Basic Dosimetric Parameters Research Articles

A new approach to the 2D radiation dosimetry based on optically stimulated luminescence of LiF:Mg,Cu,P

A new approach to the two-dimensional (2D) spatial radiation dosimetry based on optically stimulated luminescence (OSL) phenomena is presented. By investigating prototype dosimeters in form of flat and flexible sheets made of a polymer (PDMS), with the embedded OSL active grains (LiF:Mg,Cu,P), direct measurements of the 2D dose distribution using the OSL method and self-developed optical setup were verified. We have determined the response of 2D OSL prototype silicone foils, stimulated with the blue LEDs (470 nm) and read out using the CCD camera system, after doses of beta radiation ranging from less than 0.1 Gy up to 100 Gy. We have also verified the basic dosimetric parameters of the prototype sample foils, including the sensitivity (signal per dose), linearity, repeatability and fading effect. These encouraging results are the first step towards the practical use of LiF:Mg,Cu,P 2D OSL foils as a reusable spatial dosimeter system.

Two-dimensional radiation dosimetry based on LiMgPO4 powder embedded into silicone elastomer matrix

Two-dimensional (2D) spatial radiation dosimetry based on optically stimulated luminescence (OSL) phenomena is presented. By embedding OSL active particles (LiMgPO4) into the transparent and flexible silicone elastomer matrix (polydimethylsiloxane silicone), the favorable dosimetric properties of the OSL material are exploited towards real 2D OSL signal. Direct measurement of the 2D OSL dose distribution using prototype flat foils, irradiated with beta radiation, stimulated with blue light (470 nm) and read out using a high-sensitive CCD camera has been obtained. Basic dosimetric parameters, including repeatability, dose-response, and fading has been measured. A separate experiment was dedicated to measure the real 2D proton depth dose distribution, using unmodulated and collimated 58.8 MeV proton beam used for proton radiotherapy at the IFJ PAN.

Comparison of calculated and measured basic dosimetric parameters for total body irradiation with 6- and 18-MV photon beams

AbstractPurpose:Total body irradiation (TBI) is an external beam radiation therapy in which large field size and extended source skin distances (SSDs) are applied to deliver a therapeutic dose to the whole body. As measurements in such situations are not common and have more uncertainties in comparison to standard dosimetry situations, it is more precise if calculated beam data can be used instead of measurements taken under TBI situations. The purpose of this study is to compare calculated beam data [percentage depth dose (PDD) and dose rate] with those obtained from simulated treatment measurements.Materials and methods:PDD and dose rates were measured for the 6- and 18-MV photon beams under TBI and standard conditions using 9,000 cm3 water phantom and ion chambers (Markus and Farmer). The results were then compared with the calculated PDD and dose rate data. The beam flatness was also measured under TBI and standard conditions for both 6- and 18-MV photon beams, and the results were then compared.Results:A comparison of the measurement and calculated beam data shows that the difference between calculated and measured PDD values is −6·97 and −4·14% for the 6- and 18-MV photon beams, respectively. The ratio of calculated to measured dose rate was 1·09 and 1·02 for the 6- and 18-MV photon beams, respectively. The beam flatness under TBI conditions was 4·59% for 6-MV and 5·37% for 18-MV photon beam, whereas under standard conditions, these values were 1·50 and 1·98% for 6- and 18-MV radiation beams, respectively.Findings:According to the results, due to a high error level in dose rate and PDD calculations, these parameters must be directly measured under TBI conditions; however, regarding the obtained results, direct measurement is not necessary for the 18-MV photon beam.

Clinical advantages of using unflattened 6-MV and 10-MV photon beams generated by the medical accelerator Elekta Versa HD based on their dosimetric parameters in comparison to conventional beams

Abstract Photon beams with wide energy ranges from 4 MV to 25 MV are commonly used in radiotherapy nowadays. In recent years, there has been a strong interest in a certain modification of a radiotherapeutic apparatus by the application of the so-called flattening filter-free (FFF) beam. Several advantages of FFF beams over standard flattening filter (FF) beams are noticed, and this technical solution has aroused great interest among radiotherapeutic facilities. The goal of the present study is to investigate the differences between the conventional FF and unflattened FFF 6-MV and 10-MV photon beams in some basic dosimetric parameters and their influence on the whole radiotherapeutic treatment. The data provided here include the detailed characteristics as follows: percent depth dose (PDD), beam profile, edge of a half-profile, total scatter correction factor (TSCF) and head scatter correction factor (HSCF) for FF and FFF 6-MV and 10-MV photon beams from the Elekta Versa HD accelerator in the Katowice Oncology Center in Poland.

