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The effect of magnetic resonance imaging on the position of brachytherapy seeds
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Abstracts/Physica Medica 31 (2015) S15–S21
calculated by taking the axilla TLD dose and multiplying it with the appropriate isodose percentage from the plot. All other doses were recorded as the sum of the entry + exit doses. Results: Only TBI patients who had the single slice CT scan done were included in the study. 27 patients (19 males, 8 females) were included for the time period of 1993–1996. Two dose estimates each were obtained for the lungs, sternum, ribs, cranium, eyes and testes. The two estimates were averaged for each site. All average doses are within 1 standard deviation of the prescribed dose of 12 Gy, except the eyes, which consistently show a higher dose. Conclusion: There is a significant intra- and inter-patient variability between the prescribed midline dose and measured doses. TLD dose assessments are extremely time-consuming and the practice was eventually abandoned. Doses are now confirmed with a single diode measurement per field. Keywords: Total body irradiation, TLD, Dose P.20 INTRODUCTION OF PEPTIDE RECEPTOR RADIONUCLIDE THERAPY AND ITS INTERNAL DOSIMETRY IN THE WESTERN CAPE C.J. Trauernicht *,a, N. Joubert a, L. Nonjola b, R. Steyn c. a Department of Medical Physics, Groote Schuur Hospital and University of Cape Town, LC-32, Anzio Road, Observatory, 7925, Cape Town, South Africa; b Department of Medical Physics, Steve Biko Academic Hospital, Pretoria, South Africa; c Department of Nuclear Medicine, Groote Schuur Hospital, Cape Town, South Africa Introduction: 177Lu-DOTATATE has been used successfully as a Peptide receptor radionuclide therapy (PRRNT) for a number of years to target inoperable or metastatic neuro-endocrine tumours, and it is the treatment of choice for adult patients with this diagnosis. PRRNT is a systemic radiation therapy that targets receptors specifically expressed by these tumours. Patients typically receive a standard dose of 177Lu every 2 months, repeated 4–6 times. The kidneys are usually the dose-limiting organ; therefore internal dosimetry is very important. The aim of this study was to introduce PRRNT and its dosimetry in the Western Cape. Materials and Methods: Patients are imaged at 1, 4, 24 and 48 hours after injection of the radionuclide. A whole-body scan is performed at each imaging session, together with a vial of known activity to obtain the sensitivity of the gamma camera. Regions of interest are drawn over the kidneys, liver, spleen and other organs of interest, e.g. metastases. The counts in these images (geometric mean of ant and post images) are converted to activity using the obtained sensitivity. A time activity plot is drawn with the four data points per organ, and a curve is fitted through these points. The residence time, which serves as the input for the Olinda (Organ Level INternal Dose Assessment) software, is calculated as the ratio of cumulated activity and injected activity. Olinda is a tool for calculating doses using standard models once the kinetic data are established. Results: The first patient was treated in the Western Cape. The kidney dose was calculated to be 3.2 Gy, the liver dose was 0.2 Gy and the spleen dose 2.3 Gy. Conclusion: PRRNT requires individualized internal dosimetry. Currently this is done using planar whole-body images with no attenuation correction. Further investigations will follow to improve accuracy. Keywords: PRRNT, Lu-177, Olinda, Internal dosimetry P.21 CDMAM IMAGE EVALUATION USING SOFTWARE AND HUMAN PHANTOMS A.J. van Staden *, A. Conradie. Department of Medical Physics, University of the Free State, Bloemfontein, South Africa Introduction: In mammography screening studies it is important for radiologists to be able to distinguish between small, low contrast objects in order to make an accurate diagnosis. The European guidelines for the quality control procedures in mammography provide the minimum standards for image quality in digital mammography. These standards are based on human scoring of the CDMAM type 3.4 phantom. Human scoring of the CDMAM phantom is very time consuming and suffers from a considerable interobserver error. An alternative method for scoring the CDMAM phantom by computer software was developed. The CDCOM software uses a template
