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208 oral Feasibility of using patient contours for setup verification
Symposia/Proffered papers
incidence 2% at maximum. The penumbra measured with the JFD-5 agrees well with film and diode. The reproducibility of JFD-5 measurements in the match line region is 2% (1SD). Agreement with TLD match line dosimetry during patient treatment was 0.999+0.023 (1SD). Conclusion: the JFD-5 can be used for accurate, reproducible and fast online match line in vivo dosimetry. In our institution, the JFD-5 has been used to safely introduce and monitor a new treatment technique for chest wall irradiation.
Thursday, 20 September 2001
ferences in dose between centres and form an excellent additional QA tool in the START Trial This data is presented on behalf of the START Trial management group
IMAGING 210
208
$73
invited
oral
Feasibility of using patient contours for setup verification
Techniques for measuring and correcting set-up errors and organ motion on the treatment machine
L.S. Ploeger. A. Betgen, K.G.A. Gilhuijs, M. van Herk Department of Radiotherapy, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands
M. van Herk The Netherlands Cancer Institute, Radiotherapy Department, Amsterdam, The Netherlands
Introduction: in situations where no or limited anatomy information is present in portal images, other modalities may provide useful information. The aim of this study is to establish the efficacy of body contours to verify patient setup in 3D. Materials and methods: body contours are acquired on a simulator. At the same moment, simulator images were taken as a reference. To determine the patient setup, both modalities are matched in 3D to the planning CT scan: the body contours to the CT-skin, the simulator images to the CTbone. Data of a breast phantom, lung patients (24) and head and neck patients (9) are collected. Results: the phantom study shows good agreement (better than 1 mm) between the patient setup established from the contours and the setup established from the simulator images. For the lung patients, the correlations between contour and bone matches for the X-, Y- and Z-directions are 0.4, 0.8 and 0.7, respectively, while for the head and neck patients these correlations are 0.6, 0.5 and 0. Movement of the head in the applied mask (the body contour method registers the mask) might cause the very poor correlation in the Z (A-P) direction for head & neck patients. The setup errors for head and neck are much smaller as for lung. When the patient setup would be corrected using contour data, the magnitude of the setup deviations would decrease only slightly compared with marker-based setup. Conclusion: the phantom result shows that the method for setup verification using patient contours is valid. However, the correspondence between the contour and the bone matches for these patient groups is weak. I.e., body contours can improve the patient setup for these two patient groups slightly, but cannot replace portal imaging. In future work, we will study methods to improve the body contour match, i.e., by avoiding mobile skin surfaces.
Dose escalation is often combined with margin reduction to limit normal tissue complications. A reduction of margin without introducing geometrical misses is only possible if the magnitude of all geometric errors is known and controlled. The aim of this paper is to summarize and compare methods to reduce geometrical errors. Setup error is defined as a deviation in position of bony anatomy relative to the treatment machine compared with the planned situation. Organ motion is defined as a deviation in position of target relative to the bony anatomy. Both errors are additive, have a similar impact, and both have a systematic and a random component. The major source of the systematic error is the planning CT, which takes a snapshot of a variable patient and introduces setup error and organ motion into the plan. This error is systematically reproduced in all treatment fractions and therefore impacts the target dose more than day to day variability. To correct systematic errors one should collect as many data as possible in the preparation and initial treatment phase. A formal correction protocol must be used and ad-hoc corrections should be avoided because they lead to over-correction and are often counter-productive. For correcting setup errors and organ motion, both off-line correction protocols, which correct systematic errors and on-line correction protocols, which also correct dayto-day variations, are applicable. The common way to address setup errors is portal imaging, which measures the position in the bony anatomy. The simplest (but invasive) way to make the target visible is to implant markers and use MV or kV imaging to visualize their position on the treatment machine. However, it is not strictly required to determine organ motion on the treatment machine. What we want to achieve is that the beams are aimed as well as possible on the average position of the moving target. Another way of achieving this is to "average" multiple CT scdans to estimate the mean position of the moving organ. The most advanced methods for determining the position of the target on the treatment machine is "image guided radiotherapy" where some form of 3D imaging is integrated with the accelerator. Examples of this technology are on-line ultrasound guidance, tomotherapy (integrating an accelerator on a CT gantry) and kilovoltage cone-beam CT image guidance. In this presentation, the efficiency and accuracy of these procedures will be compared.
