Anisotropic Analytical Algorithm Calculations Research Articles

Comparison of Dose Calculation Algorithms for Accelerated Partial Breast Intensity Modulated Radiation Therapy

<h3>Purpose/Objective(s)</h3> Accelerated partial breast irradiation (APBI) using intensity modulated radiation therapy (IMRT) has been introduced recently as an alternative treatment to whole breast irradiation for early-stage breast cancer after lumpectomy. Plan dose volume constraints for IMRT APBI are complex, requiring a more conformal and homogenous dose distribution compared to traditional tangential beam based whole breast planning. Anisotropic Analytical Algorithm (AAA) has been widely used for photon dose calculation. An Advanced Dose Calculation algorithm (AXB) is known to achieve comparable accuracy to Monte Carlo (MC) algorithm, the golden standard dose calculation, in heterogeneous media. However, the clinical assessment of AXB has been lacking. As a preliminary study, we investigated the dosimetric differences between the AAA, AXB and MC calculations on APBI IMRT. <h3>Materials/Methods</h3> Six patients with left breast cancer who previously received APBI IMRT were analyzed for this study. All patients received 30 Gy in 5 fractions with a multi beam IMRT technique using AAA 15.6 in the planning system. The following dose volume constraints were used for acceptable plan criteria based on the APBI IMRT Florence trial and all 6 cases previously treated met these criteria: For target (lumpectomy PTV), V28.5 Gy=100%, maximum dose to target < = 105% and V105% <= 2%. For critical organs, uninvolved breast with V15 Gy < 25%, ipsilateral lung volume with V10 Gy < 20%, contralateral breast maximal dose < 1 Gy, heart with V3 Gy < 10%. For a dosimetric comparison, plans were generated with AXB 15.6, reporting dose to medium, for each corresponding AAA plan by re-optimizing with the same dose constraints. After that, AXB plans were re-calculated with MC algorithm using XVMC and compared to AXB. <h3>Results</h3> The re-calculated plans using AXB for the same monitor units with an identical beam setup from AAA plans did not meet the acceptable dose volume criteria. For re-optimized plans with AXB, target conformity index, V28.5Gy and critical organs met the criteria but maximum dose and V105% were still higher than AAA plans (107-110% vs. 104-105.5% for max dose; <i>p</i>=0.02, 2.5- 5.0% vs. 0-2% for V105; <i>p</i> <0.001). The plan comparison between AXB and MC calculations showed similarity in dose distributions and hotspot area, and minimum difference in dose volume histogram. <h3>Conclusion</h3> The present data is the first report to assess the AXB for APBI IMRT. All 6 plans needed the re-optimization for AXB from plans with AAA to comply with the dose volume constraints. However hot spot size was better with AAA plans. MC calculation confirmed the dose distribution and hot spot area produced by AXB. Therefore, the clinical use of AXB for APBI IMRT will need careful evaluation due to a discrepancy in dose distributions and hot spot sizes between AAA and AXB calculations.

Abstract P3-19-10: Subcutaneous layer dosimetry of the breast and chest wall at clinical beam energies without bolus: A Monte Carlo and analytical anisotropic algorithm (AAA) calculation study

