Convolution Superposition Algorithm Research Articles

225. Low modulated 6 MV Flattening Filter Free Intensity Modulated Radiation Therapy (FFF-IMRT) for left breast treatments with Active Breath Coordinator™ (ABC): A feasibility study

Purpose The Flattening Filter Free (FFF) modality of the LINAC generates an unflattened X-ray beam with a dose rate up to 5 times (1200 MU/min) the maximum dose rate of a standard flattened beam. Aim of this study is to take advantage of high dose rate to spare treatment time for left breast breath-holding patients and to deliver an equal or better treatment in dose distribution. Here a 6 MV three-fields FFF-IMRT technique is proposed and compared to the standard two tangential 3D-CR conformal radiotherapy (3D-CR). Methods Our 6 MV three-fields IMRT technique adds a slightly tilted beam to the usual two tangential beams. The low modulation allows the maximum dose rate. For a group of 22 patients undergoing left breast treatment with ABC, a comparison was made between 3D-CR standard treatments and FFF-IMRT. 3D-CR plans were calculated by CMS XIO® (v.5.11 convolution superposition algorithm) and Monaco® (v.5.11.02 collapsed cone algorithm), FFF-IMRT plans by Monaco® (v.5.11.02 Monte Carlo algorithm). For plan comparison, 14 indicators were examined by a paired Student T-test to assess statistical significance of differences (p • Left lung: V 20 Gy , V 10 Gy • Heart: Mean Dose, V 25 Gy • Right breast: V 2 Gy • Patient: Maximum Dose ( D 1 % ) • PTV: V 95 % , Maximum Dose ( D 1 % ) , V 105 % (cm3), V 105 % (%), Conformity Index (as defined in Monaco® v.5.11.02) • CTV: V 98 % • Apnoeas number • Treatment time Overall treatment times were evaluated for 3D-CR and FFF-IMRT plans by simulating a patient with a 25 s breath hold phase and a breath recover phase of 30 s. Times for patient set-up, portal imaging and treatment room leaving were also taken into account (total 600 s). Results Significant differences were found for the indicators listed in Table 1 . FFF-IMRT plans showed better CTV coverage, high doses (hot spots) control and conformity. All the FFF-IMRT plans were faster and achieved a mean time gain of 15.1% (2%–18%) for 50 Gy, 2 Gy/fraction prescriptions and 14.9% (4%–18%) for 42.40 Gy, 2.65 Gy/fraction prescriptions, and a mean reduction of apnoeas number by two. Conclusions The FFF-IMRT technique delivers an equal or better dose distribution with a significant reduction of treatment time and number of apnoeas, substantially improving patient comfort.

121. Automated planning for Hodgkin lymphoma radiotherapy

PurposePurpose of the present study was to report on the evaluation of Pinnacle3Auto-Planning (AP) algorithm for Hodgkin lymphoma (HL) radiation therapy (RT). MethodsPlanning CT-scans of 10 female patients with supradiaphragmatic HL were considered. Involved site clinical target volume (CTV) included the upper mediastinal and supraclavear nodes. Planning Target Volume (PTV) was obtained by CTV uniform 10-mm expansion. A total dose of 30 Gy was prescribed in 20 fractions.A “butterfly” (BF) volumetric modulated arc therapy was planned with Pinnacle3 v. 9.10 using SmartArc module and Collapsed Cone Convolution Superposition algorithm dose calculation. Human-driven (Manual-BF) and AP-BF optimization plans were generated using published priority and constraints on the OARs. In addition to BF technique, the AP engine was applied to a 2 coplanar disjointed arches (AP-ARC) technique. A single AP optimization list of PTV/OAR clinical goals was created for each patient. For plan comparison, DVHs of PTVs and OARs were extracted; homogeneity and conformity indices (HI and CI) computed and OARs dose-volume constraints and NTCP models for RP, HT, and CD evaluated. Non-parametric Friedman and Dunn tests were used to identify significant differences between groups. ResultsAP (AP-BF or AP-ARC) offers comparable coverage of the PTV as the manual plan and a consistently better sparing of OARs. In particular, the heart and thyroid mean doses and lung V20 were significantly reduced using AP engine. Accordingly, AP provides similar, if not lower, complication risks. The median number of monitor units was slightly reduced by AP (3.5%). Hands-on planning time decreased on average by a factor of 3 by AP. ConclusionsThe AP module was able to limit heart and thyroid complication risks, producing clinically acceptable HL plans with stable quality without additional user input. Overall AP-ARC provided better results in terms of OAR sparing when compared with AP-BF.

