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ABSTRACT: This paper investigates a quality assurance (QA) phantom specially designed to verify the accuracy of dose distributions and monitor units (MU) calculated by clinical treatment planning optimization systems and by the Monte Carlo method for intensity-modulated radiotherapy (IMRT). The QA phantom is a PMMA cylinder of 30 cm diameter and 40 cm length with various bone and lung inserts. A procedure (and formalism) has been developed to measure the absolute dose to water in the PMMA phantom. Another cylindrical phantom of the same dimensions, but made of water, was used to confirm the results obtained with the PMMA phantom. The PMMA phantom was irradiated by 4, 6 and 15 MV photon beams and the dose was measured using an ionization chamber and compared to the results calculated by a commercial inverse planning system (CORVUS, NOMOS, Sewickley, PA) and by the Monte Carlo method. The results show that the dose distributions calculated by both CORVUS and Monte Carlo agreed to within 2% of dose maximum with measured results in the uniform PMMA phantom for both open and intensity-modulated fields. Similar agreement was obtained between Monte Carlo calculations and measured results with the bone and lung heterogeneity inside the PMMA phantom while the CORVUS results were 4% different. The QA phantom has been integrated as a routine QA procedure for the patient's IMRT dose verification at Stanford since 1999.
Physics in Medicine and Biology 04/2003; 48(5):561-72. · 2.83 Impact Factor
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ABSTRACT: A water beam imaging system (WBIS) has been developed and used to verify dose distributions for intensity modulated radiotherapy using dynamic multileaf collimator. This system consisted of a water container, a scintillator screen, a charge-coupled device camera, and a portable personal computer. The scintillation image was captured by the camera. The pixel value in this image indicated the dose value in the scintillation screen. Images of radiation fields of known spatial distributions were used to calibrate the device. The verification was performed by comparing the image acquired from the measurement with a dose distribution from the IMRT plan. Because of light scattering in the scintillator screen, the image was blurred. A correction for this was developed by recognizing that the blur function could be fitted to a multiple Gaussian. The blur function was computed using the measured image of a 10 cm x 10 cm x-ray beam and the result of the dose distribution calculated using the Monte Carlo method. Based on the blur function derived using this method, an iterative reconstruction algorithm was applied to recover the dose distribution for an IMRT plan from the measured WBIS image. The reconstructed dose distribution was compared with Monte Carlo simulation result. Reasonable agreement was obtained from the comparison. The proposed approach makes it possible to carry out a real-time comparison of the dose distribution in a transverse plane between the measurement and the reference when we do an IMRT dose verification.
Medical Physics 01/2002; 28(12):2466-74. · 2.83 Impact Factor
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ABSTRACT: To investigate the role of beam orientation optimization in intensity-modulated radiation therapy (IMRT) and to examine the potential benefits of noncoplanar intensity-modulated beams.
A beam orientation optimization algorithm was implemented. For this purpose, system variables were divided into two groups: beam position (gantry and table angles) and beam profile (beamlet weights). Simulated annealing was used for beam orientation optimization and the simultaneous iterative inverse treatment planning algorithm (SIITP) for beam intensity profile optimization. Three clinical cases were studied: a localized prostate cancer, a nasopharyngeal cancer, and a paraspinal tumor. Nine fields were used for all treatments. For each case, 3 types of treatment plan optimization were performed: (1) beam intensity profiles were optimized for 9 equiangular spaced coplanar beams; (2) orientations and intensity profiles were optimized for 9 coplanar beams; (3) orientations and intensity profiles were optimized for 9 noncoplanar beams.
For the localized prostate case, all 3 types of optimization described above resulted in dose distributions of a similar quality. For the nasopharynx case, optimized noncoplanar beams provided a significant gain in the gross tumor volume coverage. For the paraspinal case, orientation optimization using noncoplanar beams resulted in better kidney sparing and improved gross tumor volume coverage.
The sensitivity of an IMRT treatment plan with respect to the selection of beam orientations varies from site to site. For some cases, the choice of beam orientations is important even when the number of beams is as large as 9. Noncoplanar beams provide an additional degree of freedom for IMRT treatment optimization and may allow for notable improvement in the quality of some complicated plans.
