Superficial Dose Research Articles

Dosimetric Evaluation of Chest Wall Superficial Dose With or Without Bolus in Postmastectomy Radiotherapy

Chest wall bolus use has been standard practice in postmastectomy radiotherapy (PMRT) for patients without skin involvement, resulting in increased toxicity without strong data to show improved outcomes. Centers are moving away from use of bolus in PMRT, but the dosimetric effects have not been quantified. We aim to compare differences in dose between non-bolus and bolus plans to the superficial chest wall. We conducted a retrospective analysis on 30 patients treated with PMRT from December 2018 to June 2019 at our center. Patients received 4256 cGy in 16 fractions to chest wall and regional nodes using 4-field 3D conformal technique, 6 and/or 15 MV photons, and 0.5 cm bolus. The clinically planned datasets were used to generate non-bolus and bolus plans for each patient using the anisotropic analytical algorithm (AAA). The first 10 patients also had non-bolus and bolus plans generated using Acuros XB (AXB). Evaluation volumes were created by extracting surface layers from the clinical chest wall: 3 mm surface, 5 mm surface, and the layer between 3-5 mm depth. The 3 mm and 5 mm surface layers were chosen to match the most common definitions of skin in current breast studies, while the 3-5 mm layer represents the subcutaneous tissue immediately deep to the skin. Mean age, mean chest wall thickness, dermatitis grade level per CTCAE v5.0, and the mean V80%, V95%, and D2cc were reported for all plans. Mean patient age was 56 years (range 36 to 85 years). Mean chest wall thickness was 2.3 cm (1.1 to 6.5 cm). The most common beam energies were 6 and 15 MV photons (70%), followed by 15 MV alone (20%) and 6 MV alone (10%). Most had grade 1 (63%) and 2 (33%) dermatitis to the chest wall and axilla, with one patient developing grade 3 dermatitis. Mean V80%, V95%, and D2cc for the non-bolus and bolus plans were calculated using AAA (n = 30) and AXB (n = 10), as reported in the below table. While large differences exist in superficial layers, the 3-5 mm layer demonstrates consistent coverage for V80% with or without bolus. When AXB calculation is used, the differences are even more minimal in the 3-5 mm layer for both V80% and V95%. This result is expected based on AXB’s superior superficial dose modelling. Our findings support the reduced use of bolus for PMRT patients without risk factors for dermal or dermal-lymphatic involvement.Tabled 1Abstract 2770; Table3 mm surface5 mm surface3-5 mm layerD2cc (%)Non-BolusBolusNon-BolusBolusNon-BolusBolusNon-BolusBolusAAA V80% (%)38.497.662.397.796.498.1107107AAA V95% (%)4.788.322.390.049.594.7AXB V80% (%)60.099.676.999.799.9100109109AXB V95% (%)23.796.249.397.286.298.7 Open table in a new tab

Characteristics of Superficial Dose for the High Field MR-Linac: Measurements and Calculations

Characteristics of Superficial Dose for the High Field MR-Linac: Measurements and Calculations

59: Dosimetric Evaluation of Chest Wall Superficial Dose with or Without Bolus in Postmastectomy Radiotherapy

59: Dosimetric Evaluation of Chest Wall Superficial Dose with or Without Bolus in Postmastectomy Radiotherapy

Characterization and clinical validation of patient-specific three-dimensional printed tissue-equivalent bolus for radiotherapy of head and neck malignancies involving skin.

Megavoltage radiotherapy to irregular superficial targets is challenging due to the skin sparing effect. We developed a three-dimensional bolus (3DB) program to assess the clinical impact on dosimetric and patient outcomes. Planar commercial bolus (PCB) and 3DB density, clarity, and net bolus effect were rigorously evaluated prior to clinical implementation. After IRB approval, patients with cutaneous or locally advanced malignancies deemed to require bolus for radiotherapy treatment were treated with custom 3DB. The mean density of 3DB and PCB was of 1.07g/cm 3 and 1.12g/cm3, respectively. 3DB optic clarity was superior versus PCB at any material thickness. Phantom measurements of superficial dose with 3DB and PCB showed excellent bolus effect for both materials. 3DB reduced air gaps compared with PCB - particularly in irregular areas such as the ear, nose, and orbit. A dosimetric comparison of 3DB and PCB plans showed equivalent superficial homogeneity for 3DB and PCB (3DB median HI 1.249, range 1.111-1.300 and PCB median HI 1.165, range 1.094-1.279), but better conformity with 3DB (3DB median CI 0.993, range 0.962-0.993) versus PCB (PCB median CI 0.977, range 0.601-0.991). Patient dose measurements using 3DB confirm the delivered superficial dose was within 1% of the intended prescription (95% CI 97-102%; P=0.11). 3DB improves radiotherapy plan conformity, reduces air gap volume in irregular superficial areas which could affect superficial dose delivery, and provides excellent dose coverage to irregular superficial targets.