Treatment planning dose accuracy improvement in the presence of dental implants

Streaking artifacts in computed tomography (CT) scans caused by metallic dental implants (MDIs) can lead to inaccuracies in dose calculations. This study quantifies and compares the effect of MDIs on dose distributions using the collapsed cone convolution superposition (CCCS) and Monte Carlo (MC) algorithms, with and without correcting for the density of the MDIs. Ion chamber measurements were taken to test the ability of the algorithms in Pinnacle3 and Monaco to calculate dose near high-Z materials. Nine previously treated patients with head and neck cancer were included in this study. The MDI and the streaking artifacts on the CT images were carefully contoured. For each patient, a plan was optimized and calculated using the Pinnacle3 treatment planning system (TPS). Two dose calculations were performed for each patient: one with overridden densities of the MDI and CT artifacts and one without overridden densities of the MDI and CT artifacts. The plans were then exported to the Monaco TPS and recalculated for the same number of monitor units (MUs) using its MC dose calculation algorithm. The changes in dose to the planning target volume (PTV) and surrounding healthy tissues were examined between all the plans using VelocityAI. For the ion chamber measurements, when correct density information was used, Monaco was within 3% of the measured values, whereas the doses calculated in Pinnacle3 varied up to 7%. The CCCS algorithm in Pinnacle3 calculated only a significant decrease in PTV coverage for 1 patient when the densities were overridden. The MC algorithm in Monaco was able to calculate a significant change in PTV coverage for five of the patients when the density was overridden. Additionally, when healthy tissues affected by streaking artifacts were assigned the correct density, cumulative (from all the fractions) point doses increased up to 46.2 Gy. Not properly accounting for MDIs can impact both the high-dose regions (PTVs) and surrounding healthy tissues. This study demonstrates that if MDIs and the artifacts are not appropriately accounted for by contouring and assigning to them the correct density, there is a potential risk of compromising the quality of the plan regarding PTV coverage and dose to healthy tissues.

Comparison of Acurosand Anisotropic Analytical Algorithm for dose calculation in the treatment of Early-Stage Non-Small Cell Lung Cancer Utilizing Stereotactic Body Radiation Therapy

Stereotactic Body Radiation Therapy (SBRT) is an established technique used to treat early-stage Non-Small Cell Lung Cancer (NSCLC). Currently, photon treatment plans are calculated using convolution-superposition algorithms (CSAs) such as the Anisotropic Analytical Algorithm (AAA). The latest generation of algorithms look to solve the Linear Boltzmann Transport Equation (LBTE) in one of two ways: analytically or indirectly through statistics (Monte Carlo). CSAs are more commonly used but suffer from inaccuracies in heterogeneous media. Acuros External Beam (AXB) directly accounts for heterogeneities by solving the LBTE, providing a more accurate dose calculation than AAA. We evaluated tissue dose differences between the AAA and AXB generated plans. We identified 15 cases of Stage I-II NSCLC treated with curative intent SBRT at our institution from 2015-2016 who were planned in AAA to receive 50 Gy in 5 fractions using a treatment planning system. The patients’ delivered plans were retrospectively recalculated using AXB. The dose volume histogram was generated for structures commonly contoured in lung SBRT based on RTOG 0813; structures included gross tumor volume (GTV) and planning target volume (PTV) and the organs at risk (OARS), specifically the spinal cord, skin, heart, great vessels, chest wall, brachial plexus, total lung, and bronchi. Both peripheral and central tumors were included. Dose to 95% of the PTV volume was the primary endpoint. The Wilcoxon signed-rank test tested variance between the dose distribution generated by AXB and by AAA. PTV 95% dose differed significantly between AAA and AXB generated plans (p=0.0027).The mean, min, and max PTV 95% dose generated by AAA were 4966 cGy (SD=77.260 cGy), 4722 cGy, and 5002 cGy, respectively, whereas, the AXB generated plan yielded values of 4890 cGy (STD=118.4 cGy), 4589 cGy, and 5065 cGy, respectively. The mean GTV dose generated by AAA was higher overall (mean=5619 cGy) when compared to GTV dose calculated by AXB (mean = 5360 cGy); however, this difference was not significant in our cohort. On average, the PTV 95% dose was 70.60 cGy (SD =91.68) higher for AAA plans compared to plans re-calculated with AXB. The D0.03 cc for the esophagus, spinal cord, skin, heart, great vessels, and bronchi were on average 13.57 cGy (p=0.017), 7.293 cGy (p=0.0004), 5.488 cGy [NS], and 10.854 cGy [NS] lower when re-calculated with AXB, respectively. The D0.03 cc for the chest wall and brachial plexus were on average 46.51 cGy (p=0.04) and 8.043 cGy [NS] higher when re-calculated with AXB. We found a statistically difference in dose distribution for the PTV 95% dose for AAA plans re-calculated with AXB. Overall, AXB re-calculation of the PTV 95% dose resulted in a lower dose distribution to the target when compared to the original plan, which was calculated in AAA. Given that AXB has shown to more accurately calculate dose-distribution. Our data suggests that AAA model overestimates the PTV 95% dose in lung SBRT.

