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EP-1713: Feasibility of low dose 4D CBCT in patients with lung cancer
S939 ESTRO 36 _______________________________________________________________________________________________
Purpose or Objective Radiation-induced lung fibrosis is an unwanted side effect of curative radiotherapy. Radiological findings include changes in the mediastinum such as shift toward the ipsilateral lung due to treatment related volume loss. In this work we investigate building a standardized and semiautomatic method to quantify mediastinum changes as indicator of lung fibrosis. Material and Methods 31 patients treated with conventional chemoradiotherapy were included. This was a sub-group of a non-randomized phase I/II isotoxic trial which enrolled stage II and III NSCLC (IDEAL-CRT). Each patient underwent a baseline PET-CT or diagnostic CT before treatment, and a diagnostic CT for follow-up after 12 months (average: 433 days, range: 358-496 days). Rotation and thickening of the anterior junction line were taken as measures of mediastinal change. β was defined as the angle between the posterior-anterior direction and the line that connects the centroid of the spinal canal to the centroid of the anterior junction line at carina level in the follow-up scan; similarly, the thickness of the junction (t) was defined as the minimum distance between the two lungs at the same level (Fig. 1). Mediastinum shift was then quantified in terms of the absolute difference between the β measured on the co-registered baseline and follow-up scans (i.e., Δβ= βF- βB), and in terms of the ratio of the thicknesses (i.e., Δt = tF/tB). This was implemented as a semiautomatic workflow in Matlab using the open-source Pulmonary Toolkit (github.com/tomdoel/pulmonarytoolkit).
Fig.1 – Measures of rotation (β) and thickening (t) of the anterior junction line. Results The changes were characterized using the following grading systems: for Δβ, 0- no/small rotation (<4°), 1moderate (4-8°), 2- large (>8°); and for Δt, 0- no/small change including moderate shrinkage (<1.2), 1- mild enlargement (1.2-3), 2- moderate enlargement (>3) (Fig. 2). In the presence of disease or toxicities at the junction, the definition of its centroid is unclear; hence six patients were excluded. Significant rotation of the junction line toward the ipsilateral lung occurred in 64% of the patients (36% and 28% for grades 1 and 2, respectively). Significant enlargement of the junction was measured in 56% of the patients (equal occurrence of grades 1 and 2); shrinkage was measured in 16% of the cases. There was no correlation between rotation and thickening of the junction (ρ=0.17, Pearson’s correlation coefficient).
Fig. 2 – Colour overlay of baseline (red) and follow-up (blue) scans. Cases of grades (a) 0 and 0, (b) 0 and 2, (c) 2 and 0 for rotation and thickening, respectively. Conclusion Chronic lung fibrosis manifests radiologically as mediastinal shift. We propose a standardized method to characterize these changes based on the positioning and thickness of the anterior junction line. Further measures are needed to fully describe mediastinum change. We aim to correlate these changes with measures of lung fibrosis. EP-1713 Feasibility of low dose 4D CBCT in patients with lung cancer. A. Bryce-Atkinson1, A. McWilliam1, T. Marchant2, C. Faivre-Finn1, G. Whitfield3, M. Van Herk1 1 University of Manchester, Division of Molecular and Clinical Cancer Science- Faculty of Biology- Medicine and Health, Manchester, United Kingdom 2 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom 3 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom Purpose or Objective Respiration correlated cone-beam CT (4D CBCT) provides information on the respiratory motion, providing accurate tumour localisation in the lung taking into account breathing motion. This project aims to investigate the potential for 4D CBCT dose reduction, evaluating its effect on image quality, amplitude estimation and registration accuracy. Material and Methods 4D CBCT images were reconstructed from 9 lung cancer patients with a minimum of 800 projections (120kV, 16mA, 10-40ms), phase sorted to the nearest projection over 10 phases. The amplitudes of tumour motion ranged from 3.9-20mm. Dose reduction was simulated by reconstructing using 50%, 25%, 16.67%, 12.5% and 10% of projections and varying the number of phase bins, sorting all remaining projections. The image quality of each reconstruction was assessed visually and by testing registration accuracy for bone (3D) and tumour (4D). Registration accuracy was evaluated by comparing results to the standard reconstruction, for both amplitude of motion in the superior-inferior direction and correctable (mean) position. Results Reducing the number of projections had little effect on registration accuracy overall for both bone and soft tissue, despite very poor visual image quality at low number of projections. Reducing the number of reconstructed phases recovered visual image quality (Figure 1) at the cost of underestimating amplitude and 10 phases yielded best registration accuracy (Table 1). When using 10% of projections, motion was reported at less than 5mm for 89% of patients at 3 and 5 phases. Increasing to 10 phases recovered the tumour motion to approximately that of the standard reconstructions. Automatic soft tissue registration required manual preregistration for two patients: one consistently across all reconstructions, and the other only for the 10 phase reconstruction with 10% of projections.
