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P6. Digital breast tomosynthesis: Dose and image quality assessment
C. Legrand et al. / Physica Medica 32 (2016) 367–383
higher trunk exposure is measured. Overall, a higher mean of exposure is found for trunk than for head. Conclusion and discussion. In this study, as expected and shown in 3T, the head is exposed to greater magnetic field during staff motion in the vicinity of the bore. Indeed during needle introduction, the radiologist bends inside the bore leading to higher head exposure peaks. While during wait times when physician stand next to the bore, their trunk is directly inside magnetic field lines explaining its higher exposition compared to the head. These wait times are specific to the interventional MRI staff compared to clinical MRI staff that directly leaves the room after patient setup. Therefore, global exposure (mean and cumulative values) measured for the trunk is higher in interventional MRI when the opposite tendency was found in 3T clinical staff. These tendencies are expected to vary with physician height and posture. This is why monitoring both head and trunk magnetic field exposures seems better than a unique trunk assessment. Indeed ear defenders wore by staff during interventional MRI appears as an optimal support for head MR exposimeter devices.
Methods. Five French hospitals with three different tomosynthesis systems and seven specific phantoms have been included in the study. Average Glandular Dose and Signal Difference to Noise Ratio are assessed for different thicknesses of PMMA. Regarding image quality, reconstructed images are analyzed on global score, spatial resolution, geometrical distortion and homogeneity aspects. Results. Preliminary results on dose and image quality for different models and different acquisition modes will be presented. Phantoms’ sensitivity at different dose levels will be discussed as well. Conclusions. The variety of DBT systems design leads to an expected variability in terms of image quality and dose with breast thickness. Particular attention should be paid to the increased dose in comparison with 2D digital mammography. Works at a national level on the regulatory quality control of tomosynthesis systems should be initiated as soon as possible. The results of this study are expected to contribute to the national discussion on this topic. http://dx.doi.org/10.1016/j.ejmp.2016.11.018
see Table 1 Table 1 Comparison between head and trunk magnetic field assessment for two interventional MR radiologists at 1.5T.
B mean (T) B peak (T) B cumulative (T.min) dB/dt mean (T/s) dB/dt peak (T/s) dB/dt cumulative (T/s.min)
369
Radiologist1 Head
Radiologist1 Trunk
Radiologist2 Head
Radiologist2 Trunk
0.125 1.340 22.647
0.196 1.188 36.469
0.102 1.438 17.233
0.207 1.466 38.176
9.948E-06 2.151 5.213E-14
7.078E-05 0.934 2.356E-14
7.958E-05 1.500 6.546E-14
7.594E-06 1.706 4.607E-15
http://dx.doi.org/10.1016/j.ejmp.2016.11.017
P6. Digital breast tomosynthesis: Dose and image quality assessment K.L. Fezzani a, J. Sage a, I. Fitton b, L. Hadid c, A. Moussier d, N. Pierrat e, A. Martineau f, C. Etard a a
IRSN, Fontenay-Aux-Roses, France Hôpital Européen Georges Pompidou, Paris, France c Hôpital Jean Verdier, Bondy, France d Institut Gustave Roussy, Villejuif, France e Institut Curie, Paris, France f Hôpital Saint-Louis, Paris, France b
Introduction. Digital Breast Tomosynthesis (DBT) offers a gain in sensitivity and in specificity for the detection of breast cancers compared to 2D mammography, due to reduction of the tissues’ overlapping. DBT is already used in many centers in France. The introduction of this technique within the French breast cancer screening program is being considered by the authorities for the coming years. As it has been done for 2D digital mammography, a protocol for quality control must be developed specifically for this technic. It is therefore necessary to increase our knowledge of tomosynthesis systems and of Image quality phantoms proposed by manufacturers. The aim of the study is to compare different DBT systems in term of dose and image quality. The evaluation of different image quality phantoms could lead to recommendations for internal quality control (regulatory or not).
