Dual application of Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue Fricke hydrogel in clinical practice: Surface dosimeter and bolus.

An essential issue is an accurate evaluation of surface dose distribution for such sensitive treatments. This work aimed to feasibility of the dual application of the Ferrous Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue (PVA-GTA-MTB) gel as a bolus compensator and surface dosimeter in breast radiotherapy. The differences between the surface dose measured using PVA-GTA-MTB gel and film dosimetry in the medial and lateral parts of the breast were 3.74% and 4.18%, respectively. A qualitative comparison of the isodose curves showed that the PVA-GTA-MTB bolus creates a uniform dose distribution similar to the superflab bolus in the target volume.

Assessment of Field-in-Field, 3-Field, and 4-Field Treatment Planning Methods for Radiotherapy of Gastro-Esophageal Junction Cancer.

Background: Gastro-esophageal (GE) junction cancer is the fastest-growing tumor, particularly in the United States (US). Objective: This study aimed to compare dosimetric and radiobiological factors among field-in-field (FIF), three-field (3F), and four-field box (4FB) radiotherapy planning techniques for gastro-esophageal junction cancer. Material and Methods: In this experimental study, thirty patients with GE junction cancer were evaluated, and three planning techniques (field-in-field (FIF), three-field (3F), and four-field box (4FB)) were performed for each patient for a 6-MV photon beam. Dose distribution in the target volume, the monitor units (MUs) required, and the dose delivered to organs at risk (OARs) were compared for these techniques using the paired-sample t-test. Results: A significant difference was measured between the FIF and 3F techniques with respect to conformity index (CI), dose homogeneity index (HI), and tumor control probability (TCP) for the target organ, as well as the Dmean for the heart, kidneys, and liver. For the spinal cord, the FIF technique showed a slight reduction in the maximum dose compared to the other two techniques. In addition, the V20 Gy of the lungs and the normal tissue complication probability (NTCP) of all OARs were reduced with FIF method. Conclusion: The FIF technique showed better performance for treating patients with gastro-esophageal junction tumors, in terms of dose homogeneity in the target, conformity of the radiation field with the target volume, TCP, less dose to healthy organs, and fewer MU.

Dosimetry of small photon fields in the presence of bone heterogeneity using MAGIC polymer gel, Gafchromic film, and Monte Carlo simulation.

Background: The presence of heterogeneity within the radiation field increases the challenges of small field dosimetry. In this study, the performance of MAGIC polymer gel was evaluated in the dosimetry of small fields beyond bone heterogeneity. Materials and methods: Circular field sizes of 5, 10, 20 and 30 mm were used and Polytetrafluoroethylene with density of 2.2 g/cm3 was used as the bone equivalent material. The PDD curves, beam profiles, and penumbra widths were measured using MAGIC polymer gel, EBT2 film, and Monte Carlo simulation. Results: The maximum differences between MAGIC and EBT2 are 6.1, 4.7, 2.4, and 2.2 for PDD curves at 5, 10, 20, and 30 mm circular fields, respectively. The dose differences and distance to agreement between MAGIC and MC were within 1.89%/0.46 mm, 1.66%/0.43 mm, 1.28%/0.77 mm, and 1.31%/0.81 mm for beam profile values behind bone heterogeneity at 5, 10, 20, and 30 mm field sizes, respectively. Conclusion: The results presented that the MAGIC polymer gel dosimeter is a proper instrument for dosimetry beyond high density heterogeneity.

Evaluation of field-in-field, three-field, and four-field techniques for treatment planning of radiotherapy of pancreatic cancer.

Background: Pancreatic adenocarcinoma is a lethal condition with poor outcomes by various treatment modalities and an increasing incidence. Aim: The aim of this study is to evaluate the advantages of field-in-field (FIF) versus three-field and four-field radiation treatment planning techniques in three-dimensional treatment of patients with pancreatic cancer. Materials and Methods: The evaluations of these planning techniques were performed in terms of physical and biological criteria. Radiotherapy treatment data of 20 patients with pancreatic cancer were selected and evaluated for FIF, three-field, and four-field treatment techniques. The patients were treated by 6 MV photon beam of a medical linac, and these three treatment planning techniques were evaluated for all the 20 patients. The plans were compared based on dose distribution in the target volume, monitor unit (MU), and dose to organs at risk (OARs). Results: The results have shown that, with assuming the same prescribed dose to planned target volume, FIF plans have some advantages over three-field and four-field treatment plans, based on MU values, V20 Gy in the right lung, V20 Gy in the left lung, Dmean in the left kidney, Dmean in the liver, and Dmean in the spinal cord. Based on the obtained results, the use of FIF technique reduces MUs compared to the three-field and four-field techniques. Conclusion: Having a less MU for performing treatment reduces scattered radiation and therefore reduces the risk of secondary cancer in normal tissues. In addition, the use of FIF technique has advantage of less radiation dose to some OARs.

Bismuth oxide nanoparticles as agents of radiation dose enhancement in intraoperative radiotherapy.

