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Functional intercomparison of intraoperative radiotherapy equipment - Photon Radiosurgery System.

Armoogum KS, Parry JM, Souliman SK, Sutton DG, Mackay CD - Radiat Oncol (2007)

Bottom Line: The average output level over a period of 30 minutes was found to be 99.12%.For three x-ray sources, the average difference between the calculated and actual treatment times was found to be 0.62% (n = 30).Most measurements were found to lie within the manufacturer's tolerances and an intercomparison of these checks suggests that the four x-ray sources have similar performance characteristics.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Medical Physics, Ninewells Hospital and Medical School, Tayside University Hospitals NHS Trust, Dundee, UK. kris.armoogum@nhs.net

ABSTRACT

Background: Intraoperative Radiotherapy (IORT) is a method by which a critical radiation dose is delivered to the tumour bed immediately after surgical excision. It is being investigated whether a single high dose of radiation will impart the same clinical benefit as a standard course of external beam therapy. Our centre has four Photon Radiosurgery Systems (PRS) currently used to irradiate breast and neurological sites.

Materials and methods: The PRS comprises an x-ray generator, control console, quality assurance tools and a mobile gantry. We investigated the dosimetric characteristics of each source and its performance stability over a period of time. We investigated half value layer, output diminution factor, internal radiation monitor (IRM) reproducibility and depth-doses in water. The half value layer was determined in air by the broad beam method, using high purity aluminium attenuators. To quantify beam hardening at clinical depths, solid water attenuators of 5 and 10 mm were placed between the x-ray probe and attenuators. The ion chamber current was monitored over 30 minutes to deduce an output diminution factor. IRM reproducibility was investigated under various exposures. Depth-dose curves in water were obtained at distances up to 35 mm from the probe.

Results: The mean energies for the beam attenuated by 5 and 10 mm of solid water were derived from ICRU Report 17 and found to be 18 and 24 keV. The average output level over a period of 30 minutes was found to be 99.12%. The average difference between the preset IRM limit and the total IRM count was less than 0.5%. For three x-ray sources, the average difference between the calculated and actual treatment times was found to be 0.62% (n = 30). The beam attenuation in water varied by approximately 1/r(3).

Conclusion: The x-ray sources are stable over time. Most measurements were found to lie within the manufacturer's tolerances and an intercomparison of these checks suggests that the four x-ray sources have similar performance characteristics.

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Output Diminution Factor. To determine the constancy of output from the x-ray sources, the ion chamber current was monitored over a period of 30 minutes equivalent to typical clinical treatment duration. A difference between the initial and final current readings was consistently observed and the mean reduction was 1.58%.
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Figure 5: Output Diminution Factor. To determine the constancy of output from the x-ray sources, the ion chamber current was monitored over a period of 30 minutes equivalent to typical clinical treatment duration. A difference between the initial and final current readings was consistently observed and the mean reduction was 1.58%.

Mentions: A plot of output versus elapsed time shows definite, reproducible output reduction as seen in figure 5. A difference between the initial and final current readings was consistently observed and the mean reduction was 1.58%, (range 0.54% – 2.22%). The average output level for all sources over a period of 30 minutes was found to be 99.12%, (range 97.78% – 100%). This reduction in output is small but for the purposes of dose accuracy, should be included in the dose calculation [14].


Functional intercomparison of intraoperative radiotherapy equipment - Photon Radiosurgery System.

Armoogum KS, Parry JM, Souliman SK, Sutton DG, Mackay CD - Radiat Oncol (2007)

Output Diminution Factor. To determine the constancy of output from the x-ray sources, the ion chamber current was monitored over a period of 30 minutes equivalent to typical clinical treatment duration. A difference between the initial and final current readings was consistently observed and the mean reduction was 1.58%.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1808461&req=5

Figure 5: Output Diminution Factor. To determine the constancy of output from the x-ray sources, the ion chamber current was monitored over a period of 30 minutes equivalent to typical clinical treatment duration. A difference between the initial and final current readings was consistently observed and the mean reduction was 1.58%.
Mentions: A plot of output versus elapsed time shows definite, reproducible output reduction as seen in figure 5. A difference between the initial and final current readings was consistently observed and the mean reduction was 1.58%, (range 0.54% – 2.22%). The average output level for all sources over a period of 30 minutes was found to be 99.12%, (range 97.78% – 100%). This reduction in output is small but for the purposes of dose accuracy, should be included in the dose calculation [14].

Bottom Line: The average output level over a period of 30 minutes was found to be 99.12%.For three x-ray sources, the average difference between the calculated and actual treatment times was found to be 0.62% (n = 30).Most measurements were found to lie within the manufacturer's tolerances and an intercomparison of these checks suggests that the four x-ray sources have similar performance characteristics.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Medical Physics, Ninewells Hospital and Medical School, Tayside University Hospitals NHS Trust, Dundee, UK. kris.armoogum@nhs.net

ABSTRACT

Background: Intraoperative Radiotherapy (IORT) is a method by which a critical radiation dose is delivered to the tumour bed immediately after surgical excision. It is being investigated whether a single high dose of radiation will impart the same clinical benefit as a standard course of external beam therapy. Our centre has four Photon Radiosurgery Systems (PRS) currently used to irradiate breast and neurological sites.

Materials and methods: The PRS comprises an x-ray generator, control console, quality assurance tools and a mobile gantry. We investigated the dosimetric characteristics of each source and its performance stability over a period of time. We investigated half value layer, output diminution factor, internal radiation monitor (IRM) reproducibility and depth-doses in water. The half value layer was determined in air by the broad beam method, using high purity aluminium attenuators. To quantify beam hardening at clinical depths, solid water attenuators of 5 and 10 mm were placed between the x-ray probe and attenuators. The ion chamber current was monitored over 30 minutes to deduce an output diminution factor. IRM reproducibility was investigated under various exposures. Depth-dose curves in water were obtained at distances up to 35 mm from the probe.

Results: The mean energies for the beam attenuated by 5 and 10 mm of solid water were derived from ICRU Report 17 and found to be 18 and 24 keV. The average output level over a period of 30 minutes was found to be 99.12%. The average difference between the preset IRM limit and the total IRM count was less than 0.5%. For three x-ray sources, the average difference between the calculated and actual treatment times was found to be 0.62% (n = 30). The beam attenuation in water varied by approximately 1/r(3).

Conclusion: The x-ray sources are stable over time. Most measurements were found to lie within the manufacturer's tolerances and an intercomparison of these checks suggests that the four x-ray sources have similar performance characteristics.

Show MeSH
Related in: MedlinePlus