Development and characterisation of a plastic scintillator dosemeter in high-energy photon beams.

The radioluminescent (RL) dosemeter is excellent for real-time radiation measurement and can be used in various applications. A plastic scintillator is often the choice sensor because of its size and tissue equivalency. This study aims to characterise a novel plastic scintillator irradiated with high-energy photon beams. An RL dosimetry system was developed using the plastic scintillator. The RL dosimetry system was irradiated using a linear accelerator to characterise the dose linearity, dose rate, energy dependency and depth dose. The developed system showed a linear response toward the dose and dose rate. An energy dependency factor of 1.06 was observed. Depth dose measurement showed a mean deviation of 1.21% from the treatment planning system. The response and characteristics of the plastic scintillator show that it may be used as an alternative in an RL dosimetry system.

Graphite foils as potential skin and epithelium dosimeters at therapeutic photon energies.

This work builds upon a prior study, examining the dosimetric utility of pencil lead and thin graphitic sheets, focusing upon the measurement of skin doses within the mammographic regime. In recognizing the near soft-tissue equivalence of graphite and the earlier-observed favourable thermoluminescence yield of thin sheets of graphite, this has led to present study of 50 µm thick graphite for parameters typical of external beam fractionated radiotherapy and skin dose evaluations. The graphite layers were annealed and then stacked to form an assembly of 0.5 mm nominal thickness. Using a 6 MV photon beam and delivering doses from 2- to 60 Gy, irradiations were conducted, the assembly first forming a superficial layer to a solid water phantom and subsequently underlying a 1.5 cm bolus, seeking to circumvent the build-up to electronic equilibrium for skin treatments. Investigations were made of several dosimetric properties arising from the thermoluminescence yield of the 50 µm thick graphite slabs, in particular proportionality and sensitivity to dose. The results show excellent sensitivity within the dose range of interest, the thermoluminescence response varying with increasing depth through the stacked graphite layers, obtaining a coefficient of determination of 90%. Acknowledging there to be considerable challenge in accurately matching skin thickness with dose, the graphite sheets have nevertheless shown considerable promise as dosimeters of skin, sensitive in determination of dose from the surface of the graphite through to sub-dermal depth thicknesses.

Exploring the thermoluminescence characteristics of smartphone screen safety glasses for retrospective dosimetry applications.

In clinical settings, standard dosimeters might miss radiation mishaps. Retrospective dosimeters could help to track personnel (such as patients and other staff who don't wear dosimeters) exceeding safe limits and assess long-term exposure trends. This study has investigated key thermoluminescence (TL) dosimetric characteristics, including the glow curve structure, dose-response, energy dependence, sensitivity and fading of various safety glasses that are used as screen protectors of smartphones subjected to photon irradiation. Among the studied glasses, the HD Anti-Peep safety glass for iPhone has been found to exhibit a linear dose-response with a regression coefficient of 99% within the dose range of 2-10 Gy. Moreover, all the safety glasses showed independence with respect to photon energy of 6 MV and 10 MV. The TL glow curves of the samples showed a broad glow peak between 125 °C and 325 °C at 10 Gy. The TL kinetic parameters of the safety glasses were also studied by analyzing the glow curves using the peak shape and initial rise method. The geometric factor (µg) is found to be within the range of 0.43-0.53, which indicates the suitability of applying Chen's general-order formula to calculate the kinetic parameters such as activation energy, frequency factor and trap lifetime. The activation energy (E) and frequency factor (s) are found in the range of 0.31-0.54 eV and 4.55 × 103 to 2.12 × 106 s-1 respectively obtained via the peak shape method. The relatively long trap lifetime and observed thermoluminescence features indicate that the HD Anti-Peep safety glass offers a better option to estimate dose retrospectively to ensure the safety of human health.

Cumulative sum method in nonzero fixed action level setup correction strategy: an application of statistical process control for targeted prostate radiotherapy.

