Pretreatment verification of dose calculation and delivery by means of measurements with PLEXITOM™ phantom.

AIM: To validate a pretreatment verification method of dose calculation and dose delivery based on measurements with Metaplex PTW phantom. BACKGROUND: The dose-response relationships for local tumor control and radiosensitive tissue complications are strong. It is widely accepted that an accuracy of dose delivery of about 3.5% (one standard deviation) is required in modern radiotherapy. This goal is difficult to achieve. This paper describes our experience with the control of dose delivery and calculations at the ICRU reference point. MATERIALS AND METHODS: The calculations of dose at the ICRU reference point performed with the treatment planning system CMS XiO were checked by measurements carried out in the PLEXITOM™ phantom. All measurements were performed with the ion chamber positioned in the phantom, at the central axis of the beam, at depth equivalent to the radiological depth (at gantry zero position). The source-to-phantom surface distance was always set to keep the source-to-detector distance equal to the reference point depth defined in the ICRU Report 50 (generally, 100 cm). The dose was measured according to IAEA TRS 398 report for measurements in solid phantoms. The measurement results were corrected with the actual accelerator's output factor and for the non-full scatter conditions. Measurements were made for 111 patients and 327 fields. RESULTS: The average differences between measurements and calculations were 0.03% (SD = 1.4%), 0.3% (SD = 1.0%), 0.1% (SD = 1.1%), 0.6% (SD = 1.8%), 0.3% (SD = 1.5%) for all measurements, for total dose, for pelvis, thorax and H&N patients, respectively. Only in 15 cases (4.6%), the difference between the measured and the calculated dose was greater than 3%. For these fields, a detailed analysis was undertaken. CONCLUSION: The verification method provides an instantaneous verification of dose calculations before the beginning of a patient's treatment. It allows to detect differences smaller than 3.5%.

Monte Carlo dosimetry using Fluka code and experimental dosimetry with Gafchromic EBT2 and XR-RV3 of self-built experimental setup for radiobiological studies with low-energy X-rays.

Purpose: The aim of this research was to simulate self-built experimental setup for radiobiological research using X-ray diffraction C-tech tube and PW 3830 generator (PANalytical, Netherlands) and to calculate absorbed dose and to compare it with experimental dose measurements. The maximum X-ray energy was 60 keV.Materials and methods: Petri dish was specially adapted to hold biological cells during the irradiation process. Rotation of Petri dish ensured radiation homogeneity and effectiveness of rotation process was confirmed using EBT2 Gafchromic film. Monte Carlo simulation using Fluka 2011 2c.4 was used to model the setup and to calculate dose absorbed by live cells. The EBT2 and XR-RV3 Gafchromic films were used to estimate relative experimental absorbed dose.Results: The radiation homogeneity provided values with maximum deviation equal to ±3.5% from the average value and the absorbed dose rate was 0.9 Gy/min using simulation process and 1 Gy/min or 0.8 Gy/min using experimental methods (XR-RV3 and EBT2 Gafchromic film, respectively). All dose rate values show metrological compatibility.Conclusions: Influence of specially constructed Petri dish on absorbed dose was determined using simulations that showed that low-energy photons, emitted as characteristic line from borosilicate glass forming component of Petri dish, were source of increase in dose absorbed by cells. This experimental setup will be used to conduct radiobiological research.HighlightsA low-energy X-ray system constructed for radiobiological studies was used.Dosimetry was based on a Monte Carlo simulation using Fluka 2011 code version 2c.4.A specially designed rotating Petri dish ensured the uniformity of the radiation distribution.Gafchromic EBT2 and XR-RV3 films were used to experimental dosimetry.Monte Carlo and experimental dosimetry showed metrological compatibility.

CALIBRATION OF LOW ENERGY X-RAY EXPERIMENTAL SETUP WITH STRONGLY FILTERED BEAM USING DATA FROM A SEMICONDUCTOR AND A THERMOLUMINESCENT DETECTORS.

The calibration of low energy X-ray experimental setup with strongly filtered beam dedicated to radiobiological research was performed using the absorbed dose calculated from the data collected by two types detectors. For this purpose a semiconductor (Amptek, USA) and a thermoluminescent (Institute of Nuclear Physics, Krakow, Poland) detectors were applied. The absorbed dose in water values estimated by both detectors are in good agreement.