3D printed copper-plastic composite material for use as a radiotherapy bolus

The purpose of this work is to evaluate a commercially available copper-plastic composite material for use as a custom fit 3D printed bolus. Superficial dose under copper-plastic composite bolus was assessed for 0.4 mm, 0.6 mm, and 0.8 mm thicknesses. Superficial dose measurements were performed with an Attix parallel plate ionization chamber and radiochromic film. Additionally, a custom-fit bolus was designed for the temporal-frontal cranial region of an anthropomorphic phantom. A treatment plan with a tangential field arrangement was designed, and radiochromic film was used to measure the dose enhancement to the surface of the phantom from the bolus and compared to the calculated dose. It was shown that 3D printed copper-plastic composite bolus can provide the equivalent dose enhancement of thicker conventional bolus. Due to the limited thickness of the copper-plastic composite the bolus can remain flexible, which can aid in the placement of the bolus and improve patient comfort.

In search of a one plan solution for VMAT post-mastectomy chest wall irradiation.

PurposeThis study was designed to evaluate skin dose in both VMAT and tangent treatment deliveries for the purpose of identifying suitable bolus use protocols that should produce similar superficial doses.MethodsPhantom measurements were used to investigate skin dose in chest wall radiotherapy with and without bolus for 3D and rotational treatment techniques. Optically stimulated luminescence dosimeters (OSLDs) with and without housing and EBT3 film were used. Superflab (3, 5, and 10 mm) and brass mesh were considered. Measured doses were compared with predictions by the Eclipse treatment planning system. Patient measurements were also performed and the bolusing effect of hospital gowns and blankets were highlighted. The effect of flash for VMAT plans was considered experimentally by using 2 mm couch shifts.ResultsFor tangents, average skin doses without bolus were 0.64 (EBT3), 0.62 (bare OSLD), 0.77 (jacketed OSLD), and 0.68 (Eclipse) as a fraction of prescription. For VMAT, doses without bolus were 0.53 (EBT3), 0.53 (bare OSLD), 0.64 (jacketed OSLD), and 0.60 (Eclipse). For tangents, the average doses with different boluses as measured by EBT3 were 0.99 (brass mesh), 1.02 (3 mm), 1.03 (5 mm), and 1.07 (10 mm). For VMAT with bolus, average doses as measured by EBT3 were 0.83 (brass), 0.96 (3 mm), 1.03 (5 mm), and 1.04 (10 mm). Eclipse doses agreed with measurements to within 5% of measurements for all Superflab thicknesses and within 15% of measurements for no bolus. The presence of a hospital gown and blanket had a bolusing effect that increased the surface dose by approximately 10%.ConclusionsResults of this work allow for consideration of different bolus thicknesses, materials, and usage schedules based on desired skin dose and choice of either tangents or an arc beam techniques.

Increase in Superficial Dose in Whole-Breast Irradiation with O-Ring Straight-through 6X FFF Linac Compared to Traditional C-arm Linac with Flattening Filter: In-vivo Dosimetry and Planning Study

Increase in Superficial Dose in Whole-Breast Irradiation with O-Ring Straight-through 6X FFF Linac Compared to Traditional C-arm Linac with Flattening Filter: In-vivo Dosimetry and Planning Study

Increase in Superficial Dose in Whole-Breast Irradiation With Halcyon Straight-Through Linac Compared With Traditional C-arm Linac With Flattening Filter: In vivo Dosimetry and Planning Study