Abstract PURPOSE: Breast skin thickness is 3 mm (1). The subcutaneous layer (SL) lies immediately beneath the skin and is at risk for local recurrence after breast cancer surgery and adjuvant radiotherapy. As the SL lies within the buildup region for megavoltage radiation treatment, placement of bolus for patients receiving chest wall (CW) radiotherapy (RT) is routine at many centers. The dermal toxicity of bolus is well known: in 12 studies of CW RT, the pooled risk of Grade 3 acute toxicity is 9.6% with bolus and 1.2% without bolus (2). Meanwhile, bolus is rarely used after breast-conserving surgery (BCS) RT for patients with similar cancers. This study examines variation in tangential RT dose coverage of the SL in the intact breast and bolus-free CW with clinically relevant photon beam energies using Monte Carlo (MC) calculations and a commercial treatment planning system (TPS). METHODS: Thirty CT datasets from patients without skin involvement were identified. There were two groups of patients: 15 treated with BCS RT and 15 treated with CW RT. In each group, 5-patient subgroups had tangent-beam RT planned without bolus with 6, 10, and 15 MV photons, respectively, using the Analytical Anisotropic Algorithm (AAA) algorithm (v.13.6.23) in Eclipse v.15.6 (Varian Medical Systems Inc., Palo Alto, CA). On each CT, the SL was segmented as a high-resolution shell from 3 to 5 mm below the body contour in the Eclipse TPS v.15.6 (Varian Medical Systems Inc., Palo Alto, CA). A 1x1x1 mm MC dose simulation was performed using EGSnrc code (BEAMnrc/DOSXYZnrc). The MC dose distributions were imported back into the TPS for comparison with AAA calculations. The V95% and V90% for the SL were calculated for each case and the mean V95% and V90% were reported for each subgroup. A t-test was used with a two-sided alpha = 0.05 for statistical analysis. RESULTS: The mean separation increased with use of higher energies for both BCS and CW RT. The MC-calculated mean SL V90% and V95% were higher for CW RT than for BCS RT at each energy. The V90% coverage was 91.5% for CW and 74.4 % for BCS at 6 MV (p&amp;lt;0.001), 89.3% for CW and 61.3% for BCS (p&amp;lt;0.001) at 10 MV and 87.1% for CW and 60.9% for BCS (p&amp;lt;0.001) at 15 MV (Table 1). For SL V95% the CW coverage was higher than the BCS coverage for every energy. For SL V90% at 6 MV, the AAA and MC calculations agreed within 2.5%, with the MC being slightly higher. The agreement between AAA and MC decreased for higher energies with MC reporting higher SL V90% coverage by up to 16.3%. The higher MC-calculated dose to the SL is consistent with the literature (3). CONCLUSION: MC and AAA SL dose calculations agreed well for 6 MV, but AAA underestimated the dose for 10 and 15 MV. For 6-15 MV photons, the MC-calculated dosimetric coverage of the SL is higher for CW RT than BCS RT. Since radiation oncologists are satisfied with the SL coverage by BCS RT, bolus is not needed for CW RT, because, without bolus, CW RT delivers a higher SL dose than BCS RT. REFERENCES:. 1.Pope TL Jr, et al.J Can Assoc Radiol. 1984 Dec;35(4):365-8. PMID: 6526847. 2.Dahn HM, et al. Crit Rev Oncol Hematol. 2021 Jun 5;163:10339. PMID: 34102286. 3.Panettieri V, et al., Radiother Oncol 2009; 93: 94-101 Table 1.Monte Carlo calculated mean V90% and V95% for Breast and Chest Wall for each energyV95%V95%V95%V90%V90%V90%Energy(MV)Chest Wall(Mean)Breast. (Mean)p-valueChest Wall(Mean)Breast. (Mean)p-value661.9%35.1%&amp;lt;0.00191.5%74.4%&amp;lt;0.0011065.2%39.7%&amp;lt;0.00189.3%61.3%&amp;lt;0.0011561.7%38.9%0.01287.1%60.9%&amp;lt;0.001 Citation Format: Dylan Narinesingh, Alan Nichol, Alanah Bergman, Tony Popescu. Subcutaneous layer dosimetry of the breast and chest wall at clinical beam energies without bolus: A Monte Carlo and analytical anisotropic algorithm (AAA) calculation study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-19-10.

The impact of dose calculation algorithm for SBRT lung cancer radiotherapy treatment

Introduction: The study aimed to provide the dose accuracy effects between Anisotropic Analytical algorithm (AAA) and the deterministic solver Acuros XB (AXB) that are available on Eclipse TPS (Varian Medical Systems, Palo Alto, CA) treatment planning system (TPS). The different is due to the electron transport difference in case of small fieldsMaterial and methods: For the study non-small cell lung cancer (NSCLC) patient CT scans are used to do retrospective SBRT plans via AAA and recalculated by AXB dose calculation algorithms using Eclipse treatment planning system. The main dosimetric comparison parameters are: Conformity index (CI), Homogeneity Index (HI), Gradient Index (GI), Target mean dose and calculation time. Results: Based on the results, the CI is (1.45±0.55) to (1.85±0.7). The HI are (0.15±0.07) and (0.13±0.08), the Gradient index GI for AAA were (4.8±2.6) and for AXB reaches to (7.4±3.8) and the maximum dose for PTV are differed about 2.3% to 4.5%, mean dose and the calculation time significant similar for AAA and AXB respectively.Conclusion: As the findings using the deterministic solver AXB in calculation for case of low density like lung cases is more accurate than AAA calculation Algorithm in SBRT treatment

Clinical verification of treatment planning dose calculation in lung SBRT with GATE Monte Carlo simulation code

Purpose This study aims to use GATE/Geant4 simulation code to evaluate the performance of dose calculations with Anisotropic Analytical Algorithm (AAA) in the context of lung SBRT for complex treatments considering images of patients. Methods Four cases of non-small cell lung cancer treated with SBRT were selected for this study. Irradiation plans were created with AAA and recalculated end to end using Monte Carlo (MC) method maintaining field configurations identical to the original plans. Each treatment plan was evaluated in terms of PTV and organs at risk (OARs) using dose-volume histograms (DVH). Dosimetric parameters obtained from DVHs were used to compare AAA and MC. Results The comparison between the AAA and MC DVH using gamma analysis with the passing criteria of 3%/3% showed an average passing rate of more than 90% for the PTV structure and 97% for the OARs. Tightening the criteria to 2%/2% showed a reduction in the average passing rate of the PTV to 86%. The agreement between the AAA and MC dose calculations for PTV dosimetric parameters (V100; V90; Homogeneity index; maximum, minimum and mean dose; CIPaddick and D2cm) was within 18.4%. For OARs, the biggest differences were observed in the spinal cord and the great vessels. Conclusions In general, we did not find significant differences between AAA and MC. The results indicate that AAA could be used in complex SBRT cases that involve a larger number of small treatment fields in the presence of tissue heterogeneities.

Validating Acuros XB with heterogeneous phantoms: can film orientation have an impact?

