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Due to the rapid development and further improvement of radiation treatment technologies oncologists have an opportunity to precisely deliver individual dose distributions to the tumor, minimizing the doses obtained by critical organs and healthy structures. For the correct and successful application of these complex methods of radiation therapy, it was necessary to enforce the requirements for the technical and dosimetric parameters of the radiotherapy equipment. The purpose of the research is to determine the magnitude of the possible error for patients’ positioning during their radiotherapy treatments using medical linear accelerators by modeling the impact of the patient’s body on the treatment couch. To determine the values of a possible error, the authors have considered the design and characteristics of a typical treatment couch, developed a model of the “average” patient’s body (phantom), which allowed changing the load to the treatment couch with a step of 1 kg. The position parameters of treatment couches were determined for the main types of localization of radiation therapy for malignant tumors: head and neck tumors, breast tumors and pelvic tumors. Numerical values of the treatment coach deviations from prescribed horizontal position were experimentally established for a load from 40 to 180 kg for a treatment couch used at the N.N. Alexandrov National Cancer Centre of Belarus. Based on the obtained experimental data, the necessity to correct the patient's treatment conditions at the stage of treatment planning were confirmed in order to ensure the delivery accuracy of individual dose distributions as required by the radiation therapy protocols. Authors stated that an analysis of the dependence of the deviations in the dose delivered to the patients on the deviation of the radiotherapy table from its horizontal position should be carried out for each radiotherapy table used in clinical practice. The development and implementation of a mechanism that will allow considering this information when choosing the parameters of the patient’s treatment session and prescribing the dose for any localization of malignant neoplasms is needed.

Introduction: According to the American Society of Radiation Oncology, all patients receive radiation therapy during their illness, where radiation is delivered by the medical linear accelerator (Linac). The aim of this study was to evaluate the quality assurance (QA) of the Linac in analyzing the used dose profile in the treatment of cancer tumors. Material and Methods: This experimental study was performed using Linac (synergy device type) at Baghdad Radiotherapy and Nuclear Medicine laboratories, Baghdad, Iraq. The Star Track device was used for the routine quality assurance of the Linac, using photon beam for the reference Dmax and source to surface distance of 100 cm. The Star Track consists of 453 vented parallel plate ionization chambers. Results: The flatness and symmetry of beams for the reference field size did not exceed from ±2%, as they were within the allowed range. Moreover, the penumbra region showed a change in value that did not exceed from ±0.2 cm. using the Star Track method; maximum differences in beam symmetry and beam flatness were measured at 0.76%±2% and 1.17%±2%, respectively. Moreover, the maximum difference in the penumbra region was estimated at 0.12±0.2 cm. Conclusion: The results indicated, the Star Track could successfully calculate the characteristics of dose profile during a time period of 2,500 ms, showing the superiority of this instrument over other verification devices.

The Korea Research Institute of Standards and Science (KRISS) established a new standard of the absorbed dose to water in LINAC X-ray beams. To confirm the equivalence of the new standard with other national metrology institutes (NMIs), a bilateral comparison study of the absorbed dose to water in high energy X-ray beams was performed between the KRISS and the National Metrology Institute of Japan (NMIJ). The comparison was made in-directly. Three transfer chambers were calibrated in the high energy X-ray beams by both laboratories and the calibration coefficients were compared. The average ratios of the calibration coefficients of the three transfer chambers obtained by the KRISS to those obtained by the NMIJ were 1.004, 1.006, 1.006, 1.007 for 6, 10, 15 and 18 MV X-ray beams, respectively. The calibration coefficients obtained at the KRISS were higher than those at the NMIJ but they were in good agreement within the expanded uncertainty of 1.0% (k = 2). The results of this study will be used as the evidence for the KRISS standard being comparable with those of other NMIs, temporarily, in the interim period up to finalizing a key comparison study, BIPM.RI(I)–K6 managed by the Consultative Committee for Ionizing Radiation.

Introduction: This study aimed to measure the neutron contamination of flattening filter (FF) and flattening filter-free (FFF) 10-MV photon beams delivered by the Elekta InfinityTM accelerator. Material and Methods: The photoneutron spectrum produced by the Linac head was evaluated using a Monte Carlo (MC) simulation. The geometry and composition of the head Linac material were modelled based on information obtained from the manufacturer. In this simulation, MC N-Particle Transport Code software (MCNP6) was utilized to model the Linac head and simulate the particle transport. Evaluation of neutron contamination was carried out for the Linac with FF and without it (i.e., FFF). In this regard, the FFF beam was built by removing the FF from the Linac components. The scoring plane, as the neutron spectra calculation area for FF and FFF beams, was placed 99 cm from the target. Results: The neutron type produced by the head Linac Elekta InfinityTM 10-MV photon mode was mostly thermal and fast. Although there were differences in the neutron intensity of FF and FFF beams, the type of neutrons produced by these two modes had the same energy. Based on the photoneutron reaction energy threshold, it can be concluded that the neutrons produced from the head Linac were the result of photoneutron interactions of high-energy photons with molybdenum-96 and tungsten-184 isotopes. Conclusion: The photoneutron quantity did not change for FF and FFF beams; however, a larger quantity of neutrons was produced in the FF beam.

In this paper, we illustrate the RF design and measurements of a C-band prototype structure for an Ultra High Dose Rate medical linac. (1) Background: FLASH Radiotherapy (RT) is a revolutionary new technique for cancer cure. It releases ultra-high radiation dose rates (above 100 Gy/s) in microsecond short pulses. In order to obtain a high dose in a very short time, accelerators with high-intensity currents (the order of 100 mA peak currents) have to be developed. In this contest, Sapienza University, in collaboration with SIT-Sordina IORT Technology spa, is developing a new C-band linac to achieve the FLASH regime. (2) Methods: We performed the RF electromagnetic design of the prototype of the C band linac using CST STUDIO Suite Code and the RF low power RF test at Sapienza University of Rome. The measurements of the field in the cavity have been done with the bead-pull technique. (3) Results: This device is a nine-cell structure operating on the π/2 mode at 5.712 GHz (C-band). We report and discuss the test measurement results on a full-scale copper prototype, showing good agreement with CST RF simulations. A tuning procedure has been implemented in order to ensure proper operating frequency and to reach a field profile flatness of the order of a few percent. (4) Conclusions: The prototype of a C-band linac for FLASH applications was successfully tested with low RF power at Sapienza University. The fabrication and ad hoc tuning procedures have been optimized and discussed in the paper.

This paper describes the design of an innovative linear accelerator image-guided radiosurgery (IGRS) device, which is based on a composite twofold rotary gantry structure. The paper discusses five aspects of the innovative device: its overall composition, the safety net space created by the accelerator radiation head as it rotates around the patient's longitudinal axis, the non-coplanar spherical coverage in the direction of the incidence angle for quasi-4π delivery, the structural features of the composite twofold rotary gantry, and the processes of treatment planning and implementation. It elaborates on the device's manufacturing feasibility, safety, effectiveness, accuracy, and efficiency. The conclusion is that this innovative device design holds significant development value and market promotion potential.

