19- IMRT - Intensity-Modulated Radiation Therapy (IMRT)...

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Unformatted text preview: Intensity-Modulated Radiation Therapy (IMRT) Tarun K. Podder, PhD, DABR Department of Radiation Oncology Brody School of Medicine Leo Jenkins Cancer Center East Carolina University March 29, 2011 Lecture # 19 (Ch. 20) What is IMRT? Traditional 3D Conformal Radiation Therapy (3DCRT) The best way to describe Intensity Modulated Radiation Therapy (IMRT) is to compare this new treatment modality to older dose delivery methods. Flat radiation beams have traditionally been used to treat deep tumors. X-ray source H 2 O Relatively flat portion of treatment beam A single RT field distributes dose along the path of the treatment beam Target Critical Structure Patient outline Critical structure can receive more dose than target! Additional beams can be used to spread the dose and spare critical healthy tissues Even more beams can be added to obtain a conformal dose distribution The end result is a highly conformal circular dose distributions Notice that a much reduced dose reaches the critical structure 90% isodose 50% isodose Intensity Modulated Radiation Therapy (IMRT) or “Dose Painting” can handle this treatment situation. Irregular beam absorber Modulated beam profile How does modulating treatment beams help us “bend” isodose lines and “sculpt” dose distributions? Example: Prostate and rectum • The technique of using many different beam directions can be applied to the situation where the prostate is irradiated • The result is a dose distributions that conforms to the prostate plus margin. Notice that a very small portion of the rectum is spared. 90% Isodose b margin An example that uses simple parallel opposed fields • One simple way of protecting more of the rectum is to shield this structure with a block that transmits some reduced amount of the beam intensity • The obvious tradeoff is a dose shadow that passes through the prostate 90% isodose Beam absorb er Simple IMRT Example: Prostate Cancer • It is possible to combine the last two approaches. last two approaches....
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This note was uploaded on 01/21/2012 for the course PHYS 6720 taught by Professor Hu during the Spring '10 term at East Carolina University .

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19- IMRT - Intensity-Modulated Radiation Therapy (IMRT)...

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