The aim of this study was to measure doses using films placed parallel and perpendicular to a 6MV radiation beam in heterogeneous phantoms, and to compare these doses to those calculated using the dose calculation algorithms Acuros XB and Analytical Anisotropic Algorithm (AAA). A heterogeneous slab phantom composed of SB5 bone equivalent material sandwiched between WTe solid water, and another composed of cork between WTe solid water were studied. Dose measurements were carried out using Gafchromic EBT-3 and EBT-XD films placed parallel to the radiation beam through the centre of the phantom setup. Each film was then placed perpendicular to the beam, at four depths along the beam axis, with a similar method reported by Delbaere et al. Each phantom was CT scanned and a 3x3cm2 beam was calculated using Acuros XB dose-to-medium/ dose-to-water and AAA. The results showed agreement between the film measurements and dose calculations in the solid water and cork regions of the phantoms. However, deviations were observed in the bone where vertical film measurements agreed with doses calculated by Acuros dose-to-water, whereas horizontal film measurements agreed with AAA calculations. Horizontal and vertical film doses differed by up to 8%. Acuros dose-to-medium calculations were not in agreement with either film orientation. In conclusion, the orientation of the film when measuring the dose delivered by a radiation beam does have an impact on the measured dose. However, for the horizontal film measurements there were air gaps on either side of the film which may have affected the results.Reference: Delbaere A, Younes T, Vieillevigne L. On the conversion from dose-to-medium to dose-to-water in heterogeneous phantoms with Acuros XB and Monte Carlo calculations. Phys Med Biol. 2019 Oct;64.

Comparison of Air-Gaps Effect in a Small Cavity on Dose Calculation for 6 MV Linac.

Background: Many authors stated that cavities or air-gaps were the main challenge of dose calculation for head and neck with flattening filter medical linear accelerator (Linac) irradiation.Objective: The study aimed to evaluate the effect of air-gap dose calculation on flattening-filter-free (FFF) small field irradiation.Material and Methods: In this comparative study, we did the experimental and Monte Carlo (MC) simulation to evaluate the presence of heterogeneities in radiotherapy. We simulated the dose distribution on virtual phantom and the patient’s CT image to determine the air-gap effect of open small field and modulated photon beam, respectively. The dose ratio of air-gaps to tissue-equivalent was calculated both in Analytical Anisotropic Algorithm (AAA) and MC.Results: We found that the dose ratio of air to tissue-equivalent tends to decrease with a larger field size. This correlation was linear with a slope of -0.198±0.001 and -0.161±0.014 for both AAA and MC, respectively. On the other hand, the dose ratio below the air-gap was field size-dependent. The AAA to MC dose calculation as the impact of air-gap thickness and field size varied from 1.57% to 5.35% after the gap. Besides, patient’s skin and oral cavity on head and neck case received a large dose discrepancy according to this study. Conclusion: The dose air to tissue-equivalent ratio decreased with smaller air gaps and larger field sizes. Dose correction for AAA calculation of open small field size should be considered after small air-gaps. However, delivered beam from others gantry angle reduced this effect on clinical case.

Dosimetric Accuracy Comparison between ACUROSE XB, AAA and PBC Dose Calculation Algorithms in EclipseTM TPS Using a Heterogeneous Phantom

Purpose: The aim of this study is to compare the accuracy of different algorithms in EclipseTM Treatment Planning System (TPS) using a heterogeneous phantom.&#x0D; Materials and Methods: The method is based on the International Atomic Energy Agency's TEC-DOC 1583 report. The chest phantom of CIRS, PTW30010 ionization chamber and an electrometer (PTW, Freiburg) were used for the measurements.&#x0D; Three ACUROSE XB (AXB), Analytical Anisotropic Algorithm (AAA) and Pencil Beam Convolution (PBC) dose calculation algorithms available in Eclipse TM TPS were considered in this study.&#x0D; Results: Based on the measurements, the maximum differences between calculated dose by TPS and measured dose in TEC-DOC 1583 tests were 2.5%, 8.6% and 16.1% for the AXB, AAA and PBC algorithms in heterogeneous media, respectively.&#x0D; Conclusion: The Acuros XB algorithm has superior accuracy to predict the dose distribution in the heterogeneous tissues such as lung compared to AAA and PBC algorithms

Monte Carlo simulation using PRIMO code as a tool for checking the credibility of commissioning and quality assurance of 6 MV TrueBeam STx varian LINAC.

To validate and implement Monte Carlo simulation using PRIMO code as a tool for checking the credibility of measurements in LINAC initial commissioning and routine Quality Assurance (QA). Relative and absolute doses of 6MV photon beam from TrueBeam STx Varian Linear Accelerator (LINAC) were simulated and validated with experimental measurement, Analytical Anisotropic Algorithm (AAA) calculation, and golden beam. Varian phase-space files were imported to the PRIMO code and four blocks of jaws were simulated to determine the field size of the photon beam. Water phantom was modeled in the PRIMO code with water equivalent density. Golden beam data, experimental measurement, and AAA calculation results were imported to PRIMO code for gamma comparison. PRIMO simulations of Percentage Depth Dose (PDD) and in-plane beam profiles had good agreement with experimental measurements, AAA calculations and golden beam. However, PRIMO simulations of cross-plane beam profiles have a better agreement with AAA calculation and golden beam than the experimental measurement. Furthermore, PRIMO simulations of absolute dose agreed well with experimental results with ±0.8% uncertainty. The PRIMO code has good accuracy and is appropriate for use as a tool to check the credibility of beam scanning and output measurement in initial commissioning and routine QA.

