Studies of the radiation environment on the Mars surface using the Geant4 toolkit

The radiation environment on the surface of Mars is a potential threat for future manned exploration missions to this planet.In this study,a simple geometrical model was built for simulating the radiation environment on the Mars surface caused by galactic cosmic rays;the model was built and studied using the Geant4 toolkit.The simulation results were compared with the data reported by a radiation assessment detector(RAD).The simulated spectra of neutrons,photons,protons,α particles,and particle groups Z=3-5,Z=6-8,Z=9-13,and Z=14-24 were in a reasonable agreement with the RAD data.However,for deuterons,tritons,and 3He,the simulations yielded much smaller values than for the corresponding RAD data.In addition,the particles’spectra within the 90 zenith angle were also obtained.Based on these spectra,we calculated the radiation dose that would have been received by an average human body on Mars.The distribution of the dose throughout the human body was not uniform.The absorbed and equivalent doses for the brain were the highest among all of the organs,reaching 62.0±1.7 mGy/y and 234.1±8.0 mSv/y,respectively.The average absorbed and equivalent doses for the entire body were approximately 44 mGy/y and 153 mSv/y,respectively.Further analysis revealed that most of the radiation dose was owing to a particles,protons,and heavy ions.We then studied the shielding effect of the Mars soil with respect to the radiation.The body dose decreased significantly with increasing soil depth.At the depth of 1.5 m,the effective dose for the entire body was 17.9±2.4 mSv/y,lower than the dose limit for occupational exposure.At the depth of 3 m,the effective dose to the body was 2.7±1.0 mSv/y,still higher than the accepted dose limit.

Investigation of combined degrader for proton facility based on BDSIM/FLUKA Monte Carlo methods

The significant advantage of proton therapy over other particle-based techniques is in the unique physical characteristics of the Bragg peak.It can achieve a highly conformal dose distribution and maximize the probability of tumor control by varying the irradiation energy.Most proton facilities use cyclotrons for fixed energy beam extraction and are equipped with degrader and collimator systems for energy modulation and emittance suppression.However,interactions between charged particles and degrader materials inevitably cause beam loss and divergence and deteriorate beam performance,which present great challenges for downstream transport and clinical treatment.In this work,we investigate a method of energy reduction by combining boron carbide and graphite in a degrader to obtain greater beam transmission at lower energy.The results demonstrate that the beam size and emittance at the exit of the combined degrader diverge less than those of multi-wedge one in the energy range of 70-160 MeV.Correspondingly,the transmission efficiency after the first dipole also shows improvements of 36.26%at 70 MeV and 70.55%at 110 MeV.As a component with a high activity level,the degrader causes additional ambient radiation during operation.Residual induced radiation even remains several hours after system shutdown.Analysis of material activation and induced radiation based on 1 h irradiation with a 400 nA beam current shows that the combined degrader has a definite advantage in shielding despite producing more secondary particles.Both radioactivity and average ambient dose equivalent are reduced by 50%compared with the multiwedge degrader at the important cooling time of 1 h.After 12 h and 24 h of cooling,the radiation levels of degraders decrease slightly due to the presence of long half-life residual nuclides.The average dose generated from the multi-wedge degrader is still 1.25 times higher than that of the combined one.

Application of biological optimization of hypofractionated radiotherapy post conservative surgery for breast cancer

Objective The aim of the study was to discuss the application of biological optimization and its difference from physical optimization in hypofractionated radiotherapy for breast cancer after conservative surgery.Methods This retrospective study enrolled 15 randomly chosen patients with left-sided breast cancer who received radiotherapy.The volumetric arc therapy(VMAT)technique was used to redesign treatment plans with physical functions(PF)group,biological-physical functions combined(BF+PF and PF+BF)groups,and biological functions(BF)group.The dosimetric differences based on the above four optimization methods were assessed by calculating and analyzing the corresponding dose-volume parameters.Results The target parameters of the four groups differed significantly(P<0.05)except for the conformity index(CI).The tumor control probability(TCP)values in the BF and BF+PF groups were higher than those in the PF and PF+BF groups.Moreover,the dose-volume parameters of the ipsilateral lung in the BF group were less than those of three other groups,while the monitor unit(MU)in the BF group was approximately 16%lower than those of the PF and PF+BF groups.Conclusion Biological functions were useful to increase the equivalent uniform dose(EUD)and TCP values of the target,decrease the dose-volume parameters of the organs-at-risk(OARs),and improve treatment efficiency.