Auto- versus human-driven plan in mediastinal Hodgkin lymphoma radiation treatment

BackgroundTechnological advances in Hodgkin lymphoma (HL) radiation therapy (RT) by high conformal treatments potentially increase control over organs-at-risk (OARs) dose distribution. However, plan optimization remains a time-consuming task with great operator dependent variability. Purpose of the present study was to devise a fully automated pipeline based on the Pinnacle3 Auto-Planning (AP) algorithm for treating female supradiaphragmatic HL (SHL) patients.MethodsCT-scans of 10 female patients with SHL were considered. A “butterfly” (BF) volumetric modulated arc therapy was optimized using SmartArc module integrated in Pinnacle3 v. 9.10 using Collapsed Cone Convolution Superposition algorithm (30 Gy in 20 fractions). Human-driven (Manual-BF) and AP-BF optimization plans were generated. For AP, an optimization objective list of Planning Target Volume (PTV)/OAR clinical goals was first implemented, starting from a subset of 5 patients used for algorithm training. This list was then tested on the remaining 5 patients (validation set). In addition to the BF technique, the AP engine was applied to a 2 coplanar disjointed arc (AP-ARC) technique using the same objective list. For plan evaluation, dose-volume-histograms of PTVs and OARs were extracted; homogeneity and conformity indices (HI and CI), OARs dose-volume metrics and odds for different toxicity endpoints were computed. Non-parametric Friedman and Dunn tests were used to identify significant differences between groups.ResultsA single AP objective list for SHL was obtained. Compared to the manual plan, both AP-plans offer comparable CIs while AP-ARC also achieved comparable HIs. All plans fulfilled the clinical dose criteria set for OARs: both AP solutions performed at least as good as Manual-BF plan. In particular, AP-ARC outperformed AP-BF in terms of heart sparing involving a lower risk of coronary events and radiation-induced lung fibrosis. Hands-on planning time decreased by a factor of 10 using AP on average.ConclusionsDespite the high interpatient PTV (size and position) variability, it was possible to set a standard SHL AP optimization list with a high level of generalizability. Using the implemented list, the AP module was able to limit OAR doses, producing clinically acceptable plans with stable quality without additional user input. Overall, the AP engine associated to the arc technique represents the best option for SHL.

P249] Influence of gamma index comparison on differences in dose calculation algorithm deposition method

Purpose Phantomless patient specific QA saves time and is able to detect errors by comparing the TPS dose distribution with a secondary independent dose calculation. TG 218 recommends that gamma analysis should be performed on metrics such as, mean gamma, γ > 1 and γ > 1.5, per structure. The aim of this study is to investigate how gamma index comparison is affected by differences on dose calculation algorithms when treating bone metastases. Methods 10 patients treated for bone metastases in different sites were chosen and 3D and VMAT plans were created using Elekta Monaco TPS in a Versa linac and 10 MV photons. Both 3D and VMAT dose distributions were calculated with Monaco XVMC Monte Carlo (MC) calculation algorithm using dose to medium in medium MC(Dm,m) and dose to water in medium MC(Dw,m) dose deposition modes. All plans were also calculated and evaluated using IBA Compass incorporating a Collapsed Cone convolution superposition algorithm calculating dose to water in medium CC(Dw,m). 3D dose distribution evaluation was performed in terms of gamma metrics such as mean gamma values and % PTV with γ > 1 and γ > 1.5 using 3%, 3 mm criteria for the following combinations: (a) MC(Dw,m) vs CC(Dw,m) and (b) MC(Dm,m) vs CC(Dw,m). Results For the 3D plans, average mean gamma values for MC(Dw,m) vs CC(Dw,m) and MC(Dm,m) vs CC(Dw,m) were found 0.37 ± 0.1 and 0.52 ± 0.12 respectively. The average % PTV points with γ > 1 were found 6.34 ± 5.7% and 12.6 ± 7.5% and the average % PTV points with γ > 1.5 1.45 ± 1.87% and 2.21 ± 2.28%, respectively. Corresponding values for the VMAT plans were 0.46 ± 0.12 and 0.68 ± 0.09 (mean gamma values), 9.48 ± 7.26% and 21.5 ± 7.3% (% PTV points with γ > 1) and 2.37 ± 2.8% and 7.95 ± 7.4% (% PTV points with γ > 1.5). Conclusions Gamma index comparison revealed that both MC and CC calculation algorithms are in fair agreement in dose calculation determination providing that the same dose deposition mode (i.e. Dw,m or Dm,m) is used. The use of different dose deposition mode, results in increased differences in dose calculation determination in structures/areas where materials different than water, such as bone, is included. The observed differences are also increased as the complexity of the plan increases (e.g. VMAT vs 3D).

