Didvalis, Tadas

In vivo dosimetry involves the assessment of external irradiation doses to cancer patients with the aim to ensure high precision and accuracy in dose planning and delivery during radiotherapy procedure. In vivo dosimetry can also be used for the estimation of uncertainties that may occur during radiotherapy treatment and for prevention against systematic errorsand undesirable exposure. Implementation of in vivo dosimetry during irradiation can assist in detecting of doses that exceed the limits or are insufficient to treat the cancer according to the prepared dose plan. However, the availability of the various in vivo dosimetry systems remains is limited. This is partially related to the needs for the new installations of doserecording and dose verification systems and the general belief in the usefulness of these systems in detecting patient set-up errors, as well as beam energy, treatment accessory and geometry errors. Despite of this, implementation of in vivo dosimetry systems is ongoing and is seen as a crucial part of a radiation safety system in radiotherapy department […].

Gamma knife radiosurgery is a very precise method to treat the brain diseases. Since high energy gamma rays are very focused to the target accurate dosimetry solutions are mandatory [1]. Due to the steep dose gradients in the irradiation field close to the target, dosimetry method is required which provides information on 3D dose distribution and might be followed visually. Polymer gel dosimetry is the only method which fulfils these requirements [2]. Polymerized gels are sensitive enough to register absorbed doses in the wide range from starting from 0.1 Gy [3] to tens of Gy. According to the type of ionising radiation and target volume different formulations of dose gels are possible, however the quality of the final measurement result depends on the individual physical properties of dose gels, on accuracy and precision of gel dosimeters and their read out methods. The aim of this work was to initiate application of gel dosimetry for dose verification in gamma knife treatment.

In this study we present experimentally evaluated relative ROS generation with and without side scattering effect in affected media and in cells and outof- field dose effect to cell viability. We found that due to the side scattering of X-ray photons the applied energy to the in-field cells differs significantly from the energy delivered to out-of-field cells, thus indicating differences in ROS generation and cell viability. Performed cell viability test revealed positive cell growth effect in media affected by side scattering of ionizing radiation

In this study we present experimentally obtained relative ROS generation with and without side scattering effect in affected media and in cells. Black flat bottom 96 well plate (Thermo Fisher) was placed in a laboratory made PMMA phantom with 4 cm of build-up plastic below and above plate. We applied ionizing radiation dose of 8 Gy with a linear accelerator Varian Clinac DMX with 6 MeV energy X-ray photons and 4x4 cm2 irradiation field. Dose distribution simulation were performed using AAA algorithm on Varian Eclipse treatment planning. Chinese hamster ovary cells (CHO-K1) were irradiated. Our recent study [1] showed that ROS generation during and after irradiation correlates to cell DNA damage and cell death, therefore we used DCFDA dye method for ROS evaluation. DCF fluorescence after irradiation was measured using spectrophotometer (TECAN Genios Pro 96/384). For the experiments with additional scattering material,100 μl of water were added between each well. We found a significant (p < 0.001) increase of generated ROS in wells with scatter material in both in-field and out-of-field wells by 28.18 % for in-field and by 45.07 % for out-of-field wells. It is notable that scatter material increases relative in-field and out-of-field ROS concentration by 4.6 %, from 34.95 % to 39.56 %. The experimental results go with an agreement with dose distribution simulation. Side scattering of an applied x-ray energy is significantly changing applied energy to affected cells in the in-field and out-of-field cells, thus in turn ROS generation is altered.

Radiotherapy is conventional type of cancer treatment. However, a fundamental research on ionising radiation application to cells and tissues is still in need.. The rise of complex and multi-field radiotherapy techniques, such as IMRT, VMAT and SRS usage in patient treatment, suggests that the evaluation of low doses impact for healthy and malignant tissue is in need[1]. In this study we present a simulation of scattered radiation doses, and experimentally obtained relative ROS generation with and without side scattering effect in affected media and in cells. Materials and methods. We compare obtained modeling results with ionizing radiation induced ROS generation by irradiating 96 well plate with and without water between plate wells. Water works as scattering material between individual wells and, in addition to the primary photons from the radiation source, increase the number of scattered and secondary photons in a medium. For this study black flat bottom 96 well plate (Thermo Fisher) was placed in a laboratory made PMMA phantom with 4 cm of build-up plastic below and above plate. We applied ionizing radiation dose of 8 Gy with a linear accelerator Varian Clinac DMX with 6 MeV energy X-ray photons and 4x4 cm2 irradiation field. This field size allows to fully covers 36 wells. Linear accelerator gantry was positioned from the bottom of the phantom to reduce dose distribution distortions induced by air gaps above medium. Monitor unit calculation and dose distribution simulation were performed using AAA algorithm on Varian Eclipse treatment planning system on computed tomography scans of phantom withplate with scatter material and without scatter material. Obtained values for in-field and out-offield doses were used for comparison with experimental results of this study. Chinese hamster ovary cells (CHO-K1) were used for this study. Our recent study [2] showed that one of the parameters that can be monitored.[...].

