- Email: [email protected]
Implementation of the new TG-51 addendum in clinical practice
Abstracts / Physica Medica 30 (2014) e75ee121
determined in a region of interest (ROI) around the tumor, liver, kidneys and spleen. In planar technique, the ROIs were drawn in both anterior and posterior images while in SPECT counts measured per slice. For counts conversion to activities, system calibration factors were measured. Planar and SPECT images of cylindrical water - filled phantom, with five different known amounts of activity, were obtained. Corrections for scatter attenuation, collimator efficiency and detector response were obtained. In bone marrow dosimetry, blood based methods were used as in 177Lu images no significant radiopeptide data of bone or red plasma activity are displayed. Absorbed doses were calculated using MIRD formalism and S values were calculated using the RADAR system. Results: The calculated absorbed doses to organ per unit administered activity, for both planar and SPECT techniques, were comparable. On average, the tumor dose was [4-40] mGy/MBq, the kidney dose [0.25-1.05]mGy/MBq, the bone marrow dose [0.01-0.13]mGy/MBq, the spleen dose [0.3-2.1]mGy/MBq and the liver dose [0.05-0.34]mGy/ MBq. Conclusion: In order to deliver higher dose to tumor and avoid kidneys and red marrow toxicity, accurate individualized dosimetry is obligatory. Furthermore, the results quantitatively confirm the therapeutic efficacy of transhepatic administration and introduce 177Lu labeled peptide as an ideal for peptide receptor radiotherapy. IMPLEMENTATION OF THE NEW TG-51 ADDENDUM IN CLINICAL PRACTICE S. Papageorgiou a, P. Georgolopoulou b, S. Nikoletopoulos a, b, G. Laskaratos a, b, S. Xenofos a, b. a Physics Department, IASO Hospital, Athens, Greece; b Physics Department, “St. SAVVAS” G. Anticancer Hospital, Athens, Greece Introduction: Since the original publication by AAPM of the TG-51 protocol for clinical reference dosimetry of high-energy photon beams in 1999, changes have occurred in the dosimetry chain that required revision of the protocol. In the recently published addendum (2014) more accurate Kq values are presented for currently available chamber models and specifications are provided for reference-class dosimetry chambers. This work evaluates the implementation of the new addendum in the clinical practice of two institutions. Method: The set of MV dosimetry chambers available for clinical work was evaluated in view of the recent recommendations. Chamber characteristics including settling, polarity dependence, recombination correction and stability, were measured so as to evaluate compliance with suggested specifications for a reference dosimeter. Absolute dose was specified using new Kq values, based on Monte Carlo calculations, for a range of high energy clinical beams. Results: Absolute dose determination for the typical range of clinical high energy beams using the new recommended values for beam quality correction shows insignificant changes for corrections determined by kQ ¼ A + B $ 10 e 3 $ % dd (10)x + C$10 5 $ (% dd(10)x) 2 with A, B, C ¼ fit parameters and 63 < % dd (10) X < 86. Application of chamber-specific correction is not required for reference-class dosimeters. Factors contributing to combined uncertainties, as analyzed in the TG-51 addendum, are addressed. Conclusions: More accurate, Monte Carlo based, kq values can now be applied for absolute dosimetry in radiotherapy clinics equipped with modern design chambers. Selection of a reference dosimeter can be based in a given chamber’s compliance with specific performance recommendations that exclude small field dosimetry instruments.
EFFECT OF METALLIC SPINAL IMPLANT ON RADIATION THERAPY DOSE DISTRIBUTION: A CASE STUDY S. Kanellopoulou a, I. Stamatelatos a, A. Miliadou b, P. Georgolopoulou c, J. Kalef-Ezra d. a Institute of Nuclear & Radiological Sciences, Technology, Energy & Safety, National Centre for Scientific Research 'Demokritos' Aghia Paraskevi, Greece; b Radiation Oncology Department, “Saint Savvas”
e115
General Anticancer Hospital of Athens, Greece; c Department of Medical Physics, “Saint Savvas” General Anticancer Hospital of Athens, Greece; d Department of Medical Physics, University Hospital of Ioannina, Ioannina, Greece Introduction: Presence of metallic implants in radiotherapy patients affects calculated dose distributions and hence, clinical decisions on the optimum treatment scheme. Monte Carlo simulations have been shown to improve calculation accuracy in such cases. In this work Monte Carlo tools were used to determine the dose distribution in the case of a spinal implant patient in need of radiotherapy. Method: A patient was planned for radiotherapy of a primitive neuroectodermal tumor in the vicinity of a metallic spinal implant. Both the implant and the spinal cord had to be included in the irradiated volume, raising concern over the accuracy of the treatment dose calculations. The treatment plan was recalculated using the collapsed cone convolution algorithm and a Monte Carlo model of the patient was developed using the MCNP code. Dose perturbation due to the implant was calculated. Results: The presence of the implant affected significantly the dose distribution in close vicinity, causing increased backscatter and attenuation. Nevertheless, the dose to target volume and critical organs was not affected and the results obtained by the collapsed cone convolution algorithm could still be considered valid for calculating daily and total dose to the target volume and the spinal cord. Treatment was completed and the patient was free from disease and side effects at the 2-year follow up. Conclusion: Although this study was focused on a specific case and results therefore cannot be generalized, it showed the important role of Monte Carlo tools in evaluating the accuracy of dose calculations in cases where metallic implants are involved in the treatment field.
