Revistas
Revista:
RADIATION PHYSICS AND CHEMISTRY
ISSN:
0969-806X
Año:
2023
Vol.:
204
Págs.:
110708
This work tackles the commissioning and validation of a novel combination of a synchrotron-based proton beam therapy system (Hitachi, Ltd.) for use with a Monte Carlo treatment planning system (TPS). Four crucial aspects in this configuration have been investigated: (1) Monte Carlo-based correction performed by the TPS to the measured integrated depth-dose curves (IDD), (2) circular spot modelling with a single Gaussian function to characterize the synchrotron physical spot, which is elliptical, (3) the modelling of the range shifter that enables using only one set of measurements in open beams, and (4) the Monte Carlo dose calculation model in small fields.Integrated depth-dose curves were measured with a PTW Bragg peak chamber and corrected, with a Monte Carlo model, to account for energy absorbed outside the detector. The elliptical spot was measured by IBA Lynx scintillator, EBT3 films and PTW microDiamond. The accuracy of the TPS (RayStation, RaySearch Laboratories) at spot modelling with a circular Gaussian function was assessed.The beam model was validated using spread-out Bragg peak (SOBP) fields. We took single-point doses at several depths through the central axis using a PTW Farmer chamber, for fields between 2 x 2cm and 30 x 30cm. We checked the range-shifter modelling from open-beam data. We tested clinical cases with film and an ioni-zation chamber array (IBA Matrix).Sigma differences for spots fitted using 2D images and 1D profiles to elliptical and circular Gaussian models were below 0.22 mm. Differences between SOBP measurements at single points and TPS calculations for all fields between 5 x 5 and 30 x 30cm were below 2.3%. Smaller fields had larger differences: up to 3.8% in the 2 x 2cm field. Mean differences at several depths along the central axis were generally below 1%. Differences in range -shifter doses were below 2.4%. Gamma test (3%, 3 mm) results for clinical cases were generally above 95% for Matrix and film.Approaches for modelling synchrotron proton beams have been validated. Dose values for open and range -shifter fields demonstrate accurate Monte Carlo correction for IDDs. Elliptical spots can be successfully modelled using a circular Gaussian, which is accurate for patient calculations and can be used for small fields. A double-Gaussian spot can improve small-field calculations. The range-shifter modelling approach, which reduces clinical commissioning time, is adequate.
Revista:
PHYSICS IN MEDICINE AND BIOLOGY
ISSN:
0031-9155
Año:
2023
Vol.:
68
N°:
1
Págs.:
015005
Objective. Periodic respiratory motion and inter-fraction variations are sources of geometric uncertainty in stereotactic body radiation therapy (SBRT) of pulmonary lesions. This study extensively evaluates and validates the separate and combined dosimetric effect of both factors using 4D-CT and daily 4D-cone beam CT (CBCT) dose accumulation scenarios. Approach. A first cohort of twenty early stage or metastatic disease lung cancer patients were retrospectively selected to evaluate each scenario. The planned-dose (3D(Ref)) was optimized on a 3D mid-position CT. To estimate the dosimetric impact of respiratory motion (4D(Ref)), inter-fractional variations (3D(Acc)) and the combined effect of both factors (4D(Acc)), three dose accumulation scenarios based on 4D-CT, daily mid-cone beam CT (CBCT) position and 4D-CBCT were implemented via CT-CT/CT-CBCT deformable image registration (DIR) techniques. Each scenario was compared to 3D(Ref.) A separate cohort of ten lung SBRT patients was selected to validate DIR techniques. The distance discordance metric (DDM) was implemented per voxel and per patient for tumor and organs at risk (OARs), and the dosimetric impact for CT-CBCT DIR geometric errors was calculated. Main results. Median and interquartile range (IQR) of the dose difference per voxel were 0.05/2.69 Gy and -0.12/2.68 Gy for 3DAcc-3DRef 4DAcc-3DRef. 4DRef-3DRef
Revista:
CLINICAL AND TRANSLATIONAL ONCOLOGY
ISSN:
1699-048X
Año:
2023
Vol.:
25
N°:
5
Págs.:
1268 - 1276
Introduction: A rapid deploy of unexpected early impact of the COVID pandemic in Spain was described in 2020. Oncology practice was revised to facilitate decision-making regarding multimodal therapy for prevalent cancer types amenable to multidisciplinary treatment in which the radiotherapy component searched more efficient options in the setting of the COVID-19 pandemic, minimizing the risks to patients whilst aiming to guarantee cancer outcomes.
