Dosimetric effect of tissue heterogeneity for 125I prostate implants

AimTo use Monte Carlo (MC) together with voxel phantoms to analyze the tissue heterogeneity effect in the dose distributions and equivalent uniform dose (EUD) for ¹²⁵I prostate implants.BackgroundDose distribution calculations in low dose-rate brachytherapy are based on the dose deposition around a single source in a water phantom. This formalism does not take into account tissue heterogeneities, interseed attenuation, or finite patient dimensions effects. Tissue composition is especially important due to the photoelectric effect.Materials and methodsThe computed tomographies (CT) of two patients with prostate cancer were used to create voxel phantoms for the MC simulations. An elemental composition and density were assigned to each structure. Densities of the prostate, vesicles, rectum and bladder were determined through the CT electronic densities of 100 patients. The same simulations were performed considering the same phantom as pure water. Results were compared via dose–volume histograms and EUD for the prostate and rectum.ResultsThe mean absorbed doses presented deviations of 3.3–4.0% for the prostate and of 2.3–4.9% for the rectum, when comparing calculations in water with calculations in the heterogeneous phantom. In the calculations in water, the prostate D₉₀ was overestimated by 2.8–3.9% and the rectum D_0.1cc resulted in dose differences of 6–8%. The EUD resulted in an overestimation of 3.5–3.7% for the prostate and of 7.7–8.3% for the rectum.ConclusionsThe deposited dose was consistently overestimated for the simulation in water. In order to increase the accuracy in the determination of dose distributions, especially around the rectum, the introduction of the model-based algorithms is recommended.     

Monte Carlo simulation of the dose distribution of ICRP adult reference computational phantoms for acquisitions with a 320 detector-row cone-beam CT scanner

PurposeThe purpose of this study was to develop and validate a Monte Carlo (MC) simulation tool for patient dose assessment for a 320 detector-row CT scanner, based on the recommendations of International Commission on Radiological Protection (ICRP). Additionally, the simulation was applied on four clinical acquisition protocols, with and without automatic tube current modulation (TCM).MethodsThe MC simulation was based on EGS4 code and was developed specifically for a 320 detector-row cone-beam CT scanner. The ICRP adult reference phantoms were used as patient models. Dose measurements were performed free-in-air and also in four CTDI phantoms: 150 mm and 350 mm long CT head and CT body phantoms. The MC program was validated by comparing simulations results with these actual measurements acquired under the same conditions. The measurements agreed with the simulations across all conditions within 5%. Patient dose assessment was performed for four clinical axial acquisitions using the ICRP adult reference phantoms, one of them using TCM.ResultsThe results were nearly always lower than those obtained from other dose calculator tools or published in other studies, which were obtained using mathematical phantoms in different CT systems. For the protocol with TCM organ doses were reduced by between 28 and 36%, compared to the results obtained using a fixed mA value.ConclusionsThe developed simulation program provides a useful tool for assessing doses in a 320 detector-row cone-beam CT scanner using ICRP adult reference computational phantoms and is ready to be applied to more complex protocols.     

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

Monte Carlo (MC) dose calculation algorithms have been widely used to verify the accuracy of intensity-modulated radiotherapy (IMRT) dose distributions computed by conventional algorithms due to the ability to precisely account for the effects of tissue inhomogeneities and multileaf collimator characteristics. Both algorithms present, however, a particular difference in terms of dose calculation and report. Whereas dose from conventional methods is traditionally computed and reported as the water-equivalent dose (D_w), MC dose algorithms calculate and report dose to medium (D_m). In order to compare consistently both methods, the conversion of MC D_m into D_w is therefore necessary.This study aims to assess the effect of applying the conversion of MC-based D_m distributions to D_w for prostate IMRT plans generated for 6 MV photon beams. MC phantoms were created from the patient CT images using three different ramps to convert CT numbers into material and mass density: a conventional four material ramp (CTCREATE) and two simplified CT conversion ramps: (1) air and water with variable densities and (2) air and water with unit density. MC simulations were performed using the BEAMnrc code for the treatment head simulation and the DOSXYZnrc code for the patient dose calculation. The conversion of D_m to D_w by scaling with the stopping power ratios of water to medium was also performed in a post-MC calculation process.The comparison of MC dose distributions calculated in conventional and simplified (water with variable densities) phantoms showed that the effect of material composition on dose-volume histograms (DVH) was less than 1% for soft tissue and about 2.5% near and inside bone structures. The effect of material density on DVH was less than 1% for all tissues through the comparison of MC distributions performed in the two simplified phantoms considering water. Additionally, MC dose distributions were compared with the predictions from an Eclipse treatment planning system (TPS), which employed a pencil beam convolution (PBC) algorithm with Modified Batho Power Law heterogeneity correction. Eclipse PBC and MC calculations (conventional and simplified phantoms) agreed well (<1%) for soft tissues. For femoral heads, differences up to 3% were observed between the DVH for Eclipse PBC and MC calculated in conventional phantoms. The use of the CT conversion ramp of water with variable densities for MC simulations showed no dose discrepancies (0.5%) with the PBC algorithm. Moreover, converting D_m to D_w using mass stopping power ratios resulted in a significant shift (up to 6%) in the DVH for the femoral heads compared to the Eclipse PBC one.Our results show that, for prostate IMRT plans delivered with 6 MV photon beams, no conversion of MC dose from medium to water using stopping power ratio is needed. In contrast, MC dose calculations using water with variable density may be a simple way to solve the problem found using the dose conversion method based on the stopping power ratio.     

