| 1. |
- Giantsoudi, D., et al.
(författare)
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A gEUD-based inverse planning technique for HDR prostate brachytherapy : Feasibility study
- 2013
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405 .- 2473-4209. ; 40:4, s. 041704-
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this work was to study the feasibility of a new inverse planning technique based on the generalized equivalent uniform dose for image-guided high dose rate (HDR) prostate cancer brachytherapy in comparison to conventional dose-volume based optimization. Methods: The quality of 12 clinical HDR brachytherapy implants for prostate utilizing HIPO (Hybrid Inverse Planning Optimization) is compared with alternative plans, which were produced through inverse planning using the generalized equivalent uniform dose (gEUD). All the common dose-volume indices for the prostate and the organs at risk were considered together with radiobiological measures. The clinical effectiveness of the different dose distributions was investigated by comparing dose volume histogram and gEUD evaluators. Results: Our results demonstrate the feasibility of gEUD-based inverse planning in HDR brachytherapy implants for prostate. A statistically significant decrease in D-10 or/and final gEUD values for the organs at risk (urethra, bladder, and rectum) was found while improving dose homogeneity or dose conformity of the target volume. Conclusions: Following the promising results of gEUD-based optimization in intensity modulated radiation therapy treatment optimization, as reported in the literature, the implementation of a similar model in HDR brachytherapy treatment plan optimization is suggested by this study. The potential of improved sparing of organs at risk was shown for various gEUD-based optimization parameter protocols, which indicates the ability of this method to adapt to the user's preferences.
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| 2. |
- Mavroidis, Panayiotis, et al.
(författare)
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Analysis of fractionation correction methodologies for multiple phase treatment plans in radiation therapy
- 2013
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405 .- 2473-4209. ; 40:3, s. 031715-
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Radiation therapy is often delivered by multiple sequential treatment plans. For an accurate radiobiological evaluation of the overall treatment, fractionation corrections to each dose distribution must be applied before summing the three-dimensional dose matrix of each plan since the simpler approach of performing the fractionation correction to the total dose-volume histograms, obtained by the arithmetical sum of the different plans, becomes inaccurate for more heterogeneous dose patterns. In this study, the differences between these two fractionation correction methods, named here as exact (corrected before) and approximate (after summation), respectively, are assessed for different cancer types. Methods: Prostate, breast, and head and neck (HN) tumor patients were selected to quantify the differences between two fractionation correction methods (the exact vs the approximate). For each cancer type, two different treatment plans were developed using uniform (CRT) and intensity modulated beams (IMRT), respectively. The responses of the target and normal tissue were calculated using the Poisson linear-quadratic-time model and the relative seriality model, respectively. All treatments were radiobiologically evaluated and compared using the complication-free tumor control probability (P+), the biologically effective uniform dose ((D) double under bar) together with common dosimetric criteria. Results: For the prostate cancer patient, an underestimation of around 14%-15% in P+ was obtained when the fractionation correction was applied after summation compared to the exact approach due to significant biological and dosimetric variations obtained between the two fractionation correction methods in the involved lymph nodes. For the breast cancer patient, an underestimation of around 3%-4% in the maximum dose in the heart was obtained. Despite the dosimetric differences in this organ, no significant variations were obtained in treatment outcome. For the HN tumor patient, an underestimation of about 5% in treatment outcome was obtained for the CRT plan as a result of an underestimation of the planning target volume control probability by about 10%. An underestimation of about 6% in the complication probability of the right parotid was also obtained. For all the other organs at risk, dosimetric differences of up to 4% were obtained but with no significant impact in the expected clinical outcome. However, for the IMRT plan, an overestimation in P+ of 4.3% was obtained mainly due to an underestimation of the complication probability of the left and right parotids (2.9% and 5.8%, respectively). Conclusions: The use of the exact fractionation correction method, which is applying fractionation correction on the separate dose distributions of a multiple phase treatment before their summation was found to have a significant expected clinical impact. For regions of interest that are irradiated with very heterogeneous dose distributions and significantly different doses per fraction in the different treatment phases, the exact fractionation correction method needs to be applied since a significant underestimation of the true patient outcome can be introduced otherwise.
