Iranian Journal of Medical Physics
Volume:19 Issue: 4, Jul-Aug 2022

High-intensity Focused Ultrasound (HIFU) treatment is a non-invasive technology. The purpose of this study was to explore the effects of different treatment depths, tissue types and treatment interval on biological tissue thermal lesions under continuous and intermittent treatment modes. A simulation model of biological tissue irradiated by HIFU was established by finite difference time domain (FDTD). The thermal lesion of biological tissue irradiated by HIFU was calculated using the spherical beam equation (SBE) and Pennes biological heat transfer equation (PBHTE). Parameters such as treatment depth, tissue type, and treatment interval were varied to explore their effects on the thermal lesion to biological tissues in both continuous and intermittent treatment modes. For the same biological tissue or treatment depth, with the increase of HIFU irradiation time, the focal temperature under continuous treatment was higher than that under intermittent treatment, and the thermal lesion area under continuous treatment was greater than that under intermittent treatment. Whether continuous or intermittent treatment, with the increase of treatment depth, the temperature rise rate of deep tissue was slower than that of superficial tissue, and the thermal lesion area decreased gradually. Moreover, in the intermittent treatment mode with a long single treatment time and short treatment interval, the focal temperature rase quickly and the thermal lesion area was large. For the same tissue type, treatment depth, or any treatment interval, the focal temperature and thermal lesion area corresponding to continuous treatment were greater than those corresponding to intermittent treatment.

The stimulation of DNA repair mechanisms is an immediate response to radiation-induced damage. Monitoring the expression of DNA-repair-related genes would be a beneficial method to identify bio-dosimeter of radiation exposure, particularly for challenging low-dose radiation. In this study, we aimed to evaluate the effect of different low doses of gamma radiation on the expression of DDB2, XPC, and GADD45A genes involved in DNA-damage repair mechanisms.

Forty-eight male rats were divided into a control group and five exposure groups. The latter groups exposed to various doses of γ-rays (Co-60) ranged from 20 mGy to 1000 mGy. 24 h after irradiation, isolated lymphocytes from collected blood samples were used for evaluating gene expression levels by real-time quantitative polymerase chain reaction (qRT-PCR). Data were expressed as means ± SD and were statistically evaluated using one‑way ANOVA or Kruskal-Wallis test. P value<0.05 was considered as a significant value.

DDB2, GADD45A, and XPC expression remained unchanged at a dose of 20 mGy, and at doses above 20 mGy, they changed significantly. XPC and GADD45A altered significantly at 50 mGy while DDB2 changed significantly after exposure to 100, 500, and 1000 mGy.

Low doses of gamma radiation (less than 1 Gy) can significantly affect DDB2, XPC, and GADD45A expression, three central genes in the DNA-damage repair process. The extent of the gene expression changes at higher doses of 100, 500, and 1000 mGy seems more severe than that of their lower counterparts (50 mGy).

The purpose of this study is to evaluate and compare treatment plan quality metrics for postmastectomy breast cancer patients using 3-Dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) planning techniques. The current study included 50 postmastectomy breast cancer patients out of which 24 were planned with 3DCRT and 26 with IMRT technique. Treatment plan quality metrics, namely homogeneity index (HI), conformity index (CI), conformation number (CN), uniformity index (UI) and spillage index (R50), volume receiving 110% and 95% of the prescribed dose (V110% and V95%) were calculated and compared for the two planning techniques. IMRT plans have better conformity, homogeneity indices, and lower V110% than 3DCRT plans with an almost similar R50% and V95%. Quantitative values of radiotherapy treatment plan quality metrics for the target are found in favour of the IMRT technique rather than 3DCRT. Implementation of these five parameters is helpful for evaluating treatment plans along with slice by slice and DVH analysis.

Radiation-induced secondary primary cancer is one of the significant late side effects and an undesired outcome of radiotherapy that can be observed in long-term cancer survivors. The present study aimed to estimate the risk of second cancer risk after Three-dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT) for early stage prostate cancer patient. In this study, 10 patients with early stage prostate cancer have been chosen. Three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) plans were designed. The organ equivalent dose (OED) was calculated based on linear, linear-exponential, and plateau dose-response models. The Second cancer risks (SCR) were estimated by Excess absolute risk (EAR). The target dose coverage parameters were significantly improved in IMRT compared to 3DCRT. The rectum and bladder mean dose DMean, V50Gy% and V40Gy % were significantly decreased with IMRT. The maximum dose (DMax), DMean, V30Gy % and V20Gy % for head of femurs significantly decreased with IMRT plans. However, the colon DMean significantly increased with in IMRT compared with 3DCRT. The IMRT plans were decreased SCR for the rectum by 10%, 26.6% and 19.5% for linear, plateau and linear-exponential dose- response models respectively. The bladder second cancer risk was decreased by 14% with linear dose-response model in comparison to 3DCRT plans. However, the second cancer risk for colon was significantly increased in average by 91.2% with IMRT plans. IMRT technique demonstrated a clear advantage in dose coverage, conformity, and homogeneity over 3DCRT and was superior in terms of OAR-sparing. The Second cancer risk for in field organs (rectum and bladder) was decreased with IMRT compared 3DCRT plan.

