Surface Dose Distribution Research Articles

Flexible and Ecological Cotton-Based Dosimeter for 2D UV Surface Dose Distribution Measurements.

This work presents a 2D radiochromic dosimeter for ultraviolet (UV) radiation measurements, based on cotton fabric volume-modified with nitroblue tetrazolium chloride (NBT) as a radiation-sensitive compound. The developed dosimeter is flexible, which allows it to adapt to various shapes and show a color change from yellowish to purple-brown during irradiation. The intensity of the color change depends on the type of UV radiation and is the highest for UVC (253.7 nm). It has been shown that the developed dosimeters (i) can be used for UVC radiation dose measurements in the range of up to 10 J/cm2; (ii) can be measured in 2D using a flatbed scanner; and (iii) can have the obtained images after scanning be filtered with a medium filter to improve their quality by reducing noise from the fabric structure. The developed cotton-NBT dosimeters can measure UVC-absorbed radiation doses on objects of various shapes, and when combined with a dedicated computer software package and a data processing method, they form a comprehensive system for measuring dose distributions for objects with complex shapes. The developed system can also serve as a comprehensive method for assessing the quality and control of UV radiation sources used in various industrial processes.

Dual application of Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue Fricke hydrogel in clinical practice: Surface dosimeter and bolus

An essential issue is an accurate evaluation of surface dose distribution for such sensitive treatments. This work aimed to feasibility of the dual application of the Ferrous Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue (PVA-GTA-MTB) gel as a bolus compensator and surface dosimeter in breast radiotherapy. The differences between the surface dose measured using PVA-GTA-MTB gel and film dosimetry in the medial and lateral parts of the breast were 3.74% and 4.18%, respectively. A qualitative comparison of the isodose curves showed that the PVA-GTA-MTB bolus creates a uniform dose distribution similar to the superflab bolus in the target volume.

Influence of Pitch on Surface Dose Distribution and Image Noise of Computed Tomography Scans.

This study evaluated the effect of pitch on 256-slice helical computed tomography (CT) scans. Cylindrical water phantoms (CWP) were measured using axial and helical scans with various pitch values. The surface dose distributions of CWP were measured, and reconstructed images were obtained using filtered back-projection (FBP) and iterative model reconstruction (IMR). The image noise in each reconstructed image was decomposed into a baseline component and another component that varied along the z-axis. The baseline component of the image noise was highest at the center of the reconstructed image and decreased toward the edges. The normalized 2D power spectra for each pitch were almost identically distributed. Furthermore, the ratios of the 2D power spectra for IMR and FBP at different pitch values were obtained. The magnitudes of the components varying along the z-axis were smallest at the center of the reconstructed image and increased toward the edge. The ratios of the 3D power spectra on the fx axis for IMR and FBP at different pitch values were obtained. The results showed that the effect of the pitch was related to the component that varied along the z-axis. Furthermore, the pitch had a smaller effect on IMR than on FBP.

An Investigation into the Surface Dose Using Eclipse Treatment Planning System and Film Dosimetry for Treatment of Breast Cancer

Purpose: Accurate knowledge about surface dose distribution is a critical issue in skin irradiation. This study was conducted to investigate the surface dose using the Eclipse Treatment Planning System (TPS) calculation and GAF chromic film measurement for breast cancer treatment. Materials and Methods: An inhomogeneous chest phantom was used in the present study. Irradiations were done with a 6 MV energy beam of a linear accelerator (Varian 2100C/D). TPS calculations and film measurements were compared for surface dose estimations. Results: The average difference between film measurements and TPS calculations was 7.1%. Surface doses were lower in TPS calculations in comparison with film measurements. Conclusion: TPS plays a significant role in radiotherapy. However, they have many errors in measuring surface doses. Because of the inaccuracy of the majority of treatment planning systems in calculating the surface dose, the need for practical measurements is essential.

