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Techniques for performing treatment planning calculations on varian CBCT images
950
Abstracts / Physica Medica 32 (2016) 948–959
The Intrabeam is a mobile intraoperative radiotherapy system that can be used to treat selected breast cancer patients with a highly localised dose of radiation (50 kV). The commissioning project involved verifying the key dosimetric parameters of the Intrabeam including (A) absorbed dose, (B) percentage depth dose and (C) dose distribution. The absolute dose determined for all applicators at a clinically relevant depth (5 mm in water) satisfied a distance to agreement criteria of 1 mm (i.e. the dose fall off is approximately 12% per mm at 5 mm depth, and agreement with the calibration files was within 12%). Excellent agreement (<1%) was seen when the depth dose curves were normalised to the point of dose determination at 5mm. The X-ray emission pattern was measured using film and found to be isotropic in both planes for all applicators – the radius of a chosen colour plane at 5 mm depth did not vary by more than 1.4 mm for any of the eight applicators. The effect of dose enhancement due to shielding was approximately 6% at the surface in an extreme case (where only 1 mm of plastic was placed between the source and the film). The key dosimetric parameters of the Intrabeam were independently verified and were within acceptable tolerances. The device will be used for the first time in Ireland and will provide a quicker alternative to external beam radiotherapy treatment for selected breast cancer patients. http://dx.doi.org/10.1016/j.ejmp.2016.05.014
Monte Carlo in assessment of brachytherapy dose distributions Patrick Leydon Galway Clinic, Ireland
low
dose
rate
prostate
The purpose of this study was to investigate differences in dose distributions when Monte Carlo models included interseed attenuation of I125 seeds and tissue heterogeneity effects and when these interactions are ignored. The Monte Carlo calculations were performed using the PENELOPE/penEasy system code. The code is implemented in FORTRAN 77 and its structure is based on a set of subroutines that are invoked from a main program written by the user. The code simulates incoherent scattering, coherent scattering and Bremsstrahlung X-ray production at energies ranging from 1 keV to 1 GeV for photons and from 0.1 keV to 1 GeV for electrons. For simulations, a simplified array of 3 3 3 seeds was placed in a sphere of water (radius of 5 cm). The geometry and energy spectrum of individual seeds was based on the manufacturer’s description. The seeds were positioned in order to mimic a simplified clinical arrangement for various separations and tissue heterogeneities. All simulations were conducted using an off the shelf laptop computer of 1.8 GHz AMD A6 processor with a RAM memory of 6 GB. From the results observed it is clear that there are differences in dose distributions between simulations that account for interseed attenuation and tissue heterogeneity and those that do not. Future work would be to develop more accurate voxel based anatomical phantom models for simulations, with more particle histories and the inclusion of other Monte Carlo tallies would allow for a more robust quantitative analysis of the results and a thorough assessment the differences observed.
The purpose of this work was to compare the efficacy and accuracy of techniques to overcome image quality limitations of CBCT images and enable accurate treatment planning calculations using their anatomical data. Patient CBCTs that closely matched their planning CT anatomy were selected for this investigation. Three techniques were evaluated: using the default HU/qe calibration curve with unmodified CBCT images, performing density overrides to limit the images to 6 discrete density values (corresponding to tissues ranging from air to dense bone) and creating a new CT image set through deformable registration of the planning CT to the CBCT (Figure (A)). Each technique was evaluated for a head and neck, lung and prostate patient treated via VMAT with dose calculation results compared to the planning CT results. Agreement was assessed using DVHs for key structures (B) and by performing 3D gamma analysis of the resultant dose distributions (C). For the lung and prostate cases, results from each of the techniques were found to closely match the planning CT dose distributions with c_3D pass-rates >96% (2%/1 mm) and mean structure doses within 1% of the planning CT calculations. Poorer consistency was observed in the head and neck case with deformable registration identified as the more accurate technique (c_3D = 96.0% compared to c_3D = 70% for the two alternative techniques). The results of this study indicate that simple techniques can be employed to accurately perform dose calculations on CBCT images. However, some limitations were identified where more robust image manipulation can improve calculation accuracy. http://dx.doi.org/10.1016/j.ejmp.2016.05.016