International Journal of Radiation OncologyBiologyPhysics 07/2001; 50(2):551-60. · 4.11 Impact Factor
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ABSTRACT: A simple analytical approach has been developed to model extrafocal radiation and monitor chamber backscatter for clinical photon beams. Model parameters for both the extrafocal source and monitor chamber backscatter are determined simultaneously using conventional measured data, i.e., in-air output factors for square and rectangular fields defined by the photon jaws. The model has been applied to 6 MV and 15 MV photon beams produced by a Varian Clinac 2300C/D accelerator. Contributions to the in-air output factor from the extrafocal radiation and monitor chamber backscatter, as predicted by the model, are in good agreement with the measurements. The model can be used to calculate the in-air output factors analytically, with an accuracy of 0.2% for symmetric or asymmetric rectangular fields defined by jaws when the calculation point is at the isocenter and 0.5% when the calculation point is at an extended SSD. For MLC-defined fields, with the jaws at the recommended positions, calculated in-air output factors agree with the measured data to within 0.3% at the isocenter and 0.7% at off-axis positions. The model has been incorporated into a Monte Carlo dose algorithm to calculate the absolute dose distributions in patients or phantoms. For three MLC-defined irregular fields (triangle shape, C-shape, and L-shape), the calculations agree with the measurements to about 1% even for points at off-axis positions. The model will be particularly useful for IMRT dose calculations because it accurately predicts beam output and penumbra dose.
Medical Physics 02/2001; 28(1):55-66. · 2.83 Impact Factor
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Medical Physics 12/2000; 27(11):2477-9. · 2.83 Impact Factor
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ABSTRACT: The task of treatment planning for prostate implants is to find an optimal seed configuration, comprising the target coverage and dosimetric consideration of critical structures such as the rectum and urethra. An efficient method to accomplish this is to use an inverse planning technique that derives the optimized solution from a prescribed treatment goal. The goal can be specified in the voxel domain as the desired doses to the voxels of the target and critical structures, or in the dose volume representation as the desired dose volume histograms (DVHs) of the target and critical structures. The DVH based optimization has been successfully used in plan optimization for intensity-modulated radiation therapy (IMRT) but little attention has been paid to its application in prostate implants. Clinically, it has long been known that some normal structure tolerances are more accurately assessed by volumetric information. Dose-volume histograms are also widely used for plan evaluation. When working in the DVH domain for optimization one has more control over the final DVHs. We have constructed an objective function sensitive to the DVHs of the target and critical structures. The objective function is minimized using an iterative algorithm, starting from a randomly selected initial seed configuration. At each iteration step, a trial position is given to a randomly selected source and the trial position is accepted if the objective function is decreased. To avoid being trapped in a less optimal local minimum, the optimization process is repeated. The final plan is selected from a pool of optimized plans obtained from a series of randomized initial seed configurations.
Medical Physics 11/2000; 27(10):2286-92. · 2.83 Impact Factor
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ABSTRACT: The purpose of this work was to use Monte Carlo simulations to verify the accuracy of the dose distributions from a commercial treatment planning optimization system (Corvus, Nomos Corp., Sewickley, PA) for intensity-modulated radiotherapy (IMRT). A Monte Carlo treatment planning system has been implemented clinically to improve and verify the accuracy of radiotherapy dose calculations. Further modifications to the system were made to compute the dose in a patient for multiple fixed-gantry IMRT fields. The dose distributions in the experimental phantoms and in the patients were calculated and used to verify the optimized treatment plans generated by the Corvus system. The Monte Carlo calculated IMRT dose distributions agreed with the measurements to within 2% of the maximum dose for all the beam energies and field sizes for both the homogeneous and heterogeneous phantoms. The dose distributions predicted by the Corvus system, which employs a finite-size pencil beam (FSPB) algorithm, agreed with the Monte Carlo simulations and measurements to within 4% in a cylindrical water phantom with various hypothetical target shapes. Discrepancies of more than 5% (relative to the prescribed target dose) in the target region and over 20% in the critical structures were found in some IMRT patient calculations. The FSPB algorithm as implemented in the Corvus system is adequate for homogeneous phantoms (such as prostate) but may result in significant under or over-estimation of the dose in some cases involving heterogeneities such as the air-tissue, lung-tissue and tissue-bone interfaces.
