Introduction: The determination of accurate dose distribution is an issue of fundamental importance in radiotherapy, especially with regard to the fact that the human body is a HETEROGENEOUS medium. Therefore, the present study aimed to analyze the density and isodose depth profiles of 6 MV beam in a SP34 SLAB‐wooden dust (pine) ‐SP34 SLAB (SWS) HETEROGENEOUS PHANTOM.Materials and Methods: The density of SP34 SLAB, wooden dust of pine, and thoracic region of 10 patients were calculated using computed tomography (CT) images. The depths of isodose lines were measured for 6 MV beam on the CT images of the chest, SP34 SLAB PHANTOM, and SWS PHANTOM. Dose calculation was performed at the depths of 2, 13, and 21 cm in both PHANTOMs. Furthermore, patient-specific quality assurance (QA) was implemented using both PHANTOMs.Results: The mean densities of the lung, SP34 SLABs, and wooden dust were 0.29, 0.99, and 0.27 gm/cc respectively. The mean depths of different isodose lines in the SWS PHANTOM were found to be equivalent to those in actual patients. Furthermore, the percentage variation between the planned and measured doses was higher in the SWS PHANTOM as compared to that in the SP34 PHANTOM. Furthermore, the percentage variation between the planned and measured doses in patient‐specific QA was higher in the SWS PHANTOM as compared to that in the SP34 PHANTOM.Conclusion: As the findings indicated, the density and isodose depth profiles of the SWS PHANTOM were equivalent to those of the actual thoracic region of human.

Introdution: In advanced radiotherapy techniques such as intensity modulated radiation therapy (IMRT), the quality assurance (QA) is essential. This study aimed to compare the performance between GafchromicTM EBT3 film and Delta4® PHANTOM (2D and 3D) in HETEROGENEOUS chest PHANTOM using IMRT technique. Methods: In this experimental study, two IMRT plans (A and B) were prepared for radiotherapy of HETEROGENEOUS chest PHANTOM. EBT3 film and Delta4 were used for dose measurement in the PHANTOM. The 95% global gamma index accepted by the criteria of 3. 3% mm and the dose threshold 20% as the standard criteria were considered in this study. The gamma index of the film and Delta4 were acquired by the verisoft and Delta4 software, respectively. Results: The mean gamma index with standard criteria between treatment planning system (TPS) dose calculations and film measurements was 96. 95%, while it was equal to 97. 7% and 98. 45% between TPS calculations and 2D and 3D Delta4 cases, respectively. The mean 3D gamma analysis of the Delta4 with the given standard criteria was 0. 75% and 1. 5% higher than their 2D gamma analysis of the Delta4 and film, respectively. The mean gamma index value of film and Delta4 according to the plan B at the standard criteria was 0. 24% higher than plan A (97. 7% vs 97. 46%). Conclusion: Both film and Delta4 showed acceptable standard gamma index for two plans implemented on the chest PHANTOM using IMRT technique. So, according to the results of this study, it is concluded that in the centers where Delta4 is not available, EBT3 films with a simple HETEROGENEOUS PHANTOM can be an alternative method.

Background: In treating patients with radiation, the degree of accuracy for the delivery of tumor dose is recommended to be within ± 5% by ICRU in report 24. The experimental studies have shown that the presence of low-density inhomogeneity in areas such as the lung can lead to a greater than 30% change in the water dose data. Therefore, inhomogeneity corrections should be used in treatment planning especially for lung cancer. The usual methods for inhomogeneity correction are the Tissue-Air Ratio (TAR) method, the power low tissue-air ratio (Batho) method, and the Equivalent Tissue-Air Ratio (ETAR) method. But they are not able to calculate the dose with required accuracy in all cases. New and more accurate methods are based on Monte Carlo methods. They are able to account for all aspects of photon and electron transport within a HETEROGENEOUS medium. The focus of this paper is the application of MCNP (Monte Carlo N-Particle) code in radiotherapy treatment planning. Materials and methods: Some special test PHANTOMs were made of cork and Perspex instead of lung and normal tissue respectively (with electron densities relative to water equal to 0.2 and 1.137 respectively). Measurements were obtained using cobalt-60 radiation for four different fields. Then the results of RTAR, Batho and MCNP methods were compared to the measurements. Results: RTAR method has an error equal to 10% approximately. Also Batho method has an error especially in the low-density material. At least, MCNP method calculates correction factors very accurately. Its average error is less than 1% but it takes a long time to calculate the dose.Conclusion: Monte Carlo method is more accurate than other methods and it is currently used in the process of being implemented by various treatment planning vendors and will be available for clinical use in very near future

