
validation
can also be conducted by computing the field parameters using an error-free
delivery as the reference metric.
[0077] While certain features have been illustrated and described herein,
many modifications, substitutions, changes, and equivalents will now occur to
those of ordinary skill in the art. It is, therefore, to be understood that
the
appended claims are intended to cover all such modifications and changes as
fall
within the true spirit of the invention.
-16-
