Optimal Fluence Research Articles

TU-G-BRB-03: Iterative Optimization of Normalized Transmission Maps for IMRT Using Arbitrary Beam Profiles.

Newly available flattening filter free (FFF) beam increases the dose rate by 3∼6 times at the central axis. In reality, even flattening filtered beam is not perfectly flat. In addition, the beam profiles across different fields may not have the same amplitude. The existing inverse planning formalism based on the total-variation of intensity (or fluence) map cannot consider these properties of beam profiles. The purpose of this work is to develop a novel dose optimization scheme with incorporation of the inherent beam profiles to maximally utilize the efficacy of arbitrary beam profiles while preserving the convexity of the optimization problem. To increase the accuracy of the problem formalism, we decompose the fluence map as an elementwise multiplication of the inherent beam profile and a normalized transmission map (NTM). Instead of attempting to optimize the fluence maps directly, we optimize the NTMs and beam profiles separately. A least-squares problem constrained by total-variation of NTMs is developed to derive the optimal fluence maps that balances the dose conformality and FFF beam delivery efficiency. With the resultant NTMs, we find beam profiles to renormalized NTMs. The proposed method iteratively optimizes and renormalizes NTMs in a closed loop manner. The advantage of the proposed method is demonstrated by using a head-neck case with flat beam profiles and a prostate case with non-flat beam profiles. The obtained NTMs achieve more conformal dose distribution while preserving piecewise constancy compared to the existing solution. The proposed formalism has two major advantages over the conventional inverse planning schemes: (1) it provides a unified framework for inverse planning with beams of arbitrary fluence profiles, including treatment with beams of mixed fluence profiles; (2) the use of total-variation constraints on NTMs allows us to optimally balance the dose confromality and deliverability for a given beam configuration. This project was supported in part by grants from the National Science Foundation (0854492), National Cancer Institute (1R01 CA104205), and Leading Foreign Research Institute Recruitment Program by the Korean Ministry of Education, Science and Technology (K20901000001-09E0100-00110). To the authors' best knowledgement, there is no conflict interest.

Total body irradiation dose optimization based on radiological depth

We have previously demonstrated the use of Eclipse fluence optimization to define aperture sizes for a novel aperture modulated translating bed total body irradiation (TBI) technique. The purposes of the present study were to identify, characterize, and correct for sources of error inherent in our previous fluence optimization technique, and to develop a clinically viable fluence optimization module for the translating bed TBI technique. Aperture modulated TBI is delivered by translating the patient at constant speed on a custom bed under a modulated radiation beam. The patient is then turned from supine to prone and the process repeated, resulting in an AP‐PA treatment. Radiological depths were calculated along divergent ray lines through individual CT slices of a RANDO phantom. Beam apertures, defined using a dynamic multileaf collimator (DMLC), were generated using calculated radiological depths and calibration factors that relate fluence to aperture size in a dynamic environment. These apertures were defined every 9 mm along the phantom superior‐inferior axis. The calculated beam apertures were further modified to account for scatter within the patient. For dose calculation purposes the individual MLC files were imported into Eclipse. For treatment delivery, dynamic MLC files for both AP and PA beams were generated and delivered dynamically. Dose homogeneity in the head and neck region of the RANDO phantom was within ± 4% of the prescribed dose with this novel technique compared to −5% to +7% with our previous aperture modulated technique based on Eclipse fluence optimization. Fluence optimization and beam aperture calculation using the new technique offers a ten‐fold reduction in planning time and significantly reduces the likelihood of user error during the planning process. In conclusion, a clinically viable aperture modulated translating bed TBI technique that employs dynamically shaped MLC‐defined beam apertures based on radiological depth calculations, has been developed.PACS numbers: 87.55.‐x, 87.55.D‐

Tailoring the Conductivity of Polypyrrole Films Using Low-Energy Platinum Ion Implantation

