Radiotherapy Linear Accelerator Research Articles

9375 Acth-Producing Pituitary Carcinoma in the Falx Cerebri and Other Unusual Locations

Abstract Disclosure: J.E. Esquivel Vargas: None. A. Cob Guillén: None. A.B. Santos Rojo: None. A. Hong Lo: None. ACTH-producing Pituitary Carcinoma in the Falx Cerebri and other unusual locations Background: Pituitary carcinoma is a condition defined by metastasis of a pituitary tumor to a distant location. Pituitary carcinomas are very rare and account for approximately 0.12% of adenohypophyseal tumors (1). Clinical case: We present a case of a 29-year-old female who was followed up in our Endocrinology Department. Past medical history included the diagnosis of Cushing Disease and transsphenoidal tumor resection at 12 years of age, followed by transcranial resection two years later because of persistently elevated adrenocorticotropic hormone (ACTH). Despite the surgical management, the patient persisted with increased ACTH and hypercortisolism, so bilateral adrenalectomy was performed a year later. Two years after the procedure, the patient presented with a newly diagnosed pituitary macroadenoma, so the diagnosis of Nelson Syndrome was made. Linear accelerator radiotherapy was given, which reduced the size of the tumor. Later, multiple imaging studies showed multiple lesions on the falx cerebri, posterior clinoid process, retroclival region, cerebellopontine angle, pterygopalatine fossa, infratentorial region, and posterior ethmoidal cells. Biopsy and immunohistochemistry of the falx cerebri lesions described ACTH-producing pituitary adenocarcinoma. Treatment was given with intramuscular octreotide, dabrafenib, and trametinib. Despite persistently elevated ACTH levels, the patient has since remained clinically stable, without new development or worsening of symptoms. Conclusion: There are 3 unique aspects of our case. First, we reported an unusual presentation of this disease, because the patient in our case was a female with an early age of onset, in contrast with the reported literature. Second, this is the first reported case demonstrating pituitary carcinoma in the falx cerebri. Third, the prognosis of pituitary carcinoma is very poor, and mortality is extremely high, however, the patient in our case has been followed up for 7 years since the diagnosis of the metastatic lesions and has remained clinically stable.

Challenges and Considerations in Transitioning from Cobalt-60 to Linear Accelerators for Radiotherapy in LMICs Healthcare Settings: A Case Study of Nepal.

Nepal's move from Cobalt-60 machines to modern linear accelerators in radiation therapy presents significant challenges. Infrastructure limitations demand substantial investments for facility upgrades, particularly in retrofitting existing cobalt-60 bunkers and ensuring stable power supplies. The scarcity of skilled personnel underscores the need for comprehensive education initiatives and international collaborations. Regulatory compliance requires the establishment of robust frameworks, emphasizing the urgency of an independent regulatory authority. Collaborations with international institutions offer expertise and resources crucial for capacity building. Financial constraints necessitate innovative financing models to mitigate procurement and maintenance costs. Unforeseen circumstances, exemplified by the Covid-19 pandemic, highlight the importance of adaptability in implementation strategies. Despite challenges, Nepal's transition signifies an opportunity to enhance cancer care, emphasizing the need for a tailored, multidimensional approach addressing infrastructure, workforce, regulatory, financial, and collaborative aspects.

3D printed heterogeneous paediatric head and adult thorax phantoms for linear accelerator radiotherapy quality assurance: from fabrication to treatment delivery.