Assessment of out-of-field doses in radiotherapy treatments of paediatric patients using Monte Carlo methods and measurements

PurposeTo assess out-of-field doses in radiotherapy treatments of paediatric patients, using Monte Carlo methods to implement a new model of the linear accelerator validated against measurements and developing a voxelized anthropomorphic paediatric phantom.MethodsCT images of a physical anthropomorphic paediatric phantom were acquired and a dosimetric planning using a TPS was obtained. The CT images were used to perform the voxelization of the physical phantom using the ImageJ software and later implemented in MCNP. In order to validate the Monte Carlo model, dose measurements of the 6 MV beam and Linac with 120 MLC were made in a clinical setting, using ionization chambers and a water phantom. Afterwards TLD measurements in the physical anthropomorphic phantom were performed in order to assess the out-of-field doses in the eyes, thyroid, c-spine, heart and lungs.ResultsThe Monte Carlo model was validated for in-field and out-of-field doses with average relative differences below 3%. The average relative differences between TLD measurements and Monte Carlo is 14,3% whilst the average relative differences between TLD and TPS is 55,8%. Moreover, organs up to 22.5 cm from PTV center show TLD and MCNP6 relative differences and TLD and TPS relative differences up to 21.2% and 92.0%, respectively.ConclusionsOur study provides a novel model that could be used in clinical research, namely in dose evaluation outside the treatment fields. This is particularly relevant, especially in pediatric patients, for studying new radiotherapy treatment techniques, since it can be used to estimate the development of secondary tumours.     

A Monte Carlo simulation for the estimation of patient dose in rest and stress cardiac computed tomography with a 320-detector row CT scanner

PurposeTo estimate organ dose and effective dose for patients for cardiac CT as applied in an international multicenter study (CORE320) with a 320-Detector row CT scanner using Monte Carlo (MC) simulations and voxelized phantoms. The effect of positioning of the arms, off-centering the patient and heart rate on patient dose was analyzed.MethodsA MC code was tailored to simulate the geometry and characteristics of the CT scanner. The phantoms representing the adult reference male and female were implemented according to ICRP 110. Effective dose and organ doses were obtained for CT acquisition protocols for calcium scoring, coronary angiography and myocardial perfusion.ResultsFor low heart rate, the normalized effective dose (E) for cardiac CT was higher for female (5.6 mSv/100 mAs) compared to male (2.2 mSv/100 mAs) due to the contribution of female breast tissue. Averaged E for female and male was 11.3 mSv for the comprehensive cardiac protocol consisting of calcium scoring (1.9 mSv); coronary angiography including rest cardiac perfusion (5.1 mSv) and stress cardiac perfusion (4.3 mSv). These values almost doubled at higher heart rates (20.1 mSv). Excluding the arms increased effective dose by 6–8%, centering the patient showed no significant effect. The k-factor (0.028 mSv/mGy.cm) derived from this study leads to effective doses up to 2–3 times higher than the values obtained using now outdated methodologies.ConclusionMC modeling of cardiac CT examinations on realistic voxelized phantoms allowed us to assess patient doses accurately and we derived k-factors that are well above those published previously.     