Physics in Medicine and Biology 10/2000; 45(9):2483-95. · 2.83 Impact Factor
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ABSTRACT: A ray tracing based method has been developed to calculate the x-ray transmission through a multileaf collimator (MLC) for beam delivery verification and dose calculation in intensity modulated radiotherapy (IMRT). The path length of a ray line in the MLC is accurately calculated using the exact geometry of the MLC leaves. The fluence distribution of an IMRT field is calculated first using a point source. The fluence distribution for a realistic beam model is obtained, as an approximation, by convolving the point source fluence distribution with the distribution of source strength. Full ray tracing calculations are performed using analytic and Monte Carlo simulated beam models to verify the accuracy of the convolution method. The calculation is in better agreement with measurements using either film or a beam imaging system (BIS) than previous calculations for MLC transmission using a simplified model. This ray tracing calculation can be applied to the problem of verifying dynamic MLC leaf sequences as part of a patient-specific quality assurance process for IMRT.
Medical Physics 09/2000; 27(8):1717-26. · 2.83 Impact Factor
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ABSTRACT: This work investigates the feasibility of optimizing energy- and intensity-modulated electron beams for radiation therapy. A multileaf collimator (MLC) specially designed for modulated electron radiotherapy (MERT) was investigated both experimentally and by Monte Carlo simulations. An inverse-planning system based on Monte Carlo dose calculations was developed to optimize electron beam energy and intensity to achieve dose conformity for target volumes near the surface. The results showed that an MLC with 5 mm leaf widths could produce complex field shapes for MERT. Electron intra- and inter-leaf leakage had negligible effects on the dose distributions delivered with the MLC, even at shallow depths. Focused leaf ends reduced the electron scattering contributions to the dose compared with straight leaf ends. As anticipated, moving the MLC position toward the patient surface reduced the penumbra significantly. There were significant differences in the beamlet distributions calculated by an analytic 3-D pencil beam algorithm and the Monte Carlo method. The Monte Carlo calculated beamlet distributions were essential to the accuracy of the MERT dose distribution in cases involving large air gaps, oblique incidence and heterogeneous treatment targets (at the tissue-bone and bone-lung interfaces). To demonstrate the potential of MERT for target dose coverage and normal tissue sparing for treatment of superficial targets, treatment plans for a hypothetical treatment were compared using photon beams and MERT.
Physics in Medicine and Biology 09/2000; 45(8):2293-311. · 2.83 Impact Factor
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ABSTRACT: To explore the feasibility of a multi-modality breast-conserving radiation therapy treatment technique to reduce high dose to the ipsilateral lung and the heart when compared with the conventional treatment technique using two tangential fields.
An electron beam with appropriate energy was combined with four intensity modulated photon beams. The direction of the electron beam was chosen to be tilted 10-20 degrees laterally from the anteroposterior direction. Two of the intensity-modulated photon beams had the same gantry angles as the conventional tangential fields, whereas the other two beams were rotated 15-25 degrees toward the anteroposterior directions from the first two photon beams. An iterative algorithm was developed which optimizes the weight of the electron beam as well as the fluence profiles of the photon beams for a given patient. Two breast cancer patients with early-stage breast tumors were planned with the new technique and the results were compared with those from 3D planning using tangential fields as well as 9-field intensity-modulated radiotherapy (IMRT) techniques.
The combined electron and IMRT plans showed better dose conformity to the target with significantly reduced dose to the ipsilateral lung and, in the case of the left-breast patient, reduced dose to the heart, than the tangential field plans. In both the right-sided and left-sided breast plans, the dose to other normal structures was similar to that from conventional plans and was much smaller than that from the 9-field IMRT plans. The optimized electron beam provided between 70 to 80% of the prescribed dose at the depth of maximum dose of the electron beam.
The combined electron and IMRT technique showed improvement over the conventional treatment technique using tangential fields with reduced dose to the ipsilateral lung and the heart. The customized beam directions of the four IMRT fields also kept the dose to other critical structures to a minimum.
Radiotherapy and Oncology 08/2000; 56(1):65-71. · 5.58 Impact Factor
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ABSTRACT: PURPOSE AND OBJECTIVE: The primary goal of this study was to examine systematically the dosimetric effect of small patient movements and linear accelerator angular setting misalignments in the delivery of intensity modulated radiation therapy. We will also provide a method for estimating dosimetric errors for an arbitrary combination of these uncertainties.
