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OC-0279: Removing the blindfold - a new take on real-time brachytherapy dosimetry
S144 ESTRO 36 _______________________________________________________________________________________________ was also used to assess the registration error of CTTOTS. To prove the overall accuracy of this approach, another inhouse developed phantom was used, equipped with eleven catheters and eight IR-markers. The feasibility of a daily patient data acquisition was examined in an institutional review board-approved study by using the afterloader prototype and the OTS in addition to regular iBT treatments. Results Based on different poses of the calibration tool, the root mean square errors for OTSTEMT and CTTOTS were 0.56 mm and 0.49 mm, respectively. The overall accuracy of CTTEMT resulted in 0.74 mm. The determined transformations were applied to the phantom measurements and showed a mean deviation to the CT data of 0.92 mm. Currently, 65 catheters from four patients were tracked by the EMT system in combination with the OTS. The deviations of the implant geometry, determined by this hybrid tracking approach, are comparable to the previous results, obtained using only the EMT procedure. Conclusion The novel hybrid tracking system allows direct mapping of EMT and CT data. So far, the system was successfully used to measure the implant of four patients. The clinical study is ongoing.
HDR prostate plan. The fluctuation could be reduced to <0.5% by mixing the Y2O3:Eu and YVO4:Eu phosphors in a ratio 1-to-10. The stem signal of the ruby, Y2O3:Eu and YVO4:Eu ISDs was up to 3%, 1% and 2%, respectively, of the total signal, and the photoluminescence was <1%, when the BT source moved 8 cm away from the detector and 1 cm from the fiber-optic cable. In contrast, the stem signal of the PSD was up to 70%.
OC-0278 Red-emitting inorganic scintillation detectors to verify HDR brachytherapy treatments in real time G. Kertzscher1, S. Beddar1 1 The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, Houston, USA Purpose or Objective Treatment verification during brachytherapy (BT) is presently limited because only few detectors can measure accurate and precise dose rates in the steep gradients that are characteristic for HDR BT. Red-emitting inorganic scintillation detectors (ISDs) are promising for BT because they can generate large signal intensities. Furthermore, they facilitate efficient background suppression because of the small overlap with the Cerenkov and fluorescence light contamination induced in the fiber-optic cable (the stem signal) primarily emitted in blue/green regions. The purpose of this study was to assess the suitability of redemitting ISDs for real-time verification during BT. Material and Methods We investigated ISDs based on the 5 inorganic scintillators ruby, Y2O3:Eu, YVO4:Eu, Y2O2S:Eu and Gd2O2S:Eu, of which the first was rigid and the others in powder form. The ISDs were compared with plastic scintillation detectors (PSDs) based on the organic scintillator BCF-12. Each detector consisted of a 1 mm-diameter scintillator that was coupled to a 1 mm-diameter and 15 m-long fiber-optic cable. Optical filters were placed between the ISD volume and the fiber-optic cable to prevent the stem signal from striking the scintillator and inducing photoluminescence. The fiber-optic cable was coupled to a charge-coupled device camera or a spectrometer to measure signal intensities and emission spectra, respectively. The detectors were exposed to an 192Ir HDR BT source in experiments dedicated to determine their scintillation intensities, the influence of the stem signal and photoluminescence, and time-dependent luminescence properties. Results Figure 1 shows the emission spectra of all detectors (left) and that the scintillation intensities were up to 19, 44, 16, 54 and 130 times larger than that of the PSD (right). Figure 2 shows time dependent luminescence properties of the ISDs. The Y2O2S:Eu and Gd2O2S:Eu ISDs are not recommended because their accuracy was compromised by their time dependence. The scintillation of the ruby, Y2O3:Eu and YVO4:Eu ISDs changed by +1.6%, -2.8% and +1.1%, respectively, during 20 Gy, which is the dose that the ISD inserted in urethra could absorb during a typical
Conclusion Red-emitting ISDs based on ruby, Y2O3:Eu and YVO4:Eu are suitable for HDR BT treatment verification in real time. Their large signal intensities and emission properties facilitate accurate detector systems that are straightforward to manufacture and use which can result in widespread dissemination and improved patient safety during BT. OC-0279 Removing the blindfold - a new take on realtime brachytherapy dosimetry J. Johansen1, S. Rylander1, S. Buus1, L. Bentzen1, S.B. Hokland1, C.S. Søndergaard1, A.K.M. With2, G. Kertzscher3, C.E. Andersen4, K. Tanderup1 1 Aarhus University Hospital, Department of oncology, Aarhus C, Denmark 2 Örebro University Hospital, Department of Medical Physics, Örebro, Sweden 3 The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, Houston- TX, USA 4 Technical University of Denmark, Center for Nuclear Technologies, Roskilde, Denmark Purpose or Objective Although in-vivo dosimetry has been available for decades it is still not a standardized verification tool in brachytherapy (BT). Major limitations are that in-vivo dosimeters only provide point dose information and that the steep dose gradient leads to strong positional dependency. The aim of this study is to examine whether it is possible to utilise in-vivo dosimetry for evaluation of the implant geometry during irradiation in addition to post hoc dose verification. Material and Methods This study includes in-vivo dosimetry measurements from 22 HDR BT procedures for prostate cancer. Needles were placed in the prostate guided by TRUS with a subsequent
