Objective:To explore the accuracy of in-room on-rails CT (IRCT) for image-guided radiotherapy (IGRT) and adaptive radiotherapy (ART) during proton and heavy-ion radiotherapy.Methods:The positioning accuracy and registration accuracy of IRCT were tested by using the spherical phantom and multiple imaging modality iso-centricity, and the positioning accuracy of isocenter geometric mapping and 3D-3D registration accuracy were evaluated when the phantoms were applied to IGRT. Standard water-aluminum phantom and ACR467 phantom were utilized to establish and evaluate the HU value-relative linear stopping power to water (RLSP) conversion curve. By scanning the same rigid phantom images on both IRCT and planned CT, followed by dose calculation and comparison of dose differences, the consistency of dose distribution between 2 modalities was evaluated when applied to ART in relation to the planned CT. Pre-treatment CT of patient was acquired using IRCT scan before treatment. Online qualitative analysis and offline quantitative analysis were performed. A case of prostate cancer was selected, and its online qualitative analysis ability was tested by evaluating whether IRCT could effectively identify changes in the position of clinical target volume (CTV) and critical organs at risk. One case of prostate cancer and 1 case of breast cancer were selected, and the offline quantitative analysis ability was tested by the key dose volume histogram parameters of dose recalculation on CT before treatment.Results:In IGRT application, the isocenter geometric mapping positioning accuracy was 0.1 mm. The displacement accuracy for 3D-3D registration was 0.8 mm, with a rotational accuracy of 0.6°. In ART application, a CT HU value-RLSP conversion curve was established using standard methods. The RLSP variation range for 24 representative tissues was -3.91% to 1.49%, with an average variation of -0.75%±0.95%. Calculation results performed on rigid phantoms for head, chest, and abdominal-pelvic regions showed that compared to the planned CT, the γ pass rate for proton plan dose distribution consistency on IRCT was>97%, and >95% for carbon-ion plan, both using 2%/2 mm criteria with a 10% threshold. The results of 2 representative clinical applications showed that online qualitative analysis of carbon-ion plans for prostate cancer could identify changes in patient soft tissue position relative to the planned CT, CTV, and critical organs at risk before treatment. Offline quantitative analysis could quantify dose changes in patients undergoing treatment. In the prostate cancer original plan for prostate cancer, the relative volume of CTV receiving 95% (V 95%) of the prescribed dose was 100%, which were 97.63% and 99.91% before different fractions of treatment, respectively. For the bladder and rectum, V 95% was 3.00% and 3.80%, which were changed to 0.75% and 12.36% for one session of treatment, and 2.76% and 3.08% for another session of treatment, aligning with the results of online qualitative analysis. In the original plan for breast cancer, tumor bed CTV and breast CTV V 95% were 99.93% and 99.93%, which were 100.00% and 99.57% for one session of treatment and 92.32% and 93.13% for another session of treatment, triggering re-planning. The re-planned results were improved to 99.82% and 99.93%. Conclusions:IRCT can be applied to IGRT and ART in proton and heavy-ion radiotherapy, enabling accurate patient positioning verification and adjustment, as well as online anatomical qualitative analysis and offline dose quantitative analysis.