Introduction: In vitro dosimetric verification prior to patient treatment plays a key role in accurate and precision radiotherapy treatment delivery. Since the human body is a HETEROGENEOUS medium, the aim of this study was to design a HETEROGENEOUS pelvic PHANTOM for radiotherapy quality assurance. Material and Methods: A pelvic PHANTOM was designed using wax, pelvic bone, borax powder, and water mimicking different biological tissues. Hounsfield units and relative electron densities were measured. Various intensity-modulated radiotherapy (IMRT) plans were imported to the pelvic PHANTOM for verification and implemented on the Delta 4 PHANTOM. The quantitative evaluation was performed in terms of dose deviation, distance to agreement, and gamma index passing rate. Results: According to the results of the CT images of an actual patient, relative electron densities for bone, fat, air cavity, bladder, and rectum were 1. 335, 0. 955, 0. 158, 1. 039, and 1. 054, respectively. Moreover, the CT images of a HETEROGENEOUS pelvic PHANTOM showed the relative electron densities for bone, fat (wax), air cavity, bladder (water), and rectum (borax powder) as 1. 632, 0. 896, 0. 159, 1. 037, and 1. 051, respectively. The mean percentage variation between planned and measured doses was found to be 2. 13% within the tolerance limit (< ± 3%). In all test cases, the gamma index passing rate was greater than 90%. Conclusion: The findings showed the suitability of the materials used in the design of the HETEROGENEOUS PHANTOM. Therefore, it can be concluded that the designed PHANTOM can be used for regular radiotherapy quality assurance.

Background: The HETEROGENEOUS composition of the human body presents numerous tissue types and cavities with widely differing radiologic properties. The aim of the present work was to develop a low cost homogeneous and HETEROGENEOUS PHANTOM and the absorbed dose were measured by ionization chamber for different radiotherapy treatment techniques and compared with treatment planning system absorbed dose values.Materials and Methods: Present work deals with the fabrication of inexpensive homogeneous and HETEROGENEOUS tissue equivalent SLAB PHANTOM using polymethyl methacrylate, cork, teflon and perspex as a tissue, lung, spine and tumor simulating materials respectively. These PHANTOMs were used for different treatment techniques and full rotation techniques in SSD and SAD techniques.Results: The measured dose values for the different positions of both PHANTOMs were compared with the TPS values. The values are coinciding with each other and the percentage of deviation varies from 0.47 to 2.8 and 0.49 to 2.86 for HETEROGENEOUS and homogeneous PHANTOMs respectively.Conclusion: The measured values from ion chamber were compared with 3-D Plato Treatment Planning System (TPS). TPS values were also revealed the same result for homogeneous and HETEROGENEOUS PHANTOMs. The dose value of tumor is found to be gradually decreased with increase in arc angle. The dose value of spine is also found to be gradually decreased up to 90o and increased in 360o. Heterogeneity correction would definitely improve the cancer treatment of the heterogeneity region. This in-house PHANTOM is inexpensive, easy to handle and very useful one to verify the TPS calculation.

