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Aims: This study aimed to compare the skin dose calculated by treatment planning system (TPS) and measured with thermoluminescent dosimeters (TLDs) in brachytherapy of prostatic cancer to show the skin TLD dosimetry as an appropriate quality assurance procedure for TPS dose calculations. Methods: The skin dose of 15 patients with prostatic cancer treated by high dose rate brachytherapy technique was assessed by two types of TLD dosimeters (GR-200 and TLD-100). The TLDs were placed on the patient's skin at three different points (anterior, left, and right) using five TLDs for each point. The dose values of TLDs and TPS were compared using paired t-test and the percentages of difference were reported. Results: There was a good agreement between TPS calculations and TLDs measurements for both of the GR-200 and TLD-100 dosimeters. The mean skin dose values for anterior, left, and right points were 65.06±21.88, 13.88±4.1, and 10.05±4.39 cGy, respectively, for TPS. These values were 65.70±23.2, 14.51±4.3, and 10.54±5 cGy for GR-200, and 64.22±23.5, 13.43±4.4, and 9.99±4.1 cGy for TLD-100, respectively. Conclusion: The TPS skin dose calculations in brachytherapy of prostatic cancer had a good agreement with the TLD-100 and GR-200 measurements at the three different points on patients' skin. TLD-100 had lower differences with TPS calculations compared to GR-200. Relevance for Patients: The outcome of this research shows that for people with prostatic cancer, TPS can estimate accurately the skin dose of different points including anterior, left, and right in brachytherapy technique.
RESUMO
Gafchromic films are utilized for two-dimensional dose distribution measurements, especially in radiotherapy. In this study, we investigated a close connection between energy and dose rate of Gafchromic EBT3 films irradiating with 6 MV and Co-60 photon beams over a broad dose range. EBT3 films were exposed to 6 MV and Co-60 photon beams using 4 and 2 Gy/min dose rates over a 10-400 cGy dose range. The films were scanned in red, green, and blue channels to obtain the optical density (OD)-dose curves. The OD-dose curves resulted from three-color scans for different photon energies and dose rates were compared by statistical independent t-test. For the radiations of Co-60 and 6 MV photon beams, the highest correlation was obtained between the 2 and 4 Gy/min dose rates with red and green channels, respectively. Moreover, the red channel had a greater OD response per dose value, following the green and blue channels. There was no significant difference between different photon energies' (Co-60 and 6 MV) and dose rates' (2 and 4 Gy/min) dependence on OD-dose response of EBT3 films over a broad domain of radiation dose, except for different photon energies in the blue channel. Our results revealed that the OD-dose response of EBT3 films is independent on photon energies (Co-60 and 6 MV) and dose rate (2 and 4 Gy/min) in the evaluated dose range (10-400 cGy). Therefore, the EBT3 films are suitable, consistent, and reliable instruments for dose measurements in radiotherapy.
RESUMO
BACKGROUND: Melatonin is a natural body product that has shown potent antioxidant property against various toxic agents. For more than two decades, the abilities of melatonin as a potent radioprotector against toxic effects of ionizing radiation (IR) have been proved. However, in the recent years, several studies have been conducted to illustrate how melatonin protects normal cells against IR. Studies proposed that melatonin is able to directly neutralize free radicals produced by IR, leading to the production of some low toxic products. DISCUSSION: Moreover, melatonin affects several signaling pathways, such as inflammatory responses, antioxidant defense, DNA repair response enzymes, pro-oxidant enzymes etc. Animal studies have confirmed that melatonin is able to alleviate radiation-induced cell death via inhibiting pro-apoptosis and upregulation of anti-apoptosis genes. These properties are very interesting for clinical radiotherapy applications, as well as mitigation of radiation injury in a possible radiation disaster. An interesting property of melatonin is mitochondrial ROS targeting that has been proposed as a strategy for mitigating effects in radiosensitive organs, such as bone marrow, gastrointestinal system and lungs. However, there is a need to prove the mitigatory effects of melatonin in experimental studies. CONCLUSION: In this review, we aim to clarify the molecular mechanisms of radioprotective effects of melatonin, as well as possible applications as a radiation countermeasure in accidental exposure or nuclear/radiological disasters.
