Volumen 24 (2018): Edición 3 (September 2018)

The aim of this work was to investigate the potential of high frequency ultrasound for the cleaning of a Polysulfone (PSU) ultrafiltration membrane used in hemodialysis. The blood substitute solution flowing through the hollow fiber membrane used in the High Flux F60 dialyzers has been sonicated by ultrasonic (US) waves with 1 MHz frequency and 2 W/cm2 in situ intensity. The solution was comprised of toxic compounds such as Urea, Creatinine, Vitamin B12 and Inulin. The effect of US was represented by comparison of the clearance in both OFF and ON ultrasound conditions. The results of these studies have been demonstrated that US can enhance the permeability of the PSU dialyzer membrane. Results revealed that US had significant effect (p-value ˂ 0.05) on the clearance of Inulin as a large molecule (5200 D) and accelerated its filtration by 28%. The proposed dialysis method can be used alongside the existing dialysis machine.

Gold markers (GM) are increasingly used for CT and MRI registration during in intensity-modulated radiation therapy for prostate cancer. Additionally, diffusion-weighted imaging has been adopted to measure the effects of radiotherapy for prostate cancer, similar to tests of blood prostate-specific antigen levels. As diffusion-weighted imaging (DWI) is often affected by a magnetic component, we evaluated the influence of GM on the Diffusion weighted images in three cases. We found that the size range of signal void of GM in MRI was 2–5 mm. We conclude that a GM would not affect the quality of DWI in daily practice.

Purpose: To estimate the midpoint dose delivered to cervical cancer patients treated by conventional technique using Electronic Portal Imaging Device (EPID).

Materials and Methods: Clinac 2100 equipped with aS500 EPID was used in this study. A methodology was developed to generate a Gy/Calibration Unit (CU) look up table for the determination of midpoint dose of patients. 25 patients of cervical cancer were included in this study and the delivered dose to the midpoint of the patients was estimated using EPID. The deviation between the prescribed and the measured dose was calculated and analysed.

Results: EPID showed a linear response with increase in Monitor unit and the Gy/CU look up table was validated for different field sizes and depth. 250 fields were measured for 25 patients, 10 measurements per patient, weekly once and for 5 weeks. The results show that out of 250 measurements, 98% of the measurements are within ±5% and 83.2% are within ±3% for with a standard deviation of 1.66%.

Conclusion: The outcome of this study proves the efficacy of this methodology for the estimation of midpoint dose using EPID with minimal effort, time and without any inconvenience to the patients unlike other in-vivo dosimeters.

The goal of radiotherapy is to deliver prescribed dose to the target volume and simultaneously minimize the dose to the healthy organs. The purpose of this work was to verify the accuracy of calculations carried out with a treatment planning system (TPS). Measurements carried out with thermoluminescence detectors (TLDs) were compared with doses calculated with TPS. Doses were measured and calculated both in the open beam’s region and under individual blocks. Measurements were performed in the Randophantom. The work was carried out for photon beams generated in the Varian CLINAC 2100C accelerator. The maximum / minimum percentage differences between measured and calculated doses were 4.9/0.6%, 2.6/0%, and 3.5%/0.5% in open, shielded and partially shielded points, respectively. Differences between the measured and calculated doses were within acceptable limits.

The aim of this study was to investigate the impact of heterogeneity on the dose calculation for two algorithms implemented in the TPS “Analytical Anisotropic Algorithm (AAA) and Acuros XB” and validated the use of Acuros XB algorithm in clinical routine. First, we compare the dose calculated by these algorithms and the dose measured at the given point P, which is found after heterogeneity insert. Second, we extend our work on clinical cases that present a complex heterogeneity. By evaluating the impact of the choice of the algorithm on the dose coverage of the tumor, and the dose received by the organs at risk for 20 patients affected by lung cancer.

The result of our phantom study showed a good agreement with several studies that showed the superiority of the Acuros XB over the AAA in predicting dose when it concerns heterogeneous media. The treatment plans for 20 lung cancers were calculated by two algorithms AAA and Acuros XB, the results show a statistical significant difference between algorithms for Homogeneity Index and the maximum dose of planning target volume (HI: 0.11±0.01 vs 0.05±0.01 p = 0.04; Dmax: 69.30±3.12 vs 68.51±2.64 p = 0.02). Instead, no statistically significant difference was observed for conformity index CI and mean dose (CI: 0.98±0.18 vs 0.99±0.14 p = 0.33; Dmean: 66.3±0.65 vs 66.10 ±0.61 p = 0.54). For organs at risk, the maximum dose for spinal cord, mean dose and D37 % of lung minus GTV (dose receiving 37% of lung volume) were found to be lower for AAA plans than Acuros XB and the differences were statistically significant (p<0.05). For the heart D33% and D67% were found to be higher for AAA plans than Acuros XB and the differences were statistically significant (p<0.05), but No difference was observed for D100% of the heart.