PurposeSuperficial dose is an important parameter in breast cancer radiation therapy. When treated with conventional linacs, bolus is commonly applied to improve target coverage near the surface while also managing the risk of severe skin reactions and negative cosmesis. With the introduction of modern linacs with 6X flattening filter free (FFF) photon beams, the effect on superficial dose and the need for bolus must be evaluated. Methods and MaterialsIn vivo measurements of superficial dose were made with optically stimulated luminescence dosimeters on 11 breast cancer patients treated with the Halcyon 6X FFF linac (Varian Medical Systems, Palo Alto, CA). Additionally, measurements were made with the Halycon 6X FFF beam and a 6X beam with flattening filter (FF) delivered to an anthropomorphic phantom. A planning study was carried out in which 14 patients treated on the Halcyon were replanned with a conventional linac to determine the difference in superficial dose predicted by the treatment planning system. Measures were taken to increase the accuracy of the treatment planning system superficial dose. ResultsThe use of the Halcyon 6X FFF beam led to higher superficial dose compared with 6X FF beams. The in vivo measurements show an average superficial dose of 83.8% ± 0.6%, which is an increase of approximately 10% compared with published measurements for a 6X FF linac. Comparison of superficial dose for 6X FF and 6X FFF beams in the phantom measurements show an increase from 70% ± 1.3% to 84% ± 1.3%, which is consistent with the in vivo measurements. The planning comparison shows an increase in V70%Rx from 62% ± 4.4% to 81% ± 2.2% for the superficial breast tissue for the Halcyon 6X FFF beam compared with a standard C-arm linac with FF. ConclusionsThe use of the Halcyon 6X FFF beam was associated with higher superficial dose which may obviate the use of bolus.

A GATE/Geant4 Monte Carlo toolkit for surface dose calculation in VMAT breast cancer radiotherapy

The accuracy of superficial dose calculations for breast cancer treatments with Volumetric Modulated Arc Therapy (VMAT) is of major importance. For target volumes close to the surface, the inverse dosimetric planning can lead to very high fluences in the build-up region to properly cover the volume to be treated. Various radiotherapy modalities are currently used in parallel with additional protocols to enable a better control on the dose delivery (bolus, target volume margins). One of the difficulties currently facing medical physicists is the lack of available tools to test the impact of these different solutions on the superficial dose distribution. We present a new open source toolkit to assist medical physicists in evaluating the 3D distributions of superficial dose in VMAT breast cancer treatments. This tool is based on the GATE Monte Carlo software, a Geant4 application dedicated to medical physics. A set of macros has been developed to simulate in an easy way a full VMAT plan from the information available in the DICOM-RT files (image, plan, structure and dose). The toolkit has been tested on a 6 MV Varian NovalisTx™ accelerator. The paper presents a precise comparison of 3D surface dose distributions from experimental measurements (EBT3 films), TPS (Varian Eclipse) and Monte Carlo simulation (GATE). The comparison made it possible to highlight both the TPS biases for the surface dose calculation and the good performances of the developed toolkit. The simulation of surface dose distributions on a real patient has also been performed to illustrate the potential clinical applications.

Novel intraoperative radiotherapy utilizing prefabricated custom three-dimensionally printed high-dose-rate applicators

BackgroundIntraoperative radiotherapy (IORT) is an effective strategy for the delivery of high doses of radiotherapy to a residual tumor or resection cavity with relative sparing of nearby healthy tissues. This strategy is an important component of the multimodality management of pediatric soft tissue sarcomas, particularly in cases where patients have received prior courses of external beam radiotherapy. PurposeTumor beds with significant topographic irregularity remain a therapeutic challenge because existing IORT technologies are typically most reliable with flat surfaces. To address this limitation, we have developed a novel strategy to create custom, prefabricated high-dose-rate (HDR)-IORT applicators designed to match the shape of an anticipated surgical cavity. Methods and MaterialsSilastic applicators are constructed using three-dimensional (3D) printing and are derived from volumetric segmentation of preoperative imaging. ResultsHDR preplanning with the applicators improves dosimetric accuracy and minimizes incremental operative time. In this report, we describe the fabrication process for the 3D-printed applicators and detail our experience utilizing this strategy in two pediatric patients who underwent HDR-IORT as part of complex base of skull sarcoma resections. ConclusionsEarly experience suggests that usage of the custom applicators is feasible, versatile for a variety of clinical situations, and enables the uniform delivery of high superficial doses of radiotherapy to irregularly shaped surgical cavities.