Low-energy platinum ions were implanted with 15 keV under normal incidence into synthesized conducting polymer films with the aim to improve film conductivity and to demonstrate the use of implanted platinum in a simple sensing design. Conductivity measurements, cyclic voltammetry, and Raman spectroscopy were performed on samples both before and following ion implantation. Results display an optimum fluence of ion implantation for which polypyrrole films implanted with 2 × 1016 at. cm–2 display and retain enhanced conductivity compared with nonimplanted samples. X-ray photoelectron spectroscopy (XPS) and scanning electron microscope–energy-dispersive X-ray spectroscopy (SEM-EDS) confirmed that implanted platinum is present mainly as Pt0 and indicated that the depth and amount of ion implantation are in agreement with a simulated implantation profile. Raman spectroscopy showed a surface-enhanced Raman spectroscopy (SERS) effect with platinum’s presence. The advantageous increase in conductivity can be rationalized by two chemical modifications to the polymer upon high-fluence implantation: (1) an increase in the number of charge carriers (dications) within the polymer and (2) the presence of elemental platinum metal and its synergistic effect on conductivity. A simple DNA sensor was constructed on the basis of polypyrrole/Pt0 films where Pt0 was able to serve as anchoring points for DNA attachment as well as an enhancer of the film’s conductivity. This enabled a DNA sensor capable of successful detection of cDNA, and a good discrimination of noncDNA, thus opening a way to direct electrochemical biosensing on the basis of ion implanted highly conducting polymer films.

Beam rate influence on dose distribution and fluence map in IMRT dynamic technique

AimTo examine the impact of beam rate on dose distribution in IMRT plans and then to evaluate agreement of calculated and measured dose distributions for various beam rate values. BackgroundAccelerators used in radiotherapy utilize some beam rate modes which can shorten irradiation time and thus reduce ability of patient movement during a treatment session. This aspect should be considered in high conformal dynamic techniques. Materials and methodsDose calculation was done for two different beam rates (100MU/min and 600MU/min) in an IMRT plan. For both, a comparison of Radiation Planning Index (RPI) and MU was conducted. Secondly, the comparison of optimal fluence maps and corresponding actual fluence maps was done. Next, actual fluence maps were measured and compared with the calculated ones. Gamma index was used for that assessment. Additionally, positions of each leaf of the MLC were controlled by home made software. ResultsDose distribution obtained for lower beam rates was slightly better than for higher beam rates in terms of target coverage and risk structure protection. Lower numbers of MUs were achieved in 100MU/min plans than in 600MU/min plans. Actual fluence maps converted from optimal ones demonstrated more similarity in 100MU/min plans. Better conformity of the measured maps to the calculated ones was obtained when a lower beam rate was applied. However, these differences were small. No correlation was found between quality of fluence map conversion and leaf motion accuracy. ConclusionExecution of dynamic techniques is dependent on beam rate. However, these differences are minor. Analysis shows a slight superiority of a lower beam rate. It does not significantly affect treatment accuracy.

Micropatterning of proteins on ion beam‐induced poly(acrylic acid)‐grafted polyethylene film

AbstractMicropatterns of proteins were created by using patterned ion beam irradiation onto a polyethylene film and graft polymerization of acrylic acid. Acrylic acid was selectively graft polymerized on the irradiated regions. The results of the grafting study revealed that the optimum fluence to achieve the maximum grafting degree was 1 × 1015 ions/cm2. Biotin was covalently immobilized on the grafted regions of the polyethylene film. Protein patterning was achieved through specific binding of biotin and streptavidin. The resolved protein patterns with the maximum fluorescence intensity were achieved on the poly(acrylic acid) (PAA)‐grafted polyethylene films prepared at the fluence of 1 × 1015 ions/cm2. This method can be used for patterning of various biomolecules and for further biological applications. Copyright © 2010 John Wiley & Sons, Ltd.

