Pencil Beam Convolution Algorithm Research Articles

Investigation of Dose Calculation Accuracy of Eclipse Treatment Planning System in the Presence of Metal Hip Prosthesis with Thermoluminescence Dosimeters

Aim: This study investigated the dose calculation accuracy of different treatment planning algorithms used in radiotherapy patients with hip prostheses. Method: The current research produced a tissue-equivalent cylindrical phantom that imitates a leg using a 3D printer. Co-Cr-Mo alloy and Ti-6AI-4V alloy prostheses were placed in the centre of the phantom, respectively. Both prostheses' dose measurements were taken with thermoluminescent dosimeters (TLD) at 92 points. The dose calculation accuracy of the Analytical Anisotropic Algorithm (AAA) and Pencil Beam Convolution (PBC) algorithms, widely used in radiotherapy, were compared with the measurement results. Results: Since the Co-Cr-Mo hip prosthesis has a high density, the number of backscattered photons around it was higher than the Ti-6AI-4V hip prosthesis. The average surface dose of the Co-Cr-Mo alloy was 364.05 cGy, while the average surface dose of the Ti-6AI-4V alloy was 347.79 cGy. Conclusion: It was observed that the dose estimation abilities of the AAA and PBC algorithms decreased as the density of the hip replacement increased. In addition, the AAA algorithm predicted the surface dose in the phantom better than the PBC algorithm.

Investigation of Surface Dose Accuracy of Two Dose Calculation Algorithms Using Thermoluminescent Dosimeters

Accurate estimation of the surface dose in radiotherapy is very important in reducing skin reactions. This study aims to evaluate the accuracy of two different treatment planning algorithms in calculating the surface dose in a specially designed phantom using thermoluminescent dosimetry (TLD). In this study, a special phantom was designed for surface dose measurement. The phantom surface consisted of an adhesive bolus for the adhesion of TLDs. 121 TLDs were placed 1 cm apart on the bolus surface. In TPS, irradiation plans were created at different fields and source-surface distances (SSD). Dose calculations were made with Anisotropic Algorithm algorithms (AAA) and Pencil Beam Convolution (PBC) algorithms for all plans. The mean dose was measured for each point. For each of the 4x4, 6x6, 8x8, 10x10, and 12x12 cm2 domains, the TLDs within the domain were approximately 1 cm inward from the edge. To measure the effect of SSD on surface dose, the isocenter point was located at depths of 0 cm, 2.5 cm and 5.0 cm, respectively. The surface dose at each depth was measured with TLDs. The doses calculated by the AAA and PBC algorithms were compared with the doses measured by TLDs. The AAA algorithm overestimates the surface dose by 4% compared to the TLD measurement for the 4x4 field. The surface dose calculation of the PBC algorithm was found to be high when compared to TLD measurements for all SSDs and fields. There was a significant difference between the PBC algorithm dose calculation and TLD measurements in all fields and SSDs (p<0.001). It was observed that the AAA algorithm performed better in calculating the surface dose than the PBC algorithm. AAA and PBC algorithm users are advised to be more careful about surface dose calculation.

Accuracy of In-Field and Out-Field Doses Calculated by Analytical Anisotropic and Pencil Beam Convolution Algorithms: A Dosimetric Study

