Ditte Nygaard - Academia.edu (original) (raw)

Papers by Ditte Nygaard

Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), 2014

With 4DCT the risk of introducing positional systematic errors in lung cancer radiotherapy can be... more With 4DCT the risk of introducing positional systematic errors in lung cancer radiotherapy can be minimised. A common approach is to plan on the phase bin of the 4DCT best representing the tumour's time-weighted mean position also called the midventilation scan. However breathing irregularities can introduce uncertainties and potentially misrepresent both the tumour trajectory and the determination of the midventilation phase. In this study we evaluated the robustness of the midventilation approach in the presence of irregular breathing patterns. A LEGO Mindstorms(®) phantom with compact balls simulating lung tumours was constructed. The breathing curves loaded in the phantom were either acquired from a human volunteer or constructed with various magnitudes (ranging from 12 to 29 mm) as well as various irregularities of motion pattern. Repeated 4DCT scans were performed while tumour trajectories were recorded with two motion tracking systems. The time-weighted mean tumour positi...

Radiotherapy and Oncology, 2010

Background and purpose: Four-dimensional computed tomography (4DCT) is used for breathing-adapted... more Background and purpose: Four-dimensional computed tomography (4DCT) is used for breathing-adapted radiotherapy planning. Irregular breathing, large tumour motion or interpolation of images can cause artefacts in the 4DCT. This study evaluates the impact of artefacts on gross tumour volume (GTV) size. Material and methods: In 19 4DCT scans of patients with peripheral lung tumours, GTV was delineated in all bins. Variations in GTV size between bins in each 4DCT scan were analysed and correlated to tumour motion and variations in breathing signal amplitude and breathing signal period. End-expiration GTV size (GTVexp) was considered as reference for GTV size. Intra-session delineation error was estimated by redelineation of GTV in eight of the 4DCT scans. Results: In 16 of the 4DCT scans the maximum deviations from GTVexp were larger than could be explained by delineation error. The deviations were largest in the bins adjacent to the end-inspiration bin. The coefficient of variation of GTV size was significantly correlated to tumour motion in the cranio-caudal direction, but no significant correlation was found to breathing signal variations. Conclusion: We found considerable variations in GTV size throughout the 4DCT scans. Awareness of the error introduced by artefacts is important especially if radiotherapy planning is based on a single 4DCT bin.

International Journal of Radiation Oncology*Biology*Physics, 2012

This study quantified the treatment field margins needed for various motion management strategies... more This study quantified the treatment field margins needed for various motion management strategies including 4DCT, respirationcorrelated image guidance, and beam gating, in the treatment of lung cancer. AAPM task group report 76, recommends that respiratory compensation should be considered during beam delivery for tumor motion above 5 mm. This study contests this recommended threshold, and presents Purpose: The purpose of this study was to quantify the effects of four-dimensional computed tomography (4DCT), 4D image guidance (4D-IG), and beam gating on calculated treatment field margins in a lung cancer patient population. Materials and Methods: Images were acquired from 46 lung cancer patients participating in four separate protocols at three institutions in Europe and the United States. Seven patients were imaged using fluoroscopy, and 39 patients were imaged using 4DCT.

British Journal of Radiology, 2012

Objectives: In radiotherapy, delineation uncertainties are important as they contribute to system... more Objectives: In radiotherapy, delineation uncertainties are important as they contribute to systematic errors and can lead to geographical miss of the target. For margin computation, standard deviations (SDs) of all uncertainties must be included as SDs. The aim of this study was to quantify the interobserver delineation variation for stereotactic body radiotherapy (SBRT) of peripheral lung tumours using a crosssectional study design. Methods: 22 consecutive patients with 26 tumours were included. Positron emission tomography/CT scans were acquired for planning of SBRT. Three oncologists and three radiologists independently delineated the gross tumour volume. The interobserver variation was calculated as a mean of multiple SDs of distances to a reference contour, and calculated for the transversal plane (SD trans ) and craniocaudal (CC) direction (SD cc ) separately. Concordance indexes and volume deviations were also calculated. Results: Median tumour volume was 13.0 cm 3 , ranging from 0.3 to 60.4 cm 3 . The mean SD trans was 0.15 cm (SD 0.08 cm) and the overall mean SD cc was 0.26 cm (SD 0.15 cm). Tumours with pleural contact had a significantly larger SD trans than tumours surrounded by lung tissue. Conclusions: The interobserver delineation variation was very small in this systematic cross-sectional analysis, although significantly larger in the CC direction than in the transversal plane, stressing that anisotropic margins should be applied. This study is the first to make a systematic cross-sectional analysis of delineation variation for peripheral lung tumours referred for SBRT, establishing the evidence that interobserver variation is very small for these tumours.