Refinement of MLC modeling improves commercial QA dosimetry system for SRS and SBRT patient-specific QA.

Mobius 3D (M3D) provides a volumetric dose verification of the treatment planning system's calculated dose using an independent beam model and a collapsed cone convolution superposition algorithm. However, there is a lack of investigation into M3D's accuracy and effectiveness for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) quality assurance (QA). Here, we collaborated with the vendor to develop a revised M3D beam model for SRS/SBRT cases treated with a 6X flattening filter-free (FFF) beam and high-definition multiple leaf collimator (HDMLC) on an Edge linear accelerator. Eighty SRS/SBRT cases, planned with AAA dose algorithm and validated with Gafchromic film, were compared to M3D dose calculations using 3D gamma analysis with 2%/2 mm gamma criteria and a 10% threshold. A revised beam model was developed by refining the HD-MLC model in M3D to improve small field dose calculation accuracy and beam profile agreement. All cases were reanalyzed using the revised beam model. The impact of heterogeneity corrections for lung cases was investigated by applying lung density overrides to five cases. For the standard and revised beam models, respectively, the mean gamma passing rates were 94.6% [standard deviation (SD): 6.1%] and 98.0% [SD: 1.7%] (for the overall patient), 88.2% [SD: 17.3%] and 93.8% [SD: 6.8%] (for the brain PTV), 71.4% [SD: 18.4%] and 81.5% [SD: 14.3%] (for the lung PTV), 83.3% [SD: 16.7%] and 67.9% [SD: 23.0%] (for the spine PTV), and 78.6% [SD: 14.0%] and 86.8% [SD: 12.5%] (for the PTV of all other sites). The lung PTV mean gamma passing rates improved from 74.1% [SD: 7.5%] to 89.3% [SD: 7.2%] with the lung density overridden. The revised beam model achieved an output factor within 3% of plastic scintillator measurements for 2 × 2 cm2 MLC field size, but larger discrepancies are still seen for smaller field sizes which necessitate further improvement of the beam model. Special attention needs to be paid to small field dosimetry, MLC modeling, and inhomogeneity corrections in the beam model for SRS/SBRT QA. The improvements noted in this study, and further collaborations between clinical physicists and the vendor to refine the M3D beam model could enable M3D to become a premier SRS/SBRT QA tool.

Imaging and Dosimetric Consideration for Titanium Prosthesis Implanted within the Irradiated Region by Cobalt-60 Teletherapy Unit

The aim of this research is to observe dose distributions in the vicinity of titanium prosthetic implants during radiotherapy procedures on 60Co teletherapy machine, Prowess Panther treatment planning system (TPS). Data were obtained using a locally fabricated tissue equivalent phantom CT images with titanium prosthesis which was irradiated with 60Co gamma radiation. Prowess TPS (1.25 MeV) estimated less variations. Proximal ends of the metal recorded slight increase in doses as a result of backscatter with dose increment below acceptable tolerance of ±3%. Doses measured decreases on the distal side of the prosthesis at a distance less than dmax from the plate on each beam energy. The depth dose increases marginally after a certain depth level which generally originated from the unperturbed dose due to increase in the electron fluence. The percentage of depth doses decrease with the increase in plate thickness. A reduction in the above trend was also noticed with an increase in beam energy primarily because scattered photons are more forwardly directed. Prowess TPS (convolution superposition algorithm) was found to be better at reducing dose variation when correction for artifact. Manual calculations on blue phantom data agree with results from Prowess. This treatment system is capable of simulating dose around titanium prosthesis as its range of densities, 0.00121 to 2.83, excludes titanium density (rED for titanium is 3.74).

Single fraction computed tomography-guided high-dose-rate brachytherapy or stereotactic body radiotherapy for primary and metastatic lung tumors?

