Rando Phantom Research Articles

Impact of respiratory motion on lung dose during total marrow irradiation.

We evaluated the impact of respiratory motion on the lung dose during linac-based intensity-modulated total marrow irradiation (IMTMI) using two different approaches: (1) measurement of doses within the lungs of an anthropomorphic phantom using thermoluminescent detectors (TLDs) and (2) treatment delivery measurements using ArcCHECK where gamma passing rates (GPRs) and the mean lung doses were calculated and compared with and without motion. In the first approach, respiratory motions were simulated using a programmable motion platform by using typical published peak-to-peak motion amplitudes of 5, 8, and 12mm in the craniocaudal (CC) direction, denoted here as M1, M2, and M3, respectively, with 2mm in both anteroposterior (AP) and lateral (LAT) directions. TLDs were placed in five selected locations in the lungs of a RANDO phantom. Average TLD measurements obtained with motion were normalized to those obtained with static phantom delivery. The mean dose ratios were 1.01 (0.98-1.03), 1.04 (1.01-1.09), and 1.08 (1.04-1.12) for respiratory motions M1, M2, and M3, respectively. To determine the impact of directional respiratory motion, we repeated the experiment with 5-, 8-, and 12-mm motion in the CC direction only. The differences in average TLD doses were less than 1% when compared with the M1, M2, and M3 motions indicating a minimal impact from CC motion on lung dose during IMTMI. In the second experimental approach, we evaluated extreme respiratory motion 15 mm excursion in only the CC direction. We placed an ArcCHECK device on a commercial motion platform and delivered the clinical IMTMI plans of five patients. We compared, with and without motion, the dose volume histograms (DVHs) and mean lung dose calculated with the ArcCHECK-3DVH tool as well as GPR with 3%, 5%, and 10% dose agreements and a 3-mm constant distance to agreement (DTA). GPR differed by 11.1 ± 2.1%, 3.8 ± 1.5%, and 0.1 ± 0.2% with dose agreement criteria of 3%, 5%, and 10%, respectively. This indicates that respiratory motion impacts dose distribution in small and isolated parts of the lungs. More importantly, the impact of respiratory motion on the mean lung dose, a critical indicator for toxicity in IMTMI, was not statistically significant (p > 0.05) based on the Student's t-test. We conclude that most patients treated with IMTMI will have negligible dose uncertainty due to respiratory motion. This is particularly reassuring as lung toxicity is the main concern for future IMTMI dose escalation studies.

Development and Evaluation of a Thimble-Like Head Bolus Shield for Hemi-Body Electron Beam Irradiation Technique

Background: The hemi-body electron beam irradiation (HBIe<sup>–</sup>) technique has been proposed for the treatment of mycosis fungoides. It spares healthy skin using an electron shield. However, shielding electrons is complicated owing to electron scattering effects. In this study, we developed a thimble-like head bolus shield that surrounds the patient’s entire head to prevent irradiation of the head during HBIe<sup>–</sup>.Materials and Methods: The feasibility of a thimble-like head bolus shield was evaluated using a simplified Geant4 Monte Carlo (MC) simulation. Subsequently, the head bolus was manufactured using a three-dimensional (3D) printed mold and Ecoflex 00-30 silicone. The fabricated head bolus was experimentally validated by measuring the dose to the Rando phantom using a metal-oxide-semiconductor field-effect transistor (MOSFET) detector with clinical configuration of HBIe<sup>–</sup>.Results and Discussion: The thimble-like head bolus reduced the electron fluence by 2% compared with that without a shield in the MC simulations. In addition, an improvement in fluence degradation outside the head shield was observed. In the experimental validation using the inhouse- developed bolus shield, this head bolus reduced the electron dose to approximately 2.5% of the prescribed dose.Conclusion: A thimble-like head bolus shield for the HBIe<sup>–</sup> technique was developed and validated in this study. This bolus effectively spares healthy skin without underdosage in the region of the target skin in HBIe<sup>–</sup>.