3D SPECT THYROID VOLUME ALGORITHM IN MATLAB
QUANTIFICATION
BY
THYR-VOL
S. Synefia a, M. Gavrilelli c, A. Valassi a, M. Argyrou a, M. Rouchota a, J. Floros a, M. Mihalitsi a, I. Baka a, M. Lyra a, b. a Radiation Physics Unit, 1st Radiology Department, University of Athens, Athens, Greece; b Nuclear Medicine Section, 1st Radiology Department, University of Athens, Athens, Greece; c Paediatric Nuclear Medicine Center, Athens, Greece Purpose: The aim of this work consists of a method of determination of the thyroid gland’s volume using the SPECT data in order to calculate the absorbed patient dose from the radioactive substances injected to the patient during thyroid treatment. Further than thyroid function diagnosis, thyroid SPECT scintigraphy is used for thyroid volume estimation. In this study, a MatLab algorithm which integrates 3D visualization is used and thus volume estimation of the thyroid gland is achieved. Materials and methods: 14 patients completed thyroid SPECT examination by a gamma camera GE SPECT Star Cam4000. SPECT image acquisition was performed for angles -90 to +90 degrees, in 32 projections. Images of thyroid gland were reconstructed by the GE Volumetrix software in the GE Xeleris-2 processing system using Ramp and Hanning filters. Dicom data was extracted for each patient and an algorithm that integrates 3D visualization has been used for image processing analysis by MatLabR2012b. We used Thyroid transaxial slices in Dicom format and we created Thyr-Vol algorithm by Matlab. Ellipse ROIs are created around each thyroid lobe while rectangular ROIs include both lobes uptake data. Matrices of the maps of the counted voxels of the slices of the organ were created. Their total is multiplied by the elementary voxel size in mm to obtain the final organ volume. The appropriate threshold value was identified by creating intensity isocontours. Results: The “Thyr-Vol” MatLab algorithm, we have created, detects the segmented regions automatically and the outer contour can be specified. Therefore, the thyroid volume was evaluated and reconstructed as 3D image based on the threshold value. Using this method, numerical errors are eliminated because the images are filtered and reconstructed.
determined in a region of interest (ROI) around the tumor, liver, kidneys and spleen. In planar technique, the ROIs were drawn in both anterior and posterior images while in SPECT counts measured per slice. For counts conversion to activities, system calibration factors were measured. Planar and SPECT images of cylindrical water - filled phantom, with five different known amounts of activity, were obtained. Corrections for scatter attenuation, collimator efficiency and detector response were obtained. In bone marrow dosimetry, blood based methods were used as in 177Lu images no significant radiopeptide data of bone or red plasma activity are displayed. Absorbed doses were calculated using MIRD formalism and S values were calculated using the RADAR system. Results: The calculated absorbed doses to organ per unit administered activity, for both planar and SPECT techniques, were comparable. On average, the tumor dose was [4-40] mGy/MBq, the kidney dose [0.25-1.05]mGy/MBq, the bone marrow dose [0.01-0.13]mGy/MBq, the spleen dose [0.3-2.1]mGy/MBq and the liver dose [0.05-0.34]mGy/ MBq. Conclusion: In order to deliver higher dose to tumor and avoid kidneys and red marrow toxicity, accurate individualized dosimetry is obligatory. Furthermore, the results quantitatively confirm the therapeutic efficacy of transhepatic administration and introduce 177Lu labeled peptide as an ideal for peptide receptor radiotherapy. IMPLEMENTATION OF THE NEW TG-51 ADDENDUM IN CLINICAL PRACTICE S. Papageorgiou a, P. Georgolopoulou b, S. Nikoletopoulos a, b, G. Laskaratos a, b, S. Xenofos a, b. a Physics Department, IASO Hospital, Athens, Greece; b Physics Department, “St. SAVVAS” G. Anticancer Hospital, Athens, Greece Introduction: Since the original publication by AAPM of the TG-51 protocol for clinical reference dosimetry of high-energy photon beams in 1999, changes have occurred in the dosimetry chain that required revision of the protocol. In the recently published addendum (2014) more accurate Kq values are presented for currently available chamber models and specifications are provided for reference-class dosimetry chambers. This work evaluates the implementation of the new addendum in the clinical practice of two institutions. Method: The set of MV dosimetry chambers available for clinical work was evaluated in view of the recent recommendations. Chamber characteristics including settling, polarity dependence, recombination correction and stability, were measured so as to evaluate compliance with suggested specifications for a reference dosimeter. Absolute dose was specified using new Kq values, based on Monte Carlo calculations, for a range of high energy clinical beams. Results: Absolute dose determination for the typical range of clinical high energy beams using the new recommended values for beam quality correction shows insignificant changes for corrections determined by kQ ¼ A + B $ 10 e 3 $ % dd (10)x + C$10 5 $ (% dd(10)x) 2 with A, B, C ¼ fit parameters and 63 < % dd (10) X < 86. Application of chamber-specific correction is not required for reference-class dosimeters. Factors contributing to combined uncertainties, as analyzed in the TG-51 addendum, are addressed. Conclusions: More accurate, Monte Carlo based, kq values can now be applied for absolute dosimetry in radiotherapy clinics equipped with modern design chambers. Selection of a reference dosimeter can be based in a given chamber’s compliance with specific performance recommendations that exclude small field dosimetry instruments.