RADIONUCLIDES IN NOODLES AND BREAD CONSUMED IN HONG KONG

Most of the natural occurring radionuclides in both noodles and bread are found to have specific activities below the detectable limit of the high purity germanium (n-type) spectrometer system of the EG&G Ortec Company. For dried bread, 40K,137Cs and 60Co are found to be 44.45￣84.52, < 0.012 ￣0.052, < 0.018 ￣0.054 Bq/kg;for noodles, to be 29.55￣64.54, < 0.01 ￣0.069 and < 9.8× 10-3 ￣ 0.074 Bq/kg,respectively. The weighted committed dose equivalents due to the ingestion of 137Csfrom noodles and bread for a male and female adults have been estimated to be 0.5and 0.6μSv, respectively, being less than the values recommended by ICRP.

RADIONUCLIDES IN RICE IN HONG KONG

Radionuclide contents in imported rice are determined using the EG&G ORTEC photon spectrometer system. Most of the natural radionuclides are found to have specific activities below the detectable limit. 40K has values ranging from 0.104to 32.97 Bq/kg; 137Cs from 0.009 to 0.52 Bq/kg; and 95Zr less than 0.077 Bq/kg. The annual effective dose for a male and a female adult is 18μSv and 12.7μSv, respectively. Both are less than the value recommended by the International Commission of Radiological Protection.

Annual Committed Effective Dose from Various Phytotherapeutic Preparations (due to 238U, 232Th, 222Rn and 220Rn) Estimated for Adult Moroccan Patients

We use a nuclear technique based on the determination of the detection efficiencies of solid state nuclear track detectors CR-39 and LR-115 type II (SSNTDs) for alpha particles emitted from the series of uranium-238 and thorium-232 in a phytotherapeutic sample and the measurement of alpha track densities registered on these detectors to assess alpha activities due to uranium-238;thorium-232;radon and thoron in samples of phytotherapeutic preparations consumed by Moroccan adult patients. For modern preparations, the alpha activities due to 238U, 232Th and 222Rn range from 14.27 mBq/kg to 22.02 mBq/kg, from 6.27 mBq/kg to 9.64 mBq/kg and from 14.27 Bq/kg to 22.02 Bq/kg respectively. For classical preparations, the alpha activities due to 238U, 232Th and 222Rn range from 16.73 mBq/kg to 24 mBq/kg, from 7.34 mBq/kg to 10.82 mBq/kg and from 16.73 Bq/kg to 24.72 Bq/kg respectively. A dosimetric model for ingestion has been highlighted to determine committed equivalent dose to different compartments of human gastrointestinal system due to the ingestion of phytotherapeutic preparations by Moroccan adult patients. The maximum overall effective dose due to 238U, 232Th, and 222Rn after the ingestion of the studied phytotherapeutic preparations, was found equal to 38 × 10-8 S·vy-1 which is less than the dose limit given by the international commission for radiological protection in it publication 56.

Calculation of Mass Stopping Power and Range of Protons as Well as Important Radiation Quantities in Some Biological Human Bodyparts (Water, Muscle, Skeletal and Bone, Cortical)

In this work, the electronic mass stopping power and the range of protons in some biological human body parts (Water, Muscle, Skeletal and Bone, Cortical) were calculated in the energy range of protons 0.04 to 200 MeV using the theory of Bethe-Bloch formula as giving in the references. All these calculations were done using Matlab program. The data related to the densities, average atomic number to mass number and excitation energies for the present tissues and substances were collected from ICRU Report 44 (1989). The present results for electronic mass stopping powers and ranges were compared with the data of PSTAR and good agreements were found between them, especially at energies between 1 - 200 MeV for stopping power and 4 - 200 MeV for the range. Also in this study, several important quantities in the field of radiation, such as thickness, linear energy transfer (LET), absorbed dose, equivalent dose, and effective dose of the protons in the given biological human body parts were calculated at protons energy 0.04 - 200 MeV.

