Radiosurgery : Dept. of Neurosurgery
Robert Ayer, MD Radiosurgery A Brief Introduction to
Basic Science and Modes of Delivery Outline : Outline Definitions
The Basic Science of Radiotherapy
Types of Radiation
The effect of Radiation on tissues
Modes of Delivery
HEAVY PARTICLE (Proton)
CYBER KNIFE Stereotactic Radiosurgery : Stereotactic Radiosurgery “Stereo” Greek: Solid or 3 dimensional
“tact” Latin: to touch
Stereotactic: 3 dimensional arrangement to touch
Technique of delivering high dose radiation to a specific target while delivering minimal dose to surrounding tissues
Radiation as a treatment for disease is based on the concept that such energy has the capability to alter cellular function, primarily by interfering with cellular reproduction. Radiation results in the formation of free radicals as electrons are freed from their atoms, the presence of which results in disruption of normal cellular activity. Hallmarks of Radiosurgery : Hallmarks of Radiosurgery High Precision
High degree of reproducible spatial correlation of the target and the radiation source
Delivery of the intended dose within 1mm of the planned position
Rapid fall off of radiation dose at the periphery of the target
Minimal dose to surrounding normal tissues
High dose conformity Semantics of Radiation Therapy : Semantics of Radiation Therapy Slide 6: Radiation therapy / Radiotherapy / XRT
Stereotactic Radiation Therapy (SRT)
Intensity-Modulated Radiation Therapy (IMRT)
Image Guided Radiotherapy / Radiosurgery
Radiosurgery / Stereotactic Radiosurgery (SRS)
Fractionated Radiosurgery Semantics of Radiation Therapy Slide 7: Isodose line
All the points with the same dose connected in a line. The maximum dose is usually observed in the center of the target, stiff dose fall-offs near the target boundary. RADIOBIOLOGY OF RADIOSURGERY : RADIOBIOLOGY OF RADIOSURGERY ABSORBED DOSE AND UNITS OF RADIATION : ABSORBED DOSE AND UNITS OF RADIATION The amount of energy absorbed per unit mass is the absorbed radiation dose.
Historically, the term rad was used as the unit of absorbed radiation dose.1
The International System of Units (SI) now identifies the gray (Gy) as the unit of absorbed dose; it is equivalent to 1 joule per kilogram.2 One hundred centigrays (cGy) or 100 rad is equivalent to 1 Gy. Historical Considerations of Radiotherapy and Radiosurgery : Historical Considerations of Radiotherapy and Radiosurgery The first therapeutic use of radiation in medicine began in the 1920s using low-voltage machines.
Over the following decades, steady advances in the voltage (first orthovoltage, then megavoltage) of x-ray machines allowed the treatment of lesions at greater depths from the body surface.
By the 1970s, fractionated radiotherapy delivered by medical linear accelerators (linacs) was a standard adjunctive treatment for a wide range of neoplasms, including those in the brain and spinal cord. Historical Landmarks in Radiation Therapy : Historical Landmarks in Radiation Therapy 1895: Wilhelm Conrad Röntgen in Würzburg (Germany) discovers X-rays.
1895: First therapeutic attempt to treat a local relapse of breast carcinoma by Emil Grubbe (Chicago) After noting pealing of his hands exposed to x-rays, a medical student in Chicago named Emil Grubbe convinced one of his professors to allow him to irradiate a cancer patient, a woman named Rose Lee, suffering from locally advanced breast cancer. No longer responding to medical treatments, Ms. Lee benefited greatly from Grubbe’s intervention, demonstrating the potential value of x-ray treatments. Historical Landmarks in Radiation Therapy : Historical Landmarks in Radiation Therapy 1896: Irradiation of a skin tumour in a 4-year-old by Léopold Freund (Vienna - Austria)
Early radiation (Xray producing machines) were low-voltage, and the radiation could only penetrate the most superficial layers of the skin.