S145 ESTRO 36 _______________________________________________________________________________________________ T2W MRI with 2mm slice thickness for treatment planning. Dose rates were measured using a fiber-coupled Al2O3:C luminescent crystal placed in a dedicated needle in the prostate. The dose measurements were analysed retrospectively. The total accumulated dose was compared to the predicted dose. Secondly, the measured dose rate originating from each dwell position in a needle was compared to the predicted dose rate obtained from the dose planning system. The discrepancies between measured and predicted dose rates were assumed to be caused by geometrical offsets of the needles relative to the dosimeter from the treatment plan. An algorithm shifted each treatment needle virtually in radial and longitudinal directions relative to the dosimeter until optimal agreement between the predicted and measured dose rates was achieved. Results Table 1 shows the relative difference between the measured and predicted accumulated dose and the average radial and longitudinal shifts of 337 needles in 22 treatments. The average shifts are expected to correspond to systematic uncertainties in dosimeter positions, and the standard deviations reflect the shift of needles relative to the dosimeter. Two treatments were not further analysed because of dosimeter drift by >15mm.
needle movements between MR-scan and treatment.
There was no relation between deviations in measured dose and shifts of needles. E.g. patient 6 and patient 7 have similar shifts but very different accumulated dose deviations. This illustrates how a small shift in a nearby needle can lead to significant changes in the measured dose, making it hard to use the accumulated dose for treatment verification. Conclusion Accumulated dose and dose rate have been measured in real-time for 22 treatments. We have used real-time invivo dosimetry to determine the rela tive geometry between needles and dosimeter with high precision. This could potentially lead to real-time treatment verification in BT. OC-0280 Benefit of repeat CT in high-dose rate brachytherapy as radical treatment for rectal cancer R.P.J. Van den Ende1, E.C . Rijkmans1, E.M. Kerkhof1, R.A. Nout1, M. Ketelaars1, M.S. Laman1, C.A.M . Marijnen1, U.A. Van der Heide1 1 Leiden Univers ity Medical Center, Department of Radiation Oncology, Leiden, The Netherlands
The longitudinal and radial shifts of each needle are plotted in Fig. 1. The relative needle-dosimeter geometry was determined with sub-millimetre precision for 98% of the treatment needles (error bars in Fig. 1). More than 90% of the needles were shifted less than 4mm longitudinally and 2mm radially, which is consistent with typical uncertainties in needle and dosimeter reconstructions and
Purpose or Objective High-dose rate endorectal brachytherapy (HDR-BT) for rectal cancer can be used to increase the dose to the tumor while sparing surrounding organs due to a smaller treated volume and the steep dose gradient. Conventionally, one treatment plan is derived from a planning CT with applicator in situ prior to the start of treatment, which is then used for all further applications (non-adaptive approach). An adaptive approach would be to acquire a repeat CT scan at each application for treatment planning. The purpose of this study was to evaluate the difference in dose conformity and clinical target volume (CTV) coverage between the non-adaptive and the adaptive approach. Material and Methods Eleven patients included in a dose-escalation study were included in this study. Patients received a radical treatment consisting of 13x3 Gy external beam radiotherapy (EBRT) followed by three weekly applications HDR-BT of 5-8 Gy. A planning CT with applicator in situ was acquired at application one and repeat CT scans with applicator in situ were acquired at application two and three. The CTV was defined as residual macroscopic tumor or scarring after EBRT. The CTV, rectal wall without CTV, mesorectum and anus were delineated by an expert
HDR prostate plan. The fluctuation could be reduced to <0.5% by mixing the Y2O3:Eu and YVO4:Eu phosphors in a ratio 1-to-10. The stem signal of the ruby, Y2O3:Eu and YVO4:Eu ISDs was up to 3%, 1% and 2%, respectively, of the total signal, and the photoluminescence was <1%, when the BT source moved 8 cm away from the detector and 1 cm from the fiber-optic cable. In contrast, the stem signal of the PSD was up to 70%.