Effects of metal implants and a metal artifact reduction tool on calculation accuracy of AAA and Acuros XB algorithms in small fields.

In this study, the dosimetric accuracy of analytical anisotropic algorithm (AAA) and Acuros XB (AXB) dose calculation algorithms (Varian Medical Systems, Palo Alto, CA) was investigated for small radiation fields incident on phantoms of various metals that include stainless steel grade 316L (SS316L) and titanium alloy grade 5 (Ti5) implants. In addition, the effects of using metal artifact reduction for orthopedic implants (O-MAR, Philips Healthcare, Cleveland, OH) were evaluated. The evaluations of AAA and AXB were performed by comparing the crossline profiles calculated by AAA and AXB with GafChromicTM EBT3 film measurements at the phantom-implant interfaces and in close vicinity of implant materials for small field sizes (1×1cm2 , 2×2cm2 , 3×3cm2 , and 4×4cm2 ) of a 6MV flattening filter free photon beam. O-MAR corrected and uncorrected (UC) computed tomography (CT) images were used for dose calculations. The values of average and standard deviations (SD) of Hounsfield unit (HU) for selected regions of each case were evaluated. The differences in average dose percentages in defined regions were calculated to quantify the relative dosimetric changes between doses calculated on UC and O-MAR corrected CT images. Compared to UC images, the values of SD were reduced, and the average HU became closer to its reference value in the O-MAR images. There was some discrepancy in average dose percentage differences between calculations using UC and O-MAR images at 1cm above the SS316L implant (average dose percentage differences were AXB/UC=5.9% and AXB/O-MAR=-1.2%; AAA/UC=2.2%, and AAA/O-MAR=-0.8%). Neither AAA nor AXB algorithms predict increase in dose at upper phantom-implant interface (4.9%, 9.9%. 13.5%, and 13.8% for the fields from 1×1cm2 to 4×4cm2 , respectively). At the side of the SS316L implant (where dark streak artifacts exist), dose difference averages were estimated as-1.1% and 22.3% when AXB/O-MAR and AXB/UC calculations are compared with EBT3 measurements, respectively. Dose predictions at 1cm below the SS316L implant were underestimated by AXB/O-MAR (average -0.5%) and AXB/UC (average 2.0%). The O-MAR tool was shown to have a favorable dosimetric effect or no effect on the calculations in the upper proximity of the implant materials. The dose differences between EBT3 film measurements and calculations at upper phantom-implant interfaces were smaller when they were calculated using O-MAR images. However, the dose differences increased when O-MAR corrected images were used for AAA calculations at lower phantom-implant interfaces. Use of O-MAR enabled closer agreement for the AXB algorithm, especially in the dark streak artifact regions. The O-MAR algorithm should be used when the dose is calculated with the AXB algorithm in cases of patients with the metal implants. The estimations using AAA and AXB algorithms, in phantom setups, with Ti5 implant material were found to be closer to the EBT3 film measurements, when compared with the same estimations using SS316L implant material.

Evaluating small field dosimetry with the Acuros XB (AXB) and analytical anisotropic algorithm (AAA) dose calculation algorithms in the eclipse treatment planning system

AbstractBackground:An increasing number of external beam treatment modalities including intensity modulated radiation therapy, volumetric modulated arc therapy (VMAT) and stereotactic radiosurgery uses very small fields for treatment planning and delivery. However, there are major challenges in small photon field dosimetry, due to the partial occlusion of the direct photon beam source’s view from the measurement point, lack of lateral charged particle equilibrium, steep dose-rate gradient and volume averaging effect of the detector response and variation of the energy fluence in the lateral direction of the beam. Therefore, experimental measurements of dosimetric parameters such as percent depth doses (PDDs), beam profiles and relative output factors (ROFs) for small fields continue to be a challenge.Materials and Methods:In this study, we used a homogeneous water phantom and the heterogeneous anthropomorphic stereotactic end-to-end verification (STEEV) head phantom for all dose measurements and calculations. PDDs, lateral dose profiles and ROFs were calculated in the Eclipse Treatment Planning System version 13·6 using the Acuros XB (AXB) and the analytical anisotropic algorithms (AAAs) in a homogenous water phantom. Monte Carlo (MC) simulations and measurements using the Exradin W1 Scintillator were also accomplished for four photon energies: 6 MV, 6FFF, 10 MV and 10FFF. Two VMAT treatment plans were generated for two different targets: one located in the brain and the other in the neck (close to the trachea) in the head phantom (CIRS, Norfolk, VA, USA). A Varian Truebeam linear accelerator (Varian, Palo Alto, CA, USA) was used for all treatment deliveries. Calculated results with AXB and AAA were compared with MC simulations and measurements.Results:The average difference of PDDs between W1 Exradin Scintillator measurements and MC simulations, AAA and AXB algorithm calculations were 1·2, 2·4 and 3·2%, respectively, for all field sizes and energies. AXB and AAA showed differences in ROF of about 0·3 and 2·9%, respectively, compared with W1 Exradin Scintillator measured values. For the target located in the brain in the head phantom, the average dose difference between W1 Exradin Scintillator and the MC simulations, AAA and AXB were 0·2, 3·2 and 2·7%, respectively, for all field sizes. Similarly, for the target located in the neck, the respective dose differences were 3·8, 5·7 and 3·5%.Conclusion:In this study, we compared dosimetric parameters such as PDD, beam profile and ROFs in water phantom and isocenter point dose measurements in an anthropomorphic head phantom representing a patient. We observed that measurements using the W1 Exradin scintillator agreed well with MC simulations and can be used efficiently for dosimetric parameters such as PDDs and dose profiles and patient-specific quality assurance measurements for small fields. In both homogenous and heterogeneous media, the AXB algorithm dose prediction agrees well with MC and measurements and was found to be superior to the AAA algorithm.