PURPOSE: This study aims to incorporate a statistical process control tool, the cumulative sum (CUSUM) method, in the nonzero fixed action level setup correction strategy for the detection and correction of systematic shifts in prostate position during prostate image-guided radiotherapy. METHODS: A daily nonzero action level setup correction strategy using CUSUM chart was proposed and tested retrospectively on 34 nonrandomized patients with prostate-implanted fiducial markers in situ plus daily localization via stereoscopic electronic portal imaging. A cumulative error index, which monitors a cumulative process index over time, was implemented in parallel with the localization offsets of the prostate. A value of this index exceeding a decision interval H indicated that a systematic change in the mean value of localization had occurred. When a value of the index exceeding H was recorded, the magnitude of the systematic shift was estimated and the subsequent prescribed offsets were corrected to account for the new setup positions. With the new protocol, the authors produced simulated treatment histories in which the detection of systematic shifts and the frequency of localization offset exceeding action level were evaluated. The protocol was examined against three levels of mean systematic shifts of localization for detection (µ(1)) of 3, 5, and 7 mm. RESULTS: The overall rates of detection of systematic shifts using this algorithm were relatively high. The level µ(1) = 3 mm resulted in the highest rate of detection of systematic offset change, in 42% of the charts. For larger values of µ(1), the overall detection numbers fell to 18% and 12% of the charts for µ(1) = 5 and 7 mm, respectively. The mean magnitude of change in systematic offset at time of detection was 3.1, 4.4, and 5.2 mm for µ(1) = 3, 5, and 7 mm, respectively. By adapting the setup position for any change in systematic localization offset over a course of treatment using the new protocol, it has been shown that the frequency of localization offsets exceeding action levels was reduced. For the optimal choice of intervention levels for correction and µ(1), the number of localization offsets exceeding action levels has been reduced by approximately half. CONCLUSIONS: The nonzero fixed action level setup correction strategy incorporating CUSUM charts has been shown to provide an objective method for (i) detecting a systematic shift of a patient localization offset, (ii) quantifying the magnitude of a systematic change based on previous observations, and (iii) correcting the prescribed offset by accounting for the systematic shift(s) in patient setup position.

On the accuracy of localization achievable in fiducial-based stereoscopic image registration system using an electronic portal imaging device.

Portal imaging using electronic portal imaging device (EPID) is a well-established image-guided radiation therapy (IGRT) technique for external beam radiation therapy. The aims of this study are threefold; (i) to assess the accuracy of isocentre localization in the fiducial-based stereoscopic image registration, (ii) to investigate the impact of errors in the beam collimation device on stereoscopic registration, and (iii) to evaluate the intra- and inter-observer variability in stereoscopic registration. Portal images of a ball bearing phantom were acquired and stereoscopic image registrations were performed based on a point centred in the ball bearing as the surrogate for registration. Experiments were replicated by applying intentional offsets in the beam collimation device to simulate collimation errors. The accuracy of fiducial markers localization was performed by repeating the experiment using three spherical lead shots implanted in a pelvic phantom. Portal images of pelvis phantom were given to four expert users to assess the inter-observer variability in performing registration. The isocentre localization accuracy tested using ball bearing phantom was within 0.3 mm. Gravity-induced systematic errors of beam collimation device by 2 mm resulted in positioning offsets of the order of 2 mm opposing the simulated errors. Relatively large inter-portal pair projection errors ranges from 1.3 mm to 1.8 mm were observed with simulated errors in the beam collimation device. The intra-user and inter-user variabilities were observed to be 0.8 and 0.4 mm respectively. Fiducial-based stereoscopic image registration using EPID is robust for IGRT procedure.

Low-cost commercial graphite-rich pencils subjected to electron irradiation for passive radiation dosimetry.

Various thicknesses of 2B grade polymer pencil lead graphite (PPLG) were used in the present study, which focussed on the alteration in crystalline lattice and the structural defect caused by the electron irradiation dosage ranging from 0.5 to 20 Gy delivered by an Elekta HD Linac. The fundamental trap parameters i.e. kinetics order (b), activation energy (E), and frequency factor (s) of the PPLG samples have been estimated using the initial rise and peak shape approaches by fitting the thermoluminescence (TL) glow peaks of the PPLG samples exposed to 20 Gy. The lifetime of the TL glow peak is also presented, which provides information on the stability of the TL signal at maximum temperatures. Raman, Photoluminescence (PL), and X-ray diffraction (XRD) spectra are being used to observe the structural changes that have occurred as a result of the radiation doses. These spectroscopies offer an understanding of the physical parameters that are related to the defects and taking part in the luminescence process. When all of the data are taken into account, it is anticipated that 0.3 mm PPLG is an effective material for dosimetry. The results of these lines of research are intended to educate the innovation of versatile graphite radiation dosimeters as a low-cost efficient system for radiation detection. The studied PPLG offers tissue equivalence as well as high spatial resolution, both are desirable criteria for a material to be used in the monitoring of ionising radiation or a variety of medical applications.