This study aims to design and fabricate a 3D printed heterogeneous paediatric head phantom and to customize a thorax phantom for radiotherapy dosimetry. 
Approach: This study designed, fabricated, and tested 3D printed radiotherapy phantoms that can simulate soft tissue, lung, brain, and bone. Various polymers were considered in designing the phantoms. Polylactic acid+, nylon, and plaster were used in simulating different tissue equivalence. Dimensional accuracy, and CT number were investigated. The phantoms were subjected to a complete radiotherapy clinical workflow. Several treatment plans were delivered in both the head and the thorax phantom from a simple single 6 MV beam, parallel opposed beams, and five-field intensity modulated radiotherapy (IMRT) beams. Dose measurements using an ionization chamber and radiochromic films were compared with the calculated doses of the Varian Eclipse treatment planning system (TPS). 
Main results: The fabricated heterogeneous phantoms represent paediatric human head and adult thorax based on its radiation attenuation and anatomy. The measured CT number ranges are within -786.23 ± 10.55, 0.98 ± 3.86, 129.51 ± 12.83, and 651.14 ± 47.76 HU for lung, water/brain, soft tissue, and bone, respectively. It has a good radiological imaging visual similarity relative to a real human head and thorax depicting soft tissue, lung, bone, and brain. The accumulated dose readings for both conformal radiotherapy and IMRT match with the TPS calculated dose within ±2% and ±4% for head and thorax phantom, respectively. The mean pass rate for all the plans delivered are above 90% for gamma analysis criterion of 3% / 3 mm.
Significance and conclusion: The fabricated heterogeneous paediatric head and thorax phantoms are useful in Linac end-to-end radiotherapy quality assurance based on its CT image and measured radiation dose. The manufacturing and dosimetry workflow of this study can be utilized by other institutions for dosimetry and trainings. &#xD.

Feasibility of determining external beam radiotherapy dose using LuSy dosimeter.

Radiation dose measurement is an essential part of radiotherapy to verify the correct delivery of doses to patients and ensure patient safety. Recent advancements in radiotherapy technology have highlighted the need for fast and precise dosimeters. Technologies like FLASH radiotherapy and magnetic-resonance linear accelerators (MR-LINAC) demand dosimeters that can meet their unique requirements. One promising solution is the plastic scintillator-based dosimeter with high spatial resolution and real-time dose output. This study explores the feasibility of using the LuSy dosimeter, an in-house developed plastic scintillator dosimeter for dose verification across various radiotherapy techniques, including conformal radiotherapy (CRT), intensity-modulated radiation therapy (IMRT), volumetric-modulated arc therapy (VMAT), and stereotactic radiosurgery (SRS). A new dosimetry system, comprising a new plastic scintillator as the sensing material, was developed and characterized for radiotherapy beams. Treatment plans were created for conformal radiotherapy, IMRT, VMAT, and SRS and delivered to a phantom. LuSy dosimeter was used to measure the delivered dose for each plan on the surface of the phantom and inside the target volumes. Then, LuSy measurements were compared against an ionization chamber, MOSFET dosimeter, radiochromic films, and dose calculated using the treatment planning system (TPS). For CRT, surface dose measurement by LuSy dosimeter showed a deviation of -5.5% and -5.4% for breast and abdomen treatment from the TPS, respectively. When measuring inside the target volume for IMRT, VMAT, and SRS, the LuSy dosimeter produced a mean deviation of -3.0% from the TPS. Surface dose measurement resulted in higher TPS discrepancies where the deviations for IMRT, VMAT, and SRS were -2.0%, -19.5%, and 16.1%, respectively. The LuSy dosimeter was feasible for measuring radiotherapy doses for various treatment techniques. Treatment delivery verification enables early error detection, allowing for safe treatment delivery for radiotherapy patients.

Improving Management and Compliance of Radiation Therapy Linear Accelerator Quality Assurance Program With Automated Tracking Tools

PurposeWhile Quality Assurance (QA) is crucial in radiation oncology departments, substantial efforts are required to monitor and ensure compliance to high standards. This work aims to analyze the impact of implementing a centralized and automated tracking dashboard on compliance and variance observed in radiotherapy QA results for linear accelerators. MethodsThe study was performed in a large academic center with 7 linear accelerators. In-house QA Dashboard was implemented in 2019 with design specifications including automated monitoring and visualization of QA progress, ease of use and accessibility, ease of integration, adaptability to new technologies, and facilitation of automated reminders. Monthly quality assurance data was collected between 2016 and 2022 to analyze compliance pre- and post-dashboard implementation. Compliance was characterized as the percentage of tests completed on time. In addition, variance trends for linear accelerator dosimetry measurements and imaging were analyzed over seven years. ResultsIn total, 76, 066 records were analyzed. Out of these records, 73,187 QA measurements were completed on time. Overall QA compliance increased from 75% in 2016 to >99% in 2019 following successful implementation of the QA Dashboard. The main improvement was observed for tests that were implemented more recently, e.g., imaging QA and formal recording of daily QA review by physicists. The coefficient of variation was reduced by approximately a factor of two for imaging QA following the implementation of the QA Dashboard. For recorded dosimetry measurements, no substantial change in variance was observed. ConclusionsImplementation of the QA Dashboard resulted in a distinct increase in QA compliance. Reduction in the variance in QA measurements was observed for all imaging modalities. These findings demonstrate high impact of automated tracking QA tools on improved compliance and accuracy of QA.

