Radiation Therapy for Prostate Cancer Flashcards
HISTORICAL PERSPECTIVE AND TECHNOLOGICAL ADVANCES. The first documented radiotherapeutic approach to treatment of
prostate cancer was by Pasteau and Degrais in 1911, who described using an intraurethral ___ source, with modifications of this approach later utilized by Young and Fronz in 1917.
However, a problem inherent to kilovoltage radiation is ____ , limiting the ability to deliver tumoricidal doses of radiation to the prostate because of unacceptable skin and normal tissue toxicity.
HISTORICAL PERSPECTIVE AND TECHNOLOGICAL ADVANCES. The first documented radiotherapeutic approach to treatment of
prostate cancer was by Pasteau and Degrais in 1911, who described using an intraurethral radium source, with modifications of this approach later utilized by Young and Fronz in 1917.
However, a problem inherent to kilovoltage radiation is a high deposition of dose at the skin, limiting the ability to deliver tumoricidal doses of radiation to the prostate because of unacceptable skin and normal tissue toxicity.
High-Energy Linear Accelerators
Linear accelerators function by ___ (usually electrons) to high speeds using a series of oscillating electric potentials along a linear beamline. The electrons strike a target (____) that then produces ____ (x-rays). The photon beam can then be shaped using variable collimators or ____ within the machine before exiting to the patient (older units used custom-cut lead blocks). The physical property that permits the photon radiation generated from a linear accelerator to penetrate deeply and spare normal tissue is
As the energy of the beam increases, the beam penetrates deeper before exerting its cytotoxic effect. Whereas older orthovoltage (100 to 500 kilovolts) and cobalt-60 units (1.17 to 1.33 megavolts) deposited their maximum dose at approximately 1.25 cm below the skin surface, modern high-energy linear accelerators (6 to 15
megavolts) deliver the maximum dose of radiation at ____ below the skin surface.
High-Energy Linear Accelerators
Linear accelerators function by accelerating charged particles (usually electrons) to high speeds using a series of oscillating electric potentials along a linear beamline. The electrons strike a target (typically tungsten) that then produces photons (x-rays). The photon beam can then be shaped using variable collimators or tungsten “leaves” within the machine before exiting to the patient (older units used custom-cut lead blocks). The physical property that permits the photon radiation generated from a linear accelerator to penetrate deeply and spare normal tissue is . As the energy of the beam increases, the beam penetrates deeper before exerting its cytotoxic effect. Whereas older orthovoltage (100 to 500 kilovolts) and cobalt-60 units (1.17 to 1.33 megavolts) deposited their maximum dose at approximately 1.25 cm below the skin surface, modern high-energy linear accelerators (6 to 15
megavolts) deliver the maximum dose of radiation at 15 cm or more below the skin surface.
CT-Based Treatment Planning and Three-Dimensional Conformal Radiotherapy
Radiation oncologists became adept at designing radiation fields on the basis of ___. For the treatment of prostate cancer, the radiation portals were centered near the ___ and ___. The location of the prostate was often inferred indirectly by introducing a contrast-filled Foley catheter and rectal tube into the patient and obtaining ____ images. These techniques were employed as recently as the mid-1980s.
. This was a dramatic breakthrough in radiation treatment for prostate cancer, because it allowed the ability to design radiation beams to directly target the prostate and for the first time accurately calculate doses received by nearby organs such as the ___ and ___
Radiation penetration and dose deposited within tissues is generally a function of ____, which varies most significantly among bone, air, and soft tissues. The combination of widespread CT availability and computers with improved graphics and computational power significantly changed the field of radiation oncology by allowing better tissue delineation and advanced dose computation that accurately accounted for tissue inhomogeneities. With modern CT-based treatment planning, the treatment process is initiated by having the patient scanned with CT in the treatment position to be utilized for daily treatment, a procedure called ___. The imaging data are then transferred to a treatment-planning system which allows the radiation oncologist to delineate the target volume (i.e., the prostate) and relevant normal tissues (otherwise known as _____). The _____ determines and prescribes the dose of radiation to be delivered
CT-Based Treatment Planning and Three-Dimensional Conformal Radiotherapy
Radiation oncologists became adept at designing radiation fields on the basis of skeletal anatomy. For the treatment of prostate cancer, the radiation portals were centered near the pubic symphysis and femoral heads. The location of the prostate was often inferred indirectly by introducing a contrast-filled Foley catheter and rectal tube into the patient and obtaining orthogonal x-ray images. These techniques were employed as recently as the mid-1980s.
. This was a dramatic breakthrough in radiation treatment for prostate cancer, because it allowed the ability to design radiation beams to directly target the prostate and for the first time accurately calculate doses received by nearby organs such as the rectum and bladder.
Radiation penetration and dose deposited within tissues is generally a function of electron density, which varies most significantly among bone, air, and soft tissues. The combination of widespread CT availability and computers with improved graphics and computational power significantly changed the field of radiation oncology by allowing better tissue delineation and advanced dose computation that accurately accounted for tissue inhomogeneities. With modern CT-based treatment planning, the treatment process is initiated by having the patient scanned with CT in the treatment position to be utilized for daily treatment, a procedure called simulation. The imaging data are then transferred to a treatment-planning system which allows the radiation oncologist to delineate the target volume (i.e., the prostate) and relevant normal tissues (otherwise known as regions of interest, or ROIs). The radiation oncologist determines and prescribes the dose of radiation to be delivered
CT-Based Treatment Planning and Three-Dimensional Conformal Radiotherapy
Doses received by the delineated tissues/tumor can be represented graphically using a ___, which plots the dose received by varying volumes of the target and the normal tissues/organs. An example is ___.
CT-Based Treatment Planning and Three-Dimensional Conformal Radiotherapy
Doses received by the delineated tissues/tumor can be represented graphically using a dose-volume histogram (DVH), which plots the dose received by varying volumes of the target and the normal tissues/organs. An example is IMRT.
