Scientific validation of clinical visual scales and Antera 3D™ consistency with derived measurements in the assessment of infantile haemangioma after laser therapy.

BACKGROUND: Laser therapy is a treatment for infantile haemangiomas. The efficacy of laser therapy for red lesions is determined by visual evaluation; however, this assessment is inaccurate and lacks objectivity. OBJECTIVE: To scientifically validate the consistency between pre- and post-treatment visual assessment grades for infantile haemangioma treated with pulsed dye laser (PDL) and the values calculated from images obtained with Antera 3D™. METHODS: This study involved 81 cases of infantile haemangiomas treated with PDL alone from 2012 to 2015 and with Antera 3D™ images of the lesions. Using images obtained before treatment and 4-6 weeks after the last treatment, the lesions were rated using a visual four-step scale. Ratings were categorised as Poor/Fair/Good/Excellent by the degree of improvement in the red colour tone. The red colour ratio was calculated using the haemoglobin distribution in the lesion and surrounding skin, and the improvement difference and improvement rate were then obtained. The correlation between the improvement difference and improvement rate, and visual evaluation was statistically analysed. RESULTS: No serious adverse effects were observed, with an average of 4.3 treatments per patient; 60.1% of the patients achieved Good/Excellent results. There were statistically significant differences in the post-treatment red colour ratio and improvement ratio in each category after visual evaluation classification. The improvement rate and the four visual grades were statistically correlated. CONCLUSION: This study confirmed the scientific validity of visual evaluation and the evaluation criteria calculated from Antera 3D™. This method could objectively determine treatment effectiveness.

75Se - A promising alternative to 192Ir for potential use in the skin cancer brachytherapy: A Monte Carlo simulation study using FLUKA code.

This study aimed to evaluate the possibility of utilizing the HDR 75Se source for skin cancer brachytherapy. In this work, based on the BVH-20 skin applicator, two cup-shaped applicators, without and with the flattening filter, were modeled. To obtain the optimal flattening filter shape, an approach based on the MC simulation in combination with an analytical estimation was used. Then, the dose distributions for 75Se-applicators were generated using MC simulations in water, and their dosimetric characterizations such as flatness, symmetry, and penumbra were evaluated. Furthermore, the radiation leakage in the backside of the applicators was estimated by additional MC simulation. Finally, to evaluate the treatment times, calculations were performed for two 75Se-applicators assuming 5 Gy per fraction. The flatness, symmetry, and penumbra values for the 75Se-applicator without the flattening filter were estimated to be 13.7%, 1.05, and 0.41 cm respectively. The corresponding values for 75Se-applicator with the flattening filter were estimated to be 1.6%, 1.06, and 0.10 cm respectively. The radiation leakage value at a distance of 2 cm from the applicator surface was calculated to be 0.2% and 0.4% for the 75Se-applicator without and with the flattening filter respectively. Our results showed that the treatment time for the 75Se-applicator is comparable with that of the 192Ir-Leipzig applicator. The findings revealed that the dosimetric parameters of the 75Se applicator are comparable with the 192Ir skin applicator. Overall, the 75Se source can be an alternative to 192Ir sources for HDR brachytherapy of skin cancer.

A novel tool for predicting the dose distribution of non-sealed 188 Re (Rhenium) resin in non-melanoma skin cancers (NMSC) patients.