93. Estimation of doses to the extremities during manipulation of radiopharmaceuticals in nuclear medicine: A Monte Carlo calculation approach in realistic geometric lay-outs

Purpose The aim of this study was to introduce a calculation approach, based on a simple and user-friendly interface to Monte Carlo simulation, for the estimation of the radiation dose to the extremities of the personnel professionally exposed to the ionizing radiations emitted by radionuclides employed in nuclear medicine. Methods Monte Carlo simulations in GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations) were carried out for 18F, 68Ga, 90Y, 99mTc, 111In, 131I and 177Lu nuclides in water solutions enclosed either in glass or in plastic receptacles, such as vials or syringes of different sizes and filling fractions. Superficial and deep dose equivalents were estimated, around the lateral surface of the receptacle, at different distances. A comparison was made with the results from VARSKIN 5.3, which were computed in the standard VARSKIN geometric lay-out of a volume source. Results Skin and deep dose equivalents, at 70 μm and 1 cm of depth, are reported for all the considered configurations, highlighting the importance of adopting a realistic geometrical configuration. The comparison made between the average exposition below the source bottom, computed through VARSKIN, and the maximum exposition on the lateral surface at the source middle plane, evaluated by Monte Carlo simulations, reveals a qualitative agreement for a limited number of configurations only, since the different geometries affect the dose deposited in the scoring volumes. A further source of disagreement is related to the deterministic approach in which electron energy deposition is treated in VARSKIN and its influence in proximity of electron maximum range, and to the absence of bremsstrahlung emission. Another source of discrepancy, for some nuclides, is the difference in radionuclide emission spectra. Conclusions Due to the easiness of implementation of GAMOS simulations, case-specific realistic geometries and nuclides can be adopted and results can be obtained in very reasonable computation times.

Effect of cavity under bolus on the dose of superficial tissue

Objective To investigate the effect of cavity thickness, area and distance under the bolus upon the dose in the superficial tissues. Methods An accelerator model was constructed based on Geant4.The model accuracy was validated by the comparison of the calculated data with the measured data. A 30×30×30 cm3 water phantom with the upper surface located at the isocenter level and a 30×30×1 cm3 water film were constructed. Different models with the water film close to or different cavities with the water phantom were established. Under the 10×10 cm2 field with 6 MV X-ray beam, the central axis depth dose distribution and the lateral dose profiles at a depth of 0.1 cm (profile1) of the models with different cavities were calculated. The calculated data of different model with the water film close to or different cavities with the water phantom were statistically compared. Results When the cavity thickness was ≤ 0.5 cm, the cavity exerted slight effect upon the depth of maximum dose (Dmax) and superficial dose. As the cavity thickness was increased, the Dmax was also increased, the PDD at 0.1 cm (PDD1) was decreased rapidly and the profile1 was increased from the cavity center to the edge. Along with the increase of cavity area, the Dmax was initially increased and then decreased, whereas the PDD1 was first decreased followed by an increase. When the cavity area was small, the profile1 was gradually increased from the cavity center to the edge. When the cavity area was large, the profile1 was initially decreased and subsequently increased. When the distance was ≥ 0.2 cm, it was qualified for the clinical requirement and it exerted no effect when the distance was ≥ 1.0 cm. The profile1 distant from the cavity was not affected. Conclusion The cavity under the bolus should be minimized to reduce the cavity thickness, area and distance as possible. Key words: Monte Carlo; Bolus; Cavity; Superficial dose; Profile

Patient-Specific, Tissue-Equivalent Three-Dimensional Printed Bolus Improves Dosimetric Outcomes to Superficial and Irregular Radiation Targets

