Review of electron beam therapy physics

Abstract

For over 50 years, electron beams have been an important modality for providing an accurate dose of radiation to superficial cancers and disease and for limiting the dose to underlying normal tissues and structures. This review looks at many of the important contributions of physics and dosimetry to the development and utilization of electron beam therapy, including electron treatment machines, dose specification and calibration, dose measurement, electron transport calculations, treatment and treatment-planning tools, and clinical utilization, including special procedures. Also, future changes in the practice of electron therapy resulting from challenges to its utilization and from potential future technology are discussed.

Evaluation of lens dose from anterior electron beams: comparison of Pinnacle and Gafchromic EBT3 film

“…The second effect is due to the increased lateral scatter of the electron beam as the bolus thickness is increased. The increased width of the angular distribution of the electron beam at the level of the lead shielding with increasing bolus thickness results in a larger proportion of electrons deflected laterally, directly increasing the dose deposited at depth beneath the lead shielding (1) . Thus, for each electron energy, as the bolus thickness increases, the dose gradient at the lead edge becomes less steep due to increased lateral scattering of the electrons at increased depths.…”

“…The penumbra of electron beams, however, broadens with depth due to increased multiple Coulomb scattering, (1) leading to a bulging out of the low‐dose region. This bulging of the low isodose lines can pose a problem for radiosensitive organs at risk (OARs) directly adjacent to targets regardless of whether or not they are within the direct field.…”

Utilization of a 3D printer to fabricate boluses used for electron therapy of skin lesions of the eye canthi

“…Such a bolus increases skin dose, homogenizes dose heterogeneity resulting from the irregular skin surface, and protects distal tissues by conforming dose line to the distal PTV surface 9. Similarly, bolus electron conformal therapy (ECT) has been shown clinically useful for many clinical sites10 such as chest wall irradiation (postmastectomy irradiation),11, 12, 13 head and neck radiotherapy,14, 15, 16, 17, 18, 19, 20, 21, 22, 23 paraspinal muscle region,24 and extremities 25…”

“…One of the methods of bolus production involves hand molding on the patient — a method vitiated by the very fact that pressing individual layers of paraffin or polymer bolus directly on the patient's skin will affect the shape of the bolus and dose distribution in relation to the reference model (planned in TPS). Another methods of bolus production is using milled electron bolus technology, being fabricated using computer‐controlled milling machines 9, 13, 22, 24. Although milled bolus ECT technology is the only commercially available design and fabrication technology (decimal LLC, Sanford, FL, USA), its availability is largely limited to the United States of America.…”

“…Recently, there has been increased interest in investigating three‐dimensional (3D) printing technologies to produce patient‐specific objects for use in a medical context, including boluses in radiotherapy 9, 10, 11, 12, 13, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31. Although 3D printing technology offers a viable technology for small boluses designed by individual clinics, its clinical use in radiotherapy is relatively recent.…”