EFFECT OF METALLIC SPINAL IMPLANT ON RADIATION THERAPY DOSE DISTRIBUTION: A CASE STUDY S. Kanellopoulou a, I. Stamatelatos a, A. Miliadou b, P. Georgolopoulou c, J. Kalef-Ezra d. a Institute of Nuclear & Radiological Sciences, Technology, Energy & Safety, National Centre for Scientific Research 'Demokritos' Aghia Paraskevi, Greece; b Radiation Oncology Department, “Saint Savvas”
e115
General Anticancer Hospital of Athens, Greece; c Department of Medical Physics, “Saint Savvas” General Anticancer Hospital of Athens, Greece; d Department of Medical Physics, University Hospital of Ioannina, Ioannina, Greece Introduction: Presence of metallic implants in radiotherapy patients affects calculated dose distributions and hence, clinical decisions on the optimum treatment scheme. Monte Carlo simulations have been shown to improve calculation accuracy in such cases. In this work Monte Carlo tools were used to determine the dose distribution in the case of a spinal implant patient in need of radiotherapy. Method: A patient was planned for radiotherapy of a primitive neuroectodermal tumor in the vicinity of a metallic spinal implant. Both the implant and the spinal cord had to be included in the irradiated volume, raising concern over the accuracy of the treatment dose calculations. The treatment plan was recalculated using the collapsed cone convolution algorithm and a Monte Carlo model of the patient was developed using the MCNP code. Dose perturbation due to the implant was calculated. Results: The presence of the implant affected significantly the dose distribution in close vicinity, causing increased backscatter and attenuation. Nevertheless, the dose to target volume and critical organs was not affected and the results obtained by the collapsed cone convolution algorithm could still be considered valid for calculating daily and total dose to the target volume and the spinal cord. Treatment was completed and the patient was free from disease and side effects at the 2-year follow up. Conclusion: Although this study was focused on a specific case and results therefore cannot be generalized, it showed the important role of Monte Carlo tools in evaluating the accuracy of dose calculations in cases where metallic implants are involved in the treatment field.
3D SPECT THYROID VOLUME ALGORITHM IN MATLAB
QUANTIFICATION
BY
THYR-VOL
S. Synefia a, M. Gavrilelli c, A. Valassi a, M. Argyrou a, M. Rouchota a, J. Floros a, M. Mihalitsi a, I. Baka a, M. Lyra a, b. a Radiation Physics Unit, 1st Radiology Department, University of Athens, Athens, Greece; b Nuclear Medicine Section, 1st Radiology Department, University of Athens, Athens, Greece; c Paediatric Nuclear Medicine Center, Athens, Greece Purpose: The aim of this work consists of a method of determination of the thyroid gland’s volume using the SPECT data in order to calculate the absorbed patient dose from the radioactive substances injected to the patient during thyroid treatment. Further than thyroid function diagnosis, thyroid SPECT scintigraphy is used for thyroid volume estimation. In this study, a MatLab algorithm which integrates 3D visualization is used and thus volume estimation of the thyroid gland is achieved. Materials and methods: 14 patients completed thyroid SPECT examination by a gamma camera GE SPECT Star Cam4000. SPECT image acquisition was performed for angles -90 to +90 degrees, in 32 projections. Images of thyroid gland were reconstructed by the GE Volumetrix software in the GE Xeleris-2 processing system using Ramp and Hanning filters. Dicom data was extracted for each patient and an algorithm that integrates 3D visualization has been used for image processing analysis by MatLabR2012b. We used Thyroid transaxial slices in Dicom format and we created Thyr-Vol algorithm by Matlab. Ellipse ROIs are created around each thyroid lobe while rectangular ROIs include both lobes uptake data. Matrices of the maps of the counted voxels of the slices of the organ were created. Their total is multiplied by the elementary voxel size in mm to obtain the final organ volume. The appropriate threshold value was identified by creating intensity isocontours. Results: The “Thyr-Vol” MatLab algorithm, we have created, detects the segmented regions automatically and the outer contour can be specified. Therefore, the thyroid volume was evaluated and reconstructed as 3D image based on the threshold value. Using this method, numerical errors are eliminated because the images are filtered and reconstructed.