conformal 4ch3.pdf

CONFORMAL RADIOTHERAPY ❑Basic of conformal radiotherapy is that, in comparison with traditional dose delivery techniques, treatment outcomes will be improved by using special techniques that allow maximum target dose (improved tumor control probability) while maintaining an acceptable l...

CONFORMAL RADIOTHERAPY ❑Basic of conformal radiotherapy is that, in comparison with traditional dose delivery techniques, treatment outcomes will be improved by using special techniques that allow maximum target dose (improved tumor control probability) while maintaining an acceptable level of normal tissue complications. ❑Conformal radiotherapy conforms or shapes the prescription dose volume to the planning target volume (PTV) while at the same time keeping the dose to specified organs at risk below their tolerance dose. 32 M.Sc. Medical Physics Dr. Khalid I Hussein  CONFORMAL RADIOTHERAPY Target localization is achieved through: ❑Anatomical imaging such as: ❑Computerized tomography (CT). ❑Magnetic resonance imaging (MRI). ❑Single photon emission tomography (SPECT). ❑Ultrasound (US). ❑Functional imaging such as: ❑Positron emission tomography (PET). ❑Functional magnetic resonance imaging (fMRI). ❑Molecular imaging. 34 M.Sc. Medical Physics Dr. Khalid I Hussein  CONFORMAL RADIOTHERAPY Treatment planning process for 3-D CRT consists of 4 steps: ❑Acquisition of anatomic information in the form of transverse (axial) images. ❑Determination of the planning target volume (PTV) by the radiation oncologist by contouring the PTV on each individual axial image (segmentation process). ❑Design of radiation fields using the beam’s-eye-view option in the treatment planning software. ❑Optimization of the treatment plan through the design of optimal field sizes, beam directions, beam energies, etc. 35 M.Sc. Medical M.Sc. Medical Physics Physics Dr. Khalid Dr. Khalid II Hussein Hussein  CONFORMAL RADIOTHERAPY ❑Modern linacs are equipped with MLCs that incorporate from 20 to 60 pairs of narrow, closely tungsten leaves, each leaf projecting a typical width of between 5 and 10 mm at the linac isocentre. ❑MLCs projecting leaf widths less than 5 mm at the isocentre are referred to as microMLCs. They are used for: ❑Shaping irregular fields of less than 10 cm in maximal field dimension, such as head and neck fields. ❑Irregular fields with less than 3 cm in largest dimension that are used in radiosurgery. 36 M.Sc. Medical Physics Dr. Khalid I Hussein