Abstract
The purpose of this study was to compare the dosimetric properties of small field electron beams shaped by circular Cerrobend blocks and stainless steel tubular applicators. Percentage depth dose curves, beam profiles, and output factors of small‐size circular fields from 2 to 5 cm diameter, obtained either by tubular applicators and Cerrobend blocks, were measured for 6, 10, and 15 MeV electron beam energies. All measurements were performed using a PTW microDiamond 60019 premarket prototype. An overall similar behavior between the two collimating systems can be observed in terms of PDD and beam profiles. However, Cerrobend collimators produce a higher bremsstrahlung background under irradiation with high‐energy electrons. In such irradiation condition, larger output factors are observed for tubular applicators. Similar dosimetric properties are observed using circular Cerrobend blocks and stainless steel tubular applicators at lower beam energies. However, Cerrobend collimators allow the delivery of specific beam shapes, conformed to the target area. On the other hand, in high‐energy irradiation conditions, tubular applicators produce a lower bremsstrahlung contribution, leading to lower doses outside the target volume. In addition, the higher output factors observed at high energies for tubular applicators lead to reduced treatment times.PACS number: 87.53.Bn, 87.55.Qr, 87.56.Fc
Highlights
330 Di Venanzio et al.: Electron beams by Cerrobend and tubular applicators alloy that can be molded into various sizes and forms and placed at the end of standard electron beam applicators
The percentage depth dose curves (PDDs) curves measured for both the tubular applicators and Cerrobend apertures are reported in Fig. 1 for all the investigated field sizes, under irradiation with 6 MeV (Fig. 1(a)) and 15 MeV (Fig. 1(b)) electron beams
A shift towards the phantom surface of R100 and R50 can be noticed by decreasing the field size, which is definitively more evident for the higher energies as already reported in literature.[16]. This can be explained in terms of lack of lateral scatter equilibrium occurring in small fields, as discussed in Bagalà et al[9] In the case of 15 MeV, higher Dx values are measured for Cerrobend shielding blocks, indicating the presence of a higher bremsstrahlung component when such collimators are used
Summary
330 Di Venanzio et al.: Electron beams by Cerrobend and tubular applicators alloy that can be molded into various sizes and forms and placed at the end of standard electron beam applicators. The thickness of the Cerrobend block is usually chosen to reduce the dose under the block by 95%–98% of the open beam dose Such applicators are expected to affect output factors (OFs), percentage depth dose curves (PDDs), and the shape of beam profiles. The aim of this work is to compare the dosimetric properties of small circular fields shaped by home-made Cerrobend blocks and commercial tubular applicators in high-energy electron beams. To this purpose, a reliable tissue-equivalent detector is needed, characterized by a high spatial resolution capability.[8] A synthetic single crystal diamond diode (SCDD) was chosen for the present study, which was already demonstrated to be a suitable detector for small field sizes electron dosimetry.[9]
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