Methods: A novel Proton Beam Therapy (PBT), Unit activity was analyzed in the period of March 2020 to March 2021. Institutional urgent, strict and mandatory clinical care standards for early diagnosis and treatment of COVID-19 infection were stablished in the hospital following national health-authorities' recommendations. The temporary trends of patients care and research projects proposals were registered.
Results: 3 out of 14 members of the professional staff involved in the PBR intra-hospital process had a positive test for COVID infection. Also, 4 out of 100 patients had positive tests before initiating PBT, and 7 out of 100 developed positive tests along the weekly mandatory special checkup performed during PBT to all patients. An update of clinical performance at the PBT Unit at CUN Madrid in the initial 500 patients treated with PBT in the period from March 2020 to November 2022 registers a distribution of 131 (26%) pediatric patients, 63 (12%) head and neck cancer and central nervous system neoplasms and 123 (24%) re-irradiation indications. In November 2022, the activity reached a plateau in terms of patients under treatment and the impact of COVID pandemic became sporadic and controlled by minor medical actions. At present, the clinical data are consistent with an academic practice prospectively (NCT05151952). Research projects and scientific production was adapted to the pandemic evolution and its influence upon professional time availability. Seven research projects based in public funding were activated in this period and preliminary data on molecular imaging guided proton therapy in brain tumors and post-irradiation patterns of blood biomarkers are reported.
Conclusions: Hospital-based PBT in European academic institutions was impacted by COVID-19 pandemic, although clinical and research activities were developed and sustained. In the post-pandemic era, the benefits of online learning will shape the future of proton therapy education.
Revista:
FRONTIERS IN ONCOLOGY
ISSN:
2234-943X
Año:
2023
Vol.:
12
Págs.:
1116433
Revista:
RADIATION PHYSICS AND CHEMISTRY
ISSN:
0969-806X
Año:
2023
Vol.:
208
Págs.:
110891
Background
It is widely accepted that Monte Carlo dose calculations offers a higher precision that the commercially available dose calculation algorithms. This advantage may be especially relevant for lung Stereotactic Body Radiation Therapy (SBRT), as this is a precise technique applied to an area of big inhomogeneity.
Purpose
We conducted a comparative study to reveal the differences between the doses calculated using the Collapsed Cone Convolution algorithm and the GAMOS/Geant4 Monte Carlo calculation for lung cancer patients treated with Stereotactic Body Radiation Therapy on an Elekta Versa HD linac.
Methods
For this study a set of ten patient treatments carried out at the Clínica Universidad de Navarra was selected. Theanalysis is based on the comparison of several dosimetric quantities for the Gross Tumor Volume (GTV) and several OrgansAt Risk (OARs), and also a gamma index calculation with distance-to-agreement set to 2 mm and dose difference to 3%, as recommended by ICRU to assess clinical impact. In order to guarantee a small uncertainty in the Monte Carlo calculation of the dosimetric quantities, we studied in detail the validity of different methods that may be used to determine this uncertainty.
To compensate for lung movements, a 4D-Cone-beam Computed Tomography (CBCT) was acquired before treatment, whichallowed us to identify eight respiratory phases using a temporal binning. Using commercial MIM software®, we performed a deformable image registration between the eight CT respiration phases to construct the 4D doses. The same procedure was applied for the Treatment Planning System (TPS) dose files and for the Monte Carlo dose files.
Results
The differences between the two algorithms reveal the known weaknesses of the Collapsed Cone Convolution (CCC) algorithm for the calculation of lateral doses and in regions of large density change. The comparison between the two algorithms for individual phase doses shows differences up to 5% of the GTV D95 or 3¿4 Gy in some OARs, which may have a clinical impact. Nevertheless these differences are reduced for the 4D dose in most quantities under study.
Conclusions
Comparing the dose calculated with a Collapsed Cone Convolution algorithm with GAMOS/Geant4 for ten patients and eight respiratory phases, we found some differences that could have a clinical impact. When combining the eight temporal phases into a 4D dose using the MIM Deformable Image Registration software, the differences diminished substantially.
Our statistical analysis concludes that dose uncertainty in the voxels with a maximum dose below a given percentage guarantees uncertainty in the dosimetric quantities below that figure.
