Daniel Letourneau - Academia.edu (original) (raw)

Papers by Daniel Letourneau

International Journal of Radiation Oncology Biology Physics, 2004

International Journal of Radiation Oncology Biology Physics, 2004

International Journal of Radiation Oncology Biology Physics, 2005

Radiotherapy and Oncology, 2005

This paper presents efficient and generalized processes for the clinical application of on-line X... more This paper presents efficient and generalized processes for the clinical application of on-line X-ray volumetric cone-beam CT imaging (XVI) to improve the accuracy of patient set-up in radiation therapy. XVI image-guided therapy is illustrated by application to two contrasting sites, intra-cranial radiosurgery and prostate radiation therapy, with very different characteristics regarding organ motion, treatment precision, and imaging conditions. On-line set-up errors are determined in a two-step process. First the XVI data is registered to the planning data by matching the machine-isocenter with the planning-isocenter, respectively. The machine isocenter is defined in the XVI data during the reconstruction. The planning-isocenter is defined during the planning process in the planning CT data. Set-up errors are then determined from a second registration to remove residual displacements. The accuracy of the entire procedure for on-line set-up error correction was investigated in precision radiosurgery phantom studies. The phantom studies showed that sub-pixel size set-up errors (down to 0.5mm) can be correctly determined and implemented in the radiosurgery environment. XVI is demonstrated to provide quality skull detail enabling precise skull based on-line alignment in radiosurgery. A 'local XVI' technique was found to give encouraging soft-tissue detail in the high-scatter pelvic environment, enabling on-line soft-tissue based set-up for prostate treatment. The two-step process for determination of set-up errors was found to be efficient and effective when implemented with a dedicated six panel interface enabling simultaneous visualization on the XVI and planning CT data sets. XVI has potential to significantly improve the accuracy of radiation treatments. Present image quality is highly encouraging and can enable bony and soft-tissue patient set-up error determination and correction. As with all image guided treatment techniques the development of efficient procedures to utilize on-line data are of paramount importance.

International Journal of Radiation Oncology Biology Physics, 2005

associated with equivalent patient satisfaction. least 95% of dose to 98% AE 2% and 97% AE 5% of ... more associated with equivalent patient satisfaction. least 95% of dose to 98% AE 2% and 97% AE 5% of the PCT PTV, respectively. The mean time for the online planning and treatment process was 32.7 AE 4.0 minutes. Patient satisfaction was high, with a trend for superior satisfaction with the cone-beam CTeenabled process. Conclusions: The cone-beam CTeenabled palliative treatment process is feasible and is ready for clinical implementation for the treatment of bone metastases using simple beam geometry, providing a streamlined one-step process toward palliative radiotherapy. Ó 2012 Elsevier Inc.

Radiotherapy and Oncology, 2004

Background and purpose: The QA of intensity modulated radiotherapy (IMRT) dosimetry is a laboriou... more Background and purpose: The QA of intensity modulated radiotherapy (IMRT) dosimetry is a laborious task. The goal of this work is to evaluate the dosimetric characteristics of a new 2D diode array (MapCheck from Sun Nuclear Corporation, Melbourne, Florida) and assess the role it can play in routine IMRT QA.

International Journal of Radiation Oncology Biology Physics, 2003

Radiotherapy and Oncology, 2005

Background and purpose: X-ray volumetric imaging system (XVI) mounted on a linear accelerator is ... more Background and purpose: X-ray volumetric imaging system (XVI) mounted on a linear accelerator is available for image guidance applications. In preparation for clinical implementation, phantom and patient imaging studies were conducted to determine the irradiation parameters that would trade-off image quality, patient dose and scanning time.

