Iranian Journal of Medical Physics
Volume:19 Issue: 1, Jan-Feb 2022

Dose reduction to the duodenum is important to decrease gastrointestinal toxicities in patients with locally advanced pancreatic cancer (LAPC) treated with definitive chemoradiotherapy. We aimed to compare dynamic wave arc (DWA), a volumetric-modulated beam delivery technique with simultaneous gantry/ring rotations passing the waved trajectories, with coplanar VMAT (co-VMAT) with respect to dose distributions in LAPC cases.
DWA and co-VMAT plans were created for 13 patients with LAPC. The prescribed dose was 45.6 or 48 Gy in 15 fractions. The dose volume indices (DVIs) for target volumes and organs at risk were compared between the corresponding plans. Gamma passing rate, monitor unit (MU), and beam-on time were also compared. 
DWA significantly reduced the duodenal V39Gy, V42Gy, and V45Gy by 1.1, 0.8, and 0.2 cm3, and increased the liver mean dose and D2cm3 of the spinal cord planning volume by 1.0 and 1.5 Gy, respectively. Meanwhile, there was no significant difference in the target volumes except for D2% of PTV (111.5% in DWA vs. 110.5% in co-VMAT). Further, the gamma passing rate was similar in both plans. MU and beam-on time increased in DWA by 31 MUs and 15 seconds, respectively. 
DWA generated significantly lower duodenal doses in LAPC cases, albeit with slight increasing liver and spinal cord doses and increasing MU and the beam delivery time. Further evaluation is needed to know how the dose differences would affect the clinical outcomes in chemoradiotherapy for LAPC.

The aim of the present study was to understand the effect of low-doses of ionizing radiation (LDIR) on repair genes expression in blood samples that were taken from healthy donors. The next purpose was to examine the time-effect on the modified gene expression caused by low-doses of ionizing radiation.

The RNA of peripheral blood lymphocytes (PBLs) taken from four healthy donors was isolated at different time points after exposure including 4, 24, 48, 72, and 168 hours and then cDNA was synthesized. Modification of XPA and RAD51 expression levels due to LDIR (2, 5, 10 cGy) were evaluated by relative quantitative reverse transcription-polymerase chain reaction.

Significant up-regulation of both repair genes was observed at the 4 and 168 h following to 10 cGy.  Also, this dose could increase expression levels of RAD51 at 48 and 72 h after radiation. For lower doses at 5 cGy, only XPA levels were significantly up-regulated after 168 h. A significant regression was found between the XPA levels and the dose, at 168 h after irradiation to PBLs that can represent a new potential biomarker for biological dosimetry purposes.

The results of this study could support the hypothetical role of the different DNA repair pathways in response to LDIR. This led us to propose a molecular biodosimetry method for ionizing radiation in the range of LDIR.

Treatment planning systems use TG-43 dose calculation protocol for brachytherapy sources. Dose calculations based on TG-43 formalism do not correct the perturbations due to the presence of tissue inhomogeneity, applicators, and inter-seed effects. Inter-seed attenuation has an important effect on dosimetry in permanent implant brachytherapy. The aim of this study is to evaluate the inter-seed attenuation effect for I-125 permanent implants. Then, software was developed to find the real dose distribution for different combinations of sources. In the first step, a hypothetical generic source model was designed based on the configurations of different commercial source types. MCNP5 Monte Carlo code was utilized to simulate the single active generic source at the center of the phantom, and an inactive placed at various positions inside the phantom. An algorithm was introduced using artificial neural network models that can estimate the dose distribution in presence of inactive sources. The Monte Carlo calculation results showed that the dose distribution is affected by the inter-seed attenuation effect. Comparison of the artificial neural network results with the Monte Carlo simulation results show that the artificial neural networks can predict the inter-seed attenuation with acceptable accuracy. Comparison of the MC calculations, and the ANN output does not show statistically significant differences between the results (P value>0.95). Inter-seed effect is dependent on the distance between the seeds. Decreasing distances would cause more effect. According to the results, it seems that the artificial neural network can be used as a tool for correction of inter-seed attenuation effect in treatment planning systems.

The calibration process is usually limited to the depth of maximum energy. This study aimed to determine the depth dose in a heterogeneous medium using diodes and to evaluate a dose calculation algorithm.
Measurements were done at three depths (4, 8, and 12 cm) using ten QEDTM diodes on heterogeneous phantoms (HPH), composed of poly(methyl methacrylate) (PMMA) and expanded polystyrene, roughly simulating the rib cage. These phantoms were irradiated with 6-MV and 18-MV photon beams from a Varian linear accelerator by plans calculated by the Eclipse treatment planning system, equipped with the Anisotropic Analytical Algorithm (AAA). The calibration curves were drawn by considering several measurement points in depth by a graphite ionization chamber in the HPH. The diode calibration factor was taken from the curves via interpolation. The measured and calculated values were compared to evaluate the AAA.
Depending on the depth, the deviations between the measurements and calculations predicted by the TPS remained less than 2%. Some measurements had an order of magnitude of nearly 3%. An average deviation of 1.13% was obtained for all measurements, with an average deviation of 0.66% and a standard deviation of 0.80%. The upper bound of the confidence interval was 1.41%.
The deviations obtained in this study remained within the recommended standard range for validation of a dose calculation algorithm in a heterogeneous medium. The calibration method based on dose profiles provided further information about the dose in a heterogeneous medium, based on a single diode reading.

