Volume 26 (2020): Issue 4 (December 2020)

Objective: The objective of the study was to determine the correct CTV-PTV margin, depending on the method used to verify the PG position. In the study, 3 methods of CBCT image superimposition were assessed as based on the location of the prostate gland (CBCT images), a single gold marker, and pubic symphysis respectively.

Materials and methods: The study group consisted of 30 patients undergoing irradiation therapy at the University Hospital in Zielona Góra. The therapy was delivered using the VMAT (Volumetric Modulated Arc Therapy) protocol. CBCT image-based superimposition (prostate-based alignment) was chosen as the reference method. The uncertainty of the PG positioning method was determined and the margin to be used was determined for the CBCT-based reference method. Then, changes in the position of the prostate gland relative to these determined using the single marker and pubic symphysis-based methods were determined. The CTV-PTV margin was calculated at the root of the sum of the squares for the doubled value of method uncertainty for the CBCT image-based alignment method and the value of the difference between the locations of planned and actual isocenters as determined using the method of interest and the CBCT-based alignment method for which the total number of differences accounted for 95% of all differences.

Results: The CTV-PTV margins to be used when the prostate gland is positioned using the CBCT imaging, single marker, and pubic symphysis-based methods were determined. For the CBCT-based method, the following values were obtained for the Vrt, Lng, and Lat directions respectively: 0.43 cm, 0.48 cm, 0.29 cm. For the single marker-based method, the respective values were 0.7 cm, 0.88 cm, and 0.44 cm whereas for the pubic symphysis-based method these were 0.65 cm, 0.76 cm, and 0.46 cm.

Conclusions: Regardless of the method, the smallest margin values were obtained for the lateral direction, with the CBCT-based method facilitating the smallest margins to be used. The largest margins were obtained using the single marker-based alignment method.

Purpose: To test the NAL and eNAL correction protocols using daily patient setup displacements.

Methods and material: In total, the analysis was performed for 749 and 797 kV CBCT images for gynecological and prostate patients, respectively, each of 30 patients. After the planning procedure, patients were set up on the treatment table in the treatment position every day. The on-line correction protocol was applied. KV CBCT images were acquired by means of x-ray lamp mounted orthogonally on Linac. Patient setup displacement was assigned. NAL and eNAL corrections protocols were simulated using daily data from online corrections for these two groups of patients. The overall systematic error and random error were calculated for each direction.

Results: For the prostate group, the random errors for daily Raw data (no correction) in LAT, LONG, and VERT directions were 2.0 mm, 1.6 mm, and 3.2 mm, respectively. For NAL and eNAL protocols, they were in the range of 1.8 mm to 3.2 mm. For the gynecological group, the random errors were: for daily Raw data 2.2 mm, 1.7 mm, and 3.2 mm, respectively. For NAL and eNAL protocols, they were in the range of 2.0 to 3.4 mm.

For the prostate group, values of systematic errors 1.8 mm, 1.8 mm, and 3.3 mm, respectively for Raw data. For NAL and eNAL protocols, these values were less than 1.8 mm. For the gynecological group, the systematic errors were 2.6 mm, 2.3 mm, and 2.8 mm, respectively, for Raw data. For NAL ana eNAL protocols less than 1.8 mm.

For the gynecological group, for Raw data, 45% of the total displacement vectors exceeded 5 mm, whereas only 25% did after the NAL procedure and 29% after the eNAL procedure. For the prostate group, for Raw data, 34% of the total displacement vectors exceeded 5 mm, whereas only 22% did after NAL procedure and 28% after eNAL procedure Conclusions: For gynecological and prostate cancer patients, the NAL and eNAL correction protocols can be safely applied to substantially reduce setup errors.

Introduction: One of many procedures to control the quality of radiotherapy is daily imaging of the patient’s anatomy. The CBCT (Cone Beam Computed Tomography) plays an important role in patient positioning, and dose delivery monitoring. Nowadays, CBCT is a baseline for the calculation of fraction and total dose. Thus, it provides the potential for more comprehensive monitoring of the delivered dose and adaptive radiotherapy. However, due to the poor quality and the presence of numerous artifacts, the replacement of the CBCT image with the corrected one is desired for dose calculation. The aim of the study was to validate a method for generating a synthetic CT image based on deformable image registration.

