Bolus Material Research Articles

Exploring the impact of filament density on the responsiveness of 3D-Printed bolus materials for high-energy photon radiotherapy

Background3D-printed boluses in radiation therapy receive consideration for their ability to enhance treatment precision and patient comfort. Yet, thorough validation of 3D-printed boluses using various validation procedures and statistical analysis is missing. This study aims to determine the effectiveness of using 3D-printed boluses in radiation therapy. MethodThe CT Hounsfield Unit (HU) profiles of the 3D-printed materials were compared to those of the commercial bolus using the Eclipse Treatment Planning System (TPS) unit. Furthermore, absolute dose measurements were carried out to assess the efficacy of the 3D-printed samples by using concordance correlation coefficient to assess the agreement between 3D materials and the commercial bolus. ResultsThe average HU profiles of 3D-printed materials were: −144.53 (ABS), −124.40 (ASA), 9.55 (PLA-P), −140.79 (Polycarbonate), −68.58 (PLA-S), and −113.159 (PET-G), respectively. PDD scans showed that air gaps between the bolus and surface shifted the maximum dose depth. Whereas dosimetry has shown that ASA and Polycarbonate are different in attenuation from other tested filaments. This limitation could affect their performance in specific applications within radiation therapy. The final analysis, using the TPS-generated datasets to assess the area under the dose curve in the build-up zone of each 3D-bolus, excluded ABS. ConclusionsThe results from PDD scans and dose assessments offer compelling proof that 3D-printed boluses are effective for delivering surface dosage and are like commercially available boluses. Moreover, specific materials showed a statistically significant improvement in delivering the dose. The results highlight the capability of 3D-printed boluses to enhance the effectiveness of radiation therapy.

A Dosimetric Comparison Study for Blood Irradiation Employing Different Medium and Algorithms in Clinical Linear Accelerator.

To identify a suitable approach for blood irradiation other than the commonly used water medium and to study the impact of different algorithm dose computations. Water is the commonly used medium for blood irradiation. In this study computed tomography scans were taken with locally made blood irradiation phantoms other than water, by using air, rice powder and thermocole using parallel beam for 25 Gy. Plans were recalculated for different algorithms such as collapsed cone (CC), Monte Carlo (MC) and pencil beam (PB). The dose-volume parameters and measured doses were collected and analyzed for each medium and algorithm. The monitor unit (MU) for rice powder and water are close (2461±57 and 2469±61, respectively), with a maximum dose of 28.0±1.8 and 28.0±1.9 Gy. The PB algorithm resulted in lower monitor unit values regardless of the medium used, generating values of 2418, 2406, 2382, and 2362 for water, rice powder, air, and Thermocol, respectively. A significant increase in dose was observed irrespective of the medium used when the MC algorithm was employed, with a maximum of 30.26 Gy in rice powder; a smaller dose was used when the CC algorithm was employed, with 26.3 Gy in water medium. The average maximum doses of all groups were equal using the one-way Anova statistical test. Regarding the impact of field size, rice powder appears to have consistent doses across various field sizes, with slight increases as field size grows, which is similar to water. While water is the conventional medium, this study highlights the potential benefits of rice powder, such as eliminating the risks associated with bubble formation and water spillage, which can lead to equipment malfunction and safety hazards. Although previous studies have explored rice powder as a bolus and tissue-equivalent material, this study uniquely applies this knowledge to blood irradiation, an area where rice powder has not been thoroughly investigated.

1364: Exploring properties of 3D-Printed Bolus materials for radiation therapy

1364: Exploring properties of 3D-Printed Bolus materials for radiation therapy

Comprehensive clinical implementation, workflow, and FMEA of bespoke silicone bolus cast from 3D printed molds using open-source resources.