Dose reduction to the duodenum is important to decrease gastrointestinal toxicities in patients with locally advanced pancreatic cancer (LAPC) treated with definitive chemoradiotherapy. We aimed to compare dynamic wave arc (DWA), a volumetric-modulated beam delivery technique with simultaneous gantry/ring rotations passing the waved trajectories, with coplanar VMAT (co-VMAT) with respect to dose distributions in LAPC cases.

DWA and co-VMAT plans were created for 13 patients with LAPC. The prescribed dose was 45.6 or 48 Gy in 15 fractions. The dose volume indices (DVIs) for target volumes and organs at risk were compared between the corresponding plans. Gamma passing rate, monitor unit (MU), and beam-on time were also compared.

DWA significantly reduced the duodenal V39Gy, V42Gy, and V45Gy by 1.1, 0.8, and 0.2 cm3, and increased the liver mean dose and D2cm3 of the spinal cord planning volume by 1.0 and 1.5 Gy, respectively. Meanwhile, there was no significant difference in the target volumes except for D2% of PTV (111.5% in DWA vs. 110.5% in co-VMAT). Further, the gamma passing rate was similar in both plans. MU and beam- on time increased in DWA by 31 MUs and 15 seconds, respectively.

DWA generated significantly lower duodenal doses in LAPC cases, albeit with slight increasing liver and spinal cord doses and increasing MU and the beam delivery time. Further evaluation is needed to know how the dose differences would affect the clinical outcomes in chemoradiotherapy for LAPC.

In Yttrium-90 SPECT imaging, the energy window and collimator used during projection acquisition can significantly affect image quality. In this work, we used a new and independent method to verify previous results, which suggest suitable energy around 130 keV.
We used Siemens Symbia SPECT-CT system fitted with High Energy General Purpose (HEGP), Medium Energy General Purpose (MEGP), and Low Energy High Resolution (LEHR) to acquire data from NEMA IEC PET Body Phantom filled with 90Y chloride. ISO-counting curve is a new method analysed in this study to evaluate the adequate parameters for 90Y SPECT imaging.
HEGP collimator was the most suitable for acquisitions of 90Y bremsstrahlung radiation from the point of view of the correct volume reproduction. ISO-counting analyses have shown that for the bigger phantom spheres, the optimum acquisition energy is centered on 130 keV.
The ISO-counting curve method is consistent to previous studies’ results and can help to improve image quality.

The development of nanoparticles as computed tomography contrast agents has increased significantly. However, few reports have been published on the use of silver and platinum nanoparticles as contrast agents. These nanomaterials are a good candidatefor contrast agents because of their high atomic number and high durability against corrosion.
Experimentally, a Nd:YAG laser (1064 nm, 45 mJ, 10 Hz) was focused on a high-purity metal plate including Ag and Pt plates, which are placed in deionized water medium. Colloidal nanoparticles of Ag and Pt were then mixed to obtain a mixture composition of Ag and Pt with ratios of Ag:Pt of 75:25%, 50:50%, 25:75%, respectively.The Ag, Pt, and Ag-Pt NPs mixture were then examined as contrast agents in CT scan.
The imaging results of the quantitative analysiswere measured in the Hounsfield Unit(HU), showing 13.5, 12.8, 13.3, 14.1, and 17.3 HU for colloidal 100% AgNPs, colloidal Ag and Pt NPs with volume ratios of Ag:Pt of 75:25%, 50:50%, 25:75%, and colloidal 100%Pt NPs, respectively.
Results reveal the highest absorbent power was found in the colloidal contrast agent of Pt NPs 100% is 17.3 HU, followed by the 25:75% Ag-Pt NPs is 14.1 HU. The higher HU value for platinum can be attributed to its higher density since the effective energy of 80 kVp is about 42 keV, which is lower than the K-edge of Pt (K-edge ≈ 78 keV), which means that the attenuation of X-ray in Pt is due to Compton scattering dominantly.

Photodynamic therapy (PDT) can be considered as a non-invasive method for cancer treatment. One of the most commonly of a water-soluble dye photosensitizer (PS) used in photothermal therapy (PTT) and PDT is Indocyanine Green (ICG). However, high ‎cytotoxicity in high concentration and instability in aqueous media were limited its application. ‎It was shown that using nanoparticles or plant extracts in combination with PS could improve PDT efficiency. In this study, anti-cancer properties of crocetin (Crt) loaded PLGA (Poly lactic-co-glycolic acid) nanoparticles (NPs) were utilized to increase the PDT efficacy with ICG on the MCF-7 cells.
Crt was encapsulated into PLGA NPs and its particle size distribution and encapsulation efficiency were evaluated. IC10 of Crt, PLGA-Crt NPs and ICG was determined by MTT assay in MCF-7 cancer cells. At these concentrations, the cells were pre-treated with Crt or PLG-Crt, then treated with ICG and finally exposure to near infrared (NIR) laser with 2.5 W powers at different times. The cells viability was evaluated by the MTT assay.
The findings showed no dark cytotoxicity due to ICG (12.9 μM), Crt or PLGA-Crt alone. But NIR laser irradiation in the presence of ICG after cells pre-treatment by the Crt or PLGA-Crt NPs leads to induce cell death to (61.6 ±7) % and (75.5 ±5) %, respectively (P<0.05).
The results demonstrated that PLGA-Crt NPs in combination with ICG could improve PDT outcomes more efficiently in comparison with Crt and ICG. Therefore, this method could be effective in breast cancer therapy with low cytotoxicity.