PURPOSE: Intraoperative radiotherapy (IORT) technique is an advanced radio therapeutic method used for delivery of a single high-dose radiation during surgery while removing healthy tissues from the radiation field. Nowadays, growing attention is being paid to IORT for its low-energy (kilovoltage) delivery as it requires less radiation protection, but suffers several disadvantages, including high-dose delivery and prolonged treatment time. The application of nanoparticles with high atomic number and high attenuation coefficients in kilovoltage energy may help overcome the mentioned shortcomings. This study was designed to investigate and quantify the mean dose enhancement factor (DEF) in the presence of nanoparticles using IORT method. METHODS: Bismuth oxide nanoparticles (Bi2 O3 NPs), both in sheet and spherical formats, were synthesized using a novel hydrothermal method and characterized with x-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis. Genipin-gelatin gel dosimeter (GENIPIN) was produced in three batches of pure with sheet and with spherical nanoparticles in concentration of 46.596 µg/ml, and irradiated with 50 kV x-rays. RESULTS: Samples were scanned by a spectrophotometer, which indicated a DEF of 3.28  ±  0.37 and 2.50  ±  0.23 for sheet and spherical NPs, respectively. According to the results of this study, GENIPIN is a suitable dosimeter for the evaluation of three-dimensional dose distribution in the presence Bi2 O3 NPs. CONCLUSION: As a result, IORT along with Bi2 O3 NPs has the potential to reduce treatment time and/or normal tissue dose; moreover, it could provide localized dose enhancement.

Evaluation of ferrous benzoic methylthymol-blue gel as a dosimeter via magnetic resonance imaging.

PURPOSE: In previous studies, methylthymol-blue and benzoic acid have been introduced as a diffuser limiter and sensitivity enhancer in the gel dosimeter composition, respectively. This work focused on analyzing a formulation of the Fricke gel dosimeter consisting of methylthymol-blue and benzoic acid through magnetic resonance imaging. METHODS: The gel dosimeter samples were irradiated using 6, 10, and 15 MV photons with different levels of doses and read using a 1.5 T scanner in order to evaluate the dose-response sensitivity and to study the effect of benzoic acid concentration, diffusion coefficient and temperature and to determine the temporal stability of the gel dosimeter. RESULTS: Inspection of radiological properties revealed that this gel dosimeter can be considered as a tissue equivalent medium. Within the dose range 0 to 1000 cGy, the R1 sensitivity and R2 sensitivity of the gel dosimeter equaled 0.058 ± 0.003 and 0.092 ± 0.004 s-1Gy-1, respectively. The diffusion coefficient was less than 0.85 ± 0.02mm2h-1 for doses higher than 200 cGy. In addition, by changing the temperature from 15C to 25, the R1 sensitivity and R2 sensitivity decreased about 5 and 11%, respectively. Further, no significant energy and dose rate dependence were observed over photon energies of 6, 10, and 15 MV and over the range 65 to 525 cGy min-1. CONCLUSIONS: Based on our observation, the ferrous benzoic acid methylthymol-blue gel dosimeter can be suggested to measure the dose distribution. Further analysis is required to clarify its performance in clinical situations.

Evaluation of lung heterogeneity effects on dosimetric parameters in small photon fields using MAGIC polymer gel, Gafchromic film, and Monte Carlo simulation.

In this work, the performance of MAGIC polymer gel in measuring dosimetric parameters beyond lung heterogeneity in small fields was investigated. All data were obtained using MAGIC, EBT2, and MC in four small field sizes. The maximum local differences between MAGIC and MC were less than 5.1, 3.9, 3.1, and 2.6% for PDD values behind lung heterogeneity at 5, 10, 20, and 30 mm field sizes, respectively. The findings showed that MAGIC is a suitable tool for dosimetry behind low-density heterogeneity.

Targets for improving tumor response to radiotherapy.

Radiotherapy is one of the most common treatment modalities for controlling a wide range of tumors. However, it has been shown that radiotherapy alone is unable to completely eradicate some tumors and could be associated with a high possibility of tumor recurrence. To date, various experimental and clinical studies have been conducted to explore some efficient targets within tumor microenvironment (TME) to enhance tumor response to radiotherapy; thus help eliminate or eradicate tumors. Although targeting DNA damage responses (DDRs) is associated with severe toxicities, studies in recent decade suggest that inhibition of some apoptosis/survival targets within TME is promising. This is also associated with changes in the numbers of T regulatory cells (Tregs) and cytotoxic T lymphocytes (CTLs). The inhibition of cyclooxygenase-2 (COX-2), phosphoinositide 3-kinase (PI3K), mammalian target of rapamycin (mTOR), mitogen-activated protein kinases (MAPKs) and vascular endothelial growth factor (VEGF) have also shown promising results. The combination of receptor tyrosine kinase (RTK) inhibitors with radiotherapy is interesting as well as the clinical use of some drugs and antibodies. Epidermal growth factor receptor (EGFR) inhibitors are the most common RTK inhibitors. Some clinical trials in recent years have shown very interesting results for immune checkpoint inhibitors (ICIs), especially programmed death-ligand 1 (PD-L1) and CTLs-associated antigen 4 (CTLA-4) inhibitors. It has been suggested that administration of ICIs during or after hypofractionated radiotherapy could lead to best results. In this review, we explain TME response to radiotherapy and potential targets for sensitization of cancer cells to radiotherapy.

Different Dosimeters/Detectors Used in Small-Field Dosimetry: Pros and Cons.

With the advent of complex and precise radiation therapy techniques, the use of relatively small fields is needed. Using such field sizes can cause uncertainty in dosimetry; therefore, special attention is required both in dose calculations and measurements. There are several challenges in small-field dosimetry such as the steep gradient of the radiation field, volume averaging effect, lack of charged particle equilibrium, partial occlusion of radiation source, beam alignment, and unable to use a reference dosimeter. Due to these challenges, special dosimeters are needed for small-field dosimetry, and this review article discusses this topic.