Background: Radiation-induced changes (RICs) post-stereotactic radiosurgery (SRS) critically influence outcomes in arteriovenous malformation (AVM) treatments. This study aimed to identify predictors of RICs, described the types and severity of RICs, and assessed their impact on patient's functional outcomes to enhance risk assessment and treatment planning for AVM patients., Methods: This retrospective study analyzed 87 AVM patients who underwent SRS at Hospital Kuala Lumpur between January 2015 and December 2020. RICs were identified through detailed magnetic resonance imaging evaluations, and predictive factors were determined using multiple logistic regression. Functional outcomes were assessed with the modified Rankin scale (mRS)., Results: Among the cohort, 40.2% developed RICs, with radiological RICs in 33.3%, symptomatic RICs in 5.7%, and permanent RICs in 1.1%. Severity categorization revealed 25.3% as Grade I, 13.8% as Grade II, and 1.1% as Grade III. Notably, higher Pollock-Flickinger scores and eloquence location were significant predictors of RIC occurrence. There was a significant improvement in functional outcomes post-SRS, with a marked decrease in non-favorable mRS scores from 8.0% pre-SRS to 1.1% post-SRS ( P = 0.031)., Conclusion: The study identified the eloquence location and Pollock-Flickinger scores as predictors of RICs post-SRS. The significant reduction in non-favorable mRS scores post-SRS underscores the efficacy of SRS in improving patient outcomes. Their results highlighted the importance of personalized treatment planning, focusing on precise strategies to optimize patient outcomes in AVM management, reducing adverse effects while improving functional outcomes., Competing Interests: There are no conflicts of interest., (Copyright: © 2024 Surgical Neurology International.)

Hippocampus protection, as an organ at risk in brain radiotherapy, might protect patients' quality of life. Prophylactic cranial irradiation (PCI) has been used traditionally in small cell lung cancer (SCLC) patients as it increases survival. This study aimed to discover the contributing parameters for a successful PCI with simultaneous protection of the hippocampus by using three different treatment machines. For this purpose, treatment plans were generated for 45 SCLC patients using three half-arcs in three linear accelerators (LINACs; Elekta Infinity, Synergy, and Axesse; Elekta Ltd, Stockholm, Sweden) with different radiation field sizes and multileaf collimator (MLC) leaf thickness characteristics. The prescribed dose was 25 Gy in 10 fractions. Thresholds for the hippocampus were calculated based on the Radiation Therapy Oncology Group 0933 dose constraints. The planning and treatment system templates were common to all three LINACs. Plan evaluation was based on the dosimetric target coverage by the 95% isodose, the maximum dose of the plan, the conformity index (CI), the degree of plan modulation (MOD), and the patient-specific quality assurance (QA) pass rate. The mean target coverage was highest for Infinity (97.3%), followed by Axesse (96.6%) and Synergy (95.5%). The mean maximum dose was higher for Synergy (27.5 Gy), followed by Infinity (27.0 Gy) and Axesse (26.9 Gy). Axesse plans had the highest CI (0.93), followed by Infinity (0.91) and Synergy (0.88). Plan MOD was lower for Synergy (2.88) compared with Infinity (3.07) and Axesse (3.69). Finally, patient-specific QA was successful in all Infinity plans, in all but one Synergy plan, and in 17/45 Axesse plans, as was expected from the field size in that treatment unit. Based on overall performance, the most favorable combination of target coverage, hippocampus sparing, and plan deliverability was obtained with the LINAC, which has the largest field opening and thinnest MLC leaves., Competing Interests: Human subjects: Consent was obtained or waived by all participants in this study. School of Medicine of Aristotle University of Thessaloniki issued approval 7149/28-6-2019. Patients who were eligible received written informed consent to store their anonymized data and publish the study results. If the patient could not give written informed consent (e.g., due to aphasia or altered consciousness state), it was asked for from the patient's legal representative. In the event that the patient withdraws their permission, the data will not be used. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Giakoumettis et al.)

Current online adaptive radiotherapy (oART) workflows require dedicated equipment. Our aim was to develop and implement an oART workflow for a C-arm linac which can be performed using standard clinically available tools. A workflow was successfully developed and implemented. Three patients receiving palliative radiotherapy for bladder cancer were treated, with 33 of 35 total fractions being delivered with the cone-beam computed tomography (CBCT)-guided oART workflow. Average oART fraction duration was 24 min from start of CBCT acquisition to end of beam on. This work shows how oART could be performed without dedicated equipment, broadening oART availability for application at existing treatment machines., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Our department has a research agreement with Elekta AB on the development of adaptive strategies for the CBCT-linac. The first author is working on a grant for this purpose, which is partly financed by Elekta AB. Elekta AB had no role in the preparation, review, or approval of the manuscript and the decision to submit the manuscript., (© 2024 The Author(s).)

• ASPS has the highest incidence of brain metastasis amongst sarcomas. • High prescription doses necessary to achieve local tumour control. • Retreatment of lesions with SRS local recurrence is effective. • SRS can be used for ASPS brain metastases that are not surgically accessible. Alveolar soft part sarcoma (ASPS) has the highest incidence of brain metastasis amongst sarcomas. There is a paucity of literature published focusing on radiation therapy for this condition. This is a single centre retrospective review of the treatment of three patients with 12 ASPS brain metastasis using single dose stereotactic radiosurgery (SRS). Five lesions were treated with low (<25 Gy) and seven with high (≥25 Gy) dose. Four lesions had a volume of >1.5 cm3 and were defined as large, while seven had a volume of ≤0.5 cm3 and were defined as small. The local tumor control as well as the clinical complication rates were studied. There was a statistically significant relation between treatment dose and tumor control rate. All large tumors treated with low dose recurred and required surgical removal within two months following SRS, while the large lesion treated with high dose recurred after 11 months. Five of the six small tumors treated with high doses were controlled, while the sixth required retreatment and was stable thereafter. No patient suffered from undue symptomatic radiation effects. The success rate following SRS for small ASPS metastases treated with high doses seems to be sufficient to justify the treatment. The short time for large tumor to recur, significant increase in tumor size requiring surgical removal of the tumors, makes low dose SRS unattractive. Based on this limited patient population, it seems that high dose SRS should be used for all ASPS brain metastases except for large tumors deemed surgically accessible. [ABSTRACT FROM AUTHOR]