Optimal radiotherapy (RT) dose delivery to superficial and irregular target volumes poses a unique challenge. Herein we quantitatively evaluate material properties of common commercially available water-equivalent planar bolus (CB) and a tissue-equivalent, three-dimensional printed bolus (3DB). We also evaluate dosimetric outcomes for volumetric modulated arc therapy (VMAT) patient treatment in various disease sites for improved superficial dose delivery. Patients requiring bolus were simulated per departmental protocol. After simulation, a virtual 3DB was contoured in treatment planning software and printed on a 3D printer using a commercially available, flexible, clear photopolymer. We analyzed the bolus density and optic properties using CT and laser, respectively. In vivo dosimetry was performed on an anthropomorphic phantom, then on patients, with calibrated metal-oxide semiconductor field-effect transistors (MOSFET). Dosimetric comparison was accomplished using dose-volume histograms (DVH). Homogeneity index (HI) and conformity index (CI) of delivered plans was calculated to 0.5 cm depth using standard definitions. Statistical analysis was performed with t-test and significance set at p < 0.05. We evaluated 15 patients from head and neck (H&N, 10), anal (4), and breast (1) disease sites. 3DB density (1.087 g/cm3, range 1.086-1.088) was significantly more uniform than CB (1.125 g/cm3, range 1.080-1.150). Relative optic clarity of 0.5 cm bolus was 300% better with 3DB vs CB, and the difference further increased with increasing bolus thickness in favor of 3DB. Compared with the prescription dose, phantom 3DB MOSFET was 104% vs 105% with CB. On average, patient 3DB MOSFET measurement of superficial dose was 99% of prescription over 129 measurements. The average maximum skin-to-bolus air distance (cm) was 0.6 vs 1.0 for 3DB vs PB, respectively. The average air gap volume (cc) normalized by bolus size (cm2) was less for 3DB vs PB. For complex H&N plans, 3DB HI and CI was significantly better compared with CB plans. No patient treated with 3DB experienced a clinically adverse event. The 3DB is clinically safe, and effective in improving superficial dose confirmed with in vivo measurement. Superior 3DB clarity allows more efficient, reproducible bolus placement with fewer air gaps. 3DB density is significantly more uniform than PB, and homogeneity and conformity indices demonstrate improved dosimetric outcomes of complex and/or irregular superficial RT targets.

Dosimetric effects of brass mesh bolus on skin dose and dose at depth for postmastectomy chest wall irradiation

PurposeTo investigate the feasibility of using the brass mesh bolus as an alternative to tissue- equivalent bolus for post mastectomy chest wall cancer by characterizing the dosimetric effects of the 2-mm fine brass bolus on both the skin dose, the dose at depth and spatial distribution. Materials and methodsSurface dose and percent depth dose data were acquired for a 6 MV photon beam in a solid water phantom using MOSkin™, Gafchromic EBT3 film and an Advanced Markus ionization chamber. Data were acquired for the case of: no bolus, Face-up bass bolus, Face-down brass bolus, double brass bolus, 0.5 cm and 1.0 cm of Superflab TE bolus. The exit doses were also measured via MOSkin™ dosimeter and Markus ionization chamber. Gafchromic EBT3 film strips were used to plot dose profile at surface and 10 cm depth for Face-up brass, Face-down brass, double brass, 0.5 cm and 1.0 cm of Superflab TE bolus. ResultsThe surface dose measured via MOSkin™ dosimeter increased from 19.2 ± 1.0% to 63.1 ± 2.1% under Face-up brass discs, 51.2 ± 1.2% under Face-up brass spaces, 61.5 ± 0.5% under Face-down brass discs, and 41.3 ± 2.1% under Face-down brass spaces. The percentage difference in the dose measured under brass discs between Face-up versus Face-down was less than 2% for entrance dose and 10% for exit dose, whereas the percentage difference under brass spaces was approximately 3% for entrance dose and about 5% for the exit dose. Gafchromic EBT3 film strip measurements show that the mesh bolus produced ripple beam profiles due to the mesh brass construction. ConclusionsBrass bolus does not significantly change dose at depth (less than 0.5%), and the surface dose is increased similar to TE bolus. Considering this, brass mesh may be used as a substitute for TE bolus to increase superficial dose for chest wall tangent plans.

A mathematical deconvolution formulation for superficial dose distribution measurement by Cerenkov light dosimetry.

