| 1. |
- Dzintars, Erik, et al.
(författare)
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Application of an independent dose calculation software for estimating the impact of inter-fractional setup shifts in Helical Tomotherapy treatments
- 2013
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 29:6, s. 615-623
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to validate the capability of in-house independent point dose calculation software to be used as a second check for Helical Tomotherapy treatment plans. The software performed its calculations in homogenous conditions (using the Cheese phantom, which is a cylindrical phantom with radius 15 cm and length 18 cm) using a factor-based algorithm. Fifty patients, who were treated for pelvic (10), prostate (14), lung (10), head 82 neck (12) and brain (4) cancers, were used. Based on the individual patient kVCT images and the pretreatment MVCT images for each treatment fraction, the corresponding daily patient setup shifts in the IEC-X, IEC-Y, and IEC-Z directions were registered. For each patient, the registered fractional setup shifts were grouped into systematic and random shifts. The average systematic dosimetric variations showed small dose deviation for the different cancer types (1.0%-3.0%) compared to the planned dose. Of the fifty patients, only three had percent differences larger than 5%. The average random dosimetric variations showed relatively small dose deviations (0.2%-1.1%) compared to the planned dose. None of the patients had percent differences larger than 5%. By examining the individual fractions of each patient, it is observed that only in 31 out of 1358 fractions the percent differences exceeded the border of 5%. These results indicate that the overall dosimetric impact from systematic and random variations is small and that the software is a capable platform for independent point dose validation for the Helical Tomotherapy modality.
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| 2. |
- Dzintars, Eric, et al.
(författare)
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Performance of independent dose calculation in helical tomotherapy : implementation of the mcsim code
- 2012
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Ingår i: Australasian Physical & Engineering Sciences in Medicine. - : Springer Science and Business Media LLC. - 0158-9938 .- 1879-5447. ; 35:4, s. 423-438
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Tidskriftsartikel (refereegranskat)abstract
- Currently, a software-based second check dose calculation for helical tomotherapy (HT) is not available. The goal of this study is to evaluate the dose calculation accuracy of the in-house software using EGS4/MCSIM Monte Carlo environment against the treatment planning system calculations. In-house software was used to convert HT treatment plan information into a non-helical format. The MCSIM dose calculation code was evaluated by comparing point dose calculations and dose profiles against those from the HT treatment plan. Fifteen patients, representing five treatment sites, were used in this comparison. Point dose calculations between the HT treatment planning system and the EGS4/MCSIM Monte Carlo environment had percent difference values below 5 % for the majority of this study. Vertical and horizontal planar profiles also had percent difference values below 5 % for the majority of this study. Down sampling was seen to improve speed without much loss of accuracy. EGS4/MCSIM Monte Carlo environment showed good agreement with point dose measurements, compared to the HT treatment plans. Vertical and horizontal profiles also showed good agreement. Significant time saving may be obtained by down-sampling beam projections. The dose calculation accuracy of the in-house software using the MCSIM code against the treatment planning system calculations was evaluated. By comparing point doses and dose profiles, the EGS4/MCSIM Monte Carlo environment was seen to provide an accurate independent dose calculation.
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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. |
- Komisopoulos, Georgios, et al.
