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4D Radiotherapy Overcomes Respiratory Motion Challenges
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- 4. 4 GI motion Cardiac motion Skeletal motion Respiratory motion Respiratory motion affects all tumor sites in the thorax andRespiratory motion affects all tumor sites in the thorax and abdomenabdomen
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- 7. 7 Conventional With gated imaging Tumor Distortion along the axis of motion could lengthen or shorten theDistortion along the axis of motion could lengthen or shorten the target volume.target volume.
- 8. 8 „ Breathing motion increases the apparent size of the tumor Increases portal sizes „ Increases normal organ irradiation
- 9. Increases normal tissue dose and limits target dose 9 PTV CT V Conventional With gating PTV CT V
- 10. • Breath-hold techniques . – Uncomfortable for patients, limited applicability . – Increases treatment time • Respiratory gating – Residual motion within gating window – Increases treatment time • 4D Radiotherapy – Hardware/Software complexity 10
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- 12. “The explicit inclusion of the temporal changes in anatomy during the imaging, planning and delivery of radiotherapy” 12
- 13. 13 4D Radiotherapy 4D CT Imaging 4D Treatment Planning 4D Treatment Delivery Acquisition of a sequence of CT image sets over consecutive phases of a breathing cycle The explicit inclusion of the temporal changes in anatomy during the imaging, planning and delivery of radiotherapy Designing treatment plans on CT image sets obtained for each phase of the breathing cycle Continuous delivery of the 4D treatment plans throughout the breathing cycle
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- 17. 17 Acquire 4D CT Define anatomy Create/adjust treatment plan Evaluate dose distribution 1 4 3 2 Proceed to treatment 6 … Plan acceptable? No Yes Deformableregistration … Automatedplanning … Deform able registration 5 4D Planning Flow Chart4D Planning Flow Chart
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- 20. 4D Radiotherapy 20 ntroller MLC Workstation MLC Controller4DC Tracking Signal ntroller MLC Workstation MLC Controller4DC Tracking Signal
- 21. Respiratory motion causes problems during the imaging, planning and treatment stages of radiotherapy Several methods have been proposed to address respiratory motion 4D radiotherapy has some advantages over existing methods 21
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Editor's Notes
- Shown is a fluoroscopy video of a lung tumor. The patient was undergoing quiet respiration, though the tumor, visible just above the diaphragm, is moving 2 cm during inhale and exhale. 3D methods do not account for this motion, which causes errors and inaccuracies during the imaging, planning and delivery of radiation. Thus, 4D methods are required.
- One of the problems with applying 3D techniques in the presence of respiratory motion occurs during imaging This slide shows a conventional CT scan image on the left, and a gated CT scan image of the same patient on the right. The tumor is seen above the diaphragm in the right lung. In the conventional scan, because of respiration motion the tumor, lung and liver are interspersed, making tumor definition very difficult. In the gated scan, the tumor is clearly seen, and boundaries can be confidently drawn.
- A second limitation of applying 3D techniques in the presence of respiratory motion occurs during planning Because of the motion of the tumor during radiotherapy, if we do not account for this motion (we don’t during conventional radiotherapy) we need larger radiation beams to cover the extent of the motion than if we used methods that explicitly accounted for this tumor motion during treatment. Larger radiation beams mean that more healthy lung is irradiated, increasing the chance of radiation-induced pneumonitis and limiting the tumor dose.
- There are two existing methods that explicitly account for respiratory motion during radiotherapy. These are breathhold techniques and gating techniques, and have been successfully applied clinically. However, both of these methods increase the treatment time, that causes accuracy as well as patient throughput problems. Breathhold techniques require patients to have adequate lung function and thus has limited applicability. Gating has other limitations explained in detail in the application. 4D IMRT can potentially overcome these problems, though this solution is more complex.