CONTRIBUTION OF ORGAN-BASED TUBE CURRENT MODULATION TO THE REDUCTION OF LENS EXPOSURE DOSE IN HEAD 4D CT IMAGING: A PHANTOM STUDY.

The purpose of this study was to evaluate the effectiveness of organ effect modulation (OEM) in reducing the lens dose in 4D computed tomography (CT) of the head in volume-acquisition (NVA) mode. Six radiophotoluminescent dosemeters were placed on the head of a RANDO phantom. The doses absorbed by the organs and image noise change rate were determined. The lens doses without OEM (i.e. in the OEMoff case) were higher than those with the same target standard deviation and volume-computed tomography dose index (CTDIvol) as in the OEMoff case (p<0.01). The image noise change rate was 11%. OEM reduced the lens dose during head 4D CT imaging in the NVA mode by 18%. Furthermore, the feasibility of lens dose reduction while ensuring sufficient image quality was confirmed under the condition in which OEM was employed with the same CTDIvol as in the OEMoff case.

DOSE MEASUREMENT PRECISION OF AN RPLD-BASED EYE LENS DOSEMETER APPLICABLE TO THE MEDICAL SECTOR.

We demonstrate a practical calibration method and its applicability for a commercially available radiophotoluminescence dosemeter (RPLD), i.e. the GD-352M (AGC Techno Glass, Shizuoka, Japan) to eye lens dose monitoring, by performing the calibration according to the ISO recommendations. The calibration was then verified through a series of experiments. For verification of the derived calibration factor (1.21 ± 0.04, k = 1) of the RPLD, we performed standard irradiations in the ISO narrow series X-ray reference fields and the simulation measurements in the actual radiation fields in a hospital. The TLD-based commercially available dosemeters, DOSIRIS™ was also put on the ISO cylinder phantom and the RANDO phantom together with the GD-352M in the verification experiments. The personal dose equivalents Hp(3) obtained from the GD-352M and those obtained from the DOSIRIS™ were in good agreement with each other. Our results demonstrate the proper calibration of a commercially available RPLD that is applicable to the additional monitoring of the lens of the eyes for medical staff.

Skin Surface Dose for Whole Breast Radiotherapy Using Personalized Breast Holder: Comparison with Various Radiotherapy Techniques and Clinical Experiences.

Simple SummaryBreast immobilization with personalized breast holder (PERSBRA) is a promising approach to reduce the toxicity in the lungs and heart during whole breast radiotherapy. In this study, we designed PERSBRA with three different mesh sizes (large, fine and solid) and applied them on a Rando phantom. Hybrid, intensity modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) techniques were used to deliver a prescribed dose. The dose measurement with EBT3 film and TLD were taken on Rando phantom with no PERSBRA, large mesh, fine mesh, and solid PERSBRA for tumor doses and surface doses. This innovative PERSBRA provides another radiotherapy option for patients with left breast cancer.Purpose: Breast immobilization with personalized breast holder (PERSBRA) is a promising approach for normal organ protection during whole breast radiotherapy. The aim of this study is to evaluate the skin surface dose for breast radiotherapy with PERSBRA using different radiotherapy techniques. Materials and methods: We designed PERSBRA with three different mesh sizes (large, fine and solid) and applied them on an anthropomorphic(Rando) phantom. Treatment planning was generated using hybrid, intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques to deliver a prescribed dose of 5000 cGy in 25 fractions accordingly. Dose measurement with EBT3 film and TLD were taken on Rando phantom without PERSBRA, large mesh, fine mesh and solid PERSBRA for (a) tumor doses, (b) surface doses for medial field and lateral field irradiation undergoing hybrid, IMRT, VMAT techniques. Results: The tumor dose deviation was less than five percent between the measured doses of the EBT3 film and the TLD among the different techniques. The application of a PERSBRA was associated with a higher dose of the skin surface. A large mesh size of PERSBRA was associated with a lower surface dose. The findings were consistent among hybrid, IMRT, or VMAT techniques. Conclusions: Breast immobilization with PERSBRA can reduce heart toxicity but leads to a build-up of skin surface doses, which can be improved with a larger mesh design for common radiotherapy techniques.