Purpose/objective: Linear accelerator (LINAC) based stereotactic radiosurgery (SRS) for arteriovenous malformations (AVMs) is delivered with cone or multileaf collimators (MLCs), and favorable dosimetry is associated with reduced radionecrosis in normal brain tissue. This study aims to determine whether cones or MLCs has better dosimetric characteristics, to predict differences in toxicity. Methods: All patients treated for AVMs using LINAC SRS from 2003-2017 were examined retrospectively. Demographic data, volumes of normal tissue exposed to 12Gy (V12Gy[cc]) and 4Gy (V4Gy[cc]), maximal dose, and dose gradient were analyzed. Univariate and multivariate analyses were used to evaluate relationships between collimator type, dosimetric parameters, and toxicity. Propensity score matching was used to adjust for AVM size. Results: Compared to MLC, cones were independently associated with reduced V12Gy[cc] after propensity score matching (p=0.008) and reduced neurotoxicity (p=0.016). Higher V12Gy[cc] (p=0.0008) and V4Gy[cc] (p=0.002) were associated with increased neurotoxicity. Conclusions: Treating AVMs with cone-based SRS over MLC-based SRS may improve dosimetry and reduce toxicities. [ABSTRACT FROM AUTHOR]

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Purpose: Recently, high‐precision radiotherapy systems have been developed by integrating computerized tomography or magnetic resonance imaging to enhance the precision of radiotherapy. For integration with additional imaging systems in a limited space, miniaturization and weight reduction of the linear accelerator (linac) system have become important. The aim of this work is to develop a compact medical linac based on 9.3 GHz X‐band RF technology instead of the S‐band RF technology typically used in the radiotherapy field. Methods: The accelerating tube was designed by 3D finite‐difference time‐domain and particle‐in‐cell simulations because the frequency variation resulting from the structural parameters and processing errors is relatively sensitive to the operating performance of the X‐band linac. Through the 3D simulation of the electric field distribution and beam dynamics process, we designed an accelerating tube to efficiently accelerate the electron beam and used a magnetron as the RF source to miniaturize the entire linac. In addition, a side‐coupled structure was adopted to design a compact linac to reduce the RF power loss. To verify the performance of the linac, we developed a beam diagnostic system to analyze the electron beam characteristics and a quality assurance (QA) experimental environment including 3D lateral water phantoms to analyze the primary performance parameters (energy, dose rate, flatness, symmetry, and penumbra) The QA process was based on the standard protocols AAPM TG‐51, 106, 142 and IAEA TRS‐398. Results: The X‐band linac has high shunt impedance and electric field strength. Therefore, even though the length of the accelerating tube is 37 cm, the linac could accelerate an electron beam to more than 6 MeV and produce a beam current of more than 90 mA. The transmission ratio is measured to be approximately 30% ~ 40% when the electron gun operates in the constant emission region. The percent depth dose ratio at the measured depths of 10 and 20 cm was approximately 0.572, so we verified that the photon beam energy was matched to approximately 6 MV. The maximum dose rate was measured as 820 cGy/min when the source‐to‐skin distance was 80 cm. The symmetry was smaller than the QA standard and the flatness had a higher than standard value due to the flattening filter‐free beam characteristics. In the case of the penumbra, it was not sufficiently steep compared to commercial equipment, but it could be compensated by improving additional devices such as multileaf collimator and jaw. Conclusions: A 9.3 GHz X‐band medical linac was developed for high‐precision radiotherapy. Since a more precise design and machining process are required for X‐band RF technology, this linac was developed by performing a 3D simulation and ultraprecision machining. The X‐band linac has a short length and a compact volume, but it can generate a validated therapeutic beam. Therefore, it has more flexibility to be coupled with imaging systems such as CT or MRI and can reduce the bore size of the gantry. In addition, the weight reduction can improve the mechanical stiffness of the unit and reduce the mechanical load. [ABSTRACT FROM AUTHOR]

Due to the increase in the survival probability for patients treated with modern radiotherapy techniques to live enough for experimenting the late radiation effect, low dose outside the treatment volume becomes a concern. However, besides the absorbed dose, the beam quality outside the field edge should be taken into account. This work aimed at investigating the photon and electron fluence spectra outside the field edges for several small radiotherapy fields for determining the quality of the beams in order to better evaluate the secondary effect after modern radiotherapy treatments. Phase-space files of a 6 MV X-ray beam produced by a Varian iX linac for eight small fields of 0.7 × 0.7 cm2, 0.9 × 0.9 cm2, 1.8 × 1.8 cm2, 2.2 × 2.2 cm2, 2.7 × 2.7 cm2, 3.1 × 3.1 cm2, 3.6 × 3.6 cm2, and 4.5 × 4.5 cm2 and for the reference 10 × 10 cm2 field at SSD = 100 cm were generated using the BEAMnrc code. The photon and electron fluences in each field were calculated at 0.15, 1.35, and 9.85 cm water depth and several off-axis distances using FLURZnrc. The number of low-energy electrons between 1 and 10 keV at 2 cm outside the field edge increases by 60% compared to the central axis. Due to the relatively high linear energy transfer (LET) of these electrons, the results of this work should help to better evaluate the possible late effect of secondary radiation on healthy organs close to the tumor volume after radiotherapy treatment. We also observed high-energy electrons outside the field edge that are attributed to the leakage of the primary electron beam from the head of the linac. From a standpoint of radiological protection, these electrons should be taken into account when evaluating the dose delivered to the patient’s skin.

Three-dimensional printing technology has the advantage of facilitating the construction of complex three-dimensional shapes. For this reason, it is widely used in medical and radiological fields. However, few materials with high electron density similar to that of bone exist for fabricating a human phantom. In this study, commercially available filament materials were used with an FDM 3D printer to perform delivery quality assurance (DQA) and were evaluated for medical use. For the bone filament material, BaSO4 was synthesized in five ratios of 2%, 4%, 6%, 8%, and 10% with 40% PBAT and 50~58% PLA. The electron density for the 3D printing material fabricated was obtained using kV energy CT and compared with the electron density of human organs and bones. The radiation beam properties of the 3D printed structures were analyzed as films for treatment using a linear accelerator. As a result, by changing the infill density of the material, it was possible to produce a material similar to the density of human organs, and a homogeneous bone material with HU values ranging from 371 ± 9 to 1013 ± 28 was produced. The 3D printing material developed in this study is expected to be usefully applied to the development of a patient-specific phantom to evaluate the accuracy of radiotherapy.