(författare)
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Radiobiologic comparison of helical tomotherapy, intensity modulated radiotherapy, and conformal radiotherapy in treating lung cancer accounting for secondary malignancy risks
- 2014
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Ingår i: Medical Dosimetry. - : Elsevier BV. - 0958-3947 .- 1873-4022. ; 39:4, s. 337-347
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study is to examine the importance of using measures to predict the risk of inducing secondary malignancies in association with the clinical effectiveness of treatment plans in terms of tumor control and normal tissue complication probabilities. This is achieved by using radiobiologic parameters and measures, which may provide a closer association between clinical outcome and treatment delivery. Overall, 4 patients having been treated for lung cancer were examined. For each of them, 3 treatment plans were developed based on the helical tomotherapy (HT), multileaf collimator-based intensity modulated radiation therapy (IMRT), and 3-dimensional conformal radiation therapy (CRT) modalities. The different plans were evaluated using the complication-free tumor control probability (p(t)), the overall probability of injury (p(1)), the overall probability of control/benefit (p(B)), and the biologically effective uniform dose (15). These radiobiologic measures were used to develop dose-response curves (p-D diagram), which can help to evaluate different treatment plans when used in conjunction with standard dosimetric criteria. The risks for secondary malignancies in the heart and the contralateral lung were calculated for the 3 radiation modalities based on the corresponding dose-volume histograms (DVHs) of each patient. Regarding the overall evaluation of the different radiation modalities based on the p(+) index, the average values of the HT, IMRT, and CRT are 67.3%, 61.2%, and 68.2%, respectively. The corresponding average values of p(B) are 75.6%, 70.5%, and 71.0%, respectively, whereas the average values of p(1) are 8.3%, 9.3%, and 2.8%, respectively. Among the organs at risk (OARS), lungs show the highest probabilities for complications, which are 7.1%, 8.0%, and 1.3% for the HT, IMRT, and CRT modalities, respectively. Similarly, the biologically effective prescription doses (D-B) for the HT, IMRT, and CRT modalities are 64.0, 60.9, and 60.8 Gy, respectively. Regarding the risk for secondary cancer, for the heart, the lowest average risk is produced by IMRT (0.10%) compared with the HT (0.17%) and CRT (0.12%) modalities, whereas the 3 radiation modalities show almost equivalent results regarding the contralateral lung (0.8% for HT, 0.9% for IMRT, and 0.9% for CRT). The use of radiobiologic parameters in the evaluation of different treatment plans and estimation of their expected clinical outcome is shown to provide very useful clinical information. The radiobiologic analysis of the response probabilities showed that different radiation modalities appear to be more effective in different patient geometries and target sizes and locations. Furthermore, there is not a clear pattern between the plans that appear to be more effective for the treatment and the risk of secondary malignancy. It seems that radiobiologically based treatment planning taking into account the risk of secondary cancer can be established as an effective clinical tool for a more clinically relevant treatment optimization.
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| 5. |
- Lavdas, Eleftherios, et al.
(författare)
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Comparison of BLADE and conventional T2-TSE sequences for the sagittal visualization of the cervical spinal cord in multiple sclerosis patients - A case report
- 2013
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Ingår i: Magnetic Resonance Imaging. - : Elsevier BV. - 0730-725X .- 1873-5894. ; 31:10, s. 1766-1770
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to report the significant differences found in the identification of lesions in cervical spinal cord of two patients with multiple sclerosis when using the BLADE T2-TSE and BLADE T2-TIRM sequences as opposed to the conventional T2-TSE and T2-TIRM sequences for sagittal acquisition at 1.5 T. In both patients, one more lesion was identified with the BLADE sequences than with the conventional ones. Consequently, we suggest the use of BLADE T2-TSE and BLADE T2-TIRM sequences in place of conventional ones for sagittal examination of the cervical spinal cord of multiple sclerosis patients. The advantages of TIRM to reveal the pathology of the cervical spinal cord and the advantage of BLADE sequences to improve image quality should be combined in a sequence that could be ideal for cervical spinal cord examinations.
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| 6. |
- Lavdas, Eleftherios, et al.