Cerenkov photons are created by high-energy radiation beams used for radiation therapy. In this study, we developed a Cerenkov light dosimetry technique to obtain a two-dimensional dose distribution in a superficial region of medium from the images of Cerenkov photons by using a deconvolution method. An integral equationwas derived to represent the Cerenkov photon image acquired by a camera for a given incident high-energy photon beam by using convolution kernels. Subsequently, an equationrelating the planar dose at a depth to a Cerenkov photon image using the well-known relationship between the incident beam fluence and the dose distribution in a medium was obtained. The final equationcontained a convolution kernel called the Cerenkov dose scatter function (CDSF). The CDSF function was obtained by deconvolving the Cerenkov scatter function (CSF) with the dose scatter function (DSF). The GAMOS (Geant4-based Architecture for Medicine-Oriented Simulations) Monte Carlo particle simulation software was used to obtain the CSF and DSF. The dose distribution was calculated from the Cerenkov photon intensity data using an iterative deconvolution method with the CDSF. The theoretical formulation was experimentally evaluated by using an optical phantom irradiated by high-energy photon beams. The intensity of the deconvolved Cerenkov photon image showed linear dependence on the dose rate and the photon beam energy. The relative intensity showed a field size dependence similar to the beam output factor. Deconvolved Cerenkov images showed improvement in dose profiles compared with the raw image data. In particular, the deconvolution significantly improved the agreement in the high dose gradient region, such as in the penumbra. Deconvolution with a single iteration was found to provide the most accurate solution of the dose. Two-dimensional dose distributions of the deconvolved Cerenkov images agreed well with the reference distributions for both square fields and a multileaf collimator (MLC) defined, irregularly shaped field. The proposed technique improved the accuracy of the Cerenkov photon dosimetry in the penumbra region. The results of this study showed initial validation of the deconvolution method for beam profile measurements in a homogeneous media. The new formulation accounted for the physical processes of Cerenkov photon transport in the medium more accurately than previously published methods.

Radiation characterisation and dosimetric measurements of a femtosecond pulsed laser ablation system

This work describes the radiation characterisation and dosimetric measurements performed on the low-energy micromachining station of the femtosecond STELA (Santiago TErawatt LAser) at the University of Santiago de Compostela (Spain). For this aim, ionisation chambers, solid state detectors, and radiochromic films were used. The results show the emission of pulsed x-ray produced by laser-accelerated electrons from the ablated material exhibiting both bremsstrahlung and characteristic radiation. Although this radiation was produced unintentionally, a high superficial dose rate can be achieved. This radiation can be successfully stopped using small shielding to protect personnel from its effects. Based on the results of this work, the yearly dose equivalent after installing the shielding was negligible.

Clinical implementation of AXB from AAA for breast: Plan quality and subvolume analysis.

PurposeTwo dose calculation algorithms are available in Varian Eclipse software: Anisotropic Analytical Algorithm (AAA) and Acuros External Beam (AXB). Many Varian Eclipse‐based centers have access to AXB; however, a thorough understanding of how it will affect plan characteristics and, subsequently, clinical practice is necessary prior to implementation. We characterized the difference in breast plan quality between AXB and AAA for dissemination to clinicians during implementation.MethodsLocoregional irradiation plans were created with AAA for 30 breast cancer patients with a prescription dose of 50 Gy to the breast and 45 Gy to the regional node, in 25 fractions. The internal mammary chain (IMCCTV) nodes were covered by 80% of the breast dose. AXB, both dose‐to‐water and dose‐to‐medium reporting, was used to recalculate plans while maintaining constant monitor units. Target coverage and organ‐at‐risk doses were compared between the two algorithms using dose–volume parameters. An analysis to assess location‐specific changes was performed by dividing the breast into nine subvolumes in the superior–inferior and left–right directions.ResultsThere were minimal differences found between the AXB and AAA calculated plans. The median difference between AXB and AAA for breastCTV V 95%, was <2.5%. For IMCCTV, the median differences V 95%, and V 80% were <5% and 0%, respectively; indicating IMCCTV coverage only decreased when marginally covered. Mean superficial dose increased by a median of 3.2 Gy. In the subvolume analysis, the medial subvolumes were “hotter” when recalculated with AXB and the lateral subvolumes “cooler” with AXB; however, all differences were within 2 Gy.ConclusionWe observed minimal difference in magnitude and spatial distribution of dose when comparing the two algorithms. The largest observable differences occurred in superficial dose regions. Therefore, clinical implementation of AXB from AAA for breast radiotherapy is not expected to result in changes in clinical practice for prescribing or planning breast radiotherapy.

Monte Carlo evaluation of the potential benefits of flattening filter free beams from the Oncor® clinical linear accelerator.