ПРИМЕНЕНИЕ НОВЫХ МЕТОДИК ЛУЧЕВОЙ ТЕРАПИИ В ЛЕЧЕНИИ РАКА МОЛОЧНОЙ ЖЕЛЕЗЫ И РАКА ПРЕДСТАТЕЛЬНОЙ ЖЕЛЕЗЫ В РАМКАХ РЕАЛИЗАЦИИ НАЦИОНАЛЬНОГО ПРОЕКТА «ЗДРАВООХРАНЕНИЕ» В НОВОСИБИРСКОЙ ОБЛАСТИ

In 2023, within the framework of the national project “Healthcare”, two state of the art linear accelerators for radiation therapy were put into operation at the State Budgetary Healthcare Institution of the Novosibirsk Region “Novosibirsk Regional Clinical Oncology Dispensary”: Elekta Versa HD and Elekta Infinity. Thanks to the new equipment and the new dosimetric planning system, it became possible to use modern radiation therapy technologies in the Novosibirsk Region. The use of the new equipment is becoming especially relevant for the treatment of leading tumor diseases – breast cancer in women and prostate cancer in men.

IPEM topical report: results of a 2022 UK survey on the use of linac manufacturer integrated quality control (MIQC)

In recent years Radiotherapy linear accelerator (linac) vendors have developed their own integrated quality control (QC) systems. Such manufacturer-integrated-quality-control (MIQC) has the potential to improve both the quality and efficiency of linac QC but is currently being developed and utilised in the absence of specific best-practice guidance. An Institute of Physics and Engineering in Medicine working party was commissioned with a view to develop guidance for the commissioning and implementation of MIQC. This study is based upon a survey of United Kingdom (UK) radiotherapy departments performed by the working party. The survey was distributed to all heads of radiotherapy physics in the UK and investigated availability and uptake, community beliefs and opinions, utilisation, user experience and associated procedures. The survey achieved a 95% response rate and demonstrated strong support (>95%) for its use and further development. MIQC systems are available in 79% of respondents’ centres, and are in clinical use in 66%. The most common MIQC system was Varian MPC, in clinical use in 58% of responding centres, with CyberKnife AQA\\E2E in 11%, TomoTherapy TQA in 8% and no users of Elekta Machine QA. A majority of users found their MIQC to be easy to use, reliable, and had five or more years of experience. Most users reported occasions of discrepancy in results between MIQC and conventional testing, but the majority considered this acceptable, indicating a false reporting frequency of quarterly or less. MIQC has shown value in preventative maintenance and early detection of machine deviations. There were inconsistent approaches in the utilisation and commissioning tests performed. Fewer than half of users perform QC of MIQC. 45% of responders have modified their QC processes with the introduction of MIQC, via replacement of conventional tests or reduction in their frequency. Future guidance is recommended to assist in the implementation of MIQC.

Editorial

Dear Readers, It is with great pleasure that we introduce the much anticipated first issue of the Armenian Journal of Health & Medical Sciences (AJHMS) in 2023. As always, we gather in one issue a wide variety of medical disciplines including review articles, original research, case reports and traditionally for our journal we reserve space for special and historical articles. In their comprehensive review Antonyan et al. discuss an important aspect of quality assurance of contemporary linear accelerators in radiation therapy. It is followed by another short review by Muradyan L. et al. on radiomodification in radiation therapy. In the next section dedicated to special articles, we present an important work by Nanushyan et al. who present a timely update on recent developments of the state-initiated reforms and future perspectives of the continuous professional development system among healthcare workers in Armenia. Another special topic is presented by Vardanyan’s overview on Yerevan’s green infrastructure, history of its creation and current problems. In an article by Muradyan A. et al. patients with intergluteal pilonidal disease were divided into two groups to compare two different surgical techniques, drawing conclusions on cost-effectiveness and speed of recovery.