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| 3. |
- Knaup, Courtney, et al.
(författare)
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Investigating the dosimetric and tumor control consequences of prostate seed loss and migration
- 2012
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 39:6, s. 3291-3298
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Low dose-rate brachytherapy is commonly used to treat prostate cancer. However, once implanted, the seeds are vulnerable to loss and movement. The goal of this work is to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy. Methods: Five patients were used in this study. For each patient three treatment plans were created using Iodine-125, Palladium-103, and Cesium-131 seeds. The three seeds that were closest to the urethra were identified and modeled as the seeds lost through the urethra. The three seeds closest to the exterior of prostatic capsule were identified and modeled as those lost from the prostate periphery. The seed locations and organ contours were exported from Prowess and used by in-house software to perform the dosimetric and radiobiological evaluation. Seed loss was simulated by simultaneously removing 1, 2, or 3 seeds near the urethra 0, 2, or 4 days after the implant or removing seeds near the exterior of the prostate 14, 21, or 28 days after the implant. Results: Loss of one, two or three seeds through the urethra results in a D-90 reduction of 2%, 5%, and 7% loss, respectively. Due to delayed loss of peripheral seeds, the dosimetric effects are less severe than for loss through the urethra. However, while the dose reduction is modest for multiple lost seeds, the reduction in tumor control probability was minimal. Conclusions: The goal of this work was to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy. The results presented show that loss of multiple seeds can cause a substantial reduction of D-90 coverage. However, for the patients in this study the dose reduction was not seen to reduce tumor control probability. (C) 2012 American Association of Physicists in Medicine.
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| 4. |
- Mavroidis, Panayiotis, et al.
(författare)
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Expected Clinical Impact of the Differences Between Planned and Delivered IMRT Dose Distributions
- 2007
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Ingår i: Proceedings in 49th AAPM Annual Meeting, Minneapolis, Minnesota, USA, July 22-26, 2007. - : Wiley.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: Due to the highly conformal distributions that can be obtained with intensity modulated radiation therapy (IMRT), any discrepancy between the intended and delivered distributions would likely affect the clinical outcome. Consequently, there is a need for a measure that would quantify those differences in terms of a change in the expected clinical outcome.Material and Methods: To evaluate such a measure, the case of a cervix cancer was used where the bladder and rectum, are proximal and partially overlapping with the internal target volume. A solid phantom simulating the pelvic anatomy was fabricated and a treatment plan was developed to deliver the prescribed dose to the phantom. The phantom was then irradiated with films positioned in several transverse planes. The racetrack microtron at 50MV was used in the treatment planning and delivery processes. The dose distribution delivered was analyzed based on the film measurements and compared against the treatment plan. The differences in the measurements were evaluated using both physical and biological criteria.Results: For the computerized treatment plan, the maximum value of P+ was 84.1%, for a mean dose to the ITV of = 93.3Gy, associated relative standard deviation D/ = 16.8% and biologically effective uniform dose, ITV of 89.2 Gy. The delivered dose distribution from all the beams produced a P+ value of 77.0% for ITV = 93.2Gy, D/ = 19.0% and ITV of 83.5 Gy.Discussion and Conclusions: Whereas the physical comparison of dose distributions can assess the geometric accuracy of delivery, it does not reflect the clinical impact of any measured dose discrepancies. With highly conformal IMRT, the accuracy of the patient setup and treatment delivery, are critical for the success of the treatment. A method is proposed to evaluate the precision of the delivered plan based on changes in complication and control rates as they relate to uncertainties in dose delivery.
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| 5. |
- Mavroidis, Panayiotis, et al.
(författare)
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Interpretation of the dosimetric results of three uniformity regularization methods in terms of expected treatment outcome.