Local Diagnostic Reference Levels (LDRLs) for routine X-ray examinations in Morocco

In Morocco, the radiation protection of patients undergoing medical imaging examinations using ionizing radiation sources is now governed by specific provisions of Chapter VII of Law no142-12 (Loi no142-12 – AMSSNuR, 2015). The principle of justification of procedures and the principle of optimization of doses delivered constitute the basis of the legislation governing medical exposure. DRLs are considered as an important optimization tool encouraging healthcare professionals to optimize their practice and assure a better patient safety. In this survey, Local Diagnostic Reference Levels (LDRLs) were established for the eight most frequent examinations in Morocco. Data from 1747 patients were collected from seven regional hospitals. The proposed LDRLs were defined as the 75th percentile of the mean entrance surface dose distribution (ESD) in mGy using the indirect dosimetry method according to the IAEA Report Series No. 457. The LDRLs values reported in this study were for the eight examinations: skull (PA) 2.8 mGy, chest (PA) 0.51 mGy, abdomen (AP) 7.6 mGy, pelvis (AP) 6.45 mGy, lumbar (AP) 7.8 mGy, lumbar (Lat) 10.7 mGy, cervical (AP) 2.2 mGy, and cervical (Lat) 2.4 mGy. The DRLs reported in Morocco were compared with those of international authorities and other countries: IRSN (France), NRPB (UK), Japan, Sudan, and Iran. The present work assesses the local DRLs in Morocco and constitutes a starting point that will provide professionals with a tool to help them optimize the doses delivered to patients. Furthermore, the definition of national DRLs by radiography is an essential step in the process of optimizing medical exposures.

Spatial and temporal dosimetry of individual electron FLASH beam pulses using radioluminescence imaging

Purpose. In this study, spatio-temporal beam profiling for electron ultra-high dose rate (UHDR; >40 Gy s−1) radiation via Cherenkov emission and radioluminescence imaging was investigated using intensified complementary metal–oxide–semiconductor cameras. Methods. The cameras, gated to FLASH optimized linear accelerator pulses, imaged radioluminescence and Cherenkov emission incited by single pulses of a UHDR (>40 Gy s−1) 10 MeV electron beam delivered to the isocenter. Surface dosimetry was investigated via imaging Cherenkov emission or scintillation from a solid water phantom or Gd2O2S:Tb screen positioned on top of the phantom, respectively. Projected depth–dose profiles were imaged from a tank filled with water (Cherenkov emission) and a 1 g l−1 quinine sulfate solution (scintillation). These optical results were compared with projected lateral dose profiles measured by Gafchromic film at different depths, including the surface. Results. The per-pulse beam output from Cherenkov imaging agreed with the photomultiplier tube Cherenkov output to within 3% after about the first five to seven ramp-up pulses. Cherenkov emission and scintillation were linear with dose (R 2 = 0.987 and 0.995, respectively) and independent of dose rate from ∼50 to 300 Gy s−1 (0.18–0.91 Gy/pulse). The surface dose distribution from film agreed better with scintillation than with Cherenkov emission imaging (3%/3 mm gamma pass rates of 98.9% and 88.8%, respectively). Using a 450 nm bandpass filter, the quinine sulfate-based water imaging of the projected depth optical profiles agreed with the projected film dose to within 5%. Conclusion. The agreement of surface dosimetry using scintillation screen imaging and Gafchromic film suggests it can verify the consistency of daily beam quality assurance parameters with an accuracy of around 2% or 2 mm. Cherenkov-based surface dosimetry was affected by the target’s optical properties, prompting additional calibration. In projected depth–dose profiling, scintillation imaging via spectral suppression of Cherenkov emission provided the best match to film. Both camera-based imaging modalities resolved dose from single UHDR beam pulses of up to 60 Hz repetition rate and 1 mm spatial resolution.

