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529 oral CLINICAL EVALUATION OF A SPEED OF SOUND ABERRATION CORRECTION ALGORITHM IN QUANTITATIVE ULTRASOUND-AIDED IMAGE GUIDED RADIOTHERAPY.
W EDNESDAY, M AY 11, 2011
of deformable registration and GPU-based computation, accurate dose accumulation may be achievable in the next years.
P ROFFERED PAPER
S 215
practice and we expect that the use of this method will improve the agreement between calculations and IN-VIVO measurements.
528 oral ANGULAR CORRECTION OF THE IN-VIVO RECTUM PROBE READINGS IN ROUTINE GYNECOLOGICAL BRACHYTHERAPY TREATMENT. V. Stserbakov1 1 N ORTH E STONIA R EGIONAL H OSPITAL, Department of Radiotherapy, Tallinn, Estonia
Purpose: The aim of this study was to find out the cause of disagreement between point doses values, which were measured (IN-VIVO) and calculated for some patients. For this purpose additional studies of the detector response as a function of the angle of the diode to the direction of radiation coming from the source were performed. Materials: All measurements were done with rectal Fivefold Detector Probe PTW Type 9112. For angular calibration set-up the adapter for probe and the Afterloading Calibration phantom for IN-VIVO calibration PTW T 9193 were used. An angular calibration scale was applied on the phantom body for determining the rotation angle of the detector to a radiation source (angle step = 15). Accumulated charges (nC) of the diodes (collecting time = 1 min) were measured with electrometer PTW VIVODOS in Multichannel Mode. GammaMed Plus remote afterloader with source Ir-192 (decay factor ~2) was used. The 0.6 cc Farmer chamber type 30001, placed inside the adapter 30001 on the opposite side of the phantom, was taken as a reference chamber. Results: The directional dependence (up to 12%) of IN-VIVO detector response was found. In the figure 1a normalized readings of the rectal probes (R1 R5) as function of the diode angle to the radiation source φ are shown. Additionally, it can be noticed that the manufacturer has built detectors inside the catheter directionally on about the same angle (figure 1c) and therefore behavior of the detectors‘ readings is quite consistent. Surprisingly, the signals of the diodes were higher (few %) when the radiation was parallel to the plates of the detectors (angles 0◦ and 180◦ ).
Figure 1. Results of the measurements. Definitions of the angular scale.a) The charges of the diodes are accumulated during 1 min and then normalized to some arbitrary value.b) Schematic cross-section of the IN-VIVO catheter; definition of the angular scale: for the null angle (φ=0) is chosen direction, which is parallel to the plates of the detectors. c) Fluoroscopic images of "source-eye view" of the IN-VIVO probe for two orientations: φ=0 and φ=90. Conclusions: Performed measurements provide useful ideas for calibration technique and clinical use of rectal IN-VIVO probe.Firstly, the angular response of the detectors is sharp for the angles close to 0 and 180. Therefore it is reasonable to perform the long-term reproducibility calibration of the detectors for angular ranges 50 110 or 240 300.Secondly, after the brachytherapy treatment of gynecological patient is finished and the IN-VIVO measurements for this treatment are done, the final angular correction for diodes readings should be applied. The angle φ detector to radiation source can be estimated from the fluoroscopic images (AP, anteriorposterior, or LAT, lateral) quite precisely, ± 10.At present we are introducing this technique into clinical
Physics Proffered Papers 12: Image registration and segmentation 529 oral CLINICAL EVALUATION OF A SPEED OF SOUND ABERRATION CORRECTION ALGORITHM IN QUANTITATIVE ULTRASOUNDAIDED IMAGE GUIDED RADIOTHERAPY. D. Fontanarosa1 2 , S. van der Meer1 , F. Verhaegen1 3 1 MAASTRO C LINIC, Physics Research, Maastricht, Netherlands 2 T ECNOLOGIE AVANZATE TA, RD, Torino, Italy 3 M C G ILL U NIVERSITY, Montreal, Canada