Bolus materials have been used for decades in radiotherapy. Most frequently, these materials are utilized to bring dose closer to the skin surface to cover superficial targets optimally. While cavity filling, such as nasal cavities, is desirable, traditional commercial bolus is lacking, requiring other solutions. Recently, investigators have worked on utilizing 3D printing technology, including commercially available solutions, which can overcome some challenges with traditional bolus. To utilize failure modes and effects analysis (FMEA) to successfully implement a comprehensive 3D printed bolus solution to replace commercial bolus in our clinic using a series of open-source (or free) software products. 3D printed molds for bespoke bolus were created by exporting the DICOM structures of the bolus designed in the treatment planning system and manipulated to create a multipart mold for 3D printing. A silicone (Ecoflex 00-30) mixture is poured into the mold and cured to form the bolus. Molds for sheet bolus of five thicknesses were also created. A comprehensive FMEA was performed to guide workflow adjustments and QA steps. The process map identified 39 and 30 distinct steps for the bespoke and flat sheet bolus workflows, respectively. The corresponding FMEA highlighted 119 and 86 failure modes, with 69 shared between the processes. Misunderstanding of plan intent was a potential cause for most of the highest-scoring failure modes, indicating that physics and dosimetry involvement early in the process is paramount. FMEA informed the design and implementation of QA steps to guarantee a safe and high-quality comprehensive implementation of silicone bolus from 3D printed molds. This approach allows for greater adaptability not afforded by traditional bolus, as well as potential dissemination to other clinics due to the open-source nature of the workflow.

Thermal, dosimetric and thermo-mechanical characterization of ABS and PLA polymer materials via plastic injection molding for innovative bolus materials in radiotherapy applications

The impact of radiation on polymer materials, and consequently on their mechanical and physical properties, is a burgeoning field of research. This research assesses the dosimetric, mechanical, and thermal characteristics of Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA) materials developed through plastic injection molding as possible alternatives to commercial bolus used in radiotherapy. The materials were thoroughly compared with the commercial bolus material, EXAFLEX, by various tests such as Hounsfield Unit (HU) Analysis, Radiation Transmittance, Thermogravimetric Analysis (TGA), Thermomechanical Analysis (TMA), and Fourier Transform Infrared Spectroscopy (FTIR). The research indicates that ABS and PLA materials have similar radiological qualities to EXAFLEX, showing constant surface and accumulation area doses. Minor differences are seen deeper inside the phantom, indicating a stable tissue equivalency. ABS demonstrated strong resistance to radiation-induced chemical modifications, but PLA exhibited susceptibility to molecular changes. The TMA findings showed that radiation caused a decrease in softening temperatures and an increase in the coefficient of thermal expansion for both ABS and PLA, indicating changes in their thermal stability and mechanical characteristics after irradiation. The study highlights the potential of ABS and PLA materials made through plastic injection molding as efficient and safety substitutes for commercial bolus materials, particularly for large area irradiation. This requires more research into their clinical uses and consequences.

Effect of Bolus Thickness-Based Base Eichhornia crassipes Powder (Water Hyacinth) on Radiotherapy Bolus Homogeneity

Bolus radiotherapy aims to make the radiation dose more homogeneous, and increase the surface dose to the skin. Exploration of alternative materials for substitute mixtures that are relatively safer is needed to reduce the weaknesses in the use of plasticine mixtures. To develop the basic ingredients for making bolus using biopolymers in water hyacinth (Eichhornia crassipes). This research was conducted using the method of Research and Development. The suitability of the physical characteristics of the bolus (homogeneity judged by CT number; Relative Electron Density is calculated by a formula ?b;% surface dose is obtained from TPS (Treatment Planning System) in the test and the 3 variations of the thickness (0.5 cm, 1.0 cm and 1.5 cm). The feasibility of the bolus product was determined based on the flexibility of the texture and resistance to cold temperatures. Result: Water hyacinth (Eichhornia crassipes) can be used as a reference for alternative bolus materials in radiotherapy due to the response of water hyacinth (Eichhornia crassipes) to radiation Water hyacinth (Eichhornia crassipes-based bolus has same RED (Relative Electron Density) value as soft and solid tissue in all thickness variations and has a surface dose value of ±100% for all thickness variations. Water hyacinth (Eichhornia crassipes) based bolus is homogeneous against radiation and can increase the dose surface so that water hyacinth (Eichhornia crassipes) has benefits and can be used as an alternative bolus material in radiotherapy

Patient-Specific Three-Dimensional-Printed and Bolus Material-Based Localization Grids for Magnetic Resonance Imaging-Guided Interventional Procedures