Effective dose for kidney-ureter-bladder plain radiography, intravenous urography, and abdominal computed tomography scan: A phantom study

Abdominal colic pain or hematuria is suspected to be caused by urinary tract stones. Commonly used X-ray examinations include kidney-ureter-bladder plain radiography (KUB), intravenous urography (IVU), and abdominal computed tomography (CT). In this study, a high-sensitivity thermoluminescent dosimeter (TLD) was embedded in a Rando phantom to directly measure organ dose and evaluate effective dose. During each experiment, 139 TLD measurement points that cover almost all organs (as recommended by the ICRP 103 report) were examined. Red bone-marrow and remainder tissues have a high tissue weighting factor (0.12), and they are widely distributed. In the phantom, 34 TLDs and 31 TLDs were embedded in the red bone-marrow and remainder tissues to improve the accuracy and representativeness of organ doses. The detailed organ dose distributions for KUB, IVU, and abdominal CT are presented. The effective doses for KUB and IVU were 0.22 and 1.51 mSv, respectively, and those for two abdominal CTs were 8.21 and 9.27 mSv. This experiment presents a conversion factor of 0.0177 mSv·mGy−1 cm−1 for the abdominal CT examination, which differs from most of the conversion factors obtained through the Monte Carlo simulation method.

Impact of Different Beam Energies on The Incidence of Thyroid Cancer in Breast Cancer Radiotherapy

Purpose: During breast radiotherapy, the organs which are located out of the radiation field such as the thyroid are prone to secondary cancers. The present study aims to evaluate the risk of thyroid cancer in breast cancer radiotherapy in conventional and conformal radiation therapy.&#x0D; Materials and Methods: The data related to the thyroid dose in radiotherapy of breast cancer from the study by Behmadi et al. were used. In their study, the thyroid dose was measured on the Alderson RANDO phantom for four different breast cancer treatment plans and two photon energies. Using the Biological Effects of Ionizing Radiation (BEIR) VII model, the risk of thyroid cancer was estimated in conventional and conformal plans with two photon energies (6 and 15 MV) in breast cancer radiotherapy.&#x0D; Results: The Lifetime Attributable Risk (LAR) for thyroid cancer in the conventional technique was only 7.5% higher than that in the conformal technique. In the conventional treatment technique, LAR for thyroid cancer at 6 MV in all age groups was 17% higher than the 15 MV energy. However, the LAR for thyroid cancer in conformal technique at 15 MV energy was 50% higher than at 6 MV energy.&#x0D; Conclusion: Applying high energy for radiotherapy of breast cancer, in the conventional technique, could reduce the risk of thyroid cancer. But at high energies, the risk of thyroid cancer in the conformal technique is considerably higher than that at low energy. Therefore, it is suggested that the impact of energies be evaluated to reduce the risk of thyroid cancer in breast cancer radiotherapy.

Adaptive dual-energy algorithm based on pre-calibrated weighting factors for chest radiography

Objective. To develop a dual-energy (DE) algorithm with spatially varying weighting factors for material selection and noise suppression. Approach. Calibration step-phantoms, with overlapping slabs of solid water and bone with different thicknesses, were used to obtain the pre-calibrated material selection and noise reduction weighting factors. The Material selection weighting factors were calculated by finding a zero of contrast-to-noise-ratio (CNR) between regions with two overlapping materials and regions of only target material, while noise suppression weighting factors were determined by maximizing signal-to-noise ratio for overlapping regions. The pre-calibrated weighting factors were fitted with low and high energy radiograph of two Rando phantoms to create maps of material selection and noise suppression weighting factors, which used with DE algorithm and anti-correlated noise reduction (ACNR) algorithm to generate DE images. Three different implementations, including two different sizes of Rando phantoms and two different orientations (oblique and anterior-posterior), were investigated. Soft-tissue and bone only images of Rando phantoms were obtained with five combinations of DE algorithms and CNR, contrast, and noise values of selected regions of interest were compared to evaluate the performance of the novel method: simple log subtraction (SLS), SLS with uniform ACNR, adaptive DE (aDE), aDE with uniform ACNR, and aDE and adaptive ACNR (aACNR). Main results. Compared to SLS, the aDE algorithm demonstrated improved image quality in all three orientations. CNR increased with better contrast for both soft-tissue and bone images. Implementation of aACNR algorithm resulted in further reduction of image noise and improvements in CNR at the cost of contrast. However, aACNR algorithm showed better contrast compared to ACNR method. Significance. A novel DE algorithm was proposed, which showed improved material selection and noise suppression as compared to the conventional DE techniques and can be easily implemented in a clinical environment for real-time DE image generation.