Quality Control Analysis of Linear Accelerator Radiotherapy Device in the Department of Radiotherapy at Pasar Minggu District Hospital

Radiation accidents pose a significant risk, often stemming from inadequate calibration of radiation output, procedural lapses, and faults in radiation monitoring systems. Addressing these risks is pivotal, particularly in radiotherapy, where the precise functioning of linear accelerator (Linac) devices is crucial. This study delves into the quality control procedures applied to the Linac radiotherapy device within the Department of Radiotherapy at Pasar Minggu District Hospital. Drawing upon the renowned reference standards set by the AAPM Task Group 142 and BAPETEN Regulation No. K2N.2/MT-08, this research, conducted in November 2022, rigorously evaluated the mechanical, dosimetry, and safety aspects of the Linac device. The examination encompassed critical elements, including gantry angles, optical distance indicators, laser precision, collimator angles, light field size, and photon and electron beam outputs. Safety features such as door interlocks, audiovisual indicators, and radiation alert systems were scrutinized. The analysis reveals a reassuring finding: the Linac device at Pasar Minggu District Hospital adheres commendably to tolerance limits specified by reference standards across all measured parameters, indicating robust performance in mechanics, dosimetry, and safety. This meticulous quality control regimen has proven highly effective in ensuring the device's operational integrity and safety, affirming its reliability for precise radiotherapy treatments.

Practice of Tumor Bed Boost in Patients after Oncoplastic Breast-Conserving Surgery.

The practice of boost to the tumor bed after treatment with oncoplastic breast-conserving surgery (BCS) remains variable. Using a survey, the present study evaluated the current practice of tumor bed boost administered in women after oncoplastic BCS. Actively practicing radiation oncologists across India were sent a questionnaire on the practice of adjuvant whole-breast radiotherapy and tumor bed boost after oncoplastic BCS via email and encouraged to participate. Of the 54 radiation oncologists who participated, most (98.1%) used a linear accelerator for radiotherapy. Hypofractionation was preferred by 59.26%, standard fractionation by 7.41%, and the remaining selected the fractionation strategy based on various patient factors. In addition, 83.33% participants reported that they always planned tumor boost, 51.85% preferred photons for the boost, and 75.93% administered sequential boost. The most common dose for the boost was 12.5Gy in five fractions (40.74%). Most participants (77.78%) revealed that they used a combination of methods for identifying the tumor bed. With respect to clip placement, most surgeons (96%) at the participants' centers placed ≥ 4 clips at the tumor site, with both the base and margins being preferred by surgeons (81.48%) for placement. Finally, 12.96% participants revealed that the surgeons always involved them during surgical planning, whereas 7.4% participants reported that they always included the surgeons during radiotherapy planning, suggesting that radiation oncologists and oncoplastic surgeons do not involve each other during surgical and radiotherapy planning, possibly leading to suboptimal treatment. This may be attributed to the absence of guidelines regarding boost practices after oncoplastic BCS.

Radiotherapy Capabilities, Population, Average Income, and Health Insurance Status as Predictors of Cancer Mortality at the County Level in the United States

Sufficient radiotherapy capacity at the country level is commonly seen in high income countries and is an essential factor in access to high quality cancer care. However, universal access is not always possible due to other factors beyond the commonly used parameter of machines per million population. This study aims to assess the barriers cancer patients in a high-income country face in accessing radiotherapy, and how this impacts cancer mortality. This cross-sectional study utilized United States county level oncologic and demographic data obtained from Centers for Disease Control and Prevention and the International Atomic Energy Agency Directory of Radiotherapy Centers. Radiotherapy facilities in the United States were mapped using Geographic Information Systems software. Univariate analysis was used to identify whether distance to a radiotherapy center or various socioeconomic factors were predictive of all-cancer mortality-to-incidence ratios. Variables that were deemed to be significant (p ≤ 0.05) on univariate analysis were then included in a step-wise backwards elimination method of multiple regression analysis. Among the United States counties studied, 31.3% of counties have at least one radiotherapy facility and 8.3% have five or more radiotherapy facilities. Median linear distance from a county's centroid to the nearest radiotherapy center was 36 Km and the median county all-cancer mortality to incidence ratio (MIR) was 0.37. The ratio of radiotherapy centers, linear accelerators and brachy therapy units per 1 million people were significantly associated with all-cancer MIR (p<0.05). Greater distance to radiotherapy facilities, lower county population, lower average income per county, and higher proportion of patients without health insurance were statistically significant predictors of increased all-cancer MIR (R-squared: 0.2113, F = 94.22, p<0.001). This analysis used unique high-quality datasets to identify significant barriers to radiotherapy access that correspond to higher cancer mortality at the county level. Geographic access, personal income, and insurance status all contribute to these concerning disparities. Efforts and novel strategies to address and minimize these barriers are needed to ensure access to care and improve oncologic outcomes.