Background and purpose:The ripple filter(RiFi)is a passive energy modulator used in particle beam therapy to broaden the Bragg peak.The 1D-RiFi features a wavy structure that can broaden a monoenergetic carbon ion beam to 3 mm,while the 2D-RiFi employs a two-dimensional groove structure to achieve a 6 mm beam broadening.This study aimed to evaluate the potential advantages of the 2D-RiFi over the 1D-RiFi in terms of dose distribution optimization,treatment efficiency,and organ at risk(OAR)dose control by comparing water phantom and clinical patient plans.Methods:Carbon ion treatment plans were designed for water phantoms and 20 patients using both 1D-RiFi and 2D-RiFi.The water phantom plans targeted a cubic region of interest(80 mm×80 mm×80 mm)at ranges of 95,105,190 and 290 mm.From patients who underwent carbon ion therapy at Shanghai Proton and Heavy Ion Center,20 cases were selected via simple random sampling with computer-generated random numbers,stratified by the proportion of different tumor sites(6 head and neck tumors,4 prostate tumors,4 lung tumors,2 pancreatic tumors,2 liver tumors and 2 shoulder tumors).Key dosimetric metrics,including homogeneity index(HI),conformity index(CI)and clinical target volume(CTV)coverage by 95%prescription dose(V95),were analyzed along with OAR doses.Energy layers,beam time,and irradiation time were compared between the two RiFi types.Statistical analysis was performed using the Wilcoxon rank-sum test,with a significance level of P＜0.05.This study was approved by the ethics committee of Shanghai Proton and Heavy Ion Center(approval number:240311EXP-01).Results:For water phantom plans,the 1D-RiFi plans achieved HI of 0.04±0.01,CI of 1.10±0.03,V95 of 99.92%±0.06%and flatness of 6.52%±0.61%,while the 2D-RiFi plans achieved HI of 0.04±0.01,CI of 1.11±0.04,V95 of 99.92%±0.06%,and flatness of 7.52%±0.81%.The mean doses to the distal and lateral block in 1D-RiFi plans were(1.34 Gy±0.43)Gy[relative biological effectiveness(RBE)]and(0.98±0.05)Gy(RBE),respectively,compared to(1.47±0.33)Gy(RBE)and(0.94±0.03)Gy(RBE)for 2D-RiFi plans.The use of 2D-RiFi reduced the average beam-on time by 43%and the number of energy layers by 48%.For clinical plans,the 1D-RiFi plans had HI of 0.07±0.04,CI of 1.94±0.67,and V95 of 98.81%±1.61%,compared to HI of 0.07±0.05,CI of 1.95±0.70,and V95 of 98.79%±1.69%for the 2D-RiFi plans,with no statistically significant differences(P=0.77,0.65 and 0.66,respectively).OAR mean doses increased slightly with the 2D-RiFi plans(average increase of 0.8%,P=0.62)but remained within clinically acceptable limits.The 2D-RiFi plans reduced energy layers by 45%-50%(average 48%),beam time by 32%-49%(average 44%),and irradiation time by 28%-41%(average 36%).Conclusion:Treatment plans using the 2D-RiFi achieved comparable target coverage to those using the 1D-RiFi,with a slight but clinically acceptable increase in OAR doses.The application of the 2D-RiFi significantly reduced the number of energy layers,beam time and irradiation time in carbon ion therapy,enhancing treatment efficiency.

Background and purpose:The ripple filter(RiFi)is a passive energy modulator used in particle beam therapy to broaden the Bragg peak.The 1D-RiFi features a wavy structure that can broaden a monoenergetic carbon ion beam to 3 mm,while the 2D-RiFi employs a two-dimensional groove structure to achieve a 6 mm beam broadening.This study aimed to evaluate the potential advantages of the 2D-RiFi over the 1D-RiFi in terms of dose distribution optimization,treatment efficiency,and organ at risk(OAR)dose control by comparing water phantom and clinical patient plans.Methods:Carbon ion treatment plans were designed for water phantoms and 20 patients using both 1D-RiFi and 2D-RiFi.The water phantom plans targeted a cubic region of interest(80 mm×80 mm×80 mm)at ranges of 95,105,190 and 290 mm.From patients who underwent carbon ion therapy at Shanghai Proton and Heavy Ion Center,20 cases were selected via simple random sampling with computer-generated random numbers,stratified by the proportion of different tumor sites(6 head and neck tumors,4 prostate tumors,4 lung tumors,2 