Generation of cavities in silicon wafers by laser ablation using silicon nitride as sacrificial layer

Throughout this investigation, experiments on laser ablation with silicon (Si) wafers have been performed using silicon nitride (Si3N4) as a sacrificial layer to find the optimal fluence capable of removing the Si3N4, which allows the subsequent anisotropic etching in Si with potassium hydroxide. As a result, an alternative to the traditional micromachining techniques that require more steps and processing times has been introduced. The effect of the pulse numbers on Si wafers has been studied and it has been observed that when increasing the pulse numbers at the same fluence, the capacity of the pyramidal cavity formed was greater than using only one pulse at higher fluences.Microcavities were performed with a floating Si3N4 layer. This happens to be very useful for the development of drug delivery systems and the manufacture of microarrays. Microcavities were also used as masters for the fabrication of microionizers in polydimethyl siloxane (PDMS).

Sequential Intensity Modulated Arc Therapy (IMAT) Optimization Planning For Improving Dose Homogeneity In Heterogeneous Media

To describe an intensity modulated arc therapy (IMAT) planning technique using sequential optimizations in heterogeneous media for evaluation against conventional IMAT planning. IMAT planning systems often use different algorithms for fluence optimization than for dose calculation which, in heterogeneous media, can lead to a very different dose distribution than what was initially intended. During optimization, dose objectives may appear more achievable than what is reported after final dose calculation. This effect can be reduced by creating a conventional IMAT plan with partial prescription dose as a base plan and sequentially re-optimizing with the initial objectives for the remaining prescription dose. 10 patients were selected with peripheral and central lung tumors undergoing IMAT planning. Conventional IMAT plans were created as baseline and compared with sequentially optimized plans for dose volume histogram (DVH), isodose distribution, and dose conformity index. Using sequential optimizations, the max dose to the internal target volume (ITV) was reduced by 10 - 20% depending on target geometry and location, while maintaining no significant change in mean dose. Dose conformity was improved significantly with magnitudes dependent upon selected index. Sequentially optimized IMAT plans provide a more accurate starting point for a second fluence optimization when planning in low density media. Sequential optimizations can compensate for lateral electronic non-equilibrium with higher success; further study may show this method to be valid for conventional intensity modulated static angle planning as well.

Dosimetrischer Vergleich eines erweiterten Collapsed-Cone-Algorithmus mit einem neuen kommerziell verfügbaren Monte-Carlo-Algorithmus anhand klinisch relevanter Fälle

Comparison of the dosimetric accuracy of the enhanced collapsed cone (eCC) algorithm with the commercially available Monte Carlo (MC) dose calculation for complex treatment techniques. A total of 8 intensity-modulated radiotherapy (IMRT) and 2 stereotactic body radiotherapy (SBRT) lung cases were calculated with eCC and MC algorithms with the treatment planning systems (TPS) Oncentra MasterPlan 3.2 (Nucletron) and Monaco 2.01 (Elekta/CMS). Fluence optimization as well as sequencing of IMRT plans was primarily performed using Monaco. Dose prediction errors were calculated using MC as reference. The dose-volume histrogram (DVH) analysis was complemented with 2D and 3D gamma evaluation. Both algorithms were compared to measurements using the Delta4 system (Scandidos). Recalculated with eCC IMRT plans resulted in lower planned target volume (PTV) coverage, as well as in lower organs-at-risk (OAR) doses up to 8%. Small deviations between MC and eCC in PTV dose (1-2%) were detected for IMRT cases, while larger deviations were observed for SBRT (up to 5%). Conformity indices of both calculations were similar; however, the homogeneity of the eCC calculated plans was slightly better. Delta4 measurements confirmed high dosimetric accuracy of both TPS. Mean dose prediction errors < 3% for PTV suggest that both algorithms enable highly accurate dose calculations under clinical conditions. However, users should be aware of slightly underestimated OAR doses using the eCC algorithm.