BACKGROUND: High-dose rate brachytherapy using a non-sealed 188 Rhenium resin (188 Re) is a recently approved treatment option for non-melanoma skin cancer (NMSC). The treatment goal is to deliver a personalized absorbed dose to the deepest point of neoplastic infiltration corresponding to the minimal target dose. The treatment consists of the application of a 188 Re-based resin over a plastic foil placed on the target skin surface. However, there is no treatment planning tool to assess the 188 Re activity needed for a personalized treatment. PURPOSE: The paper aims to present a novel Monte Carlo (MC)-based tool for 188 Re-based resin activity and dose calculation, experimentally validated using Gafchromic EBT3 films. METHODS: MC simulations were carried out using FLUKA modeling density and composition of 188 Re resin. The MC-based look up table (LUT) was incorporated in an ad hoc developed tool. The proposed tool allows the personalized calculation of treatment parameters (i.e., activity to be dispensed, the treatment duration, and dose volume histograms), according to the target dimension. The proposed tool was compared using Bland-Altman analysis to the previous calculation approaches conducted using VARSKIN in a retrospective cohort of 76 patients. The tool was validated in ad hoc experimental set ups using a stack of calibrated Gafchromic EBT3 films covered by a plastic film and exposed using a homogenous activity distribution of 188 Re eluate and a heterogeneous activity distribution of 188 Re resin mimic the patient treatment. RESULTS: The agreement between the proposed tool and VARSKIN was evaluated on the investigated cohort with median range of target area, target depth, and treatment time equal to 4.8 [1.0-60.1] cm2 , 1.1 [0.2-3.0] mm, and 70 [21-285] min, with a median range of target dose (Gy) of 23.5 [10-54.9]. The calculated minimal target doses, ranged from 1% to 10% for intermediate target depths (1.2 ± 0.7 mm), while showing significant differences in the estimation of superficial (maximal) target doses. The agreement between MC calculation and measurements at different plans in a stack of Gafchromic EBT3 films was within 10% for both the homogenous and heterogeneous activity distribution of 188 Re. Worst agreements were observed for absorbed doses lower than 0.3 Gy. CONCLUSIONS: Our results support the implementation of our MC-based tool in the practical routine for calculating the 188 Re resin activity and treatment parameters necessary for obtaining the prescribed minimal target dose.

Computational dose visualization & comparison in total skin electron treatment suggests superior coverage by the rotational versus the Stanford technique.

INTRODUCTION/BACKGROUND: The goal of Total Skin Electron Therapy (TSET) is to achieve a uniform surface dose, although assessment of this is never really done and typically limited points are sampled. A computational treatment simulation approach was developed to estimate dose distributions over the body surface, to compare uniformity of (i) the 6 pose Stanford technique and (ii) the rotational technique. METHODS: The relative angular dose distributions from electron beam irradiation was calculated by Monte Carlo simulation for cylinders with a range of diameters, approximating body part curvatures. These were used to project dose onto a 3D body model of the TSET patient's skin surfaces. Computer animation methods were used to accumulate the dose values, for display and analysis of the homogeneity of coverage. RESULTS: The rotational technique provided more uniform coverage than the Stanford technique. Anomalies of under dose were observed in lateral abdominal regions, above the shoulders and in the perineum. The Stanford technique had larger areas of low dose laterally. In the rotational technique, 90% of the patient's skin was within ±10% of the prescribed dose, while this percentage decreased to 60% or 85% for the Stanford technique, varying with patient body mass. Interestingly, the highest discrepancy was most apparent in high body mass patients, which can be attributed to the loss of tangent dose at low angles of curvature. DISCUSSION/CONCLUSION: This simulation and visualization approach is a practical means to analyze TSET dose, requiring only optical surface body topography scans. Under- and over-exposed body regions can be found, and irradiation could be customized to each patient. Dose Area Histogram (DAH) distribution analysis showed the rotational technique to have better uniformity, with most areas within 10% of the umbilicus value. Future use of this approach to analyze dose coverage is possible as a routine planning tool.

Characterization of a novel material to be used as bolus in radiotherapy with electrons.

Features of new material to be used as bolus in external radiotherapy were determined and their performance were evaluated. The characterization was carried out using Monte Carlo methods with the Geant4 code where the Percentage Depth Dose (PDD) due to electrons was estimated. In the Monte Carlo model the linear accelerator head was included. Calculated results were experimentally validated with measurements made for 6, 9, 12 and 16 MeV electron beams. The key characteristics of the implemented material were identified, guaranteeing a low cost bolus, easy to be customized and to be used in clinical applications. In comparison with commercial materials the new materials are superior from the cost to the effectiveness of their use in clinical treatments.

High-dose-rate brachytherapy for facial skin cancer: Outcome and toxicity assessment for 71 cases.