Material and methods: A Head & Torso Freepoint phantom, model 002H9K (Computerized Imaging Reference Systems, Norfolk, USA) with inserts was imaged with CT (Computed Tomography). Then, contouring and treatment plan were created in Eclipse (Varian Medical Systems, Palo Alto, CA, USA) treatment planning system. The phantom was scanned again with the CBCT. The planning CT was registered and deformed to the CBCT, resulting in a synthetic CT in Velocity software (Varian Medical Systems, Palo Alto, CA, USA). The dose distribution was recalculated based on the created CT image.

Results: Differences in structure volumes and dose statistics calculated both on CT and synthetic CT were evaluated. Discrepancies between the original and delivered plan from 0.0 to 2.5% were obtained. Dose comparison was performed on the DVH (Dose-Volume Histogram) for all delineated inserts.

Conclusions: Our findings suggest the potential utility of deformable registration and synthetic CT for providing dose reconstruction. This study reports on the limitation of the procedure related to the limited length of the CBCT volume and deformable fusion inaccuracies.

Purpose: To evaluate the breathing amplitude, tumor motion, patient positioning, and treatment volumes among consecutive four-dimensional computed tomography (4D-CT) scans, during the simulation for lung stereotactic body radiation therapy (SBRT).

Material and methods: The variation and shape of the breathing amplitude, patient positioning, and treatment volumes were evaluated for 55 lung cancer patients after consecutive 4D-CT acquisitions, scanned at one-week intervals. The impact of variation in the breathing amplitude on lung tumor motion was determined for 20 patients. The gross tumor volume (GTV) was contoured from a free-breathing CT scan and at ten phases of the respiratory cycle, for both 4D-CTs (440 phases in total).

Results: Breathing amplitude decreased by 3.6 (3.4-4.9) mm, tumor motion by 3.2 (0.4-5.0) mm while breathing period increased by 4 (2-6) s, inter-scan for 20 patients. Intra-scan variation was 4 times greater for the breathing amplitude, 5 times for the breathing period, and 8 times for the breathing cycle, comparing irregular versus regular breathing patterns for 55 patients. Using coaching, the breathing amplitude increases 3 to 8 mm, and the breathing period 2 to 6 s. Differences in the contoured treatment volumes were less than 10% between consecutive scans. Patient positioning remained stable, with a small inter-scan difference of 1.1 (0.6-1.4) mm.

Conclusion: Decreasing the inter-scan breathing amplitude decreases the tumor motion reciprocally. When the breathing amplitude decreases, the breathing period increases at inter- and intra-scan, especially during irregular breathing. Coaching improves respiration, keeping the initial shape of the breathing amplitude. Contoured treatment volumes and patient positioning were reproducible through successive scans.

Here we projected a model-based IMRT treatment plan to produce the optimal radiation dosage by considering that the maximum amount of prescribed dose should be delivered to the target without affecting the surrounding healthy tissues especially the OARs. Fluence mapping is used for inverse planning. This suggested method can generate global minima for IMRT plans with reliable plan quality among diverse treatment planners and to provide better safety for significant parallel OARs in an effective way. The whole methodology is having the capability to handles various objectives and to generate effective treatment procedures as validated with illustrations on the CORT dataset. For the validation of our methodology, we have compared our result with the two other approaches for calculating the objectives based on dose-volume bounds and found that in our methodology dose across the prostate and lymph nodes is maximum and the time required for the convergence is minimum.

Purpose: Carbon fibre treatment couches on linear accelerators provide a strong, rigid framework for patient support. Patient safety is a priority, therefore the dosimetric properties of treatment couches need to be accurately incorporated in treatment plans, to minimize differences between planned and delivered dose. This study aims to determine the attenuation effect of treatment couches for 3-D Conformal Radiotherapy (3-D CRT) and to validate the implementation thereof in the XiO and Monaco treatment planning systems (TPS).

Material and methods: Attenuation measurements were performed on the ELEKTA Connexion couches of the ELEKTA Precise and Synergy-Agility linear accelerators. Measurements were made at 10° intervals in RMI-457 Solid water (30 cm x 30 cm x 30 cm) using a PTW Farmer-type ionization chamber (TW30013) positioned at the accelerator’s isocentre. The percentage attenuation was calculated as the ratio of the electrometer readings for parallel-opposed fields. The Computed Tomography (CT) data sets of the set-ups were obtained on a Philips Big Bore 16-slice CT scanner and exported to the TPS. The individual couch structures were delineated and electron density (ED) values were assigned using the commissioned CT-to-ED curve. Test treatment plans were generated with 100MU per field at 10° gantry intervals.