Sites in two patients (lumbar-vertebra and nasopharynx) were studied. Optimized intensity modulated radiation therapy treatment plans were computed for each patient using a commercially available inverse planning system (CORVUS, NOMOS Corporation, Sewickley, PA). The plans used nine coplanar beams. For each patient the dose distributions and relevant dosimetric quantities were calculated, including the maximum, minimum, and average doses in targets and sensitive structures. The corresponding dose volumetric information was recalculated by purposely varying the collimator angle or gantry angle of an incident beam while keeping other beams unchanged. Similar calculations were carried out by varying the couch indices in either horizontal or vertical directions. The intensity maps of all the beams were kept the same as those in the optimized plan. The change of a dosimetric quantity, Q, for a combination of collimator and gantry angle misalignments and patient displacements was estimated using Delta=Sigma(DeltaQ/Deltax(i))Deltax(i). Here DeltaQ is the variation of Q due to Deltax(i), which is the change of the i-th variable (collimator angle, gantry angle, or couch indices), and DeltaQ/Deltax(i) is a quantity equivalent to the partial derivative of the dosimetric quantity Q with respect to x(i).
While the change in dosimetric quantities was case dependent, it was found that the results were much more sensitive to small changes in the couch indices than to changes in the accelerator angular setting. For instance, in the first example in the paper, a 3-mm movement of the couch in the anterior-posterior direction can cause a 38% decrease in the minimum target dose or a 41% increase in the maximum cord dose, whereas a 5 degrees change in the θ(1)=20 degrees beam only gave rise to a 1.5% decrease in the target minimum or 5.1% in the cord maximum. The effect of systematic positioning uncertainties of the machine settings was more serious than random uncertainties, which tended to smear out the errors in dose distributions.
The dose distribution of an intensity modulated radiation therapy (IMRT) plan changes with patient displacement and angular misalignment in a complex way. A method was proposed to estimate dosimetric errors for an arbitrary combination of uncertainties in these quantities. While it is important to eliminate the angular misalignment, it was found that the couch indices (or patient positioning) played a much more important role. Accurate patient set-up and patient immobilization is crucial in order to take advantage fully of the technological advances of IMRT. In practice, a sensitivity check should be useful to foresee potential IMRT treatment complications and a warning should be given if the sensitivity exceeds an empirical value. Quality assurance action levels for a given plan can be established out of the sensitivity calculation.
Radiotherapy and Oncology 07/2000; 56(1):97-108. · 5.58 Impact Factor
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ABSTRACT: Beam direction optimization is an important problem in radiation therapy. In intensity modulated radiation therapy (IMRT), the difficulty for computer optimization of the beam directions arises from the fact that they are coupled with the intensity profiles of the incident beams. In order to obtain the optimal incident beam directions using iterative or stochastic methods, the beam profiles ought to be optimized after every change of beam configuration. In this paper we report an effective algorithm to optimize gantry angles for IMRT. In our calculation the gantry angles and the beam profiles (beamlet weights) were treated as two separate groups of variables. The gantry angles were sampled according to a simulated annealing algorithm. For each sampled beam configuration, beam profile calculation was done using a fast filtered backprojection (FBP) method. Simulated annealing was also used for beam profile optimization to examine the performance of the FBP for beam orientation optimization. Relative importance factors were incorporated into the objective function to control the relative importance of the target and the sensitive structures. Minimization of the objective function resulted in the best possible beam orientations and beam profiles judged by the given objective function. The algorithm was applied to several model problems and the results showed that the approach has potential for IMRT applications.
Medical Physics 07/2000; 27(6):1238-45. · 2.83 Impact Factor
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ABSTRACT: An important issue in intensity modulated radiation therapy (IMRT) is the verification of the monitor unit (MU) calculation of the planning system using an independent procedure. Because of the intensity modulation and the dynamic nature of the delivery process, the problem becomes much more involved than that in conventional radiation therapy. In this work, a closed formula for MU calculation is derived. The approach is independent of the specific form of leaf sequence algorithms. It is straightforward to implement the procedure using a simple computer program. The approach is illustrated by a simplified example and is demonstrated by a few CORVUS (NOMOS Corporation, Sewickley, PA) treatment plans. The results indicate that it is robust and suitable for IMRT MU verification.