International Journal of Radiation Oncology Biology Physics, 2008

were imported into a TPS (Pinnacle, Philips Medical Systems). Five planners from each of 3 instit... more were imported into a TPS (Pinnacle, Philips Medical Systems). Five planners from each of 3 institutions identified the markers on each dataset and recorded their coordinates. Each planner repeated the coordinate's extraction process 3 times. No specific instructions were given to the physicists on how to identify the markers. Results: The coordinates of each marker were recorded for each dataset. The results from all physicists, for all attempts, from all institutions, were combined. The mean coordinates and standard deviations were computed and analyzed. The planners, working independently, were all able to pinpoint the position of the markers in 3D with inter-observer variability of less than 0.9mm for the 1st dataset, 1.3 mm for the 2nd dataset, and 0.4mm for the last dataset. The variability decreases with CT slice thickness. Conclusions: This study shows that these novel fiducial markers can be easily identified on CT images. Results show consistency in localizing the markers amongst different planners at different centers. TX Purpose/Objective(s): This study compares and evaluates radiation therapy plans for prostate cases using both 3D conformal treatment (3D-CRT) plans and IMRT plans, to ascertain if there are dosimetric advantages to IMRT, given the current constraints. Planning system, energy, and dose volume constraints were varied to find the most ideal combination. Materials/Methods: A single physician outlined the prostate (GTV), rectum, bladder, femoral heads and penile bulb of 10 consecutive prostate patients. 3D-CRT plans, using 6 MV and 18 MV photons, were created with the Pinnacle treatment planning system (TPS). IMRT plans were generated by the Pinnacle, HiArt Tomotherapy, and Corvus TPSs, using two sets of constraints: from RTOG study 0415, and from Fox Chase Cancer Center (FCCC).

Medical Physics, 2007

The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear ac... more The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear accelerators capable of cone-beam CT (CBCT) image guided and intensity-modulated radiotherapy (IG-IMRT). This phantom is to be used in an integral test to quantify in real-time both the performance of the image guidance and the dose delivery systems in terms of dose localization. The prototype IG-IMRT QA phantom consisted of a cylindrical imaging phantom (CatPhan) combined with an array of 11 radiation diodes mounted on a 10 cm diameter disk, oriented perpendicular to the phantom axis. Basic diode response characterization was performed for 6 and 18 MV photons. The diode response was compared to planning system calculations in the open and penumbrae regions of simple and complex beam arrangements. The clinical use of the QA phantom was illustrated in an integral test of an IG-IMRT treatment designed for a clinical spinal radiosurgery case. The sensitivity of the phantom to multileaf collimator (MLC) calibration and setup errors in the clinical setting was assessed by introducing errors in the IMRT plan or by displacing the phantom. The diodes offered good response linearity and long-term reproducibility for both 6 and 18 MV. Axial dosimetry of coplanar beams (in a plane containing the beam axes) was made possible with the nearly isoplanatic response of the diodes over 360 degrees of gantry (usually within +/-1%). For single beam geometry, errors in phantom placement as small as 0.5 mm could be accurately detected (in gradient > or = 1% /mm). In clinical setting, MLC systematic errors of 1 mm on a single MLC bank introduced in the IMRT plan were easily detectable with the QA phantom. The QA phantom demonstrated also sufficient sensitivity for the detection of setup errors as small as 1 mm for the IMRT delivery. These results demonstrated that the prototype can accurately and efficiently verify the entire IG-IMRT process. This tool, in conjunction with image guidance capabilities has the potential to streamline this QA process and improve the level of performance of image guided and intensity modulated radiotherapy.

International Journal of Radiation Oncology Biology Physics, 2003

International Journal of Radiation Oncology Biology Physics, 2004

Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image... more Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment. The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 degrees to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images. For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/-1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/-0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm. On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study.

