Optimized point dose measurement: An effective tool for QA in intensity-modulated radiotherapy (original) (raw)
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Iranian Journal of Radiation Research, 2021
Background: The intensity-modulated radiotherapy (IMRT) enables personalized treatment; the complexity of this technique increased the need for patient-specific quality assurance (QA). Objective: Comparing three dosimeters that common for patient-specific QA of IMRT. Material and Method: cases were planned at Eclipse treatment planning system (TPS) to receive radiotherapy at Unique VARIAN linear accelerator LINAC; Patient-specific QA was performed with three independent dosimeters: Gafchromic films EPT2, Electronic Portal Image Device (EPID), and PTW 2D array. The absolute dose was measured and analysis of 2D gamma index was performed, then compared with the plan calculated in TPS. Results: Analysis of absolute dose measured have highest difference from dose in Gafchromic film (89.1±4) % while EPID had a lower range (96.6 ± 1.2) and 2Darray showed an agreement up to (99±1.2) for patient specific QA both EBT2 and EPID enable to compare the measured map with TPS calculations, for plan conformity the gafchromic film enable measurement with lower accuracy even with localized brain tumor, the heterogeneity in lung case slightly affect the EPID measurement, this found also with irregular surface of head and neck and increased depth within pelvic case examine. Measurement with 2D array found to be the optimum dosimeter within different conditions. Conclusion: different parameters might affect the accuracy of gafchromic film including film scanning, storing, and calibration curve. EPID has an average deviation appears in beam fluence and 2D array as a 2D ion chamber found to have the most accurate dosimeter, but still time consuming when compared to EPID.
Reports of Practical Oncology & Radiotherapy, 2018
This study aims at examining absolute dose verification of step-and-shoot intensity modulated radiation treatment (IMRT) of prostate and brain patients by use of ion chambers of two different volumes and thermoluminescent detectors (TLD). Background: The volume of the ion chamber (IC) is very important for absolute dose verification of IMRT plans since the IC has a volume average effect. With TLD detectors absolute dose verification can be done measuring the dose of multiple points simultaneously. Materials and methods: Ion chambers FC65-P of volume 0.65 cc and semiflex of volume 0.125 cc as well as TLDs were used to measure the central axis absolute dose of IMRT quality assurance (QA) plans. The results were compared with doses calculated by a treatment planning system (TPS). The absolute doses of off axis points located 2 cm and 4 cm away from the isocenter were measured with TLDs. Results: The measurements of the 0.125 cc ion chamber were found to be closer to TPS calculations compared to the 0.65 cc ion chamber, for both patient groups. For both groups the root mean square (RMS) differences between doses of the TPS and the TLD detectors are within 3.0% for the central axis and points 2 cm away from the isocenter of each axis. Larger deviations were found at the field edges, which have steep dose gradient. Conclusions: The 0.125 cc ion chamber measures the absolute dose of the isocenter more accurately compared to the 0.65 cc chamber. TLDs have good accuracy (within 3.0%) for absolute dose measurements of in-field points.
Context: In radiation treatments, estimation of the dose distribution in the target volume is one of the main components of the treatment planning procedure. To estimate the dose distribution, the information of electron densities is necessary. The standard curves determined by computed tomography (CT) scanner that may be different from that of other oncology centers. In this study, the changes of dose calculation due to the different calibration curves (HU‑ρel) were investigated. Materials and Methods: Dose values were calculated based on the standard calibration curve that was predefined for the treatment planning system (TPS). The calibration curve was also extracted from the CT images of the phantom, and dose values were calculated based on this curve. The percentage errors of the calculated values were determined. Statistical Analysis Used: The statistical analyses of the mean differences were performed using the Wilcoxon rank‑sum test for both of the calibration curves. Results and Discussion: The results show no significant difference for both of the measured and standard calibration curves (HU‑ρel) in 6, 15, and 18 MeV energies. In Wilcoxon ranked sum nonparametric test for independent samples with P < 0.05, the equality of monitor units for both of the curves to transfer 200 cGy doses to reference points was resulted. The percentage errors of the calculated values were lower than 2% and 1.5% in 6 and 15 MeV, respectively. Conclusion: From the results, it could be concluded that the standard calibration curve could be used in TPS dose calculation accurately.
Dosimetric verification of clinical radiotherapy treatment planning system
Vojnosanitetski pregled, 2020
Background/Aim. In the past two decades, we have witnessed the emergence of new radiation therapy techniques, radiotherapy treatment planning system (TPS) with calculating algorithms for the dosage calculation in a patient, units for multislice computed tomography (CT) and image-guided treatment delivery. The aim of the study was investigating the significant difference in dosimetric calculation of radiotherapy TPS in relation to the values obtained by measuring on the linear accelerator (LINAC), and the accuracy of dosimetric calculation between calculating algorithms Analytical Anisotropic Algorithm (AAA) and Acuros XB in various tissues and photon beam energies. Methods. For End-to-End test we used the hetero-geneous phantom CIRS Thorax002LFC, which anatomically represents human torso with a set of inserts known as relative electron densities (RED) for obtaining a CT calibration curve, comparable to the ?reference? CIRS 062M phantom. For the AAA and Acuros XB algorithms and for 6...
