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[P175] Simultaneous boost in breast radiotherapy requires increased margins or revised match strategy
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Abstracts / Physica Medica 52 (2018) 99–187
obtained evaluating, for each pencil beam (PB) giving dose contribution in the considered position, both the absorbed dose and the measured one and, finally, their ratio. Dedicated software in MATLAB has been developed for attaining the corrected images. Results. Correction algorithms require 3D knowledge of both absorbed and measured doses for each PB. Measurements and calculations have been performed with PBs of various energies and fitting parameters were deduced. Conclusions. The proposed method for amending the experimental images has proved to be promising and, upon completion of the software, will be suitable for the use in clinical practice.
References 1. Gambarini G, Bettega D, Camoni G, Felisi M, Gebbia A, Massari E, et al. Correction method of measured images of absorbed dose for quenching effects due to relatively high LET. Radiat Phys Chem 2017;140:15–9. 2. Gambarini G, Bettega D, Camoni G, Giove D, Mirandola A, Ciocca M. Development of a procedure for quenching-effect correction in images of absorbed dose from protons or carbon ions acquired with Gafchromic EBT3 films. In IRRMA-X conference, Chicago, 9– 13 July; 2017. https://doi.org/10.1016/j.ejmp.2018.06.474
Results. Based on the systematic (R) and random errors (r) between the chest wall-match and the boost match the CTV-toPTV margins of the boost volume were calculated. Margins needed for the boost volume to receive the prescribed dose using a match based on the total target volume are (lateral, longitudinal, vertical) = (7.3, 8.4, 8.5) mm and (5.1, 7.5, 4.3) mm, for the patients with lymph node involvement and without lymph node involvement data, respectively. Conclusions. CTV-to-PTV margin for the boost area are normally set to 5 mm when using a sequential boost strategy. Our study suggests that with simultaneous boost radiotherapy larger margins are required. Further, patients with lymph node involvement compared to patients with only the breast involved requires a larger CTV-toPTV margin. Another solution can be to use an adaptive protocol for daily IGRT which can reduce the required CTV to PTV margin for the boost region by re-scanning and re-matching the boost region for patients where the two regions differ by more than a pre-set threshold.
https://doi.org/10.1016/j.ejmp.2018.06.475
[P176] Evaluating automatic contour propagation for estimating tumour shrinkage in small-cell lung cancer patients treated with chemo-radiotherapy Alan McWilliam a,*, Jona Khalifa b, Nicolette O’Connell c, Marcel van Herk a, Corinne Faivre-Finn a a
[P175] Simultaneous boost in breast radiotherapy requires increased margins or revised match strategy Karina Lindberg Gottlieb a,*, Karen Andersen b, Faisal Mahmood c, Ebbe Laugaard Lorenzen d a
Laboratory of Radiation Physics, Department of Oncology, Odense University Hospital, Odense S, Denmark b Radiotherapy Research Unit, Department of Oncology, Herlev and Gentofte Hospital, University of Copenhagen, Herlev, Denmark c Laboratory of Radiation Physics, Odense University Hospital, Institute of Clinical Research, University of Southern Denmark, Radiotherapy Research Unit, Department of Oncology, Herlev and Gentofte Hospital, University of Copenhagen, Odense S, Denmark d Laboratory of Radiation Physics, Department of Oncology, Odense University Hospital, Institute of Clinical Research, University of Southern Denmark, Odense S, Denmark ⇑ Corresponding author. Purpose. In radiotherapy simultaneous boost compared to sequential boost allows shortening of the overall treatment time. Challenges remain in obtaining good image match concurrently within the boost volume and total target volume. The present study evaluated the difference between match based on boost volume and total target volume, with the overall aim to suggest treatment margins if treating both boost and total target volume using the same registration. Methods. A total of 358 cone-beam CT (CBCT) s from 55 patients were analysed retrospectively. Of these 250 CBCTs were performed before each fraction on 16 patients receiving radiotherapy after breast conserving surgery and with lymph node involvement, and 39 patients receiving radiotherapy after breast conserving surgery without lymph node involvement were scheduled for CBCT once a week, and reached a total of 108 CBCTs. Two matches were performed with each CBCT: A chest wall-match where CBCTs were auto-registered to the planning CT, lymph nodes included if relevant (a match on the total volume). Further a boost specific match using manual registration of surgical clips.
