Modification of the 4 MeV electron beam from a linear accelerator for irradiation of small superficial skin tumors

Abstract

Uniform dose distribution with steep lateral gradient within depth range of 0-0.5 cm is crucial to be able to treat small skin lesions. The standard nominal 4 MeV electron beam from Elekta Versa HD linear accelerator was modified with degrading filter to remove the lateral scatter from treatment head and minimize the penumbra. The energy degrading method was verified based on dosimetric properties and output factors (OFs) with comparison of four types of measurement methods. The properties of degraded 4 MeV electron beam and developed electron applicators seem optimal for treating small targets near the skin surface.

Early clinical experience with a degraded 4 MeV electron beam in radiotherapy of superficial basal cell carcinoma

“…The beam output factors (OF) were reduced significantly in modification as compared with the standard 10 cm × 10 cm 4 MeV open field (OF = 1.000) [12] . This resulted in quite a low dose rate and long delivery time, for instance 7 Gy dose at dose maximum took 10 min at 600 MU/min for the 30 mm collimator.…”

“…The inner diameters of the collimators were 2.5, 3, 4 and 5 cm. The modification of the electron beam has been described previously in more detail [12] .…”

The Measurement of the Surface Dose in Regular and Small Radiation Therapy Fields Using Cherenkov Imaging

“…In a given field, the dose on the surface central point of the phantom can be calculated by multiplying the corresponding surface dose OF by the dose on the same point in the reference field. 3,32 In this study, an open field with size of 10 × 10 cm 2 , a wedge field with size of 10 × 10 cm 2 and an electron field with size of 10 × 10 cm 2 were selected as reference fields for OF measurement in OPFs (including ROPFs and SPFs), RWPFs and REFs, respectively. The OF calculation region of surface dose was defined as a central square subregion of 5 × 5mm 2 in area in Cherenkov or film images.…”

On the measurement of scaling factors in the RW3 plastic phantom during high energy electron beam dosimetry

“…The type of ionizing radiation selected for tumor irradiation depends on factors such as tumor location, size of the radiation eld (region to be covered by the ionizing radiation), treatment phase (main treatment or boost), treatment sessions, etc.. High energy electron beams are widely used for radiotherapy using different techniques such as external irradiation of super cial tumors, intraoperative radiotherapy (IORT) of the tumor bed after surgery in the operating theater, and total skin irradiation [7][8][9][10][11]. Although the use of electron beam for IORT purposes has been promoted in recent years, the most common application of electron beams is external radiotherapy of super cially distributed tumors [12,13]. In this regard, dedicated electron accelerators have been introduced that produce clinical electron beams in the energy range of 4 MeV to 24 MeV [14].…”