S940 ESTRO 36 _______________________________________________________________________________________________
Three-dimensional (3D) isotropic volumes were created for each data set and the correspondence between points on the GTV surface of each case was established. To fit the model to an unknown data set texture analysis features were calculated in 5x5 volumes perpendicular to the boundary between the interior and exterior of the GTV surface. This estimates the location of the GTV boundary. At each point a search for the GTV shape was conducted by calculating the texture features and moving within the established shape limits until reaching convergence. Training was performed on 32 randomly selected cases and testing on the remaining 10 cases. The Dice similarity coefficient was used to compare the model results with the clinically defined volumes. Results Figure 1 shows an example of a typical GTV produced by the algorithm in which the seminal vesicles have been included in the apical slice (left). Table 1 shows a summary of the results obtained on the 10 test cases. The mean clinical volume of the test cases was 64.5 cm3 and calculated by the model was 60.3 cm3. The largest difference was observed in the cases with the largest GTV.
Conclusion Registration remains accurate even for as little as 10% of projection data, but with significant limitations in visual image quality at 10 phase reconstructions and motion detection at 3 phases. Simulating 25% dose over 10 phases allows for accurate registration without significant loss of image quality or motion detection and is therefore acceptable for 4D CBCT. This result is particularly relevant for patients with a good prognosis as it limits the radiation exposure. EP-1714 Automatic delineation of the gross-tumour volume in prostate cancer using shape models K. Cheng1, Y. Feng1, D. Montgomery1, D.B. McLaren2, S. McLaughlin3, W. Nailon1 1 Edinburgh Cancer Centre Western General Hospital, Department of Oncology Physics, Edinburgh, United Kingdom 2 Edinburgh Cancer Centre Western General Hospital, Department of Clinical Oncology, Edinburgh, United Kingdom 3 Heriot Watt University, School of Engineering and Physical Sciences, Edinburgh, United Kingdom Purpose or Objective Digital models of anatomy have potential for assisting in the segmentation of the prostate and organs at risk (OAR) in radiotherapy planning of prostate cancer. However, manual alteration of automatically generated contours is often necessary to produce an accurate gross-tumour volume (GTV). This is generally the case when the tumour extends beyond the prostatic capsule into the bladder or invades the seminal vesicles (>T3a tumours). The aim of this study was to develop a digital model of the GTV in prostate cancer that incorporates the range of shape variability associated with different T-stages. Material and Methods Computerised tomography (CT) images from 42 prostate cancer patients, which contained a range of T-stages and had the prostate GTV and OARs outlined, were selected.
Figure 1: Clinical contour in green, model result in red. Left: apical slice taken form the inferior of the GTV including the seminal vesicles. Middle: central slice of the GTV shape. Right: basal slice from the superior of the GTV.