International Journal of Radiation Oncology Biology Physics, 2008

Medical Physics, 2010

The beam model in a three dimensional treatment planning system (TPS) defines virtually the mecha... more The beam model in a three dimensional treatment planning system (TPS) defines virtually the mechanical and dosimetric characteristics of a treatment unit. The manual optimization of a beam model during commissioning can be a time consuming task due to its iterative nature. Furthermore, the quality of the beam model commissioning depends on the user's ability to manage multiple parameters and assess their impact on the agreement between measured and calculated dose. The objective of this work is to develop and validate the performance of an automated beam model optimization system (ABMOS) based on intensity modulated radiotherapy (IMRT) beam measurements to improve beam model accuracy while streamlining the commissioning process. The ABMOS was developed to adjust selected TPS beam model parameters iteratively to maximize the agreement between measured and calculated 2D dose maps obtained for an IMRT beam pattern. A 2D diode array with high spatial resolution detectors was used to sample the entire IMRT beam pattern in a single dose measurement. The use of an IMRT beam pattern with large number of monitor units was selected to highlight the difference between planned and delivered dose and improve the signal to noise ratio in the low dose regions. ABMOS was applied to the optimization of a beam model for an Elekta Synergy S treatment unit. The optimized beam model was validated for two anatomical sites (25 paraspinal and 25 prostate cases) using two independent patient-specific IMRT quality control (QC) methods based on ion chamber and 2D diode array measurements, respectively. The conventional approach of comparing calculated and measured beam profiles and percent-depth dose curves was also used to assess improvement in beam model after ABMOS optimization. Elements of statistical process control were applied to the process of patient-specific QC performed with the ion chamber and the 2D array to complement the model comparison. After beam model optimization with ABMOS, improvement in planned to delivered dose agreement was demonstrated with both patient-specific IMRT QC methods and the calculated to measured profile comparison. In terms of ion chamber measurements, the largest improvement was observed for the paraspinal cases with the mean measured to calculated dose difference at the low dose points decreasing from - 13.8% to 2.0% with the optimized beam model. The 2D diode array patient-specific QC also demonstrated clearly the improvement in beam model for both paraspinal and prostate cases with, on average, more than 96% of the diodes satisfying tolerances of 3% of dose difference or 2 mm of distance to agreement after ABMOS optimization. The capability index (C(pk)) for both patient-specific QC methods also increased with the optimized beam model. In this work, ABMOS was developed to use 2D diode array measurements of an IMRT beam pattern for the automated multivariable optimization of a TPS beam model. Based on the observed improvements in patient-specific QC results for 25 paraspinal and 25 prostate plans, optimization of the remaining clinical beam models using ABMOS is now ongoing in the institution.

Medical Physics, 2008

A treatment process which integrates simulation, planning, and delivery in one single session of ... more A treatment process which integrates simulation, planning, and delivery in one single session of < or =30 min on a treatment unit capable of cone-beam CT imaging (CBCT) is under development in our institution for palliation of spinal metastases. The objective of this work is to develop and validate a semiautomatic vertebra detection and identification algorithm to streamline the target definition process and improve the consistency of online planning on cone-beam CT data sets while the patient is on the treatment couch. Key issues pertaining to this work are the limited field of view and image quality of CBCT, the inter- and intrapatient variation of vertebra morphology, and the spine curvature. An initial library of ten patient CBCT data sets was used to derive the vertebra detection and identification method and set the parameters used by the algorithm. In this method, sagittal and coronal "curved" digitally reconstructed radiographs (cDRRs) are first created by projecting a subvolume of the CBCT data orthogonally to the centerline of a cylinder model positioned manually. The detection of the vertebra centers is then performed on the cDRRs based on an edge detection algorithm. The identification of the vertebrae by name is based on the detection of one or more of four different reference anatomical landmarks on cDRRs. The validation of the vertebra detection and identification algorithm was performed on a library of 27 patient CBCT data sets with an average detection success rate of 92.8% and 89.9% for sagittal and coronal cDRRs, respectively, for three different users. The entire process including manual steps and user approval was performed on average in 3.23-3.45 min (n=37, three users), with only 0.14 min for the automatic detection and identification of the vertebrae. The semiautomatic identification and segmentation of vertebrae on CBCT images was shown to be robust and effective. The next step will be the clinical implementation of the algorithm within the online planning and delivery treatment technique for patients with spinal bone metastases.