Study of neutron dose equivalent at the HIRFL deep tumor therapy terminal

The secondary neutron fields at the deep tumor therapy terminal at HIRFL（Heavy Ion Research Facility in Lanzhou） were investigated. The distributions of neutron ambient dose equivalent were measured with a FHT762Wendi-II neutron ambient dose equivalent meter as ^（12）C ions with energies of 165, 207, 270, and 350 Me V/u were bombarded on thick tissue-like targets. The thickness of targets used in the experiments was larger than the range of the carbon ions. The neutron spectra and dose equivalent were simulated by using FLUKA code, and the results agree well with the experimental data. The experiment results showed that the neutron dose produced by fragmentation reactions in tissue can be neglected in carbon-ion therapy, even considering their enhanced biological effectiveness.These results are also valuable for radiation protection, especially in the shielding design of high energy heavy ion medical machines.

The Characteristic of Dose Equivalent Rates of Photon and Neutron Outside the Treatment Room under High-energy Electron Mode of Linac

Objective:The study aimed to explore the characteristic of dose equivalent rates(DERs)of photon and neutron outside the treatment room under high-energy electron mode(dose rate 1000 MU/min)of linac and to evaluate the effectiveness of treatment room protection.Methods:A 451 P pressurized ion chamber and a thermo neutron detector were used to measure the DERs of the photon and neutron at selected points.The effects of field size,applicator size,applicator,anthropomorphic phantom(CDP)and lead block on DER were investigated respectively.Results:The DERs of a photon at the center of shielding door(point A),control console(point B),primary shielding walls(point C,D)and roof of treatment room(point E)increased with increasing electron energy,but decreased with the increasing field size.The DERs of a photons at points A and B are smaller than 2.5μSv/h for all scenarios,while those at point D greater than 2.5μSv/h when irradiated by 18-22 Me V electron.In addition,CDP may change the DERs of a photon at points C and D about 5% to 30%.On the other hand,the DERs of neutron increase with increasing electron energy but decrease with the increase of field size and applicator size,however,the lead block and the applicator itself will change the DERs of leak neutron at point A,but its amplitude is less than 0.5μSv/h.The maximum DER of neutron at point A is 6.18μSv/h irradiated by 22 Me V electron.For other scenarios,they are all in the range of national standards limits.Conclusion:The DERs of a photon and neutron outside the treatment room mainly depend on the energy,field size and irradiation direction of the electron beam.If high-energy 18 Me V and 22 Me V electron beams will be used,the primary shielding walls and shielding doors need reconstructing or increasing thickness.

EQUIVALENT UNIFORM DOSE SENSITIVITY TO CHANGES IN ABSORBED DOSE DISTRIBUTION

Treatment planning in external beam radiation therapy （EBRT） utilizes dose volume histograms （DVHs） as optimization and evaluation tools. They present the fraction of planning target volume （PTV） receiving more than a given absorbed dose, against the absorbed dose values, and a number of radiobiological indices can be computed with their help. Equivalent uniform dose （EUD） is the absorbed dose that, uniformly imparted, would yield the same biological effect on a tumor as the dose distribution described by the DVH. Uncertainty and missing information can affect the dose distribution, therefore DVHs can be modeled as samples from a set of possible outcomes. This work studies the sensitivity of the EUD index when a small change in absorbed dose distribution takes place. EUD is treated as a functional on the set of DVHs. Defining a Levy distance on this set and using a suitable expansion of the functional, a very simple expression for a bound on the variation of EUD when the dose distribution changes is found. This bound is easily interpreted in terms of standard treatment planning practice.

Conceptual design of the CEPC dumping system

Background The circular electron–positron collider(CEPC)is a double-ring collider proposed by Chinese scientists.It will be operated at centre-of-mass energy of 240,90,160 GeV and maybe also 360 GeV.Purpose The total energy stored in the collider is up to 20 MJ.It is important to extract beams safely and not to damage the dump.In this paper,a dumping system including dilution kickers and absorber core with iron shielding is discussed.Methods The Monte Carlo code FLUKA is used to obtain the deposited energy and dose-equivalent distributions.The temperature rises are calculated assuming no heat conduction.Results Compared with the melting point and upper limit of dose equivalent,the magnets parameters are determined and the dimensions of the core and shielding are optimized.Conclusion The design of the dumping system meets the requirement that the energy stored in the collider can be absorbed safely.