Table 1: Dice coefficients and volumes obtained on the 10 test cases. Conclusion The proposed model has potential for automatically contouring the GTV when the tumour extends beyond the prostatic capsule into the bladder or invades the seminal vesicles. However, more cases must be included in the model to ensure that the full range of shape variability is represented. EP-1715 Differences in delineation uncertainty using MR images only vs CT-MR in recurrent gynaecological GTV D. Bernstein1, A. Taylor1, S. Nill1, U. Oelfke1 1 Royal Marsden Hospital Trust & Institute of Cancer Research, Department of Medical Physics, London, United Kingdom Purpose or Objective To build upon previous work [1] to utilise a new contouring concept to quantify the differences in delineation uncertainty when using co-registered CT-MR images vs MRI only for recurrent gynaecological GTVs. Material and Methods A contouring concept was developed in which clinicians draw up to two GTV boundaries per CT slice corresponding to the inner (GTV_i) and outermost (GTV_o) possible boundaries the GTV may have and therefore define a boundary interval for the GTV. Observers contoured centrally recurrent gynaecological GTVs in accordance with this concept first on MRI images
Purpose or Objective Radiation-induced lung fibrosis is an unwanted side effect of curative radiotherapy. Radiological findings include changes in the mediastinum such as shift toward the ipsilateral lung due to treatment related volume loss. In this work we investigate building a standardized and semiautomatic method to quantify mediastinum changes as indicator of lung fibrosis. Material and Methods 31 patients treated with conventional chemoradiotherapy were included. This was a sub-group of a non-randomized phase I/II isotoxic trial which enrolled stage II and III NSCLC (IDEAL-CRT). Each patient underwent a baseline PET-CT or diagnostic CT before treatment, and a diagnostic CT for follow-up after 12 months (average: 433 days, range: 358-496 days). Rotation and thickening of the anterior junction line were taken as measures of mediastinal change. β was defined as the angle between the posterior-anterior direction and the line that connects the centroid of the spinal canal to the centroid of the anterior junction line at carina level in the follow-up scan; similarly, the thickness of the junction (t) was defined as the minimum distance between the two lungs at the same level (Fig. 1). Mediastinum shift was then quantified in terms of the absolute difference between the β measured on the co-registered baseline and follow-up scans (i.e., Δβ= βF- βB), and in terms of the ratio of the thicknesses (i.e., Δt = tF/tB). This was implemented as a semiautomatic workflow in Matlab using the open-source Pulmonary Toolkit (github.com/tomdoel/pulmonarytoolkit).
Fig.1 – Measures of rotation (β) and thickening (t) of the anterior junction line. Results The changes were characterized using the following grading systems: for Δβ, 0- no/small rotation (<4°), 1moderate (4-8°), 2- large (>8°); and for Δt, 0- no/small change including moderate shrinkage (<1.2), 1- mild enlargement (1.2-3), 2- moderate enlargement (>3) (Fig. 2). In the presence of disease or toxicities at the junction, the definition of its centroid is unclear; hence six patients were excluded. Significant rotation of the junction line toward the ipsilateral lung occurred in 64% of the patients (36% and 28% for grades 1 and 2, respectively). Significant enlargement of the junction was measured in 56% of the patients (equal occurrence of grades 1 and 2); shrinkage was measured in 16% of the cases. There was no correlation between rotation and thickening of the junction (ρ=0.17, Pearson’s correlation coefficient).
Fig. 2 – Colour overlay of baseline (red) and follow-up (blue) scans. Cases of grades (a) 0 and 0, (b) 0 and 2, (c) 2 and 0 for rotation and thickening, respectively. Conclusion Chronic lung fibrosis manifests radiologically as mediastinal shift. We propose a standardized method to characterize these changes based on the positioning and thickness of the anterior junction line. Further measures are needed to fully describe mediastinum change. We aim to correlate these changes with measures of lung fibrosis. EP-1713 Feasibility of low dose 4D CBCT in patients with lung cancer. A. Bryce-Atkinson1, A. McWilliam1, T. Marchant2, C. Faivre-Finn1, G. Whitfield3, M. Van Herk1 1 University of Manchester, Division of Molecular and Clinical Cancer Science- Faculty of Biology- Medicine and Health, Manchester, United Kingdom 2 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom 3 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom Purpose or Objective Respiration correlated cone-beam CT (4D CBCT) provides information on the respiratory motion, providing accurate tumour localisation in the lung taking into account breathing motion. This project aims to investigate the potential for 4D CBCT dose reduction, evaluating its effect on image quality, amplitude estimation and registration accuracy. Material and Methods 4D CBCT images were reconstructed from 9 lung cancer patients with a minimum of 800 projections (120kV, 16mA, 10-40ms), phase sorted to the nearest projection over 10 phases. The amplitudes of tumour motion ranged from 3.9-20mm. Dose reduction was simulated by reconstructing using 50%, 25%, 16.67%, 12.5% and 10% of projections and varying the number of phase bins, sorting all remaining projections. The image quality of each reconstruction was assessed visually and by testing registration accuracy for bone (3D) and tumour (4D). Registration accuracy was evaluated by comparing results to the standard reconstruction, for both amplitude of motion in the superior-inferior direction and correctable (mean) position. Results Reducing the number of projections had little effect on registration accuracy overall for both bone and soft tissue, despite very poor visual image quality at low number of projections. Reducing the number of reconstructed phases recovered visual image quality (Figure 1) at the cost of underestimating amplitude and 10 phases yielded best registration accuracy (Table 1). When using 10% of projections, motion was reported at less than 5mm for 89% of patients at 3 and 5 phases. Increasing to 10 phases recovered the tumour motion to approximately that of the standard reconstructions. Automatic soft tissue registration required manual preregistration for two patients: one consistently across all reconstructions, and the other only for the 10 phase reconstruction with 10% of projections.