Out-of-field doses may affect the formation of secondary cancers, especially in radiosensitive organs, in patients treated with radiotherapy. The aim of this study is to investigate the in-field dose and out-of-field dose accuracy of Eclipse's analytic anisotropic algorithm (AAA) and pencil beam convolution (PBC) algorithms using TLDs. A tissue equivalent phantom containing a total of 21 measurement points at a depth of 5 cm from the anterior and posterior was created. Using Eclipse AAA and PBC algorithms in TPS, 100 MU for AP/PA fields and 95 cm source-skin distance (SSD) were planned. In-field measurement points including isocenter were 3, 5, 7 and 11 points for 3x3, 5x5, 7x7 and 10x10 cm2, respectively. Measuring points outside the field edge were 38, 36, 34 and 30 points for 3x3, 5x5, 7x7 and 10x10 cm2, respectively. In-field point dose values calculated by TPS for different fields were compared with TLD doses measured at the same location. The difference between in-field dose estimation and TLD measurements of both algorithms was generally below 1%. The difference between TPS and TLD was found to be 4.41% for the 10x10 cm2 irradiation field, due to the field edge at a distance of 5 cm from the isocenter. As the field size decreased, the out-of-field dose calculation performance of the AAA and PBC algorithms was adversely affected. For the 10x10 cm2 irradiation field, the TLD measurements and the out-of-field point dose difference of the PBC algorithm were found to be 39.40%. This difference was at most 12.06% for the AAA algorithm. The Eclipse TPS is good at calculating the in-field dose but underestimates the off-field dose. In out-of-field dose calculation, the AAA algorithm gives more accurate results than the PBC algorithm. Additionally, the smaller the field size, the worse the outfield dose accuracy. The use of in vivo dosimeters is recommended in order to estimate the out-of-field dose with great accuracy in radiotherapy.

Uncertainties in the dosimetric heterogeneity correction and its potential effect on local control in lung SBRT

Objective. Dose calculation in lung stereotactic body radiation therapy (SBRT) is challenging due to the low density of the lungs and small volumes. Here we assess uncertainties associated with tissue heterogeneities using different dose calculation algorithms and quantify potential associations with local failure for lung SBRT. Approach. 164 lung SBRT plans were used. The original plans were prepared using Pencil Beam Convolution (PBC, n = 8) or Anisotropic Analytical Algorithm (AAA, n = 156). Each plan was recalculated with AcurosXB (AXB) leaving all plan parameters unchanged. A subset (n = 89) was calculated with Monte Carlo to verify accuracy. Differences were calculated for the planning target volume (PTV) and internal target volume (ITV) Dmean[Gy], D99%[Gy], D95%[Gy], D1%[Gy], and V100%[%]. Dose metrics were converted to biologically effective doses (BED) using α/β = 10Gy. Regression analysis was performed for AAA plans investigating the effects of various parameters on the extent of the dosimetric differences. Associations between the magnitude of the differences for all plans and outcome were investigated using sub-distribution hazards analysis. Main results. For AAA cases, higher energies increased the magnitude of the difference (ΔDmean of −3.6%, −5.9%, and −9.1% for 6X, 10X, and 15X, respectively), as did lung volume (ΔD99% of −1.6% per 500cc). Regarding outcome, significant hazard ratios (HR) were observed for the change in the PTV and ITV D1% BEDs upon univariate analysis (p = 0.042, 0.023, respectively). When adjusting for PTV volume and prescription, the HRs for the change in the ITV D1% BED remained significant (p = 0.039, 0.037, respectively). Significance. Large differences in dosimetric indices for lung SBRT can occur when transitioning to advanced algorithms. The majority of the differences were not associated with local failure, although differences in PTV and ITV D1% BEDs were associated upon univariate analysis. This shows uncertainty in near maximal tumor dose to potentially be predictive of treatment outcome.

Evaluating impact of medium variation on dose calculated through planning system in a low cost in-house phantom

