Estimation of photoneutron dosimetric characteristics in tissues/organs using an improved simple model of linac head

Simulation and prediction of the attenuation behaviour of the KNN-LMN-based lead-free ceramics by FLUKA code and artificial neural network (ANN)-based algorithm

The significance and novelty of the present work are the preparation of the non-lead ceramic by the general formula of (1-x) K_0.5Na₀.₅NbO₃-xLa Mn_0.5Ni_0.5O₃ (KNN-LMN) with different x (0<x<0.295) (mol) to examine the shielding qualities of KNN-LMN non-lead ceramic via FLUKA code. The obtained results via FLUKA code are used as input data for training the artificial neural network algorithm and prediction. For this purpose, the radio isotopic ²⁵²Cf neutron source is simulated by the HI-PROBE, RADDECAY and DCYSCORE cards using the FLUKA code. As a result, the neutron-gamma photon shielding ability of the KNN-LMN lead-free ceramics exposed to the ²⁵²Cf neutron source is estimated and predicted. Findings show that by increasing the concentration of the x in (1-x) K_0.5Na₀.₅NbO₃-xLa Mn_0.5Ni_0.5O₃ lead-free ceramics results in an ascending trend in density. In addition, the increment of the x rate (x refers to the concentration of La Mn_0.5Ni_0.5O₃ in KNN-LMN non-lead ceramics) causes an increase in the value of the neutron attenuation parameter (∑t), and a strong relationship is monitored between ∑t and density. Moreover, descending order of (HVL)x=0.01>(HVL)x=0.04>(HVL)x=0.07>…>(HVL)x=0.25 is reported for half-value layer values against gamma photon. From the attained results, it can be concluded that increaisng the rate of x results in the better shielding proficiency in terms of neutron and gamma photon for chosen KNN-LMN-based lead-free ceramics.

An extensive study on the neutron-gamma shielding and mass stopping power of (70-x) CRT-30K2O-xBaO glass system for 252Cf neutron source

The present study focuses on the charged-uncharged particles shielding performance of the addition of a mixed type of cathode ray tube (CRT) in a glass system that is irradiated by the ²⁵²Cf neutron source via the MCNPX simulation and analytical calculations, as well as Phy-X: PSD and SRIM software. The CRT waste glass is inserted into the glass system with (70-x) CRT-30K₂O-xBaO general formula for x = 0, 10, 20 mol% that produces CG1, CG2, and CG3 glass shielding materials. Using Watt Fission Distribution (WFD) and Doppler Effect (DE) the neutron-gamma photon spectra were extracted for shielded (in the presence of the glass materials) and unshielded (in air) cases. Some calculated attenuation parameters related to the neutron deduced that CG1 is the best neutron attenuator among the selected glass samples. Moreover, by increasing the density of the glass from CG1 to CG3, the ascending trend is observed for the linear attenuation coefficient (LAC, cm^-1) of the studied glass, and the best shielding competence is monitored for CG3. Furthermore, two sharp peaks are found in Z_eff graphs which may be due to K-edge absorption of Ba and Pb elements and by decreasing the Pb element from CG1 to CG3 the second peak gradually becomes smooth. In addition, Mass Stopping Power/ Projected Ranges of the proton (H¹) and alpha particles (He⁺²) are also estimated by SRIM code and findings show that CG1 can better stop proton and alpha particles in comparison with the other chosen glass structures.

Monte Carlo study of organ doses and related risk for cancer in Algeria from scattered neutrons in prostate treatment involving 3D-CRT

The present study aimed to evaluate organ doses and related risk for cancer from scattered neutrons involving 3D Conformational Radiotherapy (3D-CRT) for patients with prostate cancer in Algeria based on Monte Carlo technique and to estimate the secondary cancer risks. To this purpose, a detailed geometric Monte Carlo (MC) modeling of the LINAC Varian 2100C combined with a computational whole-body phantom was carried out. The neutron equivalent doses were calculated in-field and out-of field of patient's organs using the phase-space method. The obtained neutron equivalent doses were used to estimate the Lifetime Attributable Risks (LARs) for cancer incidence in out of field organs. LARs was evaluated assuming Biological Effects of Ionizing Radiation VII (BEIR VII) risk model for exposure age in the range 35-70 years, according to the interval's age of treated patients in Algeria. The baselines cancer risks and survival data were associated with the statistical data for the Algerian population. The results showed that the neutrons equivalent doses per prescribed dose (Photon Dose) mostly depend on the distance of organs from the treated volume. The highest and lowest equivalent doses of 1.18 mSv/Gy and 0.25 mSv/Gy were recorded in the bladder and heart, respectively. The highest estimated lifetime attributable risk per 100,000 population was found for 35 yrs' exposure age in colon 49.94, lung 16.63 and stomach 11.17. The lowest risks were found for 70 yrs' age, in spine 0.06 and thyroid 0.14. The results showed that LARs values decrease with the increase of the exposure age and cancer incidence risk is lower than the baseline cancer risk incidence for all organs. The present study may help in providing a database on the impact of radiotherapy-induced secondary cancer incidence during 3D-CRT for prostate cancer in Algeria.