Dosimetric impact of systematic MLC positional errors on step and shoot IMRT for prostate cancer: a planning study.

The positional accuracy of multileaf collimators (MLC) is crucial in ensuring precise delivery of intensity-modulated radiotherapy (IMRT). The aim of this planning study was to investigate the dosimetric impact of systematic MLC positional errors on step and shoot IMRT of prostate cancer. A total of 12 perturbations of MLC leaf banks were introduced to six prostate IMRT treatment plans to simulate MLC systematic positional errors. Dose volume histograms (DVHs) were generated for the extraction of dose endpoint parameters. Plans were evaluated in terms of changes to the defined endpoint dose parameters, conformity index (CI) and healthy tissue avoidance (HTA) to planning target volume (PTV), rectum and bladder. Negative perturbations of MLC had been found to produce greater changes to endpoint dose parameters than positive perturbations of MLC (p < 0.01). Negative and positive asynchronised MLC perturbations of -1 mm resulted in median changes in D(95) of -1.2 and 0.9% respectively. Negative and positive synchronised MLC perturbations of 1 mm in one direction resulted in median changes in D(95) of -2.3 and 1.8% respectively. Doses to rectum were generally more sensitive to systematic MLC errors compared to bladder (p < 0.01). Negative and positive synchronised MLC perturbations of 1 mm in one direction resulted in median changes in endpoint dose parameters of rectum and bladder from 1.0 to 2.5%. Maximum reduction of -4.4 and -7.3% were recorded for conformity index (CI) and healthy tissue avoidance (HTA) respectively due to synchronised MLC perturbation of 1 mm. MLC errors resulted in dosimetric changes in IMRT plans for prostate.

Correlation analysis of CT-based rectal planning dosimetric parameters with in vivo dosimetry of MOSkin and PTW 9112 detectors in Co-60 source HDR intracavitary cervix brachytherapy.

Intracavitary cervical brachytherapy delivers high doses of radiation to the target tissue and a portion of these doses will also hit the rectal organs due to their close proximity. Rectal dose can be evaluated from dosimetric parameters in the treatment planning system (TPS) and in vivo (IV) dose measurement. This study analyzed the correlation between IV rectal dose with selected volume and point dose parameters from TPS. A total of 48 insertions were performed and IV dose was measured using the commercial PTW 9112 semiconductor diode probe. In 18 of 48 insertions, a single MOSkin detector was attached on the probe surface at 50 mm from the tip. Four rectal dosimetric parameters were retrospectively collected from TPS; (a) PTW 9112 diode maximum reported dose (RPmax) and MOSkin detector, (b) minimum dose to 2 cc (D2cc), (c) ICRU reference point (ICRUr), and (d) maximum dose from additional points (Rmax). The IV doses from both detectors were analyzed for correlation with these dosimetric parameters. This study found a significantly high correlation between IV measured dose from RPmax (r = 0.916) and MOSkin (r = 0.959) with TPS planned dose. The correlation between measured RPmax with both D2cc and Rmax revealed high correlation of r > 0.7, whereas moderate correlation (r = 0.525) was observed with ICRUr. There was no significant correlation between MOSkin IV measured dose with D2cc, ICRUr and Rmax. The non-significant correlation between parameters was ascribable to differences in both detector position within patients, and dosimetric volume and point location determined on TPS, rather than detector uncertainties.

Borosilicate glass 60Co high dose rate brachytherapy thermoluminescence dosimetry.

Brachytherapy is commonly used in treatment of cervical, prostate, breast and skin cancers, also for oral cancers, typically via the application of sealed radioactive sources that are inserted within or alongside the area to be treated. A particular aim of the various brachytherapy techniques is to accurately transfer to the targeted tumour the largest possible dose, at the same time minimizing dose to the surrounding normal tissue, including organs at risk. The dose fall-off with distance from the sources is steep, the dose gradient representing a prime factor in determining the dose distribution, also representing a challenge to the conduct of measurements around sources. Amorphous borosilicate glass (B2O3) in the form of microscope cover slips is recognized to offer a practicable system for such thermoluminescence dosimetry (TLD), providing for high-spatial resolution (down to < 1 mm), wide dynamic dose range, good reproducibility and reusability, minimal fading, resistance to water and low cost. Herein, investigation is made of the proposed dosimeter using a 1.25 MeV High Dose Rate (HDR) 60Co brachytherapy source, characterizing dose response, sensitivity, linearity index and fading. Analysis of the TL glow curves were obtained using the Tmax-Tstop method and first-order kinetics using GlowFit software, detailing the frequency factors and activation energy.