Radiation Protection in Radiotherapy Depends on Uncertainties in Small Field Dosimetry
RAD Association Journal, 2018
Technological improvements in radiotherapy machines using small fields (SF) have improved mechanical accuracy and stability, as well as dosimetric control. Small fields are nonstandard radiation fields, for which reference dosimetry cannot be reliably performed using the existing protocols. Field size definition, difficulties of accurate measurements, modeling of SF dose calculations in Treatment Planning System (TPSs), calibration protocol establishing, reference condition achievements, are some of the challenges in SF Dosimetry. Small and Intensity Modulated Radiation Therapy (IMRT) field dosimetry can be very complex-large perturbation effects could make a significant impact on reference dosimetry procedures and output factors. Comparison between different detectors provides valuable information. The aim of this paper is to evaluate the differences of dose profiles and depth dose measured in the same conditions for standard and non-standard radiation fields. Measurements are performed using detectors with different sensitive volumes. Beam quality as well as symmetry and flatness are analyzed. Results from the measurements show that the differences for SF are obvious at the edge of the profiles and in the penumbra region, as well as in the build-up region into depth dose curves. To avoid the uncertainties, for static SF where reference conditions cannot be met and for IMRT fields where delivery conditions are far removed from calibration conditions, the new formalism should be implemented.
Dosimetric Verification of the Dynamic Intensity-Modulated Radiation Therapy of 92 Patients
International Journal of Radiation Oncology*Biology*Physics, 1998
Purpose: To verify that optimized dose distributions provided by an intensity-modulated radiation therapy (IMRT) system are delivered accurately to human patients. Methods and Materials: Anthropomorphic phantoms are used to measure IMRT doses. Four types of verification are developed for: I) system commissioning with beams optimized to irradiate simulated targets in phantoms, II) plans with patient-optimized beams directed to phantoms simulating the patient, III) patient-phantom hybrid plans with patient-optimized beams calculated in phantom without further optimization, and IV) in vivo measurements. Phantoms containing dosimeters are irradiated with patient-optimized beams. Films are scanned and data were analyzed with software. Percent difference between verified and planned maximum target doses is defined as "dose discrepancy" (⌬ vp ). The frequency distribution of type II ⌬ vp from 204 verification films of 92 IMRT patients is fit to a Gaussian. Measurements made in vivo yield discrepancies specified as ⌬ ivp , also fit to a Gaussian. Results and Discussion: Verification methods revealed three systematic errors in plans that were corrected prior to treatment. Values of |⌬ vp | for verification type I are <2%. Type II verification discrepancies are characterized by a Gaussian fit with a peak 0.2% from the centroid, and 158 |⌬ vp | <5%. The 46 values of |⌬ vp | >5% arise from differences between phantom and patient geometry, and from simulation, calculation, and other errors. Values of |⌬ vp | for verification III are less than half of the values of |⌬ vp | for verification II. A Gaussian fit of ⌬ ivp from verification IV shows more discrepancy than the fit of ⌬ vp , attributed to dose gradients in detectors, and exacerbated by immobilization uncertainty. Conclusions: Dosimetric verification is a critical step in the quality assurance (QA) of IMRT. Hybrid Verification III is suggested as a preliminary quality standard for IMRT.
Journal of Cancer Therapy, 2013
This work aimed at evaluating the effect of 6-and 10-MV photon energies on intensity-modulated radiation therapy (IMRT) treatment plan outcome in different selected diagnostic cases. For such purpose, 19 patients, with different types of non CNS solid tumers, were selected. Clinical step-and-shoot IMRT treatment plans were designed for delivery on a Siemens Oncor accelerator with 82 leafs; multi-leaf collimators (MLCs). To ensure that the similarity or difference among the plans is due to energy alone, the same optimization constraints were applied for both energy plans. All the parameters like beam angles, number of beams, were kept constant to achieve the same clinical objectives. The Comparative evaluation was based on dose-volumetric analysis of both energy IMRT plans. Both qualitative and quantitative methods were used. Several physical indices for Planning Target Volume (PTV), the relevant Organs at Risk (OARs) as mean dose (Dmean), maximum dose (Dmax), 95% dose (D95), integral dose, total number of segments, and the number of MU were applied. Homogeneity index and conformation number were two other evaluation parameters that were considered in this study. Collectively, the use of 6 MV photons was dosimetrically comparable with 10 MV photons in terms of target coverage, homogeneity, conformity, and OAR savings. While 10-MV plans showed a significant reduction in the number of MUs that varied between 4.2% and 16.6% (P-value = 0.0001) for the different cases compared to 6-MV. The percentage volumes of each patient receiving 2 Gy and 5 Gy were compared for the two energies. The general trend was that 6-MV plans had the highest percentage volume, (P-value = 0.0001, P-value = 0.006) respectively. 10-MV beams actually decreased the integral dose (from average 183.27 ± 152.38 Gy-Kg to 178.08 ± 147.71 Gy-Kg, P-value = 0.004) compared with 6-MV. In general, comparison of the above parameters showed statistically significant differences between 6-MV and 10-MV groups. Based on the present results, the 10-MV is the optimal energy for IMRT, regardless of the concerns about a potential risk of radiation-induced malignancies. It is recommended that the choice to treat at 10 MV be taken as a risk vs. benefit as the clinical significance remains to be determined on case by case basis.
Uncertainty Estimation in Intensity-Modulated Radiotherapy Absolute Dosimetry Verification
International Journal of Radiation Oncology*Biology*Physics, 2007
Purpose: Intensity-modulated radiotherapy (IMRT) represents an important method for improving RT. The IMRT relative dosimetry checks are well established; however, open questions remain in reference dosimetry with ionization chambers (ICs). The main problem is the departure of the measurement conditions from the reference ones; thus, additional uncertainty is introduced into the dose determination. The goal of this study was to assess this effect systematically.