Induction of Apoptotic Temperature in Photothermal Therapy under Various Heating Conditions in Multi-Layered Skin Structure

Recently, photothermal therapy has attracted attention as an alternative treatment to conventional surgical techniques because it does not lead to bleeding and patients quickly recover after treatment compared to incisional surgery. Photothermal therapy induces tumor cell death through an increase in the temperature using the photothermal effect, which converts light energy into thermal energy. This study was conducted to perform numerical analysis based on heat transfer to induce apoptosis of tumor tissue under various heating conditions in photothermal therapy. The Monte Carlo method was applied to evaluate a multi-layered skin structure containing squamous cell carcinoma. Tissue-equivalent phantom experiments verified the numerical model. Based on the effective apoptosis retention ratio, the numerical analysis results showed the quantitative correlation for the laser intensity, volume fraction of gold nanorods injected into the tumor, and cooling time. This study reveals optimal conditions for maximizing apoptosis within tumor tissue while minimizing thermal damage to surrounding tissues under various heating conditions. This approach may be useful as a standard treatment when performing photothermal therapy.

Influence of Different Percentages of Binders on the Physico-Mechanical Properties of Rhizophora spp. Particleboard as Natural-Based Tissue-Equivalent Phantom for Radiation Dosimetry Applications

Rhizophora spp. particleboard with the incorporation of lignin and soy flour as binders were fabricated and the influence of different percentages of lignin and soy flour (0%, 6% and 12%) on the physico-mechanical properties of the particleboard were studied. The samples were characterised by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray fluorescence (XRF) and internal bonding. The results stipulated that the addition of binders in the fabrication of the particleboard did not change the functional groups according to the FTIR spectrum. For XRD, addition of binders did not reveal any major transformation within the composites. SEM and EDX analyses for all percentages of binders added showed no apparent disparity; however, it is important to note that the incorporation of binders allows better bonding between the molecules. In XRF analysis, lower percentage of chlorine in the adhesive-bonded samples may be advantageous in maintaining the natural properties of the particleboard. In internal bonding, increased internal bond strength in samples with binders may indicate better structural integrity and physico-mechanical strength. In conclusion, the incorporation of lignin and soy flour as binders may potentially strengthen and fortify the particleboard, thus, can be a reliable phantom in radiation dosimetry applications.

A phantom study to contrast and compare polymer and gold fiducial markers in radiotherapy simulation imaging

To assess visibility and artifact characteristics of polymer fiducials compared to standard gold fiducials for radiotherapy CT and MRI simulation. Three gold and three polymer fiducials were inserted into a CT and MRI tissue-equivalent phantom that approximated the prostate cancer radiotherapy configuration. The phantom and fiducials were imaged on CT and MRI. Images were assessed in terms of fiducial visibility and artifact. ImageJ was employed to quantify the pixel gray-scale of each fiducial and artifact. Fiducial gray-scale histograms and profiles were generated for analysis. Objective measurements of the contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and artifact index (AI) were calculated. The CT images showed that the gold fiducials are visually brighter, with greater contrast than the polymer. The higher peak values illustrate this in the line profiles. However, they produce bright radiating and dark shadowing artifacts. This is depicted by the greater width of line profiles and the disruption of phantom area profiles. Quantitatively this results in greater percentile ranges of the histograms. Furthermore, for CT, gold had a higher CNR than polymer, relative to the phantom. However, the gold CNR and SNR were degraded by the greater artifact and thus AI. Both fiducials were visible on MRI and had similar histograms and profiles that were also reflected in comparable CNR, SNR and AI. Polymer fiducials were well visualized in a phantom on CT and MR and produce less artifact than the gold fiducials. Polymer markers could enhance the quality and accuracy of radiotherapy co-registration and planning but require clinical confirmation.