Abstract In view of the lack of commercially available localization grids for magnetic resonance imaging (MRI)-guided interventional procedures, two customizable and easily fabricable grids are proposed. The first one is a patient-specific three-dimensional-printed localization grid that incorporates MRI markers while the second one is a grid constructed with Superflex Transparent Bolus material. MRI scans were performed with the grids attached on an abdominal phantom. The patient-specific three-dimensional-printed grid is visible in T1-weighted, T2-weighted, proton density (PD) and fluid attenuated inversion recovery MR images, whereas the Superflex grid is visible only in T1-weighted and PD images. However, the Superflex grid offers the advantage of a simpler fabrication process and is more cost-effective. Both proposed localization grids can facilitate the determination of the optimal needle entry positions for MRI-guided interventional procedures, leading to reduced overall procedure time and improved efficiency.

Effect of bolus materials on dose deposition in deep tissues during electron beam radiotherapy.

Several materials are utilized in the production of bolus, which is essential for superficial tumor radiotherapy. This research aimed to compare the variations in dose deposition in deep tissues during electron beam radiotherapy when employing different bolus materials. Specifically, the study developed general superficial tumor models (S-T models) and postoperative breast cancer models (P-B models). Each model comprised a bolus made of water, polylactic acid (PLA), polystyrene, silica-gel or glycerol. Geant4 was employed to simulate the transportation of electron beams within the studied models, enabling the acquisition of dose distributions along the central axis of the field. A comparison was conducted to assess the dose distributions in deep tissues. In regions where the percentage depth dose (PDD) decreases rapidly, the relative doses (RDs) in the S-T models with silica-gel bolus exhibited the highest values. Subsequently, RDs for PLA, glycerol and polystyrene boluses followed in descending order. Notably, the RDs for glycerol and polystyrene boluses were consistently below 1. Within the P-B models, RDs for all four bolus materials are consistently below 1. Among them, the smallest RDs are observed with the glycerol bolus, followed by silica-gel, PLA and polystyrene bolus in ascending order. As PDDs are ~1-3% or smaller, the differences in RDs diminish rapidly until are only around 10%. For the S-T and P-B models, polystyrene and glycerol are the most suitable bolus materials, respectively. The choice of appropriate bolus materials, tailored to the specific treatment scenario, holds significant importance in safeguarding deep tissues during radiotherapy.

Scalp Irradiation with 3D-Milled Bolus: Initial Dosimetric and Clinical Experience.

A bolus is required when treating scalp lesions with photon radiation therapy. Traditional bolus materials face several issues, including air gaps and setup difficulty due to irregular, convex scalp geometry. A 3D-milled bolus is custom-formed to match individual patient anatomy, allowing improved dose coverage and homogeneity. Here, we describe the creation process of a 3D-milled bolus and report the outcomes for patients with scalp malignancies treated with Volumetric Modulated Arc Therapy (VMAT) utilizing a 3D-milled bolus. Twenty-two patients treated from 2016 to 2022 using a 3D-milled bolus and VMAT were included. Histologies included squamous cell carcinoma (n = 14, 64%) and angiosarcoma (n = 8, 36%). A total of 7 (32%) patients were treated in the intact and 15 (68%) in the postoperative setting. The median prescription dose was 66.0 Gy (range: 60.0-69.96). The target included the entire scalp for 8 (36%) patients; in the remaining 14 (64%), the median ratio of planning target volume to scalp volume was 35% (range: 25-90%). The median dose homogeneity index was 1.07 (range: 1.03-1.15). Six (27%) patients experienced acute grade 3 dermatitis and one (5%) patient experienced late grade 3 skin ulceration. With a median follow-up of 21.4 months (range: 4.0-75.4), the 18-month rates of locoregional control and overall survival were 75% and 79%, respectively. To our knowledge, this is the first study to report the clinical outcomes for patients with scalp malignancies treated with the combination of VMAT and a 3D-milled bolus. This technique resulted in favorable clinical outcomes and an acceptable toxicity profile in comparison with historic controls and warrants further investigation in a larger prospective study.