- 2008
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 35:11, s. 5009-18
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Tidskriftsartikel (refereegranskat)abstract
- In IMRT treatment plan optimization there are various methods that try to regularize the variation of dose nonuniformity using purely dosimetric measures. However, although these methods can help in finding a good dose distribution, they do not provide any information regarding the expected treatment outcome. When a treatment plan optimization is performed using biological measures, the final goal should be some indication about the expected tumor control or normal tissue complications, which is the primary goal of treatment planning (the association of treatment configurations and dose prescription with the treatment outcome). In this study, this issue is analyzed distinguishing the dose-oriented treatment plan optimization from the response-oriented optimization. Three different dose distributions were obtained by using a dose-based optimization technique, an EUD-based optimization without applying any technique for regularizing the nonuniformity of the dose distribution, and an EUD-based optimization using a variational regularization technique, which controls dose nonuniformity. The clinical effectiveness of the three dose distributions was investigated by calculating the response probabilities of the tumors and organs-at-risk (OARs) involved in two head and neck and prostate cancer cases. The radiobiological models used are the linear-quadratic-Poisson and the Relative Seriality models. Furthermore, the complication-free tumor control probability and the biologically effective uniform dose (D) were used for treatment plan evaluation and comparison. The radiobiological comparison shows that the EUD-based optimization using L-curve regularization gives better results than the EUD-based optimization without regularization and dose-based optimization in both clinical cases. Concluding, it appears that the applied dose nonuniformity regularization technique is expected to improve the effectiveness of the optimized IMRT dose distributions. However, more patient cases are needed to validate the statistical significance of the results and conclusions presented in this paper.
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| 6. |
- Mavroidis, Panayiotis, et al.
(författare)
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Response-probability volume histograms and iso-probability of response charts in treatment plan evaluation
- 2011
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 38:5, s. 2382-2397
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: This study aims at demonstrating a new method for treatment plan evaluation and comparison based on the radiobiological response of individual voxels. This is performed by applying them on three different cancer types and treatment plans of different conformalities. Furthermore, their usefulness is examined in conjunction with traditionally applied radiobiological and dosimetric treatment plan evaluation criteria. Methods: Three different cancer types (head and neck, breast and prostate) were selected to quantify the benefits of the proposed treatment plan evaluation method. In each case, conventional conformal radiotherapy (CRT) and intensity modulated radiotherapy (IMRT) treatment configurations were planned. Iso-probability of response charts was produced by calculating the response probability in every voxel using the linear-quadratic-Poisson model and the dose-response parameters of the corresponding structure to which this voxel belongs. The overall probabilities of target and normal tissue responses were calculated using the Poisson and the relative seriality models, respectively. The 3D dose distribution converted to a 2 Gy fractionation, D(2GY) and iso-BED distributions are also shown and compared with the proposed methodology. Response-probability volume histograms (RVH) were derived and compared with common dose volume histograms (DVH). The different dose distributions were also compared using the complication-free tumor control probability, P(+), the biologically effective uniform dose, (sic), and common dosimetric criteria. Results: 3D Iso-probability of response distributions is very useful for plan evaluation since their visual information focuses on the doses that are likely to have a larger clinical effect in that particular organ. The graphical display becomes independent of the prescription dose highlighting the local radiation therapy effect in each voxel without the loss of important spatial information. For example, due to the exponential nature of the Poisson distribution, cold spots in the target volumes or hot spots in the normal tissues are much easier to be identified. Response-volume histograms, as DVH, can also be derived and used for plan comparison. RVH are advantageous since by incorporating the radiobiological properties of each voxel they summarize the 3D distribution into 2D without the loss of relevant information. Thus, more clinically relevant radiobiological objectives and constraints could be defined and used in treatment planning optimization. These measures become increasingly important when dose distributions need to be designed according to the microscopic biological properties of tumor and normal tissues. Conclusions: The proposed methods do not aim to replace quantifiers like the probabilities of total tissue response, which ultimately are the quantities of interest to evaluate treatment success. However, iso-probability of response charts and response-probability volume histograms illustrates more clearly the difference in effectiveness between different treatment plans than the information provided by alternative dosimetric data. The use of 3D iso-probability of response distributions could serve as a good descriptor of the effectiveness of a dose distribution indicating primarily the regions in a tissue that dominate its response.
