A simulation study on using 252Cf for the treatment of esophagus tumor in human phantom

Abstract

Due to the sensitivity of this tissue, and the potential for metastasis of its cancer as well, finding accurate methods to be employed for the treatment of esophagus tumors is of especial interest for the researchers. The present study deals with a Monte Carlo simulation of 252Cf neutron brachytherapy for treating these tumors using MCNPX (Version 2.6.0) code. The widely accepted AAPM TG-43 protocol has been used to benchmark the simulated source and to examine the accuracy of the modeling. The MIRD human phantom has been used for dose evaluation in the mentioned tumor and in the surrounding normal tissues as well. To decrease the dose delivered to the healthy tissue, using appropriate shields has been proposed. Through dosimetric calculations for several candidates, Pt-Ir 10% with a thickness of 1 cm has been selected as the optimized shield. The depth-dose results as well as the isodose curves corresponding to the presence of the shielded 252Cf neutron source in the center of the simulated tumor offer this source as an appropriate candidate to be used for the treatment of the esophagus tumors and sparing normal tissues. For a suggested clinical condition of positioning the source inside the esophagus, the damage to the first depth in spine can be avoided by managing the treatment time.

Microdosimetry-based investigation of biological effectiveness of 252Cf brachytherapy source: TOPAS Monte Carlo study

“…Note that the RBE and ̅ Q are sensitive to neutron energy and greater than unity whereas for photons, value of these parameters is unity, independent of photon energy (Karimi-Shahri et al 2021). Rasouli et al (2020) demonstrated that the contribution of neutrons to the total dose is maximum and the equivalent gamma dose is negligible when compared to those of neutrons. The above findings showed that in terms of RBE-weighted dose or equivalent gamma dose, relative contribution from neutrons is maximum as compared to photons.…”

“…Hence, the present study considers only the neutron components of 252 Cf. In the Monte Carlo calculations, the neutron energy spectrum of a 252 Cf source was modeled as a Watt fission spectrum (Brown et al 2002, Rasouli et al 2020, and it is given by the equation:…”

“…252 Cf is a suitable neutron brachytherapy source because of its long half-life (2.6 years) and relatively high neutron yield (Wierzbicki et al 1997). The advantages and limitations of using 252 Cf source for various brachytherapy applications were reported elsewhere (Maruyama and Beach 1986, Maruyama et al 1991, Wierzbicki et al 1994, Abd El-Hafez et al 1997, Rivard 2000, Ghassoun et al 2010, Lei et al 2011, Ghassoun 2013, Yadollahpour et al 2015, Zhou et al 2016, Qian et al 2017, Xiong et al 2017, Rasouli et al 2020, Karimi-Shahri et al 2021.…”

“…Several published studies were centered on radiobiological experiment-based investigation of Relative Biologic Effectiveness (RBE) of 252 Cf brachytherapy sources (Hall et al 1974, Feola et al 1982, Maruyama 1984, Maruyama et al 1991, Fairchald et al 1997, Wierzbicki 2012, Zhou et al 2016, Rasouli et al 2020, Karimi-Shahri et al 2021. Wang and Zhang (2004) developed a new formula based on the theory of compound-dual-radiation-action to predict the cell-survival fraction for a mixed-radiation field of 252 Cf.…”