(författare)
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Elimination of motion, pulsatile flow and cross-talk artifacts using blade sequences in lumbar spine MR imaging
- 2013
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Ingår i: Magnetic Resonance Imaging. - : Elsevier BV. - 0730-725X .- 1873-5894. ; 31:6, s. 882-890
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to evaluate the ability of T2 turbo spin echo (TSE) axial and sagittal BLADE sequences in reducing or even eliminating motion, pulsatile flow and cross-talk artifacts in lumbar spine MRI examinations. Forty four patients, who had routinely undergone a lumbar spine examination, participated in the study. The following pairs of sequences with and without BLADE were compared: a) 12 TSE Sagittal (SAG) in thirty two cases, and b) 12 TSE Axial (AX) also in thirty two cases. Both quantitative and qualitative analyses were performed based on measurements in different normal anatomical structures and examination of seven characteristics, respectively. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion, pulsatile flow and cross-talk artifacts was evaluated. Based on the results of the qualitative analysis for the different sequences and anatomical structures, the BLADE sequences were found to be significantly superior to the conventional ones in all the cases. The BLADE sequences eliminated the motion artifacts in all the cases. In our results, it was found that in the examined sequences (sagittal and axial) the differences between the BLADE and conventional sequences regarding the elimination of motion, pulsatile flow and cross-talk artifacts were statistically significant. In all the comparisons, the 12 TSE BLADE sequences were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. In conclusion, this technique appears to be capable of potentially eliminating motion, pulsatile flow and cross-talk artifacts in lumbar spine MR images and producing high quality images in collaborative and non-collaborative patients.
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| 7. |
- Lavdas, Eleftherios, et al.
(författare)
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Reduction of motion, truncation and flow artifacts using BLADE sequences in cervical spine MR imaging
- 2015
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Ingår i: Magnetic Resonance Imaging. - : Elsevier BV. - 0730-725X .- 1873-5894. ; 33:2, s. 194-200
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To assess the efficacy of the BLADE technique (MR imaging with 'rotating blade-like k-space covering') to significantly reduce motion, truncation, flow and other artifacts in cervical spine compared to the conventional technique.Materials and methods: In eighty consecutive subjects, who had been routinely scanned for cervical spine examination, the following pairs of sequences were compared: a) T2 TSE SAG vs. T2 TSE SAG BLADE and b) T2 TIRM SAG vs. T2 TIRM SAG BLADE. A quantitative analysis was performed using the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measures. A qualitative analysis was also performed by two radiologists, who graded seven image characteristics on a 5-point scale (0: non-visualization; 1: poor; 2: average; 3: good; 4: excellent). The observers also evaluated the presence of image artifacts (motion, truncation, flow, indentation).Results: In quantitative analysis, the CNR values of the CSF/SC between TIRM SAG and TIRM SAG BLADE were found to present statistically significant differences (p < 0.001). Regarding motion and truncation artifacts, the T2 TSE BLADE SAG was superior compared to the T2 TSE SAG, and the T2 TIRM BLADE SAG was superior compared to the T2 TIRM SAG. Regarding flow artifacts, T2 TIRM BLADE SAG eliminated more artifacts than T2 TIRM SAG.Conclusions: In cervical spine MRI, BLADE sequences appear to significantly reduce motion, truncation and flow artifacts and improve image quality. BLADE sequences are proposed to be used for uncooperative subjects. Nevertheless, more research needs to be done by testing additional specific pathologies.
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| 8. |
- Mavroidis, Panayiotis, et al.
(författare)
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Comparison of Different Fractionation Schedules Toward a Single Fraction in High-Dose-Rate Brachytherapy as Monotherapy for Low-Risk Prostate Cancer Using 3-Dimensional Radiobiological Models
- 2014
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Ingår i: International Journal of Radiation Oncology, Biology, Physics. - : Elsevier BV. - 0360-3016 .- 1879-355X. ; 88:1, s. 216-223
