Objective:To develop a spot scanning carbon ion beam model based on Monte Carlo code FLUKA and verify the accuracy of physical dose.Methods:A geometric model of the treatment nozzle was established in FLUKA. Various parameters such as monoenergy nominal energy, Gaussian energy spectrum distribution, initial spot size, and beam angular distribution in the model were adjusted to match the reference data of integral depth dose (IDD) and in-air spot size measuremed experimentally. Carbon ion beam plans were generated by using the treatment planning system (TPS). The difference in output dose distribution between FLUKA and TPS was compared by the gamma analysis.Results:The differences in Bragg peak width, beam range, and distal falloff width extracted from the IDD curve between the FLUKA model and measured vaues were less than 0.1 mm, with the maximum difference in spot sizes of 0.17 mm. Under the criterion of 2 mm/2% in all the simulations, 2D- and 3D-γ pass rates were all above 95%.Conclusions:An accurate spot scanning carbon beam model was developed based on the Monte Carlo code FLUKA. It has the potential to be used for not only the verification of clinical treatment plans, but also the development of new ion beam therapy equipment and the calculation of biologically effective dose.

BackgroundIn particle radiotherapy, the Bragg peak (BP) width of carbon ion beam is required to be broadened whilst Ripple filter (RiFi) is often used as a clinical broadening device. However, it may cause extra lateral scattering. Porous material expressed as the porous structure 1.0 (PS 1.0) can be used to reduce such scattering but bring an oversized distal falloff width (DFW).PurposeThis study aims to develop a novel porous structure, described as a porous structure 2.0 (PS 2.0), to broaden the BP width.MethodsFirst of all, the Monte Carlo code, FLUKA was selected as the tool for this simulation. Two geometry models of broadening structure (1D-RiFi and PS 1.0) were built. Then, the PS 2.0 was simulated by inserting numerous of Polymethyl Methacrylate (PMMA) sticks in the PS 1.0 with a certain proportion. The performance of PS 2.0 was evaluated by analyzing the DFW and isocenter spot size of the modulated carbon ion beams. Finally, a plane homogeneous radiation field was simulated and fluence homogeneities were compared by using a 2D (X-Z) dose distribution and quantized by calculating the 1D-lateral flatness.ResultsCompared to the PS 1.0, the DFW is reduced by at most 1.11 mm by using PS 2.0 with a similar BP width broadening ability at the same beam range. Fluence homogeneity of PS 2.0 is excellent in all the downstream locations, and the isocenter spot size is reduced by at most 1.72 mm at the same beam range.ConclusionsThis study provides a new method for simulating the PS 2.0 as a BP broadening device with smaller DFW, better homogeneous and reduced isocenter spot size in comparison to PS 1.0.

Objective:Patients are breathing freely during adjuvant proton pencil beam radiotherapy after breast conserving surgery. Fluctuation of the thorax may affect the position of the end of the proton beam flow, which needs to be precisely evaluated on a millimeter scale.Methods:For 20 patients with breast cancer treated with proton radiotherapy after breast conserving surgery, PET-CT scan was performed approximately 10 min after the end of proton radiotherapy. The images of PET-CT were processed for ROI determination and sampling line (profile) extraction on a Raystation RV workstation to calculate the actual difference between the predicted and real radioactivity from the same spatial location as obtained by PET acquisition R50. Then, the differences in the spatial location between the actual process of proton irradiation and the planned process were obtained. Depth difference values for each pair of sampling lines were presented. Results:For 20 patients with breast cancer with a median follow-up of 22 months (range 12 - 46 months), all patients survived at the last follow-up, and no radiation pneumonitis was observed during the follow-up period. Among the verification results of 21 cases, the depth difference of evenly distributed was (-0.75±1.89) mm in the primary field and (-0.82±2.06) mm in the secondary field; The depth difference of sequential treatment was (1.81±1.87) mm in the primary field and (1.32±1.74) mm in the secondary field; The depth difference of synchronous addition in the primary field was (-1.47±1.44) mm, and the depth difference in the secondary field was (-1.48±2.11) mm.Conclusion:The results of off-line PET-CT in vivo biological verification show that the accuracy of the dose boundary cut-off was within 3 mm in breast cancer patients, which meets the clinical and physician requirement for the precision in breast cancer treatment.