To evaluate the potential privileges of flattening filter-free (FFF) photon beams from Oncor® linac for 6 MV and 18 MV energies. A Monte Carlo (MC) model of Oncor® linac was built using BEAMnrc MCCode and verified by the measured data using 6 MV and 18 MV energies. A comprehensive set of data was also characterized for MC model of Oncor® machine running with and without flattening filter (FF) for 6 MV and 18 MV beams in six field sizes. The investigated characteristics included mean energy, energy spectrum, photon spatial fluence, superficial dose, percent depth dose (PDD), dose output, and out-of-field dose with two indexes of lateral dose profile and isodose curve at three depths. Using FFF enhanced the energy uniformity 3.4±0.11% (6 MV) and 2.05±0.09% (18 MV) times and improved dose output by factor of 2.91 (6 MV) and 4.2 (18 MV) on the central axis, respectively. Using FFF also reduced the PDD dependencies by 9.1% (6 MV) and 5.57% (18 MV). In addition, using FFF had a lower out-of-field dose due to the reduced head scatter and softer spectra. The findings in this study suggested that using FFF, Oncor® machine could achieve better treatment results with lower dose toxicity and a shorter beam-on time.

Fabrication and characterization of bolus material using polydimethyl-siloxane

Bolus has been used in radiotherapy to reduce tissue harm and to increase the superficial dose for skin cancer treatment. Commonly, a bolus is made of melamine in several hospitals. In this research, polydimethyl-siloxane (PDMS) material was used for bolus fabrication. The aims of the study are to investigate bolus density, percentage surface dose and its structural strength for each various composition. In bolus preparation, bolus material used composition variation between PDMS volume and catalyst volume. Composition variation were 20:1, 22:1, 24:1, 26:1, 28:1, 30:1 and 32:1. PDMS and catalyst were mixed by chemical solution deposition method. Bolus was molded by using glass cast with the size of 10 × 10 × 0.5 cm3. Bolus density was analyzed by mass per volume equation, for bolus radiation was examined by the linear accelerator using two electron energy (5 and 7 MeV) and bolus strain and tensile strength were examined by Brookfield CT 3 machine. The results of bolus density were similar with soft tissue density, while the lowest and highest density each variation are 22:1 and 28:1. In general, the use of bolus has increased the surface dose. Percentage of surface dose at 5 MeV energy is higher than 7 MeV energy. The highest percentage of surface dose at 5 MeV energy with 0.5 and 1.0 cm bolus thickness was achieved at composition of 32:1. For strain and tensile strength result, the lowest and highest strain each variation are 22:1 and 28:1, then the lowest and highest tensile strength each variation are 32:1 and 28:1. These results is important to select composition material for bolus fabrication in radiotherapy treatment.

Evaluation of Superficial Dosimetry in Postmastectomy Radiotherapy using High-energy Electromagnetic Radiation Treatment

The present study evaluated surface and superficial doses delivered by high-energy electromagnetic radiation treatment in patients who received postmastectomy radiotherapy. Computed tomography was performed using an RW3 slab phantom, and hypothetical target volumes were delineated. 6MV electromagnetic radiation beams were generated with five treatment plans: 2-field 3-dimentional conformal radiation therapy, 4-field intensitymodulated radiation therapy, 7-field intensity-modulated radiation therapy, TomoHelical 3-dimentional conformal radiation therapy, and TomoHelical intensity-modulated radiation therapy. Film dosimetry was performed with Gafchromic EBT3 film for dose measurement of high-energy electromagnetic radiation. The dose profile at the surface and superficial regions (1-6 mm depth) of the phantom obtained for each treatment technique. Compared to other techniques, Tomo 3-dimentional conformal radiation therapy had the highest surface dose (47-71 %). The superficial doses of TomoHelical 3-dimentional conformal radiation therapy and TomoHelical intensity-modulated radiation therapy were > 75 %, 80 %, and 90 % of the prescribed dose at 1, 2, and 5 mm depths, respectively. For postmastectomy radiotherapy, TomoHelical 3-dimentional conformal radiation therapy and TomoHelical intensity-modulated radiation therapy had higher surface and superficial doses than linear accelerator-based treatment techniques, with a sufficient dose of ≥ 75 % being delivered to the skin region at depths of 1 mm.