Development of all-in-one phantom dosimeter to measure multidimensional dose distribution for 60Co radiotherapy unit

In this study, we used square-type organic scintillating fibers and polymethyl methacrylate phantoms to develop an all-in-one phantom dosimeter measure the multidimensional dose distributions for a 60Co radiotherapy source. Multidimensional dose distributions, which include the transverse, depth, and surface dose distributions, can be obtained by measuring scintillating light simultaneously in real time. An additional phantom for quality assurance before radiotherapy is not required because square-type organic scintillating fibers are directly inserted into the polymethyl methacrylate phantom. Multidimensional dose distributions can also be measured simultaneously by changing the arrangement of one-dimensional phantom dosimeters, which are very thin and can be stacked, similar to books placed on a shelf. Therefore, the proposed dosimeter can be applied as an all-in-one phantom dosimeter with a variable structure that can respond to changes in various radiotherapy treatment environments. Through experiments, the multidimensional dose distributions for the 60Co radiotherapy unit were measured to evaluate the performance of the proposed all-in-one phantom dosimeter. The results were compared and evaluated using external beam therapy films and Monte Carlo simulations. Based on the results of this study, significant time is expected to be saved during dose measurements for quality assurance in radiotherapy, as simultaneous measurements can yield multidimensional data on the transverse, depth and surface dose distributions in real time.

Simple and Rapid Creation of Customized 3D Printed Bolus Utilizing iPhone X True Depth Camera

Three-dimensional (3D) printing has effectively produced patient-specific bolus materials during radiation treatment for superficial tumors along irregular skin surfaces. Traditional bolus materials in comparison, are often difficult to manipulate for proper fit, and can be difficult to reproduce. Current 3D printed boluses are made from either pre-existing computed tomography (CT) scans or complex surface scanning methods. Here, we introduce an inexpensive, convenient approach to generating 3D printed bolus from surface scanning technology available in common smartphones. 3D printed bolus was designed using surface scans from iphone X true depth cameras and a low cost 3D printer. The percentage density infill was adjusted to achieve tissue equivalence. To evaluate the clinical feasibility, fit against skin surface and radiation dose distribution was compared to traditional bolus. We fabricated customized 3D printed bolus for different areas of the face utilizing an iphone X camera and an inexpensive commercially available 3D printer. When printed at 100% density this bolus material approximated soft tissue/water and provided an equivalent dose distribution to that found with standard bolus materials on direct comparison. The bolus material was inexpensive and produces an ideal fit with the scanned anatomy. We present a simplified method of highly customized bolus production that requires minimal experience with computer modeling programs and can be accomplished with an iphone true depth camera.

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.

Simple and Rapid Creation of Customized 3-dimensional Printed Bolus Using iPhone X True Depth Camera

PurposeThree-dimensional printing has produced customized bolus during radiation therapy for superficial tumors along irregular skin surfaces. In comparison, traditional bolus materials are often difficult to manipulate for a proper fit. Current 3-dimensional printed boluses are made from either preexisting computed tomography scans or complex surface scanning methods. Herein, we introduce an inexpensive, convenient approach to generate a 3-dimensional printed bolus from surface scanning technology available in common smartphones. Methods and materialsA three-dimensional printed bolus was designed using surface scans from iPhone X true depth cameras and a low-cost 3-dimensional printer. The percentage density infill was adjusted to achieve tissue equivalence. To evaluate the clinical feasibility, fit against the skin surface and radiation dose distribution were compared with those of the traditional bolus. ResultsWe fabricated a customized 3-dimensional printed bolus for different areas of the face using an iPhone X camera and inexpensive commercially available 3-dimensional printer. When printed at 100% density, the bolus material approximated soft tissue/water and provided an equivalent dose distribution to that found with standard bolus materials on direct comparison. The bolus material is inexpensive and produces an ideal fit with the scanned anatomy. ConclusionsWe present a simplified method of highly customized bolus production that requires minimal experience with computer modeling programs and can be accomplished with an iPhone true depth camera.