209
oral
In vivo dosimetry for patients in the START trial K. Venables1, E.A. Winfield1, E.G.A. Aird2, P.J. Hoskin 1 1Mount Vernon Hospital, Marie Curie Research Wing, Northwood, Middlesex, UK, 2Mount Vernon Hospital, Physics Department, Northwood, Middlesex, UK
Introduction: The START trial is a UK trial testing the effects of different fractionation regimes for breast cancer. In order to ensure that the doses given in each department are within a specified tolerance (4% of prescribed dose), a program of phantom and in vivo measurements has been carried out Method: Each centres technique and dosimetry were checked at an initial visit with a 2D phantom, a further visit with a 3D phantom has been carried out. Since April 00 1 in 9 patients randomised in the START trial has been allocated to have in vivo measurements performed using TLD. The TLD with build up material are posted to the department to be used on the patient's third treatment. All calibration, preparation and readout of the TLD are carried out by members of the QA team. Results: Preliminary analysis of the results has shown that there is a correlation between the average dose measured by the TLD for a given centre and the dose measured by the QA team using a 3D breast phantom at the centre. Differences are seen for individual patient measurements and these will reflect the tissue density within the breast, positioning error of the TLD and uncertainty in the TLD readout. To the end of March 2001, 179 patient measurements had been performed. The mean measured/expected dose was 0.986 SD 0.035, which agrees well with the mean dose measured in the 3D phantom of 0.979. Conclusion: The TLD are providing an accurate indication of the minor dif-
211
oral
Conformal and intensity modulated radiotherapy using cobalt-60 and 6 MV X-ray beams: a treatment planning comparison of different sites A.P. Warrinaton. E.J. Adams Royal Marsden Hospital, Physics Department, Sutton, Surrey, U.K. The viability of external beam cobalt-60 treatments in radiotherapy is reexamined in light of improved technology for multi-aperture conformal blocking, compensator production, treatment planning and the reduced energy dependence of intensity modulated photon treatments. A treatment planning comparison has therefore been undertaken comparing treatments for different sites using either linear accelerator based 6MY x-ray or "telecobalt" beams. The sites compared in this study include prostate, breast, bronchus, head & neck and brain. Dose Volume Histogram (DVH) analyses have been carried out comparing MLC based conformal and intensity modulated linac treatments with corresponding blocked and/or compensated cobalt treatments. The DVH results presented show that cobalt unit beams provide robustly comparable quality treatments for the selected sites in the head and neck (thyroid, parotid, maxillary antrum), brain (meningioma, pituitary) and breast (small, small medium). Less favourable sites were the deeply seated lesions in the chest and pelvis. However, further investigations show that satisfactory treatments can be achieved on the latter sites by the addition of
incidence 2% at maximum. The penumbra measured with the JFD-5 agrees well with film and diode. The reproducibility of JFD-5 measurements in the match line region is 2% (1SD). Agreement with TLD match line dosimetry during patient treatment was 0.999+0.023 (1SD). Conclusion: the JFD-5 can be used for accurate, reproducible and fast online match line in vivo dosimetry. In our institution, the JFD-5 has been used to safely introduce and monitor a new treatment technique for chest wall irradiation.
Thursday, 20 September 2001
ferences in dose between centres and form an excellent additional QA tool in the START Trial This data is presented on behalf of the START Trial management group
IMAGING 210
208
$73
invited
oral
Feasibility of using patient contours for setup verification
Techniques for measuring and correcting set-up errors and organ motion on the treatment machine
L.S. Ploeger. A. Betgen, K.G.A. Gilhuijs, M. van Herk Department of Radiotherapy, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands
M. van Herk The Netherlands Cancer Institute, Radiotherapy Department, Amsterdam, The Netherlands
Introduction: in situations where no or limited anatomy information is present in portal images, other modalities may provide useful information. The aim of this study is to establish the efficacy of body contours to verify patient setup in 3D. Materials and methods: body contours are acquired on a simulator. At the same moment, simulator images were taken as a reference. To determine the patient setup, both modalities are matched in 3D to the planning CT scan: the body contours to the CT-skin, the simulator images to the CTbone. Data of a breast phantom, lung patients (24) and head and neck patients (9) are collected. Results: the phantom study shows good agreement (better than 1 mm) between the patient setup established from the contours and the setup established from the simulator images. For the lung patients, the correlations between contour and bone matches for the X-, Y- and Z-directions are 0.4, 0.8 and 0.7, respectively, while for the head and neck patients these correlations are 0.6, 0.5 and 0. Movement of the head in the applied mask (the body contour method registers the mask) might cause the very poor correlation in the Z (A-P) direction for head & neck patients. The setup errors for head and neck are much smaller as for lung. When the patient setup would be corrected using contour data, the magnitude of the setup deviations would decrease only slightly compared with marker-based setup. Conclusion: the phantom result shows that the method for setup verification using patient contours is valid. However, the correspondence between the contour and the bone matches for these patient groups is weak. I.e., body contours can improve the patient setup for these two patient groups slightly, but cannot replace portal imaging. In future work, we will study methods to improve the body contour match, i.e., by avoiding mobile skin surfaces.