Acta Oncologica, 2013

Background. In lung cancer radiotherapy, planning on the midventilation (MidV) bin of a four-dime... more Background. In lung cancer radiotherapy, planning on the midventilation (MidV) bin of a four-dimensional (4D) CT scan can reduce the systematic errors introduced by respiratory tumour motion compared to conventional CT. In this study four different methods for MidV bin selection are evaluated. Material and methods. The study is based on 4DCT scans of 19 patients with a total of 23 peripheral lung tumours having peak-to-peak displacement Ն 5 mm in at least one of the left-right (LR), anterior-posterior (AP) or cranio-caudal (CC) directions. For each tumour, the MidV bin was selected based on: 1) visual evaluation of tumour displacement; 2) rigid registration of tumour position; 3) diaphragm displacement in the CC direction; and 4) carina displacement in the CC direction. Determination of the MidV bin based on the displacement of the manually delineated gross tumour volume (GTV) was used as a reference method. The accuracy of each method was evaluated by the distance between GTV position in the selected MidV bin and the time-weighted mean position of GTV throughout the bins (i.e. the geometric MidV error). Results. Median (range) geometric MidV error was 1.4 (0.4 -5.4) mm, 1.4 (0.4 -5.4) mm, 1.9 (0.5 -6.9) mm, 2.0 (0.5 -12.3) mm and 1.1 (0.4 -5.4) mm for the visual, rigid registration, diaphragm, carina, and reference method. Median (range) absolute difference between geometric MidV error for the evaluated methods and the reference method was 0.0 (0.0 -1.2) mm, 0.0 (0.0 -1.7) mm, 0.7 (0.0 -3.9) mm and 1.0 (0.0 -6.9) mm for the visual, rigid registration, diaphragm and carina method. Conclusion. The visual and semi-automatic rigid registration methods were equivalent in accuracy for selecting the MidV bin of a 4DCT scan. The methods based on diaphragm and carina displacement cannot be recommended without modifi cations.

Acta Oncologica, 2008

Background. The image quality of 4DCT depends on breathing regularity. Respiratory audio coaching... more Background. The image quality of 4DCT depends on breathing regularity. Respiratory audio coaching may improve regularity and reduce motion artefacts. We question the safety of coached planning 4DCT without coaching during treatment. We investigated the possibility of coaching to a more stable breathing without changing the breathing amplitude. The interfraction variation of the breathing cycle amplitude in free and coached breathing was studied as well as the possible impact of fatigue on longer coaching sessions. Methods. Thirteen volunteers completed respiratory audio coaching on 3 days within a 2 week period. An external marker system monitoring the motion of the thoraco-abdominal wall was used to track the respiration. On all days, free breathing and two coached breathing curves were recorded. We assumed that free versus coached breathing from day 1 (reference session) simulated breathing during an uncoached versus coached planning 4DCT, respectively, and compared the mean breathing cycle amplitude to the free versus coached breathing from day 2 and 3 simulating free versus coached breathing during treatment. Results. For most volunteers it was impossible to apply coaching without changes in breathing cycle amplitude. No significant decrease in standard deviation of breathing cycle amplitude distribution was seen. Generally it was not possible to predict the breathing cycle amplitude and its variation the following days based on the breathing in the reference session irrespective of coaching or free breathing. We found a significant tendency towards an increased breathing cycle amplitude variation with the duration of the coaching session. Conclusion. These results suggest that large interfraction variation is present in breathing amplitude irrespective of coaching, leading to the suggestion of daily image guidance for verification of respiratory pattern and tumour related motion. Until further investigated it is not recommendable to use coached 4DCT for planning of a free breathing treatment course.