Exposure dose measurement during diagnostic pediatric X-ray examination using an optically stimulated luminescence (OSL) dosimeter based on precise dose calibration taking into consideration variation of X-ray spectra

When dosimetry is performed in actual clinical situations using diagnostic X-rays, the energy dependence of the dosimeter should be taken into consideration. Although the dosimeter is calibrated with standard X-rays, it is unclear whether this dosimeter can be used in various clinical situations in which radiation exposure is not only caused by direct X-rays but also scattered X-rays. In this paper, in order to evaluate the applicability of an OSL dosimeter, we propose a novel method to derive a proper calibration factor using X-ray spectrum and the efficiency of the dosimeter. The X-ray spectra were calculated by means of a Monte-Carlo simulation code taking into consideration the effects of beam hardening, scattered X-rays and backscattering X-rays. As a result of analysis of calibration factors, we found that the difference of calibration factors from the standard, which was determined with 80 kV X-rays, was within 30%. Here, we focused our attention on dose measurement of medical staff who held a patient during pediatric X-ray examination; in this examination, a calibration factor can be determined precisely. In order to determine the dosimetric points, we mimicked a clinical situation using a neonate phantom and human dummies, and surface dose distributions to the human dummies were visualized. Based on the phantom study, we determined that the dosimetric positions of both hands and neck of the assistant during the actual clinical measurement were most important. Then, actual dosimetry in a clinical situation was performed. The OSL dosimeters were attached to the neck and hands of assistants during a pediatric X-ray examination, and doses were evaluated individually for each examination (N = 163). By analyzing data trends, we found that the dose to the assistant's hands was relatively higher when a younger patient was examined. In contrast, the dose to the neck position was the same regardless of the patient's age. In conclusion, we performed accurate dosimetry taking into consideration differences of X-ray spectra being incident to the dosimeter, and using our method, we can analyze individual doses to assistants for each pediatric X-ray examination.

Dosimetric effects of a repositioning head frame system and treatment planning system dose calculation accuracy.

This work aims to study the effect on surface dose and dose distribution caused by the Elekta Fraxion cranial immobilization system. The effect of Fraxion inclusion in Elekta Monaco treatment planning system and its calculation accuracy is also checked. To study the dose attenuation, a cylindrical phantom was located over the Elekta Fraxion with an IBA CC13 ionization chamber placed in the central insert at the linac isocenter. Dose measurements at multiple gantry angles were performed for three open fields, 10 × 10 cm, 5 × 5 cm and other smaller 2 × 2 cm. Measured doses were compared with the ones calculated by Monaco. Surface dose and dose distribution in the buildup region were measured placing several Gafchromic Films EBT3 at linac CAX between the slabs of a RW3 phantom located over Fraxion and read using FilmQA Pro software. Measures were performed for two open field sizes and results were compared with Monaco calculations. Measurements show a 1% attenuation for 180° gantry angle but it can be as high as 3.4% (5 × 5 open field) for 150°/210° gantry angle, as with these angles the beam goes through the Fraxion's headrest twice. If Fraxion is not included in the calculation Monaco calculation can result in a 3% difference between measured and calculated doses, while with Fraxion in the calculation, the maximum difference is 0.9%. Fraxion increases 3.7 times the surface dose, which can be calculated by Monaco with a difference lower than 2%. Monaco also calculated correctly the PDD for both open fields (2%) when Fraxion is included in the calculation. This work shows that the attenuation varies with gantry angle. The inclusion of Fraxion in Monaco improves the calculation from 3% difference to 1% in the worst case. Furthermore, the surface dose increment and the dose in the buildup region are correctly calculated.

A Study on the Surface Dose Distribution by Scattered and Leakage Radiation in Radiation Therapy

During radiation therapy, the patient is exposed to secondary radiation by scattered and leakage radiation. For the diagnostic radiation, guidelines for reducing the patient's exposure as the diagnostic reference level are provided. However, in the case of therapeutic radiation, even though the radiation dose by the secondary radiation is considerable, the prescription dose is not limited because of the reason of the therapeutic efficiency. The purpose of this study was to evaluate the secondary radiation that the patient could be received at the peripheral tissue during the radiotherapy using the linear accelerator with the radiophotoluminescent glass dosimeter. In addition, we measured the degree of saturation of the luminescent amount according to the build-up characteristic of the radiophotoluminescent glass dosimeter. As a result of carrying out this study, the exposure dose decreased drastically farther away from the treatment field. When the head was irradiated with 1 Gy, the neck could be exposed to 18.45 mGy. When the same dose was irradiated at the neck, 15.55 mGy of the head and irradiated at the chest, 14.26 mGy of the neck and irradiated at the pelvis, 1.14 mGy of the chest were exposed separately. The degree of saturation of the luminescent intensity could be overestimated by 1.8 ~ 4.8% depending on time interval for 3 days.