Karakterisasi Bolus Berbahan Campuran Beeswax dan Petroleum Jelly Menggunakan Berkas Elektron Pada Energi 6 MeV dan 9 MeV

In radiotherapy cases of cancer on the surface of the skin generally use electron beams. The electron beam has not been able to provide the optimum surface radiation dose. Therefore, a material that is able to increase the dose of surface radiation is needed, which is called a bolus. This study tested a bolus made from a mixture of beeswax and petroleum jelly. The bolus test includes the determination of density, the value of Relative Electron Density (RED) and the determination of the absorbed dose. The absorbed dose value was obtained by irradiating using a Linear Accelerator (LINAC) at 6 MeV and 9 MeV energies. The RED value was obtained from the bolus tomography image using a CT-simulator by determining the Region of Interest (ROI). The bolus density values obtained from physical measurements using the TPS program have almost the same average density values. The RED bolus value obtained at a thickness of 0.2 cm to 0.8 cm has a lower RED value than the RED value of the breast, which is 0.976. However, at 1.0 cm thickness, the RED value is equivalent to breast tissue. The value of the absorbed dose in a bolus made from a mixture of beeswax and petroleum jelly, the thicker the bolus used, the smaller the increase in the absorbed dose. The results of this study indicate that a bolus made from a mixture of beeswax and petroleum jelly can be the choice of bolus material during radiotherapy.

Feasibility of Customized Thermoplastic Patient-Specific Helmet Bolus for Scalp Irradiation Using Volumetric-Modulated Arc Therapy Planning.

Introduction: In this study, we sought to develop a thermoplastic patient-specific helmet bolus that could deliver a uniform therapeutic dose to the target and minimize the dose to the normal brain during whole-scalp treatment with a humanoid head phantom. Methods: The bolus material was a commercial thermoplastic used for patient immobilization, and the holes in the netting were filled with melted paraffin. We compared volumetric-modulated arc therapy treatment plans with and without the bolus for quantitative dose distribution analysis. We analyzed the dose distribution in the region of interest to compare dose differences between target and normal organs. For quantitative analysis of treatment dose, OSLD chips were attached at the vertex (VX), posterior occipital (PO), right (RT), and left temporal (LT) locations. Results: The average dose in the clinical target volume was 6553.8 cGy (99.3%) with bolus and 5874 cGy (89%) without bolus, differing by more than 10% from the prescribed dose (6600 cGy) to the scalp target. For the normal brain, it was 3747.8 cGy (56.8%) with bolus and 5484.6 cGy (83.1%) without bolus. These results show that while the dose to the treatment target decreased, the average dose to the normal brain, which is mostly inside the treatment target, increased by more than 25%. With the bolus, the OSLD measured dose was 102.5 ± 1.2% for VX and 101.5 ± 1.9%, 95.9 ± 1.9%, and 81.8 ± 2.1% for PO, RT, and LT, respectively. In addition, the average dose in the treatment plan was 102%, 101%, 93.6%, and 80.7% for VX, PO, RT, and LT. When no bolus was administered, 59.6 ± 2.4%, 112.6 ± 1.8%, 47.1 ± 1.6%, and 53.1 ± 2.3% were assessed as OSLD doses for VX, PO, RT, and LT, respectively. Conclusion: This study proposed a method to fabricate patient-specific boluses that are highly reproducible, accessible, and easy to fabricate for radiotherapy to the entire scalp and can effectively spare normal tissue while delivering sufficient surface dose.

Investigation of Effect of Air Gap between Surface and Bolus on Dose Distribution for 6 MV Photon Beam

In radiotherapy, tissue equivalent boluses are frequently used in the treatment of superficially located tumors. The air gap between the patient's skin and the bolus may cause dosimetric uncertainties. This study aims to dosimetrically investigate the effect of the air gap between the surface and the bolus on dose distribution. Computed tomography (CT) images of the phantom were obtained and transferred to the treatment planning system (TPS). In the TPS, a bolus was placed on the phantom surface and then air gaps were created between the bolus and the surface. The effect of the air gaps between the surface and the 5 mm thick bolus on the dose distribution was analyzed with the point doses obtained from the TPS. For the 6 MV X-ray, it was observed that the air gap negatively affected the surface doses calculated by TPS. Accordingly, an inverse correlation was found between air gap and surface dose. It is recommended that bolus use, especially in curved anatomical regions, should be applied before CT scanning as much as possible. When using bolus material in radiotherapy, it is recommended to be careful not to leave an air gap between the surface and the bolus.