The European Spallation Source (ESS) accelerator is composed of superconducting elliptical cavities. When the facility is running, the cavities are fed with an electric field from klystrons. Parameters of this field are monitored and controlled by the low-level radio frequency (LLRF) system. Its main goal is to keep the amplitude and phase at a given set point. The LLRF system is also responsible for the reference clock distribution. During operation, the cavities are periodically experiencing strain caused by the Lorentz force, while the high gradient of the electric field is generated for the beam acceleration. Even small changes in the physical dimensions of a cavity shift its resonance frequency. This phenomenon, called detuning, causes significant power losses. It is actively compensated by the LLRF control system, which can physically tune lengths of the accelerating cavities with stepper motors (slow, coarse-grained control) and piezo elements (active compensation during operation). This article describes the implementation and tests of the software supporting various aspects of the LLRF system and cavities management. The Piezo Driver management and monitoring tool is dedicated to a piezo controller device. The LO distribution application is responsible for configuration of the local oscillator. The cavity simulator tool was designed to provide access to properties of the hardware device, emulating behavior of the elliptical cavities. IPMI Manager Software was implemented to monitor the state of MicroTCA.4 crates, which are a major part of the LLRF system architecture. All applications have been created using the experimental physics and industrial control system (EPICS) framework and built in the ESS EPICS Environment (E3). [ABSTRACT FROM AUTHOR]

Introduction: Cancer patients receive radiation therapy (RT) as part of their treatment as monotherapy or as part of a combination treatment. Radiation therapy uses high-energy radiation such as photons and strong ions. Nanoparticles (NPs) are used for magnetic hyperthermia, which increases the efficacy of RT and generates heat to kill cancer cells by destroying their DNA. Material and Methods: Nanoparticles were prepared using the co-precipitation method and characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffractometer. Fifty-six male mice were housed under similar environmental conditions. The animals were injected into the right flank with 0.25 mL of 106 cells/mL Ehrlich tumor suspension. When tumors reached 5-10 mm in diameter, the mice were randomly divided into eight groups as follows: 1st group: used as the control group injected with 25 μL of phosphate buffer saline without treatment, 2nd group: injected with Fe3O4-NPs, 3rd group: injected with Fe2O3-NPs, 4th group: injected with methotrexate (MTX), 5th group: injected with MTX, Fe3O4, and Fe2O3-NPs, 6th group: as the 5th group with microwave hyperthermia, 7th group: as the 5th group then treated with high-energy photons, and 8th group: as the 5th group and exposed to electron beam therapy. Tumor volume and weight were measured after 15 days. Tumor apoptosis was studied using histopathology, and the tumor's side effects on the biological systems were investigated. Results: The results indicated that magnetic hyperthermia with microwave and linear accelerator treatment coupled with drugs was suitable for cancer treatment. A significant decrease in tumor size, tumor necrosis, and fibrosis was observed. Conclusion: It was found that Fe3O4 and Fe2O3-NPs coupled with MTX and exposure to photon and electron beam therapy and microwave radiation are the best methods for cancer treatment. [ABSTRACT FROM AUTHOR]

Background: Single-isocenter dynamic conformal arc (SIDCA) therapy is a technically efficient way of delivering stereotactic radiosurgery (SRS) to multiple metastases simultaneously. This study reports on the safety and feasibility of linear accelerator (LINAC) based SRS with SIDCA for patients with multiple brain metastases. Methods: All patients who received SRS with this technique between November 2017 and June 2019 within a prospective registry trial were included. The patients were irradiated with a dedicated planning tool for multiple brain metastases using a LINAC with a 5 mm multileaf collimator. Follow-up was performed every 3 months, including clinical and radiological examination with cranial magnetic resonance imaging (MRI). These early data were analyzed using descriptive statistics and the Kaplan–Meier method. Results: A total of 65 patients with 254 lesions (range 2–12) were included in this analysis. Median beam-on time was 23 min. The median follow-up at the time of analysis was 13 months (95% CI 11.1–14.9). Median overall survival and median intracranial progression-free survival was 15 months (95% CI 7.7–22.3) and 7 months (95% CI 3.9–10.0), respectively. Intracranial and local control after 1 year was 64.6 and 97.5%, respectively. During follow-up, CTCAE grade I adverse effects (AE) were experienced by 29 patients (44.6%; 18 of them therapy related, 27.7%), CTCAE grade II AEs by four patients (6.2%; one of them therapy related, 1.5%), and CTCAE grade III by three patients (4.6%; none of them therapy related). Two lesions (0.8%) in two patients (3.1%) were histopathologically proven to be radiation necrosis. Conclusion: Simultaneous SRS using SIDCA seems to be a feasible and safe treatment for patients with multiple brain metastases. [ABSTRACT FROM AUTHOR]

The scientific and technical status after renovation and restoration works of the linear electron accelerator LUE-75 of the Alikhanyan National Science Laboratory is presented, and some computed data on the effect of frequency, phase, and temperature changes in the high-frequency power supply path and the accelerating system on the stability of the electron beam energy, associated with the use of an additional accelerating station. [ABSTRACT FROM AUTHOR]

Modern lineer hızlandırıcı (Linak), kanserli hastaların tedavisi için yüksek enerjili X ışınları ve elektron demetleri üreten bir cihazdır. Radyasyon tedavisinin temeli madde ve radyasyon arasındaki etkileşime dayanır. Bu nedenle, radyasyon ve madde arasındaki etkileşim, radyasyon fiziği bilimini kanserin klinik tedavisine dönüştürür. Radyoterapide, dozimetrik ölçümler için en temel rölatif değerlendirmeler; X- ışınının derinliğe bağlı olarak değişimi gösteren yüzde derin doz (%DD) ve belli bir derinlikte ışının düzgünlüğünü ve simetrisini gösteren ışın profil (IP) ölçümlerden oluşmaktadır. %DD, belli bir derinlikte ölçülen radyasyon dozunun, maksimum doz derinliğinde ölçülen doza bölünmesiyle hesaplanır. Bu çalışmada, lineer hızlandırıcıda hasta öncesi başlangıç ölçümlerinde yapılabilecek ≤ 3 mm geometrik hatanın farklı alan boyutları için %DD ve farklı derinlikteki IP parametreleri üzerindeki etkisini görmek amaçlanmıştır. Ayrıca yapılabilecek geometrik hatanın iyon odası farkına göre değişimi araştırılmıştır. Sonuçlar, ölçümler sırasında yapılabilecek ≤3 mm geometrik hatanın, özellikle yüzde derin doz parametreleri ve küçük alan simetrisi üzerinde etkisinin oldukça fazla olduğunu göstermektedir.

