The gamma evaluation method as a routine QA procedure of IMRT

BackgroundThe conventional QA procedures dedicated to 3D CRT are unsatisfactory if the dMLC is in operation. In the case of IMRT not only should the dose on the beam axis, but also its distribution in the total plane perpendicular to the beam be taken under control. The comparison between the predicted and the observed fluence can be achieved using the gamma method. It takes into consideration the dose difference and the spatial displacement between analyzed points to provide a γ-index as a result of comparison.AimThe aim of the investigation was to develop the procedure of IMRT verification based on the gamma algorithm.Materials and Methods700 patients have been irradiated using IMRT since 2002. Over 1500 images recorded on the film and/or EPID have been analyzed with the help of self-made software. Histograms of γ-value and the γ-images have been created for each field. The fields have been classified depending on tumour location and the method of dose delivery, to obtain an average result for each class. We have performed a comparison of γ-histograms acquired with the help of different methods of recording.ResultsWe have observed a correlation between results of verification obtained with the help of the gamma algorithm and the method of intensity modulation.ConclusionGamma evaluation allows one to find local hot-spots caused by irregularities in leaf motion or the tongue-and-groove effect

The prototype of EPID-based in vivo dose verification for VMAT treatments in patients with prostate cancer

Introduction. The volumetric modulated arc therapy technique (VMAT) is now widely used in radiotherapy. Verifica­tion of the dose delivered to the patient is performed prior to the treatment (pre-treatment mode). However, during the therapeutic session, only the patient’s position is verified and monitored. AnEPID’s (electronic portal imaging device) matrices can measure the intensity of radiation passing through the patient, but the calculation of the dose distribution from this measurement is limited due to the lack of reliable algorithms and software. Therefore, it seems promising to develop a method to estimate the dose in the patient’s body based on the measured calibration units (CU) values. Material and methods. The material consists of 53 patients treated for prostate cancer with the VMAT technique. The CU signal is measured during the treatment and its value is then transformed according to the self-developed algorithm into a dose. This delivered dose is then compared with the planned dose in the target. Results. The performed measurements of the CU and preliminary calculations indicate that it is possible to estimate the dose that the patient receives during the therapeutic session. The mean difference between the prescribed and me­asured dose values is less than 1%, however, there are differences of 17%. Conclusions. The proposed method can be used in clinical practice for actual dose estimation. The uncertainty of the proposed method was estimated at 5%. In the event of differences above 10%, the treatment realization should be verified by additional tests including patient positioning and technical tests of accelerator, such as verification of kV and MV isocenter compatibility

The prototype of EPID-based in vivo dose verification for VMAT treatments in patients with prostate cancer

Introduction. The volumetric modulated arc therapy technique (VMAT) is now widely used in radiotherapy. Verifica­tion of the dose delivered to the patient is performed prior to the treatment (pre-treatment mode). However, during the therapeutic session, only the patient’s position is verified and monitored. AnEPID’s (electronic portal imaging device) matrices can measure the intensity of radiation passing through the patient, but the calculation of the dose distribution from this measurement is limited due to the lack of reliable algorithms and software. Therefore, it seems promising to develop a method to estimate the dose in the patient’s body based on the measured calibration units (CU) values. Material and methods. The material consists of 53 patients treated for prostate cancer with the VMAT technique. The CU signal is measured during the treatment and its value is then transformed according to the self-developed algorithm into a dose. This delivered dose is then compared with the planned dose in the target. Results. The performed measurements of the CU and preliminary calculations indicate that it is possible to estimate the dose that the patient receives during the therapeutic session. The mean difference between the prescribed and me­asured dose values is less than 1%, however, there are differences of 17%. Conclusions. The proposed method can be used in clinical practice for actual dose estimation. The uncertainty of the proposed method was estimated at 5%. In the event of differences above 10%, the treatment realization should be verified by additional tests including patient positioning and technical tests of accelerator, such as verification of kV and MV isocenter compatibility

Basic Characteristics of Dose Distributions of Photons Beam for Radiotherapeutic Applications Using YAG:Ce Crystal Detectors

Thermostimulated luminescence (TSL) dosimetry is a versatile tool for the assessment of dose from ionizing radiation. In this work, the Ce3+ doped Y3Al5O12 garnet (YAG:Ce) with a density ρ = 4.56 g/cm3 and effective atomic number Zeff = 35 emerged as a prospective TSL material in radiotherapy applications due to its excellent radiation stability, uniformity of structural and optical properties, high yield of TSL, and good position of main glow peak around 290–300 °C. Namely, the set of TSL detectors produced from the YAG:Ce single crystal is used for identification of the uniformity of dose and energy spectra of X-ray radiation generated by the clinical accelerator with 6 MV and 15 MV beams located in Radiotherapy Department at the Oncology Center in Bydgoszcz, Poland. We have found that the YAG:Ce crystal detects shows very promising results for registration of X-ray radiation generated by the accelerator with 6 MV beam. The next step in the research is connected with application of TSL detectors based on the crystals of much heavier garnets than YAG. It is estimated that the LuAG:Ce garnet crystals with high density ρ = 6.0 g/cm3 and Zeff = 62 can be used to evaluate the X-rays produced by the accelerator with the 15 MV beam

