A generic off-axis energy correction for linac photon beam dosimetry

• Published in: Medical physics (Lancaster) Vol. 25; no. 5; pp. 662 - 667
• Main Authors: Tailor, R. C., Tello, V. M., Schroy, C. B., Vossler, M., Hanson, W. F.
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-05-1998
• Subjects: 87.53.01; Accelerators; attenuation coefficient; beam quality; Clinical Protocols; dosimetry; Dosimetry/exposure assessment; Equipment Design; half‐value layer; Humans; linear accelerators; off‐axis; Particle Accelerators; Phantoms, Imaging; photon dosimetry; Photons; Physicists; Polystyrenes; radiation therapy; Radiation therapy equipment; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; tissue‐air‐ratio; photon dosimetry; half-value layer; attenuation coefficient; tissue-air-ratio; beam quality; 87.53.01; off-axis
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.598249

Cooperative clinical trial group protocols frequently require off-axis point dose calculations. The Radiological Physics Center uses the calculative technique developed by Hanson et al. [Med. Phys. 7, 145–146 (1980); 7, 147–150 (1980)] to verify these calculations. In order to correct for off-axis energy changes, this technique requires off-axis half-value layer data, HVL, as a function of off-axis ray angle for the specific beam. This paper presents a formulism based on HVL measurements on a limited number of therapy beams, which allows the calculation of an off-axis energy-correction factor for any clinical photon beam created by a linear accelerator using conventional flattening filters.