Pilot scale validation campaign of gel dosimetry for pre-treatment quality assurance in stereotactic radiotherapy

Purpose: Complex stereotactic radiotherapy treatment plans require prior verification. A gel dosimetry system was developed and tested to serve as a high-resolution 3D dosimeter for Quality Assurance (QA) purposes.Materials and Methods: A modified version of a polyacrylamide polymer gel dosimeter based on chemical response inhibition was employed. Different sample geometries (cuvettes and phantoms) were manufactured for calibration and QA acquisitions. Irradiations were performed with a Varian Trilogy linac, and analyses of irradiated gel dosimeters were performed via MRI with a 1.5 T Philips Achieva at 1 mm3 or 2 mm3 isotropic spatial resolution. To assess reliability of polymer gel data, 54 stereotactic clinical treatment plans were delivered both on dosimetric gel phantoms and on the Delta4 dosimeter. Results from the two devices were evaluated through a global gamma index over a range of acceptance criteria and compared with each other.Results: A quantitative and tunable control of dosimetric gel response sensitivity was achieved through chemical inhibition. An optimized MRI analysis protocol allowed to acquire high resolution phantom dose data in time -frames of approximate to 1 h. Conversion of gel dosimeter data into absorbed dose was achieved through internal calibration. Polymer gel dosimeters (2 mm3 resolution) and Delta4 presented an agreement within 4.8 % and 2.7 % at the 3 %/1 mm and 2 %/2 mm gamma criteria, respectively.Conclusions: Gel dosimeters appear as promising tools for high resolution 3D QA. Added complexity of the gel dosimetry protocol may be justifiable in case of small target volumes and steep dose gradients

ПРОБЛЕМИ МАРКЕТИНГОВИХ ДОСЛІДЖЕНЬ ПРОГНОЗУВАННЯ ЗБУТУ НА ПІДПРИЄМСТВІ

The author considers the principal methods, both qualitative and quantitative ones, as well as simulation in forecasting product sales. The author suggests a system simulation method, which will enable to obtain indexes complementing each other and will ensure all-round investigations into the phenomenon on the well-grounded basis.Рассматриваются основные методы прогнозирования продаж продукции, а именно, качественные, количественные, а также моделирование. Предложено системное моделирование, которое позволит получить показатели продажи взаимно дополняющие один другого, что даст комплексное изучение явления и высокий уровень обоснованности.Розглядаються основні методи прогнозування збуту продукції, а саме якісні, кількісні, а також моделювання. Запропоноване системне моделювання, яке дозволить отримати показники збуту взаємно доповнюючи один одного, що забеспечить комплексне вивчення прогнозного явища і високий ступень обґрунтованості