Purpose: The concept of 4πc radiotherapy is a radiotherapy planning technique receiving much attention in recent times. The aim of this article is to disprove the feasibility of the 4π radiotherapy using a cantilever-type linear accelerator or any other external-beam delivery machines. Materials and Methods: A surface integral-based mathematical derivation for the maximum achievable solid angle for a linear accelerator was carried out respecting the rotational boundary conditions for gantry and couch in three-dimensional Euclidean space. The allowed movements include a gantry rotation of 0–2πc and a table rotation of πc/2 - 0 - 3πc/2) . Results: Total achievable solid angle by cantilever-type linear accelerator (or any teletherapy machine employing a cantilever design) is 1/r2 π ∫ - θ=0 π ∫ φ=0 (rSinθdφ). (rdθ) = 2πc, which is applicable only for the foot and brain radiotherapy where the allowed table rotation is 90°–0°–270°. For other sites such as pelvis, thorax, or abdomen, achievable solid angle as the couch rotation comes down significantly. Practically, only suitable couch angle is 0° by avoiding gantry–couch–patient collision. Conclusions: Present cantilever design of linear accelerator prevents achieving a 4π radian solid angle at any point in the patient. Even the most modern therapy machines like CyberKnife which has a robotic arm also cannot achieve 4π geometry. Maximum achievable solid angle under the highest allowable boundary condition(s) cannot exceed 2πc, which is restricted for only extremities such as foot and brain radiotherapy. For other parts of the body such as pelvis, thorax, and abdomen, the solid angle is reduced to 1/5th (maximum value) of the 4πc. To obtain a 4πc solid angle in a three-dimensional Euclidean space, the patient has to be a zero-dimensional point and X-ray head of the linear accelerator has a freedom to rotate in every point of a hypothetical sphere of radius 1 m. This article establishes geometrically why it is not possible to achieve a 4πc solid angle.

Stereotactic radiosurgery (SRS) is generally considered a substitute for cranial cavernous malformations (CCMs). However, prognostic factors for post-radiosurgery CCM rebleeding and adverse radiation effects have not been well evaluated, and the effect of timing and optimal treatment remains controversial. Therefore, this study evaluated prognostic factors for post-radiosurgical rebleeding and focal edematous changes in 30 patients who developed symptomatic intracranial hemorrhage due to solitary non-brainstem CCM and received linear accelerator (LINAC) SRS in a single medical center from October 2002 to June 2018. An overall post-radiosurgical annual hemorrhage rate with 4.5% was determined in this study. In addition, a higher marginal dose of >1600 centigray and earlier LINAC SRS intervention were correlated with a significantly lower post-radiosurgical annual hemorrhage rate. A lesion size larger than 3 cm3 and a coexisting developmental venous anomaly were significant risk factors for post-radiosurgical focal brain edema but mostly resulted in no symptoms and were temporary. This study demonstrated the efficacy of LINAC SRS in preventing CCM rebleeding and suggests that earlier radiosurgery treatment with a higher dose for non-brainstem symptomatic CCMs be considered.

Boron neutron capture therapy (BNCT) is a radiation therapy that selectively kills cancer cells and is being actively researched and developed around the world. In Korea, development of the proton linear accelerator-based BNCT system has completed development, and its anti-cancer effect in the U-87 MG subcutaneous xenograft model has been evaluated. To evaluate the efficacy of BNCT, we measured 10B-enriched boronophenylalanine (BPA) uptake in U-87 MG, FaDu, and SAS cells and evaluated cell viability by clonogenic assays. In addition, the boron concentration in the tumor, blood, and skin on the U-87 MG xenograft model was measured, and the tumor volume was measured for 4 weeks after BNCT. In vitro, the intracellular boron concentration was highest in the order of SAS, FaDu, and U-87 MG, and cell survival fractions decreased depending on the BPA treatment concentration and neutron irradiation dose. In vivo, the tumor volume was significantly decreased in the BNCT group compared to the control group. This study confirmed the anti-cancer effect of BNCT in the U-87 MG subcutaneous xenograft model. It is expected that the proton linear accelerator-based BNCT system developed in Korea will be a new option for radiation therapy for cancer treatment.

Control applications targeting fast industrial processes rely on real-time feasible implementations. One of such applications is the stabilization of an electron bunch arrival time in the context of a linear accelerator. In the past, only the electric field accelerating the electron bunches was actively controlled in order to implicitly stabilize the accelerated electron beam. Nowadays, beam properties are specifically measured at a target position and then stabilized by a dedicated feedback loop acting on the accelerating structures. This dedicated loop is usually referred to as a beam-based feedback (BBF). Following this, the control system of the electron linear accelerator for beams with high brilliance and low emittance (ELBE) is planned to be upgraded by the BBF, and the problem of implementing a designed control algorithm becomes highly relevant. In this work, we propose a real-time feasible implementation of a high-order H2 regulator based on a field-programmable gate array (FPGA). By presenting simulation and synthesis results made in hardware description language (HDL) VHDL, we show that the proposed digital solution is fast enough to cover the bunch repetition rates frequently used at ELBE, such as 100 kHz. Finally, we verify the implementation by using a dedicated FPGA testbench.

We synthesized an alcohol-based liquid scintillator (AbLS), and we implemented an auxiliary monitoring system with short calibration intervals using AbLS for particle therapy. The commercial liquid scintillator used in previous studies did not allow the user to control the chemical ratio and its composition. In our study, the chemical ratio of AbLS was freely controlled by simultaneously mixing water and alcohol. To make an equivalent substance to the human body, 2-ethoxyethanol was used. There was no significant difference between AbLS and water in areal density. As an application of AbLS, the range was measured with AbLS using an electron beam in an image analysis that combined AbLS and a digital phone camera. Given a range–energy relationship for the electron expressed as areal density, the electron beam range (cm) in water can be easily estimated. To date, no literature report for the direct comparison of a pixel image analysis and Monte Carlo (MC) simulation has been published. Furthermore, optical tomography of the inverse problem was performed with AbLS and a mobile phone camera. Analyses of optical tomography images provide deeper insight into Radon transformation. In addition, the human phantom, which is difficult to compose with semiconductor diodes, was easily implemented as an image acquisition and analysis system.

Abstract Background PRIMO is a dose verification system based on the general-purpose Monte Carlo radiation transport code penelope, which implements an accurate physics model of the interaction cross sections and the radiation transport process but with low computational efficiency as compared with fast Monte Carlo codes. One of these fast Monte Carlo codes is the Dose Planning Method (DPM). The purpose of this work is to describe the adaptation of DPM as an alternative PRIMO computation engine, to validate its performance against penelope and to validate it for some specific cases. Methods DPM was parallelized and modified to perform radiation transport in quadric geometries, which are used to describe linacs, thus allowing the simulation of dynamic treatments. To benchmark the new code versus penelope, both in terms of accuracy of results and simulation time, several tests were performed, namely, irradiation of a multi-layer phantom, irradiation of a water phantom using a collimating pattern defined by the multileaf collimator (MLC), and four clinical cases. The gamma index, with passing criteria of 1 mm/1%, was used to compare the absorbed dose distributions. Clinical cases were compared using a 3-D gamma analysis. Results The percentage of voxels passing the gamma criteria always exceeded 99% for the phantom cases, with the exception of the transport through air, for which dose differences between DPM and penelope were as large as 24%. The corresponding percentage for the clinical cases was larger than 99%. The speedup factor between DPM and penelope ranged from 2.5 ×, for the simulation of the radiation transport through a MLC and the subsequent dose estimation in a water phantom, up to 11.8 × for a lung treatment. A further increase of the computational speed, up to 25 ×, can be obtained in the clinical cases when a voxel size of (2.5 mm)3 is used. Conclusions DPM has been incorporated as an efficient and accurate Monte Carlo engine for dose estimation in PRIMO. It allows the concatenated simulation of the patient-dependent part of the linac and the patient geometry in static and dynamic treatments. The discrepancy observed between DPM and penelope, which is due to an artifact of the cross section interpolation algorithm for low energy electrons in air, does not affect the results in other materials.