Improving treatment geometries in total skin electron therapy: Experimental investigation of linac angles and floor scatter dose contributions using Cherenkov imaging.

The purpose of this study was to identify the optimal treatment geometry for total skin electron therapy (TSET) using a new optimization metric from Cherenkov image analysis, and to investigate the sensitivity of the Cherenkov imaging method to floor scatter effects in this unique treatment setup. Cherenkov imaging using an intensified charge coupled device (ICCD) was employed to measure the relative surface dose distribution as a 2D image in the total skin electron treatment plane. A 1.2 m × 2.2 m × 1 cm white polyethylene sheet was placed vertically at a source to surface distance (SSD) of 300 cm, and irradiated with 6 MeV high dose rate TSET beams. The linear accelerator coordinate system used stipulates 0° is the bottom of the gantry arc, and progresses counterclockwise so that gantry angle 270° produces a horizontal beam orthogonal to the treatment plane. First, all unique pairs of treatment beams were analyzed to determine the performance of the currently recommended symmetric treatment angles (±20° from the horizontal), compared to treatment geometries unconstrained to upholding gantry angle symmetry. This was performed on two medical linear accelerators (linacs). Second, the extent of the floor scatter contributions to measured surface dose at the extended SSD required for TSET were imaged using three gantry angles of incidence: 270° (horizontal), 253° (-17°), and 240° (-30°). Images of the surface dose profile at each angle were compared to the standard concrete floor when steel plates, polyvinyl chloride (PVC), and solid water were placed on the ground at the base of the treatment plane. Postprocessing of these images allowed for comparison of floor material-based scatter profiles with previously published simulation results. Analysis of the symmetric treatment geometry (270 ± 20°) and the identified optimal treatment geometry (270 + 23° and 270 - 17°) showed a 16% increase in the 90% isodose area for the latter field pair on the first linac. The optimal asymmetric pair for the second linac (270 + 25° and 270 - 17°) provided a 52% increase in the 90% isodose area when compared to the symmetric geometry. Difference images between Cherenkov images captured with test materials (steel, PVC, and solid water) and the control (concrete floor) demonstrated relative changes in the two-dimensional (2D) dose profile over a 1 × 1.9 m region of interest (ROI) that were consistent with published simulation data. Qualitative observation of the residual images demonstrates localized increases and decreases with respect to the change in floor material and gantry angle. The most significant changes occurred when the beam was most directly impinging the floor (gantry angle 240°, horizontal -30°), where the PVC floor material decreased scatter dose by 1-3% in 7.2% of the total ROI area, and the steel plate increased scatter dose by 1-3% in 7.0% of the total ROI area. An updated Cherenkov imaging method identified asymmetric, machine-dependent TSET field angle pairs that provided much larger 90% isodose areas than the commonly adopted symmetric geometry suggested by Task Group 30 Report 23. A novel demonstration of scatter dose Cherenkov imaging in the TSET field was established.

In-vivo dosimetric analysis in total skin electron beam therapy.

Background and purposeThermoluminescent dosimetry (TLD) is an important element of total skin electron beam therapy (TSEBT). In this study, we compare radiation dose distributions to provide data for dose variation across anatomic sites.Materials and methodsRetrospectively collected data on 85 patients with cutaneous lymphoma or leukemia underwent TSEBT were reviewed. Patients were irradiated on two linear accelerators, in one of two positions (standing, n = 77; reclined, n = 8) and 1830 in vivo TLD measurements were obtained for various locations on 76 patients.ResultsThe TLD results showed that the two TSEBT techniques were dosimetrically heterogeneous. At several sites, the dose administered correlated with height, weight, and gender. After the first TLD measurement, fourteen patients (18%) required MU modification, with a mean 10% reduction (range, −25 to +35). Individual TLD results allowed us to customize the boost treatment for each patient. For patients who were evaluated in the standing position, the most common underdosed sites were the axilla, perineum/perianal folds, and soles (each receiving 69%, 20%, and 34% of the prescribed dose, respectively). For patients evaluated in a reclining position, surface dose distribution was more heterogeneous. The sites underdosed most commonly were the axilla and perineum/perianal folds (receiving less than one third of prescribed dose). Significant variables were detected with model building.ConclusionTLD measurements were integral to quality assurance for TSEBT. Dose distribution at several anatomical sites correlated significantly with gender, height, and weight of the treated individual and might be predicted.

