Monte Carlo estimation of electron contamination in a 18 MV clinical photon beam

The electron contamination may reduce or even diminish the skin sparing property of the megavoltage beam. The detailed characteristics of contaminant electrons are presented for different field sizes and cases. The Monte Carlo code, MCNPX, has been used to simulate 18 MV photon beam from a Varian Linac-2300 accelerator. All dose measurements were carried out using a PTW-MP2 scanner with an ionization chamber [0.6 CC] at the water phantom. The maximum electron contaminant dose at the surface ranged from 6.1% for 5 x 5 cm[2]to 38.8% for 40 x 40 cm[2] and at the depth of maximum dose was 0.9% up to 5.77% for the 5 x 5 cm[2] to the 40 x 40 cm[2] field sizes, respectively. The additional contaminant electron dose at the surface for the field with tray increased 2.3% for 10 x 10 cm[2], 7.3% for 20 x 20 cm[2], and 21.4% for 40 x 40 cm[2] field size comparing to the standard field without any accessories. This increase for field with tray and shaping block was 5.3% and 13.3% for 10 x 10 and 20 x 20 cm[2], respectively, while, the electron contamination decreased for the fields with wedge, i.e. 2.2% for the 10 x 10 cm[2] field. The results have provided more comprehensive knowledge of the high-energy clinical beams and may be useful to develop the accurate treatment planning systems capable of taking the electron contamination in to account

new approach to contrast enhancement in MAGICA gel dosimeter image with MRI technique

Sensitivity and resolution are two main parameters that have to be measured in gel dosimetry. However, the resolution in gel is strongly dependant on gel composition. Selection of optimum method in dose response readout and proper values of parameters can result in noise reduction as well as improvement of contrast, and spatial resolution considerably. MAGICA polymer gel dosimeters were manufactured and irradiated to different doses using a 60Co therapy unit. Imaging was performed in a 0.5T MRI with 8 echoes in air and water as a hydrogenous environment. Imaging condition was kept constant, as much as possible, in both imaging modalities. Images obtained from these two procedures were compared quantitatively. R2- dose curves have three different sections, sensitivity obtained in these three sections were 1.039, 1.671, 1.260 Gy[-1]S[-1] and 1.032, 1.729, 1.37 Gy[-1]S[-1] for water and air respectively. Calibration errors were investigated and graphically were compared in two different methods. Imaging in water medium for doses lower than 17 Gy led to a small reduction in spatial resolution was exchanged to a considerable increase of contrast in R2 map. For doses higher than17 Gy, imaging in water or air was preferred depending on the importance of contrast or spatial resolution

[Monte Carlo stimulation of the angular, radial and energy distribution of a medical linear accelerator using MCNP4C code]

Previous investigations have shown that Monte Carlo methods are suitable for the simulation of the transportations photon beam in medical linear accelerators. The simulated beams could be used for the measurement of the dose distribution in phantoms and patients' body. Angular, energy and radial distributions are the most important data of photon beams and can be used for clinical applications of simulation. The phase-space data of the Elekta SL75/25 Linac was simulated for MCNP4C code. In this investigation, we have presented detailed data of the angular, energy and radial distributions at four scoring plate perpendicular to the central axis of the photon beam. Firstly, we simulated the linac head geometry and verified its' accuracy. The mean energy and radial intensity distribution of the linac electron beam was determined by the comparison of the simulated and measured percentage depth doses [PDDs] and beam profile curves. Four scoring plates located 0.1cm under the target, the primary collimator, the flattening filter and the secondary collimator were simulated as concentric circles starting at 0.1cm radius and with 0.1cm intervals up to 3.5cm. Thereafter, bremsstrahlung radiations were simulated and transported in the linac head down to the water phantom and the angular, energy and radial distributions at the four scoring plate were scored. Comparison of our results with the previous reports from the EGS4 code indicated that the simulated photon spectra resulted from the MCNP4C code is a little more at high energies. The mean energy was 2.18MeV having being in good agreement with previous investigations. At all the scoring planes, the beam becomes softer as we get away from the central axis of the beam. The maximum and minimum variation happens for the target and the secondary collimators with a value of 1.24MeV and 0.13MeV respectively. The head structures of the linac, altogether, caused a beam hardening of 0.61MeV, but among all the components of the head structures, the flattening filter has most effect in this regard. The radial distributions of the primary collimator and flattening filter indicate a difference of 0.6% and 0.05% from that of the central bin respectively. The photon fluence is reduced to 50.04% after crossing the flattening filter with the majority of them being at low energies. Higher energy noted from the use of MCNP4C Code is due to the energy physics cut-off card used, causing a shift in the mean energy of the primary electrons toward the higher energies and consequently increasing the relevant photon fluence. The primary collimators and the flattening filter have the most effect on the fluence uniformity and the energy fluence uniformity respectively. Passing the radiation through the head structures causes the beam hardening with the flattening having the most effect