Introduction: To study the effect of the International Atomic Energy Agency (IAEA) TRS-483 recommended beam quality correction factor in reference dosimetry and to examine the recommended field output correction factor for relative dosimetry of 6-MV flattening filter free (FFF) small fields, used in a Varian TrueBeam linear accelerator (LINAC). Material and Methods: The beam quality and field output correction for 6-MV FFF beams were adopted from the TRS-483 protocol. Monte Carlo (MC) simulation of the output factor was performed using the PENELOPE-based PRIMO software and compared with the TRS-483 corrected output factors. Two analytical anisotropic algorithm (AAA) models in the EclipseTM treatment planning system (TPS) were created; one with an output factor taken as the ratio of meter readings and one with an output factor obtained by multiplying the TRS-483 correction factor by the ratio of meter readings. Besides, box field and dynamic conformal arc (DCA) plans were created for both AAA models for verification and validation. The patientspecific quality assurances (QA) for ten different targets were performed, and deviations between the measured and TPS-calculated point doses in both models were examined. Results: Separate beam quality correction factors for FFF beams in the TRS-483 protocol only resulted in an improvement of 0.1% in reference dosimetry. The TRS-483 corrected output factor was in a better agreement with the MC-calculated output factor. For a patient-specific QA of DCA plans, the output factor-corrected AAA dose calculation algorithm showed a better agreement between the measured and simulated doses. Also, there was a smaller deviation (1.2%) for the smallest target of 0.23 cc (8 mm equivalent sphere diameter) used in this study. Conclusion: The field output factors for the LINAC small beams can be improved by incorporating the TRS-483 correction factors. However, the extent of improvement that can be expected depends on the source model of the calculation algorithm and how these well-generalized corrections are suitable for user beams and detectors. [ABSTRACT FROM AUTHOR]

Introduction: The current study aimed to compare linear accelerator-based three-dimensional conformal radiotherapy (Linac-3DCRT) technique with different techniques of the Radixact-X9 for the treatment of craniospinal irradiation (CSI). Material and Methods: Following a retrospective design, 22 CSI patients (Medulloblastoma) treated with Linac-3DCRT using the Novalis-Tx unit were selected for analysis. For each patient plan, additional sets of plans were generated using Helical, Direct-3DCRT, and Direct-intensity-modulated radiotherapy (Direct-IMRT) techniques of the Radixact-X9 unit. The dose prescription for brain planning target volume (brain PTV) and spine PTV were 36 Gy in 20 fractions and kept the same for all techniques. Planning time, patient setup time, homogeneity index (HI), and different dose-volume parameters for both PTV and organs at risk (OARs) were evaluated for comparison. Results: The Radixact-X9-Helical technique can generate a plan in a more comparable and better manner in respect of maximum and minimum doses for most of the organs. The Radixact-X9-Helical technique resulted in better PTV homogeneity in comparison with Linac-3DCRT, Radixact-X9-Direct-3DCRT, and Radixact-X9-Direct-IMRT. The values of HI were 3.57±0.77, 17.37±1.44, 8.15±1.02, and 8.62±0.98, respectively. Conclusion: Not only administration of the Radixact-X9-Helical treatment technique is easier, but also can generate a better homogeneous plan than other treatment techniques like 3DCRT and IMRT regarding different parameters for comparisons like dose-volume received by OARs, patient setup time, move isocenter, and many more. So it can be an integral part of the radiotherapy department, according to their clinical needs like shorter treatment time with good sparing of critical OARs. [ABSTRACT FROM AUTHOR]

Total ionizing dose (TID) effects induced by different photon sources are studied in MOS devices. The dose factor (DF), defined as the ratio between dose deposition in dosimeter and actual dose deposition in MOS-sensitive oxides (SOs), is estimated using Monte-Carlo simulations of energetic photons striking simple device structures. An effective TID approach is proposed to account for both the real ionizing dose depositions in small volumes and the charge yield. This method is applied to a silicon-on-insulator (SOI) technology using three photon sources: the usual ARACOR and 60Co sources, which deliver several tens of kiloelectron volt photons and ~1.25-MeV photons, respectively, and a third facility named ORIATRON, a 6-MeV electron linear accelerator that produces photons on a wide energy spectrum. This topic, investigated intensively in the literature a few decades ago, is revisited in the context of several evolutions including: new radiation sources, novel simulation tools, and device scaling, which all impact ionizing dose deposition in microsensitive volumes of current electronic technologies. Dedicated numerical simulations demonstrate the importance of taking into account the entire stack of materials in order to get the most accurate estimations of TID in the SO. Descriptions of the back-end-of-line (BEOL) layers (especially when the technology uses copper), the polysilicon gate, the Buried OXide (BOX) (for SOI devices), but also of the substrate and package are mandatory in these simulations, since dose enhancement and/or backscattered photons can be a significant source of TID variation in the gate oxide. Also the package lid composition and its thickness can be major TID contributors. The results show that the use of a prefilter with lead and aluminum can optimize ionizing dose deposition [ABSTRACT FROM AUTHOR]

The total ionizing dose (TID) sensitivity of mature and innovative technologies is investigated using both ionizing radiation experiments and Monte-Carlo simulations to discuss the potential of spectral photon radiation sources as an alternative for radiation effects studies. The impact of both technological and radiation test parameters on effective TID deposition is also discussed. All the layers struck by the incident radiation flux before reaching the targeted sensitive oxide are the major contributors of final ionizing dose deposits, rather than the actual sensitive oxide itself. Index Terms—ARACOR, back-end-of-line (BEOL), backside irradiation, Bremsstrahlung, bulk, CMOS, device packaging, dosimeters, front-end-of-line (FEOL), frontside irradiation, gamma, GAMRAY, LINAC, linear accelerator, metal–oxide–semiconductor field effect transistor (MOSFET), ORIATRON, radiation laboratory sources, silicon, silicon-on-insulator (SOI), SiO2, total ionizing dose (TID), X-rays. [ABSTRACT FROM AUTHOR]