Development and dosimetric verification of 3D customized bolus in head and neck radiotherapy

The commercial flat bolus cannot form perfect contact with the irregular surface of the patient’s skin, resulting in an air gap. The purpose of this study was to evaluate the feasibility of using a 3D customized bolus from silicone rubber. The silicone rubber boluses were studied in basic characteristics. The 3D customized bolus was fabricated at the nose, cheek and neck regions. The point dose and planar dose differences were evaluated by comparing with virtual bolus. The hardness, thickness, density, Hounsfield unit (HU) and dose attenuation of the customized bolus were quite similar to a commercial bolus. When a 3D customized bolus was placed on the RANDO phantom, it can significantly increase buildup region doses and perfectly fit against the irregular surface shape. The average point dose differences of 3D customized bolus were −1.1%, while the commercial bolus plans showed −1.7%. The average gamma results for planar dose differences comparison of 3D customized bolus were 93.9%, while the commercial bolus plans were reduced to 91.9%. Overall, A silicone rubber bolus produced the feasible dosimetric properties and could save cost compared to a commercial bolus. The 3D printed customized bolus is a good buildup material and could potentially replace and improve treatment efficiency.

Measurement of neutron equivalent dose in the thyroid, chiasma, and lens for patients undergoing pelvic radiotherapy: A phantom study

Radiotherapy is one of the most common methods for treating malignant diseases, whose ultimate goal is to deliver lethal doses to tumor cells. One of the unwanted consequences of radiotherapy is secondary radiation outside the treatment field, which imposes additional doses to healthy tissues and organs, specifically neutron doses, which we aim to evaluate. Therefore, this study aims to measure the fast neutron equivalent dose and the risk of secondary cancer in the thyroid, chiasm, and lenses in the treatment of the pelvic area. In this study, CR-39 detectors were used to measure the equivalent fast neutron dose in different sections of the RANDO Phantom (thyroid, chiasm, and lenses) and were irradiated by the energy of 18 MV on Varian Clinac 2100 C-D linear accelerator. CR-39 detectors were calibrated with predetermined doses by an Am–Be neutron source. Then, after etching and reading processes, the equivalent dose of fast neutrons was determined. According to the results, the fast neutron doses in the thyroid, right and left eye lenses, and chiasm were 0.613 ± 0.024, 0.835 ± 0.040, 0.866 ± 0.016, and 0.685 ± 0.045 mSv/Gy, respectively. Moreover, the secondary cancer risks in the unshielded organs are 0.004, 0.029, 0.030, and 0.025 for the thyroid, right and left eye lenses, and chiasm, respectively. In conclusion, the contribution of neutrons to the secondary doses in the out-of-field organs is significant and should not be ignored.

Examination of applicability of the ISO slab phantom as calibration phantom for the new ICRU 95 operational quantity personal dose

In this article, the proposal of the International Commission on Radiation Units and Measurements/International Commission on Radiological Protection (ICRU/ICRP), that the ISO slab phantom should continue to be used as a calibration phantom for the new ICRU Report 95 operational quantity personal dose should be legitimised by simulation and performance of experiments to determine backscatter factors on the ISO slab phantom and, in comparison, on an anthropomorphic Alderson Rando phantom. The scope of this work was restricted to the photon energy range of radiation qualities commonly used in x-ray diagnostics. For this purpose, a shadow-free diagnostic (SFD) ionisation chamber was used to measure backscatter factors for X radiation in the energy range of 24 keV to 118 keV. The Monte Carlo code MCNP 6.2 was used to validate measurement results on the ISO slab phantom. Additionally, the influence of varying the SFD position on the Rando phantom on the backscatter factor was determined. Since backscatter factors on the ISO slab phantom differ only up to 5% from those on the Rando phantom, it could be concluded that it is not necessary to develop a new phantom for calibrations in terms of personal dose. A position variation of the detector by a few centimeters on the surface of the Rando phantom causes similarly large deviations and thus alone represents an equally large uncertainty contribution in practical personal dosimetry than that arising from the dissimilarity of the real human body to the ISO slab phantom.