Control of material removal of fused silica with single pulses of few optical cycles to sub-picosecond duration

Surface ablation of a dielectric material (fused silica) by single femtosecond pulses is studied as a function of pulse duration (7–450 fs) and applied fluence (F th<F<10F th). We show that varying the pulse duration gives access to high selectivity (with resolution ∼10 nm) for axial removal of matter but does not influence the transverse ablation selectivity, which only depends on the normalized applied fluence F/F th. The ablation efficiency is shown to be inversely dependent on the pulse duration and saturates with respect to the applied fluence earlier at ultra-short pulse durations (≤30 fs). The deduced optimal fluence F opt corresponding to the highest ablation efficiency for each pulse width defines two regimes of laser application. Below F opt, the removed material depth can be accurately adjusted in a large range (∼40–200 nm) as a function of the applied fluence and the morphology of the ablated pattern almost reproduces the Gaussian beam distribution. Above F opt, the material removal depth tends to saturate and the morphology of the ablated pattern evolves to a top-hat distribution. The coupled evolution of depth and morphology is related to the dynamics of formation of dense plasma at the surface of the material, acting as an ultra-fast optical shutter.

316 oral A STUDY OF ICRU 83 GUIDELINES FOR DOSE REPORTING OF H&N IMRT PATIENTS.

non-convex BAO problem. PSM are organized around two phases at every iteration: one where convergence to a local minimum is assured (poll), and the other (search) where flexibility is conferred to the method allowing searches away from the neighborhood of the current iterate. Any global search strategy can be applied in the search step including the insertion of previously used and tested strategies. Due to the myopia of pattern search methods, caused by the non-use of derivatives, these methods have the ability to avoid being trapped by the closest local minima and to find a local minimum in a lowest region. Locally advanced head and neck clinical cases were selected for this study. The planning target volumes included the primary tumor, the high and low risk lymph nodes. Organs-at-risk (OARs) included both parotids, the brainstem, and the spinal cord. For each case, a collection of seven equidistant beams were planned using CERR (computational environment for radiotherapy research). The resulting treatment plan was then compared with the plan using the optimal beam set obtained by PSM. Results: The plan using the optimal beam set obtained by PSM lead to better quality plans for IMRT delivery. The objective function value of the fluence optimization problem was reduced 15% when using the optimal beam set obtained by PSM instead of the traditional equidistant beam set. OARs sparing was improved for the plan using the optimal beam set obtained by PSM. For the same target volume coverage, the mean dose in the right and left parotid was reduced by 4.62Gy and 2.81Gy, respectively. Conclusions: PSM have shown the ability to avoid the local minima closest to the initial angle configuration with a fast convergence. The efficiency on the number of function value computation is of the utmost importance in a busy clinical practice, particularly when adding beam direction to the optimization problem. Our results have shown that a global beam angle search using derivative-free optimization methods yields superior quality plans.

Ablation of PEDOT/PSS with excimer lasers for micro structuring of organic electronic devices

In this paper we present a potentially fast method for high resolution micro structuring of organic electronics via laser patterning. An investigation of the absorption spectrum in the UV/VIS regime of poly (3,4-ethylene dioxythiophene) poly (styrene-sulfonate) (PEDOT/PSS) has shown that UV-laser radiation should be used for optimal laser ablation of the material. Hence, the ablation characteristics of PEDOT/PSS with two different excimer lasers are compared with each other. The optimal fluence for the ablation of the material has been determined. The lasers used in this study are ArF ( λ = 193 nm) and KrF ( λ = 248 nm) excimer lasers.