Purpose: To investigate the clinical impact of a recently introduced speed of sound (SOS) aberration correction algorithm in ultrasound (US) imaging systems for image guided radiotherapy (IGRT). The SOS algorithm was applied to four prostate cancer patients and two liver cancer patients to assess in a real clinical application the extent and spatial distribution of the corrections. Materials: The developed algorithm transforms the simulation computerized tomography (CT) scan, available in IGRT applications co-registered to the US scan, into a SOS map, using an empirical relationship between the physical density, provided by the CT scan, and the SOS. These SOS values are then used to correct the distances in US images. Four prostate cancer and two liver cancer patients, for whom both simulation co-registered CT/US scans and treatment US scans were available, were considered. All patients had an US scan at the simulation stage (USref) and daily scans at the treatment stage (UStrt). The same simulation CT scan was used to correct all USref and UStrt images. For this work, the latter was always chosen as the last US scan performed in order to have the maximum time period between the two, and therefore possibly also the maximum difference in patients’ shape. The SOS algorithm was applied and a cumulative shift image was plotted (Fig. 1), which shows the total spatial shift undergone by each voxel due to SOS aberration correction.
Fig. 1: In the top row, SOS map, and non-corrected simulation and treatment US images. In the bottom row, shift map, and comparison between corrected and non-corrected USref and UStrt images for one of the prostate cancer patients. Results: Significant shifts (up to 4 mm) are present in the corrected US images. The shifts map derived from the simulation CT scan affects the USref and UStrt images differently (Fig. 1) the same way as SOS aberrations affect along different paths due to the different tissue distributions non corrected US images. Conclusions: Significant SOS corrections were found, especially for patients where large changes occurred between simulation and treatment stages. This error has probably affected several previous US-CT studies reported in the literature: the corrections improve accuracy in direct USCT comparisons but also yield an improved image quality (reducing defocusing and geometric distortion) and more accurate outline of regions of interest. Other sites (gynaecological, head and neck) are likely to benefit from the SOS correction.
of deformable registration and GPU-based computation, accurate dose accumulation may be achievable in the next years.
P ROFFERED PAPER
S 215
practice and we expect that the use of this method will improve the agreement between calculations and IN-VIVO measurements.
528 oral ANGULAR CORRECTION OF THE IN-VIVO RECTUM PROBE READINGS IN ROUTINE GYNECOLOGICAL BRACHYTHERAPY TREATMENT. V. Stserbakov1 1 N ORTH E STONIA R EGIONAL H OSPITAL, Department of Radiotherapy, Tallinn, Estonia
Purpose: The aim of this study was to find out the cause of disagreement between point doses values, which were measured (IN-VIVO) and calculated for some patients. For this purpose additional studies of the detector response as a function of the angle of the diode to the direction of radiation coming from the source were performed. Materials: All measurements were done with rectal Fivefold Detector Probe PTW Type 9112. For angular calibration set-up the adapter for probe and the Afterloading Calibration phantom for IN-VIVO calibration PTW T 9193 were used. An angular calibration scale was applied on the phantom body for determining the rotation angle of the detector to a radiation source (angle step = 15). Accumulated charges (nC) of the diodes (collecting time = 1 min) were measured with electrometer PTW VIVODOS in Multichannel Mode. GammaMed Plus remote afterloader with source Ir-192 (decay factor ~2) was used. The 0.6 cc Farmer chamber type 30001, placed inside the adapter 30001 on the opposite side of the phantom, was taken as a reference chamber. Results: The directional dependence (up to 12%) of IN-VIVO detector response was found. In the figure 1a normalized readings of the rectal probes (R1 R5) as function of the diode angle to the radiation source φ are shown. Additionally, it can be noticed that the manufacturer has built detectors inside the catheter directionally on about the same angle (figure 1c) and therefore behavior of the detectors‘ readings is quite consistent. Surprisingly, the signals of the diodes were higher (few %) when the radiation was parallel to the plates of the detectors (angles 0◦ and 180◦ ).