Purpose: In radiotherapy, accuracy in dose estimation of dose calculation methods is critical. The influence of deformity on radiation dose calculations derived by planning system is evaluated in present study. The goal of study was to create a low-cost inhomogeneous phantom for measuring absorbed dose using an Ionisation chamber and Gafchromic film, which was validated using treatment planning system (TPS) dose outcome. Methods:and Materials: The central axis dose calculations were computed using Pencil Beam Convolution algorithm (PBC), Collapsed Cone Convolution (CCC) and Monte Carlo (MC) algorithm in the Monaco treatment planning system using an In-house phantom (20 × 20 × 20cm3) made up of acrylic sheet containing water and inhomogeneous material wooden powder equivalent to lung. Phantom was scanned in Computed Tomography (CT) scanner and image set was sent to the planning workstation. The depth dose evaluations were performed using ionization chamber and Gafchromic film with same beam settings and monitor units in every setup. Following that, the calculated doses obtained from TPS and measured depth doses were compared. Results: The results was reported for photon energies 6MV, 10MV, 15MV, 6FFF and 10FFF at varying field sizes of 4 × 4 cm2, 5 × 5 cm2, 10 × 10 cm2, and 15 × 15 cm2. MC maximum dose variation predicted was 2.06% in 15MV of measured chamber dose and −2.06% of measured gafchromic film dose in 6MVFFF. CCC maximum dose variation predicted was 2.68% of measured chamber dose in 6MV and 3.31% of measured gafchromic film dose in 6MV whereas PB maximum dose variation predicted was −5.94% in 15MV of measured chamber dose and −11.6% of measured gafchromic film dose in 6MVFFF. Conclusion: Low-cost in-house phantoms can be utilised to assess point and planar doses during patient-specific quality assurance in centres that don’t have accessibility to phantoms due to the high cost of commercially available tools.

Dose distrubution evaluation of different dental implants on a real human dry-skull model for head and neck cancer radiotherapy

ObjectivesIn this study, the effect of different dental implant materials on dose distribution in head and neck cancer radiotherapy planning was investigated in a real human dry-skull taken from cadaver. MethodsThe effect of Root-shaped Yttrium (Y) stabilized tetragonal Zr polycrystalline (Y-TZP), Titanium (Ti), Alumina (Al2O3) and polyether ether ketone (PEEK) dental implants on dose distribution was investigated by three different methods; Monte Carlo (MC) simulation, Eclipse Treatment Planning System's (TPS) Pencil Beam Convolution (PBC) algorithm and Thermoluminescence Dosimeter (TLD). The 6 MV photon beam simulation was performed for the Varian 2300 C/D linear accelerator using the EGSnrc based BEAMnrc MC Code. To perform MC simulation on skull phantom, phantom CT images with extended CT scale were imported to BEAMnrc/EGSnrc MC code via CTCREATE code. ResultsAccording to the dose distribution measurement in dry skull, the calculated dose differences between PBC and MC algorithms were in the range of 0.6–4.5% whereas the dose difference between MC and TLD were in the range of 1,1–14.6% range depending on implant material. The PBC calculated dose increase difference range confirmed with TLD measurements was between 1.7% and 19.8%. The PBC algorithm could not fully determine the dose due to backscattering caused by dental implants. This is probably due to the limitations and shortcomings of the PBC algorithm. ConclusionThe maximum dose increase was observed for the Y-TZP dental implant material, which has the highest physical density. No significant dose increase was observed for the PEEK implant probably due to the low physical density of implants close to the physical density of water.

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.
 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.
 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.
 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.
 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

Ipsilateral lung normal tissue complication probability parameters for different dose calculation algorithms in radiotherapy of breast cancer.

Different dose calculation algorithms (DCAs) predict different dose distributions for the same treatment. Awareness of optimal model parameters is vital for estimating normal tissue complication probability (NTCP) for different algorithms. The aim is to determine the NTCP parameter values for different DCAs in left-sided breast radiotherapy, using the Lyman-Kutcher-Burman (LKB) model. First, the methodology recommended by International Atomic Energy Agency TEC-DOC 1583 was used to establish the accuracy of dose calculations of different DCAs including: Monte Carlo (MC) and collapsed cone algorithms implemented in Monaco, pencil beam convolution (PBC) and analytical anisotropic algorithm (AAA) implemented in Eclipse, and superposition and Clarkson algorithms implemented in PCRT3D treatment planning systems (TPSs). Then, treatment planning of 15 patients with left-sided breast cancer was performed by the mentioned DCAs and NTCP of the left-lung normal tissue were calculated for each patient individually, using the LKB model. For the PB algorithm, the NTCP parameters were taken from previously published values and new model parameters obtained for each DCA, using the iterative least squares methods. For all cases and DCAs, NTCP computation with the same model parameters resulted in >15% deviation in NTCP values. The new NTCP model parameters were classified according to the algorithm type. Thus, the discrepancy of NTCP computations was reduced up to 5% after utilizing adjusted model parameters. This paper confirms that the NTCP values for a given treatment type are different for the different DCAs. Thus, it is essential to introduce appropriate NTCP parameter values according to DCA adopted in TPS, to obtain a more precise estimation of lung NTCP. Hence, new parameter values, classified according to the DCAs, must be determined before introducing NTCP estimation in clinical practice.