Radiation Therapy Generates Release of Microvesicle Particles in Keratinocytes

Ionizing radiation (IR) exerts both tissue and systemic effects. However, the exact mechanism by which radiation therapy to skin results in local and systemic effects is incompletely defined. Previously our group has reported that IR of tumors results in the generation of the lipid mediator Platelet-activating factor (PAF) which resulted in systemic immunosuppressive effects via activation of regulatory T cells. Since PAF acting on the PAF receptor (PAFR) has been demonstrated to generate high levels of subcellular microvesicle particles (100-1000nm; MVP), and MVP are known to be able to signal systemically, the current studies seek to define whether IR of keratinocyte cells generates MVP, and to define the role of the PAFR in this process. Thus, we examine MVP release in the human keratinocyte cell line HaCaT. Moreover, the PAFR-dependency of IR-generated MVP is assessed by use of PAFR-positive KBP and PAFR-negative KBM cells. HaCaT cells (human keratinocytes), KBM cells (PAFR-negative), and KBP cells (PAFR-positive) were grown in 10cm dishes and treated with IR at either no treatment 0 Gy (NT), 4 Gy and 10 Gy. IR was delivered utilizing a technology company's medical linear accelerator radiotherapy system set up with dosimetry verified by nanodot optical stimulated luminescence (Landauer, Glenwood, IL). Some cell lines were treated with PAFR agonist N-methyl carbamoyl PAF (CPAF) and a phorbol ester TPA, known inducers of MVP release. A set of cells were treated with only 90% DMSO/10% ethanol vehicle in HBSS with BSA. After treatments, cells were incubated for 4 hours prior to extraction of MVPs. MVPs were isolated through centrifuging at 2000G for 20, supernatant was collected, transferred into different tubes, and centrifuged at 20,000 G for 70 mins. MVP was detected using a NanoSight NS300 instrument. MVP concentrations were recorded, and the data was statistically analyzed using Student's t-test (JMP, Cary, NC). IR treatment of HaCaT cells at various fluences exhibited statistically significant increases in MVP generation when compared to NT. Of note, 4 Gy resulted in the most fluence for MVP release but was not significant. IR treatment of KB cells resulted in MVP release in both KBM and KBP cells at both 4 and 10Gy. Augmented levels of MVP release were noted in KBP over KBM cells with any IR dose suggesting that the presence of the PAFR is involved in MVP release. Testing of inhibitors of the MVP generating enzyme acid sphingomyelinase (aSMase) also revealed involvement of this lipid metabolizing enzyme. The present studies indicate that RT can generates MVP production in epithelial cells. The mechanism for IR-generated MVP appears to involve aSMase and the PAFR. Target cell MVP release may provide a mechanism for RT effects, including the release of cytokines that influence systemic and local inflammation. Elucidation of this novel pathway may provide insights into IR effects on skin along with new therapeutic strategies.

End-to-end quality assurance for stereotactic radiotherapy with Fricke-Xylenol orange-Gelatin gel dosimeter and dual-wavelength cone-beam optical CT readout

PurposeThe end-to-end (E2E) quality assurance (QA) test is a unique tool for validating the treatment chain undergone by patients in external radiotherapy. It should be conducted in three dimensions (3D) to get accurate results. This study aims to implement these tests with Fricke-Xylenol orange-Gelatin (FXG) gel dosimeter and a newly developed dual-wavelength reading method on the Vista16™ optical Computed Tomography (CT) scanner (ModusQA) for three treatment techniques in stereotactic radiotherapy, on Novalis (Varian) and CyberKnife (Accuray) linear accelerators. MethodsThe tests were performed in head phantoms. Gel measurements were compared with planned dose distributions and measured by film and ion chamber measurements by plotting isodose curves and dose profiles, and by conducting a 3D local gamma-index analysis (2%/2mm criteria). ResultsGamma passing rates were higher than 95 %. Point dose differences between treatment planning and gel and ion chamber measurements at the isocenter were < 2.3 % for both treatments delivered on the Novalis accelerator, while this difference was higher than 4 % for the treatment delivered on the CyberKnife, highlighting a small overdosing of the tumor volume. A good agreement was observed between gel and film dose profiles. ConclusionsThis study presents the successful implementation of 3D E2E QA tests for stereotactic radiotherapy with FXG gel dosimetry and a dual-wavelength reading method on an optical CT scanner. This dosimetric method provides 3D absolute dose distributions in the 0.25 – 10 Gy dose range with a high spatial resolution and a dose uncertainty of around 2 % (k=1).