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| 7. |
- Milickovic, Natasa, et al.
(författare)
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4D analysis of influence of patient movement and anatomy alteration on the quality of 3D U/S-based prostate HDR brachytherapy treatment delivery
- 2011
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 38:9, s. 4982-4993
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Modern HDR brachytherapy treatment for prostate cancer based on the 3D ultrasound (U/S) plays increasingly important role. The purpose of this study is to investigate possible patient movement and anatomy alteration between the clinical image set acquisition, made after the needle implantation, and the patient irradiation and their influence on the quality of treatment. Methods: The authors used 3D U/S image sets and the corresponding treatment plans based on a 4D-treatment planning procedure: plans of 25 patients are obtained right after the needle implantation (clinical plan is based on this 3D image set) and just before and after the treatment delivery. The authors notice the slight decrease of treatment quality with increase of time gap between the clinical image set acquisition and the patient irradiation. 4D analysis of dose-volume-histograms (DVHs) for prostate: CTV1 - PTV, and urethra, rectum, and bladder as organs at risk (OARs) and conformity index (COIN) is presented, demonstrating the effect of prostate, OARs, and needles displacement. Results: The authors show that in the case that the patient body movement/anatomy alteration takes place, this results in modification of DVHs and radiobiological parameters, hence the plan quality. The observed average displacement of needles (1 mm) and of prostate (0.57 mm) is quite small as compared with the average displacement noted in several other reports [A. A. Martinez et al., Int. J. Radiat. Oncol., Biol., Phys. 49(1), 61-69 (2001); S. J. Damore et al., Int. J. Radiat. Oncol., Biol., Phys. 46(5), 1205-1211 (2000); P. J. Hoskin et al., Radiotherm. Oncol. 68(3), 285-288 (2003); E. Mullokandov et al., Int. J. Radiat. Oncol., Biol., Phys. 58(4), 1063-1071 (2004)] in the literature. Conclusions: Although the decrease of quality of dosimetric and radiobiological parameters occurs, this does not cause clinically unacceptable changes to the 3D dose distribution, according to our clinical protocol. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3618735]
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| 8. |
- Papanikolaou, N, et al.
(författare)
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Investigation of the Use of Transmission Type Detectors for Daily IMRT Patient Dose Reconstruction
- 2007
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Ingår i: Proceedings in 49th AAPM Annual Meeting, Minneapolis, Minnesota, USA, July 22-26, 2007. - : Wiley.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: To study the feasibility of using transmission type detectors for daily IMRT patient dose reconstruction and verification. Methods and Materials: Because of the complexity of IMRT there is a need for quality assurance for every patient. However, the daily delivered intensities may vary slightly from the planned ones. In this work we investigated the use of transmission type detectors and films for the verification of daily dose delivered to the patient. Films were placed at various distances from the source in air to measure the beam intensity. The fluence maps were also reconstructed from calculations of the TPS at the same planes. Monte Carlo simulations of the same geometries were performed and the intensity maps were also extracted at the same planes. Intead of film, a tray mounted transmission detector can also be used. Results: The film measurements were compared to TPS predicted intensity maps. Corrections based on the Monte Carlo study were applied to remove the electron contamination from the measured intensity maps since it was not accounted by the TPS. MC results indicate that the corrections due to the contaminant electrons can be 15 to 20% for 6MV beams. The corrected measured intensity map was used to calculate and reconstruct the daily dose to the patient using Monte Carlo. The results show good agreement between measurements using films and Monte Carlo calculations. Conclusions: Transmission detectors such as films can be used in order to compare the delivered intensity maps against the TPS predicted ones. The dose to the patient can be reconstructed using Monte Carlo based on the delivered intensity map and the dose can be potentially verified for each fraction, especially if a cone beam CT is performed daily.
