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  • 1
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    SU‐E‐T‐221: An In‐House Developed Resettable MOSFET Dosimeter for Radiotherapy
    Wiley ; 2011
    In:  Medical Physics Vol. 38, No. 6Part13 ( 2011-06), p. 3537-3537
    Details
    In: Medical Physics, Wiley, Vol. 38, No. 6Part13 ( 2011-06), p. 3537-3537
    Kurzfassung: Purpose: To report the feasibility and clinical validation of an in‐house developed MOSFET dosimetry system and describe an integrated nondestructive reset procedure. Methods: Off‐the‐shelf MOSFETs are connected to a PC using an 18 bit/analogue‐input and 16 bit/output data acquisition card. A reading algorithm was developed defining the zero‐temperature‐coefficient point (ZTC) to determine the threshold voltage. The reset procedure consists of an internal circuit generating a local heating induced by an electrical current. Sensitivity has been investigated as a function of bias voltage (0—9 V) to the gate. Dosimetric properties have been evaluated for 6 MV and 15 MV clinical photon beams and in vivo benchmarking was performed against TLD for conventional treatments and total body irradiation (TBI). Results: Sensitivity of 0.08 mV cGy & #8722;1 can be obtained for 200 cGy irradiations at 5 V bias voltage. Ten consecutive measurements at 200 cGy yield a SD of 2.08 cGy (1.05%). Increasing the dose in steps from 5 cGy to 1000 cGy yields a 1.00 Pearson correlation coefficient and agreement within 2.0%. Dose rate dependence (160–800 cGy min & #8722;1) was within 2.5%, temperature dependence within 2.0% (25–37° C). Dose response is stable up to 50 Gy (saturation occurs at approximately 90 Gy), which is used as threshold dose before resetting the MOSFET. An average measured‐over‐calculated dose ratio within 1.05 (SD: 0.04) has been obtained in vivo. TBI midplane‐dose assessed by entrance and exit dose measurements agreed within 1.9% with ionization chamber in phantom, and within 1.0% with TLD in vivo. Conclusions: An in‐house developed resettable MOSFET‐based dosimetry system is proposed. The system has been validated and is currently used for in vivo entrance dose measurement in clinical routine for open field treatment configurations.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Article
    DOI: 10.1118/1.3612171
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2011
    ZDB Id: 1466421-5
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  • 2
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    SU‐E‐J‐136: Clinical Evaluation of a Robotic 6‐Degree of Freedom Treatment Couch for Frameless Radiosurgery
    Wiley ; 2011
    In:  Medical Physics Vol. 38, No. 6Part9 ( 2011-06), p. 3474-3474
    Details
    In: Medical Physics, Wiley, Vol. 38, No. 6Part9 ( 2011-06), p. 3474-3474
    Kurzfassung: Purpose: To evaluate the added value of 6 degree‐of‐freedom (DOF) patient positioning with robotic couch compared to 4DOF positioning for intracranial lesions and to estimate the immobilization characteristics of the Brainlab frameless mask, more specifically the setup errors and the intrafraction motion. Methods: Forty patients with 66 brain metastases treated with frameless stereotactic radiosurgery and 6DOF robotic couch were enrolled. Patient positioning was performed with the Brainlab ExacTrac stereoscopic x‐ray system. Positioning results were collected before and after treatment to assess patient setup error and intrafraction motion. Existing treatment plannings were loaded and simulated for 4DOF positioning and compared to the 6DOF positioning. The clinical relevance was analyzed by means of the Paddick conformity index (CI) and the ratio of prescribed isodose volume covered with 4DOF to that obtained with the 6DOF positioning. Results: Results. The mean 3D setup error before 6DOF correction was 1.91 mm (SD1.25mm). The rotational errors were larger in the longitudinal (0.23° SD0.82°) direction compared to the lateral (−0.09° SD0.72°) and vertical (−0.10° SD1.03°) ones (p 〈 0.05). The mean 3D intrafraction shift was 0.58 (SD0.42mm). The intrafractional rotational errors were comparable,0.01° (SD0.35°), 0.03° (SD0.31°), −0.03° (SD0.33°), for the vertical, longitudinal and lateral, respectively. The mean CI decreased from 0.68 (SD 0.08) (6DOF) to 0.59 (SD 0.12) (4DOF) (p 〈 0.05). A loss of prescribed isodose coverage of 5% (SD0.08) was found with the 4DOF positioning (p 〈 0.05). Half a degree for longitudinal and lateral rotations can be identified as a threshold for coverage loss. Conclusions: With a mask immobilization, patient setup error and intrafraction motions need to be evaluated and corrected for. The 6DOF patient positioning with 6DOF robotic couch to correct translational and rotational setup errors improves target positioning with respect to treatment isocenter, which is in direct relation with the clinical outcome, compared to 4DOF positioning.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Article