Phantom Verification of AAA and Acuros Dose Calculations for Lung Cancer: Do Tumor Size and Regression Matter?

PurposeThis study aimed to evaluate dose calculation accuracy for the Eclipse Analytical Anisotropic Algorithm (AAA) and Acuros XB algorithm for various lung tumor sizes and to investigate dosimetric changes associated with treatment of regressing tumors. Methods and materialsA water phantom with cylindrical cork inserts (lung surrogates) was fabricated. Large (202 cm3), medium (54 cm3), and small (3 cm3) solid water tumors were implanted within cork inserts. A plain cork insert was used to simulate a lung without a tumor. The cork inserts and tumors were cut along the long axis, and Gafchromic film was placed between the sections to measure dose distributions. Three-dimensional conformal plans were created using 6 MV and 10 MV beams, and volumetric modulated arc therapy plans were created using 6 MV beams for each tumor size. Doses were calculated using Eclipse AAA and Acuros XB. The measured and calculated dose distributions were compared for each tumor size and treatment algorithm. To simulate a regressing tumor, the original plans created for the large tumor were separately delivered to the phantom that contained a small, medium, or no tumor. The dosimetric effects were evaluated using gamma passing rates with a 2%/2 mm criterion and dose profile comparisons. ResultsAgreement between the measurements and AAA calculations decreased as tumor size decreased, but Acuros XB showed better agreement for all tumor sizes. The largest difference was observed for a 6 MV volumetric modulated arc therapy plan created to treat the smallest tumor. The gamma passing rate was 89.7% but that of Acuros was 99.5%. For the tumor regression evaluation, the gamma passing rates ranged from 53% to 99% for AAA. For Acuros XB, the gamma passing rates were >98% for all scenarios. ConclusionBoth AAA and Acuros XB calculated the dose accurately for the largest lung tumor. For the smallest and regressing tumors, Acuros XB more accurately modelled the dose distribution compared with AAA.

Comparison of Different Algorithms in the Radiotherapy Plans of Breast Cancer

It is aimed to evaluate portal dosimetry results of planned breast cancer patients with intensity-modulated radiotherapy (YART) of Anisotropic Analytical Algorithm (AAA) and Pencil Beam Convolution (PBC) dose calculation algorithms. The plans of 10 treated patients will receive 6 MV photon energy and a total of 25 fractions of 50 Gray dose using the inverse YART technique, which is reverse planned in the Eclipse (ver.13.6) treatment planning system with Varian Trilogy Linear Accelerator prescribing. For each plan, dose was calculated after optimization using PBC and then AAA algorithms. The quality controls of the plans were made using the Electronic Portal Imaging Device (EPID) by creating individual verification plans for each algorithm. In addition, the maximum and average dose values in the target volume were compared in inverse YART plans calculated using PBC and AAA. When treatment plans generated by AAA and PBC dose calculation algorithms are analyzed using EPID, for the PBC algorithm, the mean values of VArea and VAvg are 98.15 ± 1.07, 0.40 ± 0.048 and 98.72 ± 1.13, 0.37 ± 0.051, respectively, for the AAA algorithm. The PTV Dmax value for the PBC algorithm is 109.3 ± 1.09 and the DAvg value is 101.7 ± 0.51. For the AAA algorithm, the PTV Dmax value is 110.6 ± 1.12 and the DAvg value is 102.9 ± 0.62. When the mean values of portal dosimetry VArea and VAvg evaluated using PBC and AAA algorithms were compared, the differences between the algorithms were not statistically significant (p&gt; 0.05). Differences between the algorithms for PTV Dmax and DAvg values are not statistically significant (p&gt; 0.05).