Adaptation of daily dose using CBCT imaging Daniel Foley, Brendan McClean, Peter McBride St Luke’s Radiation Oncology Network (SLRON), Ireland The feasibility of a technique using analysis of on-board CBCT images to adapt the dose to the target on a fraction by fraction basis was investigated. A 3D phase-correlation registration algorithm was used to retrospectively register CBCT images to the planning CT for 11 patients receiving VMAT prostate treatments of 74 Gy. The original plan was recalculated on the registered CT image to provide daily dose statistics. To determine how the dose could be changed, the DVCs were used as limits such that the dose was increased until the tightest constraint was just met, or if a DVC was already broken for a given fraction the dose was reduced by the minimum amount required to ensure that the DVC was within tolerance. Three of the patients investigated could have received higher accumulative doses during their entire treatment without exceeding their OAR DVCs. In the remaining 8 patients, for only 3 fractions could an increase in dose been given while staying below the DVC limits. If all changes were made, the accumulated increase in dose possible for the three patients were 3.98 Gy, 6.89 Gy, and 7.70 Gy. Adapting the dose to be delivered to the patient on a fraction by fraction basis has the potential to allow for significant dose escalation while staying within institutional DVCs. Although it is unlikely that in the clinic the dose level would be reduced below 2 Gy per fraction, such reductions were included in the calculations here to see how it could theoretically impact the treatment. http://dx.doi.org/10.1016/j.ejmp.2016.05.017
http://dx.doi.org/10.1016/j.ejmp.2016.05.015
Techniques for performing treatment planning calculations on varian CBCT images Raymond King a, Suneil Jain b, Kevin Prise a, Alan Hounsell b, Conor McGarry b a Queen’s University Belfast, UK b Belfast Health and Social Care Trust, UK
Characterisation of a MatriXX Evolution ionisation chamber array for stereotactic body radiotherapy (SBRT) plan validation Robert Lally, Denise Irvine, Conor McGarry Belfast Health and Social Care Trust, UK The aim of this work was to assess the long-term stability of the MatriXX Evolution and to evaluate its suitability for the validation
Abstracts / Physica Medica 32 (2016) 948–959
The Intrabeam is a mobile intraoperative radiotherapy system that can be used to treat selected breast cancer patients with a highly localised dose of radiation (50 kV). The commissioning project involved verifying the key dosimetric parameters of the Intrabeam including (A) absorbed dose, (B) percentage depth dose and (C) dose distribution. The absolute dose determined for all applicators at a clinically relevant depth (5 mm in water) satisfied a distance to agreement criteria of 1 mm (i.e. the dose fall off is approximately 12% per mm at 5 mm depth, and agreement with the calibration files was within 12%). Excellent agreement (<1%) was seen when the depth dose curves were normalised to the point of dose determination at 5mm. The X-ray emission pattern was measured using film and found to be isotropic in both planes for all applicators – the radius of a chosen colour plane at 5 mm depth did not vary by more than 1.4 mm for any of the eight applicators. The effect of dose enhancement due to shielding was approximately 6% at the surface in an extreme case (where only 1 mm of plastic was placed between the source and the film). The key dosimetric parameters of the Intrabeam were independently verified and were within acceptable tolerances. The device will be used for the first time in Ireland and will provide a quicker alternative to external beam radiotherapy treatment for selected breast cancer patients. http://dx.doi.org/10.1016/j.ejmp.2016.05.014
Monte Carlo in assessment of brachytherapy dose distributions Patrick Leydon Galway Clinic, Ireland
low
dose
rate
prostate
The purpose of this study was to investigate differences in dose distributions when Monte Carlo models included interseed attenuation of I125 seeds and tissue heterogeneity effects and when these interactions are ignored. The Monte Carlo calculations were performed using the PENELOPE/penEasy system code. The code is implemented in FORTRAN 77 and its structure is based on a set of subroutines that are invoked from a main program written by the user. The code simulates incoherent scattering, coherent scattering and Bremsstrahlung X-ray production at energies ranging from 1 keV to 1 GeV for photons and from 0.1 keV to 1 GeV for electrons. For simulations, a simplified array of 3 3 3 seeds was placed in a sphere of water (radius of 5 cm). The geometry and energy spectrum of individual seeds was based on the manufacturer’s description. The seeds were positioned in order to mimic a simplified clinical arrangement for various separations and tissue heterogeneities. All simulations were conducted using an off the shelf laptop computer of 1.8 GHz AMD A6 processor with a RAM memory of 6 GB. From the results observed it is clear that there are differences in dose distributions between simulations that account for interseed attenuation and tissue heterogeneity and those that do not. Future work would be to develop more accurate voxel based anatomical phantom models for simulations, with more particle histories and the inclusion of other Monte Carlo tallies would allow for a more robust quantitative analysis of the results and a thorough assessment the differences observed.