of the phantom to detect and predict the threshold contrast for human observers. The aim of this study is to evaluate the software for use as part of a standard QA program. Materials and Methods: In this study phantom images that were acquired on a digital mammography unit were scored by three independent radiology registrars with at least three years’ experience each. The CDCOM software was used with CDMAM Analyser to predict the threshold contrasts for the same images scored by human observers. The results from the human observers were compared graphically with that from the software. Both sets of results were compared with the accepted and achievable contrastdetail values from the European Guidelines. Results: The graphs show a clear distinction between the software values and those for the human observers. The software scored higher detail at lower contrast disks with a relatively small error. There is a considerable error visible in the readings of the human observers that makes it unreliable. Conclusion: The software is a viable alternative to human scoring that would allow the scoring of the CDMAM phantom to become part of any general QC program. It is more accurate than human readings and takes a considerably less time. Keywords: CDMAM, Contrast detail, CDCOM, Mammography, Quality control P.22 LUTETIUM-177 ( 177 LU) DOSIMETRY IN PATIENTS TREATED FOR NEUROENDOCRINE TUMOURS (NETS) IN JOHANNESBURG, SOUTH AFRICA B.P. Van Wyk *,a,b, M.D.T.H. Vangu a,b, K. Purbhoo a,b, L. Africa b, R. Mosley b. a Nuclear Medicine, Charlotte Maxeke Johannesburg Academic Hospital, South Africa; b Donald Gordon Medical Centre, University of the Witwatersrand, Johannesburg, South Africa Introduction: Peptide receptor radionuclide therapy (PRRT) with 177LuDOTATATE is an important option in the treatment of neuroendocrine tumours (NETs). Complete, partial and minor responses have been reached in a large group of patients treated with 177Lu-DOTATATE. However the absorbed dose to the tumour is limited by the irradiation of the kidney and red marrow. The gamma decay branch of 177Lu allows for immediate imaging. This is very important as one may take patient images after injection and perform the kidney dosimetry. The MIRD formulism, taking into account the rate at which the kidney clears activity (specific activity) and the S-factor taken from OLINDA/EXM software, can be used to quantify the kidney dose. Materials and Methods: This is a retrospective study in nine patients, five females and four males (age: 36–68, mean age 54.2). The dose usually administered was 7400 MBq, each patient was planned to receive four to six cycles at three months interval. All nine patients have already received at least one therapeutic dose. Patients had undergone whole body 177LuDOTATATE scanning. Patient images were taken at numerous hours following administration of the therapeutic dose. Results: The time–activity curve (obtained from using data from Image J) of all patients was drawn using the trapezoidal method, and the kidney dose determined using the S-factor from the OLINDA program. Results of the first nine patients have shown an average dose of 1.1 Gy to the kidney for the first fraction. These average doses are well below the tolerance of the kidney. These doses can be used as a guide for future patient treatments, whereby the clinician can either increase future doses (when the kidney dose is low) or decrease future dose (when the kidney dose is high). Conclusion: The nine patients presented showed that dosimetry on these cases can be achieved and be used as a guide for clinicians when prescribing future doses. Keywords: Peptide receptor radionuclide therapy (PRRT), 177Lu-DOTATATE, Kidney, Dose P.23 THE EFFECT OF MAGNETIC RESONANCE IMAGING ON THE POSITION OF BRACHYTHERAPY SEEDS A.M. Walters-Burger *. Department of Medical Physics, Equra Health Introduction: The effect of MRI on the positioning of brachytherapy seeds was evaluated by means of making a prostate seed impregnated phantom
Abstracts/Physica Medica 31 (2015) S15–S21
and taking a CT scan prior to MRI scanning and repeating a CT scan thereafter. Materials and Methods: Prostate brachytherapy implant patients are often imaged by magnetic resonance, well within the active treatment time. Imaging artefacts, caused by MRI of the prostate seeds, is a well-known fact. After collecting I-125 seeds with a magnet, the effect of MRI on the position of seeds interstitially was questioned. A phantom was constructed of gelatine and psyllium husks. Seeds were implanted with graph paper in a grid of 4 × 4 seeds at 2 cm intervals. This was done on 3 overlapping levels within the phantom. The phantom was CT scanned to determine the exact dimensions of the seed placement. The phantom was MRI scanned on a 1.5 Tesla, Siemens MRI scanner with a T1-gated sequence and a Gradient-Echo pulse sequence.