Location of radiosensitive organs inside pediatric anthropomorphic phantoms: Data required for dosimetry

PurposeThe aim of this study was to determine the location of radiosensitive organs in the interior of four pediatric anthropomorphic phantoms for dosimetric purposes.MethodsFour pediatric anthropomorphic phantoms representing the average individual as newborn, 1-year-old, 5-year-old and 10-year-old child underwent head, thorax and abdomen CT scans. CT and MRI scans of all children aged 0–16 years performed during a 5-year-period in our hospital were reviewed, and 503 were found to be eligible for normal anatomy. Anterior-posterior and lateral dimensions of twelve of the above children closely matched that of the phantoms' head, thoracic and abdominal region in each four phantoms. The mid-sagittal and mid–coronal planes were drawn on selected matching axial images of patients and phantoms. Multiple points outlining large radiosensitive organs in patient images were identified at each slice level and their orthogonal distances from the mid-sagittal and mid–coronal planes were measured. In small organs, the coordinates of organs' centers were similarly determined. The outlines and centers of all radiosensitive organs were reproduced using the coordinates of each organ on corresponding phantoms’ transverse images.ResultsThe locations of the following radiosensitive organs in the interior of the four phantoms was determined: brain, eye lenses, salivary glands, thyroid, lungs, heart, thymus, esophagus, breasts, adrenals, liver, spleen, kidneys, stomach, gallbladder, small bowel, pancreas, colon, ovaries, bladder, prostate, uterus and rectum.ConclusionsThe production of charts of radiosensitive organs inside pediatric anthropomorphic phantoms was feasible and may provide users reliable data for positioning of dosimeters during direct organ dose measurements.     

The construction of computer tomographic phantoms and their application in radiology and radiation protection

Summary In order to assess human organ doses for risk estimates under natural and man made radiation exposure conditions, human phantoms have to be used. As an improvement to the mathematical anthropomorphic phantoms, a new family of phantoms is proposed, constructed from computer tomographic (CT) data. A technique is developed which allows any physical phantom to be converted into computer files to be used for several applications. The new human phantoms present advantages towards the location and shape of the organs, in particular the hard bone and bone marrow. The CT phantoms were used to construct three dimensional images of high resolution; some examples are given and their potential is discussed. The use of CT phantoms is also demonstrated to assess accurately the proportion of bone marrow in the skeleton. Finally, the use of CT phantoms for Monte Carlo (MC) calculations of doses resulting from various photon exposures in radiology and radiation protection is discussed.Dedicated to Prof. W. Jacobi on the occasion of his 60th birthday     

Radiochromic films for dental CT dosimetry: A feasibility study

Dental CT dose evaluations are commonly performed using thermoluminescent dosimeters (TLD) inside anthropomorphic phantoms. Radiochromic films with good sensitivity in the X-ray diagnostic field have recently been developed and are commercially available as GAFCHROMIC XR-QA. There are potential advantages in the use of radiochromic films such as a more comprehensive dosimetry thanks to the adjustable size of the film samples. The purpose of this study was to investigate the feasibility of using radiochromic films for dental CT dose evaluations.Film samples were cut with a width of 5 mm and a length of 25 mm (strips), the same size as the Alderson Rando anthropomorphic phantom holes used in this study. Dental CT dose measurements were performed using simultaneously both TLD and radiochromic strips in the same phantom sites. Two equipment types were considered for dental CT examinations: a 16 slice CT and a cone beam CT. Organ equivalent doses were then obtained averaging the measurements from the sites of the same organ and effective doses were calculated using ICRP 103 weighting factors. The entire procedure was repeated four times for each CT in order to compare also the repeatability of the two dosimeter types.A linear correlation was found between the absorbed dose evaluated with radiochromic films and with TLD, with slopes of 0.930 and 0.944 (correlation r > 0.99). The maximum difference between the two dosimeter’s measurements was 25%, whereas the average difference was 7%. The measurement repeatability was comparable for the two dosimeters at cumulative doses above 15 mGy (estimated uncertainty at 1 sigma level of about 5%), whereas below this threshold radiochromic films show a greater dispersion of data, of about 10% at 1 sigma level. We obtained, using respectively Gafchromic and TLD measurements, effective dose values of 107 μSv and 117 μSv (i.e. difference of 8.6%) for the cone beam CT and of 523 μSv and 562 μSv (i.e. difference of 7%) for the multislice CT.This study demonstrates the feasibility of radiochromic films for dental CT dosimetry, pointing out a good agreement with the results obtained using TLD, with potential advantages and the chance of a more extensive dose investigation.     