Analysis of Dose Load on a Pregnant patient in Radiotherapy of Oropharal Cancer

Purpose: The assessment of the dose load on a pregnant patient during irradiation of the oropharyngeal tumor at different distances from the border of the irradiated field, including at the level corresponding to the position of the fetus, based on phantom measurements.Material and methods: To calculate the exposure plan, the ECLIPSE planning system with the AAA algorithm was used. Irradiation was performed on a LinacClinaciX (Varian, USA) with a nominal photon energy of 6 MeV. The tissue equivalent phantom Alderson–Rando was used to assess the dose load on the fetus.Results and conclusions: It was shown that the total absorbed dose at the level and below the diaphragm (the level of the fetus) at a distance of more than 40 cm from the border of the irradiation field for the entire course of radiation therapy turned out to be significantly less than the permissible limits indicated in the literature and amounted from 41.71 to 14.03 mGy.

Physical and mechanical properties of soy-lignin bonded Rhizophora spp. particleboard as a tissue-equivalent phantom material

Experimental binderless and adhesive-bonded particleboards were made from three different sample sizes, 0 to 103 µm, 104 to 210 µm, and 211 to 500 µm from Rhizophora spp. wood trunk at 1.0 g cm-3. The objective was to evaluate the physical and mechanical properties of the particleboards. The binderless and soy-lignin bonded particleboards were fabricated and studied based on the density, internal bonding, modulus of rupture, water absorption, and thickness swelling. Microstructure study using scanning electron microscopy (SEM) and elemental analysis by carbon hydrogen nitrogen (CHN) analyser were also performed. Particleboards with adhesives improved the internal bond strength. Smaller particle sizes also were shown to be able to improve the thickness swelling outcomes, with lower hygroscopic properties. The SEM images showed that smaller particle size allowed better bonding with adhesives and provided superior strength in the fabrication of tissue equivalent phantom material. The CHN ratio demonstrated by soy flour and lignin revealed no major difference when compared with the Rhizophora spp. samples, showing basic chemical composition of natural adhesives, which was crucial in the fabrication of tissue-mimicking phantom. The study revealed the potential of soy flour and lignin as adhesives for the fabrication of Rhizophora spp. particleboard as a tissue equivalent phantom material.

TISSUE EQUIVALENT MATERIALS FROM SPC-SPI/NAOH/IA-PAE BONDED MANGROVE WOOD CHARACTERIZED FOR RADIATION THERAPY DOSIMETRY

This research focuses on dosimetric measurements in bio-based tissue equivalent phantom materials, designed using soy protein concentrate (SPC), soy protein isolate (SPI), Rhizophora spp. wood, sodium hydroxide, and itaconic acid polyamidoamine-epichlorohydrin resin with an ionization chamber and GafchromicTH EBT3 film dosimeters. The measurements were performed under exposure to 6 MV and 10 MV photon, and 6 MeV and 15 MeV electron beams. The particleboard samples were exposed to a dose of 100 cGy and 10 x 10 cm2 field size at a source-to-surface distance of 100 cm. The dosimeters were irradiated at measurement depths of 1.5, 2.5 and 3.0 cm, respectively, inside the phantom slabs. The particleboards presented superior physical and mechanical properties. The dose measurements revealed excellent agreement with that of water and solid water phantoms. In addition, comparison between the measured dosimetric properties is well within 2%, 2%, 10% and 5.5% for 6 MV, 6 MeV, 10 MV and 15 MeV energies of the maximum dose for the field size tested. This study had successfully shown that SPC-SPI/NaOH/IA-PAE bonded Rhizophora spp. particleboards are promising tissue equivalent phantom materials with merit for medical applications.

THERMAL AND FAST NEUTRON DOSE EQUIVALENT DISTRIBUTION MEASUREMENT OF 15-MV LINEAR ACCELERATOR USING A CR-39 NUCLEAR TRACK DETECTORS