HyperArc VMAT stereotactic radiotherapy for locally recurrent previously-irradiated head and neck cancers: Plan quality, treatment delivery accuracy, and efficiency.

PurposeThis paper demonstrates the clinical feasibility and efficacy of HyperArc VMAT treatments for locally recurrent, locally advanced, or previously irradiated head and neck cancers treated with stereotactic radiotherapy (SRT).Materials/MethodsFirst, an anthropomorphic SRS head phantom from the MD Anderson's IROC credentialing laboratory containing a 1.9 cm diameter spherical target, including in vivo dosimetry system, was imaged, planned, and irradiated (25 Gy in 1 fraction) using HyperArc VMAT with a 6 MV flattening filter free (FFF) beam. Second, RANDO phantom was imaged, planned, and irradiated (35 Gy in 5 fractions) by generating eight HyperArc VMAT plans (4 right, 4 left neck tumors) at different anatomical locations (C1–C4). Average tumor volume was 21.7 cm3 up to 32.3 cm3. Distance to isocenter from the central marker of the Encompass device down to neck was 25.8 cm up to 28.0 cm and 24.3 cm up to 27.1 cm for left‐ and right‐sided neck tumors, respectively, and 9 cm from both lateral markers defined by the patient protection zone. Third, seven recurrent head and neck cancer patients with 80.3 cm3 tumors on average, and up to 159 cm3, were imaged, planned, and treated with 30–40 Gy in 5 fractions with HyperArc SRT. Plan quality, treatment delivery accuracy, and efficiency are reported herein.ResultsPhantom irradiation results met all the compliance requirements set forth by the IROC for HyperArc SRS treatment. For end‐to‐end RANDO phantom tests, a highly conformal target dose distribution with 50% isodose fall‐off within 5 mm from the surface of the target was obtained. Average beam modulation factor, beam‐on‐time, and overall treatment time were 2.9, 2.56 min, and 13.96 min with 99.1% pre‐treatment quality assurance pass rate for the 2%/2 mm gamma criteria, respectively. Immediately adjacent critical structures, such as the spinal cord (maximum, 3.9 Gy and 0.35 cm3 of cord, 3.7 Gy) and skin (maximum, 10.3 Gy and 10 cm3 of skin, 5.7 Gy), were spared. Similar results were found on the patient's HyperArc VMAT plans including highly conformal target coverage, sharp dose fall‐off, and low doses to the adjacent critical organs such as the spinal cord (< 5 Gy). Average perfect pitch couch correction was <1.5 mm and 2° in each direction. Average beam‐on‐time was approximately 3.21 min and treatments were completed within 15 min.ConclusionFor recurrent head and neck SRT treatments, HyperArc VMAT provided highly conformal dose distributions, rapid dose fall‐off, excellent sparing of adjacent critical organs, and highly accurate treatments that could be delivered down to the C4 vertebral level. This could potentially allow for delivery of HyperArc SRT to patients with glomus tumors as well to those who may not tolerate frame‐based SRS treatment. Clinical follow up of these patients is ongoing to confirm the therapeutic benefits of this novel treatment option.

Evaluation of a new acrylic-lead shielding device for peripheral dose reduction during cone-beam computed tomography.