Introduction: Nowadays radiosensitive polymer gels are used as a reliable dosimetry tool for verification of 3D dose distributions. Special characteristics of these dosimeters have made them useful for verification of complex dose distributions in clinical situations. The aim of this work was to evaluate the capability of a normoxic polymer gel to determine electron dose distributions in different SLAB PHANTOMs in presence of small heterogeneities. Materials and Methods: Different cylindrical PHANTOMs consisting gel were used under SLAB PHANTOMs during each irradiation. MR images of irradiated gel PHANTOMs were obtained to determine their R2 relaxation maps. 1D and 2D lateral dose profiles were acquired at depths of 1 cm for an 8 MeV beam and 1 and 4 cm for the 15 MeV energy, and then compared with the lateral dose profiles measured using a diode detector. In addition, 3D dose distributions around these heterogeneities for the same energies and depths were measured using a gel dosimeter. Results: Dose resolution for MR gel images at the range of 0-10 Gy was less than 1.55 Gy. Mean dose difference and distance to agreement (DTA) for dose profiles were 2.6% and 2.2 mm, respectively. The results of the MAGIC-type polymer gel for bone heterogeneity at 8 MeV showed a reduction in dose of approximately 50%, and 30% and 10% at depths 1 and 4 cm at 15 MeV. However, for air heterogeneity increases in dose of approximately 50% at depth 1 cm under the heterogeneity at 8 MeV and 20% and 45% respectively at 15 MeV were observed. Discussion and Conclusion: Generally, electron beam distributions are significantly altered in the presence of tissue inhomogeneities such as bone and air cavities, this being related to mass stopping and mass scattering powers of HETEROGENEOUS materials. At the same time, hot and cold scatter lobes under heterogeneity regions due to scatter edge effects were also seen. However, these effects (increased dose, reduced dose, hot and cold spots) at deeper depths, are compensated with the contributions of scattered electrons. Our study showed that normoxic polymer gels are reliable detectors for determination of electron dose distributions due to their characteristics such as tissue equivalence, energy independence, and 2D and 3D dose visualization capabilities.

Introduction: Patient-specific quality assurance (PSQA) assumes a vital role in precise and accurate radiation delivery to cancer patients. Since the patient body comprises HETEROGENEOUS media, the present study aimed to fabricate a HETEROGENEOUS thoracic PHANTOM for PSQA. Material and Methods: HETEROGENEOUS thoracic (HT) PHANTOM was fabricated using rib cage madeup of bone equivalent material, kailwood to mimic lungs and wax to mimic various body parts. Physical density of all these materials used in PHANTOM fabrication was measured and compared with that of the corresponding part of actual human thorax. One beam was planned on the computed tomography (CT) images of PHANTOM and actual patient thorax region. Dose distribution in both the plans was measured and analyzed. Results: The estimated densities of heart, lung, ribs, scapula, spine, and chest wall tissues were 0. 804±, 0. 007, 0. 186±, 0. 010, 1. 796±, 0. 061, 2. 017±, 0. 026, 2. 106±, 0. 029 and 0. 739±, 0. 028 respectively in case of HT PHANTOM while 1. 038±, 0. 010, 0. 199±, 0. 031, 1. 715±, 0. 040, 2. 006±, 0. 019, 1. 929±, 0. 065 and 0. 816±, 0. 028 g/cc, respectively in case of actual human thorax region. The depths of isodose curves in HT PHANTOM were also comparable to the isodose curve’, s depths inreal patient. PSQA results were within ±, 3% for flat beam (FB) and flattening filtered free beam (FFFB) of 6 megavolts (MV) energy. Conclusion: Density and dose distribution pattern in HT PHANTOM were similar to that in actual human thorax region. Thus, fabricated HT PHANTOM can be utilized for radiation dosimetry in thoracic cancer patients. The materials used to develop HT PHANTOM are easily available in market at an affordable price and easy to craft.