    DOI: 10.1118/1.3611903
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2011
    ZDB Id: 1466421-5
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  • 3
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    SU‐E‐T‐454: Feasibilty of Image‐Guided Total Marrow Irradiation Using Helical TomoTherapy
    Wiley ; 2011
    In:  Medical Physics Vol. 38, No. 6Part17 ( 2011-06), p. 3593-3593
    Details
    In: Medical Physics, Wiley, Vol. 38, No. 6Part17 ( 2011-06), p. 3593-3593
    Kurzfassung: Purpose: Investigation of the technical feasibility and dosimetry of image‐ guided total marrow irradiation using helical TomoTherapy in the treatment of relapsed multiple myeloma patients. Irradiation is followed by a hematopietic stemcell transplantation. This study concentrates on planning and dosimetry Methods: Patients are simulated in supine position with H & N mask and pelvic cast. TomoTherapy plans for the upper body (head‐knees) were generated (pitch 0.45, modulation factor 2.0, field width 5cm). Dose prescription was 4x3Gy=12Gy. Dose verification is performed with the IˈmRT MatriXX. Beam‐on‐time is +/−30min. TMI‐stability measurement was done with 2 ICs on different distances in 1.5m solid water equivalent blocks. Lower extremities were planned conventional and with TomoTherapy. Dose in the junction region between upper and lower body plans was verified with EDR2 film for both techniques. Results: It is possible to create clinically acceptable plans for the upper body with TomoTherapy. Verification shows acceptable results in the lung region (gamma 5%, 7mm). Measurement in pelvis region is less good as in lung region. TMI‐stability measurement shows differences in dose till 4% measured/calculated. During TMI a 2.5% dose drift was seen by the detectors. Plans for the extremities were more homogeneous in the junction region with TomoTherapy comparing with the conventional technique. Conclusions: TPS has difficulties to find a good ratio between couch and gantry speed. Differences seen at TMI‐stability measurements can be pointed to drift and stability of one rotation. Differences are depending on system stability (magnetron, target, …). Patient specific QA is necessary before treatment. Differences between the gamma index of the lungs and pelvis can be pointed to the fact that the planning is optimized very well for the lung region. Pitch and modulation factor are optimized for this region. For the junction region tomotherapy plans give a better homogeneity than 1 tomotherapy and 1 conventional plan.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Article
    DOI: 10.1118/1.3612408
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2011
    ZDB Id: 1466421-5
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  • 4
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    SU‐E‐T‐457: Influence of Changing Magnetron and Injector Current on the Beam Characteristics of a Tomotherapy Hi‐Art SYSTEM
    Wiley ; 2011
    In:  Medical Physics Vol. 38, No. 6Part17 ( 2011-06), p. 3594-3594
    Details
    In: Medical Physics, Wiley, Vol. 38, No. 6Part17 ( 2011-06), p. 3594-3594
    Kurzfassung: Purpose: This study investigates the influence of the magnetron and injector current on the beam characteristics of a Tomotherapy system. Methods: Treatment on tomotherapy is time‐based : the gantry rotates while the beam is on and all beam modulation is performed by the MLC. This implies that maintaining output stability is crucial. However, daily changes in output have been observed of up to 2.5% depending on external (pressure, temperature) or internal (component wear or instability). The output is tuned by adjusting the magnetron and injector current. This however, has an influence on both beam energy and profile but to which extent or magnitude has not been clear. Therefor, 144 measurements were performed by altering the magnetron current from 86,75A to 101,7A in 6 equal steps and by altering the injector current from 277,5mA to 612mA in 8 equal steps. Beam profile was measured using Tomodose (Sun Nuclear corp.). The Quality index was calculated using the absorbed dose ratio at depth 20cm and 10cm in rectangular slabs of solid water phantom with an SSD of 85cm. To estimate the influence on the cone profile the ratio between two volumes (on‐axis and off‐axis) was calculated. Results: With a magnetron current change of 14A the average quality index difference was 1.63%. Varying the injector current with 334.5mA causes the average quality index to change with 1.43%. Dose variation at 10cm from the central axis in lateral direction was 3% when changing the injector current by 334.5mA and 1.9% when changing the magnetron current by 14A Conclusions: Modifying magnetron and injector current does not have a major effect on the quality index. The lateral dose profile sagging is the most important finding since this will have an effect on off‐axis located targets. Injector current variation has more influence on the profile than magnetron current variation.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Article