To clarify the peripheral dose changes, especially in the eye lens and thyroid gland regions, using an acrylic-lead shield in cone-beam computed tomography (CBCT). The acrylic-lead shield consists of system walls and a system mat. The radiophotoluminescence glass dosemeter was set on the eye lens and thyroid gland regions on the RANDO phantom. The system mat was laid under the RANDO phantom ranging from the top of the head to the shoulders, and then, the system walls shielded the phantom's head. Additionally, the phantom was covered anteriorly with a band that had the same shielding ability as the system mat to cover the thyroid gland region. Protocols for CBCT imaging of the thoracic or pelvic region in clinical practice were used. The measurement was performed with and without the acrylic-lead shield. The dose to the eye lens region was reduced by 45% using the system wall. Conversely, the dose to the thyroid gland was unchanged. The use of the system mat reduced the dose to the thyroid gland region by 47%, and the dose to the eye lens was reduced by 22%. The dose to the eye lens region decreased to the background level using the system walls and mat. The newly proposed device using an acrylic-lead shield reduced the peripheral dose in CBCT imaging. Attention is focused on managing peripheral dose in image-guided radiation therapy. The peripheral dose reduction using the acrylic-lead shield is a new proposal in radiotherapy that has never been studied.

Dose Estimation Using Optically Stimulated Luminescence Dosimeter and EBT3 Films for Various Treatment Techniques in Alderson Rando Phantom and Estimation of Secondary Cancer Incidence for Carcinoma of Left Breast.

The aim of this study was to measure the dose to planning target and organ at risk (OAR) using Alderson Rando phantom for various treatment techniques in left breast radiotherapy and to estimate the secondary cancer incidence. Eleven different combinations of plans containing four techniques (three dimensional conformal radiotherapy, intensity-modulated radiation therapy [IMRT], volumetric modulated arc therapy [VMAT], and combination of 3DCRT and VMAT plans (HYBRID)) were created with 6 MV FF and 6 MV FFF (flattening filter and flattening filter-free) photon energies in phantom. Planned target volume and OAR doses in 23 different locations were measured using optically stimulated luminescence dosimeter (OSLD) and EBT3 films. Assuming the age of exposure as 30 years, lifetime attributable risk (LAR) was estimated based on excess absolute risk (EAR) models outlined in the Biological Effects of Ionizing Radiation VII report. Film showed maximum deviations of 6.15% with IMRT_C_FF plan when compared with treatment planning system (TPS). The maximum percentage difference of 1.7% was found with OSLD measurement when compared with TPS for VMAT_T_FFF plan. EAR estimation was done for all the OARs including target. The LARs for left lung, right lung, and right breast were evaluated. The maximum LAR values of 2.92 ± 0.14 were found for left lung with VMAT_C_FFF plans. This study shows that both OSLD and EBT3 films are suitable for dose measurements using Rando phantom. OSLD shows superior results when compared with films, especially with relatively larger distances. Maximum LAR values were found with VMAT_C_FFF plans. Considering the secondary cancer risk associated with the patients treated in the younger age group, it is suggested that in vivo dose estimation should be a part of treatment quality audit whenever possible.

Critical Factors of Dose Distribution in Breast Cancer Tomotherapy With Metallic Port Breast Tissue Expander: Image Correction, Delivery Mode, and Volume Impact.

Objectives: Breast reconstruction helps patients enhance their body image after mastectomy. Metallic ports in tissue expanders lead to dose attenuation during radiotherapy. Tissue expander volume shifts the metallic port position, possibly causing various dose alterations. This study aimed to evaluate the impact of the MAGNA-SITETM tissue expander volume on tomotherapy. Methods: Boluses and MAGNA-SITETM were placed on a Rando phantom to simulate the tissue expander under the pectoralis major. Computed tomography simulation images were transformed through replacing the electron density of (a) metallic artifact region only (Image metallic port) and (b) metallic port and artifact regions (Image Homo). Planning was calculated using fixed-beam and helical-mode techniques. Radiation was delivered with different volumes of the tissue expander. Results: Integrated 997 dose points were calculated. Planning with Image metallic port provided a calculated dose significantly closer to a realistic dose. The percentage of doses achieving the prescribed dose was significantly higher in the helical mode. In layer 2, the 100-mL tissue expander had a significantly lower measurement dose than all other volumes. Volume 150 mL had the highest increase in the measured dose difference from the plan dose at layer 2. Volume 250 mL had the highest percentage of measurement doses passing the 5% dose difference from plan dose. The coldest dose areas were noted in layers 1 and 2, especially in the metallic port–direct image mode. The average dose reduction of the measured cold areas was 6.03 ± 1.94%. Conclusion: Dose distribution was affected by the volume of the metallic port tissue expander. Tomotherapy with proper image heterogeneity correction and helical mode can reduce the attenuation from the metallic port. A tissue expander volume of 150 to 250 mL is suitable. Patients with high risk at the chest wall should be evaluated carefully to avoid underdosing. Radiation oncologists should closely cooperate with plastic surgeons to optimize treatment for each patient.