14. Dosimetric and radiobiological evaluation for the clinical validation of Acuros XB algorithm in thoracic radiation therapy

Introduction Acuros-XB (AXB) algorithm has been introduced several years ago in order to improve the accuracy of dose calculation in radiotherapy, especially in the presence of tissue heterogeneities. This type (c) algorithm is based on the deterministic resolution of the linear Boltzmann transport equation and offers results close to Monte Carlo simulations. This study aims to evaluate the clinical impact of a new algorithm by comparing the dosimetric and radiobiological results of the AXB algorithm for its two reporting modes (dose to water AXB-Dw and dose to medium AXB-Dm), compared to a reference algorithm: the Anisotropic Analytical Algorithm (AAA). Methods Ten cases of patients treated for lung cancer with conformational radiotherapy were studied. For each patient, five treatment plans were generated. The dose in plans 1, 2 and 3 was respectively calculated with AAA, AXB(Dm) and AXB(Dw), using the same prescribed dose (PD). In plans 4 and 5, the dose was calculated using the two AXB calculation modes with the same number of monitor units (MU) derived from the AAA calculation (plan 1). The dosimetric evaluation was based on the comparison of dose volume histograms (HDV) and quality metrics (i.e. Conformity, Coverage and Homogeneity indices). Radiobiological assessment was based on the comparison of tumor control probabilities (TCP) and toxicity probabilities (NTCP) for organs at risk (OARs), including lungs, esophagus and heart. Wilcoxon and Spearman’s rank tests were used to calculate p-values and the correlation coefficient (ρ). Results Using the same PD, we observed a significant increase in the number of MU (1–4%), depending on the choice of AXB-Dm or AXB-Dw. In dosimetric terms, dose calculated with AXB is more heterogeneous. This introduces a significant decrease in the minimum dose to the PTV and in the quality indices. These elements can influence the therapeutic results. In addition, the dose to OARs was increased from +2% to +10%. The increase in dose to target volumes and OARs with AXB, using the same PD, explains the increase in TCP (+1% to 2%) and in NTCP (+2%) (p Conclusions AXB algorithm is known to provide improved calculation accuracy. However, a special attention is required in order to safely implement its clinical use. Depending on the medium density, the technique and the treatment field size, MU can increase as well as the dosimetric values and the NTCPs. Radiation oncologists and medical physicists should define together the attitude to be adopted regarding these dosimetric shifts. A reasonable approach would be to keep the same PD while increasing the sparing of the OARs.

Small field depth dose profile of 6 MV photon beam in a simple air-water heterogeneity combination: A comparison between anisotropic analytical algorithm dose estimation with thermoluminescent dosimeter dose measurement.

To establish trends of estimation error of dose calculation by anisotropic analytical algorithm (AAA) with respect to dose measured by thermoluminescent dosimeters (TLDs) in air-water heterogeneity for small field size photon. TLDs were irradiated along the central axis of the photon beam in four different solid water phantom geometries using three small field size single beams. The depth dose profiles were estimated using AAA calculation model for each field sizes. The estimated and measured depth dose profiles were compared. The over estimation (OE) within air cavity were dependent on field size (f) and distance (x) from solid water-air interface and formulated as OE = - (0.63 f + 9.40) x2+ (-2.73 f + 58.11) x + (0.06 f2 - 1.42 f + 15.67). In postcavity adjacent point and distal points from the interface have dependence on field size (f) and equations are OE = 0.42 f2 - 8.17 f + 71.63, OE = 0.84 f2 - 1.56 f + 17.57, respectively. The trend of estimation error of AAA dose calculation algorithm with respect to measured value have been formulated throughout the radiation path length along the central axis of 6 MV photon beam in air-water heterogeneity combination for small field size photon beam generated from a 6 MV linear accelerator.

Dosimetric impact of Lipiodol in stereotactic body radiation therapy on liver after trans-arterial chemoembolization.

Stereotactic body radiation therapy (SBRT) combining trans-arterial chemoembolization (TACE) with Lipiodol is expected to improve local control. This study is aimed to estimate the dose enhancement in Lipiodol's proximity and to evaluate the dose calculation accuracy of the Acuros XB (AXB) algorithm and anisotropic analytical algorithm (AAA) in the Eclipse treatment planning system (TPS) (ver. 11, Varian Medical Systems, Palo Alto, USA), compared with that of the Monte Carlo (MC) calculation (using BEAMnrc/DOSXYZnrc code) for a virtual phantom and a treatment plan for liver SBRT after TACE. The MC calculation accuracy was validated by comparing its results with the percent depth dose (PDD) and the off-axis ratio (OAR) measured using a water-equivalent phantom containing Lipiodol. The dose difference in Lipiodol's proximity and the inhomogeneity correction accuracies of the AAA, AXB algorithm, and MC calculation were evaluated by calculating the PDDs and OARs for the virtual phantom with Lipiodol and the lateral profile for the clinical plan data. The measured data and the MC results agreed within 3%. The average dose in the Lipiodol uptake region was higher by 8.1% for the virtual phantom and 6.0% for the clinical case compared to that in regions without Lipiodol uptake. For the virtual phantom, compared with the MC calculation, the AAA and the AXB algorithm underestimated the doses immediately upstream of the Lipiodol region by 5.0% and 4.2%, in the Lipiodol region by 7.4% and 9.8%, and downstream of the Lipiodol region by 5.5% and 3.9% respectively. These discrepancy between the AXB and MC calculations were due to the incorrect assignment of Lipiodol material properties. Namely, the bone material was assigned automatically by the AXB algorithm as the materials for the AXB algorithm do not contain iodine, which is the main constituent of Lipiodol. The MC calculation indicated a larger and more accurate dose increase in Lipiodol compared with the TPS algorithms. The observed dose enhancement in the tumor area could be clinically significant.