Results: The percentage attenuation was determined to be within 2% and 3% for beams perpendicular to the couch surface for XiO and Monaco, respectively. The maximum attenuation was observed for oblique fields which was significantly higher than the manufacturer specified values. TPS validation showed an agreement to 1% for XiO and Monaco. At extreme oblique angles, both planning systems overestimated this effect up to a maximum of 4%.

Conclusions: Couch attenuation differs significantly with gantry angle and beam energy. As a result, the treatment couch models should be included in all treatment planning calculations.

Radiosensitization of the cancer cells by the heavy atoms of nanoparticles was the subject of some studies. But, the physical characterization to determine the weight of all interactions hasn’t been made numerically. The aim of this study was to calculate and compare the dose enhancement (DE) for different energies. The Monte Carlo simulation method was used in the current study. The influence of gold nanoparticles (GNP) size, beam quality, the GNP concentration, and dose inhomogeneity on the radiosensitization by DE was studied. A 35% increase in the photoelectric effect was observed while energy decreased from 18 MV to 300 kV. In the microscopic study which DE calculated in 30 µm from a single GNP, a 79% decreasing in DE within the first 1µm was seen and it declined to 2% in 30 µm from the GNP center. The effect was observed at small distances only. Our study revealed that the dose inhomogeneity around a nanoparticle is the main and very strong effect of DE on a macroscopic scale. In the location which 35% DE occurs most malignant cells survival will be effectively reduced. Our research indicates the need for further research.

In the current study, nanoscale physical dose distributions around five potential nanoparticles were compared. Five potential nanoparticles including bismuth, gold, gadolinium, hafnium, and iridium nanoparticles in the form of a sphere with a diameter of 50 nm were simulated in a water medium. The MCNPX (2.7.0) Monte Carlo code with updated libraries was used for calculations of electron dose deposition and electron flux in water from 25 nm up to 4000 nm with a step of 25 nm. Also, secondary electron spectra after irradiation of nanoparticles with mono-energetic photons with energies of 30, 60, 100 keV were derived. The nano-scale distance-dose curves showed a very steep gradient with distance from nanoparticle surface up to 60 nm and after this point, a gradual decrease was seen. The dose deposition characteristics in the nano-scale were dependent on the type of nanoparticle as well as photon energy. Our results concluded that for each photon energy in the energy range of 30-100 keV, a suitable nanoparticle can be selected to boost the effect of energy deposition by low energy photon beams used in brachytherapy.

Objective: The main purpose of this study is to calculate the effective source to surface distance (SSD_eff) of small and large electron fields in 10, 15, and 18 MeV energies, and to investigate the effect of SSD on the cutout factor for electron beams a linear accelerator. The accuracy of different dosimeters is also evaluated.

Materials and methods: In the current study, Elekta Precise linear accelerator was used in electron beam energies of 10, 15, and 18 MeV. The measurements were performed in a PTW water phantom (model MP3-M). A Semiflex and Advanced Markus ionization chambers and a Diode E detector were used for dosimetry. SSD_eff in 100, 105, 110, 115, and 120 cm SSDs for 1.5 × 1.5 cm² to 5 × 5 cm² (small fields) and 6 × 6 cm² to 20 × 20 cm² (large fields) field sizes were obtained. The cutout factor was measured for the small fields.

Results: SSDeff in small fields is highly dependent on energy and field size and increases with increasing electron beam energy and field size. For large electron fields, with some exceptions for the 20 × 20 cm² field, this quantity also increases with energy. The SSD_eff was increased with increasing beam energy and field size for all three detectors.

Conclusion: The SSD_eff varies significantly for different field sizes or cutouts. It is recommended that SSD_eff be determined for each electron beam size or cutout. Selecting an appropriate dosimetry system can have an effect in determining cutout factor.

Transition from low dose rate brachytherapy to high dose rate brachytherapy at our department necessitated the performance of dose verification test, which served as an end-to-end quality assurance procedure to verify and validate dose delivery in intracavitary brachytherapy of the cervix and the vaginal walls based on the Manchester system. An in-house water phantom was designed and constructed from Perspex sheets to represent the cervix region of a standard adult patient. The phantom was used to verify the whole dose delivery chain such as calibration of the cobalt-60 source in use, applicator, and source localization method, the output of treatment planning with dedicated treatment planning system, and actual dose delivery process. Since the above factors would influence the final dose delivered, doses were measured with calibrated gafchromic EBT3 films at various points within the in-house phantom for a number of clinical implants that were used to treat a patient based on departmental protocol. The measured doses were compared to those of the treatment planning system. The discrepancies between measured doses and their corresponding calculated doses obtained with the treatment planning system ranged from -29.67 to 40.34% (mean of ±13.27%). These compared similarly to other studies.