An international survey of imaging practices in radiotherapy.

Improvements in delivery of radiation dose to target tissues in radiotherapy have increased the need for better image quality and led to a higher frequency of imaging patients. Imaging for treatment planning extends to function and motion assessment and devices are incorporated into medical linear accelerators (linacs) so that regions of tissue can be imaged at time of treatment delivery to ensure dose distributions are delivered as accurately as possible. A survey of imaging in 97 radiotherapy centres in nine countries on six continents has been undertaken with an on-line questionnaire administered through the International Commission on Radiological Protection mentorship programme to provide a snapshot of imaging practices. Responses show that all centres use CT for planning treatments and many utilise additional information from magnetic resonance imaging and positron emission tomography scans. Most centres have kV cone beam CT attached to at least some linacs and use this for the majority of treatment fractions. The imaging options available declined with the human development index (HDI) of the country, and the frequency of imaging during treatment depended more on country than treatment site with countries having lower HDIs imaging less frequently. The country with the lowest HDI had few kV imaging facilities and relied on MV planar imaging intermittently during treatment. Imaging protocols supplied by vendors are used in most centres and under half adapt exposure conditions to individual patients. Recording of patient doses, a knowledge of which is important in optimisation of imaging protocols, was limited primarily to European countries.

Correction: Tailored Ge-doped fibres for passive electron radiotherapy dosimetry.

[This corrects the article DOI: 10.1371/journal.pone.0235053.].

Evaluation of rectal dose discrepancies between planned and in vivo dosimetry using MOSkin detector and PTW 9112 semiconductor probe during 60Co HDR CT-based intracavitary cervix brachytherapy.

PURPOSE: Dose to the rectum during brachytherapy treatment may differ from an approved treatment plan which can be quantified with in vivo dosimetry (IVD). This study compares the planned with in vivo doses measured with MOSkin and PTW 9112 rectal probe in patients undergoing CT based HDR cervical brachytherapy with Co-60 source. METHODS: Dose measurement of a standard pear-shaped plan carried out in phantom to verify the MOSkin dose measurement accuracy. With MOSkin attached to the third diode, RP3 of the PTW 9112, both detectors were inserted into patients' rectum. The RP3 and MOSkin measured doses in 18 sessions as well as the maximum measured doses from PTW 9112, RPmax in 48 sessions were compared to the planned doses. RESULTS: Percentage dose differences ΔD (%) in phantom study for two MOSkin found to be 2.22 ± 0.07% and 2.5 ± 0.07%. IVD of 18 sessions resulted in ΔD(%) of -16.3% to 14.9% with MOSkin and ΔD(%) of -35.7% to -2.1% with RP3. In 48 sessions, RPmax recorded ΔD(%) of -37.1% to 11.0%. MOSkin_measured doses were higher in 44.4% (8/18) sessions, while RP3_measured were lower than planned doses in all sessions. RPmax_measured were lower in 87.5% of applications (42/47). CONCLUSIONS: The delivered doses proven to deviate from planned doses due to unavoidable shift between imaging and treatment as measured with MOSkin and PTW 9112 detectors. The integration of MOSkin on commercial PTW 9112 surface found to be feasible for rectal dose IVD during cervical HDR ICBT.

Tailored Ge-doped fibres for passive electron radiotherapy dosimetry.

Study has been made of the thermoluminescence yield of various novel tailor-made silica fibres, 6 and 8 mol % Ge-doped, with four differing outer dimensions, comprised of flat and cylindrical shapes, subjected to electron irradiation. Main thermoluminescence dosimetric characteristics have been investigated, including the glow curve, dose response, energy dependence, minimum detectable dose, effective atomic number, linearity of index and sensitivity of the fibres. The studies have also established the uncertainties involved as well as the stability of response in terms of fading effect, reproducibility and annealing. In addition, dose-rate dependence was accounted for as this has the potential to be a significant factor in radiotherapy applications. The 6 and 8 mol % fibres have been found to provide highly linear dose response within the range 1 to 4 Gy, the smallest size flat fibre, 6 mol% Ge-doped, showing the greatest response by a factor of 1.1 with respect to the highly popular LiF phosphor-based medium TLD100. All of the fibres also showed excellent reproducibility with a standard deviation of < 2% and < 4% for 6 and 8 mol % Ge-doped fibres respectively. For fading evaluation, the smallest 6 mol% Ge-doped dimension flat fibre, i.e., 85 × 270 µm displayed the lowest signal loss within 120 days post-irradiation, at around 26.9% also showing a response superior to that of all of the other fibres. Moreover, all the fibres and TLD-100 chips showed independence with respect to electron irradiation energy and dose-rate. Compared with the 8 mol% Ge-doped optical fibres, the 6 mol% Ge-doped flat optical fibres have been demonstrated to possess more desirable performance features for passive dosimetry, serving as a suitable alternative to TLD-100 for medical irradiation treatment applications.