Investigation of ultrashort pulse laser ablation of solid targets by measuring the ablation-generated momentum using a torsion pendulum

50 fs - 12 ps laser pulses are employed to ablate aluminum, copper, iron, and graphite targets. The ablation-generated momentum is measured with a torsion pendulum. Corresponding time-resolved shadowgraphic measurements show that the ablation process at the optimal laser fluence achieving the maximal momentum is primarily dominated by the photomechanical mechanism. When laser pulses with specific laser fluence are used and the pulse duration is tuned from 50 fs to 12 ps, the generated momentum firstly increases and then remains almost constant, which could be attributed to the change of the ablation mechanism involved from atomization to phase explosion. The investigation of the ablation-generated momentum also reveals a nonlinear momentum-energy conversion scaling law, namely, as the pulse energy increases, the momentum obtained by the target increases nonlinearly. This may be caused by the effective reduction of the dissipated energy into the surrounding of the ablation zone as the pulse energy increases, which indicates that for femtosecond laser the dissipated energy into the surrounding target is still significant.

Study of structural changes caused by nanosecond laser annealing of Ge- and Sn-implanted Si crystal

Silicon single crystals were implanted with Ge or Sn ions and then annealed by nanosecond laser beam in a single-pulse mode. The structural changes caused by the laser annealing are studied by means of the Rutherford back-scattering and X-ray diffraction using the synchrotron radiation. In Ge-implanted Si samples in areas irradiated with a fluence below the threshold value of about 5% and with that near the threshold value of 40% of the total amount of the dopants introduced are located mainly in substitutional positions. For the Si implanted with Sn ions we observe the increase in the amount of interstitial dopants from 15% to 25% in regions annealed with the optimal fluence and with higher than that, respectively. The dependence of the lattice parameter on the laser fluence is studied. An increase in the lattice parameters for both implanted crystals in annealed regions is due to dopant ions expanding the elementary cell.

Separation of Thin GaN from Sapphire by Laser Lift-Off Technique

Laser lift-off of GaN from sapphire substrates has become a viable technique to increase the brightness of GaN-based light-emitting diodes (LEDs). The LEDs free from sapphire exhibit high luminous efficiency by placing highly reflective electrode on the back side. The devices serve low series resistance together with low thermal resistance taking advantages of the vertical structure. Thinner epitaxial structure is desired to serve better device performance, however, cracks in the film after the lift-off limits the minimum thickness. In this paper, successful laser lift-off of very thin GaN with the thickness down to 4 µm is described. The established laser lift-off system utilizes homogenized beam-profile of the employed neodymium-doped yttrium aluminium garnet (Nd:YAG) third harmonic laser in which optimization of the laser fluence minimizes the thickness of the decomposed GaN. It is also revealed by calculation that the compressive stress in the thin GaN is increased by reducing the thickness. It is demonstrated that the lattice of the GaN is relaxed after the laser lift-off, which is confirmed by photoluminescence (PL) and X-ray diffraction (XRD) measurements. In addition, reduction of the wafer bowing of GaN on sapphire is experimentally confirmed after the laser irradiation with the formation of metal Ga in between the interface.

Defect engineering in GaAs using high energy light ion irradiation: Role of electronic energy loss

We report on the application of high energy light ions (Li and O) irradiation for modification of defects, in particular, for annihilation of point defects using electronic energy loss in GaAs to minimize the defects produced by nuclear collisions. The high resolution x-ray diffraction and micro-Raman spectroscopy have been used to monitor that no lattice damage or amorphization take place due to irradiating ions. The effects of irradiation on defects and their energy levels have been studied using thermally stimulated current spectroscopy. It has been observed that till an optimum irradiation fluence of 1013 ions/cm2 there is annihilation of native defects but further increase in irradiation fluence results in accumulation of defects, which scales with the nuclear energy loss process, indicating that the rate of defects produced by the binary collision process exceeds rate of defect annihilation. Defect annihilation due to electronic energy loss has been discussed on the basis of breaking of bonds and enhanced diffusivity of ionized native defects.

