Dosimetric investigation of dual energy photon beams with assymmetric collimator jaws

• Authors: C. Varatharaj , M. Ravikumar , Sanjay Supe , S. Sathiyan , K. Ganesh , T. Arunkumar
• Languages of publication: EN

Abstracts

EN

Many modern linear accelerators are equipped with asymmetric collimators or jaws that can be moved independently. Asymmetric jaws have got many clinical applications in radiation therapy. In the present study, the dosimetric characteristics of asymmetric collimators from our linear accelerator with 6 and 18 MV X-rays were carried out. The field size factors (FSF) and half value layer (HVL) were measured in a water phantom using 0.6 cc Farmer chamber for symmetric and asymmetric fields for both 6 and 18 MV X-rays. Measurements of beam penumbra, percentage depth dose (PDD), cross beam profiles and calculated isodose curves were measured by RFA 300 for both asymmetric and symmetric fields. The FSF were found to agree with in 3% for symmetric and asymmetric fields. The HVL in water was found to be 15.8 cm and 14.4 cm for 6 MV photons and 26 cm and 22.9 cm for 18 MV photons at the central axis and at 20 cm off the central axis. At 30 cm depth the percentage depth dose for symmetric and asymmetric fields were found to differ as high as 6% for 6 MV and 4% for 18 MV fields. No observable difference in penumbra was noticed for symmetric and asymmetric fields of same dimensions. The constrictions of isodose curves at the edge nearer to central axis were noticed for asymmetrically placed fields. The observed differences could be due to the passage of primary beam through differential thickness of the flattening filter which alters the beam quality.

Keywords

EN

asymmetric field; half value layer; field size factor; percentage depth dose; beam penumbra

• Publisher: Versita
• Journal: Polish Journal of Medical Physics And Engineering
• Year: 2008
• Volume: 14
• Issue: 1
• Pages: 33-46

Dates

published

1 - 1 - 2008

online

29 - 12 - 2008

Contributors

author

C. Varatharaj

• Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, 560 029, Karnataka, India

author

M. Ravikumar

• Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, 560 029, Karnataka, India

author

Sanjay Supe

• Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, 560 029, Karnataka, India

author

S. Sathiyan

• Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, 560 029, Karnataka, India

author

K. Ganesh

• Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, 560 029, Karnataka, India

author

T. Arunkumar

• Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, 560 029, Karnataka, India

References

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• Palta JR, Ayyankar KM, Suntharalingam N. Dosimetric characteristics of a 6 MV photon beam from a linear accelerator with asymmetric collimator jaws. Int J Radiat Oncol Biol Phys. 1988; 14: 383-387.
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Identifiers

DOI

10.2478/v10013-008-0004-2