An Investigation of High-Z Material for Bolus in Electron Beam Therapy

Electron beams are frequently used for superficial tumors including: primary skin cancers, surgical scars, cutaneous lymphomas and benign conditions like keloids. However, due to electron beam characteristics the surface dose is 75-95% of the prescribed dose depending on beam energy thus requiring placement of bolus to augment surface dose. Various types of boluses; wet gauge/towel, superflab, superstuff, aquaplast, 3D printed plastics, customized dot-decimal bolus, thermoshield, brass and tantalum wire mesh are commonly used in clinics with variable difficulties that are not perfect. As majority of these devices do not snug to the skin contour and create air-gap that is known to produce significant dose perturbations creating hot and cold spot. The variable dosimetry has cosmetic implications and potentially increased risk of recurrence. A new cloth-like high-Z materials; Tungsten, (Z = 74) and Bismuth, (Z = 83) impregnated with silicone gel are now commercially available which is investigated in this study for bolus purpose. Commercially available, super soft silicone-gel based submillimeter thin Tungsten and Bismuth sheets were investigated for bolus properties in electron beams in the range of 6-12 MeV using 10x10 cm2 applicator. These materials were tested on various body contour for perfect snug without any air traps. Using parallel plate ion chamber measurements were performed in a solid water phantom on a medical linear accelerator machine. Depth dose characteristics were measured to optimize the thickness for surface dose to be 100% for selected electron therapy. Surface dose for a 10x10 cm2 cone for 6, 9, 12 MeV beams were measured to be 75.1%, 80.1% and 86.2%, respectively. Silicone-gel Tungsten and Bismuth sheets produce significant electrons thus increasing surface dose. Based on measured depth dose, our data showed that Tungsten sheets of 0.14 mm, 0.18 mm and 0.2 mm and Bismuth sheets of 0.42 mm, 0.18 mm and 0.2 mm provide 100% surface dose for 6, 9 and 12 MeV beams, respectively without any changes in depth dose except increasing surface dose. The new Tungsten and Bismuth based silicone-gel clothlike sheets are extremely soft but high tensile metallic bolus materials that can fit flawlessly on any skin contour without any air trap or variable thickness or spillage of the water as in conventionally used wet gauge. Only 0.2 mm thick sheets are needed for 100% surface dose without degradation of the depth dose characteristics. These materials are reusable and ideal for bolus in electron beam treatment. This investigation opens a new frontier in designing new bolus materials optimum for patient treatment.

A Free, Open-Source Toolkit to Produce 3D Bolus in the Clinic

Tissue-equivalent, tissue-approximating and tissue-replacing bolus materials have been in use for decades in radiotherapy. Most frequently these materials are applied to a patient's skin to bring the highest dose region towards the surface of the skin-which is the location of the target. These materials can be applied at the time of simulation and included in a planning CT scan, or can be added during the planning process and first physically applied at the time of treatment. One of the most widely adopted materials for bolus has been sheets of a commercially available proprietary synthetic gel, which is uniform in thickness, and has some ability to match the curvature of the patient's body. Recently investigators have worked to create boluses using 3D printing technology, including several commercially available offerings. We hypothesized that we could create a bespoke, 3D bolus solution, using a series of open-source and free software products. For an anthropomorphic phantom, a radiation treatment plan representative of skin cancer treatment was designed, this included a superficial target. The DICOM CT and structure set were imported into 3D Slicer, which is a free, open-source software for visualization, processing, segmentation, and registration. Using 3D Slicer, the bolus structure was saved as an STL file. Meshmixer, a free software for working with triangle meshes, was used to complete a mold design, and the mold parts were then printed using a rigid filament on a 3D printer. The mold parts were glued together, and small spring clamps were used secure the walls to the shells to ensure mold integrity. The mold was then filled with a thinned and degassed silicone. After appropriate curing, demolding was completed by removing the clamps and separating the walls. After QA, the bolus was applied to the anthropomorphic phantom and CTs were taken to compare a commercial sheet bolus with the in-house 3D printed product. The bolus made via the in-house 3D printing process fit even complicated patient geometries well, and had both an obvious visual/goodness of fit advantage over the commercial sheet bolus and a nuanced dosimetric improvement as the air gaps present in the commercial sheet bolus were not desirable nor reproducible. The overall in-house workflow was efficient, and clinically reasonable (an estimated time of 72 hours was presented to the physician team, but in testing less than 24 hours was needed from export to delivery of the finished product). In this work we explored whether motivated groups and departments could produce dosimetrically accurate and clinically reasonable custom boluses for patients undergoing radiotherapy to a superficial area of the body, using a test case on an anthropomorphic phantom. We found that this was absolutely achievable and could be implemented with no funds spent on software or licenses. Provided that a 3D printer, filament and silicone are available, any thoughtful practice can join the bespoke-bolus-club.