In vivo dosimetry using MOSkin detector during Cobalt-60 high-dose-rate (HDR) brachytherapy of skin cancer.

The MOSkin, a metal-oxide semiconductor field-effect transistor based detector, is suitable for evaluating skin dose due to its water equivalent depth (WED) of 0.07 mm. This study evaluates doses received by target area and unavoidable normal skin during a the case of skin brachytherapy. The MOSkin was evaluated for its feasibility as detector of choice for in vivo dosimetry during skin brachytherapy. A high-dose rate Cobalt-60 brachytherapy source was administered to the tumour located at the medial aspect of the right arm, complicated with huge lymphedema thus limiting the arm motion. The source was positioned in the middle of patients' right arm with supine, hands down position. A 5 mm lead and 5 mm bolus were sandwiched between the medial aspect of the arm and lateral chest to reduce skin dose to the chest. Two calibrated MOSkin detectors were placed on the target and normal skin area for five treatment sessions for in vivo dose monitoring. The mean dose to the target area ranged between 19.9 and 21.1 Gy and was higher in comparison with the calculated dose due to contribution of backscattered dose from lead. The mean measured dose at normal skin chest area was 1.6 Gy (1.3-1.9 Gy), less than 2 Gy per fraction. Total dose in EQD2 received by chest skin was much lower than the recommended skin tolerance. The MOSkin detector presents a reliable real-time dose measurement. This study has confirmed the applicability of the MOSkin detector in monitoring skin dose during brachytherapy treatment due to its small sensitive volume and WED 0.07 mm.

Evaluation of Ge-doped silica fibre TLDs for in vivo dosimetry during intraoperative radiotherapy.

Ge-doped silica fibre (GDSF) thermoluminescence dosimeters (TLD) are non-hygroscopic spatially high-resolution radiation sensors with demonstrated potential for radiotherapy dosimetry applications. The INTRABEAM® system with spherical applicators, one of a number of recent electronic brachytherapy sources designed for intraoperative radiotherapy (IORT), presents a representative challenging dosimetry situation, with a low keV photon beam and a desired rapid dose-rate fall-off close-up to the applicator surface. In this study, using the INTRABEAM® system, investigations were made into the potential application of GDSF TLDs for in vivo IORT dosimetry. The GDSFs were calibrated over the respective dose- and depth-range 1 to 20 Gy and 3 to 45 mm from the x-ray probe. The effect of different sizes of spherical applicator on TL response of the fibres was also investigated. The results show the GDSF TLDs to be applicable for IORT dose assessment, with the important incorporated correction for beam quality effects using different spherical applicator sizes. The total uncertainty in use of this type of GDSF for dosimetry has been found to range between 9.5% to 12.4%. Subsequent in vivo measurement of skin dose for three breast patients undergoing IORT were performed, the measured doses being below the tolerance level for acute radiation toxicity.

The characteristics of Fuji IP Cassette Type PII and application for radiation oncology quality assurance tests and portal imaging.

The advancement of digital imaging has prompted more medical institutions to go filmless. The computed radiography (CR) system is becoming an important tool not only in diagnostic imaging, but also in radiation oncology. A new CR system that was specially designed for the use in radiation oncology, Fuji IP cassette type PII has been introduced to the market in the middle of year 2006. This project aimed to study some basic physical characteristics of this new type of cassette and explore its application for performing quality assurance (QA) tests and portal imaging in radiotherapy. All the images were read by FCR 5000 Plus reader. The image was found to reach its saturation value of 1023 (due to the image was stored in 10 bits data) by depending on the sensitivity value being adjusted. The uniformity test gave the result of 0.12%. The cassette was used to perform the QA tests which were previously performed using film. All the results met the specification as stated in AAPM Task Group 40. The comparison for the portal images of PortalVision contrast-detail phantom showed that the spatial resolution of the images obtained by CR system (Fujifilm Co., Ltd., Tokyo, Japan) were better than the EPID (Varian Medical Systems, Inc., Palo Alto, USA) and film system (Eastman Kodak Co., New York, USA). The IP cassette type PII was found to be suitable as an alternative QA test tool and portal imaging in radiotherapy.