Monte Carlo evaluation of out-of-field dose in 18 MV pelvic radiotherapy using a simplified female MIRD phantom

This study was devoted to determining the unwanted dose due to scattered photons to the out-of-field organs and subsequently estimate the risk of secondary cancers in the patients undergoing pelvic radiotherapy. A typical 18 MV Medical Linear Accelerator (Varian Clinac 2100 C/D) was modeled using MCNPX^®code to simulate pelvic radiotherapy with four treatment fields: anterior-posterior, posterior-anterior, right lateral, left lateral. Dose evaluation was performed inside Medical Internal Radiation Dose (MIRD) revised female phantom. The average photon equivalent dose in out-of-field organs is 8.53 mSv Gy^-1, ranging from 0.17 to 72.11 mSv Gy^-1, respectively, for the organs far from the Planning Treatment Volume (Brain) and those close to the treatment field (Colon). Evidence showed that colon with 4.3049% and thyroid with 0.0020% have the highest and lowest risk of secondary cancer, respectively. Accordingly, this study introduced the colon as an organ with a high risk of secondary cancer which should be paid more attention in the follow-up of patients undergoing pelvic radiotherapy. The authors believe that this simple Monte Carlo (MC) model can be also used in other radiotherapy plans and mathematical phantoms with different ages (from childhood to adults) to estimate the out-of-field dose. The extractable information by this simple MC model can be also employed for providing libraries for user-friendly applications (e.g. '.apk') which in turn increase the public knowledge about fatal cancer risk after radiotherapy and subsequently decrease the concerns in this regard among the public.

Phantom dosimetry and cancer risks estimation undergoing 6 MV photon beam by an Elekta SL-25 linac

The High-energy linear accelerator (linac) is a valuable tool and the most commonly used devices for external beam radiation treatments in subjects suffer from cancer. To estimate the dose deposited in several organs of a female patient due to pelvic irradiation by an Elekta SL-25 linac in 6 MV photon beam mode, the MCNPX code is used considering the most details of linac. The equivalent dose in different organs is computed according to the face down position (prone) of MIRD and UFRO phantoms. The data obtained using MCNPX show that the received dose in all commons organs of MIRD and UFRO phantoms is 535.73 and 433.09 mSv/Gy_x, respectively. The risks of second cancer incidence and mortality during radiotherapy treatment are compared between MIRD and UFRO phantoms. The results indicated that bladder has the maximum risk of secondary cancer incidence risk of 142.85 and 135.34 per 10⁵ persons based on MIRD and UFRO phantoms, respectively; while the total risk is about 1 in 163 and about 1 in 101 in these phantoms.

Essential considerations for accurate evaluation of photoneutron contamination in Radiotherapy

Nowadays, high-energy X-rays produced by medical linear accelerators (LINACs) are widely used in many Radiation Therapy (RT) centers. High-energy photons (> 8 MeV) produce undesired neutrons in the LINAC head which raise concerns about unwanted neutron dose to the patients and RT personnel. Regarding the significance of radiation protection in RT, it is important to evaluate photoneutron contamination inside the RT room. Unfortunately, neutron dosimeters used for this purpose have limitations that can under the best conditions cause to > 10% uncertainty. In addition to this uncertainty, the present Monte Carlo (MC) study introduces another uncertainty in measurements (nearly up to 20%) when neutron ambient dose equivalent (H_n^*(10)) is measured at the patient table or inside the maze and the change in neutron energy is ignored. This type of uncertainty can even reach 35% if H_n^*(10) is measured by dosimeters covered by a layer of ¹⁰B as converter. So, in these cases, neglecting the change in neutron energy can threaten the credibility of measured data and one should attend to this energy change in order to reduce measurement uncertainty to the possible minimum. This study also discusses the change in neutron spectra and H_n^*(10) at the patient table caused by removing a typical RT room from MC simulations. Under such conditions, neutron mean energy (Ē_n) overestimated by 0.2-0.4 MeV at the patient table. Neutron fluence (φ_n) at the isocenter (IC) was underestimated by 23-54% for different field sizes that caused H_n^*(10) to be miscalculated up to 24%. This finding informs researchers that for accurate evaluation of H_n^*(10) at the patient table, simulating the RT room is an effective parameter in MC studies.

Effect of each component of a LINAC therapy head on neutron and photon spectra

Linear accelerators (LINACs) are widely applied in radiotherapy for their versatility and flexibility. Monte Carlo simulations were made to find the neutron and photon spectra at the isocenter (IC) of a LINAC operating at 10, 15, 18, and 24 MV by the MCNPX code. A detailed model of the LINAC head, consisting of flattening filter, secondary collimator, primary collimator, and multi-leaf collimator were used in the calculations. The effect of eliminating any of these components on contamination of a neutron spectrum and a photon spectrum was assessed. Photon and neutron ambient equivalent doses were found, and comparisons were made for the various structures. Lethargy neutron spectra at the IC were compared with spectra computed with the function reported by Tosi et al., which describes well neutron spectra for the energy region beyond 1 MeV, although tending to undervalue energy spectra below 1 MeV. The findings show that the photon and neutron fluences are enhanced when eliminating a LINAC component. The neutron and photon doses increased except when removing the primary collimator.