PURPOSE: In France, the reference technique for skin cancer was low-dose-rate brachytherapy (BT) delivered via iridium wire. At the end of their commercialization in 2015 we have replaced them by high-dose-rate (HDR) BT via interstitial catheters. We assessed efficacy and tolerance as soon as this technique was implemented. METHODS AND MATERIALS: Patients received 7 Gy on the first day, followed by 8 × 4 Gy over the next 4 days for exclusive BT and 9 × 4 Gy over 5 days for post-operative BT. RESULTS: Sixty-six patients of median age 81 years received a total of 58 primary BT and 13 post-operative BT for non-melanoma facial skin cancers. Implantation was without difficulty. Median follow up was 15.3 months. Two patients died of intercurrent diseases before first follow up. For the others, 98.5% showed complete response and 3% local recurrence after a median of 20.5 months. Four patients had grade 3 acute dermatitis and three patients had grade 3 mucositis. All the Grade 3 toxicities were resolved within 3 months. A late significant hypopigmentation occurred in 4 patients. CONCLUSIONS: HDR BT is efficient and well-tolerated with good cosmetic results. HDR catheters are similar with iridium wires in terms of technical difficulty.

Evaluating reimbursement of skin radiation therapy: Technique and fractionation.

PURPOSE: Multiple skin radiation therapy techniques exist including electron beam therapy, high-dose-rate (HDR) brachytherapy, superficial/orthovoltage, and electronic brachytherapy (EB). The purpose of this analysis was to compare reimbursement between these modalities by fractionation regimen. METHODS AND MATERIALS: Reimbursement was derived from the 2020 Medicare Physician Fee Schedule by fractionation schedule or from the 2020 Hospital Outpatient Prospective Payment national benchmarks. A secondary analysis evaluating incorporation of daily simulation codes was also performed to factor in coding heterogeneity. RESULTS: Superficial/orthovoltage was the least costly and EB the next least costly technique regardless of fractionation. When incorporating variations in coding of simulations, reimbursement with superficial/orthovoltage was still least costly, with a reduction in cost of $1,755, $2,715, $5,076, and $7,436 compared with HDR brachytherapy for 6, 10, 20, and 30 fractions, respectively, and a reduction in cost of $1,325, $2,170, $4,281, and $6,392 compared with EB. HDR brachytherapy and EB costs can increase by 63-110% based on nonrecommended variation in daily simulation billing, with superficial/orthovoltage experiencing the highest relative increase. Reimbursement per course can vary by a factor of 4.5-9.3x depending on the modality and fractionation scheme utilized. CONCLUSIONS: Superficial/orthovoltage followed by EB were the least costly modalities with regard to reimbursement; however, costs can vary with frequency of simulation code billing. Consistency and standardization in skin radiation therapy reimbursement is needed, and case rates within a radiation oncology alternative payment model may help to minimize reimbursement heterogeneity among treatment options.

Clinical implementation of a wide-field electron arc technique with a scatterer for widespread Kaposi's sarcoma in the distal extremities.

A novel wide-field electron arc technique with a scatterer is implemented for widespread Kaposi's sarcoma (KS) in the distal extremities. Monte Carlo beam modeling for electron arc beams was established to achieve <2% deviation from the measurements, and used for dose calculation. MC-based electron arc plan was performed using CT images of a foot and leg mimicking phantom and compared with in-vivo measurement data. We enrolled one patient with recurrent KS on the lower extremities who had been treated with photon radiation therapy. The 4- and 6-MeV electron arc plans were created, and then compared to two photon plans: two opposite photon beam and volumetric modulated arc with bolus. Compared to the two photon techniques, the electron arc plans resulted in superior dose saving to normal organs beneath the skin region, although it shows inferior coverage and homogeneity for PTV. The electron arc treatment technique with scatterer was successfully implemented for the treatment of widespread KS in the distal extremities with lower radiation exposure to the normal organs beyond the skin lesions, which could be a treatment option for recurrent skin cancer in the extremities.

A multiwell applicator for conformal brachytherapy of superficial skin tumors: A simulation study.

