Evaluation of Peripheral Dose for Varian Trilogy Linear Accelerator

Objective To measure and evaluate the peripheral dose(PD) for Trilogy linear accelerator in different setup condition and investigate the feasibility of the diode dosimetric system to measure the peripheral dose.Methods Peripheral dose were measured using a CC13 ionization chamber and the diode dosimetric system in a set of solid water phantom. Measurements were performed for different depths, field sizes, physical and virtual wedge, radiation beam energy and up at distance of 1cm to 31cm beyond the field edges. PD is separated into PDleakage and PDscatter by measure peripheral dose with or without scattering phantom. CRIS phantom was used for this research with the diode dosimetric system at the interest points of the breast, thyroid, and lens.Results All the measure data were normalized to isocenter. The measured PD decreases exponentially as a function of distance up to 31cm from the edge. PD shows no significant relevant to depth and it increases with the increased field size. As the physics wedge angle increase, PD increases about 1%, but enhanced dynamic wedge decreased 2-3% compared with open field. As the beam energy increase, PD decreased. All PD data difference less than 1% between CC13 ionization chamber and diode. The PD of CRIS phantom for Volume Modulated ARC Therapy (VMAT) is minimum and the mean dose for breast、thyroid and lens is 6.72 mGy、2.90 mGy and 2.37 mGy respectively.Conclusion The diode dosimetric system provides an sufficient assessment in peripheral regions of 6MV X-ray beam. PD changes because of field size、depth、beam energy etc and the assessment of PD would be helpful to evaluate the dose received by the relevant critical structures near the treatment field. Furthermore it is advantaged to use external shielding for critical organs.

Spectrophotometric Study of Polymeric DyesGels After a Gamma Irradiation Process for its Possible Use as a Radiation Dosimeter

This work aims to evaluate a dosimetric system composed of green malachite supported in agarose. Previous work showed that solutions of green malachite irradiated at 1 to 40 kGy present a linear behavior. This system is a gel composed of green malachite (2.5×10–3 M), sodium benzoate (1%),and agarose (1%) that was exposed tovarious doses of gamma irradiation. The irradiated systems were measured with a UV-V is spectrophotometer at 619 nm. Experimental parameters (such as dose rate, doses, and temperature) were controlled and optimized for reproducible and reliable results. More studies are needed to propose a dosimeter in the system in the range of 1.8 to 4.0 kGy.

Development of basic approaches to creating hardware and software for radiation monitoring information systems

Basic approaches to creating hardware and software for radiation monitoring information systems have been developed in the article. A modern information system for radiation monitoring and control that requires a comprehensive approach and an iterative process of its creation has been developed. The proposed approach to integrating local measuring devices with cloud services, using M2M/IoT technology for remote measurements, advanced semiconductor sensors based on CdTe and CdZnTe radiation detectors, modern microcontroller and communication microchips is highly promising. Developed hardware and software solutions demonstrate increased accuracy due to hardware and software correction of measurement results. A variant of the architectural solution for building a platform for remote access to dosimetric and radiometric measurements is being developed. The solution lies in the direction of improving the parameters of detectors, as well as the characteristics of electronic modules of detecting systems and creating software for controlling the detection process, collecting and digital processing of information, and its adequate presentation to users online. The architecture and structural diagram of a dosimetric system, a sequence diagram, a diagram of a dosimetric system with a subsystem for data exchange over the Internet have been created. A new algorithm for measuring the exposure dose rate of ionizing radiation has been proposed. The block diagram of a microcontroller dosimeter has been developed. The algorithm for correcting the dependence of the sensitivity of the detector based on CdZnTe on the energy of the detected gamma quanta has already been proposed. The algorithm significantly reduces the uncertainty of measuring the radiation dose rate. The architecture and block diagram of the dosimetric system with the possibility of remote access and remote control of the main functions has been presented as well. The calculation of the exposure dose of gamma radiation and the power of the exposure dose with the energy dependence correction have been used. The system elements have proved to be useful for students’ distant laboratory work during the quarantine.

Fraction-specific post-treatment quality assurance for active breath-hold radiation therapy

PurposeThe purpose of this study is to evaluate variation in the treatment hold pattern and quantify its dosimetric impact in breath-hold radiotherapy, using fraction-specific post-treatment quality assurance.Material and MethodsA patient with lung mets treated using intensity-modulated radiation therapy (IMRT) with active breath coordinator (ABC) was recruited for the study. Treatment beam hold conditions were recorded for all the 25 fractions. The linearity and reproducibility of the dosimetric system were measured. Variation in the dose output of unmodulated open beam with beam hold was studied. Patient-specific quality assurance (PSQA) was performed with and without beam hold, and the results were compared to quantify the dosimetric impact of beam hold.ResultsThere was a considerable amount of variation observed in the number of beam hold for the given field and the monitor unit at which the beam held. Linearity and reproducibility of the dosimetric system were found within the acceptable limits. The average difference over the 25 measurements was 0·044% (0·557 to −0·318%) with standard deviation of 0·248.ConclusionPatient comfort with the ABC system and responsiveness to the therapist communication help to maintain consistent breathing pattern, in turn consistent treatment delivery pattern. However, the magnitude of dosimetric error is much less than the acceptable limits recommended by IROC. The dosimetric error induced by the beam hold is over and above the dose difference observed in conventional PSQA.