Physics in Medicine and Biology 04/2000; 45(3):N1-7. · 2.83 Impact Factor
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ABSTRACT: Dose verification by ion chamber measurements Is a time-consuming
quality assurance (QA) process for intensity modulation radiotherapy
(IMRT). A Clarkson summation algorithm was investigated as an
alternative to calculate the dose to the isocenter of IMRT treatments.
Scatter contributions to the isocenter dose were calculated using a
method similar to that of the Clarkson calculation for the central axis
dose of an irregular field. The independent dose calculation was
performed using the leaf sequences generated by a commercial treatment
planning system (Corvus, NOMOS Corporation, Sewickley, PA) and the
patient geometry obtained from CT-simulations. The isocenter dose was
decomposed into contributions from the surrounding finite-size beamlets.
Each beamlet contribution was calculated by differentiating the phantom
scatter data for open fields. The result for a spherically shaped target
agreed with the Corvus calculation to within 3%. Special corrections
were needed for those cases in which the isocenter was at a low dose
point under the shadow of the MLC. This Clarkson-type calculation was
found to overestimate the dose when the beams pass through a large air
volume, since no tissue heterogeneity was considered in the algorithm.
In such cases the dose calculation is performed using a homogeneous
phantom plan with the same fields and compared with the Corvus
calculation for the same phantom
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
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ABSTRACT: The clinical objectives are usually multifaceted and
incommensurable. A set of importance factors (IFs) is often incorporated
in the objective function in inverse planning to parameterize tradeoff
strategies and to prioritize the dose conformality in different
structures. Whereas the general formalism remains the same, different
sets of IFs characterize plans of obviously different flavor and
critically influence the final plan. Up to now, the determination of
these parameters has been a “guessing” game based on
empirical knowledge because the influence of these parameters on the
plan is not known until the optimization is completed. To compromise
properly the conflicting requirements of the target and sensitive
structures, the parameters are usually adjusted through trial-and-error.
Here, the authors report a computational algorithm to automate the
selection of the parameters. The plan selection is done in two steps.
First, a set of IFs are chosen and the corresponding beam parameters are
optimized under the guidance of an objective function using an iterative
algorithm. The “optimal” plan is then evaluated by an
additional scoring function. The IFs in the objective function are
adjusted accordingly to improve the ranking of the plan. For every
change in the IFs, the beam parameters need to be re-optimized. This
process continues in an iterative fashion until the scoring function is
saturated. The algorithm was applied to two clinical cases and the
results demonstrated that it has the potential to improve significantly
the existing method of inverse planning
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
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ABSTRACT: Endovascular brachytherapy has proven to be an effective tool in the reduction of restenosis following balloon angioplasty for coronary heart disease, while the range of optimal doses and precise target tissue are still unknown. However, over-dosing has been associated with increased thrombogenicity and permanent damage to vessel walls. Under-dosing has been found to stimulate neointima formation, causing restenosis. It has been suggested that restenosis near the edges (edge effect) of the intervention may be caused by the dose falloff towards near the source ends. Monte Carlo code EGS4 was used to calculate the dose distribution around the ends of a Guidant <sup>32</sup>P source. At the ends of the source the 100% isodose curve was found to bend back toward the source starting at about 3 mm from the end of the active source (prescription to 2 mm radius). The 80% isodose line crossed the prescription line 1 mm from the source ends. Further calculations predicted improvement can be achieved by changing the specific activity within 1 mm of the ends of the source. A four-fold increase in specific activity in 0.5 mm segments at the ends of the source, followed by a 0.5 mm gap between the ends and the middle part of the source, kept the 100% isodose line at the prescription distance to within 0.5 mm of the active length of the source without any over-dosing. With five times the activity in the terminal segments, a “full length source” is achieved, involving a small over-dosing
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