Objective:To test the usefulness of PET-range verification (RV) method for proton radiation accuracy verification in poly (methyl methacrylate) (PMMA) phantom using off-line PET/CT scanning.Methods:Proton irradiation dose of 2 Gy and 4 Gy were delivered in PMMA phantom. Given the difference of clinical target volume (CTV), 7 subgroups with different depth (5.0, 7.5, 10.0, 12.5, 15.0, 17.5, 20.0 cm) were set for each dose (14 radiation plans or radiation fields). PET/CT scan was performed 10 min after irradiation of 48-221 MeV proton beam. A co-registration between CT from treatment planning system and PET/CT was performed, as well as the smoothing and normalization of PET/CT data. The region of interest (ROI) and profile lines were drawn with the Raystation PET-RV software. The predictive induced radioactivity and the measured induced radioactivity profile lines were analyzed to evaluate the Δ R50, namely, the error at the position corresponding to 50% of the maximum predictive induced radioactivity at the end of both curves. Results:The size of each ROI was 5.0 cm×5.0 cm×2.5 cm. Profile lines were evenly distributed with the interval of 3 mm, and totally 289 pairs of profile lines were drew. The 2 Gy- and 4 Gy-dose groups yielded similar mean depth errors (Δ R50 between 1 mm and -1 mm with a standard deviation <1 mm). Conclusions:The off-line PET/CT scanning of PMMA phantom reveals a good agreement between predicted and measured PET data, with error of ±1 mm. The PET-RV method can be extended to clinical cases′ verification in human body treatment with further investigation.

目的:探究脊形滤波器结构对质子束流展宽的影响.方法:利用蒙特卡罗程序FLUKA建立质子束流模型,并进行验证.模拟质子束流通过三棱柱型(A型)和金字塔型(B型)两种脊形滤波器,比较使用和不使用脊形滤波器的模拟值:束流前端最大剂量50％到束流末端最大剂量50％的宽度(E50-D50)、束流前端80％到束流末端80％的宽度(E80-D80)及束流末端80％到束流末端20％的宽度(D80-D20).结果:根据模型计算出的121.1 MeV质子对应的模拟值绘制的积分深度剂量曲线与实际测量的积分深度剂量曲线,E50、E70和D80位置偏差不超过0.06 mm;A型相比B型将E50-D50平均多展宽了0.80 mm,将E80-D80平均多展宽了0.27 mm,将D80-D20平均多展宽了0.08 mm.结论:建立的质子束流蒙特卡罗模型合理,三棱柱型(A型)脊形滤波器展宽质子束流的效果更好.

Objective To investigate the effect of lipiodol as embolization agents in liver, after transcatheter arterial chemoembolization, on dose calculation under the carbon ion treatment plan. Methods The actual relative linear stopping powers (RLSP) in pure lipiodol, pure gel and lipiodol-gel mixture, together with the correctd RLSPs from their CT images, were compared. In seven typical cases with lipiodol deposition area, carbon ion treatment plan was performed for the original lipiodol images. Successively on the basis of analysis that has made, the RLSP in lipiodol deposition area was corrected to be as in normal liver tissue, for which the carbon ion treatment plan was again performed. A comparison was made of differences in water equivalent depth ( WED) and dose distribution on different CT images. Results The RLSP value corrected according to CT image HU value, lipiodol, and lipiodol-gel mixture may increase by 4. 6％-139. 0％ compared with the measured value. In seven typical cases, deposited lipiodol can cause WED to increase by ( 0. 89 ± 0. 41 ) cm along the field track and RBE by (3. 83±1. 71) Gy within the 1 cm of distal area of target. Conclusions In order to improve the accuracy of dose distribution calculation, the HU value and/or RLSP in deposited lipiodol area in liver after transcatheter arterial chemoembolization should being corrected to be as in the normal liver tissue.