Intensity-modulated versus 3-dimensional conformal radiotherapy in the definitive treatment of esophageal cancer: comparison of outcomes and acute toxicity

BackgroundThough the vast majority of seminal trials for locally advanced esophageal cancer (EC) utilized three-dimensional conformal radiotherapy (3DCRT), the advanced and highly conformal technology known as intensity-modulated radiotherapy (IMRT) can decrease doses to critical cardiopulmonary organs. To date, there have been no studies comparing both modalities as part of definitive chemoradiation (dCRT) for EC. Herein, we investigated local control and survival and evaluated clinical factors associated with these endpoints between cohorts.MethodsWe retrospectively analyzed 93 patients (3DCRT n = 49, IMRT n = 44) who received dCRT at our institution between 2000 and 2012 with the histologic diagnosis of nonmetastatic EC, a Karnofsky performance status of ≥70, curative treatment intent, and receipt of concomitant CRT. Patients were excluded if receiving <50 Gy. Kaplan-Meier analysis was used to evaluate the endpoints of local relapse rate (LR), progression-free survival (PFS), and overall survival (OS). Cox proportional hazards modeling addressed factors associated with outcomes with univariate and multivariate approaches. Rates of acute toxicities and basic dosimetric parameters were compared between 3DCRT and IMRT patients.ResultsMean follow-up was 34.7 months. The 3-year LR was 28.6% in the 3DCRT group and 22.7% in the IMRT group (p = 0.620). Median PFS were 13.8 and 16.6 months, respectively (p = 0.448). Median OS were 18.4 and 42.0 months, respectively (p = 0.198). On univariate analysis, only cumulative radiation dose was associated with superior LR (hazard ratio (HR) 0.736; 95% confidence interval (CI) 0.635 – 0.916, p = 0.004). Factors clearly affecting survival were not observed.ConclusionsWhen comparing 3DCRT- versus IMRT-based dCRT, no survival benefits were observed. However, we found a lower local recurrence rate in the IMRT group potentially owing to dose-escalation. Prospective data are needed to verify the presented results herein.

Agreement Between Institutional Measurements and Treatment Planning System Calculations for Basic Dosimetric Parameters as Measured by the Imaging and Radiation Oncology Core-Houston

To compare radiation machine measurement data collected by the Imaging and Radiation Oncology Core at Houston (IROC-H) with institutional treatment planning system (TPS) values, to identify parameters with large differences in agreement; the findings will help institutions focus their efforts to improve the accuracy of their TPS models. Between 2000 and 2014, IROC-H visited more than 250 institutions and conducted independent measurements of machine dosimetric data points, including percentage depth dose, output factors, off-axis factors, multileaf collimator small fields, and wedge data. We compared these data with the institutional TPS values for the same points by energy, class, and parameter to identify differences and similarities using criteria involving both the medians and standard deviations for Varian linear accelerators. Distributions of differences between machine measurements and institutional TPS values were generated for basic dosimetric parameters. On average, intensity modulated radiation therapy-style and stereotactic body radiation therapy-style output factors and upper physical wedge output factors were the most problematic. Percentage depth dose, jaw output factors, and enhanced dynamic wedge output factors agreed best between the IROC-H measurements and the TPS values. Although small differences were shown between 2 common TPS systems, neither was superior to the other. Parameter agreement was constant over time from 2000 to2014. Differences in basic dosimetric parameters between machine measurements and TPS values vary widely depending on the parameter, although agreement does not seem to vary by TPS and has not changed over time. Intensity modulated radiation therapy-style output factors, stereotactic body radiation therapy-style output factors, and upper physical wedge output factors had the largest disagreement and should be carefully modeled to ensure accuracy.