Dosimetric characterisation of the optically-stimulated luminescence dosimeter in cobalt-60 high dose rate brachytherapy system.

This study investigates the characteristics and application of the optically-stimulated luminescence dosimeter (OSLD) in cobalt-60 high dose rate (HDR) brachytherapy, and compares the results with the dosage produced by the treatment planning system (TPS). The OSLD characteristics comprised linearity, reproducibility, angular dependence, depth dependence, signal depletion, bleaching rate and cumulative dose measurement. A phantom verification exercise was also conducted using the Farmer ionisation chamber and in vivo diodes. The OSLD signal indicated a supralinear response (R2 = 0.9998). It exhibited a depth-independent trend after a steep dose gradient region. The signal depletion per readout was negligible (0.02%), with expected deviation for angular dependence due to off-axis sensitive volume, ranging from 1 to 16%. The residual signal of the OSLDs after 1 day bleached was within 1.5%. The accumulated and bleached OSLD signals had a standard deviation of ± 0.78 and ± 0.18 Gy, respectively. The TPS was found to underestimate the measured doses with deviations of 5% in OSLD, 17% in the Farmer ionisation chamber, and 7 and 8% for bladder and rectal diode probes. Discrepancies can be due to the positional uncertainty in the high-dose gradient. This demonstrates a slight displacement of the organ at risk near the steep dose gradient region will result in a large dose uncertainty. This justifies the importance of in vivo measurements in cobalt-60 HDR brachytherapy.

Dosimetric evaluation near lung and soft tissue interface region during respiratory-gated and non-gated radiotherapy: A moving phantom study.

Challenges in treating lung tumours are related to the respiratory-induced tumour motion and the accuracy of dose calculation in charged particle disequilibrium condition. The dosimetric characteristics near the interface of lung and Perspex media in a moving phantom during respiratory-gated and non-gated radiotherapy were investigated using Gafchromic EBT2 and the MOSkin detector. The MOSkin detectors showed good agreement with the EBT2 films during static and gated radiotherapy. In static radiotherapy, the penumbral widths were found to be 3.66mm and 7.22mm in Perspex and lung media, respectively. In non-gated (moving) radiotherapy with 40mm respiratory amplitude, dose smearing effect was observed and the penumbral widths were increased to 28.81mm and 26.40mm, respectively. This has been reduced to 6.85mm and 9.81mm, respectively, in gated radiotherapy with 25% gating window. There were still some dose discrepancies as compared to static radiotherapy due to the residual motion. This should be taken into account in the margin generation for the target tumour.

Monte Carlo skin dose simulation in intraoperative radiotherapy of breast cancer using spherical applicators.

The relatively new treatment modality electronic intraoperative radiotherapy (IORT) is gaining popularity, irradiation being obtained within a surgically produced cavity being delivered via a low-energy x-ray source and spherical applicators, primarily for early stage breast cancer. Due to the spatially dramatic dose-rate fall off with radial distance from the source and effects related to changes in the beam quality of the low keV photon spectra, dosimetric account of the Intrabeam system is rather complex. Skin dose monitoring in IORT is important due to the high dose prescription per treatment fraction. In this study, modeling of the x-ray source and related applicators were performed using the Monte Carlo N-Particle transport code. The dosimetric characteristics of the model were validated against measured data obtained using an ionization chamber and EBT3 film as dosimeters. By using a simulated breast phantom, absorbed doses to the skin for different combinations of applicator size (1.5-5 cm) and treatment depth (0.5-3 cm) were calculated. Simulation results showed overdosing of the skin (>30% of prescribed dose) at a treatment depth of 0.5 cm using applicator sizes larger than 1.5 cm. Skin doses were significantly increased with applicator size, insofar as delivering 12 Gy (60% of the prescribed dose) to skin for the largest sized applicator (5 cm diameter) and treatment depth of 0.5 cm. It is concluded that the recommended 0.5-1 cm distance between the skin and applicator surface does not guarantee skin safety and skin dose is generally more significant in cases with the larger applicators. HIGHLIGHTS: • Intrabeam x-ray source and spherical applicators were simulated and skin dose was calculated. • Skin dose for constant skin to applicator distance strongly depends on applicator size. • Use of larger applicators generally results in higher skin dose. • The recommended 0.5-1 cm skin to applicator distance does not guarantee skin safety.