Objective To establish an accurate simulation model for proton scanning beam using Monte Carlo (MC) code.Methods The MC model of proton scanning beam treatment nozzle was established by using MC code FLUKA combined with the geometric structure of the treatment nozzle in Shanghai Proton and Heavy Ion Center (SPHIC).The MC beam model was established through the simulation of the integrated depth dose distribution (IDD) in water and the lateral profile in air at the isocenter points.The model was used to simulate the depth and lateral dose profile of Spread Out Bragg Peak (SOBP) of proton beam.The calucated result were compared with TPS calculation values.Results For the distal R90,the deviations of simulation and measurement at all energies were less than 0.5 mm.For distal fall off (R80-20),the deviations between simulation and measurement at each energy were within 0.1 mm.The biggest difference between measurement and simulation of the proton beam spot size was within 0.45 mm.The result of simulation and TPS calculation of proton SOBP matched well,with the γ index pass rate being higher than 90％ (Criteria:2 mm,2％).Conclusions The MC code FLUKA can be used to model the nozzle of scanning proton beam,which can meet the clinical requirements and accurately simulate the proton beam transport in material.After construction and verification on the basis of measurement,this model can be used as a dose verification tool to evaluate clinical proton treatment plans,in order to reduce the beam time for dose verification and thus increase the number of patient treatment in proton therapy.

Objective To investigate a system for the detection of the acoustic signal created by clinical proton and carbon ion Bragg-peaks (BPs).Methods An acoustic detector was attached to water phantoms downstream of the beam.The water-equivalent depth of this phantom was measured by a peakfinder (PTW,Siemens,Germany) using high energy proton beams.By maintaining the same particle number,either the BP to detector distance (BTD) or beam intensity was changed to investigate their relationships with the magnitude of acoustic signal.By moving the beam spot in lateral directions,the full width at half maximums (FWHMs) of BPs was measured and compared.Results The detected acoustic signal created by beam on or beam off could represent the magnitude of signal,which was proven by a statistical analysis.The magnitude of acoustic signals created by proton BPs were inversely proportional to BTD,but proportional to intensities.The measured FWHM of 125.43 MeV proton BP was 11.7％ larger than data from the treatment planning system (TPS).Carbon ion showed similar result whereas the measured FWHM of 178.89 MeV/u carbon ion BP was 45.6％ larger than the data from TPS.The BTDs could be more than 67.7 mm while maintaining enough magnitude of acoustic signal.Conclusions This acoustic detection system can detect the acoustic waves from clinical proton and carbon ion BPs.However,further investigation is ongoing to decrease the noise.

Objective To investigate EBT3 and EDR2 film responses to different linear energy transfers ( LETs) and doses from carbon ion beams. Methods EBT3 and EDR2 films were calibrated by two methods. In the first method, films were placed at the same depth within a phantom and irradiated by beams with different parameters such as beam energy. In the second method, films were separately placed at different depths in a phantom and irradiated by the same beams. These methods were used to irradiate films with ions of different LETs. Results For EBT3 film, the dose calibration curves correlated with different LETs appeared to be typical hyperbolic curves with a maximum difference between the curves of ± 17％ (1σ). Meanwhile, the shape of the dose calibration curves for EDR2 film appeared to be linear. The values along all these curves were within ± 27.4％ (1σ) of the value for the average curve. The dose responses of both films were inversely proportional to LETs. The sensitivity of EBT3 film was inversely proportional to the dose, while the sensitivity of EDR2 film showed no relationship with the dose. Conclusions Influenced by the dual factor of LET and dose, the application of EBT3 film was limited in carbon ion. However, without no dose dependence, EDR2 film could be used to measure dose distributions created by single LET carbon ion beam.