PurposeTo provide a pilot dosimetric study of computed tomography (CT)-guided high-dose-rate (HDR) brachytherapy (BRT) and stereotactic body radiotherapy (SBRT) for primary and metastatic lung lesions.Material and methodsFor nine lung primary and metastasis patients, 3D image-based BRT plan using a single virtual catheter was planned for 34 Gy in single fraction to the gross tumor volume (GTV) + 3 mm margin to account for tumor deformation. These plans were compared to margin-based (MB-) and robustness optimized (RO-) SBRT, assuming the same tumor deformation under real-time tumor tracking. Consistent dose calculation was ensured for both BRT and SBRT plans using the same class of collapsed cone convolution superposition algorithm. Plan quality metrics were compared by Friedman tests and Wilcoxon t-tests.Results and ConclusionsBrachytherapy plans showed significant higher GTV mean dose compared to MB- and RO-SBRT (122.2 Gy vs. 50.4 and 44.7 Gy, p < 0.05), and better dose gradient index (R50) = 2.9 vs. 4.3 and 8.4 for MB- and RO-SBRT, respectively. Dose constraints per the RTOG 0915 protocol were achieved for all critical organs except chest wall in BRT. All other dose-volume histograms (DVH) metrics are comparable between BRT and SBRT. Treatment delivery time of BRT and SBRT plans significantly increased and decreased with increasing GTV size, respectively. SBRT using advanced MLC tracking technique and non-coplanar VMAT can achieve comparable dosimetric quality to HDR BRT. Whether or not, the significantly higher GTV dose can increase killing of radioresistant tumor cells and offset the effect of tumor reoxygenation in single fraction BRT, requires further clinical investigation.

Abstract ID: 220 Evaluating the effect of dental implants in the treatment of head and neck cancer using Monte Carlo dose calculation

Purpose To quantify and compare the effect of metallic dental implants (MDI) on dose distributions calculated using Collapsed Cone Convolution Superposition (CCCS) algorithm or a Monte Carlo algorithm (with and without correcting for the density of the MDI). Methods Seven previously treated patients to the head and neck region were included in this study. The MDI and the streaking artifacts on the CT images were carefully contoured. For each patient a plan was optimized and calculated using the Pinnacle treatment planning system (TPS). For each patient two dose calculations were performed, a) with the densities of the MDI and CT artifacts overridden (12 g/cc and 1 g/cc respectively) and b) without density overrides. The plans were then exported to the Monaco TPS and recalculated using Monte Carlo dose calculation algorithm. The changes in dose to PTVs and surrounding Regions of Interest (ROIs) were examined between all plans. Results The Monte Carlo dose calculation indicated that PTVs received 6% lower dose than the CCCS algorithm predicted. In some cases, the Monte Carlo algorithm indicated that surrounding ROIs received higher dose (up to a factor of 2). Conclusion Not properly accounting for dental implants can impact both the high dose regions (PTV) and the low dose regions (OAR). This study implies that if MDI and the artifacts are not appropriately contoured and given the correct density, there is potential significant impact on PTV coverage and OAR maximum doses.

Assessment the accuracy of dose calculation in build-up region for two radiotherapy treatment planning systems.

Our objective is to quantify dose calculation accuracy in the build-up region using TiGRT and Prowess Panther treatment planning systems (TPSs). Thermoluminescent dosimeter-100 chips were used in a phantom for dose measurement. TiGRT Version 1.2 (LinaTech, Sunnyvale, CA, USA) and Prowess Panther version 5.1 (Prowess Inc., Concord, CA, USA) TPSs were also used for dose calculations. Finally, the confidence limit values obtained to quantify dose calculation accuracy of the TPSs at build-up region for different field sizes and various gantry angles. For 8 cm × 10 cm, 10 cm × 10 cm, and 15 cm × 10 cm field sizes, the confidence limit values for TiGRT TPS were 16.64, 16.56, and 25.85; for Prowess TPS with fast photon effective (FPE) algorithm were 15.17, 14.22, and 9.73; and for Prowess TPS with collapsed cone convolution superposition (CCCS) algorithm were 10.53, 9.97, and 9.76, respectively. For wedged field with gantry angles of 15°, 30°, and 60°, the confidence limit values for TiGRT TPS were 12.11, 12.96, and 22.69 and for Prowess TPS with FPE algorithm were 24.50, 22.07, and 7.82, respectively. It is concluded that for open field sizes without gantry angulation, dose calculation accuracy in Prowess TPS with CCCS algorithm is better than TiGRT and Prowess TPSs with FPE algorithm. Furthermore, it is concluded that for wedged field with large gantry angle, dose calculation accuracy of Prowess TPS with FPE algorithm is better than TiGRT TPS while, for medium and small gantry angles, dose calculation accuracy of TiGRT TPS is better than Prowess TPS with FPE algorithm.

An efficient method to determine double Gaussian fluence parameters in the eclipse™ proton pencil beam model.