Low-tube-voltage selection for non-contrast-enhanced CT: Comparison of the radiation dose in pediatric and adult phantoms

PurposeWe used pediatric and adult anthropomorphic phantoms to compare the radiation dose of low- and standard tube voltage chest and abdominal non-contrast-enhanced computed tomography (CT) scans. We also discuss the optimal low tube voltage for non-contrast-enhanced CT.MethodsUsing a female adult- and three differently-sized pediatric anthropomorphic phantoms we acquired chest and abdominal non-contrast-enhanced scans on a 320-multidetector CT volume scanner. The tube voltage was set at 80-, 100-, and 120 kVp. The tube current was automatically assigned on the CT scanner in response to the set image noise level. On each phantom and at each tube voltage we measured the surface and center dose using high-sensitivity metal-oxide-semiconductor field-effect transistor detectors.ResultsThe mean surface dose of chest and abdominal CT scans in 5-year olds was 4.4 and 5.3 mGy at 80 kVp, 4.5 and 5.4 mGy at 100 kV, and 4.0 and 5.0 mGy at 120 kVp, respectively. These values were similar in our 3-pediatric phantoms (p > 0.05). The mean surface dose in the adult phantom increased from 14.7 to 19.4 mGy for chest- and from 18.7 to 24.8 mGy for abdominal CT as the tube voltage decreased from 120 to 80 kVp (p < 0.01).ConclusionCompared to adults, the surface and center dose for pediatric patients is almost the same despite a decrease in the tube voltage and the low tube voltage technique can be used for non-contrast-enhanced chest- and abdominal scanning.     

Fetal radiation dose in three common CT examinations during pregnancy – Monte Carlo study

PurposeTo determine fetal doses in different stages of pregnancy in three common computed tomography (CT) examinations: pulmonary CT angiography, abdomino-pelvic and trauma scan with Monte Carlo (MC) simulations.MethodsAn adult female anthropomorphic phantom was scanned with a 64-slice CT using pulmonary angiography, abdomino-pelvic and trauma CT scan protocols. Three different sized gelatin boluses placed on the phantom’s abdomen simulated different stages of pregnancy. Intrauterine dose was used as a surrogate to a dose absorbed to the fetus. MC simulations were performed to estimate uterine doses. The simulation dose levels were calibrated with volumetric CT dose index (CTDI_vol) measurements and MC simulations in a cylindrical CTDI body phantom and compared with ten point doses measured with metal-oxide-semiconductor field-effect-transistor dosimeters. Intrauterine volumes and uterine walls were segmented and the respective dose volume histograms were calculated.ResultsThe mean intrauterine doses in different stages of pregnancy varied from 0.04 to 1.04 mGy, from 4.8 to 5.8 mGy, and from 9.8 to 12.6 mGy in the CT scans for pulmonary angiography, abdomino-pelvic and trauma CT scans, respectively. MC simulations showed good correlation with the MOSFET measurement at the measured locations.ConclusionsThe three studied examinations provided highly varying fetal doses increasing from sub-mGy level in pulmonary CT angiography to notably higher levels in abdomino-pelvic and trauma scans where the fetus is in the primary exposure range. Volumetric dose distribution offered by MC simulations in an appropriate anthropomorphic phantom provides a comprehensive dose assessment when applied in adjunct to point-dose measurements.     

Abdominal imaging dose in radiology and radiotherapy – Phantom point dose measurements,effective dose and secondary cancer risk

PurposeTo compare abdominal imaging dose from 3D imaging in radiology (standard/low-dose/dual-energy CT) and radiotherapy (planning CT, kV cone-beam CT (CBCT)).MethodsDose was measured by thermoluminescent dosimeters (TLD’s) placed at 86 positions in an anthropomorphic phantom. Point, organ and effective dose were assessed, and secondary cancer risk from imaging was estimated.ResultsOverall dose and mean organ dose comparisons yield significantly lower dose for the optimized radiology protocols (dual-source and care kV), with an average dose of 0.34±0.01 mGy and 0.54±0.01 mGy (average ± standard deviation), respectively. Standard abdominal CT and planning CT involve considerably higher dose (13.58 ± 0.18 mGy and 18.78±0.27 mGy, respectively). The CBCT dose show a dose fall-off near the field edges. On average, dose is reduced as compared with the planning or standard CT (3.79 ± 0.21 mGy for 220° rotation and 7.76 ± 0.37 mGy for 360°), unless the high-quality setting is chosen (20.30 ± 0.96 mGy). The mean organ doses show a similar behavior, which translates to the estimated secondary cancer risk. The modelled risk is in the range between 0.4 cases per million patient years (PY) for the radiological scans dual-energy and care kV, and 300 cases per million PY for the high-quality CBCT setting.ConclusionsModern radiotherapy imaging techniques (while much lower in dose than radiotherapy), involve considerably more dose to the patient than modern radiology techniques. Given the frequency of radiotherapy imaging, a further reduction in radiotherapy imaging dose appears to be both desirable and technically feasible.     

