Three-dimensional dosimetry of TomoTherapy by MRI-based polymer gel technique (original) (raw)
Related papers
1997
A dosimeter gel, based on an agarose gel infused with a ferrous sulphate solution and evaluated in a magnetic resonance scanner, was used for complete verification of calculated dose distributions. Two standard treatment procedures, treatment of cancer in the urinary bladder and treatment of breast cancer after modified radical mastectomy, were examined using pixel-by-pixel and dose volume histogram comparison. The dose distributions calculated with the dose planning system was in very good agreement with the measured ones. However. in the case of the more complicated breast cancer treatment, some discrepancies were found, mainly at the beam abutment region. This may be explained by field displacements errors and by a small limitation of the dose planning utilising small electron beams in this region. The dosimeter gel system have proven to be a useful tool for dosimetry in clinical radiation therapy applications.
MRI-based treatment planning for radiotherapy: Dosimetric verification for prostate IMRT
2004
Purpose: Magnetic resonance (MR) and computed tomography (CT) image fusion with CT-based dose calculation is the gold standard for prostate treatment planning. MR and CT fusion with CT-based dose calculation has become a routine procedure for intensity-modulated radiation therapy (IMRT) treatment planning at Fox Chase Cancer Center. The use of MRI alone for treatment planning (or MRI simulation) will remove any errors associated with image fusion. Furthermore, it will reduce treatment cost by avoiding redundant CT scans and save patient, staff, and machine time. The purpose of this study is to investigate the dosimetric accuracy of MRI-based treatment planning for prostate IMRT. Methods and Materials: A total of 30 IMRT plans for 15 patients were generated using both MRI and CT data. The MRI distortion was corrected using gradient distortion correction (GDC) software provided by the vendor (Philips Medical System, Cleveland, OH). The same internal contours were used for the paired plans. The external contours were drawn separately between CT-based and MR imaging-based plans to evaluate the effect of any residual distortions on dosimetric accuracy. The same energy, beam angles, dose constrains, and optimization parameters were used for dose calculations for each paired plans using a treatment optimization system. The resulting plans were compared in terms of isodose distributions and dose-volume histograms (DVHs). Hybrid phantom plans were generated for both the CT-based plans and the MR-based plans using the same leaf sequences and associated monitor units (MU). The physical phantom was then irradiated using the same leaf sequences to verify the dosimetry accuracy of the treatment plans. Results: Our results show that dose distributions between CT-based and MRI-based plans were equally acceptable based on our clinical criteria. The absolute dose agreement for the planning target volume was within 2% between CT-based and MR-based plans and 3% between measured dose and dose predicted by the planning system in the physical phantom. Conclusions: Magnetic resonnace imaging is a useful tool for radiotherapy simulation. Compared with CT-based treatment planning, MR imaging-based treatment planning meets the accuracy for dose calculation and provides consistent treatment plans for prostate IMRT. Because MR imaging-based digitally reconstructed radiographs do not provide adequate bony structure information, a technique is suggested for producing a wire-frame image that is intended to replace the traditional digitally reconstructed radiographs that are made from CT information.
Radiotherapy and Oncology, 2003
When planning an intensity-modulated radiation therapy (IMRT) treatment in a heterogeneous region (e.g. the thorax), the dose computation algorithm of a treatment planning system may need to account for these inhomogeneities in order to obtain a reliable prediction of the dose distribution. An accurate dose verification technique such as monomer/polymer gel dosimetry is suggested to verify the outcome of the planning system. The effects of low-density structures: (a) on narrow high-energy (18 MV) photon beams; and (b) on a class-solution IMRT treatment delivered to a thorax phantom have been examined using gel dosimetry. The used phantom contained air cavities that could be filled with water to simulate a homogeneous or heterogeneous configuration. The IMRT treatment for centrally located lung tumors was delivered on both cases, and gel derived dose maps were compared with computations by both the GRATIS and Helax-TMS planning system. Dose rebuildup due to electronic disequilibrium in a narrow photon beam is demonstrated. The gel measurements showed good agreement with diamond detector measurements. Agreement between measured IMRT dose maps and dose computations was demonstrated by several quantitative techniques. An underdosage of the planning target volume (PTV) was revealed. The homogeneity of the phantom had only a minor influence on the dose distribution in the PTV. An expansion of low-level isodoses in the lung volume was predicted by collapsed cone computations in the heterogeneous case. For the class-solution described, the dose in centrally located mediastinal tumors can be computed with sufficient accuracy, even when neglecting the lower lung density. Polymer gel dosimetry proved to be a valuable technique to verify dose calculation algorithms for IMRT in 3D in heterogeneous configurations.