To find an efficient method to configure the proton fluence for a commercial proton pencil beam scanning (PBS) treatment planning system (TPS). An in-water dose kernel was developed to mimic the dose kernel of the pencil beam convolution superposition algorithm, which is part of the commercial proton beam therapy planning software, eclipse™ (Varian Medical Systems, Palo Alto, CA). The field size factor (FSF) was calculated based on the spot profile reconstructed by the in-house dose kernel. The workflow of using FSFs to find the desirable proton fluence is presented. The in-house derived spot profile and FSF were validated by a direct comparison with those calculated by the eclipse TPS. The validation included 420 comparisons of the FSFs from 14 proton energies, various field sizes from 2 to 20 cm and various depths from 20% to 80% of proton range. The relative in-water lateral profiles between the in-house calculation and the eclipse TPS agree very well even at the level of 10-4. The FSFs between the in-house calculation and the eclipse TPS also agree well. The maximum deviation is within 0.5%, and the standard deviation is less than 0.1%. The authors' method significantly reduced the time to find the desirable proton fluences of the clinical energies. The method is extensively validated and can be applied to any proton centers using PBS and the eclipse TPS.

On the use of a convolution-superposition algorithm for plan checking in lung stereotactic body radiation therapy.

Stereotactic body radiation therapy (SBRT) aims to deliver a highly conformal ablative dose to a small target. Dosimetric verification of SBRT for lung tumors presents a challenge due to heterogeneities, moving targets, and small fields. Recent software (M3D) designed for dosimetric verification of lung SBRT treatment plans using an advanced convolution–superposition algorithm was evaluated. Ten lung SBRT patients covering a range of tumor volumes were selected. 3D CRT plans were created using the XiO treatment planning system (TPS) with the superposition algorithm. Dose was recalculated in the Eclipse TPS using the AAA algorithm, M3D verification software using the collapsed‐cone‐convolution algorithm, and in‐house Monte Carlo (MC). Target point doses were calculated with RadCalc software. Near‐maximum, median, and near‐minimum target doses, conformity indices, and lung doses were compared with MC as the reference calculation. M3D 3D gamma passing rates were compared with the XiO and Eclipse. Wilcoxon signed‐rank test was used to compare each calculation method with XiO with a threshold of significance of p<0.05. M3D and RadCalc point dose calculations were greater than MC by up to 7.7% and 13.1%, respectively, with M3D being statistically significant (s.s.). AAA and XiO calculated point doses were less than MC by 11.3% and 5.2%, respectively (AAA s.s.). Median and near‐minimum and near‐maximum target doses were less than MC when calculated with AAA and XiO (all s.s.). Near‐maximum and median target doses were higher with M3D compared with MC (s.s.), but there was no difference in near‐minimum M3D doses compared with MC. M3D‐calculated ipsilateral lung V20 Gy and V5 Gy were greater than that calculated with MC (s.s.); AAA‐ and XiO‐calculated V20 Gy was lower than that calculated with MC, but not statistically different to MC for V5 Gy. Nine of the 10 plans achieved M3D gamma passing rates greater than 95% and 80%for 5%/1 mm and 3%/1 mm criteria, respectively. M3D typically calculated a higher target and lung dose than MC for lung SBRT plans. The results show a range of calculated doses with different algorithms and suggest that M3D is in closer agreement with Monte Carlo, thus discrepancies between the TPS and M3D software will be observed for lung SBRT plans. M3D provides a useful supplement to verification of lung SBRT plans by direct measurement, which typically excludes patient specific heterogeneities.PACS number(s): 87.55.D‐, 87.55.Qr, 87.55.K‐

Comparison of the effects of two different dose algorithms in cardiac dose parameters for hodgkin lymphoma patients receiving mediastinal radiotheraphy

Objective: This study aimed to compare pencil beam (PB) and convolution superposition (CS) dose calculation algorithms with respect to cardiac dose-volume parameters V5, V25, V30 and MHD (median heart dose) in Hodgkin lymphoma (HL) patients who received mediastinal radiotherapy (RT). Material and Methods: Ten eligible cases with the diagnosis of HL who completed mediastinal RT at Dokuz Eylul University Department of Radiation Oncology before 01.01.2011 formed the study population. Related 3D conformal RT treatment plans were obtained from the Treatment Planning System (TPS) (Nucletron Oncentra Master Plan Version 3.3 SP3 program). Calculations were done for 6 and 18 MV-X beam energy, respectively by using PB and CS algorithms in the TPS. Two algorithms were compared in terms of cardiac dose-volume parameters (V5, V25, V30 and MHD). Results: Mean relative difference for both V25 and V30 was found to be significantly higher in favor of PB algorithm in both 6 MV-X and 18 MV-X photon energy. Mean relative differences were 1.75% (p=0.012) and 6.76% (p=0.028) for the V25 and V30 parameters, respectively in 6 MV-X and 3.25% (p=0.021) and 13.95% (p=0.007) for the V25 and V30 parameters, respectively in 18 MV-X energy. Conclusion: When PB algorithm is used in RT treatment planning of HL patients for the mediastinal region where tissue inhomogeneity is relatively high, heart V25 and V30 parameters were shown to result in higher values compared to CS algorithm in our study. It is more appropriate to prefer CS algorithm instead of PB algorithm since it increases accuracy of calculations in the treatment planning of mediastinal RT.