S21
The phantom was CT scanned again in order to determine the positional change of the seeds caused by the MRI. Elekta’s Focal Software was used to assess the movement of the seeds. The distance between seeds was measured on both the CT scan images and MRI scan images. Results: No significant movement of seeds in any direction was noted. Changes in distance between seeds for the different images were smaller than 2 mm which can be contributed to user error and artefacts interfering with the true centre and perceived centre of seeds. Conclusion: The results obtained confirm statements made by both seed supplier and literature that MRI has no effect on the position of I-125 seeds with the prostate. Keywords: MRI, Brachytherapy seeds, Position
Abstracts/Physica Medica 31 (2015) S15–S21
calculated by taking the axilla TLD dose and multiplying it with the appropriate isodose percentage from the plot. All other doses were recorded as the sum of the entry + exit doses. Results: Only TBI patients who had the single slice CT scan done were included in the study. 27 patients (19 males, 8 females) were included for the time period of 1993–1996. Two dose estimates each were obtained for the lungs, sternum, ribs, cranium, eyes and testes. The two estimates were averaged for each site. All average doses are within 1 standard deviation of the prescribed dose of 12 Gy, except the eyes, which consistently show a higher dose. Conclusion: There is a significant intra- and inter-patient variability between the prescribed midline dose and measured doses. TLD dose assessments are extremely time-consuming and the practice was eventually abandoned. Doses are now confirmed with a single diode measurement per field. Keywords: Total body irradiation, TLD, Dose P.20 INTRODUCTION OF PEPTIDE RECEPTOR RADIONUCLIDE THERAPY AND ITS INTERNAL DOSIMETRY IN THE WESTERN CAPE C.J. Trauernicht *,a, N. Joubert a, L. Nonjola b, R. Steyn c. a Department of Medical Physics, Groote Schuur Hospital and University of Cape Town, LC-32, Anzio Road, Observatory, 7925, Cape Town, South Africa; b Department of Medical Physics, Steve Biko Academic Hospital, Pretoria, South Africa; c Department of Nuclear Medicine, Groote Schuur Hospital, Cape Town, South Africa Introduction: 177Lu-DOTATATE has been used successfully as a Peptide receptor radionuclide therapy (PRRNT) for a number of years to target inoperable or metastatic neuro-endocrine tumours, and it is the treatment of choice for adult patients with this diagnosis. PRRNT is a systemic radiation therapy that targets receptors specifically expressed by these tumours. Patients typically receive a standard dose of 177Lu every 2 months, repeated 4–6 times. The kidneys are usually the dose-limiting organ; therefore internal dosimetry is very important. The aim of this study was to introduce PRRNT and its dosimetry in the Western Cape. Materials and Methods: Patients are imaged at 1, 4, 24 and 48 hours after injection of the radionuclide. A whole-body scan is performed at each imaging session, together with a vial of known activity to obtain the sensitivity of the gamma camera. Regions of interest are drawn over the kidneys, liver, spleen and other organs of interest, e.g. metastases. The counts in these images (geometric mean of ant and post images) are converted to activity using the obtained sensitivity. A time activity plot is drawn with the four data points per organ, and a curve is fitted through these points. The residence time, which serves as the input for the Olinda (Organ Level INternal Dose Assessment) software, is calculated as the ratio of cumulated activity and injected activity. Olinda is a tool for calculating doses using standard models once the kinetic data are established. Results: The first patient was treated in the Western Cape. The kidney dose was calculated to be 3.2 Gy, the liver dose was 0.2 Gy and the spleen dose 2.3 Gy. Conclusion: PRRNT requires individualized internal dosimetry. Currently this is done using planar whole-body images with no attenuation correction. Further investigations will follow to improve accuracy. Keywords: PRRNT, Lu-177, Olinda, Internal dosimetry P.21 CDMAM IMAGE EVALUATION USING SOFTWARE AND HUMAN PHANTOMS A.J. van Staden *, A. Conradie. Department of Medical Physics, University of the Free State, Bloemfontein, South Africa Introduction: In mammography screening studies it is important for radiologists to be able to distinguish between small, low contrast objects in order to make an accurate diagnosis. The European guidelines for the quality control procedures in mammography provide the minimum standards for image quality in digital mammography. These standards are based on human scoring of the CDMAM type 3.4 phantom. Human scoring of the CDMAM phantom is very time consuming and suffers from a considerable interobserver error. An alternative method for scoring the CDMAM phantom by computer software was developed. The CDCOM software uses a template