Coping strategies used by parents of children with cancer in Shiraz, Southern Iran

The assessment of family coping patterns and resources will provide a further basis for helping family's adaptation. This study was undertaken to assess the coping strategies used by parents of children with cancer in Aliasghar Cancer Hospital affiliated to Shiraz University of Medical Sciences. Data collection was conducted based upon Family Crisis Oriented Personal Evaluation Scale [F-COPES] including social and spiritual support, reframing, seeking help and passive appraisal. A total of 72 parents including 28 couples, 8 single mothers and 8 single fathers participated in this study. The spiritual support ranked the highest and the social help, the lowest strategies used by the parents. Seeking help, reframing and passive appraisal were the remaining strategies. Statistically significant differences were found between the age of participants and reframing and seeking help strategies. A significant difference was also observed between the level of parent's education and reframing strategy but not between gender and coping strategies. Familiarity with coping strategies and the method to use them could balance the emotional, psychological and social consequences of parents who have a child with cancer

Comparison of measured and Monte Carlo calculated dose distributions from circular collimators for radiosurgical beams

Stereotactic radiosurgery is an important clinical tool for the treatment of small lesions in the brain, including benign conditions, malignant and localized metastatic tumors. A dosimetry study was performed for Elekta 'Synergy S' as a dedicated Stereotactic radiosurgery unit, capable of generating circular radiation fields with diameters of 1-5 cm at isocentre using the BEAM/EGS4 Monte Carlo code. The linear accelerator Elekta "Synergy S" equipped with a set of 5 circular collimators from 10 mm to 50 mm in diameter at isocentre distance was used. The cones were inserted in a base plate mounted on the collimator linac head. A PinPoint chamber and Wellhofer water tank chamber were selected for clinical dosimetry of 6 MV photon beams. The results of simulations using the Monte Carlo system BEAM/EGS4 to model the beam geometry were compared with dose measurements. An excellent agreement was found between Monte Carlo calculated and measured percentage depth dose and lateral dose profiles which were performed in water phantom for circular cones with 1, 2, 3, 4 and 5 cm in diameter. The comparison between calculation and measurements showed up to 0.5% or 1mm difference for all field sizes. The penumbra [80-20%] results at 5 cm depth in water phantom and SSD=95 ranged from 1.5 to 2.1 mm for circular collimators with diameter 1 to 5 cm. This study showed that BEAMnrc code has been accurate in modeling Synergy S linear accelerator equipped with circular collimators

Frequency of hypothyroidism in Fanconi anemia

Fanconi anemia [FA] is a rare, autosomal recessive [AR] and multifactorial disorder. A high prevalence of FA observed in Iran is perhaps due to the high rate of consanguineous marriages. This study investigates the extent of short stature in patients with FA, the frequency of hypothyroidism in FA and the correlation between height and hypothyroidism. Eighteen patients with FA referred to the Pediatrics Clinic of Nemazee Hospital were selected based on specific congenital and malformational symptoms and bone marrow results. These patients were evaluated for weight, height, bone age, clinical goiter and thyroid function tests. Eleven out of 18 patients [61%] had overt or compensated hypothyroidism. Short stature was found in 89% of patients with a mean height more than two standard deviation [SD] below the mean height for that age. There was no significant correlation between short stature and overt or compensated hypothyroidism. The mean height standard deviation score [SDS] of patients with normal thyroid function was also more than two SD deviation below the normal mean, revealing that short stature is an inherent feature of FA. In seven cases with goiter, only three had hypothyroidism. The mean +/- SD weight SDS was -1.03 +/- 0.99. The mean +/- SD bone age was 12 +/- 4.5 yr. According to the results of this study, our patients had a considerable prevalence of hypothyroidism and short stature was a common feature of FA. It is recommended that thyroid function test is necessary in these patients

Measurement of organ dose in abdomen-pelvis CT exam as a function of mA, KV and scanner type by Monte Carlo method