BACKGROUND: Brachytherapy of thin skin tumors using beta particles can protect underlying sensitive structures such as the bone because of the rapid dose falloff of this type of radiation in tissue. The current work describes a skin brachytherapy applicator, based on beta radiation, that can provide the needed cell-killing radiation dose matched to the shape of individual skin tumors. MATERIALS AND METHODS: The applicator and its template were fabricated using 3D printing technology. Any clinically approved beta-emitting isotope in the form of a radioactive gel could theoretically be used in this applicator. Monte Carlo simulations were employed to study the capability of the applicator in conforming dose distribution based on the shape of the tumor. Dose profile in the shallow depth, transverse dose profiles at different depths, and the percent depth dose from this applicator were calculated. The radioisotope of choice for our calculations was Yttrium-90 (Y-90). RESULTS: Using the proposed applicator, it is possible to create a desired dose profile matching the tumor surface shape. CONCLUSION: The short-range of the beta radiation, together with the dose conforming capability of the applicator, may lead to minimal interactions with the healthy tissue around the skin lesion.

Off-axis dose distribution with stand-in and stand-off configurations for superficial radiotherapy treatments.

Current practice when delivering dose for superficial skin radiotherapy is to adjust the monitor units so that the prescribed dose is delivered to the central axis of the superficial unit applicator. Variations of source-to-surface distance due to patient's anatomy protruding into the applicator or extending away from the applicator require adjustments to the monitor units using the inverse square law. Off-axis dose distribution varies significantly from the central axis dose and is not currently being quantified. The dose falloff at the periphery of the field is not symmetrical in the anode-cathode axis due to the heel effect. This study was conducted to quantify the variation of dose across the surface being treated and model a simple geometric shape to estimate a patient's surface with stand-in and stand-off. Isodose plots and color-coded dose distribution maps were produced from scans of GAFChromic EBT-3 film irradiated by a Gulmay D3300 orthovoltage x-ray therapy system. It was clear that larger applicators show a greater dose falloff toward the periphery than smaller applicators. Larger applicators were found to have a lower percentage of points above 90% of central axis dose (SA90). Current clinical practice does not take this field variation into account. Stand-in can result in significant dose falloff off-axis depending on the depth and width of the protrusion, while stand-off can result in a flatter field due to the high-dose region near the central axis being further from the source than the peripheral regions. The central axis also received a 7% increased or decreased dose for stand-in or stand-off, respectively.

A protocol for irradiation of cell lines cultured in multi-well plates: effect of air inhomogeneity on irradiated cell survival.

Introduction: In multi-well cell culture plates, wells are bordered by air cavities. The air cavity inhomogeneities can reduce the amount of delivered dose. In this study, the effect of these cavities on cell survival was investigated.Materials and methods: A special phantom was designed to house the plates and air cavities were filled by water equivalent materials. Cultured melanoma cells were irradiated using 6MV photon for 200 cGy. MTT and clonogenic assay tests were used to evaluate cell survival.Results: Results of MTT assay showed mean survival percentage for irradiated cells in the first group, i.e. plates with air cavities, was 18.9% higher than the second group with air cavities filled with paraffin. Clonogenic assay results showed a maximum of 37% difference in the mean of number of colonies between the first group and the second group (p value < .05).Conclusions: The presence of air cavities in multi-well cell culture plates reduced radiation cell kill by up to 37%. To ensure the accuracy of delivered dose, it is necessary to replace the air cavities as well as the air surrounding the plates by a water equivalent material.

Optimization of low-energy electron beam production for superficial cancer treatments by Monte Carlo code.