Radiotherapy Infrastructure Shielding Calculations: software development for shielding calculations in a linear accelerator radiotherapy room.

This work aimed to develop and validate software that calculates the shielding thickness required for a radiotherapy room with a linear accelerator utilising geometric and dosimetric data. The software "Radiotherapy Infrastructure Shielding Calculations" (RISC) was developed using MATLAB programming. It does not require the installation of the MATLAB platform, and the user only needs to download and install the application, which displays a graphical user interface (GUI). The GUI includes empty cells to insert numerical values for several parameters to calculate the proper shielding thickness. The GUI comprises two main interfaces, one for the primary and one for the secondary barrier calculation. The interface of the primary barrier is divided into four tabs: (a) primary radiation, (b) patient scattered and leakage radiation, (c) IMRT techniques and (d) the shielding cost calculations. The interface of the secondary barrier includes three tabs: (a) patient scattered and leakage radiation, (b) IMRT techniques and (c) the shielding cost calculations. Each tab consists of two sections: one for input and one for output of the necessary data. The RISC is based on the methods and formulae of the NCRP 151 and calculates the primary and secondary barrier thickness for ordinary concrete with a density of 2.35g/cm3 and the cost for a radiotherapy room with a linear accelerator that performs conventional or IMRT techniques. Calculations can be performed for photon energies of 4, 6, 10, 15, 18, 20, 25 and 30 MV of a dual-energy linear accelerator, while instantaneous dose rate (IDR) calculations are also performed. The RISC has been validated using all comparative examples of NCRP 151 and the calculations from shielding reports of the Varian IX linear accelerator at Methodist Hospital of Willowbrook and Elekta Infinity at the University Hospital of Patras. The RISC is accompanied by two text files: (a) "Terminology," extensively describing all parameters, and (b) "User's Manual," providing useful instructions to the user. The RISC is user-friendly, simple, fast and precise, providing accurate shielding calculations and quickly and easily reproducing different shielding scenarios for a radiotherapy room with a linear accelerator. Additionally, it could be used during the educational process of shielding calculations by graduate students or trainee medical physicists. As a future work, the RISC will be updated with new features such as skyshine radiation, door shielding, and other types of machines and shielding materials.

X-ray source arrays for volumetric imaging during radiotherapy treatment

This work presents a novel hardware configuration for radiotherapy systems to enable fast 3D X-ray imaging before and during treatment delivery. Standard external beam radiotherapy linear accelerators (linacs) have a single X-ray source and detector located at ± 90° from the treatment beam respectively. The entire system can be rotated around the patient acquiring multiple 2D X-ray images to create a 3D cone-beam Computed Tomography (CBCT) image before treatment delivery to ensure the tumour and surrounding organs align with the treatment plan. Scanning with a single source is slow relative to patient respiration or breath holds and cannot be performed during treatment delivery, limiting treatment delivery accuracy in the presence of patient motion and excluding some patients from concentrated treatment plans that would be otherwise expected to have improved outcomes. This simulation study investigated whether recent advances in carbon nanotube (CNT) field emission source arrays, high frame rate (60 Hz) flat panel detectors and compressed sensing reconstruction algorithms could circumvent imaging limitations of current linacs. We investigated a novel hardware configuration incorporating source arrays and high frame rate detectors into an otherwise standard linac. We investigated four potential pre-treatment scan protocols that could be achieved in a 17 s breath hold or 2–10 1 s breath holds. Finally, we demonstrated for the first time volumetric X-ray imaging during treatment delivery by using source arrays, high frame rate detectors and compressed sensing. Image quality was assessed quantitatively over the CBCT geometric field of view as well as across each axis through the tumour centroid. Our results demonstrate that source array imaging enables larger volumes to be imaged with acquisitions as short as 1 s albeit with reduced image quality arising from lower photon flux and shorter imaging arcs.

