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

quality assurance program for an amorphous silicon electronic portal imaging device using in-house developed phantoms: a method development for dosimetry purposes

Electronic portal imaging devices [EPIDs] play an important role in radiation therapy portal imaging, geometric and dosimetric verifications. A successful utilization of EPIDs for imaging and dosimetric purposes requires a reliable quality control process routine to be carried out regularly. In this study, two in-house phantoms were developed and analyzed for implementation in a quality assurance program for dosimetry purposes. An amorphous silicon [a-Si] imager [OptiVue500] was used. A low contrast resolution phantom and an image quality phantom were constructed and implemented. Low contrast resolution of the EPID was evaluated by counting the number of holes detectable in the image of phantom using human observers and a software. The image quality phantom was used for modulation transfer function, contrast to noise ratio and noise level evaluations. This phantom contains five sets of high-contrast rectangular bar patterns of variable spatial frequencies and six uniform regions. Although the manual low contrast resolution method was observer-dependent and insensitive to artifacts, the automatic method was robust and fully objective but sensitive to artifacts. The critical frequency values for 6 and 18 MV were 0.3558 +/- 0.006 lp/mm and 0.2707 +/- 0.006 lp/mm respectively. The contrast-to-noise ratio was found to be 240% higher for 6 MV compared to 18 MV. The developed phantoms provide a convenient process for periodic performance of an EPID. These phantoms are independent of the EPID system and provide robust tools for continuous monitoring of image quality parameters as well as dosimetric parameters

comparison in cosmetic results of cobalt 60 and photon 9 mega volt for the whole breast radiotherapy in breast cancer patients with breast conserving surgery

To compare the cosmetic results of whole breast radiotherapy between cobalt 60 and photon 9MegaVolt in patients underwent breast conserving surgery. The patients with breast saving surgery who were treated by whole breast radiotherapy with either cobalt 60 or photon 9MV between 2001-2006 in Sayed-al-Shohada hospital entered the study. The cosmetic results were evaluated by an expert radiation oncologist with definite criteria. Frothy patients in cobalt 60 group and 43 patients in photon group were compared, with median follow up of 40.5 months. The patients in photon group had less telangectasia and discoloration [p=0.018 and p=0.01, respectively]. The consistency of breast in photon group was better [p=0.019], but for fibrosis the difference was not statistically significant [p=0.055].Overall cosmetic results in photon group was much better rather than cobalt 60 group [p=0.005]. No recurrences were observed in both groups. Cosmetic results in group with photon 9MV were superior to cobalt group, but the effect of these two beam energy on disease free survival [DFS] and/or overall survival [OS] should be in more consideration