Thermal therapy which involves either raising or lowering tissue temperature to treat malignant cells needs precise acknowledgment of thermal history inside the biological system to ensure effective treatment. For this purpose, this study presents a two-dimensional unsteady finite element model (FEM) of the bioheat transfer problem based on Pennes bio-heat equation to analyze the thermal response of tissue subject to external heating. Crank-Nikolson scheme was used for the unsteady solution. A finite element code was developed using C language to calculate results. The obtained numerical result was compared with the analytical and other numerical results available in the literature. A good agreement was found from the comparison. Temperature distribution inside the human body due to constant and sinusoidal spatial and surface heating were analyzed. Response to point heating was also investigated. Moreover, a sensitivity analysis was carried out to know the effect of various parameters, i.e. blood temperature, thermal conductivity, and blood perfusion rate on tissue temperature. The outcome of this study will be helpful for the researchers and physicians involved in the thermal treatment of human tissue.

Purpose: The purpose of this study was to develop software to automatically measure the main areas of the chest, i.e. soft tissue, bone, and air and to implement it in Kraton Regional General Hospital for designing a specific dosimetrical phantom for chest digital radiography (DR) examination.

Methods: This study was a retrospective study on all DR images from 2015 to 2019, and computed tomography (CT) images of 102 patients in Digital Imaging and Communications in Medicine (DICOM) format files scanned from January-December 2019 at the Kraton Regional General Hospital. We evaluated the number of basic DR chest examinations compared to all DR radiological examinations. We developed a MatLab graphical user interface (GUI) for automated measurement of the areas of the main chest components (soft tissue, bone, and air). We computed the areas of the main components of the chest in order to develop a specific chest phantom for DR in the hospital. In order to compute the areas of the main components, we used chest CT images of patients with clinical indications of chest tumors.

Results: The basic DR chest examination comprised 59.5% of all DR examinations in the hospital during 2015-2019. The average areas of soft tissue, bone, and air within the chest in all patients were 331, 20, and 125 cm2, respectively, with values of 345, 23, and 139 cm² for males, and 309, 15, and 103 cm2 for females. The areas were also dependent on age with values of 121, 10, 55 cm² for patients aged 5-11 years, 371, 27, and 88 cm2 for patients aged 12-25 years, 322, 22, and 131 cm² for patients aged 26-45 years, and 334, 19, and 126 cm2 for patients > 45 years old.

Conclusion: A GUI for computing the main composition of the chest was successfully developed. The areas of chest male patients were greater than female patients. The areas of soft tissue, bone, and air were dependent on the patient’s age. Therefore, the design of dosimetrical DR phantom must consider the gender and age of the patient.

Introduction: Magnetic Resonance Spectroscopy (MRS) is a very powerful tool to explore the tissue components, by allowing a selective identification of molecules and molecular distribution mapping. Due to intrinsic Signal-to-Noise Ratio limitations (SNR), MRS in small phantoms and animals with a clinical scanner requires the design and development of dedicated radiofrequency (RF) coils, a task of fundamental importance. In this article, the authors describe the simulation, design, and application of a ¹H transmit/receive circular coil suitable for MRS studies in small phantoms and small animal models with a clinical 3T scanner. In particular, the circular coil could be an improvement in animal experiments for tumor studies in which the lesions are localized in specific areas.

Material and methods: The magnetic field pattern was calculated using the Biot–Savart law and the inductance was evaluated with analytical calculations. Finally, the coil sensitivity was measured with the perturbing sphere method. Successively, a prototype of the coil was built and tested on the workbench and by the acquisition of MRS data.

Results: In this work, we demonstrate the design trade-offs for successfully developing a dedicated coil for MRS experiments in small phantoms and animals with a clinical scanner. The coil designed in the study offers the potential for obtaining MRS data with a high SNR and good spectral resolution.

Conclusions: The paper provides details of the design, modelling, and construction of a dedicated circular coil, which represents a low cost and easy to build answer for MRS experiments in small samples with a clinical scanner.