Development and implementation of a Monte Carlo frame work for evaluation of patient specific out- of - field organ equivalent dose

Background: The aim of this study was to develop and implement a Monte Carlo framework for evaluation of patient specific out-of-field organ equivalent dose [OED]

Materials and Methods: Dose calculations were performed using a Monte Carlo-based model of Oncor linac and tomographic phantoms. Monte Carlo simulations were performed using EGSnrc user codes. Dose measurements were performed using radiochromic films. Furthermore, the applicability of this framework was examined for a 3D conformal radiotherapy of breast

Results: Commissioning of the beam model was done by comparing the measured and calculated out-of-field dose values of several points in the physical and tomographic phantoms, respectively. The maximum percentage difference was 17%, which was smaller than 30% acceptance criteria for Monte Carlo modeling. The maximum statistical uncertainty in out -of-field dose calculation was 23%. Organ equivalent doses for out of field organs in 3D conformal radiotherapy of le1 breast varied from 2.4 cGy for right kidney to 134.6 cGy for the le1 humeral head

Conclusion: The framework developed in this research is a valuable tool for calculating peripheral dose and out-of field patient specific OEDs, the quantities needed for calculating risk of secondary cancer induction as a result of radiotherapy. This code can be used as a patient specific treatment plan optimization tool in order to select a treatment plan with the lowest risk of secondary cancer induction

Design of a generally applicable abdominal shield for reducing fetal dose during radiotherapy of common malignancies in pregnant patients

In most cancer cases, the treatment choice for a pregnant patient is radiotherapy. In these patients, the abdomen is usually not exposed; therefore fetus exposure is due to peripheral dose [PD]. The purpose of this study was to estimate the fetal dose [the maximum PD in each pregnancy stage] for modalities available and to fabricate and evaluate a generally applicable fetal shield. PD values were measured for brain, breast and mediastinum irradiation in a whole body anthropomorphic phantom using a NE 2571 ionization chamber. An external shield was then designed to reduce the fetal dose to the standard dose limit, 5 mSv. The range of PD values as a function of distance from the field's edge were as follows 1] 9.4-259 cGy for Mantel field; 2] 6.5-95 cGy for chest wall irradiation with 10 MeV electrons, 3] 8.5- 52.5 cGy for tangential field with Co-60 and 4] 4.8-7.8 cGy for brain radiotherapy with 9 MV photon. PD values for the same setups using the fetal shield were as follows: 1] 1.4-22 cGy, 2] 0.5-4 cGy, 3] 1.5-5 cGy and 4] under 1 cGy. The measured PD data sets can be used to estimate fetal dose for specific treatment setups and pregnancy stages. The use of external shield designed in this research reduced the fetal dose effectively to under the threshold [a 70-90% reduction], except for the final stages of pregnancy in Hodgkin's patients