answer that quatuions that raleted to Linac Calibration: Absolute Dosimetry 1- D

Question

answer that quatuions that raleted to Linac Calibration: Absolute Dosimetry

1- Describe the concept of absolute linac calibration.

2-What is the purpose of the TPR check and how does it serve this purpose?

3- Should we have adjusted the machine, and why or why not?

here some information >>>

Pre-Lab 5: Linac Calibration - Absolute Dosimetry Readings: Khan Sec 8.3, Sec 8.5 5th edition: pp 99-102, pp 106-113 4th edition: pp 97-101, pp 113-121 (Sec 8.6) Terminology/Background: TPR Tissue-Phantom Ratio ratio of the dose at a given point in a phantom to the dose at the same point at a fixed reference depth; F factor roentgen-to-rad conversion factor: converts exposure to dose, is a function of material composition and photon energy STP Standard Temperature and Pressure -22°C, 101.33 kPa Machines are constantly monitored for their output. At MGH, checks are done 1. Daily: the therapists perform checks on the output of the machine every 2. Monthly: a physicist is assigned to each machine. This physicist performs 3. Annually: The physicist assigned to each machine also performs a more morning before treating any patients mechanical and radiation checks on the machine once a month. robust set of checks on their machine once every year.

Explanation / Answer

1. The main aim of absolute linac callibration in photon and electron beams is to evaluate the output beam energy of the beam with best accuracy and less error within the error percentage of a few percentage by a series of chain reactions during callibration.

2. TPR is known as Tissue phantom ratio whose main objective is giving accurate measurements for high energy photon beams when there is sufficient dose of buildup in water, and it is measured by calculating the isocenter of the submerged beam in the water.

3. Yes we have to measure the machine in order to change the isocentric point of the beam. By doing this the part of beam submerged in water will change and thus there will occur a change in the tissue phantom ratio of the photon or electron beam.

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