Evaluation of surface dose and image quality using the half-scan mode in chest computed tomography-guided interventional radiology: a phantom study.

The authors aimed to evaluate the effects of the half-scan mode on image quality and physician exposure to radiation in computed tomography (CT)-guided interventional radiology (IVR) to the right lung using an intermittent CT fluoroscopy technique for measuring phantom surface dose distribution and image noise. For the half-scan mode, settings at 0°, 90°, 180°, and 270° were used as the central axis of the X-ray exposure range on the chest phantom. With the center of the ventral side in the chest phantom defined as 0°, optically stimulated luminescent dosimeters were attached at five positions at 30° intervals on the right side of the phantom surface. Securing a space for device operation during the procedure is necessary. The couch was shifted downward by 50mm to reproduce the conditions used for measurement in clinical settings. Image noise and contrast-to-noise ratio were measured to assess image quality; subjective evaluation was performed using simulated lung nodules placed in the phantom. The phantom surface dose distribution in the measured half-scan mode depended on the angle setting. Additionally, the phantom surface dose in the half-scan mode at the 90° setting was reduced by approximately 50%; however, image quality was clearly decreased. In CT-guided IVR to the right lung, using a lead drape and half-scan mode according to the procedural situation is important.

<i>In-Vivo</i> Dosimetry Method for Measuring Peak Surface Dose Using Radiochromic Films during Computed Tomography Scanning of the Sinus

Purpose: During computed tomography (CT) helical scanning mode the patient surface dose distribution is assumed to be non-uniform, therefore point dose measurement methods may lead to imprecise estimation of the radiation dose received by the patient skin in particular. We have used XRQA2 films as in-vivo dosimeters to measure the entrance skin dose during sinus exams. Methods: The films were placed under the patient head rest in order to sample the entrance surface dose in-vivo. We have performed in-vivo film irradiation on 23 patients in this study to verify the clinical suitability of the method and were found adequate. Results: The measured average ESD in the sinus exam was 11.7 ± 1.0 mGy, the PSD was 15.7 ± 1.7 mGy and the CTDI(vol) was 13.3 ± 0.1 mGy. The ratio of ESD/CTDI(vol) and PSD/CTDI(vol) was 0.88 and 1.18 respectively. The results indicate that the scanner registered CTDI(vol) underestimates the PSD and in the same time it overestimates the ESD by 18% and 13.6% respectively. Conclusion: The observed differences between the ESD, PSD and CTDI(vol) although seem small for the radiation dose range measured during CT of the sinus [13.2 - 13.4] mGy, but important for the medical physicist to know, since monitoring of patients’ doses from CT examinations is becoming more mandatory. The use of radiochromic film as in-vivo dosimeter does not interfere with the clinical radiological exam and does not produce any image artifacts. The method can be used to study other CT examinations specially the ones with large beam width, high pitch factor and high dose exams. The method allows measurement of the peak skin dose, examination of the CT dose profile and the 2D dose distribution in the XZ plan.

Assessment of organ and effective dose when using region-of-interest attenuators in cone-beam CT and interventional fluoroscopy.