CT is a diagnostic imaging modality giving higher patient dose in comparison with other radiological procedures, so the calculation of organ dose in CT exams is very important. While methods to calculate the effective dose have been established [ICRP 26 and ICRP 60], they depend heavily on the ability to estimate the dose to radiosensitive organs from the CT procedure. However, determining the radiation dose to these organs is problematic, direct measurement is not possible and comparing the dose as functions of scan protocol such as mA is very difficult. One of the most powerful tools for measuring the organ dose is Monte Carlo simulation. Materials and Today the predominant method for assessment of organ absorbed dose is the application of conversion coefficients established by the use of Monte Carlo simulations. One of the most famous dose calculation software is CTDOSE, which we have used it for calculation of organ dose. In this work we measured the relationship between the mA, KV and scanner type with the equivalent organ dose and effective dose in mathematically standard phantom [Hermaphrodite 170cm/70Kg] in an abdomen-pelvis CT exam by Monte Carlo method. For this measurement we increased the mA in steps of 10 mA and plot curves for organ dose as a function of mA for different KV setting. As expected, with increasing mA, patient organ dose increased, but the simulation results showed that the slope of organ dose as a function of mA increased with KV increasing. By increasing KV from 120 to 140 the increase in slope of curves representing patient organ dose versus mA for different scanner types show almost similar behavior whereas the slope of the corresponding curves in scanners which equipped xenon detectors was almost 22% more than the slope of scanners equipped with scintillation detectors. Our research showed that regarding equivalent dose the system incorporating scintillation detector has a superior performance. Incorporating such software in various CT scanners, marketed by different vendors, will offer the ability to get a print out of patient organ dose in any examination according to the imaging parameters used for imaging any part of the body

Prevalence of endocrine complications in beta-thalassaemia major in the Islamic Republic of Iran

To identify the prevalence of endocrine dysfunction in Iranians with beta-thalassaemia, we assessed thyroid, parathyroid, pancreatic and adrenal function in 150 beta-thalassaemic patients aged 10-22 years at the Paediatrics Unit, Shiraz University of Medical Sciences. Primary hypothyroidism was found in 6.0% of patients [mean age: 14.6 +/- 1.9 years], hypoparathyroidism in 7.3% [14.5 +/- 3.2 years], type 1 diabetes mellitus in 7.3% [13.9 +/- 2.8 years] and adrenal insufficiency in 1 patient. The relatively high frequency of endocrine dysfunction found in our study may be a result of poor disease control and management in early life when irreversible tissue damage occurs due to iron overload. These findings reinforce the importance of regular follow-up of patients with beta-thalassaemia major for early detection and management of associated complications

Linear growth deficiency in B-thalassemia patients: Is it growth hormone dependent?

beta-Thalassemia major is a serious medical problem. Growth retardation is commonly seen in poly-transfused beta- thalassemia patients. The exact mechanism of short stature in children with thalassemia major is not well understood, however, it is believed to be multi-factorial. To study the growth state and its relationship to growth hormone [GH] deficiency in beta-thalassemia patients. The extent of growth and growth hormone deficiency were evaluated in 150 patients aged 10-22 years [84 males, 66 females] residing in Shiraz. The age, sex, height, weight and serum ferritin levels were recorded using a questionnaire. Growth hormone secretion was determined with L-Dopa provocative test in 138 beta- thalassemia patients. Short stature was present in 64% of patients [63.6% of girls, 69% of boys]. Growth hormone deficiency was present in 57.5% of 138 patients, [53.5% of boys, 46.5% of girls]. Short stature was found in 83.5% of GH deficient and 74.6% of GH sufficient [p=0.22] subjects. There was no difference between the height of GH deficient and GH sufficient patients [p=0.297]. Age at the start of chelating therapy, height deficiency and serum ferritin levels did not differ in GH deficient compared to GH sufficient patients. This study suggests that growth retardation and GH deficiency are common in thalassemic patients and that height deficiency may not be related to GH reserve with the current testing methods for measurement of GH reserve

Combined coagulation factors V and VIII deficiency: report of 22 cases from 17 families

Combined coagulation factor V and VIII deficiency is very uncommon, and only 30 cases have been documented in the world literature. In this article, 22 more cases from 17 Iranian families are reported. The frequency of the presenting symptoms including gingival, post-circumcision, nasal bleeding, and retroperitoneal hematoma was similar to that reported in other works. Partial thromboplastin time prolonged in all cases and ranged from 56 to 125 seconds. The plasma factors V and VIII activities had a mean +/- SD of 12.4 +/- 5.1%, and 11.1 +/- 6.0%, respectively. Almost all patients had a factor VIII activity greater than 5%; a typical value for a mild hemophilic patient. While some studies describe no abnormal coagulation factor assay in parents of the patients, the activity of plasma factors V and VIII was mildly decreased in two mothers of our study group. Equal involvement of both sexes and the high frequency of consanguinity among our patients reflect an autosomal recessive inheritance