FLUKA Monte Carlo for Basic Dosimetric Studies of Dual Energy Medical Linear Accelerator

General purpose Monte Carlo code for simulation of particle transport is used to study the basic dosimetric parameters like percentage depth dose and dose profiles and compared with the experimental measurements from commercial dual energy medical linear accelerator. Varian Clinac iX medical linear accelerator with dual energy photon beams (6 and 15 MV) is simulated using FLUKA. FLAIR is used to visualize and edit the geometry. Experimental measurements are taken for 100 cm source-to-surface (SSD) in 50 × 50 × 50 cm3PTW water phantom using 0.12 cc cylindrical ionization chamber. Percentage depth dose for standard square field sizes and dose profiles for various depths are studied in detail. The analysis was carried out using ROOT (a DATA analysis frame work developed at CERN) system. Simulation result shows good agreement in percentage depth dose and beam profiles with the experimental measurements for Varian Clinac iX dual energy medical linear accelerator.

WE‐C‐214‐07: A Global Digital Benchmark and QA Data Center for Radiotherapy Quality Assurance

Purpose: To establish a centralized database platform for radiotherapy quality assurance (QA). This can be an interactive platform where physicists can download digital benchmark cases from, perform radiotherapy planning and QA measurements with various planning and delivery systems, and upload the results. Data retrieval and analysis functions can then be developed for the quality assessment of the radiation plan and measurement in the context of prior data with similar planning, delivery and measurement technologies. Data mining of the system can in turn generate quantitative guidance for clinical trial QA requirements that have the optimum combination of stringent mandates and realistic accommodations. Methods: Built upon prior experience of Task Group(TG) 119 from IMRT workgroup of AAPM, and digital data phantoms from EORTC, these groups collaborate with clinical trial work group of AAPM and advanced technology consortium (ATC) to establish a virtual QA environment within National Biomedical Imaging Archive (NBIA). Digital phantoms from TG 119 and EORTC dosimetric evaluation with DICOM image, structures, plan and dose were uploaded to the virtual QA environment for the established community to download and perform evaluation of basic dosimetric parameters including, structure volumes, geometric location of structure center, designated points on dose volume histogram (DVH). Nine different treatment planning or related systems with various versions are included in these evaluations. Results: Volume variations among versions of these nine systems are 2.7%, 4.2%, 14.7%, 4.7% for prostate PTV, prostate, rectum and bladder respectively. DVH reading differences are 0.1%, 2.4% and 1.5% for prostate D95, rectum D30 and bladder D30. DVH reading differences for cube 10 are 1%, 86% and 100% for V0, V20 and V30 respectively. Conclusions: A virtual QA environment has been established within NBIA for radiation oncology inter‐system and inter‐institution QA. Initial testing in reading geometric and dosimetric parameters identified significant variations among systems.

Commissioning of a double‐focused micro multileaf collimator (μMLC)

Double‐focused μMLCs are able to create fields with steeper dose gradients at the field edges and are, therefore, an advancement in delivering stereotactic treatments. A double‐focused μMLC has been installed at a Siemens Primus linear accelerator (linac) as a first research installation in Europe. The basic dosimetric parameters, such as leakage, output factors, depth‐dose curves and penumbra, have been measured in 6 and 15 MV‐mode by use of radiochromic films (GafChromic EBT), ionization chambers and our solid water QA‐phantom (Easy Cube). The leakage between the leaves is minimal and lower than that of most commercially available MLCs. Therefore, the field size of the linac can be kept constant while the leaves of the μMLC are creating different aperture shapes. Percentage depth doses (PDDs) generated by the double‐focused μMLC are equal to depth‐dose curves of the original linac. That means the μMLC affects only the off‐axis ratio (OAR). Based on the fact that the μMLC is double‐focused and the source‐to‐collimator distance is larger, the penumbra is sharper than that for fields defined by the original linac MLC. The mechanical and dosimetric investigations show the benefit of the double‐focused μMLC attached to a Siemens Primus linear accelerator.PACS number: 87.10.+e