Objective To investigate the dosimetric advantages of proton and heavy ion radiotherapy ( particle radiotherapy) for liver cancer adjacent to gastrointestinal tract. Methods Ten patients with liver cancer adjacent to gastrointestinal tract receiving radiotherapy were recruited in this study. The prescription was first given with 50 Gy ( RBE )/25 fractions to planning target volume 1 ( PTV-1 ) using proton irradiation,and then administered with 15 Gy ( RBE)/5 fractions to PTV-2 using carbon-ion irradiation. A simultaneous integrated boost regime was established using the same variables and prescription. The organ at risk ( OAR) constraints were referred to RTOG 1201. All plans were performed for dose evaluation after qualifying the OAR constraints. Results The dose coverage of 95％ of the prescribed dose ( V95) for PTV-1 from the photon plan (97.15％±4. 27％),slightly better than (96.25±6. 69％) from the particle plan (P=0. 049).The V95 of PTV-2 from the particle plan was (94.6％±6. 22％),comparable to (95.12％±3. 49％) from the photon plan (P=0. 277).The integral dose of Body-PTV-1 delivered by the particle plan was merely 39. 9％ of that delivered by the photon plan. The mean liver-GTV dose from the particle plan was only 81. 8％ of that from the photon plan. The low-dose irradiation to the stomach and duodenum from the particle plan was significantly lower than that from the photon plan. Conclusions The dose to the liver-gross tumor volume ( GTV) is the main factor limiting the increase of total dose to the tumors. When the absolute GTV in the liver is relatively large,particle radiotherapy can maintain comparable dose coverage to the tumors as the photon radiotherapy whereas significantly reduce the dose to the liver-GTV.

Objective To measure the CT Hounsfield Unit ( HU) and relative stopping power ( RSP) conversion curve. Methods In this study, the RSPs of 12 different tissue equivalent rods were measured with proton and carbon beam in the Shanghai Proton and Heavy Ion Center ( SPHIC) . The same tissue equivalent materials were scanned with CT scanner to acquire the HU. Results Conversion curve for the transformation of HU into RSP was generated for both proton and carbon ion beam. Differences between RSPs measured using proton and carbon beam were ≤0. 64%except lung material. Conclusions A RSP versus HU conversion curve was generated for both protons and carbon ions.

轫致辐射是第三代先进同步辐射光源光束线站辐射屏蔽的重点.上海光源(Shanghai Synchrotron Radiation Facility,SSRF)是国际上正在运行的第三代先进同步辐射光源之一.上海光源蛋白质微晶结构光束线(BL18U)线站是正在试运行中的光束线站.本文采用FLUKA软件模拟计算了蛋白质微晶结构光束线(BL18U)线站因轫致辐射的散射和光中子引起的辐射剂量率分布.分析了因狭缝开孔尺寸、储存环内流强的变化所引起的辐射剂量变化.用高灵敏度的光子和中子探测器测量了BL18U光学棚屋外的光子和光中子剂量率.测量结果表明模拟计算的可靠性.本研究采用的模拟和测量方法可用于其它线站的辐射剂量水平评估,并为上海光源后续线站的屏蔽设计提供参考.

同位素中子源和中子刻度室在实际使用中通常带有屏蔽体。本文采用蒙特卡罗计算与实验结合的方法,研究了散射中子对带屏蔽体的252Cf同位素中子源辐射场的影响。通过计算带屏蔽体的252Cf中子源和裸252Cf中子源的中子能谱、中子注量率和中子周围剂量当量率,分析了屏蔽体产生的散射中子对辐射场的影响。依据蒙特卡罗计算所获得的有、无源室墙壁、地面和屋顶条件下的中子注量率和中子周围剂量当量率,分析了源室墙壁、地面和屋顶所产生的散射中子对辐射场的影响。计算结果表明,该中子辐射场的平均中子通量-周围剂量当量转换因子由裸252Cf中子源的385 pSv·cm2降至280 pSv·cm2,源室的墙壁、地面和屋顶产生的散射中子对中子注量率与中子周围剂量当量率的影响与距中子源的距离平方成正比。中子周围剂量当量率仪的实验测量结果与理论计算结果符合良好,验证了计算结果的可靠性。本研究为利用非标准同位素中子源中子参考辐射场进行辐射防护仪表的校准提供了一种实践可行的方法,具有很好的实用性。

In this study,a Voxel-based Chinese Reference female Phantom(VCRP-woman) is developed from an individual female phantom which was based on high resolution cross-sectional color photographs.An in-house C+ +program was developed to adjust the phantom.Finally,a reference female phantom with have the same height,weighte and similar organs masses with the Chinese reference adult female data.The adjusted phantom is then imported to MCNPX to calculate the organs absorbed dose and effective dose conversion coefficients.Results are compared between VCRP-woman and the ICRP adult reference female phantom.