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The aim of the present study was the investigation of different fractionation schemes to estimate their clinical impact. For this purpose, widely applied radiobiological models and dosimetric measures were used to associate their results with clinical findings. Methods and Materials: The dose distributions of 12 clinical high-dose-rate brachytherapy implants for prostate were evaluated in relation to different fractionation schemes. The fractionation schemes compared were: (1) 1 fraction of 20 Gy; (2) 2 fractions of 14 Gy; (3) 3 fractions of 11 Gy; and (4) 4 fractions of 9.5 Gy. The clinical effectiveness of the different fractionation schemes was estimated through the complication-free tumor control probability (P (+)), the biologically effective uniform dose, and the generalized equivalent uniform dose index. Results: For the different fractionation schemes, the tumor control probabilities were 98.5% in 1 x 20 Gy, 98.6% in 2 x 14 Gy, 97.5% in 3 x 11 Gy, and 97.8% in 4 x 9.5 Gy. The corresponding P+ values were 88.8% in 1 x 20 Gy, 83.9% in 2 x 14 Gy, 86.0% in 3 x 11 Gy, and 82.3% in 4 x 9.5 Gy. With use of the fractionation scheme 4 x 9.5 Gy as reference, the isoeffective schemes regarding tumor control for 1, 2, and 3 fractions were 1 x 19.68 Gy, 2 x 13.75 Gy, and 3 x 11.05 Gy. The optimum fractionation schemes for 1, 2, 3, and 4 fractions were 1 x 19.16 Gy with a P+ of 91.8%, 2 x 13.2 Gy with a P+ of 89.6%, 3 x 10.6 Gy with a P+ of 88.4%, and 4 x 9.02 Gy with a P+ of 86.9%. Conclusions: Among the fractionation schemes 1 (+) 20 Gy, 2 (+) 14 Gy, 3 x 11 Gy, and 4 x 9.5 Gy, the first scheme was more effective in terms of P+. After performance of a radiobiological optimization, it was shown that a single fraction of 19.2 to 19.7 Gy (average 19.5 Gy) should produce at least the same benefit as that given by the 4 x 9.5 Gy scheme, and it should reduce the expected total complication probability by approximately 40% to 55%.
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| 9. |
- Mavroidis, Panayiotis, et al.
(författare)
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Expected clinical impact of the differences between planned and delivered dose distributions in helical tomotherapy for treating head and neck cancer using helical megavoltage CT images.
- 2009
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 10:3, s. 2969-
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Tidskriftsartikel (refereegranskat)abstract
- Helical Tomotherapy (HT) has become increasingly popular over the past few years. However, its clinical efficacy and effectiveness continues to be investigated. Pre-treatment patient repositioning in highly conformal image-guided radiation therapy modalities is a prerequisite for reducing setup uncertainties. A MVCT image set has to be acquired to account for daily changes in the patient's internal anatomy and setup position. Furthermore, a comparison should be performed to the kVCT study used for dosimetric planning, by a registration process which results in repositioning the patient according to specific transitional and rotational shifts. Different image registration techniques may lead to different repositioning of the patient and, as a result, to varying delivered doses. This study aims to investigate the expected effect of patient setup correction using the Hi-Art tomotherapy system by employing radiobiological measures such as the biologically effective uniform dose (BEUD) and the complication-free tumor control probability (P+). In this study, a typical case of lung cancer with metastatic head & neck disease was investigated by developing a Helical Tomotherapy plan. For the Tomotherapy HiArt plan, the dedicated Tomotherapy treatment planning station was used. Three dose distributions (planned and delivered with and without patient setup correction) were compared based on radiobiological measures by using the P+ index and the BEUD concept as the common prescription point of the plans and plotting the tissue response probabilities against the mean target dose for a range of prescription doses. The applied plan evaluation method shows that in this cancer case the planned and delivered dose distributions with and without patient setup correction give a P+ of 81.6%, 80.9% and 72.2%, for a BEUD to the planning target volume (PTV) of 78.0Gy, 77.7Gy and 75.4Gy, respectively. The corresponding tumor control probabilities are 86.3%, 85.1% and 75.1%, whereas the total complication probabilities are 4.64%, 4.20% and 2.89%, respectively. HT can encompass the often large PTV required while minimizing the volume of the organs at risk receiving high dose. However, the effectiveness of a HT treatment plan can be considerably deteriorated if an accurate patient setup system is not available. Taking into account the dose-response relations of the irradiated tumors and normal tissues, a radiobiological treatment plan evaluation can be performed, which may provide a closer association of the delivered treatment with the clinical outcome. In such situations, for effective evaluation and comparison of different treatment plans, traditional dose based evaluation tools can be complemented by the use of P+,BEUD diagrams.
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| 10. |
- Mavroidis, Panayiotis, et al.