International Journal of Radiation Oncology*Biology*Physics, 2011

Purpose: Artifacts impacting the imaged tumor volume can be seen in conventional three-dimensiona... more Purpose: Artifacts impacting the imaged tumor volume can be seen in conventional three-dimensional CT (3DCT) scans for planning of lung cancer radiotherapy but can be reduced with the use of respiration-correlated imaging, i.e., 4DCT or breathhold CT (BHCT) scans. The aim of this study was to compare delineated gross tumor volume (GTV) sizes in 3DCT, 4DCT, and BHCT scans of patients with lung tumors. Methods and Materials: A total of 36 patients with 46 tumors referred for stereotactic radiotherapy of lung tumors were included. All patients underwent positron emission tomography (PET)/CT, 4DCT, and BHCT scans. GTVs in all CT scans of individual patients were delineated during one session by a single physician to minimize systematic delineation uncertainty. The GTV size from the BHCT was considered the closest to true tumor volume and was chosen as the reference. The reference GTV size was compared to GTV sizes in 3DCT, at midventilation (MidV), at end-inspiration (Insp), and at end-expiration (Exp) bins from the 4DCT scan. Results: The median BHCT GTV size was 4.9 cm 3 (0.1-53.3 cm 3 ). Median deviation between 3DCT and BHCT GTV size was 0.3 cm 3 (À3.3 to 30.0 cm 3 ), between MidV and BHCT size was 0.2 cm 3 (À5.7 to 19.7 cm 3 ), between Insp and BHCT size was 0.3 cm 3 (À4.7 to 24.8 cm 3 ), and between Exp and BHCT size was 0.3 cm 3 (À4.8 to 25.5 cm 3 ). The 3DCT, MidV, Insp, and Exp median GTV sizes were all significantly larger than the BHCT median GTV size. Conclusions: In the present study, the choice of CT method significantly influenced the delineated GTV size, on average, leading to an increase in GTV size compared to the reference BHCT. The uncertainty caused by artifacts is estimated to be in the same magnitude as delineation uncertainty and should be considered in the design of margins for radiotherapy. Ó

Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), 2014

With 4DCT the risk of introducing positional systematic errors in lung cancer radiotherapy can be... more With 4DCT the risk of introducing positional systematic errors in lung cancer radiotherapy can be minimised. A common approach is to plan on the phase bin of the 4DCT best representing the tumour's time-weighted mean position also called the midventilation scan. However breathing irregularities can introduce uncertainties and potentially misrepresent both the tumour trajectory and the determination of the midventilation phase. In this study we evaluated the robustness of the midventilation approach in the presence of irregular breathing patterns. A LEGO Mindstorms(®) phantom with compact balls simulating lung tumours was constructed. The breathing curves loaded in the phantom were either acquired from a human volunteer or constructed with various magnitudes (ranging from 12 to 29 mm) as well as various irregularities of motion pattern. Repeated 4DCT scans were performed while tumour trajectories were recorded with two motion tracking systems. The time-weighted mean tumour positi...

Radiotherapy and Oncology, 2010

Background and purpose: Four-dimensional computed tomography (4DCT) is used for breathing-adapted... more Background and purpose: Four-dimensional computed tomography (4DCT) is used for breathing-adapted radiotherapy planning. Irregular breathing, large tumour motion or interpolation of images can cause artefacts in the 4DCT. This study evaluates the impact of artefacts on gross tumour volume (GTV) size. Material and methods: In 19 4DCT scans of patients with peripheral lung tumours, GTV was delineated in all bins. Variations in GTV size between bins in each 4DCT scan were analysed and correlated to tumour motion and variations in breathing signal amplitude and breathing signal period. End-expiration GTV size (GTVexp) was considered as reference for GTV size. Intra-session delineation error was estimated by redelineation of GTV in eight of the 4DCT scans. Results: In 16 of the 4DCT scans the maximum deviations from GTVexp were larger than could be explained by delineation error. The deviations were largest in the bins adjacent to the end-inspiration bin. The coefficient of variation of GTV size was significantly correlated to tumour motion in the cranio-caudal direction, but no significant correlation was found to breathing signal variations. Conclusion: We found considerable variations in GTV size throughout the 4DCT scans. Awareness of the error introduced by artefacts is important especially if radiotherapy planning is based on a single 4DCT bin.