Impact of choice of dose calculation algorithm on PTV and OAR doses in lung SBRT

Five dose calculation algorithms commonly used in lung SBRT planning are evaluated for their dosimetric impact on planning target volume (PTV) and organ-at-risk (OAR) doses. Treatment plans for thirty lung SBRT patients were included in this multi-institutional planning study. Lung SBRT plans were initially generated using BrainLab Pencil Beam (PB) convolution algorithm to deliver 50 Gy in 5 fractions to PTV (PB_OP plans). Plans were recalculated using BrainLab Monte Carlo (MC) algorithm with the same beam parameters, field settings, and MUs (MC_NO plans) to investigate accuracy limits of PB plans. Next, these plans were re-optimized via MU scaling in MC algorithm while keeping original beam parameters and settings (MC_OP). Further, with these new MUs, all patient plans were recalculated with Pinnacle collapsed cone convolution superposition (CCC), Eclipse anisotropic analytic algorithm (AAA), and Eclipse Acuros XB (AXB) algorithms, and are referred to as AP_NO, AAA_NO, and AXB_NO plans, respectively. DVH of PTV and OARs were used to calculate dosimetric parameters for comparison with MC_OP plans. Patient plans were compared based on PTV size as well as the location in the lung: island targets, adjacent to the ribs/chest wall, or mixed. Lung SBRT plans using PB dose algorithm overestimated target doses by 10–20% of prescribed dose and these differences were highlighted mainly in the target periphery/dose-buildup region as seen in Dmin and D90. Compared with MC, both Pinnacle and AAA plans overestimated PTV dose in the penumbra region, whereas Acuros plans were in good agreement with MC plans. PTV dose differences ranged 3–5% among Pinnacle, AAA, and Acuros. In general, Acuros AXB performed well for adjacent and mixed targets near the ribs and chest wall, whereas Pinnacle CCC was favored for island targets. OAR Dmax and lung V20 were better reproduced in Pinnacle, whereas Dmean were comparable among all TPS. Knowing the strengths and limitations of clinical treatment planning system allows more consistent and accurate dose comparison for patients enrolled in protocol studies.

Dosimetric comparison of different algorithms in stereotactic body radiation therapy (SBRT) plan for non-small cell lung cancer (NSCLC).