Posters - 3 Radiotherapy P7. Is one couple (T, DLS) per energy in Eclipse relevant for Varian MLC modelisation for Truebeam with IMRT SW/RapidArc techniques? C. Legrand, J.C. Mesgouez, C. Di Bartolo, M. Bremaud, S. Dufreneix, D. Autret Integrated Center For Oncology, Angers, France Introduction. For Varian Medical Systems (VMS) accelerators with ”Eclipse” TPS, whatever the intensity modulated technique (IMRT or RapidArc) or type of MLC (M120 or M120HD), the latter is modeled for a given energy by two parameters: the transmission (T) and the Dosimetric Leaf Gap (DLG). This study presents the results obtained for a Novalis Truebeam STx (NTB) and Truebeam (TB) installed in 2015 at the Integrated Center for Oncology. Material and methods. Two NTB and TB accelerators (6 MV) equipped with MLC M120HD and M120 respectively. (T, DLG) couples were determined in three steps: (i) Varian methodology [1]; (ii) 1D ionometric measurements (CC13, IBA Dosimetry) in IMRT SW technique: sliding window, dynamic ”chair” and ”squares” with different level of doses, 10 IMRT SW and RapidArc plans; (iii) 10 IMRT SW and RapidArc plans analysis via radiochromic films (EBT3, Ashland) and Portal Dosimetry (PDIPv11.031, VMS). Results. For NTB, T and DLG were set to 1.3% and 0.38 mm respectively. This result was determined from VMS methodology as good results were obtained in steps (ii) and (iii) (respectively < 2% and gamma index > 95% (3%/3 mm GA)). For TB, transmission was also determined from VMS methodology. DLG determination was not that simple because for a fixed DLG while acceptable results were obtained with IMRT SW technic, unacceptable results were obtained with RapidArc plans and vice versa. A compromise was found to match the tolerances regardless the type of plan: T and DLG were set to 1.5% and 1.45 mm respectively. These values are close to those found in publications [2–5]. Conclusion. Transmission and DLG were determined per energy for each accelerator. T and DLG choice is a compromise between VMS methodology and measurements when both IMRT SW and rapidArc technics are implemented on the same accelerator. An extreme solution would be to set T and DLG in Eclipse per energy and technique.
higher trunk exposure is measured. Overall, a higher mean of exposure is found for trunk than for head. Conclusion and discussion. In this study, as expected and shown in 3T, the head is exposed to greater magnetic field during staff motion in the vicinity of the bore. Indeed during needle introduction, the radiologist bends inside the bore leading to higher head exposure peaks. While during wait times when physician stand next to the bore, their trunk is directly inside magnetic field lines explaining its higher exposition compared to the head. These wait times are specific to the interventional MRI staff compared to clinical MRI staff that directly leaves the room after patient setup. Therefore, global exposure (mean and cumulative values) measured for the trunk is higher in interventional MRI when the opposite tendency was found in 3T clinical staff. These tendencies are expected to vary with physician height and posture. This is why monitoring both head and trunk magnetic field exposures seems better than a unique trunk assessment. Indeed ear defenders wore by staff during interventional MRI appears as an optimal support for head MR exposimeter devices.
Methods. Five French hospitals with three different tomosynthesis systems and seven specific phantoms have been included in the study. Average Glandular Dose and Signal Difference to Noise Ratio are assessed for different thicknesses of PMMA. Regarding image quality, reconstructed images are analyzed on global score, spatial resolution, geometrical distortion and homogeneity aspects. Results. Preliminary results on dose and image quality for different models and different acquisition modes will be presented. Phantoms’ sensitivity at different dose levels will be discussed as well. Conclusions. The variety of DBT systems design leads to an expected variability in terms of image quality and dose with breast thickness. Particular attention should be paid to the increased dose in comparison with 2D digital mammography. Works at a national level on the regulatory quality control of tomosynthesis systems should be initiated as soon as possible. The results of this study are expected to contribute to the national discussion on this topic. http://dx.doi.org/10.1016/j.ejmp.2016.11.018
see Table 1 Table 1 Comparison between head and trunk magnetic field assessment for two interventional MR radiologists at 1.5T.