    DOI: 10.1118/1.3612411
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2011
    ZDB Id: 1466421-5
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  • 5
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    SU‐E‐J‐172: The Effect of MVCT Image Quality Parameters on Dose Recalculation for Tomotherapy
    Wiley ; 2011
    In:  Medical Physics Vol. 38, No. 6Part10 ( 2011-06), p. 3483-3483
    Details
    In: Medical Physics, Wiley, Vol. 38, No. 6Part10 ( 2011-06), p. 3483-3483
    Kurzfassung: Purpose: The tomotherapy MVCT images should in theory allow offline adaptive treatment monitoring by recalculation of the dose on each dayˈs image and summation over the entire treatment course. However, Instabilities in the MVCT‐beam can cause shifts in the calculated doses because of shifts in the HU‐calibration (Duchateau et al,2010 Phys. Med. Biol. 55). However, the significance of these shifts can only be established by performing the recalculation again using a newly acquired hu‐calibration curve using a density phantom or patient specific datapoints. This work aims in defining a clear threshold using simple image parameters such as mean HU shift and noise level on the image. This also allows to devise a strict QA program for the MVCT beam based on image quality, which can be accessed in a simple manner, as opposed to beam characteristics, which require service interventions. Methods: Simple spherical phantom‐images were created in dicom‐format with a mean HU‐value representing air, bone, fat, lung and muscle with no superposed noise (baseline set). This set was altered by a)shifting the mean HU and b)superimposing Gaussian noise‐levels of up to 30% (clinical observation). The dose was planned on the baseline set and recalculated on the other sets using the tomotherapy DQA‐ software. Results: Results show a deviation of 2% in dose for a 30HU‐shift in the water‐like region (fat, muscle) and a much lower sensitivity for the high and low densities(air,bone, lung) of about 0.5%. Noise levels had no influence on the center of the sphere when levels were below 20%. Conclusions: It is possible to predict changes in dose from the mean HU and noise level on MVCT images. To derive a clear threshold and a QA protocol, the measurements will be repeated using multiple HU‐images and finally on patients.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Article
    DOI: 10.1118/1.3611940
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2011
    ZDB Id: 1466421-5
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  • 6
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    69 speaker 3D DOSIMETRY SYSTEMS-GELS, EPIDS AND OTHERS
    Elsevier BV ; 2011
    In:  Radiotherapy and Oncology Vol. 99 ( 2011-5), p. S27-
    Details
    In: Radiotherapy and Oncology, Elsevier BV, Vol. 99 ( 2011-5), p. S27-
    Materialart: Online-Ressource
    ISSN: 0167-8140
    URL: Article
    DOI: 10.1016/S0167-8140(11)70192-X
    Sprache: Englisch
    Verlag: Elsevier BV
    Publikationsdatum: 2011
    ZDB Id: 1500707-8
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  • 7
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    TU‐CD‐304‐03: Dosimetric Verification and Preliminary Comparison of Dynamic Wave Arc for SBRT Treatments
    Wiley ; 2015
    In:  Medical Physics Vol. 42, No. 6Part32 ( 2015-06), p. 3599-3599
    Details
    In: Medical Physics, Wiley, Vol. 42, No. 6Part32 ( 2015-06), p. 3599-3599
    Kurzfassung: To evaluate the potential dosimetric benefits and verify the delivery accuracy of Dynamic Wave Arc, a novel treatment delivery approach for the Vero SBRT system. Methods: Dynamic Wave Arc (DWA) combines simultaneous movement of gantry/ring with inverse planning optimization, resulting in an uninterrupted non‐coplanar arc delivery technique. Thirteen SBRT complex cases previously treated with 8–10 conformal static beams (CRT) were evaluated in this study. Eight primary centrally‐located NSCLC (prescription dose 4×12Gy or 8×7.5Gy) and five oligometastatic cases (2×2 lesions, 10×5Gy) were selected. DWA and coplanar VMAT plans, partially with dual arcs, were generated for each patient using identical objective functions for target volumes and OARs on the same TPS (RayStation, RaySearch Laboratories). Dosimetric differences and delivery time among these three planning schemes were evaluated. The DWA delivery accuracy was assessed using the Delta4 diode array phantom (ScandiDos AB). The gamma analysis was performed with the 3%/3mm dose and distance‐to‐agreement criteria. Results: The target conformity for CRT, VMAT and DWA were 0.95±0.07, 0.96±0.04 and 0.97±0.04, while the low dose spillage gradient were 5.52±1.36, 5.44±1.11, and 