Revista:
FRONTIERS IN ONCOLOGY
ISSN:
2234-943X
Año:
2022
Vol.:
12
N°:
1037262
Págs.:
1037262 -*
Background: Oligo-recurrent disease has a consolidated evidence of long-term surviving patients due to the use of intense local cancer therapy. The latter combines real-time surgical exploration/resection with high-energy electron beam single dose of irradiation. This results in a very precise radiation dose deposit, which is an essential element of contemporary multidisciplinary individualized oncology. Methods: Patient candidates to proton therapy were evaluated in Multidisciplinary Tumor Board to consider improved treatment options based on the institutional resources and expertise. Proton therapy was delivered by a synchrotron-based pencil beam scanning technology with energy levels from 70.2 to 228.7 MeV, whereas intraoperative electrons were generated in a miniaturized linear accelerator with dose rates ranging from 22 to 36 Gy/min (at Dmax) and energies from 6 to 12 MeV. Results: In a period of 24 months, 327 patients were treated with proton therapy: 218 were adults, 97 had recurrent cancer, and 54 required re-irradiation. The specific radiation modalities selected in five cases included an integral strategy to optimize the local disease management by the combination of surgery, intraoperative electron boost, and external pencil beam proton therapy as components of the radiotherapy management. Recurrent cancer was present in four cases (cervix, sarcoma, melanoma, and rectum), and one patient had a primary unresectable locally advanced pancreatic adenocarcinoma. In re-irradiated patients (cervix and rectum), a tentative radical total dose was achieved by integrating beams of electrons (ranging from 10- to 20-Gy single dose) and protons (30 to 54-Gy Relative Biological Effectiveness (RBE), in 10-25 fractions). Conclusions: Individual case solution strategies combining intraoperative electron radiation therapy and proton therapy for patients with oligo-recurrent or unresectable localized cancer are feasible. The potential of this combination can be clinically explored with electron and proton FLASH beams.
Revista:
PHYSICS IN MEDICINE AND BIOLOGY
ISSN:
0031-9155
Año:
2021
Vol.:
66
N°:
3
Págs.:
035025
The purpose of this study was to devise and evaluate a method to quantify the dosimetric uncertainty produced by the interplay between the movement of multileaf collimator (MLC) and respiratory motion in lung stereotactic body radiation therapy (SBRT). The method calculates the dose distribution for all control points from a dynamic treatment in all respiratory phases. The methodology includes some characteristics of a patient's irregular breathing patterns. It selects, for each control point, the phases with maximum and minimum mean dose over the tumor and their corresponding adjacent phases, whenever necessary. According to this selection, the dose matrices from each control point are summed up to obtain two dose distributions in each phase, which are accumulated in the reference phase subsequently by Deformable Image Registration (DIR). D95 and Dmin,0.035cc were calculated over those accumulated dose distributions for Gross Tumor Volume (GTV), Planning Target Volume (PTV) - based on Internal Target Volume (ITV) approach - and Evaluation Target Volume (ETV), a novel concept that applies to 4D dose accumulation. With the ETV, DIR and interplay uncertainties are separated. The methodology also evaluated how variations in the breathing rate and field size affects the mean dose received by the GTV. The method was applied retrospectively in five patients treated with intensity modulated radiotherapy (IMRT) - minimum area defined by the leaves configuration at any control point was at least 4cm2-. Uncertainties in tumor coverage were small (in most patients, changes on D95 and Dmin,0.035cc were below 2% for GTV and ETV) but significant over- and under- dosages near ETV, which can be accentuated by highly irregular breathing. Uncertainties in mean dose for GTV tended to decrease exponentially with increasing field size and were reduced by an increase of breathing rate. The implementation of this method would be helpful to assess treatment quality in patients with irregular breathing. Furthermore, it could be used to study interplay uncertainties when small field sizes are used.
Revista:
NUCLEAR INSTRUMENTS AND METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT
ISSN:
0168-9002
Año:
2020
Vol.:
964
Págs.:
163755
We have studied each of the physics options that Geant4 offers to simulate an X-ray radiotherapy treatment with the aim of obtaining those that provide the best possible match to the experimental data of dose profiles and at the same time reduce the CPU time. The procedure has been repeated for two linac setups: an ELEKTA Versa HD with an Agility Multileaf Collimator using two nominal energies, 6 MV and 10 MV, both without flattening filter. After combining the results with those of a previous similar study of a 6 MV VARIAN Clinac 2100 C/D linac with flattening filter, we can propose a set of optimized Geant4 physics options of general use for radiotherapy simulation. Together with this, we have optimized the CPU time using several of the optimization techniques that GAMOS offers, reaching a reduction of several hundred times for each setup.