Monte Carlo-based patient internal dosimetry in fluoroscopy-guided interventional procedures: A review

PurposeThis systematic review aims to understand the dose estimation approaches and their major challenges. Specifically, we focused on state-of-the-art Monte Carlo (MC) methods in fluoroscopy-guided interventional procedures.MethodsAll relevant studies were identified through keyword searches in electronic databases from inception until September 2020. The searched publications were reviewed, categorised and analysed based on their respective methodology.ResultsHundred and one publications were identified which utilised existing MC-based applications/programs or customised MC simulations. Two outstanding challenges were identified that contribute to uncertainties in the virtual simulation reconstruction. The first challenge involves the use of anatomical models to represent individuals. Currently, phantom libraries best balance the needs of clinical practicality with those of specificity. However, mismatches of anatomical variations including body size and organ shape can create significant discrepancies in dose estimations. The second challenge is that the exact positioning of the patient relative to the beam is generally unknown. Most dose prediction models assume the patient is located centrally on the examination couch, which can lead to significant errors.ConclusionThe continuing rise of computing power suggests a near future where MC methods become practical for routine clinical dosimetry. Dynamic, deformable phantoms help to improve patient specificity, but at present are only limited to adjustment of gross body volume. Dynamic internal organ displacement or reshaping is likely the next logical frontier. Image-based alignment is probably the most promising solution to enable this, but it must be automated to be clinically practical.     

Evaluation of PENFAST – A fast Monte Carlo code for dose calculations in photon and electron radiotherapy treatment planning

The aim of the present study is to demonstrate the potential of accelerated dose calculations, using the fast Monte Carlo (MC) code referred to as PENFAST, rather than the conventional MC code PENELOPE, without losing accuracy in the computed dose. For this purpose, experimental measurements of dose distributions in homogeneous and inhomogeneous phantoms were compared with simulated results using both PENELOPE and PENFAST. The simulations and experiments were performed using a Saturne 43 linac operated at 12 MV (photons), and at 18 MeV (electrons). Pre-calculated phase space files (PSFs) were used as input data to both the PENELOPE and PENFAST dose simulations. Since depth–dose and dose profile comparisons between simulations and measurements in water were found to be in good agreement (within ±1% to 1 mm), the PSF calculation is considered to have been validated. In addition, measured dose distributions were compared to simulated results in a set of clinically relevant, inhomogeneous phantoms, consisting of lung and bone heterogeneities in a water tank. In general, the PENFAST results agree to within a 1% to 1 mm difference with those produced by PENELOPE, and to within a 2% to 2 mm difference with measured values. Our study thus provides a pre-clinical validation of the PENFAST code. It also demonstrates that PENFAST provides accurate results for both photon and electron beams, equivalent to those obtained with PENELOPE. CPU time comparisons between both MC codes show that PENFAST is generally about 9–21 times faster than PENELOPE.     

A deep learning approach for converting prompt gamma images to proton dose distributions: A Monte Carlo simulation study

PurposeIn proton therapy, imaging prompt gamma (PG) rays has the potential to verify proton dose (PD) distribution. Despite the fact that there is a strong correlation between the gamma-ray emission and PD, they are still different in terms of the distribution and the Bragg peak (BP) position. In this work, we investigated the feasibility of using a deep learning approach to convert PG images to PD distributions.MethodsWe designed the Monte Carlo simulations using 20 digital brain phantoms irradiated with a 100-MeV proton pencil beam. Each phantom was used to simulate 200 pairs of PG images and PD distributions. A convolutional neural network based on the U-net architecture was trained to predict PD distributions from PG images.ResultsOur simulation results show that the pseudo PD distributions derived from the corresponding PG images agree well with the simulated ground truths. The mean of the BP position errors from each phantom was less than 0.4 mm. We also found that 2000 pairs of PG images and dose distributions would be sufficient to train the U-net. Moreover, the trained network could be deployed on the unseen data (i.e. different beam sizes, proton energies and real patient CT data).ConclusionsOur simulation study has shown the feasibility of predicting PD distributions from PG images using a deep learning approach, but the reliable prediction of PD distributions requires high-quality PG images. Image-degrading factors such as low counts and limited spatial resolution need to be considered in order to obtain high-quality PG images.     