Dose escalation is often combined with margin reduction to limit normal tissue complications. A reduction of margin without introducing geometrical misses is only possible if the magnitude of all geometric errors is known and controlled. The aim of this paper is to summarize and compare methods to reduce geometrical errors. Setup error is defined as a deviation in position of bony anatomy relative to the treatment machine compared with the planned situation. Organ motion is defined as a deviation in position of target relative to the bony anatomy. Both errors are additive, have a similar impact, and both have a systematic and a random component. The major source of the systematic error is the planning CT, which takes a snapshot of a variable patient and introduces setup error and organ motion into the plan. This error is systematically reproduced in all treatment fractions and therefore impacts the target dose more than day to day variability. To correct systematic errors one should collect as many data as possible in the preparation and initial treatment phase. A formal correction protocol must be used and ad-hoc corrections should be avoided because they lead to over-correction and are often counter-productive. For correcting setup errors and organ motion, both off-line correction protocols, which correct systematic errors and on-line correction protocols, which also correct dayto-day variations, are applicable. The common way to address setup errors is portal imaging, which measures the position in the bony anatomy. The simplest (but invasive) way to make the target visible is to implant markers and use MV or kV imaging to visualize their position on the treatment machine. However, it is not strictly required to determine organ motion on the treatment machine. What we want to achieve is that the beams are aimed as well as possible on the average position of the moving target. Another way of achieving this is to "average" multiple CT scdans to estimate the mean position of the moving organ. The most advanced methods for determining the position of the target on the treatment machine is "image guided radiotherapy" where some form of 3D imaging is integrated with the accelerator. Examples of this technology are on-line ultrasound guidance, tomotherapy (integrating an accelerator on a CT gantry) and kilovoltage cone-beam CT image guidance. In this presentation, the efficiency and accuracy of these procedures will be compared.
209
oral
In vivo dosimetry for patients in the START trial K. Venables1, E.A. Winfield1, E.G.A. Aird2, P.J. Hoskin 1 1Mount Vernon Hospital, Marie Curie Research Wing, Northwood, Middlesex, UK, 2Mount Vernon Hospital, Physics Department, Northwood, Middlesex, UK
Introduction: The START trial is a UK trial testing the effects of different fractionation regimes for breast cancer. In order to ensure that the doses given in each department are within a specified tolerance (4% of prescribed dose), a program of phantom and in vivo measurements has been carried out Method: Each centres technique and dosimetry were checked at an initial visit with a 2D phantom, a further visit with a 3D phantom has been carried out. Since April 00 1 in 9 patients randomised in the START trial has been allocated to have in vivo measurements performed using TLD. The TLD with build up material are posted to the department to be used on the patient's third treatment. All calibration, preparation and readout of the TLD are carried out by members of the QA team. Results: Preliminary analysis of the results has shown that there is a correlation between the average dose measured by the TLD for a given centre and the dose measured by the QA team using a 3D breast phantom at the centre. Differences are seen for individual patient measurements and these will reflect the tissue density within the breast, positioning error of the TLD and uncertainty in the TLD readout. To the end of March 2001, 179 patient measurements had been performed. The mean measured/expected dose was 0.986 SD 0.035, which agrees well with the mean dose measured in the 3D phantom of 0.979. Conclusion: The TLD are providing an accurate indication of the minor dif-
211
oral
Conformal and intensity modulated radiotherapy using cobalt-60 and 6 MV X-ray beams: a treatment planning comparison of different sites A.P. Warrinaton. E.J. Adams Royal Marsden Hospital, Physics Department, Sutton, Surrey, U.K. The viability of external beam cobalt-60 treatments in radiotherapy is reexamined in light of improved technology for multi-aperture conformal blocking, compensator production, treatment planning and the reduced energy dependence of intensity modulated photon treatments. A treatment planning comparison has therefore been undertaken comparing treatments for different sites using either linear accelerator based 6MY x-ray or "telecobalt" beams. The sites compared in this study include prostate, breast, bronchus, head & neck and brain. Dose Volume Histogram (DVH) analyses have been carried out comparing MLC based conformal and intensity modulated linac treatments with corresponding blocked and/or compensated cobalt treatments. The DVH results presented show that cobalt unit beams provide robustly comparable quality treatments for the selected sites in the head and neck (thyroid, parotid, maxillary antrum), brain (meningioma, pituitary) and breast (small, small medium). Less favourable sites were the deeply seated lesions in the chest and pelvis. However, further investigations show that satisfactory treatments can be achieved on the latter sites by the addition of