The main purpose of this study is to measure the contribution of the thermal and fast neutron dose along the central axis of the 15 MV Elekta Precise linac in a tissue equivalent phantom. In order to achieve this purpose, different points were selected in three field sizes of 5 × 5 cm2, 10 × 10 cm2 and 15 × 15 cm2. Fast and thermal neutrons were measured using CR-39 nuclear track detectors with and without thermal neutron converter of 10B, respectively. According to the results, the fast neutron dose equivalent was decreased as the depth increased (field size 5 × 5, 10 × 10 and 15 × 15 cm2 fall from 0.35 to 0.15, 0.5 to 0.3 and 0.5 to 0.3, respectively). Thermal dose equivalent was increased as the depth increased in the tissue equivalent phantom (field size 5 × 5, 10 × 10 and 15 × 15 cm2 rise from 0.1 to 0.4, 0.4 to 0.8 and 0.4 to 0.9, respectively). In conclusion, at depth <3 cm, most existing neutrons are fast and CR-39 films are sensitive to fast neutrons; therefore, they are more appropriate than thermoluminescent dosemeters in measuring neutron dose equivalent.

Radiation Exposure of Medical Personnel Accompanying the Patient during the Procedure of Superficial X-Ray Therapy of Children

Purpose: Assessment the radiation situation in the treatment room of superficial x-ray therapy during the irradiation process in order to inform about radiation exposure of medical personnel or a relatives. Material and methods: In the course of the study, a procedure of superficial radiotherapy was simulated using a tissue equivalent phantom with sizes 250×250×150 mm. The radiation control protocol of measurements on the Roentgen TA-02 apparatus was compiled on the basis of SanPiN 2.6.1.1192-03. With the help of a clinical dosimeter DKS-AT1123, the ambient dose-rate of short-term x-rays was measured. In accordance with the requirements for conducting radiation monitoring, measurements were taken directly near the apparatus in areas 60×60 cm at points located at heights corresponding to the head level (160 ± 20 cm), chest level (120 ± 20 cm), gonad level (80 ± 20 cm) and the level of the legs (30 ± 20 cm). On the basis of the obtained data, the value of the effective dose-rate of x-ray radiation for the whole human body was calculated for each area. Taking into account the characteristics of the irradiation regime used in the clinic, the total effective dose received by the medical personnel accompanying the patient for the entire course of radiotherapy was calculated. Results: A drawn up diagram is illustrating the radiation situation in the treatment room of superficial radiotherapy. Based on the results of calculations, it can be concluded that the radiation exposure on the accompanying person during superficial x-ray therapy of children’s hemangiomas does not exceed the maximum permissible dose specified in paragraph 5.4.4 of SanPiN 2.6.1.2523-09. Conclusion: In exceptional cases, a parent or medical personnel may be in the treatment room to support the patient.

Implementation of compensator-based intensity modulated radiotherapy with a conventional telecobalt machine using missing tissue approach

Objectives: The present study aimed to generate intensity-modulated beams with compensators for a conventional telecobalt machine, based on dose distributions generated with a treatment planning system (TPS) performing forward planning, and cannot directly simulate a compensator. Materials and Methods: The following materials were selected for compensator construction: Brass, Copper and Perspex (PMMA). Boluses with varying thicknesses across the surface of a tissue-equivalent phantom were used to achieve beam intensity modulations during treatment planning with the TPS. Beam data measured for specific treatment parameters in a full scatter water phantom with a 0.125 cc cylindrical ionization chamber, with a particular compensator material in the path of beams from the telecobalt machine, and that without the compensator but the heights of water above the detector adjusted to get the same detector readings as before, were used to develop and propose a semi-empirical equation for converting a bolus thickness to compensator material thickness, such that any point within the phantom would receive the planned dose. Once the dimensions of a compensator had been determined, the compensator was constructed using the cubic pile method. The treatment plans generated with the TPS were replicated on the telecobalt machine with a bolus within each beam represented with its corresponding compensator mounted on the accessory holder of the telecobalt machine. Results: Dose distributions measured in the tissue-equivalent phantom with calibrated Gafchromic EBT2 films for compensators constructed based on the proposed approach, were comparable to those of the TPS with deviation less than or equal to ± 3% (mean of 2.29 ± 0.61%) of the measured doses, with resultant confidence limit value of 3.21. Conclusion: The use of the proposed approach for clinical application is recommended, and could facilitate the generation of intensity-modulated beams with limited resources using the missing tissue approach rendering encouraging results.