OC-0278 Red-emitting inorganic scintillation detectors to verify HDR brachytherapy treatments in real time G. Kertzscher1, S. Beddar1 1 The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, Houston, USA Purpose or Objective Treatment verification during brachytherapy (BT) is presently limited because only few detectors can measure accurate and precise dose rates in the steep gradients that are characteristic for HDR BT. Red-emitting inorganic scintillation detectors (ISDs) are promising for BT because they can generate large signal intensities. Furthermore, they facilitate efficient background suppression because of the small overlap with the Cerenkov and fluorescence light contamination induced in the fiber-optic cable (the stem signal) primarily emitted in blue/green regions. The purpose of this study was to assess the suitability of redemitting ISDs for real-time verification during BT. Material and Methods We investigated ISDs based on the 5 inorganic scintillators ruby, Y2O3:Eu, YVO4:Eu, Y2O2S:Eu and Gd2O2S:Eu, of which the first was rigid and the others in powder form. The ISDs were compared with plastic scintillation detectors (PSDs) based on the organic scintillator BCF-12. Each detector consisted of a 1 mm-diameter scintillator that was coupled to a 1 mm-diameter and 15 m-long fiber-optic cable. Optical filters were placed between the ISD volume and the fiber-optic cable to prevent the stem signal from striking the scintillator and inducing photoluminescence. The fiber-optic cable was coupled to a charge-coupled device camera or a spectrometer to measure signal intensities and emission spectra, respectively. The detectors were exposed to an 192Ir HDR BT source in experiments dedicated to determine their scintillation intensities, the influence of the stem signal and photoluminescence, and time-dependent luminescence properties. Results Figure 1 shows the emission spectra of all detectors (left) and that the scintillation intensities were up to 19, 44, 16, 54 and 130 times larger than that of the PSD (right). Figure 2 shows time dependent luminescence properties of the ISDs. The Y2O2S:Eu and Gd2O2S:Eu ISDs are not recommended because their accuracy was compromised by their time dependence. The scintillation of the ruby, Y2O3:Eu and YVO4:Eu ISDs changed by +1.6%, -2.8% and +1.1%, respectively, during 20 Gy, which is the dose that the ISD inserted in urethra could absorb during a typical
Conclusion Red-emitting ISDs based on ruby, Y2O3:Eu and YVO4:Eu are suitable for HDR BT treatment verification in real time. Their large signal intensities and emission properties facilitate accurate detector systems that are straightforward to manufacture and use which can result in widespread dissemination and improved patient safety during BT. OC-0279 Removing the blindfold - a new take on realtime brachytherapy dosimetry J. Johansen1, S. Rylander1, S. Buus1, L. Bentzen1, S.B. Hokland1, C.S. Søndergaard1, A.K.M. With2, G. Kertzscher3, C.E. Andersen4, K. Tanderup1 1 Aarhus University Hospital, Department of oncology, Aarhus C, Denmark 2 Örebro University Hospital, Department of Medical Physics, Örebro, Sweden 3 The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, Houston- TX, USA 4 Technical University of Denmark, Center for Nuclear Technologies, Roskilde, Denmark Purpose or Objective Although in-vivo dosimetry has been available for decades it is still not a standardized verification tool in brachytherapy (BT). Major limitations are that in-vivo dosimeters only provide point dose information and that the steep dose gradient leads to strong positional dependency. The aim of this study is to examine whether it is possible to utilise in-vivo dosimetry for evaluation of the implant geometry during irradiation in addition to post hoc dose verification. Material and Methods This study includes in-vivo dosimetry measurements from 22 HDR BT procedures for prostate cancer. Needles were placed in the prostate guided by TRUS with a subsequent