Aperture modulated, translating bed total body irradiation

Total body irradiation (TBI) techniques aim to deliver a uniform radiation dose to a patient with an irregular body contour and a heterogeneous density distribution to within +/-10% of the prescribed dose. In the current article, the authors present a novel, aperture modulated, translating bed TBI (AMTBI) technique that produces a high degree of dose uniformity throughout the entire patient. The radiation beam is dynamically shaped in two dimensions using a multileaf collimator (MLC). The irregular surface compensation algorithm in the Eclipse treatment planning system is used for fluence optimization, which is performed based on penetration depth and internal inhomogeneities. Two optimal fluence maps (AP and PA) are generated and beam apertures are created to deliver these optimal fluences. During treatment, the patient/phantom is translated on a motorized bed close to the floor (source to bed distance: 204.5 cm) under a stationary radiation beam with 0 degree gantry angle. The bed motion and dynamic beam apertures are synchronized. The AMTBI technique produces a more homogeneous dose distribution than fixed open beam translating bed TBI. In phantom studies, the dose deviation along the midline is reduced from 10% to less than 5% of the prescribed dose in the longitudinal direction. Dose to the lung is reduced by more than 15% compared to the unshielded fixed open beam technique. At the lateral body edges, the dose received from the open beam technique was 20% higher than that prescribed at umbilicus midplane. With AMTBI the dose deviation in this same region is reduced to less than 3% of the prescribed dose. Validation of the technique was performed using thermoluminescent dosimeters in a Rando phantom. Agreement between calculation and measurement was better than 3% in all cases. A novel, translating bed, aperture modulated TBI technique that employs dynamically shaped MLC defined beams is shown to improve dose uniformity in three dimensions. In comparison with the fixed open beam TBI technique, homogeneity of dose distribution is greatly improved.

A comparative study on the laser removal of Cs+ ion from type 304 stainless steel

A Q-switched Nd:YAG laser with a 1,064 nm and 450 mJ/pulse was employed to study the cleaning characteristics of Type 304 stainless steel specimens artificially contaminated with Cs+ ions. Before laser irradiation, the specimens were treated with KCl and KNO3, respectively. The relative atomic molar percent of Cs+ ion on a metal surface was analyzed by EPMA. Before and after the laser irradiation, the morphology of the metal surfaces was investigated by SEM. The optimum laser fluence determined in the experimental range was 57.3 J/cm2. For all the test specimens, more than 95% of the Cs+ ions were removed by the application of 40 laser shots at 57.3 J/cm2. Cs+ ion removal efficiency was improved by the addition of nitrate ions to the contaminated metal surface. Surface temperature during the laser irradiation was calculated using Hertz-Knudsen equation to investigate the surface characteristics. A portion of particulates generated during the laser irradiation was found to accumulate around a crater of the specimen treated with the KCl solution. It was concluded that the ablated Cs+ ions formed an oxide after thermal activation on the surface and deposited on a metal surface for the KCl system. The higher Cs+ ion removal efficiency of the KNO3 system was attributed to the decomposition of the nitrate ions at a relatively low temperature and the easy reaction of the Cs+ ions with the oxygen generated from the decomposition of nitrate ions.

Fabrication of compositionally graded thin films by gravity-assisted pulsed laser ablation

A compositionally graded thin film of FeSi2 was fabricated by a gravity-assisted pulsed laser ablation (GAPLA) system. By this method, a compositionally graded structure was successfully produced under a gravity field of 5400 G. We demonstrate that the atomic fraction of Fe, the heavier component of the thin film measured by scanning electron microscope/energy dispersive X-ray (SEM-EDX), showed increasing spatial distribution with the direction of gravity. We found that optimal laser fluence exists to give a thin film having the largest possible spatial compositional gradient. We found that surface energy density on the substrate surface is the key parameter to control the composition distribution. Furthermore, the ratio of Fe/Si of the film did not match that of the target. This result shows that the Si component is selectively etched during the film-forming process. Relatively high laser fluence as well as a very narrow space between the target and the substrate are essential to etch the film once it is deposited, in order to re-ionize and etch Si selectively while gravity accelerates both Fe and Si particles to the direction of gravity. We hypothesize that this process accounts for both the change in the stoichiometry and the formation of composition distribution.