Revista:
MEDICAL PHYSICS
ISSN:
0094-2405
Año:
2019
Vol.:
46
N°:
10
Págs.:
4346 - 4355
Purpose To use four-dimensional (4D) dose accumulation based on deformable image registration (DIR) to assess dosimetric uncertainty in lung stereotactic body radiation therapy (SBRT) treatment planning. A novel concept, the Evaluation Target Volume (ETV), was introduced to achieve this goal. Methods The internal target volume (ITV) approach was used for treatment planning for 11 patients receiving lung SBRT. Retrospectively, 4D dose calculation was done in Pinnacle v9.10. Total dose was accumulated in the reference phase using DIR with MIM. DIR was validated using landmarks introduced by an expert radiation oncologist. The 4D and three-dimensional (3D) dose distributions were compared within the gross tumor volume (GTV) and the planning target volume (PTV) using the D-95 and D-min (calculated as D-min,D-0.035cc) metrics. For lung involvement, the mean dose and V-20, V-10, and V-5 were used in the 3D to 4D dose comparison, and D-max (D-0.1cc) was used for all other organs at risk (OAR). The new evaluation target volume (ETV) was calculated by expanding the GTV in the reference phase in order to include geometrical uncertainties of the DIR, interobserver variability in the definition of the tumor, and uncertainties of imaging and delivery systems. D-95 and D-min,D-0.035cc metrics were then calculated on the basis of the ETV for 4D accumulated dose distributions, and these metrics were compared with those calculated from the PTV for 3D planned dose distributions.
Revista:
MEDICAL DOSIMETRY
ISSN:
0958-3947
Año:
2017
Vol.:
42
N°:
4
Págs.:
282 - 288
This study aimed to describe the commissioning of small field size radiosurgery cones in a 6-MV flattening filter free (FFF) beam and report our measured values. Four radiosurgery cones of diameters 5, 10, 12.5, and 15¿mm supplied by Elekta Medical were commissioned in a 6-MV FFF beam from an Elekta Versa linear accelerator. The extraction of a reference signal for measuring small fields in scanning mode is challenging. A transmission chamber was attached to the lower part of the collimators and used for percentage depth dose (PDD) and profile measurements in scanning mode with a stereotactic diode. Tissue-maximum ratios (TMR) and output factors (OF) for all collimators were measured with a stereotactic diode (IBA). TMR and the OF for the largest collimator were also acquired on a polystyrene phantom with a microionization chamber of 0.016¿cm3 volume (PTW Freiburg PinPoint 3D). Measured TMR with diode and PinPoint microionization chamber agreed very well with differences smaller than 1% for depths below 20¿cm, except for the smaller collimator, for which differences were always smaller than 2%. Calculated TMR were significantly different (up to 7%) from measured TMR. OF measured with diode and chamber showed a difference of 3.5%. The use of a transmission chamber allowed the measurement of the small-field dosimetric properties with a simple setup. The commissioning of radiosurgery cones in FFF beams has been performed with essentially the same procedures and recommended ...
Revista:
JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS
ISSN:
1526-9914
Año:
2015
Vol.:
16
N°:
5
Págs.:
306 - 321
Revista:
PHYSICS IN MEDICINE AND BIOLOGY
ISSN:
0031-9155
Año:
2015
Vol.:
61
N°:
1
Págs.:
50 - 66
This paper presents a method to obtain the pencil-beam kernels that characterize a megavoltage photon beam generated in a flattening filter free (FFF) linear accelerator (linac) by deconvolution from experimental measurements at different depths. The formalism is applied to perform independent dose calculations in modulated fields. In our previous work a formalism was developed for ideal flat fluences exiting the linac's head. That framework could not deal with spatially varying energy fluences, so any deviation from the ideal flat fluence was treated as a perturbation. The present work addresses the necessity of implementing an exact analysis where any spatially varying fluence can be used such as those encountered in FFF beams. A major improvement introduced here is to handle the actual fluence in the deconvolution procedure. We studied the uncertainties associated to the kernel derivation with this method. Several Kodak EDR2 radiographic films were irradiated with a 10 MV FFF photon beam from two linacs from different vendors, at the depths of 5, 10, 15, and 20cm in polystyrene (RW3 water-equivalent phantom, PTW Freiburg, Germany). The irradiation field was a 50mm diameter circular field, collimated with a lead block. The 3D kernel for a FFF beam was obtained by deconvolution using the Hankel transform. A correction on the low dose part of the kernel was performed to reproduce accurately the experimental output factors. Error uncertainty in the kernel derivation procedure was estimated to be within 0.2%. Eighteen modulated fields used clinically in different treatment localizations were irradiated at four measurement depths (total of fifty-four film measurements). Comparison through the gamma-index to their corresponding calculated absolute dose distributions showed a number of passing points (3%, 3mm) mostly above 99%. This new procedure is more reliable and robust than the previous one. Its ability to perform accurate independent dose calculations was demonstrated.