S145 ESTRO 36 _______________________________________________________________________________________________ T2W MRI with 2mm slice thickness for treatment planning. Dose rates were measured using a fiber-coupled Al2O3:C luminescent crystal placed in a dedicated needle in the prostate. The dose measurements were analysed retrospectively. The total accumulated dose was compared to the predicted dose. Secondly, the measured dose rate originating from each dwell position in a needle was compared to the predicted dose rate obtained from the dose planning system. The discrepancies between measured and predicted dose rates were assumed to be caused by geometrical offsets of the needles relative to the dosimeter from the treatment plan. An algorithm shifted each treatment needle virtually in radial and longitudinal directions relative to the dosimeter until optimal agreement between the predicted and measured dose rates was achieved. Results Table 1 shows the relative difference between the measured and predicted accumulated dose and the average radial and longitudinal shifts of 337 needles in 22 treatments. The average shifts are expected to correspond to systematic uncertainties in dosimeter positions, and the standard deviations reflect the shift of needles relative to the dosimeter. Two treatments were not further analysed because of dosimeter drift by >15mm.
needle movements between MR-scan and treatment.
There was no relation between deviations in measured dose and shifts of needles. E.g. patient 6 and patient 7 have similar shifts but very different accumulated dose deviations. This illustrates how a small shift in a nearby needle can lead to significant changes in the measured dose, making it hard to use the accumulated dose for treatment verification. Conclusion Accumulated dose and dose rate have been measured in real-time for 22 treatments. We have used real-time invivo dosimetry to determine the rela tive geometry between needles and dosimeter with high precision. This could potentially lead to real-time treatment verification in BT. OC-0280 Benefit of repeat CT in high-dose rate brachytherapy as radical treatment for rectal cancer R.P.J. Van den Ende1, E.C . Rijkmans1, E.M. Kerkhof1, R.A. Nout1, M. Ketelaars1, M.S. Laman1, C.A.M . Marijnen1, U.A. Van der Heide1 1 Leiden Univers ity Medical Center, Department of Radiation Oncology, Leiden, The Netherlands
The longitudinal and radial shifts of each needle are plotted in Fig. 1. The relative needle-dosimeter geometry was determined with sub-millimetre precision for 98% of the treatment needles (error bars in Fig. 1). More than 90% of the needles were shifted less than 4mm longitudinally and 2mm radially, which is consistent with typical uncertainties in needle and dosimeter reconstructions and
Purpose or Objective High-dose rate endorectal brachytherapy (HDR-BT) for rectal cancer can be used to increase the dose to the tumor while sparing surrounding organs due to a smaller treated volume and the steep dose gradient. Conventionally, one treatment plan is derived from a planning CT with applicator in situ prior to the start of treatment, which is then used for all further applications (non-adaptive approach). An adaptive approach would be to acquire a repeat CT scan at each application for treatment planning. The purpose of this study was to evaluate the difference in dose conformity and clinical target volume (CTV) coverage between the non-adaptive and the adaptive approach. Material and Methods Eleven patients included in a dose-escalation study were included in this study. Patients received a radical treatment consisting of 13x3 Gy external beam radiotherapy (EBRT) followed by three weekly applications HDR-BT of 5-8 Gy. A planning CT with applicator in situ was acquired at application one and repeat CT scans with applicator in situ were acquired at application two and three. The CTV was defined as residual macroscopic tumor or scarring after EBRT. The CTV, rectal wall without CTV, mesorectum and anus were delineated by an expert