What is isodose distribution?
What is isodose distribution?
In order to represent volumetric or planar variations in absorbed dose, distributions are depicted by means of isodose curves, which are lines passing through points of equal dose. The curves are usually drawn at regular intervals of absorbed dose and may be expressed as a percentage of the dose at a reference point.
What does isodose mean?
Definition of isodose : of or relating to points or zones in a medium that receive equal doses of radiation.
What does an isodose chart represent?
An isodose curve (or contour) is a line of constant absorbed dose. The line is in a plane and, for single radi- ation beams, its value is usually related by a simple percentage value (e.g., 90 percent, 80 percent, etc.) to the peak absorbed dose (or the surface absorbed dose, for x rays below 400 kV) on the beam axis.
What is prescription isodose line?
We define the prescription isodose line, or PIDL, as the ratio of prescription dose and maximum dose, which is similar to other studies and Radiation Therapy Oncology Group (RTOG) protocols [13,25,27-28]. To quantify the dose falloff, gradient index (GI) was used [22].
Why does PDD increase with SSD?
The percentage depth dose (PDD) increases with SSD due to the effects of inverse square law. NO dependance on the SAD or SSD. and hν constant TMR decreases with increasing z. constant TMR increases with increasing hν.
What is penumbra in radiotherapy?
The region, near the edge of a radiation beam, where the dose changes rapidly according to the distance from the beam axis is known as the penumbra.
What are the two types of brachytherapy?
There are two main forms of brachytherapy – intracavitary treatment and interstitial treatment. With intracavitary treatment, the radioactive sources are put into a space near where the tumor is located, such as the cervix, the vagina or the windpipe.
What type of radiation is used in brachytherapy?
Brachytherapy is a form of radiation therapy where a sealed radioactive source is placed, inside, on or near the tumour. Brachy comes from the Greek word for short. It is often thought of as ‘internal radiation therapy’. These sources produce gamma-rays, which have the same effect on cancer cells as X-rays.
How is PDD measured?
PDDs were measured at 100 cm source-to-surface distance (SSD), for fields of size: 5 cm × 5 cm, 10 cm × 10 cm, 20 cm × 20 cm, 30 cm × 30 cm, and 40 cm × 40 cm. PDDs were measured at all available dose rates for 6 FFF and 10 FFF as PDD curves smoothing vary with dose rate.
What is PDD in radiation therapy?
In radiotherapy, a percentage depth dose curve (PDD) (sometimes percent depth dose curve) relates the absorbed dose deposited by a radiation beam into a medium as it varies with depth along the axis of the beam.
What affects penumbra?
The penumbral shape of these beams is caused by geometric penumbra and radiation penumbra; the former is affected by collimator position and focal spot size, the latter by energy and field size. This note reports measurements of penumbral width as collimator position, size and energy are varied.