Figure 1. Results of the measurements. Definitions of the angular scale.a) The charges of the diodes are accumulated during 1 min and then normalized to some arbitrary value.b) Schematic cross-section of the IN-VIVO catheter; definition of the angular scale: for the null angle (φ=0) is chosen direction, which is parallel to the plates of the detectors. c) Fluoroscopic images of "source-eye view" of the IN-VIVO probe for two orientations: φ=0 and φ=90. Conclusions: Performed measurements provide useful ideas for calibration technique and clinical use of rectal IN-VIVO probe.Firstly, the angular response of the detectors is sharp for the angles close to 0 and 180. Therefore it is reasonable to perform the long-term reproducibility calibration of the detectors for angular ranges 50 110 or 240 300.Secondly, after the brachytherapy treatment of gynecological patient is finished and the IN-VIVO measurements for this treatment are done, the final angular correction for diodes readings should be applied. The angle φ detector to radiation source can be estimated from the fluoroscopic images (AP, anteriorposterior, or LAT, lateral) quite precisely, ± 10.At present we are introducing this technique into clinical
Physics Proffered Papers 12: Image registration and segmentation 529 oral CLINICAL EVALUATION OF A SPEED OF SOUND ABERRATION CORRECTION ALGORITHM IN QUANTITATIVE ULTRASOUNDAIDED IMAGE GUIDED RADIOTHERAPY. D. Fontanarosa1 2 , S. van der Meer1 , F. Verhaegen1 3 1 MAASTRO C LINIC, Physics Research, Maastricht, Netherlands 2 T ECNOLOGIE AVANZATE TA, RD, Torino, Italy 3 M C G ILL U NIVERSITY, Montreal, Canada
Purpose: To investigate the clinical impact of a recently introduced speed of sound (SOS) aberration correction algorithm in ultrasound (US) imaging systems for image guided radiotherapy (IGRT). The SOS algorithm was applied to four prostate cancer patients and two liver cancer patients to assess in a real clinical application the extent and spatial distribution of the corrections. Materials: The developed algorithm transforms the simulation computerized tomography (CT) scan, available in IGRT applications co-registered to the US scan, into a SOS map, using an empirical relationship between the physical density, provided by the CT scan, and the SOS. These SOS values are then used to correct the distances in US images. Four prostate cancer and two liver cancer patients, for whom both simulation co-registered CT/US scans and treatment US scans were available, were considered. All patients had an US scan at the simulation stage (USref) and daily scans at the treatment stage (UStrt). The same simulation CT scan was used to correct all USref and UStrt images. For this work, the latter was always chosen as the last US scan performed in order to have the maximum time period between the two, and therefore possibly also the maximum difference in patients’ shape. The SOS algorithm was applied and a cumulative shift image was plotted (Fig. 1), which shows the total spatial shift undergone by each voxel due to SOS aberration correction.
Fig. 1: In the top row, SOS map, and non-corrected simulation and treatment US images. In the bottom row, shift map, and comparison between corrected and non-corrected USref and UStrt images for one of the prostate cancer patients. Results: Significant shifts (up to 4 mm) are present in the corrected US images. The shifts map derived from the simulation CT scan affects the USref and UStrt images differently (Fig. 1) the same way as SOS aberrations affect along different paths due to the different tissue distributions non corrected US images. Conclusions: Significant SOS corrections were found, especially for patients where large changes occurred between simulation and treatment stages. This error has probably affected several previous US-CT studies reported in the literature: the corrections improve accuracy in direct USCT comparisons but also yield an improved image quality (reducing defocusing and geometric distortion) and more accurate outline of regions of interest. Other sites (gynaecological, head and neck) are likely to benefit from the SOS correction.