Ablation Resolution in Laser Corneal Refractive Surgery: The Dual Fluence Concept of the AMARIS Platform

Purpose. To evaluate to which extent individual Zernike terms can be corrected. Methods. Ablation time and fidelity was analysed using different fluence levels (range 90–2000 mJ/) and aspheric ablation profiles. With optimal parameters, the extent to which individual Zernike modes can be corrected was evaluated.Results. The range 188–565 mJ/ resulted as optimum fluence level with an optimum proportion range 50%–90% for high fluence. With optimal parameters, it corresponds to 2.4 s/D at 6 mm OZ, with fidelity variance of 53 m RMS, and average ablation error of 0.5 m for each location. Ablation simulation of coma Z[3,1] showed 98,4% accuracy and 98% fit quality; trefoil Z[3,3], 99,9% accuracy and 98% fit quality; spherical aberration Z[4,0], 96,6% accuracy and 97% fit quality; secondary astigmatism Z[4,2], 97,9% accuracy and 98% fit quality. Real ablation on a flat plate of PMMA of coma Z[3,1] showed 96,7% accuracy and 96% fit quality; trefoil Z[3,3], 97,1% accuracy and 96% fit quality; spherical aberration Z[4,0], with 93,9% accuracy and 90% fit quality; secondary astigmatism Z[4,2], with 96,0% accuracy and 96% fit quality.Conclusions. Ablation of aspherical and customised shapes based upon Zernike polynomials up to the the 8th order seems accurate using the dual fluence concept implemented at the AMARIS platform.

Verification of IMRT dose calculations using AAA and PBC algorithms in dose buildup regions

The purpose of this comparative study was to test the accuracy of anisotropic analytical algorithm (AAA) and pencil beam convolution (PBC) algorithms of Eclipse treatment planning system (TPS) for dose calculations in the low‐ and high‐dose buildup regions. AAA and PBC algorithms were used to create two intensity‐modulated radiotherapy (IMRT) plans of the same optimal fluence generated from a clinically simulated oropharynx case in an in‐house fabricated head and neck phantom. The TPS computed buildup doses were compared with the corresponding measured doses in the phantom using thermoluminescence dosimeters (TLD 100). Analysis of dose distribution calculated using PBC and AAA shows an increase in gamma value in the dose buildup region indicating large dose deviation. For the surface areas of 1, 50 and 100cm2, PBC overestimates doses as compared to AAA calculated value in the range of 1.34%–3.62% at 0.6 cm depth, 1.74%–2.96% at 0.4 cm depth, and 1.96%–4.06% at 0.2 cm depth, respectively. In high‐dose buildup region, AAA calculated doses were lower by an average of ‐7.56%(SD=4.73%), while PBC was overestimated by 3.75%(SD=5.70%) as compared to TLD measured doses at 0.2 cm depth. However, at 0.4 and 0.6 cm depth, PBC overestimated TLD measured doses by 5.84%(SD=4.38%) and 2.40%(SD=4.63%), respectively, while AAA underestimated the TLD measured doses by ‐0.82%(SD=4.24%) and ‐1.10%(SD=4.14%) at the same respective depth. In low‐dose buildup region, both AAA and PBC overestimated the TLD measured doses at all depths except ‐2.05%(SD=10.21%) by AAA at 0.2 cm depth. The differences between AAA and PBC at all depths were statistically significant (p<0.05) in high‐dose buildup region, whereas it is not statistically significant in low‐dose buildup region. In conclusion, AAA calculated the dose more accurately than PBC in clinically important high‐dose buildup region at 0.4 cm and 0.6 cm depths. The use of an orfit cast increases the dose buildup effect, and this buildup effect decreases with depth.PACS number: 87.53.Bn