Regulation and education of the professionals administering radiotherapy treatments in the linear accelerator varies across the EU. However, how different programme characteristics affect the level of competency of these professionals has never been studied before. This study also aimed to assess which are the least and most developed competencies in radiotherapy across the EU. An online questionnaire was distributed to academic staff teaching radiotherapy across the EU. Staff were asked to identify the characteristics of the course programmes and to classify the level of competency of graduates regarding linear accelerator tasks. Fifty respondents from 19 EU countries answered the questionnaire. The least developed competency theme was pharmacology followed by equipment quality assurance and management and leadership. The most developed competency was positioning and immobilisation , followed by radiotherapy treatment delivery and professional and ethical practice. Some competencies are developed at the same level across EU countries, while others vary considerably between member-states. Longer programmes, with more placements, and larger proportions of radiotherapy in the programme showed significant increase in the development of some competencies. Longer placements in skills labs was correlated with a decrease in competency. There is no harmonisation of radiotherapy eduction across the EU and the differences in programme characteristics are reflected in differences in competency levels of radiotherapy radiographers. This may hinder movement of professionals and create disparities in the level of care offered across the EU. Longer programmes, with longer clinical practice and adequate proportion of radiotherapy in the course are essential to ensure that these professionals are competent at similar levels across the EU and to ensure patient safety. [ABSTRACT FROM AUTHOR]

Radiotherapy (or radiation therapy) uses ionizing radiation to selectively kill cancer cells, especially for solid tumours. Like surgery, it is meant to be a 'local' treatment, although its beneficial systemic effects are being discovered. It is most commonly used in addition to surgery (adjuvant, e.g. breast), but its role in the neoadjuvant setting in combination with chemotherapy for some cancers (e.g. rectum) is also established. In early stages of cancer, it can be the definitive treatment, avoiding surgery and enabling organ preservation (e.g. larynx), while in late stages, it can provide excellent palliation (e.g. bone metastasis). Radiotherapy can be delivered at various energy levels (kiloVolts, megaVolts), with various subatomic particles (e.g. electrons, protons, and high-energy electromagnetic radiation). The traditional bulky equipment (e.g. linear accelerator) needs to be housed in an underground bunker and uses complex imaging to improve precision and avoid radiation to normal tissues. Fractionated regimens spanning several days reduce individual doses. Modern techniques using mobile devices (e.g. TARGIT-IORT) can deliver radiotherapy during surgery with the highest precision and immediacy. [ABSTRACT FROM AUTHOR]

Introduction: Human resources play a highly important role in providing health services. The aim of this study was to determine the human resources required for the linear accelerator sector at Reza Radiotherapy-Oncology Center. Methods: This applied analytical-descriptive study utilized human resources determination method based on workload indicator of staffing needs. Expert meetings were held to determine the components of workload and standard time. A survey was used to confirm the standard time of main activities, and interviews and personnel information system were used to determine the amount and factors related to available working time. Furthermore, management system and registries were used to determine the annual workload. The data were analyzed using the Excel and SPSS software version 19. Results: Seven factors related to the annually available working time of employees were identified. Annually available working time for employees was set at 806 hours. Patient preparation, treatment, surgery, and case completion were identified as the main activities. The results of workload index calculations showed that the accelerator sector had a shortage of three people. Conclusion: The results of this study showed that Reza Radiotherapy- Oncology Center is experiencing a shortage of professional staff in the linear accelerator sector. It seems that using the workload indicator of staffing needs method to determine and distribute the required human recourses is a necessary step for the optimal management of human recourses in specialized sectors. [ABSTRACT FROM AUTHOR]

Introduction: Stereotactic radiosurgery (SRS) has been increasingly employed to treat patients with intracranial metastasis, both as a salvage treatment after failed whole brain radiation therapy (WBRT) and as an initial treatment. "Several studies have shown that SRS may be as effective as WBRT with the added benefit of preserving neuro-cognition". However, some patients may have local failure following SRS for intracranial metastasis, defined as increase in total lesion volume by 25% after at least 3 months of follow up. Methods: The SRS registry, established by the Neuro point alliance (NPA) under the auspices of the American Association of Neurological Surgeons (AANS), was queried for patients with intracranial metastasis receiving SRS at the participating sites. Demographic, clinical symptoms, tumor, and treatment characteristics as well as follow up status were summarized for the cohort. A multivariable explanatory cox- regression was performed to evaluate the impact of each of the factors on time to local failure.at last follow-up. Results: A total of 441 patients with 1255 intracranial metastatic lesions undergoing SRS were identified. The most common primary cancer histology was non-small cell lung cancer (43.8%, n = 193). More than half of the cohort had more than 1 metastatic lesion (2–3 lesions: 29.5%, n = 130; more than 3 lesions: 25.2% (n = 111). The average duration of follow-up for the cohort was found to be 8.4 months (SD = 7.61). The mean clinical treatment volume (CTV), after adding together the volume of each lesion for each patient was 5.39 cc (SD = 7.6) at baseline. A total of 20.2% (n = 89) had local failure (increase in volume by > 25%) with a mean time to progression of 7.719 months (SD = 6.09). The progression free survival (PFS) for the cohort at 3, 6 and 12 months were found to be 94.9%, 84.3%, and 69.4%, respectively. On multivariable cox regression analysis, factors associated with increased hazard of local failure included male gender (HR 1.65, 95% CI 1.03–2.66, p = 0.037), chemotherapy at or before SRS (HR = 2.39, 95% CI 1.41–4.05, p = 0.001), WBRT at or before SRS (HR = 2.21, 95% CI 1.16- 4.22, p = 0.017), while surgical resection (HR 0.45, 95% CI 0.21–0. 97, p = 0.04) and immunotherapy (0.34, 95% CI 0.16–0.50, p = 0.014) were associated with lower hazard of local failure. Conclusion: Factors found to be predictive of local failure included higher RPA score and those receiving chemotherapy, while patients undergoing surgical resection and those with occipital lobe lesions were less likely to experience local failure. Our analyses not only corroborate those previously reported but also demonstrate the utility of a multi-institutional registry to advance real-world SRS research for patients with intracranial metastatic lesions. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated the possible radioprotective effect of Costus afer extract (CAE) on hematological and histopathological parameters of mice. Materials and Methods: Fifty-four male mice with mass between 37-43 g, 11-13 weeks old were used for this study. We divided the mice into six different groups containing nine animals, which were then further sub-divided into irradiated groups and un-irradiated groups. Animals received 250 mg/kg body weight extract of CAE by oral gavage for 6 days in addition to feeding and water ad libitum. Animals in the irradiated group were exposed to radiation at the Department of Radiotherapy and Oncology, Grey's Hospital using a linear accelerator. Blood samples were collected at 48-hour post-irradiation for the hematology test followed by histopathology examination of kidney and liver. Results: Our findings revealed that 3 Gy and 6 Gy dose of X-ray radiation caused a significant reduction in the white blood cell, packed cell volume, hemoglobin, neutrophils, lymphocytes, eosinophils, and platelet counts compared with the control group. However, the administration of CAE before irradiation significantly increased the mentioned parameters. There was no increase in red blood cell and monocyte among treated groups compared with the control. Histopathological changes in the kidney and liver sections revealed that no visible lesion in the pretreated mice. Hepatocytes seem to be within normal histological limits. Conclusions: This study concludes that CAE offered some protection against radiation-induced hematological alterations, but there was no significant improvement in the histopathological parameters. Thus, further studies are needed to validate its radioprotective effect on histopathological variables. [ABSTRACT FROM AUTHOR]