The use of the AXB algorithm is suitable in the case of presence of heterogeneity, because it allows to have a better accuracy close to the Monte Carlo calculation.

Purpose: Hodgkin lymphoma (HL) is one of the most frequent malignancies among pediatric patients. One of the common causes of death in HL survivors after radiation therapy (RT), is radiation-induced heart disease (RIHD). The aim of this study was to compare several dosimetric parameters for two methods of early stage Hodgkin lymphoma radiotherapy with reference to potential risk of RIHD.

Materials and Methods: Using a series of computed tomography slices of 40 young patients, treatment planning was done in two methods of HL RT, including involved field (IFRT) and involved site (ISRT) in doses of 20, 30, and 35 Gy. Contouring of clinical target volume as well as the organs at risk, including the heart, was performed by a radiation oncologist. The mean and maximum dose of heart (D_heart-mean and D_heart-max), the volume of heart receiving a dose more than 25 Gy (V25), and the standard deviation of dose as a dose homogeneity index in heart, were used to compare the RIHD risk.

Results: The mean value for D_heart-mean in ISRT method in all doses was less compare to IFRT. Maximum reduction in mean value of D_heart-mean occurred at moving from 30 Gy IFRT to ISRT by 9.53 Gy (p < 0.001) and minimum was between 35 Gy IFRT and ISRT. The mean value for D_heart-max was fewer in IFRT rather than ISRT and the maximum difference was between 35 Gy IFRT and ISRT (1.35 Gy). The mean of V25 of heart was 26.66% and 23.74% in 35 Gy IFRT and ISRT, respectively, and dose distribution was more homogeneous in IFRT.

Conclusions: If D_heart-max and V25 of heart or homogeneity of dose distribution in heart are considered as determining factors in RIHD, then IFRT can be considered optimum, especially in 35 Gy IFRT; while, assuming the D_heart-mean as the most important factor in RIHD, superiority of ISRT over IFRT is observed.

In the radiotherapy practice, regulator defines risk in terms of physically measurable quantities and attempt to implement the results obtained from the risk assessment of this practice, using quantitative approach. Although such approach has significantly brought down radiation dose, injuries and fatalities to the workers as compared to the radiotherapy practices before World War II, the objectivity concept of risk that limits the assessment regarding physically measurable quantities is widely urged throughout the world. This study examined how the risk associated with radiotherapy practice has been perceived, and experienced by both professional and non-professional workers in the radiotherapy facilities located in Manipur, Meghalaya, and Assam. This study found that professional and nonprofessional workers exhibited different risk perception on the same physical risk. Such different risk perceptions influenced the establishment of radiological protection systems in the facility. Non-professional workers are more likely to be the affected group in a facility having weak radiological protection systems.

Background: ¹³¹I-metaiodobenzylguanidine (mIBG) offers an effectively targeted radionuclide therapy in pediatric patients. According to radiation protection authority in our country, the patient treated with high-dose (>1100 MBq) radioiodine is recommended to stay in the hospital. Hence, this study intends to measure the radiation exposure in nonlead-lined treatment room installing with portable lead shields located in general pediatric ward and surrounding areas. In addition, this study also aims to measure the radiation exposure to the family caregiver in pediatric patients received high dose ¹³¹I-mIBG.

Methods: Environmental OSL (optically stimulated luminescence) monitoring devices (InLight®, Al₂O₃:C) were prepared and calibrated by Thailand Institute of Nuclear Technology (TINT). Twenty-five set of OSLs were placed in and surrounded the treatment room. Dose to family caregiver was recorded by digital semiconductor dosimeter (ALOKA PDM-112) also calibrated by TINT. The measurement was carried for four pediatric patients treated with ¹³¹IMIBG (activity 3700 – 5500 MBq).

Results: The ambient doses equivalent and the dose rate were analyzed, the limit of 10 and 0.5 μSv/h are accepted for radiation worker and member of the public, respectively. The dose rate around the patient bed and toilet were high as expected. Dose rates at the wall of adjacent room and corridor were slightly greater than the public limit (range 1.82 to 4.48 μSv/h). Remarkably, the dose rates at caregiver chair (outside the shielding) were exceeded the limits (30.57 ± 5.69 μSv/h). Consequently, this was correlated with high personal dose equivalent to family caregivers which listed as 175, 1632, 6760 and 7433 μSv for the patient age of 15, 5, 1 and 1 year respectively.

Conclusion: These radiation monitoring data provided the important information to manage radiation protection and aware of radiation exposure when using non-lead-lined treatment room in general pediatric ward.