Revista:
MEDICAL PHYSICS
ISSN:
0094-2405
Año:
2014
Vol.:
41
N°:
1
Págs.:
12102-11
Revista:
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
ISSN:
1879-355X
Año:
2014
Vol.:
88
N°:
5
Págs.:
1167 - 1174
PURPOSE:
To develop a method for dose reconstruction by incorporating the interplay effect between aperture modulation and target motion, and to assess the dosimetric impact of real-time prostate motion during volumetric modulated arc therapy (VMAT).
METHODS AND MATERIALS:
Clinical VMAT plans were delivered with the TrueBeam linac for 8 patients with prostate cancer. The real-time target motion during dose delivery was determined based on the 2-dimensional fiducial localization using an onboard electronic portal imaging device. The target shift in each image was correlated with the control point with the same gantry angle in the VMAT plan. An in-house-developed Monte Carlo simulation tool was used to calculate the 3-dimensional dose distribution for each control point individually, taking into account the corresponding real-time target motion (assuming a nondeformable target with no rotation). The delivered target dose was then estimated by accumulating the dose from all control points in the plan. On the basis of this information, dose-volume histograms and 3-dimensional dose distributions were calculated to assess their degradation from the planned dose caused by target motion. Thirty-two prostate motion trajectories were analyzed.
RESULTS:
The minimum dose to 0.03 cm(3) of the gross tumor volume (D0.03cc) was only slightly degraded after taking motion into account, with a minimum value of 94.1% of the planned dose among all patients and fractions. However, the gross tumor volume receiving prescription dose (V100%) could be largely affected by motion, dropping below 60% in 1 trajectory. We did not observe a correlation between motion magnitude and dose degradation.
CONCLUSIONS:
Prostate motion degrades the delivered dose to the target in an unpredictable way, although its effect is reduced over multiple fractions, and for most patients the degradation is small. Patients with greater prostate motion or those treated with stereotactic body radiation therapy would benefit from real-time prostate tracking to reduce the margin.
Revista:
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
ISSN:
0360-3016
Año:
2013
Vol.:
86
N°:
4
Págs.:
762 - 768
Purpose: To assess the prostate intrafraction motion in volumetric modulated arc therapy treatments using cine megavoltage (MV) images acquired with an electronic portal imaging device (EPID).
Methods and Materials: Ten prostate cancer patients were treated with volumetric modulated arc therapy using a Varian TrueBeam linear accelerator equipped with an EPID for acquiring cine MV images during treatment. Cine MV images acquisition was scheduled for single or multiple treatment fractions (between 1 and 8). A novel automatic fiducial detection algorithm that can handle irregular multileaf collimator apertures, field edges, fast leaf and gantry movement, and MV image noise and artifacts in patient anatomy was used. All sets of images (approximately 25,000 images in total) were analyzed to measure the positioning accuracy of implanted fiducial markers and assess the prostate movement.
Results: Prostate motion can vary greatly in magnitude among different patients. Different motion patterns were identified, showing its unpredictability. The mean displacement and standard deviation of the intrafraction motion was generally less than 2.0 +/- 2.0 mm in each of the spatial directions. In certain patients, however, the percentage of the treatment time in which the prostate is displaced more than 5 mm from its planned position in at least 1 spatial direction was 10% or more. The maximum prostate displacement observed was 13.3 mm.
Conclusion: Prostate tracking and motion assessment was performed with MV imaging and an EPID. The amount of prostate motion observed suggests that patients will benefit from its real-time monitoring. Megavoltage imaging can provide the basis for real-time prostate tracking using conventional linear accelerators.