An Investigation of Exposure to the Eyes and Thyroid of Personnel Near to Patient in Abdominal Radiography: A Phantom Study

Abdominal radiography is beneficial in a variety of clinical situations. Prior to the introduction of multiplanar imaging, it was considered as the main examination for gastrointestinal pathology. However, the radiation dose received is considered high since it is equivalent to the dose of at least 75 chest radiographs. Personnel including staff or relatives may be required to assist patients in many conditions, increasing unnecessary radiation and the likelihood of radiation-induced cancer. The purpose of this study was to determine the radiation dose received by personnel when eyes and thyroid are exposed during abdominal radiography. The Rando and body phantoms were used to represent personnel and patients in this experimental approach. The dose was measured as entrance surface dose (ESD) by using TLD-100, which was positioned at the Rando phantom's eyes and thyroid. The study included a total of twenty exposures, five times at each of four distinct sites. The mean doses (eyes/thyroid in mGy) were (0.083/0.081), (0.090/0.087), (0.093/0.092), and (0.092/0.089), respectively, at locations 1, 2, 3, and 4. The results indicated that there was no correlation between organ and location affecting ESD measurement (p=0.960). There was no significant difference in dose between the two organs (p=0.355), with the mean difference in the eyes being 0.002 more than in the thyroid. The proximity of the eyes to the tube source contributed for the increased dose observed at the eyes. Though ESD was substantial for location pairings 1 vs. 3 (p=0.001) and 1 vs. 4 (p=0.015) owing to the anode-cathode phenomena. In conclusion, personnel should avoid the tube source and cathode region, since they give a greater dose of radiation, particularly when the personnel are closest to the patient and does not have eyes or thyroid protection.

Effect of cranium structure on dose distribution during intraoral radiography

ObjectivesThis study aimed to evaluate, the effect of the cranium structure on dose distribution by measuring the dose using the RANDO phantom for safe use of an X-ray unit during personal identification work at a large-scale disaster site. MethodsAs the subject, the head and neck of the RANDO Phantom (Alderson) containing a dry skull composed of a tissue-equivalent substance and having a shape similar to that of a living body were studied. With the body in the supine position, the air doses per second of irradiation time were measured for a total of six sections of the anterior, premolar, and molar teeth (molar on the left side) at a tube voltage of 60 kV and tube current of 10 mA during maxilla and mandible intraoral radiography. ResultsThe region having the highest exposure dose was the main X-ray direction in both the mandible and maxilla. Conversely, the dose tended to be low in the range from the temporal region to the occipital region on both sides of the horizontal plane, from the frontal region to the occipital region of the sagittal plane, and in the parietal region of the frontal plane. ConclusionsIt would be preferable to examine from the top of the body where the dose tends to decrease for all imaging sites.