The Division of Clinical Cancer Sciences, University of Manchester, Manchester, United Kingdom b Department of Radiation Oncology, Institut Universitaire du Cancer de Toulouse, Toulouse, France c Elekta Maryland Heights, Admire, MD, United States ⇑ Corresponding author. Purpose. The clinical relevance of tumour shrinkage during thoracic radiotherapy remains unknown with studies showing conflicting results whether shrinkage predicts outcome. Previous work has relied on manual contouring on cone beam CT (CBCT). To enable large scale analysis, automated methods for contour propagation and quantification of tumour shrinkage are essential. Methods. 20 small-cell lung cancer patients treated with concurrent chemo-radiotherapy were selected. All patients had a planning CT and, in total, 81 weekly CBCT scans were available. An experienced lung cancer radiation oncologist manually contoured the GTV on all scans. Additionally, the GTV contour of the planning CT was automatically propagated across the CBCTs, using ADMIRE (Research v1.13, Elekta AB, Stockholm, Sweden). To investigate the accuracy of the automated contour propagation, a comparison against the manual contours was performed using median distance to agreement (mDTA). To quantify tumour shrinkage, volumes were calculated for propagated and manual contours. Differences in volumes were assessed using a Bland–Altman plot. Finally, using the day one CBCT as reference volume, the relative percentage change was calculated at each time-point and fitted using linear regression. The slopes for manual versus propagated contours were compared. Results. ADMIRE successfully propagated GTV contours all CBCTs. Concordance between the manual and propagated contours showed an unsigned mDTA of 3 mm across all CBCT. Results were worse for GTV contours overlapping with the mediastinum. The Bland–Altman analysis for absolute differences in volume at each time-point resulted a mean of 1.6 cm3. Relative differences provided a mean of 4.8%, with manual contours showing smaller volumes.
Abstracts / Physica Medica 52 (2018) 99–187
obtained evaluating, for each pencil beam (PB) giving dose contribution in the considered position, both the absorbed dose and the measured one and, finally, their ratio. Dedicated software in MATLAB has been developed for attaining the corrected images. Results. Correction algorithms require 3D knowledge of both absorbed and measured doses for each PB. Measurements and calculations have been performed with PBs of various energies and fitting parameters were deduced. Conclusions. The proposed method for amending the experimental images has proved to be promising and, upon completion of the software, will be suitable for the use in clinical practice.
References 1. Gambarini G, Bettega D, Camoni G, Felisi M, Gebbia A, Massari E, et al. Correction method of measured images of absorbed dose for quenching effects due to relatively high LET. Radiat Phys Chem 2017;140:15–9. 2. Gambarini G, Bettega D, Camoni G, Giove D, Mirandola A, Ciocca M. Development of a procedure for quenching-effect correction in images of absorbed dose from protons or carbon ions acquired with Gafchromic EBT3 films. In IRRMA-X conference, Chicago, 9– 13 July; 2017. https://doi.org/10.1016/j.ejmp.2018.06.474
Results. Based on the systematic (R) and random errors (r) between the chest wall-match and the boost match the CTV-toPTV margins of the boost volume were calculated. Margins needed for the boost volume to receive the prescribed dose using a match based on the total target volume are (lateral, longitudinal, vertical) = (7.3, 8.4, 8.5) mm and (5.1, 7.5, 4.3) mm, for the patients with lymph node involvement and without lymph node involvement data, respectively. Conclusions. CTV-to-PTV margin for the boost area are normally set to 5 mm when using a sequential boost strategy. Our study suggests that with simultaneous boost radiotherapy larger margins are required. Further, patients with lymph node involvement compared to patients with only the breast involved requires a larger CTV-toPTV margin. Another solution can be to use an adaptive protocol for daily IGRT which can reduce the required CTV to PTV margin for the boost region by re-scanning and re-matching the boost region for patients where the two regions differ by more than a pre-set threshold.