Analysis of Radiation Dose Distribution in Nasopharyngeal and Organ Cancer Cases at Risk with Linear Accelerator Radiotherapy 6 MV Photon Energy Using the IMRT Technique at Prof. Hospital. Dr. I. G. N. G. Ngoerah

This study aims to determine the distribution of radiation doses on PTV and OAR radioteraphy planning in RSUP. Prof. Dr. I.G.N.G Ngoerah, Bali, Indonesia does no exceed a predetermined limit. The research metode used is the value of Homogenity Index (H), Conformity Index (CI), and the maximum value of radiation ose to the Organ At Risk (OAR), amely the right eye lens, left eye lens, brainstem, optic chiasma, and spinal cord. These data are compared with the provisions of ICRU report 83 and the maximum dose reference value for OAR. Using data from 30 nasopharyngeal cancer patients with a total radiation dose of 7000 cGy. Obtained a value for HI of 0.1214 with a t-test result of 0.459&gt; 0.05 which means it is not significant. While the value for CI is 0.9850 with nonparametric statistical test results of 0.285&gt; 0.05 which means it is not significant. The maximum dose value for the right eye lens is 772.7 cGy with a t-test result of 0.779&gt; 0.05 which means it is not significant. For the maximum value of the dose in the lens of the left eye of 771.0 cGy with a t test result of 0.791&gt; 0.05 which means it is not significant. For the maximum value of the dose in the brain stem of 5178.1 cGy with nonparametric test results of 0.686&gt; 0.05 which means not significant. The maximum dose value at the optic chiasma is 4,837.2 cGy with a nonparametric test result of 0.225&gt;0.05 which means it is not significant. For the maximum value of the dose in the spinal cord of 4,663.3 cGy with a t test result of 0.958&gt; 0.05 which means it is not significant.

Dose estimation for cone-beam computed tomography in image-guided radiation therapy for pelvic cancer using adult mesh-type reference computational phantoms

The use of cone-beam computed tomography (CBCT) is expanding owing to its installation in linear accelerators for radiation therapy, and the imaging dose induced by this system has become the center of attention. Here, the dose to patients caused by the CBCT imager was investigated. Organ doses and effective doses for male and female mesh-type reference computational phantoms (MRCPs) and pelvis CBCT mode, routinely used for pelvic irradiation, were estimated using the Particle and Heavy Ion Transport Code System. The simulation results were confirmed based on the point-dose measurements. The estimated organ doses for male MRCPs with/without raised arms and for female MRCPs with/without raised arms were 0.00286-35.6mGy, 0.00286-35.1mGy, 0.00933-39.5mGy, and 0.00931-39.0mGy, respectively. The anticipated effective doses for male MRCPs with/without raised arms and female MRCPs with/without raised arms irradiated by pelvis CBCT mode were 4.25mSv, 4.16mSv, 7.66mSv, and 7.48mSv, respectively. The results of this study will be useful for patients who undergo image-guided radiotherapy with CBCT. However, because this study only covered one type of cancer with one type of imager, and image quality was not considered, more studies should be conducted to estimate the radiation dose from imaging devices in radiation therapy.

First-in-human technique translation of oxygen-enhanced MRI to an MR Linac system in patients with head and neck cancer

Background and purposeTumour hypoxia is prognostic in head and neck cancer (HNC), associated with poor loco-regional control, poor survival and treatment resistance. The advent of hybrid MRI – radiotherapy linear accelerator or ‘MR Linac’ systems – could permit imaging for treatment adaptation based on hypoxic status. We sought to develop oxygen-enhanced MRI (OE-MRI) in HNC and translate the technique onto an MR Linac system. Materials and methodsMRI sequences were developed in phantoms and 15 healthy participants. Next, 14 HNC patients (with 21 primary or local nodal tumours) were evaluated. Baseline tissue longitudinal relaxation time (T1) was measured alongside the change in 1/T1 (termed ΔR1) between air and oxygen gas breathing phases. We compared results from 1.5 T diagnostic MR and MR Linac systems. ResultsBaseline T1 had excellent repeatability in phantoms, healthy participants and patients on both systems. Cohort nasal concha oxygen-induced ΔR1 significantly increased (p < 0.0001) in healthy participants demonstrating OE-MRI feasibility. ΔR1 repeatability coefficients (RC) were 0.023–0.040 s−1 across both MR systems. The tumour ΔR1 RC was 0.013 s−1 and the within-subject coefficient of variation (wCV) was 25% on the diagnostic MR. Tumour ΔR1 RC was 0.020 s−1 and wCV was 33% on the MR Linac. ΔR1 magnitude and time-course trends were similar on both systems. ConclusionWe demonstrate first-in-human translation of volumetric, dynamic OE-MRI onto an MR Linac system, yielding repeatable hypoxia biomarkers. Data were equivalent on the diagnostic MR and MR Linac systems. OE-MRI has potential to guide future clinical trials of biology guided adaptive radiotherapy.