Effect of combined scalp and body acupuncture on Parkinson’s disease:A randomized clinical trial

Objective:To observe the therapeutic effect of combined scalp and body acupuncture on the motor symptoms in Parkinson’s disease(PD),and on the score of levodopa equivalent dose(LED).Methods:This is a randomized,single blind trial.Sixty-six patients with PD were randomized into an acupuncture+medication group(33 patients)and a medication group(33 patients).The patients were aware of allocation and the assessors were blinded to group assignment and therapeutic regimen.AntiPD drugs were administered in both groups.In the acupuncture+medication group,scalp and body acupuncture therapy was added.Treatments were applied for 8 weeks.In scalp acupuncture,the anterior oblique line of the vertex-temporal(MS6),lateral line 1 of the vertex(MS8),lateral line 2 of the vertex(MS9),and lower-lateral line of the occiput(MS14)were selected.In the body acupuncture,the acupoints included Bǎihuì(百会GV20),Sìshéncōng(四神聪EX-HN1),and Dàzhuī(大椎GV14),as well as the bilateral Fēngchí(风池GB20),Nèiguān(内关PC6),Hégǔ(合谷LI4),Gānshū(肝俞BL18),Shènshū(肾俞BL23),Yánglíngquán(阳陵泉GB34),Zúsānlǐ(足三里ST36),Fēnglóng(丰隆ST40),Sānyīnjiāo(三阴交SP6),Tàixī(太溪KI3),and Tàichōng(太冲LR3).Before and after treatments,the unified Parkinson’s disease rating scale(UPDRS),3section of the UPDRS(UPDRS-Ⅲ),and motor dysfunction rating scale for Parkinson’s disease(MDRSPD)were scored in the patients.The therapeutic effect of traditional Chinese medicine(TCM)and LED score were compared between both groups.Results:Thirty-three cases were included in data analysis in each group.After treatment,UPDRS scores were(28.77±8.85)and(36.58±10.16)points,UPDRS-Ⅲscores were(12.16±1.97)and(17.47±2.93)points and MDRSPD scores were(15.56±3.31)and(19.13±4.87)points in the acupuncture+medication and medication groups respectively.The UPDRS,UPDRS-Ⅲ,and MDRSPD scores all reduced after treatments in both groups(all P<0.05).All three scores were lower in the acupuncture+medication group than in the medication group(all P<0.05).When examining the therapeutic effects of TCM,the total effective rate was 87.88%in the acupuncture+medication group and 75.76%in the medication group(P<0.05).After treatment,the LED scores were(387.55±146.24)points and(437.42±183.16)points in the acupuncture+medication and medication groups,respectively.The LED dose differences before and after treatment for the acupuncture+medication and medication groups were(40.36±16.33)points and(95.88±35.79)points,respectively.The LED scores in both groups were higher than the pre-treatment scores(P<0.05).However,the post-treatment LED score was lower in the acupuncture+medication group than in the medication group(P<0.05),as was the dose difference before and after treatment(P<0.05).No relevant adverse reaction was found in each group.Conclusion:In addition to anti-PD medication,the scalp and body acupuncture may effectively relieve the motor symptoms of PD and improve the control of LED score.

Energy response improvement for photon dosimetry using pulse analysis

During the last few years,active personal dosimeters have been developed and have replaced passive personal dosimeters in some external monitoring systems,frequently using silicon diode detectors.Incident photons interact with the constituents of the diode detector and produce electrons.These photon-induced electrons deposit energy in the detector＇s sensitive region and contribute to the response of diode detectors.To achieve an appropriate photon dosimetry response,the detectors are usually covered by a metallic layer with an optimum thickness.The metallic cover acts as an energy compensating shield.In this paper,a software process is performed for energy compensation.Selective data sampling based on pulse height is used to determine the photon dose equivalent.This method is applied to improve the energy response in photon dosimetry.The detector design is optimized for the response function and determination of the photon dose equivalent.Photon personal dose equivalent is determined in the energy range of 0.3-6 MeV.The error values of the calculated data for this wide energy range and measured data for ^133Ba,^137Cs,^60Co and ^241Am-Be sources respectively are up to 20%and 15%.Fairly good agreement is seen between simulation and dose values obtained from our process and specifications from several photon sources.