Medical Physics, 2009

The objective of this work is to assess the suitability and performance of a new dosimeter system... more The objective of this work is to assess the suitability and performance of a new dosimeter system with a novel geometry for the quality assurance (QA) of volumetric modulated arc therapy (VMAT). The new dosimeter system consists of a hollow cylinder (15 and 25 cm inner and outer diameters) with 124 diodes embedded in the phantom's cylindrical wall forming four rings of detectors. For coplanar beams, the cylindrical geometry and the ring diode pattern offer the advantage of invariant perpendicular incidence on the beam central axis for any gantry angle and also have the benefit of increasing the detector density as both walls of the cylinder sample the beam. Other advantages include real-time readout and reduced weight with the hollow phantom shape. A calibration method taking into account the variation in radiation sensitivity of the diodes as a function of gantry angle was developed and implemented. In this work, the new dosimeter system was used in integrating mode to perform composite dose measurements along the cylindrical surface supporting the diodes. The reproducibility of the dosimeter response and the angular dependence of the diodes were assessed using simple 6 MV photon static beams. The performance of the new dosimeter system for VMAT QA was then evaluated using VMAT plans designed for a head and neck, an abdominal sarcoma, and a prostate patient. These plans were optimized with 90 control points (CPs) and additional versions of each plan were generated by increasing the number of CPs to 180 and 360 using linear interpolation. The relative dose measured with the dosimeter system for the VMAT plans was compared to the corresponding TPS dose map in terms of relative dose difference (% deltaD) and distance to agreement (DTA). The dosimeter system's sensitivity to gantry rotation offset and scaling errors as well as setup errors was also evaluated. For static beams, the dosimeter system offered good reproducibility and demonstrated small residual diode angular dependence after calibration. For VMAT deliveries, the agreement between measured and calculated doses was good with > or = 86.4% of the diodes satisfying 3% of % deltaD or 2 mm DTA for the 180 CP plans. The phantom offered sufficient sensitivity for the detection of small gantry rotation offset (3 degrees) and scaling errors (1 degree) as well as phantom setup errors of 1 mm, although the results were plan dependent. With its novel geometry, the dosimeter system was also able to experimentally demonstrate the discretization effect of the number of CPs used in the TPS to simulate a continuous arc. These results demonstrate the suitability of the new dosimeter system for the patient-specific QA of VMAT plans and suggest that the dosimeter system can be an effective tool in the routine QA and commissioning of treatment machines capable of VMAT delivery and cone-beam CT image guidance.

International Journal of Radiation Oncology Biology Physics, 2004

Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image... more Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment. The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 degrees to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images. For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/-1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/-0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm. On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study.

Medical Physics, 2007

The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear ac... more The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear accelerators capable of cone-beam CT (CBCT) image guided and intensity-modulated radiotherapy (IG-IMRT). This phantom is to be used in an integral test to quantify in real-time both the performance of the image guidance and the dose delivery systems in terms of dose localization. The prototype IG-IMRT QA phantom consisted of a cylindrical imaging phantom (CatPhan) combined with an array of 11 radiation diodes mounted on a 10 cm diameter disk, oriented perpendicular to the phantom axis. Basic diode response characterization was performed for 6 and 18 MV photons. The diode response was compared to planning system calculations in the open and penumbrae regions of simple and complex beam arrangements. The clinical use of the QA phantom was illustrated in an integral test of an IG-IMRT treatment designed for a clinical spinal radiosurgery case. The sensitivity of the phantom to multileaf collimator (MLC) calibration and setup errors in the clinical setting was assessed by introducing errors in the IMRT plan or by displacing the phantom. The diodes offered good response linearity and long-term reproducibility for both 6 and 18 MV. Axial dosimetry of coplanar beams (in a plane containing the beam axes) was made possible with the nearly isoplanatic response of the diodes over 360 degrees of gantry (usually within +/-1%). For single beam geometry, errors in phantom placement as small as 0.5 mm could be accurately detected (in gradient > or = 1% /mm). In clinical setting, MLC systematic errors of 1 mm on a single MLC bank introduced in the IMRT plan were easily detectable with the QA phantom. The QA phantom demonstrated also sufficient sensitivity for the detection of setup errors as small as 1 mm for the IMRT delivery. These results demonstrated that the prototype can accurately and efficiently verify the entire IG-IMRT process. This tool, in conjunction with image guidance capabilities has the potential to streamline this QA process and improve the level of performance of image guided and intensity modulated radiotherapy.