PurposesThe main aim of the study was to investigate the dosimetric difference between acuros XB algorithm (AXB), anisotropic analytic algorithm (AAA), and pencil beam convolution (PBC) algorithm in stereotactic body radiation therapy (SBRT) plan for non-small cell lung cancer (NSCLC).Patients and MethodsThirty-eight NSCLC patients were included. GTV, PTV, and organs at risk were delineated by the radiation oncologists. Three optimized SBRT plans for each patients were gained using three algorithms of AXB, AAA, and PBC with the identical plan parameters. Dosimetric endpoints were collected and compared among the three plans, including dosimetric criteria: V100%, V90%, PTV Dmin, Dmax, Dmean, homogeneity index (HI), and Paddick conformity index (CI).ResultsAXB plan resulted in decreased V100% with a mean difference 6.14% compared with PBC plan (For V100%, AXB vs AAA vs PBC=93.44% vs 95.54% vs 99.58%, P<0.05). Three plans showed no significant difference as to the parameter V90%. AXB plan leaded to reduced Dmin of PTV compared with other two algorithms (For Dmin of PTV, AXB vs AAA vs PBC=4048cGy vs 4365Gy vs 4873Gy, P<0.05). PBC induced the enhanced trend of Dmax of PTV compared with other two algorithms (Dmax among three algorithms, P>0.05); and increased the Dmean of PTV in three algorithms with significant difference (For Dmean of PTV, AXB vs AAA vs PBC=5332cGy vs 5330Gy vs 5785Gy, P<0.05). AXB algorithm achieved a similar plan conformity with other two algorithms (For CI, AXB vs AAA vs PBC=0.80 vs 0.85 vs 0.71, P>0.05).ConclusionFor SBRT plan of NSCLC, AAA and PBC algorithms overestimate target coverage, AXB algorithm is recommended for the SBRT plan of NSCLC.

Evaluation of Dose Calculation Algorithms Accuracy for Eclipse, PCRT3D, and Monaco Treatment Planning Systems Using IAEA TPS commissioning tests in a Heterogeneous Phantom

Introduction: The accuracy of dose calculation algorithm (DCA) is highly considered in the radiotherapy sequences. This study aims at assessing the accuracy of five dose calculation algorithms in tissue inhomogeneity corrections, based on the International Atomic Energy Agency TEC-DOC 1583. Material and Methods: A heterogeneous phantom was scanned using computed tomography and tests were planned on three-dimensional treatment planning systems (3D TPSs) based on IAEA TEC-DOC 1583.Doseswere measured for 6- and 18-MV photon beams with ion chambers and then the deviation between measured and calculated TPS doses were reported. The evaluated five DCAs include Monte Carlo (MC) algorithm employed by Monaco, pencil beam convolution (PBC) and anisotropic analytical algorithms (AAA) employed by Eclipse and Superposition (SP), and Clarkson algorithms employed by PCRT3D TPSs. Results: In Clarkson algorithm, low and high energy photons indicated 7.1% and 14.8% deviations out of agreement criteria, respectively. The SP, AAA, and PBC algorithms indicated 0.9%, 7.4%, and 13.8% for low energy photon and 9.5%, 21.3%, and 23.2% for high energy photon deviations out of agreement criteria, respectively. However, MC algorithm showed 1.8% and less than 1% deviations at high and low energy photons, respectively. Conclusion: The DCAs had different levels of accuracy in TPSs. Some simple DCAs, such as Clarkson, showed large deviations in some cases. Therefore, the transition to more advanced algorithms, such as MC would be desirable, particularly for the calculation in the presence of inhomogeneity or high energy beams.

Investigating the effect of dental implant materials with different densities on radiotherapy dose distribution using Monte-Carlo simulation and pencil beam convolution algorithm.

The aim of this study was to investigate the effect of dental implant materials with different physical densities on dose distribution for head and neck cancer radiotherapy planning. Titanium (Ti), Titanium alloy (Ti-6Al-4V), Zirconia (Y-TZP), Zirconium oxide (ZrO2), Alumina (Al2O3) and polyetheretherketone (PEEK) dental implant materials were used for determination of implant material effect on dose distribution. Dental implant effect was investigated by using pencil beam convolution (PBC) algorithm of Eclipse treatment planning systems (TPS) and Monte Carlo (MC) simulation technique. 6 MV photon beam of the Varian 2300 C/D linear accelerator was simulated by EGSnrc-based BEAMnrc MC code system. Reasonable consistency was determined for percentage depth dose (PDD) curves between MC simulation and water phantom measurements at 6.4 MeV initial electron energy. The consistency between modelled linear accelerator PDD curve calculations and water-phantom PDD measurements were compatible within 1 % range. The dose increase in front of the dental implant calculated by MC simulation is in the range of 0.4-20.2%. We found by MC and PBC calculations that the differences in dose increase in front of the dental implant materials is in the range of 0.1-17.2% and is dependent on the physical density of the dental implant. Dose increase for Zirconia was noted to be maximum while PEEK implant dose increase was minimum among the whole dental implant materials studied. This study revealed that the Eclipse TPS PBC algorithm could not accurately estimate the backscatter radiation from dental implant materials.