TH‐EF‐BRB‐10: Dosimetric Validation of a Trajectory Based Cranial SRS Treatment Technique On a Varian TrueBeam Linac

Purpose:This work investigates the dosimetric accuracy of a trajectory based delivery technique in which an optimized radiation beam is delivered along a Couch‐Gantry trajectory that is formed by simultaneous rotation of the linac gantry and the treatment couch.Methods:Nine trajectory based cranial SRS treatment plans were created using in‐house optimization software. The plans were calculated for delivery on the TrueBeam STx linac with 6MV photon beam. Dose optimization was performed along a user‐defined trajectory using MLC modulation, dose rate modulation and jaw tracking. The pre‐defined trajectory chosen for this study is formed by a couch rotation through its full range of 180 degrees while the gantry makes four partial arc sweeps which are 170 degrees each. For final dose calculation, the trajectory based plans were exported to the Varian Eclipse Treatment Planning System. The plans were calculated on a homogeneous cube phantom measuring 18.2×18.2×18.2 cm3 with the analytical anisotropic algorithm (AAA) using a 1mm3 calculation voxel. The plans were delivered on the TrueBeam linac via the developer's mode. Point dose measurements were performed on 9 patients with the IBA CC01 mini‐chamber with a sensitive volume of 0.01 cc. Gafchromic film measurements along the sagittal and coronal planes were performed on three of the 9 treatment plans. Point dose values were compared with ion chamber measurements. Gamma analysis comparing film measurement and AAA calculations was performed using FilmQA Pro.Results:The AAA calculations and measurements were in good agreement. The point dose difference between AAA and ion chamber measurements were within 2.2%. Gamma analysis test pass rates (2%, 2mm passing criteria) for the Gafchromic film measurements were &gt;95%.Conclusion:We have successfully tested TrueBeam's ability to deliver accurate trajectory based treatments involving simultaneous gantry and couch rotation with MLC and dose rate modulation along the trajectory.

SU‐F‐T‐622: Comparative Analysis of Pencil Beam and Anisotropic Analytical Algorithm (AAA) for Stereotactic Body Radiation Therapy (SBRT) of Thoracic Spine

Purpose:To compare the impact of Pencil Beam(PB) and Anisotropic Analytic Algorithm(AAA) dose calculation algorithms on OARs and planning target volume (PTV) in thoracic spine stereotactic body radiation therapy (SBRT).Methods:Ten Spine SBRT patients were planned on Brainlab iPlan system using hybrid plan consisting of 1–2 non‐coplanar conformal‐dynamic arcs and few IMRT beams treated on NovalisTx with 6MV photon. Dose prescription varied from 20Gy to 30Gy in 5 fractions depending on the situation of the patient. PB plans were retrospectively recalculated using the Varian Eclipse with AAA algorithm using same MUs, MLC pattern and grid size(3mm).Differences in dose volume parameters for PTV, spinal cord, lung, and esophagus were analyzed and compared for PB and AAA algorithms. OAR constrains were followed per RTOG‐0631.Results:Since patients were treated using PB calculation, we compared all the AAA DVH values with respect to PB plan values as standard, although AAA predicts the dose more accurately than PB. PTV(min), PTV(Max), PTV(mean), PTV(D99%), PTV(D90%) were overestimated with AAA calculation on average by 3.5%, 1.84%, 0.95%, 3.98% and 1.55% respectively as compared to PB. All lung DVH parameters were underestimated with AAA algorithm mean deviation of lung V20, V10, V5, and 1000cc were 42.81%,19.83%, 18.79%, and 18.35% respectively. AAA overestimated Cord(0.35cc) by mean of 17.3%; cord (0.03cc) by 12.19% and cord(max) by 10.5% as compared to PB. Esophagus max dose were overestimated by 4.4% and 5cc by 3.26% for AAA algorithm as compared to PB.Conclusion:AAA overestimated the PTV dose values by up to 4%.The lung DVH had the greatest underestimation of dose by AAA versus PB. Spinal cord dose was overestimated by AAA versus PB. Given the critical importance of accuracy of OAR and PTV dose calculation for SBRT spine, more accurate algorithms and validation of calculated doses in phantom models are indicated.