Radiotherapy and Oncology, 2006

International Journal of Radiation Oncology Biology Physics, 2004

International Journal of Radiation Oncology Biology Physics, 2004

International Journal of Radiation Oncology Biology Physics, 2005

Radiotherapy and Oncology, 2005

This paper presents efficient and generalized processes for the clinical application of on-line X... more This paper presents efficient and generalized processes for the clinical application of on-line X-ray volumetric cone-beam CT imaging (XVI) to improve the accuracy of patient set-up in radiation therapy. XVI image-guided therapy is illustrated by application to two contrasting sites, intra-cranial radiosurgery and prostate radiation therapy, with very different characteristics regarding organ motion, treatment precision, and imaging conditions. On-line set-up errors are determined in a two-step process. First the XVI data is registered to the planning data by matching the machine-isocenter with the planning-isocenter, respectively. The machine isocenter is defined in the XVI data during the reconstruction. The planning-isocenter is defined during the planning process in the planning CT data. Set-up errors are then determined from a second registration to remove residual displacements. The accuracy of the entire procedure for on-line set-up error correction was investigated in precision radiosurgery phantom studies. The phantom studies showed that sub-pixel size set-up errors (down to 0.5mm) can be correctly determined and implemented in the radiosurgery environment. XVI is demonstrated to provide quality skull detail enabling precise skull based on-line alignment in radiosurgery. A 'local XVI' technique was found to give encouraging soft-tissue detail in the high-scatter pelvic environment, enabling on-line soft-tissue based set-up for prostate treatment. The two-step process for determination of set-up errors was found to be efficient and effective when implemented with a dedicated six panel interface enabling simultaneous visualization on the XVI and planning CT data sets. XVI has potential to significantly improve the accuracy of radiation treatments. Present image quality is highly encouraging and can enable bony and soft-tissue patient set-up error determination and correction. As with all image guided treatment techniques the development of efficient procedures to utilize on-line data are of paramount importance.

International Journal of Radiation Oncology Biology Physics, 2005

associated with equivalent patient satisfaction. least 95% of dose to 98% AE 2% and 97% AE 5% of ... more associated with equivalent patient satisfaction. least 95% of dose to 98% AE 2% and 97% AE 5% of the PCT PTV, respectively. The mean time for the online planning and treatment process was 32.7 AE 4.0 minutes. Patient satisfaction was high, with a trend for superior satisfaction with the cone-beam CTeenabled process. Conclusions: The cone-beam CTeenabled palliative treatment process is feasible and is ready for clinical implementation for the treatment of bone metastases using simple beam geometry, providing a streamlined one-step process toward palliative radiotherapy. Ó 2012 Elsevier Inc.

Radiotherapy and Oncology, 2004

Background and purpose: The QA of intensity modulated radiotherapy (IMRT) dosimetry is a laboriou... more Background and purpose: The QA of intensity modulated radiotherapy (IMRT) dosimetry is a laborious task. The goal of this work is to evaluate the dosimetric characteristics of a new 2D diode array (MapCheck from Sun Nuclear Corporation, Melbourne, Florida) and assess the role it can play in routine IMRT QA.

International Journal of Radiation Oncology Biology Physics, 2003

Radiotherapy and Oncology, 2005

Background and purpose: X-ray volumetric imaging system (XVI) mounted on a linear accelerator is ... more Background and purpose: X-ray volumetric imaging system (XVI) mounted on a linear accelerator is available for image guidance applications. In preparation for clinical implementation, phantom and patient imaging studies were conducted to determine the irradiation parameters that would trade-off image quality, patient dose and scanning time.