Evaluation of the Ethos synthetic computed tomography for bolus-covered surfaces

PurposeEthos allows online adaption of radiotherapy treatment plans. Dose is calculated on synthetic computed tomographies (sCT), CT-like images generated by deforming planning CTs (pCT) onto daily cone beam CTs (CBCT) acquired during treatment sessions. Errors in sCT density distribution may lead to dose calculation errors. sCT correctness was investigated for bolus-covered surfaces. MethodspCTs were recorded of a slab phantom covered with bolus of different thicknesses and with air gaps introduced by spacer rings of variable diameters and heights. Treatment plans were irradiated following the adaptive workflow with different bolus configurations present in the pCT and CBCT. sCT densities were compared to those of the pCT for the same air gap size. Additionally, the neck region of an anthropomorphic phantom was imaged using a plane standard bolus versus an individual bolus adapted to the phantom’s outer contour. ResultsVarying bolus thickness by 5 mm between pCT and CBCT was reproduced in the sCT within 2 mm accuracy. Different air gaps in pCT and CBCT resulted in highly variable bolus thickness in the sCT with a typical error of 5 mm or more. In extreme cases, air gaps were filled with bolus material density in the sCT or the phantom was unrealistically deformed near changed bolus geometries. Changes in bolus thickness and deformation also occurred in the anthropomorphic phantom. ConclusionsCTs must be critically examined and included in plan-specific quality assurance. The use of tight-fitting air gap-free bolus should be preferred to increase the similarity between sCT and CBCT.

Evaluation of 3D-printed bolus for radiotherapy using megavoltage X-ray beams

A radiotherapy bolus is a tissue-equivalent material placed on the skin to adjust the surface dose of megavoltage X-ray beams used for treatment. In this study, the dosimetric properties of two 3D-printed filament materials, polylactic acid (PLA) and thermoplastic polyether urethane (TPU), used as radiotherapy boluses, were investigated. The dosimetric properties of PLA and TPU were compared with those of several conventional bolus materials and RMI457 Solid Water. Percentage depth-dose (PDD) measurements in the build-up region were performed for all materials using 6 and 10 MV photon treatment beams on Varian linear accelerators. The results showed that the differences in the PDDs of the 3D-printed materials from the RMI457 Solid Water were within 3%, whereas those of the dental wax and SuperFlab gel materials were within 5%. This indicates that PLA and TPU 3D-printed materials are suitable radiotherapy bolus materials.

Development of a 3D printing process of bolus using BolusCM material for radiotherapy with electrons

This work presents the optimized parameters of 3D printing for print bolus using BolusCM material. Printing parameters were selected of the homogeneity and absence of air gaps. The dosimetric features of printed bolus were measured with a plane-parallel ionization chamber and EBT3 radiochromic film. Measured features were compared with those estimated with Monte Carlo methods. BolusCM shows good characteristics to be used as bolus material in radiotherapy with electrons, where the printing process allows personalizing the bolus in function of patient characteristics. The material low-cost, the 3D printing and the dosimetric features are few of the advantages of using BolusCM material in radiotherapy with electrons in skin cancer treatment.