Evaluation of dose calculation algorithms using different density materials for in-field and out-of-field conditions

The accuracy of the dose calculation is vital in the stereotactic ablative body radiotherapy (SABR) technique to achieve clinically effective dose distribution for better tumor control. Multiple commercial radiotherapy treatment planning systems (TPS) were implemented with different algorithms, such as Acuros XB in Eclipse and Superposition in XiO. The aim of this study is to investigate five different dose calculation algorithms, namely, pencil beam convolution (PBC), Acuros XB, AAA implemented in an Eclipse system, collapsed cone convolution (CCC) algorithm implemented in Mobius3D and superposition algorithms implemented in the XiO system, and then validate the results against measurements using an Institute of Physical Sciences in Medicine (IPSM) phantom with different density materials for in-field and out-of- field conditions. The IPSM phantom was used to investigate the dose calculation algorithm performances in four different densities (water, lung, ribs, and dense bone) using different beam configurations, including small beam fields utilised in lung SABR. Five commercial algorithms implemented in two TPS (Eclipse and XiO) and one plan check(M3D) system were used for in-field and out-of-field measurement. In the in-field condition, the Acuros XB algorithm had lower mean differences than the measured dose by the IC ranging from -0.46 to 0.24for all the densities. In the out-of-field condition, the results of eclipse system: AAA, PBC and Acuros XB algorithms demonstrated underdose point's measurements by -40% for all densities except for AAA calculations in lung density (overdosed by 40%). The measured points of the superposition algorithms were overestimated to the actual dose less than 30% in water, lung and dense bone. At the same densities, the CCC algorithms showed relatively the lowest differences in percentage compared to the superposition algorithms. Our results showed that the Acuros XB and superposition algorithms are closer to the actual measured dose than AAA, PBC and CCC for majority of the field conditions for water-equivalent, lung, rib and dense bone densities. The CCC algorithm resulted in a better agreement with the measurement of the out-of-field points compared with the other algorithms.

Clinical dosimetric impact of AAA and Acuros XB on high-density metallic implants in case of carcinoma cervix

Background: Metallic implant in radiotherapy leads to difficulty in tumor target and critical organ delineation. Four-field box technique is conventional approach to treat pelvic malignancies. Aim of the Study: The aim of study is to evaluate the dosimetric impact of calculation algorithms in the treatment of carcinoma cervix with metallic implants. Materials and Methods: A paraffin wax-coated iron rod was used to evaluate the beam characteristics under the influence of metallic implant. Beam characteristics such as tissue phantom ratio (TPR20,10) were measured and analyzed. 15 patients with and without metallic prosthesis of carcinoma cervix were compared in the study. Planning was done for the prescription dose of 45 Gy/25 fractions. Plans were calculated using AAA algorithm and recalculated using Acuros XB (AXB) and pencil beam convolution algorithms for the same monitor units. RTOG and Quantec Protocol were used for plan evaluation. Results: Transmission and TPR20,10increases with field size and beam energy. Surface dose Dsalso increases with field size. D98%and D2%of planning target volume showed a significant difference for AAA versus AXB. 4FN (AAA) are significantly better for all the 4F plans, calculated by three algorithms in case of V15Gyof small bowel. Analyzed data indicated the significant attenuation caused by high-Z material. Analyzed value of conformity index showed that value of index comes >1 in all the cases. Conclusion: The results indicate that when creating treatment plans for cervical cancer lesions with metallic prosthesis, the AAA algorithm would be a more appropriate choice.