Background: Boron neutron capture therapy (BNCT) is a binary radiotherapy combining biochemical targeting with neutron irradiation. However, monitoring the boron distribution is a fundamental problem in BNCT. Prompt gamma rays emitted by boron capture reaction can be used to address the issue. Materials and Methods: The general-purpose Monte Carlo toolkits Geant4 and MCNP were used for the simulations. A cubic PHANTOM with soft tissue was used to study the prompt gamma emission during BNCT. The Chinese hybrid PHANTOM with arbitrary tumors was constructed and used to acquire the 0. 478 MeV prompt gamma rays in BNCT. Tomographic images were reconstructed with the maximum likelihood expectation maximization (MLEM) algorithm. Results: Comparison between MCNP and Geant4 showed a similar gamma rays emission rate in soft tissue. Up to 30 gamma ray peaks were found in the simulation, and 0. 478 MeV prompt gamma ray from boron was clearly observed. The single brain tumor with variable diameter from 1 cm to 4 cm in the HETEROGENEOUS anthropomorphic PHANTOM was each time found to be recognizable in the reconstructed image. Furthermore, in a patient with four tumors, the variable distance between the source and the tumors leads to a neutron attenuation thus resulting in an inhomogeneous number of prompt gammas. Conclusion: The SPECT system for a HETEROGENEOUS PHANTOM in BNCT was simulated with Geant4. The results show that BNCT-SPECT is valid for the reconstruction of the boron capture interaction position for a HETEROGENEOUS patient.

Background: Accurate dose calculations in small beamlets and lung material have been a great challenge for most of treatment planning systems (TPS). In the current study, the dose calculaon accuracy of TiGRT TPS was evaluated for small beamlets in water and lung PHANTOM by comparison to Monte Carlo (MC) calculations.Materials and Methods: The head of Siemens Oncor-impression linac was simulated for 6 and 18 MV photon beams using MCNPX MC Code. The model was validated using measured percentage depth dose and beam profiles. Then, the validated model used for dose calculations for small beam lets in water as well as lung PHANTOMs. For treatment planning purposes, the lung PHANTOM was scanned and imported into the TPS, and then the percentage depth dose values were obtained from plans for small fields of 1×1, 2×2, 3×3 and 4×4 cm2 in water and lung PHANTOM.Results: For small fields in water PHANTOM, there was a good agreement between TPS and MC for 2×2 to 4×4 cm2 field sizes. Nevertheless, the depth doses in lung PHANTOM showed large discrepancies between TPS and MC calculations for points inside lung and lung-so4 tissue interfaces. The TPS underesmated the lung dose up to 67% and 110% for 6 and 18 MV beams compared to MC results.Conclusion: Our findings revealed that the TiGRT TPS was not able to account for lung inhomogeies in small beamlets. Besides, the TPS calculated depth doses were not accurate enough to be used for small beamlets used in IMRT of lung region.

Background: The free flattening filter (FFF) beam can affect the characteristics of the linac output such as the maximum dose depth, surface dose, dose in the fall-off area, and doses outside the field because the beam hardening effect does not occur in the FFF linac head. Therefore, the present study aimed to investigate the influence of the FFF beam on the dose distribution in an inhomogeneous PHANTOM using the EGSnrc/DOSXYZnrc Monte Carlo package. Materials and Methods: In the present study, an Elekta Infinity 10 MV photon beam equipped with a multileaf collimator Agility linear accelerator was used. Two types of virtual inhomogeneous PHANTOMs were built for percent depth doses (PDDs) and dose profiles measurement. The first PHANTOM comprised four layers: water (4 cm thickness), bone (2 cm thickness), lung tissue (5 cm thickness), and water (19 cm thickness). The second PHANTOM had a half-lung tissue SLAB and a half-bone SLAB (10 cm thickness) on the left side of the water. Results: The PDD curves in the inhomogeneous PHANTOM considerably decreased in the lung area for small exposure fields because the charged particle equilibrium was not achieved. The dose in the lung was higher than the dose in the water when the charged particle equilibrium was reached. Meanwhile, the dose in the bone is always lower than the dose in the water. Conclusions: The dose distribution of flattening filter (FF) and FFF beams in the inhomogeneous PHANTOM was the same in the small field of exposure. However, differences in dose distribution are increasingly apparent for larger field sizes.