CONTEXT: Low energy electron beam has been being used widely for superficial cancer treatments. In the current study a design for production of very low energy electron beam, by different thickness of Perspex spoilers, is presented that may be used for skin cancer. AIMS: MCNPX Monte Carlo code was used for modeling and simulations in the current study. An energy spoiler Perspex was modeled for degrading 4 MeV electron beam of Varian 2300 CD Linac. MATERIALS AND METHODS: The thicknesses of 3, 7, and 10 mm were applied before electron applicator at a distance of 42 cm from phantom surface. Dosimetric properties of new electron beams including Rp, Dmax, E0, as well as the penumbra of the beam were investigated. RESULTS: For the 3 mm spoiler, the superficial beam output decreased to 77%, and the Dmax, R90, R50, and RP were shifted to the depths of 4, 6, 9, and 12 mm, respectively. While for 10 mm filter the results were 5.2, 3.0 and 5.0 mm for R90, R50, and Rp, respectively. In addition, the surface dose was 93% and the Dmax was shifted to the depth of 1mm for the 10mm Perspex spoiler slab. CONCLUSIONS: The presented beam provides a novel surface dose, Dmax, and RP which can be applicable for treatment of skin cancers with minimum dose to the beyond normal tissues.

Development and dosimetric assessment of a patient-specific elastic skin applicator for high-dose-rate brachytherapy.

PURPOSE: The purpose of this study was to develop a patient-specific elastic skin applicator and to evaluate its dosimetric characteristics for high-dose-rate (HDR) brachytherapy. METHODS AND MATERIALS: We simulated the treatment of a nonmelanoma skin cancer on the nose. An elastic skin applicator was manufactured by pouring the Dragon Skin (Smooth-On Inc., Easton, PA) with a shore hardness of 10A into an applicator mold. The rigid skin applicator was printed using high-impact polystyrene with a shore hardness of 73D. HDR plans were generated using a Freiburg Flap (FF) applicator and patient-specific rigid and elastic applicators. For dosimetric assessment, dose-volumetric parameters for target volume and normal organs were evaluated. Global gamma evaluations were performed, comparing film measurements and treatment planning system calculations with various gamma criteria. The 10% low-dose threshold was applied. RESULTS: The V120% values of the target volume were 56.9%, 70.3%, and 70.2% for HDR plans using FF, rigid, and elastic applicators, respectively. The maximum doses of the right eyeball were 21.7 Gy, 20.5 Gy, and 20.5 Gy for the HDR plans using FF, rigid, and elastic applicators, respectively. The average gamma passing rates were 82.5% ± 1.5%, 91.6% ± 0.8%, and 94.8% ± 0.2% for FF, rigid, and elastic applicators, respectively, with 3%/3 mm criterion. CONCLUSIONS: Patient-specific elastic skin applicator showed better adhesion to irregular or curved body surfaces, resulting in better agreement between planned and delivered dose distributions. The applicator suggested in this study can be effectively implemented clinically.

Utilization and cost of electronic brachytherapy by dermatologists from 2012 to 2015.

Electronic brachytherapy (EBT) garnered interest among dermatologists as a noninvasive treatment for keratinocyte carcinomas. While the magnitude of use and cost burden had not yet been quantified, this interest prompted an official statement from the American Academy of Dermatology supporting its use as secondary option in special circumstances, and led to changes to billing and coding for the procedure. Using provider level Medicare claims, this study demonstrates increased use of EBT between 2012 and 2015. We also showed that very few dermatologists utilized EBT, with only 39 dermatologists billing for EBT in 2015. This study documents that large scale policy changes were implemented in response to the practice behaviors of a small number of dermatologists, and provides information regarding the cost of EBT for consideration on how to best optimize its use in clinical practice.

Monte Carlo based determination of dose distribution for some patch sources employed for radionuclide skin therapy.

Several methods are introduced for skin cancer treatment. An encouraging method is radionuclide skin therapy, where high-energy beta emitting radionuclides such as 32P, 90Y, 188Re and 166Ho are employed for skin irradiation. This study aimed to calculate the dose distribution for mentioned radionuclides at different layers of skin phantom through Monte Carlo simulation. Depth dose distribution, transverse dose profile and isodose curves related to the patch sources under investigation were calculated by MCNPX code. All of calculations were performed inside a developed skin phantom. Obtained results were compared with those reported by other studies to evaluate the validity of simulations. The results showed that the 166Ho and 32P have steeper dose gradient within the depth which can lead to the better normal tissue sparing. Simulated depth dose distributions were in a good agreement with other published studies and confirmed the validity of performed simulations. The obtained transverse dose profiles at 0.2 mm depth had acceptable symmetry and flatness that can improve the dose uniformity within the target area. Calculated isodose curves showed that the 90% isodose level covers a circular area with the diameter of around 8 mm for all studied beta sources. From the results, it can be concluded that 166Ho and 32P are more effective in treatment of superficial skin lesions, while, 90Y and 188Re are more rational choices in treatment of deeply distributed skin tumors. Size of employed patch source should be based on the target area to minimize the delivered dose to the adjacent tissues.