1951: Leksell originated the concept of stereotactic radiosurgery and described his basic technique
orthovoltage x-ray tube around the stereotactic instrument
patients treated with this device had been diagnosed with trigeminal neuralgia. Historical Landmarks in Radiation Therapy : Historical Landmarks in Radiation Therapy 1952: First linear accelerator (LINAC) was developed by Henry S. Kaplan in Stanford - California) 1960:
These megavoltage machines were capable of producing high energy, deeply penetrating beams, allowing for the very first time treatment of tumors deep inside the body without excessive damage to the overlying skin and other normal tissues.
The first patient treated using this machine was a child with retinoblastoma (a cancer of the eye). Treatment was highly successful for more than 40 years later, this patient remained free of disease with good vision. Historical Landmarks in RadiosurgeryRefining sources and techniques : Historical Landmarks in RadiosurgeryRefining sources and techniques Historical Landmarks in RadiosurgeryRefining sources and techniques : Historical Landmarks in RadiosurgeryRefining sources and techniques Historical Landmarks in RadiosurgeryImproved technique, image guidance, framelss radiosurgery, and Stereotactic body radiotherapy (SBRT) : Historical Landmarks in RadiosurgeryImproved technique, image guidance, framelss radiosurgery, and Stereotactic body radiotherapy (SBRT) Basic Science of Radiotherapy : Basic Science of Radiotherapy Radiotherapy uses ionizing radiation
which means that its energy is sufficient to remove an electron from the outer shell of an atom (>124 electron volts).1
When this occurs, an atom becomes more reactive and hence more apt to interact with neighboring atoms and molecules.
Water is the most commonly ionized molecule.
DNA is the critical cellular target of radiation. RADIOBIOLOGY OF CONVENTIONAL FRACTIONATED RADIOTHERAPY : RADIOBIOLOGY OF CONVENTIONAL FRACTIONATED RADIOTHERAPY Slide 19: 4 R’s of Radiation Biology Repair of cellular damage
Reoxygenation of the tumor
Redistribution within the cell cycle
Repopulation of cells Slide 20: Repair Sublethal injury – cells exposed to sparse ionization fields, can be repaired
Most tissue repair in 3 hours, up to 24 hours
Allows repair of injured normal tissue; therapeutic advantage over tumor cells Reoxygenation : Reoxygenation Hypoxic cells require more radiation to kill
Hypoxic tumor areas
Temporary vessel constriction from mass
Outgrow blood supply, capillary collapse
Tumor shrinkage decreases hypoxic areas
Hypoxic cell radiosensitizers, selective chemo Redistribution : Redistribution Cells have different radiation sensitivities in different parts of the cell cycle
Highest radiation sensitivity is in early S and late G2/M phase of the cell cycle RADIOBIOLOGY OF RADIOSURGERY : RADIOBIOLOGY OF RADIOSURGERY In this modality the therapeutic advantage is achieved by depositing more radiation dose in the tumor than in the normal tissue.
A system of three-dimensional fiducials is attached to the head ring during computed tomography acquisition, providing accurate spatial identification of each pixel within the image set. In essence, each pixel becomes a mathematical coordinate in reference to the head ring. Biological Manipulation in Radiosurgery : Biological Manipulation in Radiosurgery Basic Physics : Basic Physics Radiotherapy can be divided into
Electromagnetic radiation that behaves as both a particle and wave
result either when electrons shift to lower atomic orbits or when fast-moving electrons are made to collide with a target
most common energy range used for brain tumors is 4 to 6 MeV
Gamma rays originate from inside a nucleus, and the energy of gamma rays produced by various radioisotopes, such as cobalt 60
Energetic particle beams
rapidly moving bits of matter with known charge and mass
The characteristic Bragg peak, which describes a very narrow tissue width over which most proton energy is dissipated, is responsible for the interest in and recent enthusiasm for proton beam radiotherapy
protons Basic Physics : Basic Physics The interaction of radiation beams with matter varies, depending on the type of beam, the energy, the atomic number, and the density of the material the beam is impacting.
