Comparison between small radiation therapy electron beams collimated by Cerrobend and tubular applicators

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

Comments on the TRS‐483 protocol on small field dosimetry

“…Similar discrepancies [ Fig. 1(b)] exist between recommended microDiamond k f clin ;f msr Q clin ;Q msr factors for CyberKnife compared to the data from a large collaborative study involving [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] institutions and several microDiamonds. [5][6][7] The error bars are shown if such data exist in the publications.…”

“…11,12 Due to slight modifications of the detector housing between prototype and final product, it is not clear if the prototypes show exactly identical small field correction factors compared to the final commercial product. [13][14][15][16][17][18][19] Figure 1 data can be divided into two groups, one showing k f clin ;f msr Q clin ;Q msr <1.0 and the other >1.0. This behavior is related to the density perturbation effect and volume averaging of microdetector response that have been described in detail in the literatures.…”

Dose calculation of different eye substructures using a realistic eye model when treating ocular tumors with electron therapy

“…The shield had a hole that was substantially aligned with the tumor area and provided a 1-mm margin around the target volume. This shield is made of Cerrobend, which is an alloy consisting of bismuth (50%), lead (26.7%), tin (13.3%) and cadmium (10%), with a melting temperature of approximately 70 • C and a density of about 9.4 g cm −3 at 20 • C (Di Venanzio et al, 2015). Using Cerrobend blocks is common in radiation therapy because of its flexibility, also allowing the dose delivery by a more complex specific beam (Taherkhani et al, 2010;Farajollahi et al, 2015).…”

“…Using Cerrobend blocks is common in radiation therapy because of its flexibility, also allowing the dose delivery by a more complex specific beam (Taherkhani et al, 2010;Farajollahi et al, 2015). The dosimetric properties of small-field electron beams shaped by Cerrobend blocks were previously investigated by Di Venanzio et al (2015).…”

Monte Carlo Simulation of the Gamma-Ray Transmissions for the newly Designed Shielding Blocks used in Radiotherapy

“…Therefore, these blocks are widely used in radiation oncology centres to protect normal tissues and critical organs (Taherkhani et al, 2010). Cerrobend block thickness is commonly chosen to reduce the dose under the block by 95-98% of the open beam dose (Farajollahi et al, 2015;Di Venanzio et al, 2015). In other words, the acceptable level of the radiation transmission for Cerrobend blocks is less than 5 percentages (Farajollahi et al, 2015).…”