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ABSTRACT: A water beam imaging system (WBIS) was developed and used to verify dose distributions for intensity modulated radiotherapy (IMRT) using dynamic multileaf collimator (MLC). The WBIS consists of a water container, a scintillator screen, a CCD camera, and a portable personal computer. The scintillation image is captured by the CCD camera. The pixel value in this image indicates the dose value in the scintillation screen. The verification is performed by comparing the WBIS image achieved from the measurement with dose distribution from the IMRT plan. Because of light scattering in the WBIS the image is blurred. An iterative reconstruction algorithm is proposed to remove the blurring effect of light scattering. From the measured image of a 10 cm ×10 cm X-ray beam and the simulation result of the dose distribution using the Monte Carlo method, the blur function can be achieved. Based on this function, the proposed algorithm is applied to reconstruct the true dose distribution for an IMRT plan from the measured WBIS image. The reconstructed dose distributions are compared with Monte Carlo simulation results. Reasonable agreement can be observed from the comparison. The proposed approach makes it possible to carry out real-time quality assurance tasks for IMRT dose verification
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
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ABSTRACT: The authors have investigated the benefits of using noncoplanar
beams with optimized directions for intensity modulated radiation
therapy. They have considered three typical cases of localized prostate
cancer, nasopharyngeal cancer, and paraspinal treatment. Nine fields
were used for each treatment. For all cases, three types of treatment
plan optimization were done: (1) nine uniformly spaced coplanar beams
with optimized beam intensity profiles; (2) beam orientations and beam
profiles were optimized, but only coplanar beams were allowed; (3)
similar to (2), except that non-coplanar beams were allowed during beam
orientation optimization. Simulated annealing was used for beam
orientation optimization and an iterative optimization algorithm was
used for beam intensity profile optimization. For the localized prostate
case, all three types of optimization described above resulted in a dose
distribution of similar quality. For the nasopharyngeal case, optimized
non-coplanar beams provided a significant improvement in GTV coverage.
For the paraspinal case, orientation optimization of non-coplanar beams
resulted in significant improvement of kidney sparing and In increased
GTV coverage. It is concluded that the use of non-coplanar beams with
optimized orientations presents a viable option to improve target
coverage and critical structure sparing in complicated cases
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
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ABSTRACT: A pressing issue in intensity modulated radiation therapy (IMRT)
is the verification of the monitor unit (MU) calculation of the planning
system using an independent procedure. Because of the intensity
modulation and the dynamic nature of the delivery process, the problem
becomes much more involved than that in conventional radiation therapy.
In this work, a closed formula for MU calculation in IMRT is derived.
The formalism is quite general and independent of the specific form of
leaf sequence algorithm or delivery machine. The dose at an arbitrary
spatial point (either on the central axis or off-axis) is expressed as a
summation of the contributions from all the beamlets. The dose from each
individual beamlet can be calculated using a variety of methods, as
simple as a Clarkson type of approach or as complex as Monte Carlo
simulation. The method is demonstrated using a simple scatter-summation.
Some specific issues related to the clinical implementation of the
formalism, such as effect of skin contour variation, off-axis dose
calculation, effect of tissue density inhomogeneity, and the
verification in the low dose region, are discussed. In addition, the
implementation of the technique with different delivery schemes
(step-and-shoot, sliding-window, ...) is addressed. The approach is
illustrated by a simplified example and several CORVUS (NOMOS
corporation, Sewickley, PA) treatment plans. The results indicate that
it is robust and suitable for IMRT MU verification
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
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ABSTRACT: We have investigated a quality assurance (QA) phantom that was
specially designed to verify the accuracy of dose distributions
calculated by a commercial inverse planning optimization system (CORVUS)
and by the Monte Carlo method for intensity-modulated radiotherapy
(IMRT). The QA phantom is a PMMA cylinder of 30 cm diameter and 40 cm
length with various bone and lung inserts. A procedure was developed to
measure the absolute dose at any point inside the QA phantom. Another
cylindrical phantom of the same dimensions, but made of water, was used
to confirm the results obtained with the PMMA phantom. The PMMA phantom
was irradiated by 4, 6 and 15 MV photon beams and the dose was measured
using an ionization chamber and compared to the results calculated by
CORVUS and by the Monte Carlo method. The results show that the dose
distributions calculated by both CORVUS and Monte Carlo agreed well
(within 2% of dose maximum) with measured results in the uniform PMMA
phantom for both open and intensity-modulated fields. Similar agreement
was obtained between Monte Carlo calculation and measured results with
the bone and lung heterogeneities inside the PMMA phantom. Following the
positive results of this study, our QA phantom has been integrated as a
routine QA procedure for patient's IMRT dose verification at Stanford
since 1999
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