International Journal of Radiation Oncology Biology Physics, 2008

were imported into a TPS (Pinnacle, Philips Medical Systems). Five planners from each of 3 instit... more were imported into a TPS (Pinnacle, Philips Medical Systems). Five planners from each of 3 institutions identified the markers on each dataset and recorded their coordinates. Each planner repeated the coordinate's extraction process 3 times. No specific instructions were given to the physicists on how to identify the markers. Results: The coordinates of each marker were recorded for each dataset. The results from all physicists, for all attempts, from all institutions, were combined. The mean coordinates and standard deviations were computed and analyzed. The planners, working independently, were all able to pinpoint the position of the markers in 3D with inter-observer variability of less than 0.9mm for the 1st dataset, 1.3 mm for the 2nd dataset, and 0.4mm for the last dataset. The variability decreases with CT slice thickness. Conclusions: This study shows that these novel fiducial markers can be easily identified on CT images. Results show consistency in localizing the markers amongst different planners at different centers. TX Purpose/Objective(s): This study compares and evaluates radiation therapy plans for prostate cases using both 3D conformal treatment (3D-CRT) plans and IMRT plans, to ascertain if there are dosimetric advantages to IMRT, given the current constraints. Planning system, energy, and dose volume constraints were varied to find the most ideal combination. Materials/Methods: A single physician outlined the prostate (GTV), rectum, bladder, femoral heads and penile bulb of 10 consecutive prostate patients. 3D-CRT plans, using 6 MV and 18 MV photons, were created with the Pinnacle treatment planning system (TPS). IMRT plans were generated by the Pinnacle, HiArt Tomotherapy, and Corvus TPSs, using two sets of constraints: from RTOG study 0415, and from Fox Chase Cancer Center (FCCC).

Medical Physics, 2007

The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear ac... more The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear accelerators capable of cone-beam CT (CBCT) image guided and intensity-modulated radiotherapy (IG-IMRT). This phantom is to be used in an integral test to quantify in real-time both the performance of the image guidance and the dose delivery systems in terms of dose localization. The prototype IG-IMRT QA phantom consisted of a cylindrical imaging phantom (CatPhan) combined with an array of 11 radiation diodes mounted on a 10 cm diameter disk, oriented perpendicular to the phantom axis. Basic diode response characterization was performed for 6 and 18 MV photons. The diode response was compared to planning system calculations in the open and penumbrae regions of simple and complex beam arrangements. The clinical use of the QA phantom was illustrated in an integral test of an IG-IMRT treatment designed for a clinical spinal radiosurgery case. The sensitivity of the phantom to multileaf collimator (MLC) calibration and setup errors in the clinical setting was assessed by introducing errors in the IMRT plan or by displacing the phantom. The diodes offered good response linearity and long-term reproducibility for both 6 and 18 MV. Axial dosimetry of coplanar beams (in a plane containing the beam axes) was made possible with the nearly isoplanatic response of the diodes over 360 degrees of gantry (usually within +/-1%). For single beam geometry, errors in phantom placement as small as 0.5 mm could be accurately detected (in gradient > or = 1% /mm). In clinical setting, MLC systematic errors of 1 mm on a single MLC bank introduced in the IMRT plan were easily detectable with the QA phantom. The QA phantom demonstrated also sufficient sensitivity for the detection of setup errors as small as 1 mm for the IMRT delivery. These results demonstrated that the prototype can accurately and efficiently verify the entire IG-IMRT process. This tool, in conjunction with image guidance capabilities has the potential to streamline this QA process and improve the level of performance of image guided and intensity modulated radiotherapy.

International Journal of Radiation Oncology Biology Physics, 2003

International Journal of Radiation Oncology Biology Physics, 2004

Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image... more Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment. The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 degrees to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images. For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/-1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/-0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm. On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study.