The dose prescription point in high dose rate (HDR) intracavitory brachytherapy (ICBT) of cervical cancer is Manchester point A but the localization of this point has a wider variation. To minimize these variations, the American Brachytherapy Society (ABS) introduced a new definition of point A and named it as point H. In this study, these two points have been compared in terms of dosimetric parameters. Twenty HDR ICBT of cervical cancer patients were retrospectively evaluated with Manchester point A and ABS point H. Target volume covered by prescribed dose (TV), dose to 2cc (D2cc) of the bladder and rectum were noted for both points. Statistical analysis using a two-tailed paired t-test was performed to compare dosimetric parameters of both the points of prescription. The maximum value, minimum value, and mean ± standard deviation along with the p value have been noted. On average, point H was 4.0mm ± 6.4mm shifted (superior/inferior) from point A, along the tandem direction. The average TV when the prescription was done at point H (TVH) was 33.7cc ± 10.1cc which was higher than the average TV when the prescription was done at point A (TVA) of 33.3cc ± 9.4 cc.D2cc increased from 63% ± 23% to 68% ± 24% for the rectum and 52% ± 18% to 56% ± 20% for the bladder when the prescription point changed from A to H. As observed, average TV, D2cc of the bladder, and rectum were higher in the case of point H prescription plan (PH) as compared with point A prescription plan (PA). The dose difference between PH and PA was found to be statistically significant, so careful consideration is needed to implementation of new point H in clinical practice.

Diagnostic reference levels (DRLs) can prevent excessive, unnecessary radiation exposure to patients and reduce the dose variation during different practices. This study aims to establish local DRLs for computed tomography (CT) procedures corresponding to Head, Chest, and Abdomen-Pelvis examinations (single acquisition) in Moroccan hospitals. A total of 1917 diagnostic CT examinations were included in this study: head, chest, abdomen–pelvis, lumbar, cervical, chest-abdomen–pelvis (CAP), and scanopelvimetry. Firstly, we analyzed the CT dose indicators in terms of the Volume computed tomography dose index (CTDIvol) and the dose length product (DLP) of all the examinations collected. Local diagnostic reference levels were proposed just for the head, thorax, and abdomen-pelvis due to the lack of data for the other examinations. Furthermore, we calculated the effective dose for chest examination using CT-expo software to estimate the effective and organ dose for chest CT. The estimated local DRLs expressed as the 3rd quartile using CTDIvol were 48 mGy, 14 mGy, and 12 mGy for the head, chest, and abdomen-pelvis, respectively, and 986 mGy.cm, 496 mGy.cm, and 651 mGy.cm for DLP, respectively.  Moreover, the proposed average effective dose for chest CT examinations was 6,3 mSv. This work establishes local DRLs for CTDIvol and total DLP for head, chest, and abdomen-pelvis procedures and proposes effective doses for chest CT examinations in adult patients. The study shows that the results are conforming to the literature.

This study aimed to investigate the absorbed dose of scatter radiation in coronary angiography. The scatter radiation dose was measured for 20 patients at four different heights (50,100, 150, and 165 cm) from the floor. The spatial dose was measured by RTI Piranha r100b solid-state dose probe at different points around the patient in an actual clinical situation and with a phantom. Also, the measurement was repeated using a designed phantom in fluoroscopy and cine mode in posterior anterior (PA), left lateral (LLAT), left posterior oblique (LPO45°), right posterior oblique (RPO45°), and right-lateral (RLAT)projections . Organ-absorbed doses were normalized to dose area product (DAP).   The dose rate at different heights between the projections on the patient and the phantom as well as organ dose DAP conversion coefficients were different (p˂0.05). It was found that the dose rate changes in fluoroscopic mode compared to cine mode are significantly different (p = 0.001). The dose rate in cine mode is approximately four times that in fluoroscopy mode. The dose rate around the cardiologist's waist could be reduced by 37 – 43 % with a displacement of 20cm away. In this study, the effective dose rate received by the cardiologist’s eyes was higher than those reported by ICRP. Taking a suitable projection could reduce the dose rate delivered to the angiography team. Further studies should be conducted about the effect of different projections with the same clinical use on dose distribution in coronary angiography to provide the best working conditions for physicians and staff.

Computed Tomography (CT) is nowadays used widely to differentiate normal brain cranium sutures from abnormal ones in pediatric patients with the aim of early treatment. This study tried to develop a low-dose CT protocol with the acceptable image quality of skull bone in order to evaluate craniosynostosis. In this study a cranium bone of human cadaver was scanned with standard and reduced dose protocols. Two radiologists verified the quality of skull bone images acquired from the protocol in which there had been 60% dose reduction to scan pediatric patients. The quality of low dose protocol of three dimensional (3D) CT images of skull bone of 57 pediatric subjects suspected of craniosynostosis were compared with standard-dose skull CT images of 44 patients of the same age range. Volume CT dose index (CTDIvol), dose-length product (DLP), and effective dose (ED) were used to evaluate CT dose protocols. The comparison was made by two sample t-test. Mean and standard deviations of CTDIvol, DLP, and ED of standard and reduced doses were 12.4±2.7 mGy, 191.5±54 mGy.cm, 1.94±0.58 mSv and 5.4±0.2 mGy, 85±9 mGy.cm, 0.77±0.17 mSv, respectively, which had statistically significant difference (α=0.05). The quality of skull bone views obtained from low-dose CT protocol were found to be as good as in standard dose.  Standard-dose 3D CT protocol of skull bone can be replaced by a 60%-reduced-dose 3D CT protocol with comparable image quality in pediatric patients suspected of craniosynostosis.