3. Introduction Intensity modulated radiation therapy (IMRT) is the product of advances in the RT technology. Aims to deliver radiation more precisely to the tumor while relatively limiting dose to the surrounding normal tissues. The purpose of this presentation is to discuss the new concept of IMRT, its physical aspect, its applications and comparison with other RT methods.
4. Literature Review 1950âsï the medical linear accelerator was developed and marketed to treat cancer. 1980âsï the 3D-Conformal Radiotherapy (3D-CRT) was introduced. 3D-CRTï based on 3D dose planning system. Conform the shape of the radiation beam to that of the tumor. Problem: Cannot conform well to 3D objects due to the uniformity of beam strength. ï»30% of tumors exhibit concave featuresï difficult conventional ConfornL RT.
5. Literature Review 1960âsï IMRT was first conceptualized 1994ï the 1st commercial IMRT delivery unit was introduced. IMRTï An advanced form of 3D-CRT. Based on linear accelerator(L.A.) where the radiation intensity could be modulated during the treatment. The field is geometrically shaped by MLCâs. The intensity is varied pixel-by-pixel within the shaped field.
6. Figure: differences between (a) conventional radiotherapy, (b) conformal radiotherapy (CFRT) without intensity-modulation and (c) CFRT with intensity modulation (IMRT).
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8. Physical Aspect IMRT combines two advanced concepts to deliver 3D CRT: Inverse treatment planning with optimization by computer computer-controlled intensity modulation of the radiation beam during treatment
9. Treatment planning Based on âInverse planningâ Initially, a CT scan is performed on the affected region. A radiation oncologist defines the PTV Enters the plan criteria: max dose, mini dose, desired -limiting dose(for critical structures) and a dose-volume histogram Then, an optimisation program is run to find the treatment plan which best matches all the input criteria.
11. Dose volume histogram DVH is to summarize 3D dose distributions in a graphical 2D format
12. Treatment planning Inverse planning methods are divided into: Analytic methods Iterative methods Many computer programs use both methods to achieve a beam arrangement.
13. Analytic methods: It a mathematical techniques in which the TV dose distribution depends on the point dose intensity.
14. Iterative methods: Itis a manual technique and the beamlets depends on the cost function that is the energy dose for each point in the TV.
17. MLCâs L.A. must be equipped with computer-controlled MLCâs MLCâs consists of up to 120 individually adjusted metal leaves. The leaves move in & out contouring the radiation beam to the shape of the tumor & block out unwanted radiation.
19. Multi segmented static fields Also called, step-and-shoot or stop-and-shoot The patient is treated by multiple fields MLC divides each field into a set of subfields irradiated with uniform beam intensity levels. Delivered in an arrangement one at a time in sequence without operator intervention. The L.A is turned off while the leaves move to create the next subfield.
20. Dynamic Delivery Shift during delivery The radiation is âonâ all the time, even when the leaves are moving from one static subfield to the next.
21. Intensity modulated arc therapy Similar to step-and-shoot in that each field (positioned along the arc) is subdivided into subfields. However, the MLC moves dynamically to shape each subfield while the gantry is rotating Beam is on all the time. An alternative to tomotherapy
22. IMRT plan to treat tumor & avoid critical structures
23. Image showing TV in red and spinal cord in blue Map of intensities calculated by inverse planning software for the beam shown on the LT.
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25. Some Application of IMRT 1. Brain Tumors: IMRT can treat Intracranial tumors (benign & malignant). large, irregular, and solitary, or smaller & multiple Brain lesions. IMRT limit the dose to surrounding normal tissues; optic nerve, chiasm, lens, & brainstem. Â Brain IMRT
26. Some Application of IMRT 2. Head and Neck Cancer: Many of the technique issues for brain tumors also apply to head and neck ca. Limiting dose to the parotid gland to prevent xerostomia, or permanent dry mouth that occurs with typical head and neck radiotherapy. Head & neck IMRT
27. Some Application of IMRT 3. Prostate Cancer: RT has been a mainstay of localized prostate ca therapy for several decades. Higher doses to the prostate and better shielding of the rectum and bladder to minimize morbidity. Prostate IMRT
28. Some Application of IMRT 4. Breast cancer: IMRT is the better treatment. Gives more even dose to the breast with fewer hot spots & less dosing to normal tissues (lung & heart). Common SE of radiation, like swelling, breast heaviness and sunburn-like changes, can be reduced with IMRT.
32. Discussion IMRT & IGRT Image-guided RT is by far the most advanced form of RT today. To see the location of the tumor during the delivery treatment sessions. In IGRT, Cone Beam CT is taken just before the treatment deliveryï aligned with the previous planning CT imageï appropriate corrections are made online.  IMRT improves the radiation delivery precision IGRT improves accuracy e.g. of IGRT, CYBERKNIFE, TOMOTHERAPY
33. Conclusion Both theoretical and clinical data have shown the benefits of IMRT Tumor dose esclation and critical organ sparing would not be a problem IMRT holds promise in radiation oncology in the new century More clinical data are needed to confirm the potential promise.
34. A smiling face demonstrating how radiation can be deposited in almost any pattern.