International Journal of Radiation Oncology Biology Physics, 2008

Medical Physics, 2010

The beam model in a three dimensional treatment planning system (TPS) defines virtually the mecha... more The beam model in a three dimensional treatment planning system (TPS) defines virtually the mechanical and dosimetric characteristics of a treatment unit. The manual optimization of a beam model during commissioning can be a time consuming task due to its iterative nature. Furthermore, the quality of the beam model commissioning depends on the user's ability to manage multiple parameters and assess their impact on the agreement between measured and calculated dose. The objective of this work is to develop and validate the performance of an automated beam model optimization system (ABMOS) based on intensity modulated radiotherapy (IMRT) beam measurements to improve beam model accuracy while streamlining the commissioning process. The ABMOS was developed to adjust selected TPS beam model parameters iteratively to maximize the agreement between measured and calculated 2D dose maps obtained for an IMRT beam pattern. A 2D diode array with high spatial resolution detectors was used to sample the entire IMRT beam pattern in a single dose measurement. The use of an IMRT beam pattern with large number of monitor units was selected to highlight the difference between planned and delivered dose and improve the signal to noise ratio in the low dose regions. ABMOS was applied to the optimization of a beam model for an Elekta Synergy S treatment unit. The optimized beam model was validated for two anatomical sites (25 paraspinal and 25 prostate cases) using two independent patient-specific IMRT quality control (QC) methods based on ion chamber and 2D diode array measurements, respectively. The conventional approach of comparing calculated and measured beam profiles and percent-depth dose curves was also used to assess improvement in beam model after ABMOS optimization. Elements of statistical process control were applied to the process of patient-specific QC performed with the ion chamber and the 2D array to complement the model comparison. After beam model optimization with ABMOS, improvement in planned to delivered dose agreement was demonstrated with both patient-specific IMRT QC methods and the calculated to measured profile comparison. In terms of ion chamber measurements, the largest improvement was observed for the paraspinal cases with the mean measured to calculated dose difference at the low dose points decreasing from - 13.8% to 2.0% with the optimized beam model. The 2D diode array patient-specific QC also demonstrated clearly the improvement in beam model for both paraspinal and prostate cases with, on average, more than 96% of the diodes satisfying tolerances of 3% of dose difference or 2 mm of distance to agreement after ABMOS optimization. The capability index (C(pk)) for both patient-specific QC methods also increased with the optimized beam model. In this work, ABMOS was developed to use 2D diode array measurements of an IMRT beam pattern for the automated multivariable optimization of a TPS beam model. Based on the observed improvements in patient-specific QC results for 25 paraspinal and 25 prostate plans, optimization of the remaining clinical beam models using ABMOS is now ongoing in the institution.

Medical Physics, 2008

A treatment process which integrates simulation, planning, and delivery in one single session of ... more A treatment process which integrates simulation, planning, and delivery in one single session of < or =30 min on a treatment unit capable of cone-beam CT imaging (CBCT) is under development in our institution for palliation of spinal metastases. The objective of this work is to develop and validate a semiautomatic vertebra detection and identification algorithm to streamline the target definition process and improve the consistency of online planning on cone-beam CT data sets while the patient is on the treatment couch. Key issues pertaining to this work are the limited field of view and image quality of CBCT, the inter- and intrapatient variation of vertebra morphology, and the spine curvature. An initial library of ten patient CBCT data sets was used to derive the vertebra detection and identification method and set the parameters used by the algorithm. In this method, sagittal and coronal "curved" digitally reconstructed radiographs (cDRRs) are first created by projecting a subvolume of the CBCT data orthogonally to the centerline of a cylinder model positioned manually. The detection of the vertebra centers is then performed on the cDRRs based on an edge detection algorithm. The identification of the vertebrae by name is based on the detection of one or more of four different reference anatomical landmarks on cDRRs. The validation of the vertebra detection and identification algorithm was performed on a library of 27 patient CBCT data sets with an average detection success rate of 92.8% and 89.9% for sagittal and coronal cDRRs, respectively, for three different users. The entire process including manual steps and user approval was performed on average in 3.23-3.45 min (n=37, three users), with only 0.14 min for the automatic detection and identification of the vertebrae. The semiautomatic identification and segmentation of vertebrae on CBCT images was shown to be robust and effective. The next step will be the clinical implementation of the algorithm within the online planning and delivery treatment technique for patients with spinal bone metastases.

