Determination of an Effective Wedge Angle by Combination of Two Arbitrary Universal Wedge Fields in Radiation Therapy of Cancer Patients with Megavoltage Photon Beams

Title & Authors
Determination of an Effective Wedge Angle by Combination of Two Arbitrary Universal Wedge Fields in Radiation Therapy of Cancer Patients with Megavoltage Photon Beams

Abstract
Background: Wedge filters are commonly used in radiation oncology for eliminating hot spots and creating a uniform dose distribution in optimizing isodose curves in the target volume for clinical aspects. These are some limited standard physical wedges ($\small{15^{\circ}}$, $\small{30^{\circ}}$, $\small{45^{\circ}}$, $\small{60^{\circ}}$),or creating an arbitrary wedge angle, like motorized wedge or dynamic wedge,$\small{{\ldots}}$ The new formulation is presented by the combination of wedge fields for determining an arbitrary effective wedge angles. The isodose curves also are derived for these wedges. Materials and Methods: we performed the dosimetry of Varian Clinac 2100C/D with Scanditronix Wellhofer water blue phantom, CU500E, OmniPro - Accept software and 0.13cc ionization chamber for 6Mv photon beam in depth of 10cm (reference depth) for universal physical wedges ($\small{15^{\circ}}$, $\small{30^{\circ}}$, $\small{45^{\circ}}$, and $\small{60^{\circ}}$) and reference field $\small{10.10cm^2}$. By combining the isodose curve standard wedge fields with compatible weighting dose for each field, the effective isodose curve is calculated for any wedge angle. Results: The relation between a given effective wedge angle and the weighting of each combining wedge fields was derived. A good agreement was found between the measured and calculated wedge angles and the maximum deviation did not exceed $\small{3^{\circ}}$. The difference between the measured and calculated data decreased when the combined wedge angles were closer. The results are in agreement with the motorized single wedge appliance in the literature. Conclusions: This technique showed that the effective wedge angle that is obtained from this method is adequate for clinical applications and the motorized wedge formalism is a special case of this consideration.
Keywords
Universal physical wedge;profile;megavoltage photon beam;radiation therapy;
Language
English
Cited by
References
1.
Abrath FG, Purdy JA (1980). Wedge design and dosimetry for 25-MV x rays. Radiology, 136, 757-62.

2.
Bajusova A, Kralik G, Miglierini M (2010). Means of Intensity Modulation of Radiation in External Radiotherapy. Nuclear Physics Methods And Accelerators In Biology And Medicine: Fifth International Summer School on Nuclear Physics Methods and Accelerators in Biology and Medicine. AIP Publishing, 195-7.

3.
Bentel G, Nelson C, Noell K (1982). Treatment planning &. dose calculation in radiation.

4.
Khan FM, Gibbons JP 2014. Khan's the Physics of Radiation Therapy, Lippincott Williams & Wilkins.

5.
Kinhikar R, Sharma S, Upreti R, et al (2007a). Commissioning of motorized wedge for the first Equinox-80 telecobalt unit and implementation in the Eclipse 3D treatment planning system. Australasian Physics & Engineering Sciences in Medicine, 30, 127-34.

6.
Kinhikar RA, Sharma S, Upreti R, et al (2007b). Characterizing and configuring motorized wedge for a new generation telecobalt machine in a treatment planning system. Journal of medical physics/Association of Medical Physicists of India, 32, 29.

7.
Kumar R, Kar D, Sharma S, et al (2012). Design, implementation and validation of a motorized wedge filter for a telecobalt machine (Bhabhatron-II). Physica Medica, 28, 54-60.

8.
Petti PL, Siddon RL (1985). Effective wedge angles with a universal wedge. Physics in medicine and biology, 30, 985.

9.
Sahani G, Kumar M, Sharma PD, et al (2009). Compliance of Bhabhatron-II telecobalt unit with IEC standard-Radiation safety. Journal of Applied Clinical Medical Physics, 10.

10.
Saminathan S, Manickam R, Supe SS (2012). Comparison of dosimetric characteristics of physical and enhanced dynamic wedges. Reports of Practical Oncology & Radiotherapy, 17, 4-12.

11.
Weston S, Thompson R, Morgan A (2014). The matching of wedge transmission factors across six multi-energy linear accelerators. The British journal of radiology.

12.
Zhu J (2005). Generation of wedge-shaped dose distributions through dynamic multileaf collimator dose delivery. Journal of Applied Clinical Medical Physics, 6.