SU‐F‐T‐444: Quality Improvement Review of Radiation Therapy Treatment Planning in the Presence of Dental Implants

Purpose:To quantify and compare the effect of metallic dental implants (MDI) on dose distributions calculated using Collapsed Cone Convolution Superposition (CCCS) algorithm or a Monte Carlo algorithm (with and without correcting for the density of the MDI).Methods:Seven previously treated patients to the head and neck region were included in this study. The MDI and the streaking artifacts on the CT images were carefully contoured. For each patient a plan was optimized and calculated using the Pinnacle3 treatment planning system (TPS). For each patient two dose calculations were performed, a) with the densities of the MDI and CT artifacts overridden (12 g/cc and 1 g/cc respectively) and b) without density overrides. The plans were then exported to the Monaco TPS and recalculated using Monte Carlo dose calculation algorithm. The changes in dose to PTVs and surrounding Regions of Interest (ROIs) were examined between all plans.Results:The Monte Carlo dose calculation indicated that PTVs received 6% lower dose than the CCCS algorithm predicted. In some cases, the Monte Carlo algorithm indicated that surrounding ROIs received higher dose (up to a factor of 2).Conclusion:Not properly accounting for dental implants can impact both the high dose regions (PTV) and the low dose regions (OAR). This study implies that if MDI and the artifacts are not appropriately contoured and given the correct density, there is potential significant impact on PTV coverage and OAR maximum doses.

SU‐F‐T‐400: Clinical Comparison of An IMRT Plan Computed with Four Algorithms

Purpose:This work demonstrates clinical differences in a prostate IMRT plan DVH depending on which of four common algorithms is used for computation. Previous comparisons were often based on simple static or re‐optimized IMRT plans which may not be clearly indicative of the clinical end result due solely to the computation algorithm.Methods:A step and shoot prostate multiple field IMRT plan was created in Pinnacle with a Collapsed Cone Convolution Superposition (CCCS) algorithm. The computed patient plan with corresponding dose and the control points without dose were both independently exported to Eclipse. Using the same patient image and structure data sets the control points were recomputed with the Anisotropic Analytical Algorithm (AAA) and Acuros XB for dose‐to‐water in medium (AXBwater) and dose‐to‐medium in medium (AXBmedium). All DVH values were measured in Eclipse to eliminated known differences between various DVH systems. A 0.3cm3 volume was created at the isocenter for point dose (PD) comparison.Results:The prostate target Acuros dose‐to‐medium in medium is clearly different than the others with a mean value of 101.7 cGy versus 103.8, 103.5 and 103.1 cGy for AAA, CCCS and AXBwater respectively. The difference in other clinical parameters such as volume at 105% dose (V105) is also unexpectedly different with values of 1.6, 23.9, 16.0 and 11.6 % respectively. The mean value in a small volume around the isocenter was 99.6, 102.4, 102.2 and 101.5 respectively which though not a great difference could affect the plan normalization and add to other effects in all regions of interest. The V102 is 25% larger for AAA compared to AXBwater. The variation in V50 for the bladder and rectum was approximately 5%.Conclusion:This work demonstrates how an individual plan can be recomputed and compared directly between various algorithms and that clinical parameters can indeed vary according to which algorithm is used for computation.

SU-F-T-377: Monte Carlo Re-Evaluation of Volumetric-Modulated Arc Plans of Advanced Stage Nasopharygeal Cancers Optimized with Convolution-Superposition Algorithm

Background: Commercial treatment planning system Pinnacle3 (Philips, Fitchburg, WI, USA) employs a convolution-superposition algorithm for volumetric-modulated arc radiotherapy (VMAT) optimization and dose calculation. Study of Monte Carlo (MC) dose recalculation of VMAT plans for advanced-stage nasopharyngeal cancers (NPC) is currently limited. Methods: Twenty-nine VMAT prescribed 70Gy, 60Gy, and 54Gy to the planning target volumes (PTVs) were included. These clinical plans achieved with a CS dose engine on Pinnacle3 v9.0 were recalculated by the Monaco TPS v5.0 (Elekta, Maryland Heights, MO, USA) with a XVMC-based MC dose engine. The MC virtual source model was built using the same measurement beam dataset as for the Pinnacle beam model. All MC recalculation were based on absorbed dose to medium in medium (Dm,m). Differences in dose constraint parameters per our institution protocol (Supplementary Table 1) were analyzed. Results: Only differences in maximum dose to left brachial plexus, left temporal lobe and PTV54Gy were found to be statistically insignificant (p> 0.05). Dosimetric differences of other tumor targets and normal organs are found in supplementary Table 1. Generally, doses outside the PTV in the normal organs are lower with MC than with CS. This is also true in the PTV54-70Gy doses but higher dose in the nasal cavity near the bone interfaces is consistently predicted by MC, possibly due to the increased backscattering of short-range scattered photons and the secondary electrons that is not properly modeled by the CS. The straight shoulders of the PTV dose volume histograms (DVH) initially resulted from the CS optimization are merely preserved after MC recalculation. Conclusion: Significant dosimetric differences in VMAT NPC plans were observed between CS and MC calculations. Adjustments of the planning dose constraints to incorporate the physics differences from conventional CS algorithm should be made when VMAT optimization is carried out directly with MC dose engine.