(författare)
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Radiobiological evaluation of prostate cancer IMRT and conformal-RT plans using different treatment protocols
- 2017
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 40, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to evaluate the clinical efficacy of both step-and-shoot IMRT and 3D-Conformal Radiation Therapy modalities (CRT) in treating prostate cancer using radiobiological measures. Another aim was to estimate the risks for developing secondary malignancies in bladder and rectum due to radiotherapy from the corresponding modalities. The treatment plans of ten prostate cancer patients were developed using IMRT and CRT. For the IMRT plans, two beam energies and two treatment protocols were used (the RTOG 0415 and a most restrictive one proposed by Fox Chase Cancer Center (FCCC)). For the evaluation of these plans, the complication-free tumor control probability, the total probability of injury, the total probability of control/benefit, and the biologically effective uniform dose were employed. Furthermore, based on the dosimetric data of IMRT and CRT, the risk for secondary malignancies was calculated for bladder and rectum. The average risk for secondary malignancy was lower for the bladder (0.37%) compared to the rectum (0.81%) based on all the treatment plans of the ten prostate cancer patients. The highest average risk for secondary malignancy for bladder and rectum was for the CRT-6X modality (0.46% and 1.12%, respectively) and the lowest was for the IMRT RTOG-18X modality (0.33% and 0.56%, respectively). The > Grade 2 LENT/SOMA response probability was lower for the bladder than for the rectum in all the plans. For the bladder the highest average value was for the IMRT RTOG-18X (0.9%) and the lowest was for the CRT-18X modality (0.1%). For the rectum, the highest average value was for the IMRT RTOG-6X (11.9%) and the lowest was for the IMRT FCCC-18X modality (2.2%). By using radiobiological measures it is shown that the IMRT FCCC plans had the lowest risks for normal tissue complications, whereas the IMRT RTOG had the highest. Regarding the risk for secondary malignancies, the CRT plans showed the highest values for both bladder and rectum.
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| 11. |
- Stathakis, Sotirios, et al.
(författare)
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gamma(+) index : A new evaluation parameter for quantitative quality assurance
- 2014
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Ingår i: Computer Methods and Programs in Biomedicine. - : Elsevier BV. - 0169-2607 .- 1872-7565. ; 114:1
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The accuracy dose delivery and the evaluation of differences between calculated and delivered dose distributions, has been studied by several groups. The aim of this investigation is to extend the gamma index by including radiobiological information and to propose a new index that we will here forth refer to as the gamma plus (gamma(+)). Further more, to validate the robustness of this new index in performing a quality control analysis of an IMRT treatment plan using pure radiobiological measures such as the biologically effective uniform dose ((D) over bar) and complication-free tumor control probability (P+). Material and methods: A new quality assurance index, the (gamma(+)), is proposed based on the theoretical concept of gamma index presented by Low et al. (1998). In this study, the dose difference, including the radiobiological dose information (biological effective dose, BED) is used instead of just the physical dose difference when performing the gamma(+) calculation. An in-house software was developed to compare different dose distributions based on the gamma(+) concept. A test pattern for a two-dimensional dose comparison was built using the in-house software platform. The gamma(+) index was tested using planar dose distributions (exported from the treatment planning system) and delivered (film) dose distributions acquired in a solid water phantom using a test pattern and a theoretical clinical case. Furthermore, a lung cancer case for a patient treated with IMRT was also selected for the analysis. The respective planar dose distributions from the treatment plan and the film were compared based on the gamma(+) index and were evaluated using the radiobiological measures of P+ and (D) over bar. Results: The results for the test pattern analysis indicate that the gamma(+) index distributions differ from those of the gamma index since the former considers radiobiological parameters that may affect treatment outcome. For the theoretical clinical case, it is observed that the gamma(+) index varies for different treatment parameters (e.g. dose per fraction). The dose area histogram (DAH) from the plan and film dose distributions are associated with P+ values of 50.8% and 49.0%, for a (D) over bar to the target of 54.0 Gy and 53.3 Gy, respectively. Conclusion: The gamma(+) index shows advantageous properties in the quantitative evaluation of dose delivery and quality control of IMRT treatments because it includes information about the expected responses and radiobiological doses of the individual tissues.
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