The purpose of this work was to compare the efficacy and accuracy of techniques to overcome image quality limitations of CBCT images and enable accurate treatment planning calculations using their anatomical data. Patient CBCTs that closely matched their planning CT anatomy were selected for this investigation. Three techniques were evaluated: using the default HU/qe calibration curve with unmodified CBCT images, performing density overrides to limit the images to 6 discrete density values (corresponding to tissues ranging from air to dense bone) and creating a new CT image set through deformable registration of the planning CT to the CBCT (Figure (A)). Each technique was evaluated for a head and neck, lung and prostate patient treated via VMAT with dose calculation results compared to the planning CT results. Agreement was assessed using DVHs for key structures (B) and by performing 3D gamma analysis of the resultant dose distributions (C). For the lung and prostate cases, results from each of the techniques were found to closely match the planning CT dose distributions with c_3D pass-rates >96% (2%/1 mm) and mean structure doses within 1% of the planning CT calculations. Poorer consistency was observed in the head and neck case with deformable registration identified as the more accurate technique (c_3D = 96.0% compared to c_3D = 70% for the two alternative techniques). The results of this study indicate that simple techniques can be employed to accurately perform dose calculations on CBCT images. However, some limitations were identified where more robust image manipulation can improve calculation accuracy. http://dx.doi.org/10.1016/j.ejmp.2016.05.016
Adaptation of daily dose using CBCT imaging Daniel Foley, Brendan McClean, Peter McBride St Luke’s Radiation Oncology Network (SLRON), Ireland The feasibility of a technique using analysis of on-board CBCT images to adapt the dose to the target on a fraction by fraction basis was investigated. A 3D phase-correlation registration algorithm was used to retrospectively register CBCT images to the planning CT for 11 patients receiving VMAT prostate treatments of 74 Gy. The original plan was recalculated on the registered CT image to provide daily dose statistics. To determine how the dose could be changed, the DVCs were used as limits such that the dose was increased until the tightest constraint was just met, or if a DVC was already broken for a given fraction the dose was reduced by the minimum amount required to ensure that the DVC was within tolerance. Three of the patients investigated could have received higher accumulative doses during their entire treatment without exceeding their OAR DVCs. In the remaining 8 patients, for only 3 fractions could an increase in dose been given while staying below the DVC limits. If all changes were made, the accumulated increase in dose possible for the three patients were 3.98 Gy, 6.89 Gy, and 7.70 Gy. Adapting the dose to be delivered to the patient on a fraction by fraction basis has the potential to allow for significant dose escalation while staying within institutional DVCs. Although it is unlikely that in the clinic the dose level would be reduced below 2 Gy per fraction, such reductions were included in the calculations here to see how it could theoretically impact the treatment. http://dx.doi.org/10.1016/j.ejmp.2016.05.017
http://dx.doi.org/10.1016/j.ejmp.2016.05.015
Techniques for performing treatment planning calculations on varian CBCT images Raymond King a, Suneil Jain b, Kevin Prise a, Alan Hounsell b, Conor McGarry b a Queen’s University Belfast, UK b Belfast Health and Social Care Trust, UK
Characterisation of a MatriXX Evolution ionisation chamber array for stereotactic body radiotherapy (SBRT) plan validation Robert Lally, Denise Irvine, Conor McGarry Belfast Health and Social Care Trust, UK The aim of this work was to assess the long-term stability of the MatriXX Evolution and to evaluate its suitability for the validation