5.09±0.98 respectively. Overall, the bronchus, esophagus and spinal cord maximum doses were similar between VMAT and DWA, but highly reduced compared with CRT. For the lung cases, the mean dose and V20Gy were lower for the arc techniques compares with CRT, while for the liver cases, the mean dose and the V30Gy presented slightly higher values. The average delivery time of VMAT and DWA were 2.46±1.10 min and 4.25±1.67 min, VMAT presenting shorter treatment time in all cases. The DWA dosimetric verification presented an average gamma index passing rate of 95.73±1.54% (range 94.2%–99.8%). Conclusion: Our preliminary data indicated that the DWA is deliverable with clinically acceptable accuracy and has the potential to further improve the plan quality. This collaborative work was supported by the Flemish government through the Hercules foundation and corporate funding from BrainLab AG. The first and the sixth author are financially supported by Brainlab AG. The other authors have no conflict of interest.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Article
    DOI: 10.1118/1.4925572
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2015
    ZDB Id: 1466421-5
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  • 8
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    SU‐E‐J‐171: The Possibility of Adaptive Breast Treatment on Tomotherapy Using a Patient‐Specific Density Calibration
    Wiley ; 2011
    In:  Medical Physics Vol. 38, No. 6Part10 ( 2011-06), p. 3482-3482
    Details
    In: Medical Physics, Wiley, Vol. 38, No. 6Part10 ( 2011-06), p. 3482-3482
    Kurzfassung: Purpose: The tomotherapy MVCT images should in theory allow offline adaptive treatment monitoring by recalculation of the dose on each dayˈs image and summation over the entire treatment course. However, Instabilities in the MVCT‐beam can cause shifts in the calculated doses because of shifts in the HU‐calibration (Duchateau et al,2010 Phys. Med. Biol. 55). This work presents an approach with a patient specific HU‐calibration for breast patients. Methods: For 20 Breast patients irradiated on tomotherapy (15×2.8Gy) the daily delivered dose was calculated and summed over the entire treatment using a) the standard HU‐calibration of the MVCT (taken biweekly), b) a generic curve per patient generated by measuring the HU of breast, muscle, lung, bone and fat tissue, resulting in 15 different calibration curves/patient and c)an average for each patient of all “daily” curves. The total dose was calculated on the breast, contralateral breast, long and heart tissue and compared. Results: The generated patient‐specific HUcalibration curves show a large inter‐patient variation with shifts of up to 50HU for the breast. Also noise levels varied up to 30%. Using the standard HU‐calibration showed shifts of dose that were on average 1.3–1.5 times higher for the breast region and 1.2x higher for the organs‐at‐risk as opposed to a patient specific curve. No significant difference could be found between methods (b) and (c). Conclusions: Using the MVCT images to calculate the actual delivered dose for breast patients on tomotherapy the HU‐calibration for the MVCT is crucial to interpret the results. Using the standard calibration method can introduce large errors, even on phantoms (Duchateau et al,2010 Phys. Med. Biol. 55) This study shows that using a patient specific curve generated out of the MVCT data can solve this problem without introducing extra calibrations on phantom
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Article
    DOI: 10.1118/1.3611939
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2011
    ZDB Id: 1466421-5
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  • 9
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    Treatment delivery time optimization of respiratory gated radiation therapy by application of audio-visual feedback
    Elsevier BV ; 2011
    In:  Physica Medica Vol. 27 ( 2011-6), p. S13-
    Details
    In: Physica Medica, Elsevier BV, Vol. 27 ( 2011-6), p. S13-
    Materialart: Online-Ressource
    ISSN: 1120-1797
    URL: Article
    DOI: 10.1016/j.ejmp.2011.06.030
    Sprache: Englisch
    Verlag: Elsevier BV
    Publikationsdatum: 2011
    ZDB Id: 1122650-X
    ZDB Id: 2110535-2
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  • 10
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    SU-E-T-506: Low Dose Fluoroscopy Based Detection of Implanted Marker Position on the VERO System for Real-Time Tumor Tracking
    Wiley ; 2011
    In:  Medical Physics Vol. 38, No. 6Part18 ( 2011-06), p. 3605-3605
    Details
    In: Medical Physics, Wiley, Vol. 38, No. 6Part18 ( 2011-06), p. 3605-3605
    Materialart: Online-Ressource
    ISSN: 0094-2405
    URL: Article
    DOI: 10.1118/1.3612459
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2011
    ZDB Id: 1466421-5
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