Compton effect Basic Physics : Basic Physics Depth Dose Curves for Various Types of Radiation. Techniques of RadiosurgeryLinac Radiosurgery : Techniques of RadiosurgeryLinac Radiosurgery It was the adaptation of linear accelerators (linacs) to SRS that provided the impetus for the performance of SRS on a large scale.
The machines available in the 1970s did not offer sufficient stability and precision (<4 mm) for SRS.
The pioneering efforts by Betti in South America,2 Columbo in Italy,3 and Winston, Lutz, and Saunders4,5 at the Brigham and Women's Hospital in Boston in the early 1980s culminated in the techniques and methods that allowed linacs to be converted for use in precise, high-dose SRS.6 History of LINAC for Radiosurgery & Radiotherapy : History of LINAC for Radiosurgery & Radiotherapy Linear accelerators are the standard machine used to deliver radiation therapy treatments
Linear accelerators convert electricity into radiation
Terms: gantry, collimator History of LINAC Radiosurgery : History of LINAC Radiosurgery Linear accelerators were available during Leksell’s time, however they lacked accuracy
Betti, Derechinsky, and Colombo were the first to apply linear accelerator technology to radiosurgery in 1984
Winston and Lutz modified their LINAC in 1987 to treat neurosurgical patients (Boston)
Initial problem with this technique was a high degree of error in targeting, complicated dose planning and dose delivery How LINAC Radiosurgery Works : How LINAC Radiosurgery Works The gantry of the LINAC rotates around the patient, producing an arc of radiation focused on the target.
The couch in which the patient rests is then rotated in the horizontal plane, and another arc is performed. Slide 32: Current devices using linear accelerator sources include:
Novalis (BrainLab, Helmstetten, Germany)
Peacock (Nomos, Cranberry, PA)
X-Knife (Radionics, Burlington, MA)
Trilogy (Varian Medical Systems, Palo Alto, CA)
CyberKnife (Accuray, Sunnyvale, CA) Techniques of RadiosurgeryGamma Knife : Techniques of RadiosurgeryGamma Knife Techniques of RadiosurgeryGamma Knife : Techniques of RadiosurgeryGamma Knife Gamma Knife 4C Techniques of RadiosurgeryGamma Knife : Techniques of RadiosurgeryGamma Knife Perfexion Techniques of RadiosurgeryGamma Knife : Techniques of RadiosurgeryGamma Knife Techniques of RadiosurgeryProton Beam : Techniques of RadiosurgeryProton Beam Proton beam irradiation has played a central role since the earliest conceptualization and practice of radiosurgery.
The medical use of protons for focal irradiation of tissues was first proposed by Robert Wilson of the Research Laboratory of Physics, Harvard University, in 1947.1
An early problem was the inability to control the beam's depth of penetration in tissue precisely to take advantage of the region of highest energy release at the Bragg peak. Techniques of RadiosurgeryProton Beam : Techniques of RadiosurgeryProton Beam Techniques of RadiosurgeryProton Beam : Techniques of RadiosurgeryProton Beam Techniques of RadiosurgeryProton Beam : Techniques of RadiosurgeryProton Beam Techniques of RadiosurgeryProton Beam : Techniques of RadiosurgeryProton Beam Techniques of RadiosurgeryProton Beam : Techniques of RadiosurgeryProton Beam Techniques of RadiosurgeryCyberknife : Techniques of RadiosurgeryCyberknife Techniques of RadiosurgeryCyberknife : Techniques of RadiosurgeryCyberknife Slide 45: Intensity-Modulated Radiation Therapy (IMRT) : Advanced type of high-precision radiation that is the next generation of 3-Dimensional Conformal Radiotherapy (3DCRT)
The intensity of the radiation can be changed during treatment to spare more adjoining normal tissue than is spared during conventional radiation therapy. TomoTherapy (or Helical TomoTherapy) - is a form of CT Guided IMRT