Revista:
MEDICAL PHYSICS
ISSN:
0094-2405
Año:
2013
Vol.:
40
N°:
3
Págs.:
031708
Purpose: Real-time tracking of implanted fiducials in cine megavoltage (MV) imaging during volumetric modulated arc therapy (VMAT) delivery is complicated due to the inherent low contrast of MV images and potential blockage of dynamic leaves configurations. The purpose of this work is to develop a clinically practical autodetection algorithm for motion management during VMAT.
Methods: The expected field-specific segments and the planned fiducial position from the Eclipse (Varian Medical Systems, Palo Alto, CA) treatment planning system were projected onto the MV images. The fiducials were enhanced by applying a Laplacian of Gaussian filter in the spatial domain for each image, with a blob-shaped object as the impulse response. The search of implanted fiducials was then performed on a region of interest centered on the projection of the fiducial when it was within an open field including the case when it was close to the field edge or partially occluded by the leaves. A universal template formula was proposed for template matching and normalized cross correlation was employed for its simplicity and computational efficiency. The search region for every image was adaptively updated through a prediction model that employed the 3D position of the fiducial estimated from the localized positions in previous images. This prediction model allowed the actual fiducial position to be tracked dynamically and was used to initialize the search region. The artifacts caused by electronic interference during the acquisition were effectively removed. A score map was computed by combining both morphological information and image intensity. The pixel location with the highest score was selected as the detected fiducial position. The sets of cine MV images taken during treatment were analyzed with in-house developed software written in MATLAB (The Mathworks, Inc., Natick, MA). Five prostate patients were analyzed to assess the algorithm performance by measuring their positioning accuracy during treatment.
Results: The algorithm was able to accurately localize the fiducial position on MV images with success rates of more than 90% per case. The percentage of images in which each fiducial was localized in the studied cases varied between 23% and 65%, with at least one fiducial having been localized between 40% and 95% of the images. This depended mainly on the modulation of the plan and fiducial blockage. The prostate movement in the presented cases varied between 0.8 and 3.5 mm (mean values). The maximum displacement detected among all patients was of 5.7 mm.
Conclusions: An algorithm for automatic detection of fiducial markers in cine MV images has been developed and tested with five clinical cases. Despite the challenges posed by complex beam aperture shapes, fiducial localization close to the field edge, partial occlusion of fiducials, fast leaf and gantry movement, and inherently low MV image quality, good localization results were achieved in patient images. This work provides a technique for enabling real-time accurate fiducial detection and tumor tracking during VMAT treatments without the use of extra imaging dose.
Revista:
MEDICAL PHYSICS
ISSN:
0094-2405
Año:
2010
Vol.:
37
N°:
9
Págs.:
4634 - 4642
Purpose: This article presents an improved pencil-beam dose calculation formalism based on an experimental kernel obtained by deconvolution. The new algorithm makes it possible to calculate the absorbed dose for all field sizes.
Methods: The authors have enhanced their previous work [J. D. Azcona and J. Burguete, Med. Phys. 35, 248-259 (2008)] by correcting the kernel tail representing the contribution to the absorbed dose far from the photon interaction point. The correction was performed by comparing the calculated and measured output factors. Dose distributions and absolute dose values calculated using the new formalism have been compared to measurements. The agreement between calculated and measured dose distributions was evaluated according to the gamma-index criteria. In addition, 35 individual intensity-modulated radiation therapy (IMRT) fields were calculated and measured in polystyrene using an ionization chamber. Furthermore, a series of 541 IMRT fields was calculated using the algorithm proposed here and using a commercial IMRT optimization and calculation software package. Comparisons were made between the calculations at single points located at the isocenter for all the beams, as well as between beams grouped by anatomic location.
Results: The percentage of points passing the gamma-index criteria (3%, 3 mm) when comparing calculated and measured dose distributions is generally greater than 99% for the cases studied. The agreement between the calculations and the experimental measurements generally lies in the +/- 2% interval for single points, with a mean value of 0.2%. The agreement between calculations using the proposed algorithm and using a commercial treatment planning system is also between +/- 5%.
Conclusions: An improved algorithm based on an experimental pencil-beam kernel obtained by deconvolution has been developed. It has been validated clinically and promises to be a valuable tool for IMRT quality assurance as an independent calculation system for monitor units and dose distributions. An important point is that the algorithm presented here uses an experimental kernel, which is therefore independent of Monte-Carlo-calculated kernels.