Medical Physics, 2009

The objective of this work is to assess the suitability and performance of a new dosimeter system... more The objective of this work is to assess the suitability and performance of a new dosimeter system with a novel geometry for the quality assurance (QA) of volumetric modulated arc therapy (VMAT). The new dosimeter system consists of a hollow cylinder (15 and 25 cm inner and outer diameters) with 124 diodes embedded in the phantom's cylindrical wall forming four rings of detectors. For coplanar beams, the cylindrical geometry and the ring diode pattern offer the advantage of invariant perpendicular incidence on the beam central axis for any gantry angle and also have the benefit of increasing the detector density as both walls of the cylinder sample the beam. Other advantages include real-time readout and reduced weight with the hollow phantom shape. A calibration method taking into account the variation in radiation sensitivity of the diodes as a function of gantry angle was developed and implemented. In this work, the new dosimeter system was used in integrating mode to perform composite dose measurements along the cylindrical surface supporting the diodes. The reproducibility of the dosimeter response and the angular dependence of the diodes were assessed using simple 6 MV photon static beams. The performance of the new dosimeter system for VMAT QA was then evaluated using VMAT plans designed for a head and neck, an abdominal sarcoma, and a prostate patient. These plans were optimized with 90 control points (CPs) and additional versions of each plan were generated by increasing the number of CPs to 180 and 360 using linear interpolation. The relative dose measured with the dosimeter system for the VMAT plans was compared to the corresponding TPS dose map in terms of relative dose difference (% deltaD) and distance to agreement (DTA). The dosimeter system's sensitivity to gantry rotation offset and scaling errors as well as setup errors was also evaluated. For static beams, the dosimeter system offered good reproducibility and demonstrated small residual diode angular dependence after calibration. For VMAT deliveries, the agreement between measured and calculated doses was good with > or = 86.4% of the diodes satisfying 3% of % deltaD or 2 mm DTA for the 180 CP plans. The phantom offered sufficient sensitivity for the detection of small gantry rotation offset (3 degrees) and scaling errors (1 degree) as well as phantom setup errors of 1 mm, although the results were plan dependent. With its novel geometry, the dosimeter system was also able to experimentally demonstrate the discretization effect of the number of CPs used in the TPS to simulate a continuous arc. These results demonstrate the suitability of the new dosimeter system for the patient-specific QA of VMAT plans and suggest that the dosimeter system can be an effective tool in the routine QA and commissioning of treatment machines capable of VMAT delivery and cone-beam CT image guidance.

International Journal of Radiation Oncology Biology Physics, 2004

Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image... more Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment. The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 degrees to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images. For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/-1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/-0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm. On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study.

Medical Physics, 2007

The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear ac... more The objective of this work is to develop a dosimetric phantom quality assurance (QA) of linear accelerators capable of cone-beam CT (CBCT) image guided and intensity-modulated radiotherapy (IG-IMRT). This phantom is to be used in an integral test to quantify in real-time both the performance of the image guidance and the dose delivery systems in terms of dose localization. The prototype IG-IMRT QA phantom consisted of a cylindrical imaging phantom (CatPhan) combined with an array of 11 radiation diodes mounted on a 10 cm diameter disk, oriented perpendicular to the phantom axis. Basic diode response characterization was performed for 6 and 18 MV photons. The diode response was compared to planning system calculations in the open and penumbrae regions of simple and complex beam arrangements. The clinical use of the QA phantom was illustrated in an integral test of an IG-IMRT treatment designed for a clinical spinal radiosurgery case. The sensitivity of the phantom to multileaf collimator (MLC) calibration and setup errors in the clinical setting was assessed by introducing errors in the IMRT plan or by displacing the phantom. The diodes offered good response linearity and long-term reproducibility for both 6 and 18 MV. Axial dosimetry of coplanar beams (in a plane containing the beam axes) was made possible with the nearly isoplanatic response of the diodes over 360 degrees of gantry (usually within +/-1%). For single beam geometry, errors in phantom placement as small as 0.5 mm could be accurately detected (in gradient > or = 1% /mm). In clinical setting, MLC systematic errors of 1 mm on a single MLC bank introduced in the IMRT plan were easily detectable with the QA phantom. The QA phantom demonstrated also sufficient sensitivity for the detection of setup errors as small as 1 mm for the IMRT delivery. These results demonstrated that the prototype can accurately and efficiently verify the entire IG-IMRT process. This tool, in conjunction with image guidance capabilities has the potential to streamline this QA process and improve the level of performance of image guided and intensity modulated radiotherapy.

Radiotherapy and Oncology, 2006