A feasibility study to calculate unshielded fetal doses to pregnant patients in 6-MV photon treatments using Monte Carlo methods and anatomically realistic phantoms

Abstract

A Monte Carlo-based procedure to assess fetal doses from 6-MV external photon beam radiation treatments has been developed to improve upon existing techniques that are based on AAPM Task Group Report 36 published in 1995 [M. Stovall et al., Med. Phys. 22, 63-82 (1995)]. Anatomically realistic models of the pregnant patient representing 3-, 6-, and 9-month gestational stages were implemented into the MCNPX code together with a detailed accelerator model that is capable of simulating scattered and leakage radiation from the accelerator head. Absorbed doses to the fetus were calculated for six different treatment plans for sites above the fetus and one treatment plan for fibrosarcoma in the knee. For treatment plans above the fetus, the fetal doses tended to increase with increasing stage of gestation. This was due to the decrease in distance between the fetal body and field edge with increasing stage of gestation. For the treatment field below the fetus, the absorbed doses tended to decrease with increasing gestational stage of the pregnant patient, due to the increasing size of the fetus and relative constant distance between the field edge and fetal body for each stage. The absorbed doses to the fetus for all treatment plans ranged from a maximum of 30.9 cGy to the 9-month fetus to 1.53 cGy to the 3-month fetus. The study demonstrates the feasibility to accurately determine the absorbed organ doses in the mother and fetus as part of the treatment planning and eventually in risk management.

Electron Beam Intraoperative Radiotherapy (ELIOT) in Pregnant Women with Breast Cancer: From in Vivo Dosimetry to Clinical Practice

“…Although the well-accepted general rule is to avoid radiotherapy during pregnancy unless the tumor is threatening the mother's life [13], this value can be considered relatively low and therefore acceptable, considering the risk estimation reported in the scientific literature regarding the biological effects of radiation. However, ELIOT compares favorably regarding the well-known variables influencing the dose absorbed by a certain organ or structure at a distance [14]. In fact, as the peripheral dose increases with larger field size, greater depth of prescription, and higher energy used, ELIOT takes advantage of a small collimator diameter, low electron energy (maximum 10 MeV), and short depth of dose penetration (maximum 2.5 cm).…”

National Cost Savings From Observation Unit Management of Syncope

“…The Monte Carlo approach has also been used previously in medical research, including a recent analysis of overall cost savings generated from increased observation unit use. 12,[16][17][18] Monte Carlo simulation calculates and records the results of many simulated iterations using random values of the input variables in each iteration. These values are chosen from data distributions that are directly informed by prior studies.…”

Analytical model for out-of-field dose in photon craniospinal irradiation

“…In addition, it may be necessary to take into account dependencies on the treatment apparatus (e.g., radiotherapy equipment and its shielding) and the treatment technique (e.g., energy, field size, source-to-skin distance, and treatment site) (Taylor and Kron 2011). A number of other out-of-field dose studies involving measurements of photons produced from electron linear accelerators have been performed (Kase et al 1983, Stovall et al 1995, Howell et al 2006, Kry et al 2007, Wang and Xu 2008, Fontenot et al 2009, Georgiev 2009, Scarboro et al 2010, Ruben et al 2011, Kaderka et al 2012), as have Monte Carlo simulations (Kry et al 2006, Bednarz and Xu 2008, 2009, Athar et al 2010, Kry et al 2010). Most out-of-field dose modeling studies have applied simple empirical analytical methods or Monte Carlo techniques.…”