Correction factors for ionization chamber measurements with the 'Valencia' and 'large field Valencia' brachytherapy applicators.

Treatment of small skin lesions using HDR brachytherapy applicators is a widely used technique. The shielded applicators currently available in clinical practice are based on a tungsten-alloy cup that collimates the source-emitted radiation into a small region, hence protecting nearby tissues. The goal of this manuscript is to evaluate the correction factors required for dose measurements with a plane-parallel ionization chamber typically used in clinical brachytherapy for the 'Valencia' and 'large field Valencia' shielded applicators. Monte Carlo simulations have been performed using the PENELOPE-2014 system to determine the absorbed dose deposited in a water phantom and in the chamber active volume with a Type A uncertainty of the order of 0.1%. The average energies of the photon spectra arriving at the surface of the water phantom differ by approximately 10%, being 384 keV for the 'Valencia' and 343 keV for the 'large field Valencia'. The ionization chamber correction factors have been obtained for both applicators using three methods, their values depending on the applicator being considered. Using a depth-independent global chamber perturbation correction factor and no shift of the effective point of measurement yields depth-dose differences of up to 1% for the 'Valencia' applicator. Calculations using a depth-dependent global perturbation factor, or a shift of the effective point of measurement combined with a constant partial perturbation factor, result in differences of about 0.1% for both applicators. The results emphasize the relevance of carrying out detailed Monte Carlo studies for each shielded brachytherapy applicator and ionization chamber.

Description of patients excluded for Mohs surgery after pre-surgical evaluation: data from the Regesmohs Spanish registry. / Descripción de pacientes no aptos para ser sometidos a cirugía de Mohs tras valoración prequirúrgica: datos del registro español Regesmohs.

BACKGROUND: Regesmohs registry is a nationwide registry including patients evaluated for Mohs surgery in 17 Spanish centres since July 2013. Given that Mohs surgery is the therapy with best results for high risk basal cell carcinoma (BCC) and other skin tumours, we wanted to describe the reasons that lead to some patients being excluded from this therapy and the alternative treatments that they received. These data may be useful to avoid excluding patients for Mohs surgery use, to estimate the healthcare demand of these patients and the demand for Hedgehog inhibitors therapy in this group. OBJECTIVE: To describe patients excluded for Mohs surgery after pre-surgical assessment, and the treatments that they received. METHODS: Regesmohs includes all consecutive patients assessed for Mohs surgery in the participating centres, collecting data on patient characteristics, intervention, and short and long-term results. Patients excluded for Mohs surgery after pre-surgical evaluation were described. RESULTS: 3011 patients were included in Regesmohs from July 2013 to October 2016. In 85, Mohs surgery was not performed as they were considered inadequate candidates. 67 had BCC. Reasons for exclusion were: medical contraindication (27.1%, n=23) low-risk tumour in (18.8%, n=16) and giant tumour and bone invasion (15.3%, n=13). Only 1 patient (1.2%) showed lymph node involvement and no patients had visceral metastases. Of the 85 excluded patients, 29 (34.1%) were treated with conventional surgery, 24 (28.3%) with radiotherapy, 4 (4.7%) with inhibitors of the Hedgehog pathway (only indicated for BCC), and 2 (2.4%) received palliative care. We had no follow-up data on 14 patients (16.5%). CONCLUSION: Medical comorbidities were the most common reason for withholding Mohs surgery. Withholding therapy on the basis of distant extension is uncommon. Most excluded patients received simpler therapies: conventional surgery or radiotherapy, with hedgehog inhibitors being a new option.