2006
Several tools are used for the dosimetric verification of intensity-modulated arc therapy (IMAT) treatment delivery. However, limited information is available for composite on-line evaluation of these tools. The purpose of this study was to evaluate the dosimetric verification of IMAT treatment plans using a 2D diode array detector (2D array), radiochromic film (RCF) and radiosensitive polymer gel dosimeter (RPGD). The specific verification plans were created for IMAT for two prostate cancer patients by use of the clinical treatment plans. Accordingly, the IMAT deliveries were performed with the 2D array on a gantry-mounting device, RCF in a cylindrical acrylic phantom, and the RPGD in two cylindrical phantoms. After the irradiation, the planar dose distributions from the 2D array and the RCFs, and the 3D dose distributions from the RPGD measurements were compared with the calculated dose distributions using the gamma analysis method (3% dose difference and 3-mm distance-to-agreement criterion), dose-dependent dose difference diagrams, dose difference histograms, and isodose distributions. The gamma passing rates of 2D array, RCFs and RPGD for one patient were 99.5%, 96.5% and 93.7%, respectively; the corresponding values for the second patient were 97.5%, 92.6% and 92.9%. Mean percentage differences between the RPGD measured and calculated doses in 3D volumes containing PTVs were -0.29 ± 7.1% and 0.97 ± 7.6% for the two patients, respectively. In conclusion, IMAT prostate plans can be delivered with high accuracy, although the 3D measurements indicated less satisfactory agreement with the treatment plans, mainly due to the dosimetric inaccuracy in low-dose regions of the RPGD measurements.
Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology, 2011
Dose planning requires a CT scan which provides the electron density distribution for dose calculation. MR provides superior soft tissue contrast compared to CT and the use of MR-alone for prostate planning would provide further benefits such as lower cost to the patient. This study compares the accuracy of MR-alone based dose calculations with bulk electron density assignment to CT-based dose calculations for prostate radiotherapy. CT and whole pelvis MR images were contoured for 39 prostate patients. Plans with uniform density and plans with bulk density values assigned to bone and tissue were compared to the patient's gold standard full density CT plan. The optimal bulk density for bone was calculated using effective depth measurements. The plans were evaluated using ICRU point doses, dose volume histograms, and Chi comparisons. Differences in spatial uniformity were investigated for the CT and MR scans. The calculated dose for CT bulk bone and tissue density plans was 0.1±0....
Physica Medica
Advanced 3D dosimetry is required for verifications of complex dose distributions in modern radiotherapy. Two 3D polymer gel dosimeters, coupled with magnetic resonance (MR) imaging (3 T MRI) readout and data processing with polyGeVero® software, were tested for the verification of calculated 3D dose distributions by a treatment planning system (TPS) and ArcCHECK®-3DVH®, related to eradication of a lung tumour. Methods: N-vinylpyrrolidone-containing 3D polymer gel dosimeters were used: VIC (containing ascorbic acid and copper sulfate pentahydrate) and VIC-T (containing tetrakis(hydroxymethyl)phosphonium chloride). Three remote centers were involved in the dosimeters preparation and irradiation (Poland), and MRI (Austria). Cross beam calibration of the dosimeters and verification of a 3D dose distribution calculated with an Eclipse External Beam TPS and ArcCHECK®-3DVH® were performed. The 3D-to-3D comparisons of the VIC and VIC-T with TPS and ArcCHECK®-3DVH® along with ArcCHECK®-3DVH® versus TPS dose matrixes were performed with the aid of the polyGeVero® by analyzing dose profiles, isodoses lines, gamma index, gamma angle, dose difference, and related histograms. Results: The measured MR-relaxation rate (R 2 = 1/T 2) for the dosimeters relates to the dose, as follows: R 2 = 0.0928 ± 0.0008 [Gy −1 s −1 ] × D [Gy] + 2.985 ± 0.012 [s −1 ] (VIC) and 0.1839 ± 0.0044 [Gy −1 s −1 ] × D [Gy] + 2.519 ± 0.053 [s −1 ] (VIC-T). The 3D-to-3D comparisons revealed a good agreement between the measured and calculated 3D dose distributions. Conclusions: VIC and VIC-T with 3T MRI readout and polyGeVero® showed potential for verifications of calculated irradiation plans. The results obtained suggest the implementation of the irradiation plan for eradication of the lung tumour.