of the phantom to detect and predict the threshold contrast for human observers. The aim of this study is to evaluate the software for use as part of a standard QA program. Materials and Methods: In this study phantom images that were acquired on a digital mammography unit were scored by three independent radiology registrars with at least three years’ experience each. The CDCOM software was used with CDMAM Analyser to predict the threshold contrasts for the same images scored by human observers. The results from the human observers were compared graphically with that from the software. Both sets of results were compared with the accepted and achievable contrastdetail values from the European Guidelines. Results: The graphs show a clear distinction between the software values and those for the human observers. The software scored higher detail at lower contrast disks with a relatively small error. There is a considerable error visible in the readings of the human observers that makes it unreliable. Conclusion: The software is a viable alternative to human scoring that would allow the scoring of the CDMAM phantom to become part of any general QC program. It is more accurate than human readings and takes a considerably less time. Keywords: CDMAM, Contrast detail, CDCOM, Mammography, Quality control P.22 LUTETIUM-177 ( 177 LU) DOSIMETRY IN PATIENTS TREATED FOR NEUROENDOCRINE TUMOURS (NETS) IN JOHANNESBURG, SOUTH AFRICA B.P. Van Wyk *,a,b, M.D.T.H. Vangu a,b, K. Purbhoo a,b, L. Africa b, R. Mosley b. a Nuclear Medicine, Charlotte Maxeke Johannesburg Academic Hospital, South Africa; b Donald Gordon Medical Centre, University of the Witwatersrand, Johannesburg, South Africa Introduction: Peptide receptor radionuclide therapy (PRRT) with 177LuDOTATATE is an important option in the treatment of neuroendocrine tumours (NETs). Complete, partial and minor responses have been reached in a large group of patients treated with 177Lu-DOTATATE. However the absorbed dose to the tumour is limited by the irradiation of the kidney and red marrow. The gamma decay branch of 177Lu allows for immediate imaging. This is very important as one may take patient images after injection and perform the kidney dosimetry. The MIRD formulism, taking into account the rate at which the kidney clears activity (specific activity) and the S-factor taken from OLINDA/EXM software, can be used to quantify the kidney dose. Materials and Methods: This is a retrospective study in nine patients, five females and four males (age: 36–68, mean age 54.2). The dose usually administered was 7400 MBq, each patient was planned to receive four to six cycles at three months interval. All nine patients have already received at least one therapeutic dose. Patients had undergone whole body 177LuDOTATATE scanning. Patient images were taken at numerous hours following administration of the therapeutic dose. Results: The time–activity curve (obtained from using data from Image J) of all patients was drawn using the trapezoidal method, and the kidney dose determined using the S-factor from the OLINDA program. Results of the first nine patients have shown an average dose of 1.1 Gy to the kidney for the first fraction. These average doses are well below the tolerance of the kidney. These doses can be used as a guide for future patient treatments, whereby the clinician can either increase future doses (when the kidney dose is low) or decrease future dose (when the kidney dose is high). Conclusion: The nine patients presented showed that dosimetry on these cases can be achieved and be used as a guide for clinicians when prescribing future doses. Keywords: Peptide receptor radionuclide therapy (PRRT), 177Lu-DOTATATE, Kidney, Dose P.23 THE EFFECT OF MAGNETIC RESONANCE IMAGING ON THE POSITION OF BRACHYTHERAPY SEEDS A.M. Walters-Burger *. Department of Medical Physics, Equra Health Introduction: The effect of MRI on the positioning of brachytherapy seeds was evaluated by means of making a prostate seed impregnated phantom
Abstracts/Physica Medica 31 (2015) S15–S21
and taking a CT scan prior to MRI scanning and repeating a CT scan thereafter. Materials and Methods: Prostate brachytherapy implant patients are often imaged by magnetic resonance, well within the active treatment time. Imaging artefacts, caused by MRI of the prostate seeds, is a well-known fact. After collecting I-125 seeds with a magnet, the effect of MRI on the position of seeds interstitially was questioned. A phantom was constructed of gelatine and psyllium husks. Seeds were implanted with graph paper in a grid of 4 × 4 seeds at 2 cm intervals. This was done on 3 overlapping levels within the phantom. The phantom was CT scanned to determine the exact dimensions of the seed placement. The phantom was MRI scanned on a 1.5 Tesla, Siemens MRI scanner with a T1-gated sequence and a Gradient-Echo pulse sequence.
S21
The phantom was CT scanned again in order to determine the positional change of the seeds caused by the MRI. Elekta’s Focal Software was used to assess the movement of the seeds. The distance between seeds was measured on both the CT scan images and MRI scan images. Results: No significant movement of seeds in any direction was noted. Changes in distance between seeds for the different images were smaller than 2 mm which can be contributed to user error and artefacts interfering with the true centre and perceived centre of seeds. Conclusion: The results obtained confirm statements made by both seed supplier and literature that MRI has no effect on the position of I-125 seeds with the prostate. Keywords: MRI, Brachytherapy seeds, Position