Dosimetric evaluation of different planning techniques based on flattening filter-free beams for central and peripheral lung stereotactic body radiotherapy

This study aimed to dosimetrically compare and evaluate the flattening filter-free (FFF) photon beam-based three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) for lung stereotactic body radiotherapy (SBRT). RANDO phantom computed tomography (CT) images were used for treatment planning. Gross tumor volumes (GTVs) were delineated in the central and peripheral lung locations. Planning target volumes (PTVs) was determined by adding a 5 mm margin to the GTV. 3DCRT, IMRT, and VMAT plans were generated using a 6-MV FFF photon beam. Dose calculations for all plans were performed using the anisotropic analytical algorithm (AAA) and Acuros XB algorithms. The accuracy of the algorithms was validated using the dose measured in a CIRS thorax phantom. The conformity index (CI), high dose volume (HDV), low dose location (D2cm), and homogeneity index (HI) improved with FFF-VMAT compared to FFF-IMRT and FFF-3DCRT, while low dose volume (R50%) and gradient index (GI) showed improvement with FFF-3DCRT. Compared with FFF-3DCRT, a drastic decrease in the mean treatment time (TT) value was observed with FFF-VMAT for different lung sites between 57.09% and 60.39%, while with FFF-IMRT it increased between 10.78% and 17.49%. The dose calculation with Acuros XB was found to be superior to that of AAA. Based on the comparison of dosimetric indices in this study, FFF-VMAT provides a superior treatment plan to FFF-IMRT and FFF-3DCRT in the treatment of peripheral and central lung PTVs. This study suggests that Acuros XB is a more accurate algorithm than AAA in the lung region.

Patient-specific dose assessment using CBCT images and Monte Carlo calculations

Today, the use of Cone-Beam Computed Tomography (CBCT) is increasing rapidly in medical diagnosis, therefore evaluation of patient's dose is a very important issue in radiation protection of patients. This study aimed to evaluate the patient-specific dose using CBCT images. Since CBCT images only showed a part of the head and while, the total anatomical specification of the head should be defined for dose assessment, therefore the whole parts of the head were generated using the data of the Extended Cardiac-Torso (XCAT) reference phantoms and pseudo-images were created. Tissue densities were calculated by the voxel values of pseudo-images and were used as the input file of Gate8.2 Monte Carlo (MC) code. Also, the GIANO CBCT unit was simulated and the absorbed dose was calculated by the code. For verification of this method, Rando phantom with embedded thermoluminescence dosimeters (TLD) with different protocols was used. The results of MC calculations and TLD measurements were compared and statistical analysis was performed using IBM SPSS Statistics. The calculated effective dose values determined by CBCT images for three different Temporomandibular joint, Single-Arch, and Both-Arch protocols were found to be 87 ± 3 μSv, 64 ± 1 μSv, and 66 ± 2 μSv, and the results of thermoluminescence dosimetry were 86 ± 2 μSv, 57 ± 1 μSv, and 63 ± 3 μSv, respectively. There were no significant differences (P-Value>0.05) between the results of MC calculations using CBCT images and the results of TLD dosimeters. In this study, a method for patient-specific dose assessment using CBCT images was introduced. It was shown that the dose of patients with its specification can be evaluated by CBCT images with acceptable accuracy.

Skin Dosimetry with EBT3 Radiochromic Film in Radiotherapy of Parotid Cancer.

Background: Skin is a sensitive organ and should be spared in radiotherapy and irradiation of skin in radiotherapy can cause to acute and late skin effects such as erythema, desquamation, epilation, color change, or even necrosis. Objective: The aim of the present study is to do skin dosimetry in radiotherapy of parotid cancer using Gafchromic EBT3 radiochromic film. EBT3 radiochromic films were calibrated in 0.2-5 Gy dose range.Material and Methods: This is an experimental study in the field of radiotherapy physics. Treatment planning was performed on a RANDO phantom for treatment of parotid cancer by a clinical oncologist. Based on the treatment planning, the skin dose at various points in the overlapping region of right anterior-oblique and right posterior-oblique fields were measured using EBT3 radiochromic film.Results: The minimum and maximum skin doses in a fraction (with 2.0 Gy prescribed dose) were 0.50 Gy and 0.97 Gy, respectively. Based on these values, the total skin dose in 30 treatment fractions (for removed tumor) or in 35 treatment fractions (for unremoved tumor) was in the range of 15-33 Gy. Conclusion: Based on the skin dosimetry results of parotid cancer radiotherapy using EBT3 films, it is predicted that there will occur mild skin reactions and these reactions can be neglected due to being mild.