One of the problems performing IMRT dose planning or plan verification using anthropomorphic phantoms for head and neck cancer patients is the presence of possible artefacts (dental crowns, metal dental implants, dental restoration materials.) inside the oral cavity. In many cases these artefacts are not accounted but may cause deviations from patient treatment plans due to enhanced scattering dose from the metal artefacts. Exploiting 3D printing technologies 3D dosimetry phantom corresponding to patient-specific anatomic structures with precisely positioned artefacts can be produced. Application of such 3D phantom in radiation therapy may contribute to more accurate dose planning and thus more efficient patient treatment. In this work we propose newly developed patient-specific 3D printed phantom of lower jaw with teeth which can be used for patient specific QA in IMRT. Developing this phantom DICOM image of the real patient was used for 3D reconstruction of patient’s lower jaw with teeth. 3D shape of this anatomic structure was printed out using Zortrax M300 3D printer. High Impact Polystyrene (HIPS) which is characterized as having satisfactory bone tissue equivalency was used as printing material. Keeping in mind a real patient, possibility of covering of corresponding teeth with a metallic crown in the 3D printed jaw construction was foreseen. Prepared construction was fixed in dose gel matrix, thus forming dosimetry phantom for the evaluation of possible radiation treatment errors caused by artefacts located in this anatomic region of the patient. Investigation of 3D printed lower jaw phantom has shown its feasibility for the assessment of dose distortions related to the presence of metal artefacts in the mouth of the patient. Also potential for the application of 3D printed phantoms in radiotherapy quality assurance has been shown.

Introduction. In radiotherapy treatment high accuracy and precision is needed. The errors indicated of the limits and deficiencies of the algorithms using in treatment planning systems may initiate significant errors in dose calculation. Nowadays 3D printed technologies enable to create specific individual phantom to provide dosimetry in heterogeneous environments that physically resemble different densities tissues in human body and also artefacts (metallic implants). In order to verify dose matching and human body and also artefacts (metallic implants). In order to verify dose matching and minimize possible errors theoretically calculated patient doses using treatment planning system (TPS) are comparing with experimentally measured radiotion treatment doses adapting the same parameters. The aim. The main aim of this work is to evaluate different types of 3D printed materials, compare their dosimetric characteristics with real human body tissues and artefacts inside and select the best technique which a suitable to use for individualized patient's treatment plan dosimetry in radiotherapy. Materials and methods. 3D printed phantom has to be manufactured from nearly equivalent materials of human body which mimic the densities of soft tissues, lung, air cavities and bones. [...].

Research on in vitro X-ray irradiated cell behavior contributes significantly to the enhancement of radiotherapy treatment efficacy in clinics. The results of investigation performed with Chinese hamster ovary (CHO) cells irradiated in linear accelerator Varian Clinac DMX (X-rays, 6 MeV and 3 Gy/min) to different doses from the interval 2 - 10 Gy are presented in this paper. Irradiated cells were analyzed using COMET assay within two hours after treatment and DNA damages in cells were assessed. Also clonogenic assay was performed to determine cell viability and formed cell colony area dependence on irradiated dose. Direct dependency of cell viability, DNA damage and relative cell division capability on irradiation dose was found. It was also found that cell division arrest plateau phase starts from 6 Gy. Obtained results are discussed in the frame of radiation induced effects in irradiated cells. Introduction Radiotherapy is one of the conventional cancer treatment therapies applied in oncology clinics worldwide. For the appropriate radiotherapy tumor treatment the effects of ionizing radiation on cancer cells and healthy tissues has to be thoroughly researched. Conventional treatment strategies are in clinical use, however, for improved results further research is needed. According to 3R principle, animaluse can only be allowed if the goal cannot be reached with in vitro experiments. Therefore in vitro experiments are still important. […].

Positioning accuracy and travel speed stability of multileaf collimator leaves were evaluated. An evaluation was made in the Hospital of Lithuanian University of Health Sciences Kauno klinikos Oncology and Haematology clinic, Radiation therapy department for linear accelerator Varian Clinac iX. "Garden fence" and "speed" tests were used. Images for these tests were acquired using Varian Electronic portal imaging device, Kodak dosimetric film and Sun Nuclear Map CHE-CK dosimeter. Two image analysis programs were written using MATLAB software. Also DynaLog file analysis was made. Dependence of deviations on the gantry and collimator positions and speed of leaves were estimated. Introduction. Intensity modulated radiotherapy (IMRT) is a type of radiotherapy that has more precise dose distribution than other conventional radiotherapy types because dose intensity in the field is not homogenous. Dose distribution is modulated using multileaf collimator (MLC), which leaves move during iradiation. [...].