SU-E-T-290: Dosimetric Accuracy of Acuros XB and Analytical Anisotropic Algorithm in Stereotactic Ablative Radiotherapy of Small Lung Lesions

Purpose: The accuracy of dose calculation for lung stereotactic ablative radiotherapy (SABR) of small lesions critically depends on the proper modeling of the lateral scatter in heterogeneous media. In recent years, grid-based Boltzman solvers such as Acuros XB (AXB) have been introduced for enhanced modeling of radiation transport in heterogeneous media. The purpose of this study is to evaluate the dosimetric impact of dose calculation between AXB and convolution-superposition algorithms such as analytical anisotropic algorithm (AAA) for small lesion sizes and different beam energies. Methods: Five lung SABR VMAT cases with GTV ranged from 0.8cm to 2.5cm in diameter were studied. For each case, doses were calculated by AAA, AXB (V11031) and Monte Carlo simulation (MC) with the same plan parameters for 10MV and 6MV. The dose calculation accuracy were evaluated by comparing DVHs and dose distributions with MC as the benchmark. The accuracy of calculated dose was also validated by EBT3 film measurement with a field size of 3cmx3cm in a thorax phantom. Results: For 10MV and GTV less than 1cm, dose calculated by AXB agrees well with MC compared to AAA. Dose difference calculated with AXB and AAA could be up to 30%. For GTV greater than 2cm, calculation results of AXB and AAA agree within 5% in GTV. For 6MV, the difference between calculated doses by AXB and AAA is less 10% for GTV less than 1cm. Based on film measurements, lung dose was overestimated 10% and 20% by AAA for 6MV and 10MV. Conclusion: Lateral scatter and transport is modeled more accurately by AXB than AAA in heterogeneous media, especially for small field size and high energy beams. The accuracy depends on the assigned material in calculation. If grid-based Boltzman solvers or MC are not available for calculation, lower energy beams should be used for treatment.

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‐T‐705: Skin Dosimetry Comparisons of CyberKnife and Tomotherapy for Head‐And‐Neck Stereotatic Body Radiotherapy

Purpose:To perform a comparative evaluation of the skin dose in CyberKnife and Tomotherapy to predict an accurate dose in head‐and‐neck SBRT.Methods:Arbitrarily‐defined planning target volume (PTV) near the skin was drawn on planning CT acquired from an anthropomorphic head‐and‐neck phantom that is used to perform the end‐to‐end test in CyberKnife. Calculation doses were obtained from Multiplan treatment planning system (TPS) using ray‐tracing and monte‐carlo (MC) algorithms for CyberKnife. For Tomotherapy, the skin dose was estimated with convolution superposition (CS) algorithm from Volo TPS. We selected 90% coverage of PTV in 3Gy prescription dose. We compared skin doses near target and at 5 cm far from the target. Optically‐stimulated luminescent dosimeter (OSLD) measurements of radiation dose to the skin over the head‐and‐neck were made during PTV delivery in CyberKnife and Tomotherapy. Individually‐calibrated OSLDs were placed on the surface of the phantom at a number of test positions. The measurement doses were compared with surface doses calculated from ray‐tracing, MC and CS algorithms.Results:The calculated skin doses near target were estimated to be 78∼93% in ray‐tracing, 50∼68% in MC and 78∼97% in CS. Skin doses near target were measured to be 54∼81% of the prescription dose in CyberKnife and to be 89∼104% of the target dose in Tomotherapy. The averaging differences between calculation and measurement values at the skin near target and at 5cm far from the target were 4.7%, 3.3%, and 4.8% in ray‐tracing, MC, and CS, respectively.Conclusion:We verified the skin dose comparisons based on three algorithms used in Cyberknife and Tomotherapy. By the measurement values using OSLD, we found that skin dose could be minimized in CyberKnife compared to using Tomotherapy, which lead to a lower skin dose in head‐and‐neck SBRT. In the aspect of correlation between measured and calculated doses, MC was superior to ray‐tracing and CS