Investigations of microstructure of porous coated orthopaedic implants in the aspect of the structural-adaptive compatibility of bone-porous implant interface. Part 1, Critical view on bone-implant fixation problem

The biomechanical construction of orthopaedic implants, e.g. construction of an artificial hip joint, is characterized by a set of material, geometrical and dynamic properties, designed to fulfil required assumptions. From the biomechanical point of view the problem of structuralbiomechanical compatibility between impalnt and bone is a key-question in respect of the role performed in the skeleton. At first in the matter, the problem of structural-adaptive compatibility of orthopaedic implants porous coatings with bone tissue (natural porous biomaterial) should be stated. This problem deals with osteoinductive properties of biomaterial. The osteoinductive properties of biomaterial are determined, among others, by the poroaccessibility of porous coating for adaptive ingrowth of bone tissue into its pore space which is influenced by mechanical load history. The aim of bone ingrowth into pore space of a coating is to achieve the proper and permanent fixation of the implant in its bony surroundings. This part of the paper presents insight view into the problem of bone-implant fixation, and a critical review of the traditional approach to investigations on the cementless implant fixation conditioned by the bone tissue ingrowth, which were carried out on the basis of one-phase biomechanical model of bone

Ovaries of Chrysanthemum Irradiated with High-Energy Photons and High-Energy Electrons Can Regenerate Plants with Novel Traits

Classical mutation breeding using physical factors is a common breeding method for ornamental crops. The aim of our study was to examine the utility of ovaries excised from irradiated inflorescences of Chrysanthemum × morifolium (Ramat.) as explants for breeding purposes. We studied the in vitro regeneration capacity of the ovaries of two chrysanthemum cultivars: ‘Profesor Jerzy’ and ‘Karolina’ preceded by irradiation with high-energy photons (total dose 5, 10 and 15 Gy) and high-energy electrons (total dose 10 Gy). Growth and inflorescence parameters of greenhouse acclimatized regenerants were recorded, and ploidy level was estimated with flow cytometry. The strong impact of genotype on regeneration efficiency was recorded—cultivar ‘Karolina’ produced only 7 viable shoots, while ‘Profesor Jerzy’ produced totally 428 shoots. With an increase of irradiation dose, the regeneration decreased, the least responsive were explants irradiated with 15 Gy high-energy photons and 10 Gy high-energy electrons. Regenerants of ‘Profesor Jerzy’ obtained from these explants possessed shorter stem and flowered later. The highest number of stable, color and shape inflorescence variations were obtained from explants treated with 10 Gy high-energy photons. Variations of inflorescences were predominantly changes of shape—from full to semi-full. New color phenotypes were dark yellow, light yellow and pinkish, among them only the dark yellow phenotype remained stable during second year cultivation. None of the regenerants were haploid. The application of ovaries irradiated within the whole inflorescence of chrysanthemum can be successfully applied in the breeding programs, provided the mother cultivar regenerate in vitro efficiently

The gamma evaluation method as a routine QA procedure of IMRT

AbstractBackgroundThe conventional QA procedures dedicated to 3D CRT are unsatisfactory if the dMLC is in operation. In the case of IMRT not only should the dose on the beam axis, but also its distribution in the total plane perpendicular to the beam be taken under control. The comparison between the predicted and the observed fluence can be achieved using the gamma method. It takes into consideration the dose difference and the spatial displacement between analyzed points to provide a γ-index as a result of comparison.AimThe aim of the investigation was to develop the procedure of IMRT verification based on the gamma algorithm.Materials and Methods700 patients have been irradiated using IMRT since 2002. Over 1500 images recorded on the film and/or EPID have been analyzed with the help of self-made software. Histograms of γ-value and the γ-images have been created for each field. The fields have been classified depending on tumour location and the method of dose delivery, to obtain an average result for each class. We have performed a comparison of γ-histograms acquired with the help of different methods of recording.ResultsWe have observed a correlation between results of verification obtained with the help of the gamma algorithm and the method of intensity modulation.ConclusionGamma evaluation allows one to find local hot-spots caused by irregularities in leaf motion or the tongue-and-groove effect