Effects of heterogeneities in dose distributions under nonreference conditions: Monte Carlo simulation vs dose calculation algorithms

The purpose of this study is to evaluate the performance of dose calculation algorithms used in radiotherapy treatment planning systems (TPSs) in comparison with Monte Carlo (MC) simulations in nonelectronic equilibrium conditions. MC simulations with PENELOPE package were performed for comparison of doses calculated by pencil beam convolution (PBC), analytical anisotropy algorithm (AAA), and Acuros XB TPS algorithms. Relative depth dose curves were calculated in heterogeneous water phantoms with layers of bone (1.8 g/cm3) and lung (0.3 g/cm3) equivalent materials for radiation fields between 1 × 1 cm2 and 10 × 10 cm2. Analysis of relative depth dose curves at the water-bone interface shows that PBC and AAA algorithms present the largest differences to MC calculations (uMC = 0.5%), with maximum differences of up to 4.3% of maximum dose. For the lung-equivalent material and 1 × 1 cm2 field, differences can be up to 24.3% for PBC, 11.5% for AAA, and 7.5% for Acuros. Results show that Acurus presents the best agreement with MC simulation data with equivalent accuracy for modeling radiotherapy dose deposition especially in regions where electronic equilibrium does not hold. For typical (nonsmall) fields used in radiotherapy, AAA and PBC can exhibit reasonable agreement with MC results even in regions of heterogeneities.

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).

Clinical Validation of Proton Pencil Beam Scanning on an Anthropomorphic Lung Phantom

To validate the use of proton pencil beam scanning for the treatment of moving lung tumors. Pencil beam scanning (PBS) proton plans are generated for the standard thorax phantom designed by Imaging and Radiation Oncology Core (IROC). Two planning techniques, namely robust optimization against range and setup uncertainties, as well as layer and volumetric repainting, are used for these PBS plans. Patient specific QA measurements are performed using both a water tank and a custom heterogeneous phantom. Tumor motion in this anthropomorphic thorax phantom is 2 cm in magnitude. A custom movable insert is used with the moving IROC thorax phantom to find the optimal number of volumetric repainting. Both pencil beam convolution (PBC) and Monte Carlo (MC) algorithms are used for dose calculation and their accuracy are compared with actual measurements. Single ionization chamber, two-dimensional ionization chamber array, thermoluminescent dosimeter (TLD) and films are utilized to check the point dose and dose distribution accuracy. The optimal number of volumetric repainting is found to be 4 times in our system. The mean dose overestimation on moving target by PBC and MC algorithms are found to be 5.1% and 2.0%, respectively. The mean gamma passing rate for PBC and MC algorithms are 91% and 96% respectively. MC dose algorithm calculation is found to have a good agreement with measurements. Moving lung tumors can be treated using proton pencil beam scanning with robust optimization, volumetric repainting, and Monte Carlo dose calculation.

Experimental assessment of proton dose calculation accuracy in inhomogeneous media

PurposeProton therapy with Pencil Beam Scanning (PBS) has the potential to improve radiotherapy treatments. Unfortunately, its promises are jeopardized by the sensitivity of the dose distributions to uncertainties, including dose calculation accuracy in inhomogeneous media. Monte Carlo dose engines (MC) are expected to handle heterogeneities better than analytical algorithms like the pencil-beam convolution algorithm (PBA). In this study, an experimental phantom has been devised to maximize the effect of heterogeneities and to quantify the capability of several dose engines (MC and PBA) to handle these. MethodsAn inhomogeneous phantom made of water surrounding a long insert of bone tissue substitute (1×10×10 cm3) was irradiated with a mono-energetic PBS field (10×10 cm2). A 2D ion chamber array (MatriXX, IBA Dosimetry GmbH) lied right behind the bone. The beam energy was such that the expected range of the protons exceeded the detector position in water and did not attain it in bone. The measurement was compared to the following engines: Geant4.9.5, PENH, MCsquare, as well as the MC and PBA algorithms of RayStation (RaySearch Laboratories AB). ResultsFor a γ-index criteria of 2%/2mm, the passing rates are 93.8% for Geant4.9.5, 97.4% for PENH, 93.4% for MCsquare, 95.9% for RayStation MC, and 44.7% for PBA. The differences in γ-index passing rates between MC and RayStation PBA calculations can exceed 50%. ConclusionThe performance of dose calculation algorithms in highly inhomogeneous media was evaluated in a dedicated experiment. MC dose engines performed overall satisfactorily while large deviations were observed with PBA as expected.