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| 9. |
- Roland, Teboh, et al.
(författare)
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The radiobiological P+ index for pretreatment plan assessment with emphasis on four-dimensional radiotherapy modalities
- 2012
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 39:10, s. 6420-6430
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Radiation treatment modalities will continue to emerge that promise better clinical outcomes albeit technologically challenging to implement. An important question facing the radiotherapy community then is the need to justify the added technological effort for the clinical return. Mobile tumor radiotherapy is a typical example, where 4D tumor tracking radiotherapy (4DTRT) has been proposed over the simpler conventional modality for better results. The modality choice per patient can depend on a wide variety of factors. In this work, we studied the complication-free tumor control probability (P+) index, which combines the physical complexity of the treatment plan with the radiobiological characteristics of the clinical case at hand and therefore found to be useful in evaluating different treatment techniques and estimating the expected clinical effectiveness of different radiation modalities. Methods: 4DCT volumes of 18 previously treated lung cancer patients with tumor motion and size ranging from 2 mm to 15 mm and from 4 cc to 462 cc, respectively, were used. For each patient, 4D treatment plans were generated to extract the 4D dose distributions, which were subsequently used with clinically derived radiobiological parameters to compute the P+ index per modality. Results: The authors observed, on average, a statistically significant increase in P+ of 3.4% +/- 3.8% (p < 0.003) in favor of 4DTRT. There was high variability among the patients with a < 0.5% up to 13.4% improvement in P+. Conclusions: The observed variability in the improvement of the clinical effectiveness suggests that the relative benefit of tracking should be evaluated on a per patient basis. Most importantly, this variability could be effectively captured in the computed P+. The index can thus be useful to discriminate and hence point out the need for a complex modality like 4DTRT over another. Besides tumor mobility, a wide range of other factors, e.g., size, location, fractionation, etc., can affect the relative benefits. Application of the P+ objective is a simple and effective way to combine these factors in the evaluation of a treatment plan.
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| 10. |
- Stathakis, S, et al.
(författare)
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Monte Carlo Based Dose Verification for Serial Tomotherapy
- 2007
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Ingår i: Proceedings in 49th AAPM Annual Meeting, Minneapolis, Minnesota, USA, July 22-26, 2007. - : Wiley.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: To develop a Monte Carlo model to verify the final dose distributions and monitor units for serial tomotherapy plans developed and delivered using the Peacock system (Corvus Treatment Planning System and MIMiC collimator, Nomos Corp., Sewickley, PA). Materials and methods: The Peacock system delivers the dose to the patient using arc therapy. The treatment plan is created in Corvus were sinograms are created for each arc in order to dictate the state of each of the MIMiC leaves at different locations along the arc. In-house functions were written in Matlab (Mathworks Inc., Natick, MA) to decode these sinograms. A simple three-field plan (three gantry positions), as well as full patient treatment plans were simulated using our Monte Carlo model and the same plans were delivered using the Peacock system in solid water. Films were placed in the solid water phantom in order to measure the dose distribution for comparison against the Monte Carlo calculations. Matlab functions were written to convert the Monte Carlo output into a format RIT113 (RIT Inc., Colorado Springs, CO) could read. This allowed us to co-register the calculated dose maps and the measured ones in order to compare the two. Results: The Monte Carlo calculated dose distribution from the complete arc therapy in solid water phantom was compared against film measurements. The agreement was within 2%. The comparison between Monte Carlo results and Corvus calculated dose distribution revealed that Corvus would fail to accurately compute the dose in the region where inhomogeneities were present. Conclusions: Based on the agreement between Monte Carlo and measurements we can use the Monte Carlo system as an independent quality assurance tool in order to verify dose distributions and MUs per arc computed by the Corvus.
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