In some medical-imaging procedures using cone-beam CT (CBCT) and fluoroscopy, only the center of the field of view (FOV) may be needed to be visualized with optimal image quality. To reduce the dose to the patient while maintaining visualization of the entire FOV, a Cu attenuator with a circular aperture for the region of interest (ROI) is used. The potential organ and effective dose reductions of ROI imaging when applied to CBCT and interventional fluoroscopic procedures were determined using EGSnrc Monte Carlo code. The Monte Carlo model was first validated by comparing the surface dose distribution in a solid-water block phantom with measurement by Gafchromic film. The dependence of dose reduction on the ROI attenuator thickness, the opening size of the ROI, the axial beam position, and the location of the different organs for both neuro and thoracic imaging was evaluated. The results showed a reduction in most organ doses of 45% to 70% and in effective dose of 46% to 66% compared to the dose in a CBCT scan and in an interventional procedure without the ROI attenuator. This work provides evidence of a substantial reduction of organ and effective doses when using an ROI attenuator during CBCT and fluoroscopic procedures.

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

Abstract Background and purpose Flattening filter free (FFF) beams enable high-dose rate irradiations and have the potential to speed up breast cancer radiotherapy (RT) treatments. In this work the surface doses of FFF beams were studied with various treatment plans for breast cancer RT. The near surface dose distributions were compared to the ones delivered with conventional flattening filter (FF) beams and to the calculated dose distributions. Materials and methods The study was executed with radiochromic films. In addition to one open field, four techniques were investigated: tangential open field, tangential IMRT (IMRT), tangential VMAT (tVMAT) and continuous VMAT (cVMAT) techniques, respectively. The dose distributions were calculated with commercial Monte Carlo (MC) algorithm with energies of 6 and 10MV with both FF and FFF. The surface areas investigated were divided into depths of 0–2, 2–5 and 5–8mm. Results The largest deviations (on average 5.9%) between the measured and calculated doses were recorded at the most shallowest depths (0–2mm). At deeper depths, the differences were on average 1.4% and always less than 6%. The measured near surface doses were slightly lower (4.6%) with modulated 6MVFFF beams than with the corresponding flattened beams and on the contrary with 10MV the surface doses by FFF were slightly higher (2.8%). Conclusions The studied MC calculation algorithm was accurate in determine the near surface doses. There was no significant difference in measured or calculated surface doses between FFF and FF beams. With respect to surface dose uniformity the VMAT techniques overall resulted in the most uniform dose distributions.

Entrance surface dose distribution and organ dose assessment for cone-beam computed tomography using measurements and Monte Carlo simulations with voxel phantoms

Cone-Beam Computed Tomography (CBCT) enables high-resolution volumetric scanning of the bone and soft tissue anatomy under investigation at the treatment accelerator. This technique is extensively used in Image Guided Radiation Therapy (IGRT) for pre-treatment verification of patient position and target volume localization. When employed daily and several times per patient, CBCT imaging may lead to high cumulative imaging doses to the healthy tissues surrounding the exposed organs.This work aims at (1) evaluating the dose distribution during a CBCT scan and (2) calculating the organ doses involved in this image guiding procedure for clinically available scanning protocols. Both Monte Carlo (MC) simulations and measurements were performed. To model and simulate the kV imaging system mounted on a linear accelerator (Edge™, Varian Medical Systems) the state-of-the-art MC radiation transport program MCNPX 2.7.0 was used. In order to validate the simulation results, measurements of the Computed Tomography Dose Index (CTDI) were performed, using standard PMMA head and body phantoms, with 150mm length and a standard pencil ionizing chamber (IC) 100mm long. Measurements for head and pelvis scanning protocols, usually adopted in clinical environment were acquired, using two acquisition modes (full-fan and half fan). To calculate the organ doses, the implemented MC model of the CBCT scanner together with a male voxel phantom (“Golem”) was used.The good agreement between the MCNPX simulations and the CTDIw measurements (differences up to 17%) presented in this work reveals that the CBCT MC model was successfully validated, taking into account the several uncertainties. The adequacy of the computational model to map dose distributions during a CBCT scan is discussed in order to identify ways to reduce the total CBCT imaging dose. The organ dose assessment highlights the need to evaluate the therapeutic and the CBCT imaging doses, in a more balanced approach, and the importance of improving awareness regarding the increased risk, arising from repeated exposures.