S940 ESTRO 36 _______________________________________________________________________________________________
Three-dimensional (3D) isotropic volumes were created for each data set and the correspondence between points on the GTV surface of each case was established. To fit the model to an unknown data set texture analysis features were calculated in 5x5 volumes perpendicular to the boundary between the interior and exterior of the GTV surface. This estimates the location of the GTV boundary. At each point a search for the GTV shape was conducted by calculating the texture features and moving within the established shape limits until reaching convergence. Training was performed on 32 randomly selected cases and testing on the remaining 10 cases. The Dice similarity coefficient was used to compare the model results with the clinically defined volumes. Results Figure 1 shows an example of a typical GTV produced by the algorithm in which the seminal vesicles have been included in the apical slice (left). Table 1 shows a summary of the results obtained on the 10 test cases. The mean clinical volume of the test cases was 64.5 cm3 and calculated by the model was 60.3 cm3. The largest difference was observed in the cases with the largest GTV.
Conclusion Registration remains accurate even for as little as 10% of projection data, but with significant limitations in visual image quality at 10 phase reconstructions and motion detection at 3 phases. Simulating 25% dose over 10 phases allows for accurate registration without significant loss of image quality or motion detection and is therefore acceptable for 4D CBCT. This result is particularly relevant for patients with a good prognosis as it limits the radiation exposure. EP-1714 Automatic delineation of the gross-tumour volume in prostate cancer using shape models K. Cheng1, Y. Feng1, D. Montgomery1, D.B. McLaren2, S. McLaughlin3, W. Nailon1 1 Edinburgh Cancer Centre Western General Hospital, Department of Oncology Physics, Edinburgh, United Kingdom 2 Edinburgh Cancer Centre Western General Hospital, Department of Clinical Oncology, Edinburgh, United Kingdom 3 Heriot Watt University, School of Engineering and Physical Sciences, Edinburgh, United Kingdom Purpose or Objective Digital models of anatomy have potential for assisting in the segmentation of the prostate and organs at risk (OAR) in radiotherapy planning of prostate cancer. However, manual alteration of automatically generated contours is often necessary to produce an accurate gross-tumour volume (GTV). This is generally the case when the tumour extends beyond the prostatic capsule into the bladder or invades the seminal vesicles (>T3a tumours). The aim of this study was to develop a digital model of the GTV in prostate cancer that incorporates the range of shape variability associated with different T-stages. Material and Methods Computerised tomography (CT) images from 42 prostate cancer patients, which contained a range of T-stages and had the prostate GTV and OARs outlined, were selected.
Figure 1: Clinical contour in green, model result in red. Left: apical slice taken form the inferior of the GTV including the seminal vesicles. Middle: central slice of the GTV shape. Right: basal slice from the superior of the GTV.
Table 1: Dice coefficients and volumes obtained on the 10 test cases. Conclusion The proposed model has potential for automatically contouring the GTV when the tumour extends beyond the prostatic capsule into the bladder or invades the seminal vesicles. However, more cases must be included in the model to ensure that the full range of shape variability is represented. EP-1715 Differences in delineation uncertainty using MR images only vs CT-MR in recurrent gynaecological GTV D. Bernstein1, A. Taylor1, S. Nill1, U. Oelfke1 1 Royal Marsden Hospital Trust & Institute of Cancer Research, Department of Medical Physics, London, United Kingdom Purpose or Objective To build upon previous work [1] to utilise a new contouring concept to quantify the differences in delineation uncertainty when using co-registered CT-MR images vs MRI only for recurrent gynaecological GTVs. Material and Methods A contouring concept was developed in which clinicians draw up to two GTV boundaries per CT slice corresponding to the inner (GTV_i) and outermost (GTV_o) possible boundaries the GTV may have and therefore define a boundary interval for the GTV. Observers contoured centrally recurrent gynaecological GTVs in accordance with this concept first on MRI images