https://doi.org/10.1016/j.ejmp.2018.06.475
[P176] Evaluating automatic contour propagation for estimating tumour shrinkage in small-cell lung cancer patients treated with chemo-radiotherapy Alan McWilliam a,*, Jona Khalifa b, Nicolette O’Connell c, Marcel van Herk a, Corinne Faivre-Finn a a
[P175] Simultaneous boost in breast radiotherapy requires increased margins or revised match strategy Karina Lindberg Gottlieb a,*, Karen Andersen b, Faisal Mahmood c, Ebbe Laugaard Lorenzen d a
Laboratory of Radiation Physics, Department of Oncology, Odense University Hospital, Odense S, Denmark b Radiotherapy Research Unit, Department of Oncology, Herlev and Gentofte Hospital, University of Copenhagen, Herlev, Denmark c Laboratory of Radiation Physics, Odense University Hospital, Institute of Clinical Research, University of Southern Denmark, Radiotherapy Research Unit, Department of Oncology, Herlev and Gentofte Hospital, University of Copenhagen, Odense S, Denmark d Laboratory of Radiation Physics, Department of Oncology, Odense University Hospital, Institute of Clinical Research, University of Southern Denmark, Odense S, Denmark ⇑ Corresponding author. Purpose. In radiotherapy simultaneous boost compared to sequential boost allows shortening of the overall treatment time. Challenges remain in obtaining good image match concurrently within the boost volume and total target volume. The present study evaluated the difference between match based on boost volume and total target volume, with the overall aim to suggest treatment margins if treating both boost and total target volume using the same registration. Methods. A total of 358 cone-beam CT (CBCT) s from 55 patients were analysed retrospectively. Of these 250 CBCTs were performed before each fraction on 16 patients receiving radiotherapy after breast conserving surgery and with lymph node involvement, and 39 patients receiving radiotherapy after breast conserving surgery without lymph node involvement were scheduled for CBCT once a week, and reached a total of 108 CBCTs. Two matches were performed with each CBCT: A chest wall-match where CBCTs were auto-registered to the planning CT, lymph nodes included if relevant (a match on the total volume). Further a boost specific match using manual registration of surgical clips.
The Division of Clinical Cancer Sciences, University of Manchester, Manchester, United Kingdom b Department of Radiation Oncology, Institut Universitaire du Cancer de Toulouse, Toulouse, France c Elekta Maryland Heights, Admire, MD, United States ⇑ Corresponding author. Purpose. The clinical relevance of tumour shrinkage during thoracic radiotherapy remains unknown with studies showing conflicting results whether shrinkage predicts outcome. Previous work has relied on manual contouring on cone beam CT (CBCT). To enable large scale analysis, automated methods for contour propagation and quantification of tumour shrinkage are essential. Methods. 20 small-cell lung cancer patients treated with concurrent chemo-radiotherapy were selected. All patients had a planning CT and, in total, 81 weekly CBCT scans were available. An experienced lung cancer radiation oncologist manually contoured the GTV on all scans. Additionally, the GTV contour of the planning CT was automatically propagated across the CBCTs, using ADMIRE (Research v1.13, Elekta AB, Stockholm, Sweden). To investigate the accuracy of the automated contour propagation, a comparison against the manual contours was performed using median distance to agreement (mDTA). To quantify tumour shrinkage, volumes were calculated for propagated and manual contours. Differences in volumes were assessed using a Bland–Altman plot. Finally, using the day one CBCT as reference volume, the relative percentage change was calculated at each time-point and fitted using linear regression. The slopes for manual versus propagated contours were compared. Results. ADMIRE successfully propagated GTV contours all CBCTs. Concordance between the manual and propagated contours showed an unsigned mDTA of 3 mm across all CBCT. Results were worse for GTV contours overlapping with the mediastinum. The Bland–Altman analysis for absolute differences in volume at each time-point resulted a mean of 1.6 cm3. Relative differences provided a mean of 4.8%, with manual contours showing smaller volumes.