A practical three-dimensional dosimetry system for radiation therapy
Medical Physics, 2006
There is a pressing need for a practical three-dimensional ͑3D͒ dosimetry system, convenient for clinical use, and with the accuracy and resolution to enable comprehensive verification of the complex dose distributions typical of modern radiation therapy. Here we introduce a dosimetry system that can achieve this challenge, consisting of a radiochromic dosimeter ͑PRESAGE™͒ and a commercial optical computed tomography ͑CT͒ scanning system ͑OCTOPUS™͒. PRESAGE™ is a transparent material with compelling properties for dosimetry, including insensitivity of the dose response to atmospheric exposure, a solid texture negating the need for an external container ͑reducing edge effects͒, and amenability to accurate optical CT scanning due to radiochromic optical contrast as opposed to light-scattering contrast. An evaluation of the performance and viability of the PRESAGE™/OCTOPUS, combination for routine clinical 3D dosimetry is presented. The performance of the two components ͑scanner and dosimeter͒ was investigated separately prior to full system test. The optical CT scanner has a spatial resolution of Յ1 mm, geometric accuracy within 1 mm, and high reconstruction linearity ͑with a R 2 value of 0.9979 and a standard error of estimation of ϳ1%͒ relative to independent measurement. The overall performance of the PRESAGE™/OCTOPUS system was evaluated with respect to a simple known 3D dose distribution, by comparison with GAFCHROMIC ® EBT film and the calculated dose from a commissioned planning system. The "measured" dose distribution in a cylindrical PRESAGE™ dosimeter ͑16 cm diameter and 11 cm height͒ was determined by optical-CT, using a filtered backprojection reconstruction algorithm. A three-way Gamma map comparison ͑4% dose difference and 4 mm distance to agreement͒, between the PRESAGE™, EBT and calculated dose distributions, showed full agreement in measurable region of PRESAGE™ dosimeter ͑ϳ90% of radius͒. The EBT and PRESAGE™ distributions agreed more closely with each other than with the calculated plan, consistent with penumbral blurring in the planning data which was acquired with an ion chamber. In summary, our results support the conclusion that the PRESAGE™ optical-CT combination represents a significant step forward in 3D dosimetry, and provides a robust, clinically effective and viable high-resolution relative 3D dosimetry system for radiation therapy.
Evaluation of 3D Conformal Radiotherapy for Prostate Cancer Using Dosimetric Indices
HE PRESENT study aims to evaluate three dimensional …...conformal radiation therapy (3DCRT) for patients with prostate cancer. This will be done by the effect of 6 MV and 15 MV photon energies in addition to some of treatment fields using different of conformity indices. For such study 10 patients with prostate cancer are selected. The computed tomography CT slices are taken for each patient and transferred to XiO treatment planning system. Evaluation of treatment plans is performed by conformity indices. The 3DCRT plans are designed using CMS XiO treatment planning system using linear accelerator with multi-leaf collimator (MLC) with two energies 6 and 15 MV. The results of conformity index (CI) show an average value from 1.5± 0.03 to 1.9± 0.06 in 6-Fields with 15 MV and 3-Fields with 6MV, respectively. The results of conformation number (CN) indicate an average value from 0.51± 0.02 to 0.67± 0.02 in 3-Fields with 6MV and 6-Fields with 15MV, respectively. In conclusion, the use of high-energy 15 MV or 6 MV photons achieves the same dose coverage but in case of using 15 MV photon produces better safety for organs at risk and also improves conformity indices of dose to planning target volume (PTV). This occurs when increasing number of fields which improves conformity indices and decrease dose to organs at risk. The conformity index and conformation number give the same dosimetric information after the revision of DVH and dose distributions.
Medical Physics, 2003
A new type of polymer gel dosimeter, which responds well to absorbed dose even when manufactured in the presence of normal levels of oxygen, was recently described by Fong et al. ͓Phys. Med. Biol. 46, 3105-3113 ͑2001͔͒ and referred to by the acronym MAGIC. The aim of this study was to investigate the feasibility of using this new type of gel for intensity-modulated radiation therapy ͑IMRT͒ verification. Gel manufacturing was carried out in room atmosphere under normal levels of oxygen. IMRT inverse treatment planning was performed using the Helios software. The gel was irradiated using a linear accelerator equipped with a dynamic multileaf collimator, and intensity modulation was achieved using sliding window technique. The response to absorbed dose was evaluated using magnetic resonance imaging. Measured and calculated dose distributions were compared with regard to in-plane isodoses and dose volume histograms. In addition, the spatial and dosimetric accuracy was evaluated using the gamma formalism. Good agreement between calculated and measured data was obtained. In the isocenter plane, the 70% and 90% isodoses acquired using the different methods are mostly within 2 mm, with up to 3 mm disagreement at isolated points. For the planning target volume ͑PTV͒, the calculated mean relative dose was 96.8Ϯ2.5% ͑1 SD͒ and the measured relative mean dose was 98.6Ϯ2.2%. Corresponding data for an organ at risk was 34.4Ϯ0.9% and 32.7Ϯ0.7%, respectively. The gamma criterion ͑3 mm spatial/3% dose de-viation͒ was fulfilled for 94% of the pixels in the target region. Discrepancies were found in hot spots the upper and lower parts of the PTV, where the measured dose was up to 11% higher than calculated. This was attributed to sub optimal scatter kernels used in the treatment planning system dose calculations. Our results indicate great potential for IMRT verification using MAGIC-type polymer gel.