This paper presents the parameter optimization of a twelve-hole-slot-type magnetron based on a reverse engineering technique to improve a 6-MeV linear accelerator (LINAC) operation for fruit sterilization. The magnetron structural dimensions are measured by a coordinate measuring machine (CMM) that has tolerance on a dimension of 0.5 µm to analyze the resonant frequency with a desired operating point of the magnetron in the dominant mode. There are two methods of analysis using a proper parameter for the magnetron operation. The first method is mathematical model analysis of an equivalent resonant parallel circuit. The other is 3D-model drawing of the magnetron based on particle-in-cell (PIC) using computer simulation technology microwave studio (CST). The results are demonstrated by the position of the resonant frequency of each mode of operation, and the radius and tuner slot distance of a cavity within the structures of the magnetron cause a resonant frequency change. The suitable parameters of the voltage and magnetic field supply are desired to control a resonant frequency at 2.9982 GHz by using the Takagi–Sugeno fuzzy logic control (FLC) algorithm to control a resonant frequency at 2.9982 GHz. The results of the FLC algorithm application show that the LINAC can produce X-rays with a constant dose rate for an hour with a disturbance in the range of 38 to 42 °C temperature and 1 × 10−9 to 5 × 10−8 torr vacuum pressure. [ABSTRACT FROM AUTHOR]

Radyasyon Onkoloji Bölümlerinde Uzman doktor tarafından tedavi planlama bilgisayarında (TPS) hastanın bilgisayarlı tomografisi üzerinde üç boyutlu olarak çizilmiş hedefe, sağlık fiziği uzmanı tarafından farklı tedavi teknikleri kullanılarak planlama simulasyonları yapılır. Uzman doktor ve sağlık fiziği uzmanı ile planlama simulasyonları değerlendirilip, simulasyonlar arasından, toplam doz düşünülerek en uygun tedavi tekniğine ve bu tedavi tekniğine ait en uygun plana karar verilir. Karar verilen tedavi planı, belirlenen fraksiyon sayısında ve o fraksiyona ait doz da teknikerler eşliğinde lineer hızlandırıcıda hedef kitleye uygulanır. Burada bahsedilen farklı tedavi tekniklerinin uygulanışında, lineer hızlandırıcı hastanın etrafında dönerek ve lineer hızlandırcının sahip olduğu ışınlama alanını şekillendiren kolimatör yapısının sayesinde hedef kitleye uygulanır. Aynı tedavi içersinde lineer hızlandırıcılar birçok farklı alan (segmentler) yaratarak ve bu alanlara ait simulasyon bilgisayarının hesapladığı değişken dozlarla (MU) ve cihazın sahip olduğu farklı doz hızlarıyla (MU/Dk) ışınlamayı tekniker eşliğinde tamamlar. Sağlık fiziği uzmanı tarafından, günlük ya da haftalık olarak lineer hızlandırcıların sahip olduğu 6MV, 15MV gibi iyonize radyasyon enerjilerinin doğruluğu kontrol edilir ve gerekirse kalibre edilir. Kalibrasyon, referans dozda (100 MU) ve referans doz hızında (400MU/dk), TRS 398 protokollerinde belirtilen belirsizlikler, sıcaklık, basınç, polarite etkisi, iyon odası ve elektrometre kalibrasyon faktörü gibi düzeltmeler için hesaplanan bir çarpan dikkate alınarak tamamlanır. Radyasyon tedavisi alan başına daha küçük dozlar (MU) kullanılarak uygulandığında, cihazın anlık olarak verebildiği değişken doz hızları (100MU/dk ile 600MU/dk) arasında gerçekleşir. Bu sebeple tedavi simulasyon bilgisayarlarında planlanan doz ile lineer hızlandırıcıların performansına bağlı olarak verdiği radyasyon dozu arasında farklılıklar ortaya çıkabilmektedir. Bu farklılık kümülatifte, cihazın hastaya planlandığından daha az ya da daha çok doz verilmesine sebep olacağından, istenmeyen bir durumdur. Örneğin hastaya planlanandan az doz verilmesi tedavinin etkinliğini azaltacaktır. Cihazın verdiği doz, planlanandan daha yüksek olduğunda, tedavinin istenmeyen yan etkilerini (ödem ve cilt yan etkileri gibi) arttıracak ve hastanın konforunu düşürecektir. Bu nedenle cihazın hastaya verdiği dozun planlanan doza yüksek hassasiyetle uyması hayati önem taşımaktadır. Bu çalışmada lineer hızlandırıcıların sahip olduğu farklı doz hızlarındaki ışınlamaların tedavi kalitesine etkisi ve küçük dozlarda (MU'larda) verilen birçok alanda (segmentte), kümülatifte cihazın doz doğrusallığına bakılarak tedavi kalitesine etkisi değerlendirilmesi amaçlanmıştır. [ABSTRACT FROM AUTHOR]

Background: Thermoplastic immobilization devices are used to position the patient on the table in order to correctly reposition the patient during treatment courses. Objective: The Purpose of this work is investigating the degradation of surface dose and the dose distribution in the build-up region for photon beams associated with immobilization devices using Gafchromic films. Materials and Methods: After heating, these masks are stretched and fitted over the considered location of body before treatment simulation for insuring the reproducibility of patient position during treatment fractions. In this research, dosimetry was carried out using Gafchromic EBT3 film and three kinds of thermoplastic masks (Orfit with thickness 2.2mm, holes diameter 2.5mm, Orfit with thickness 2mm, holes diameter 1mm, and Klarity mask, thickness 2mm, holes diameter 3mm). Measurements were made with and without the mask materials on the surface of the Perspex phantom for 6 and 15 MV X-ray beams of a LINAC machine. Results: The results showed that surface dose increases 2.1 to 6.7 times and 2 to 3.9 times than the surface dose in the open field for 15 MV and 6 MV photons, respectively. According to the obtained results from the Analyses of Variances (ANOVA) test , it is defined that there is a significant difference in surface dose among three kind of thermoplastic masks (χ2 = 49.78 and df = 3 and P0.05). Conclusion: According to the results, Klarity mask is more acceptable immobilization device when compared with other masks in the test.