Dosimetric accuracy of AAA and acuros XB dose calculations within an air cavity for small fields of a 6-MV flattening filter-free beam

The purpose of this research were to verify the accuracy of dose calculation by using the analytical anisotropic algorithm (AAA) and Acuros XB (AXB) against measurements within an air cavity for small fields from a 6-MV flattening filter-free (FFF) beam. A rectangular slab phantom containing an air cavity was specially constructed for this study. Computed tomography (CT) image data sets were acquired with and without a film at four selected depths (4.5, 5.5, 6.5, and 7.5 cm) in the air cavity of the phantom for the dose calculation. The central-axis point dose (CAPD) and dose profile were measured with the film at selected depths for field sizes from 2 × 2 to 5 × 5 cm2 along the central-beam axis of a 6-MV FFF beam. The central-axis doses (CADs) and dose profiles calculated by using both the AAA and AXB were obtained by using an Eclipse treatment planning system (TPS) under the same measurement conditions. The calculation algorithms were denoted as AXB_w and AAA_w when the film was included in an air cavity of the phantom and an AXB_w/o and AAA_w/o when no film was included. The accuracy of the CAD and dose profile calculated by using both algorithms were compared with the measured CAPD and dose profile, and their differences were evaluated by using root-mean square-error (RMSE) and gamma-index analyse. The percentage difference (%Diff) of the CAD calculated by using AXB w showed good agreement (within 5%) with the measured CAPD at selected depths in the air cavity. However, the corresponding values for the other algorithms, especially AAA_w and AAA_w/o appeared to exhibit relatively high disagreement. The maximum %Diffs between the calculated CAD and the measured CAPD were 4.8% and −39.4% for the AXB_w and AXB_w/o, respectively. The %Diffs increased with decreasing field size and increasing measurement depth. For the calculated and the measured dose profiles, the RMSE values for AXB_w were within 9.3 cGy in both the inner profile and the penumbra whereas the RMSE values for AAA_w produced a wide range (52.2 − 96.8 cGy). This study demonstrated that the dose calculated by using AXB was more accurate than that calculated by using the AAA when compared to the measured dose in the air cavity. In addition, we observed that AXB_w was superior to AXB_w/o in this region with respect to the measurements.

SU-E-T-277: Dose Calculation Comparisons Between Monaco, Pinnacle and Eclipse Treatment Planning Systems

Purpose: Monaco treatment planning system (TPS) version 5.0 uses a Monte-Carlo based dose calculation engine. The aim of this study is to verify and compare the Monaco based dose calculations with both Pinnacle3 collapsed cone convolution superposition (CCC) and Eclipse analytical anisotropic algorithm (AAA) calculations. Methods: For this study, previously treated SBRT lung, head and neck and abdomen patients were chosen to compare dose calculations between Pinnacle, Monaco and Eclipse. Plans were chosen from those that had been treated using the Elekta VersaHD or a NovalisTX linac. The plans included 3D conventional and IMRT beams using 6MV and 6MV Flattening filter free (FFF) photon beams. The original plans calculated with CCCS or AAA along with the recalculated ones using MC from the three TPS were exported into Velocity software for inter-comparison. Results: To compare the dose calculations, Mean Lung Dose (MLD), lung V5 and V20 values, and PTV Heterogeneity indexes (HI) and Conformity indexes (CI) were all calculated and recorded from the dose volume histograms (DVH). For each patient, the CI values were identical but there were differences in all other parameters. The HI was computed higher by 5 and 4% for calculated plans AAA and CCCS respectively, compared to the MC ones. The DVH graphs showed large differences between the CCCS and AAA and Monaco for 3D FFF, VMAT and IMRT plans. Better DVH agreement between was observed for 3D conventional plans. Conclusion: Better agreement was observed between CCCS and MC calculations than AAA and MC calculations. Those differences were more profound as the field size was decreasing and in the presence of inhomogeneities.

SU‐E‐J‐58: Dosimetric Verification of Metal Artifact Effects: Comparison of Dose Distributions Affected by Patient Teeth and Implants

Purpose:Implant‐supported dentures seem particularly appropriate for the predicament of becoming edentulous and cancer patients are no exceptions. As the number of people having dental implants increased in different ages, critical dosimetric verification of metal artifact effects are required for the more accurate head and neck radiation therapy. The purpose of this study is to verify the theoretical analysis of the metal(streak and dark) artifact, and to evaluate dosimetric effect which cause by dental implants in CT images of patients with the patient teeth and implants inserted humanoid phantom.Methods:The phantom comprises cylinder which is shaped to simulate the anatomical structures of a human head and neck. Through applying various clinical cases, made phantom which is closely allied to human. Developed phantom can verify two classes: (i)closed mouth (ii)opened mouth. RapidArc plans of 4 cases were created in the Eclipse planning system. Total dose of 2000 cGy in 10 fractions is prescribed to the whole planning target volume (PTV) using 6MV photon beams. Acuros XB (AXB) advanced dose calculation algorithm, Analytical Anisotropic Algorithm (AAA) and progressive resolution optimizer were used in dose optimization and calculation.Results:In closed and opened mouth phantom, because dark artifacts formed extensively around the metal implants, dose variation was relatively higher than that of streak artifacts. As the PTV was delineated on the dark regions or large streak artifact regions, maximum 7.8% dose error and average 3.2% difference was observed. The averaged minimum dose to the PTV predicted by AAA was about 5.6% higher and OARs doses are also 5.2% higher compared to AXB.Conclusion:The results of this study showed that AXB dose calculation involving high‐density materials is more accurate than AAA calculation, and AXB was superior to AAA in dose predictions beyond dark artifact/air cavity portion when compared against the measurements.