Review: the reemergence of brachytherapy as treatment for non-melanoma skin cancer.

Electronic brachytherapy (EBT) has seen a significant rise in use over the past few years in treating non-melanoma skin cancer (NMSC). However, the current literature in EBT remains scarce. Existing data on high-dose rate brachytherapy (HDR-BT) with surface applicators is often used to justify its efficacy and safety. In this review we study the two treatment modalities on their efficacy in treating NMSC and we explore the reasons behind the recent uprise in EBT. A literature review using PubMed was performed for articles published until January 2017 studying efficacy of HDR-BT and EBT for treating NMSC. HDR-BT demonstrated effective local control ranging from 96.2% to 100% up to 66 months of follow-up with acceptable cosmesis. For EBT, local control rates ranged from 90% to 100% with generally favorable tolerance and cosmesis outcome after roughly one year. While longer term data on EBT is needed, its short term efficacy shows promise as a possible alternative to surgery or other radiation therapy in a select group of patients.

Experimental assessment of the Advanced Collapsed-cone Engine for scalp brachytherapy treatments.

PURPOSE: To experimentally assess the performance of the Advanced Collapsed-cone Engine (ACE) for 192Ir high-dose-rate brachytherapy treatment planning of nonmelanoma skin cancers of the scalp. METHODS AND MATERIALS: A layered slab phantom was designed to model the head (skin, skull, and brain) and surface treatment mold using tissue equivalent materials. Six variations of the phantom were created by varying skin thickness, skull thickness, and size of air gap between the mold and skin. Treatment planning was initially performed using the Task Group 43 (TG-43) formalism with CT images of each phantom variation. Doses were recalculated using standard and high accuracy modes of ACE. The plans were delivered to Gafchromic EBT3 film placed between different layers of the phantom. RESULTS: Doses calculated by TG-43 and ACE and those measured by film agreed with each other at most locations within the phantoms. For a given phantom variation, average TG-43- and ACE-calculated doses were similar, with a maximum difference of (3 ± 12)% (k = 2). Compared to the film measurements, TG-43 and ACE overestimated the film-measured dose by (13 ± 12)% (k = 2) for one phantom variation below the skull layer. CONCLUSIONS: TG-43- and ACE-calculated and film-measured doses were found to agree above the skull layer of the phantom, which is where the tumor would be located in a clinical case. ACE appears to underestimate the attenuation through bone relative to that measured by film; however, the dose to bone is below tolerance levels for this treatment.

Surface applicator of a miniature X-ray tube for superficial electronic brachytherapy of skin cancer.

PURPOSE: We designed and fabricated a surface applicator of a novel carbon nanotube (CNT)-based miniature X-ray tube for the use in superficial electronic brachytherapy of skin cancer. To investigate the effectiveness of the surface applicator, the performance of the applicator was numerically and experimentally analyzed. METHODS: The surface applicator consists of a graphite flattening filter and an X-ray shield. A Monte Carlo radiation transport code, MCNP6, was used to optimize the geometries of both the flattening filter and the shield so that X-rays are generated uniformly over the desired region. The performance of the graphite filter was compared with that of conventional aluminum (Al) filters of different geometries using the numerical simulations. After fabricating a surface applicator, the X-ray spatial distribution was measured to evaluate the performance of the applicator. RESULTS: The graphite filter shows better spatial dose uniformity and less dose distortion than Al filters. Moreover, graphite allows easy fabrication of the flattening filter due to its low X-ray attenuation property, which is particularly important for low-energy electronic brachytherapy. The applicator also shows that no further X-ray shielding is required for the application because unwanted X-rays are completely protected. As a result, highly uniform X-ray dose distribution was achieved from the miniature X-ray tube mounted with the surface applicators. The measured values of both flatness and symmetry were less than 5% and the measured penumbra values were less than 1 mm. All these values satisfy the currently accepted tolerance criteria for radiation therapy. CONCLUSIONS: The surface applicator exhibits sufficient performance capability for their application in electronic brachytherapy of skin cancers.