International Journal of Radiation Oncology*Biology*Physics, 2012

This study quantified the treatment field margins needed for various motion management strategies... more This study quantified the treatment field margins needed for various motion management strategies including 4DCT, respirationcorrelated image guidance, and beam gating, in the treatment of lung cancer. AAPM task group report 76, recommends that respiratory compensation should be considered during beam delivery for tumor motion above 5 mm. This study contests this recommended threshold, and presents Purpose: The purpose of this study was to quantify the effects of four-dimensional computed tomography (4DCT), 4D image guidance (4D-IG), and beam gating on calculated treatment field margins in a lung cancer patient population. Materials and Methods: Images were acquired from 46 lung cancer patients participating in four separate protocols at three institutions in Europe and the United States. Seven patients were imaged using fluoroscopy, and 39 patients were imaged using 4DCT.

British Journal of Radiology, 2012

Objectives: In radiotherapy, delineation uncertainties are important as they contribute to system... more Objectives: In radiotherapy, delineation uncertainties are important as they contribute to systematic errors and can lead to geographical miss of the target. For margin computation, standard deviations (SDs) of all uncertainties must be included as SDs. The aim of this study was to quantify the interobserver delineation variation for stereotactic body radiotherapy (SBRT) of peripheral lung tumours using a crosssectional study design. Methods: 22 consecutive patients with 26 tumours were included. Positron emission tomography/CT scans were acquired for planning of SBRT. Three oncologists and three radiologists independently delineated the gross tumour volume. The interobserver variation was calculated as a mean of multiple SDs of distances to a reference contour, and calculated for the transversal plane (SD trans ) and craniocaudal (CC) direction (SD cc ) separately. Concordance indexes and volume deviations were also calculated. Results: Median tumour volume was 13.0 cm 3 , ranging from 0.3 to 60.4 cm 3 . The mean SD trans was 0.15 cm (SD 0.08 cm) and the overall mean SD cc was 0.26 cm (SD 0.15 cm). Tumours with pleural contact had a significantly larger SD trans than tumours surrounded by lung tissue. Conclusions: The interobserver delineation variation was very small in this systematic cross-sectional analysis, although significantly larger in the CC direction than in the transversal plane, stressing that anisotropic margins should be applied. This study is the first to make a systematic cross-sectional analysis of delineation variation for peripheral lung tumours referred for SBRT, establishing the evidence that interobserver variation is very small for these tumours.

Acta Oncologica, 2013

Background. In lung cancer radiotherapy, planning on the midventilation (MidV) bin of a four-dime... more Background. In lung cancer radiotherapy, planning on the midventilation (MidV) bin of a four-dimensional (4D) CT scan can reduce the systematic errors introduced by respiratory tumour motion compared to conventional CT. In this study four different methods for MidV bin selection are evaluated. Material and methods. The study is based on 4DCT scans of 19 patients with a total of 23 peripheral lung tumours having peak-to-peak displacement Ն 5 mm in at least one of the left-right (LR), anterior-posterior (AP) or cranio-caudal (CC) directions. For each tumour, the MidV bin was selected based on: 1) visual evaluation of tumour displacement; 2) rigid registration of tumour position; 3) diaphragm displacement in the CC direction; and 4) carina displacement in the CC direction. Determination of the MidV bin based on the displacement of the manually delineated gross tumour volume (GTV) was used as a reference method. The accuracy of each method was evaluated by the distance between GTV position in the selected MidV bin and the time-weighted mean position of GTV throughout the bins (i.e. the geometric MidV error). Results. Median (range) geometric MidV error was 1.4 (0.4 -5.4) mm, 1.4 (0.4 -5.4) mm, 1.9 (0.5 -6.9) mm, 2.0 (0.5 -12.3) mm and 1.1 (0.4 -5.4) mm for the visual, rigid registration, diaphragm, carina, and reference method. Median (range) absolute difference between geometric MidV error for the evaluated methods and the reference method was 0.0 (0.0 -1.2) mm, 0.0 (0.0 -1.7) mm, 0.7 (0.0 -3.9) mm and 1.0 (0.0 -6.9) mm for the visual, rigid registration, diaphragm and carina method. Conclusion. The visual and semi-automatic rigid registration methods were equivalent in accuracy for selecting the MidV bin of a 4DCT scan. The methods based on diaphragm and carina displacement cannot be recommended without modifi cations.