Infant Cardiac CT Angiography with 64-Slice and 256-Slice CT: Comparison of Radiation Dose and Image Quality Using a Pediatric Phantom

Background

The aims of this study were to investigate the image quality and radiation exposure of pediatric protocols for cardiac CT angiography (CTA) in infants under one year of age.

Methodology/Principal Findings

Cardiac CTA examinations were performed using an anthropomorphic phantom representing a 1-year-old child scanned with non-electrocardiogram-gated (NG), retrospectively electrocardiogram-gated helical (RGH) and prospectively electrocardiogram-gated axial (PGA) techniques in 64-slice and 256-slice CT scanners. The thermoluminescent dosimeters (TLD) were used for direct organ dose measurement, while dose-length product and effective mAs were also used to estimate the patient dose. For image quality, noise and signal-to-noise-ratio (SNR) were assessed based on regions-of-interest drawn on the reconstructed CT images, and were compared with the proposed cardiac image quantum index (CIQI). Estimated dose results were in accordant to the measured doses. The NG scan showed the best image quality in terms of noise and SNR. The PGA scan had better image quality than the RGH scan with 83.70% dose reduction. Noise and SNR were also corresponded to the proposed CIQI.

Conclusions/Significance

The PGA scan protocol was a good choice in balancing radiation exposure and image quality for infant cardiac CTA. We also suggested that the effective mAs and the CIQI were suitable in assessing the tradeoffs between radiation dose and image quality for cardiac CTA in infants. These results are useful for future implementation of dose reduction strategies in pediatric cardiac CTA protocols.     

A new pencil beam model for photon dose calculations in heterogeneous media

The pencil beam method is commonly used for dose calculations in intensity-modulated radiation therapy (IMRT). In this study, we have proposed a novel pencil model for calculating photon dose distributions in heterogeneous media. To avoid any oblique kernel-related bias and reduce computation time, dose distributions were computed in a spherical coordinate system based on the pencil kernels of different distances from source to surface (DSS). We employed two different dose calculation methods: the superposition method and the fast Fourier transform convolution (FFTC) method. In order to render the superposition method more accurate, we scaled the depth-directed component by moving the position of the entry point and altering the DSS value for a given beamlet. The lateral components were thus directly corrected by the density scaling method along the spherical shell without taking the densities from the previous layers into account. Significant computation time could be saved by performing the FFTC calculations on each spherical shell, disregarding density changes in the lateral direction. The proposed methods were tested on several phantoms, including lung- and bone-type heterogeneities. We compared them with Monte Carlo (MC) simulation for several field sizes with 6 MV photon beams. Our results revealed mean absolute deviations <1% for the proposed superposition method. Compared to the AAA algorithm, this method improved dose calculation accuracy by at least 0.3% in heterogeneous phantoms. The FFTC method was approximately 40 times faster than the superposition method. However, compared with MC, mean absolute deviations were <3% for the FFTC method.     

Artifact-free CT images for electron beam therapy using a patient-specific non metallic shield

Patient’s CT images taken with metallic shields for radiotherapy suffer from artifacts. Furthermore, the treatment planning system (TPS) has a limitation on accurate dose calculations for high density materials. In this study, a Monte Carlo (MC)-based method was developed to accurately evaluate the dosimetric effect of the metallic shield. Two patients with a commercial tungsten shield of lens and two patients with a custom-made lead shield of lip were chosen to produce their non-metallic dummy shields using 3D scanner and printer. With these dummy shields, we generated artifact-free CT images. The maximum CT number allowed in TPS was assigned to metallic shields. MC simulations with real material information were carried out. In addition, clinically relevant dose-volumetric parameters were calculated for the comparison between MC and TPS. Relative dosimetry was performed using radiochromic films. The dose reductions below metallic structures were shown on MC dose distributions, but not evident on TPS dose distributions. The differences in dose-volumetric parameters of PTV between TPS and MC for eye shield cases were not clearly shown. However, the mean dose of lens from TPS and MC was different. The MC results were in superior agreement with measured data in relative dosimetry. The lens dose could be overestimated by TPS. The differences in dose-volumetric parameters of PTV between TPS and MC were generally larger in lip cases than in eye cases. The developed method is useful in predicting the realistic dose distributions around the organs blocked by the metallic shields.