B mean (T) B peak (T) B cumulative (T.min) dB/dt mean (T/s) dB/dt peak (T/s) dB/dt cumulative (T/s.min)
369
Radiologist1 Head
Radiologist1 Trunk
Radiologist2 Head
Radiologist2 Trunk
0.125 1.340 22.647
0.196 1.188 36.469
0.102 1.438 17.233
0.207 1.466 38.176
9.948E-06 2.151 5.213E-14
7.078E-05 0.934 2.356E-14
7.958E-05 1.500 6.546E-14
7.594E-06 1.706 4.607E-15
http://dx.doi.org/10.1016/j.ejmp.2016.11.017
P6. Digital breast tomosynthesis: Dose and image quality assessment K.L. Fezzani a, J. Sage a, I. Fitton b, L. Hadid c, A. Moussier d, N. Pierrat e, A. Martineau f, C. Etard a a
IRSN, Fontenay-Aux-Roses, France Hôpital Européen Georges Pompidou, Paris, France c Hôpital Jean Verdier, Bondy, France d Institut Gustave Roussy, Villejuif, France e Institut Curie, Paris, France f Hôpital Saint-Louis, Paris, France b
Introduction. Digital Breast Tomosynthesis (DBT) offers a gain in sensitivity and in specificity for the detection of breast cancers compared to 2D mammography, due to reduction of the tissues’ overlapping. DBT is already used in many centers in France. The introduction of this technique within the French breast cancer screening program is being considered by the authorities for the coming years. As it has been done for 2D digital mammography, a protocol for quality control must be developed specifically for this technic. It is therefore necessary to increase our knowledge of tomosynthesis systems and of Image quality phantoms proposed by manufacturers. The aim of the study is to compare different DBT systems in term of dose and image quality. The evaluation of different image quality phantoms could lead to recommendations for internal quality control (regulatory or not).
Posters - 3 Radiotherapy P7. Is one couple (T, DLS) per energy in Eclipse relevant for Varian MLC modelisation for Truebeam with IMRT SW/RapidArc techniques? C. Legrand, J.C. Mesgouez, C. Di Bartolo, M. Bremaud, S. Dufreneix, D. Autret Integrated Center For Oncology, Angers, France Introduction. For Varian Medical Systems (VMS) accelerators with ”Eclipse” TPS, whatever the intensity modulated technique (IMRT or RapidArc) or type of MLC (M120 or M120HD), the latter is modeled for a given energy by two parameters: the transmission (T) and the Dosimetric Leaf Gap (DLG). This study presents the results obtained for a Novalis Truebeam STx (NTB) and Truebeam (TB) installed in 2015 at the Integrated Center for Oncology. Material and methods. Two NTB and TB accelerators (6 MV) equipped with MLC M120HD and M120 respectively. (T, DLG) couples were determined in three steps: (i) Varian methodology [1]; (ii) 1D ionometric measurements (CC13, IBA Dosimetry) in IMRT SW technique: sliding window, dynamic ”chair” and ”squares” with different level of doses, 10 IMRT SW and RapidArc plans; (iii) 10 IMRT SW and RapidArc plans analysis via radiochromic films (EBT3, Ashland) and Portal Dosimetry (PDIPv11.031, VMS). Results. For NTB, T and DLG were set to 1.3% and 0.38 mm respectively. This result was determined from VMS methodology as good results were obtained in steps (ii) and (iii) (respectively < 2% and gamma index > 95% (3%/3 mm GA)). For TB, transmission was also determined from VMS methodology. DLG determination was not that simple because for a fixed DLG while acceptable results were obtained with IMRT SW technic, unacceptable results were obtained with RapidArc plans and vice versa. A compromise was found to match the tolerances regardless the type of plan: T and DLG were set to 1.5% and 1.45 mm respectively. These values are close to those found in publications [2–5]. Conclusion. Transmission and DLG were determined per energy for each accelerator. T and DLG choice is a compromise between VMS methodology and measurements when both IMRT SW and rapidArc technics are implemented on the same accelerator. An extreme solution would be to set T and DLG in Eclipse per energy and technique.