Acta Oncologica, 2008

Background. The image quality of 4DCT depends on breathing regularity. Respiratory audio coaching... more Background. The image quality of 4DCT depends on breathing regularity. Respiratory audio coaching may improve regularity and reduce motion artefacts. We question the safety of coached planning 4DCT without coaching during treatment. We investigated the possibility of coaching to a more stable breathing without changing the breathing amplitude. The interfraction variation of the breathing cycle amplitude in free and coached breathing was studied as well as the possible impact of fatigue on longer coaching sessions. Methods. Thirteen volunteers completed respiratory audio coaching on 3 days within a 2 week period. An external marker system monitoring the motion of the thoraco-abdominal wall was used to track the respiration. On all days, free breathing and two coached breathing curves were recorded. We assumed that free versus coached breathing from day 1 (reference session) simulated breathing during an uncoached versus coached planning 4DCT, respectively, and compared the mean breathing cycle amplitude to the free versus coached breathing from day 2 and 3 simulating free versus coached breathing during treatment. Results. For most volunteers it was impossible to apply coaching without changes in breathing cycle amplitude. No significant decrease in standard deviation of breathing cycle amplitude distribution was seen. Generally it was not possible to predict the breathing cycle amplitude and its variation the following days based on the breathing in the reference session irrespective of coaching or free breathing. We found a significant tendency towards an increased breathing cycle amplitude variation with the duration of the coaching session. Conclusion. These results suggest that large interfraction variation is present in breathing amplitude irrespective of coaching, leading to the suggestion of daily image guidance for verification of respiratory pattern and tumour related motion. Until further investigated it is not recommendable to use coached 4DCT for planning of a free breathing treatment course.

International Journal of Radiation Oncology*Biology*Physics, 2011

Purpose: Artifacts impacting the imaged tumor volume can be seen in conventional three-dimensiona... more Purpose: Artifacts impacting the imaged tumor volume can be seen in conventional three-dimensional CT (3DCT) scans for planning of lung cancer radiotherapy but can be reduced with the use of respiration-correlated imaging, i.e., 4DCT or breathhold CT (BHCT) scans. The aim of this study was to compare delineated gross tumor volume (GTV) sizes in 3DCT, 4DCT, and BHCT scans of patients with lung tumors. Methods and Materials: A total of 36 patients with 46 tumors referred for stereotactic radiotherapy of lung tumors were included. All patients underwent positron emission tomography (PET)/CT, 4DCT, and BHCT scans. GTVs in all CT scans of individual patients were delineated during one session by a single physician to minimize systematic delineation uncertainty. The GTV size from the BHCT was considered the closest to true tumor volume and was chosen as the reference. The reference GTV size was compared to GTV sizes in 3DCT, at midventilation (MidV), at end-inspiration (Insp), and at end-expiration (Exp) bins from the 4DCT scan. Results: The median BHCT GTV size was 4.9 cm 3 (0.1-53.3 cm 3 ). Median deviation between 3DCT and BHCT GTV size was 0.3 cm 3 (À3.3 to 30.0 cm 3 ), between MidV and BHCT size was 0.2 cm 3 (À5.7 to 19.7 cm 3 ), between Insp and BHCT size was 0.3 cm 3 (À4.7 to 24.8 cm 3 ), and between Exp and BHCT size was 0.3 cm 3 (À4.8 to 25.5 cm 3 ). The 3DCT, MidV, Insp, and Exp median GTV sizes were all significantly larger than the BHCT median GTV size. Conclusions: In the present study, the choice of CT method significantly influenced the delineated GTV size, on average, leading to an increase in GTV size compared to the reference BHCT. The uncertainty caused by artifacts is estimated to be in the same magnitude as delineation uncertainty and should be considered in the design of margins for radiotherapy. Ó