A planning-based feasibility study of MR-Linac treatment for anal cancer radiation therapy.

The hybrid magnetic resonance image (MRI) scanner and radiation therapy linear accelerator (MR-Linac) has the potential to enhance clinical outcomes for anal cancer (AC) patients with improved soft tissue visualization and daily plan adaption but has planning and delivery limitations due to the incorporation of MRI. We aimed to identify if Elekta Unity MR-Linac-based radiation therapy is feasible for anal cancer. Ten prospectively enrolled AC patients treated with radical chemoradiotherapy were replanned for MR-Linac treatment using departmental planning criteria. For comparison, and to reduce interobserver variability, volumetric modulated arc radiation therapy (VMAT) plans were also created for each patient by the same single senior radiation therapist. Plans were compared using departmental dosimetric plan criteria, as well as conformity and homogeneity indices, monitor units (MUs) and measured plan delivery (beam-on) time. Results were deemed clinically acceptable. Target and organ at risk (OAR) doses were comparable between MR-Linac plans and VMAT plans, although PTV45Gy D98% coverage was compromised in 3 of 10 MR-Linac plans due to caudocranial length exceeding the limits of the MR-Linac. MR-Linac plans had lower MUs, median of 689.1 vs 849.65 (p = 0.002), but took over twice as long to deliver, 529.5s vs 224s (p = <0.0001) as VMAT plans. MR-Linac planning and treatment of AC is feasible for a subset of patients. The current physical limitations of the Elekta Unity system mean patients with large caudocranial elective PTV45Gy target volumes may not be covered dosimetrically to the required clinical standard. Longer image verification and treatment delivery times of the MR-Linac also mean patient selection and intrafractional IGRT are likely to be integral to ensuring high quality clinical outcomes in this rare cancer.

Improving animal-specific radiotherapy quality assurance for kilovoltage X-ray radiotherapy using a 3D printed dog skull water phantom.

Accurate dose assessment during animal radiotherapy is beneficial for veterinary medicine and medical education. To visualize the radiation treatment distribution of orthovoltage X-ray equipment in clinical practice using Monte Carlo simulations and create a dog skull water phantom for animal-specific radiotherapy. EGSnrc-based BEAMnrc and DOSXYZnrc codes were used to simulate orthovoltage dose distributions. At 10, 20, 30, 40, 50, and 80 mm in a water phantom, the depth dose was measured with waterproof Farmer dosimetry chambers, and the diagonal off-axis ratio was measured with Gafchromic EBT3 film to simulate orthovoltage dose distributions. Energy differences between orthovoltage and linear accelerated radiotherapy were assessed with a heterogeneous bone and tissue virtual phantom. The animal-specific phantom for radiotherapy quality assurance (QA) was created from CT scans of a dog and printed with a three-dimensional printer using polyamide 12 nylon, with insertion points for dosimetry chambers and Gafchromic EBT3 film. Monte Carlo simulated and measured dose distributions differed by no more than 2.0% along the central axis up to a depth of 80 mm. The anode heel effect occurred in shallow areas. The orthovoltage radiotherapy percentage depth dose in bone was >40%. Build-up was >40%, with build-down after bone exit, whereas linear accelerator radiotherapy absorption changed little in the bone. A highly water-impermeable, animal-specific dog skull water phantom could be created to evaluate dose distribution. Animal-specific water phantoms and Monte Carlo simulated pre-treatment radiotherapy are useful QA for orthovoltage radiotherapy and yield a visually familiar phantom that will be useful for veterinary medical education.