Out-of-field in vivo dosimetry using TLD in SABR for primary kidney cancer involving mixed photon fields

PurposeTo assess out-of-field dose using three different variants of LiF thermoluminescence dosimeters (TLD) for ten patients who underwent stereotactic ablative body radiotherapy (SABR) for primary renal cell carcinoma (RCC) and compare with treatment planning system (TPS) dose calculations. Methods and materialsThermoluminescent dosimeter (TLD) measurements were conducted at 20, 30, 40 and 50cm from isocentre on ten patients undergoing SABR for primary RCC. Three types of high-sensitivity LiF:Mg,Cu,P TLD material with different 6Li/7Li isotope ratios were used. Patient plans were calculated using Eclipse Anisotropic Analytical Algorithm (AAA) for clinical evaluation and recalculated using Pencil Beam Convolution (PBC) algorithm for comparison. ResultsBoth AAA and PBC showed diminished accuracy for photon doses at increasing distance out-of-field. At 50cm, measured photon dose was 0.3cGy normalised to a 10Gy prescription on average with only small variation across all patients. This is likely due to the leakage component of the out-of-field dose. The 6Li-enriched TLD materials showed increased signal attributable to additional neutron contribution. ConclusionLiF:Mg,Cu,P TLD containing 6Li is sensitive enough to measure out-of-field dose 50cm from isocentre however will over-estimate the photon component of out-of-field dose in high energy treatments due to the presence of thermal neutrons. 7Li enriched materials which are insensitive to neutrons are therefore required for accurate photon dosimetry. Neutron signal has been shown here to increase with MUs and is higher for patients treated using certain non coplanar beam arrangements. Further work is required to convert this additional neutron signal to dose.

Reduction of Dose to the Contralateral Breast by Superflab Use in Radiation Therapy for Mammary Carcinomas

Background:Radiation therapy is an integral part of multimodality treatment for locally advanced carcinoma of breast. Radiation doses to nearby critical normal structures like heart, lungs, and contralateral breast (CLB increases risk of second malignancies. In this study, we measured doses to the CLB and studied effects of a 1 cm thickness superflap.Materials and Methods:Fifty post-mastectomy carcinoma breast patients were included in the study. Radiation therapy of 50 Gy was planned in 25 fractions, 5 days a week, using the Eclipse Treatment Planning System version 8.9.15, with a pencil beam convolution algorithm and 6 MV photon beam. Plans were transferred to a linear accelerator (Varian 2300 CD) for execution of treatment. Twenty-four CaSO4 thermoluminescent dosimeter discs (TLDs) were used for dose measurement over the CLB. The dose was measured for each patient without a superflab for ten fractions and with for another ten fractions for subsequent comparison.Results:Mean doses/fractions received by the CLB with and without a superflab? were 3.78 ± 1.29 cGy and 7.82 ± 2.62 cGy, respectively, with total dosees of 94.69 ± 32.43 cGy (1.89% of prescribed dose) and 191.14 ± 65.62 cGy (3.82% of prescribed dose). The average reduction in mean dose with a 1 cm thick superflab was 46.57 ± 17.18%, in the range of 20 to 80% and statistically significant (p < 0.001).Conclusion:Superflab? is an effective method for dose reduction to CLB. It is an easy, convenient and low time consuming method. Elucidation of any role in reduction of 2nd malignancies in CLB now needs large studies with long follow-up.