Comparing brass mesh to tissue equivalent bolus materials for volumetric modulated arc therapy chest wall irradiation.

To compare the superficial dose when using brass mesh bolus (BMB), no bolus, or 3mm tissue-equivalent bolus with a pseudo-flash volumetric modulated arc therapy (VMAT) breast treatment planning technique. Two different beam arrangements for right-sided irradiation and one beam arrangement for bilateral irradiation were planned on an inhomogeneous thorax phantom in accordance with our clinical practice for VMAT postmastectomy radiotherapy (PMRT). Plans were optimized using pseudo-flash and representative critical organ optimization structures were used to shape the dose. Plans were delivered without bolus, with 3mm tissue-equivalent bolus (TEB), or with one-layer BMB. Optically stimulated luminescence dosimeter (OSLD) and radiochromic film measurements were taken and analyzed to determine the superficial dose in each case and the relative enhancement from the no bolus delivery. Superficial dose measured with OSLDs was found to be 76.4±4.5%, 103.0±6.1%, and 98.1±5.8% of prescription for no physical bolus (NB), TEB, and BMB, respectively. Superficial dose was observed to increase from lateral to medial points when measured with film. However, the relative increase in superficial dose from NB was consistent across the profile with an increase of 43±2.1% and 34±3.3% of prescription for TEB and BMB, respectively. The results are in good agreement with expectations from the literature and the experience with tangential radiotherapy. Three millimeter TEB and one-layer BMB were shown to provide similar enhancement to the superficial dose compared to delivery without bolus. BMB, which does not significantly affect dose at depth and is more conformal to the patient surface, is an acceptable alternative to 3mm TEB for chest wall PMRT patients treated with pseudo-flash PMRT.

Technical note: Water-equivalent thickness of Superflab bolus material at diagnostic x-ray energies.

The purpose of this work was to determine the water-equivalent thickness of Superflab bolus material for narrow and broad field-of-view (FOV) x-ray geometries at diagnostic x-ray energies. Transmission measurements were performed for incremental thicknesses of Superflab bolus material and water in narrow and broad FOV x-ray geometries. The transmission data was fit to a non-linear model for x-ray transmission - the Archer model. Water-equivalent thickness of Superflab was calculated based upon fitting parameters to transmission curves for 75, 95, and 115kV x-ray tube voltages. Measured x-ray transmission factors for water and Superflab were used to determine the water equivalence of Superflab. For all x-ray tube voltages and geometries, the water equivalence of Superflab was greater than one, indicating that Superflab is more attenuating than water. This effect was stronger for broad FOV geometries. At 95kV, 30cm of Superflab corresponded to 32.0cm of water in the narrow FOV geometry, and 34.3cm of water in the broad FOV geometry. The Archer model fitting parameters and Superflab water equivalence are reported for all x-ray beam conditions explored in this work. Superflab bolus material is more attenuating than water at diagnostic x-ray energies. The Archer model and its respective fitting parameters reported in this work may be used to estimate the water-equivalent thickness of Superflab for diagnostic x-ray spectra.

Water bolus in photon-beam therapy of irregular skin lesions of extremities: a case report

Background: Mycosis fungoides (MF) represents the most common cutaneous T-cell lymphoma and approximately 4% of non-Hodgkin lymphomas. Treatment of skin lesions includes external beam radiation therapy which often provides adequate local control and symptom relief. Case presentation: A 39-year-old male with the diagnosis of MF presents with infiltrative and pruriginous plaques comprising the plantar, interdigital, lateral and posterior surfaces of the foot. A protocol using a water tank was used to provide uniform coverage to an irregular target volume. By creating a tissue-equivalent and homogenous bolus material a total dose of 8Gy in 2 fractions of photon-beam therapy was prescribed. After one month of treatment there was a partial response with minimal toxicity, achieving complete response in most lesions after six months. Conclusion: Photon-beam therapy for irregular surfaces such as extremities is a valid alternative to conventional electron-beam radiation by attaining uniform coverage while minimizing hotspots. Treatment utilizing a water tank is well-tolerated and has good clinical outcomes even in the presence of extensive skin lesions.