pancreatic tumors,2 liver tumors and 2 shoulder tumors).Key dosimetric metrics,including homogeneity index(HI),conformity index(CI)and clinical target volume(CTV)coverage by 95%prescription dose(V95),were analyzed along with OAR doses.Energy layers,beam time,and irradiation time were compared between the two RiFi types.Statistical analysis was performed using the Wilcoxon rank-sum test,with a significance level of P＜0.05.This study was approved by the ethics committee of Shanghai Proton and Heavy Ion Center(approval number:240311EXP-01).Results:For water phantom plans,the 1D-RiFi plans achieved HI of 0.04±0.01,CI of 1.10±0.03,V95 of 99.92%±0.06%and flatness of 6.52%±0.61%,while the 2D-RiFi plans achieved HI of 0.04±0.01,CI of 1.11±0.04,V95 of 99.92%±0.06%,and flatness of 7.52%±0.81%.The mean doses to the distal and lateral block in 1D-RiFi plans were(1.34 Gy±0.43)Gy[relative biological effectiveness(RBE)]and(0.98±0.05)Gy(RBE),respectively,compared to(1.47±0.33)Gy(RBE)and(0.94±0.03)Gy(RBE)for 2D-RiFi plans.The use of 2D-RiFi reduced the average beam-on time by 43%and the number of energy layers by 48%.For clinical plans,the 1D-RiFi plans had HI of 0.07±0.04,CI of 1.94±0.67,and V95 of 98.81%±1.61%,compared to HI of 0.07±0.05,CI of 1.95±0.70,and V95 of 98.79%±1.69%for the 2D-RiFi plans,with no statistically significant differences(P=0.77,0.65 and 0.66,respectively).OAR mean doses increased slightly with the 2D-RiFi plans(average increase of 0.8%,P=0.62)but remained within clinically acceptable limits.The 2D-RiFi plans reduced energy layers by 45%-50%(average 48%),beam time by 32%-49%(average 44%),and irradiation time by 28%-41%(average 36%).Conclusion:Treatment plans using the 2D-RiFi achieved comparable target coverage to those using the 1D-RiFi,with a slight but clinically acceptable increase in OAR doses.The application of the 2D-RiFi significantly reduced the number of energy layers,beam time and irradiation time in carbon ion therapy,enhancing treatment efficiency.

Objective:To explore the accuracy of in-room on-rails CT (IRCT) for image-guided radiotherapy (IGRT) and adaptive radiotherapy (ART) during proton and heavy-ion radiotherapy.Methods:The positioning accuracy and registration accuracy of IRCT were tested by using the spherical phantom and multiple imaging modality iso-centricity, and the positioning accuracy of isocenter geometric mapping and 3D-3D registration accuracy were evaluated when the phantoms were applied to IGRT. Standard water-aluminum phantom and ACR467 phantom were utilized to establish and evaluate the HU value-relative linear stopping power to water (RLSP) conversion curve. By scanning the same rigid phantom images on both IRCT and planned CT, followed by dose calculation and comparison of dose differences, the consistency of dose distribution between 2 modalities was evaluated when applied to ART in relation to the planned CT. Pre-treatment CT of patient was acquired using IRCT scan before treatment. Online qualitative analysis and offline quantitative analysis were performed. A case of prostate cancer was selected, and its online qualitative analysis ability was tested by evaluating whether IRCT could effectively identify changes in the position of clinical target volume (CTV) and critical organs at risk. One case of prostate cancer and 1 case of breast cancer were selected, and the offline quantitative analysis ability was tested by the key dose volume histogram parameters of dose recalculation on CT before treatment.Results:In IGRT application, the isocenter geometric mapping positioning accuracy was 0.1 mm. The displacement accuracy for 3D-3D registration was 0.8 mm, with a rotational accuracy of 0.6°. In ART application, a CT HU value-RLSP conversion curve was established using standard methods. The RLSP variation range for 24 representative tissues was -3.91% to 1.49%, with an average variation of -0.75%±0.95%. Calculation results performed on rigid phantoms for head, chest, and abdominal-pelvic regions showed that compared to the planned CT, the γ pass rate for proton plan dose distribution consistency on IRCT was>97%, and >95% for carbon-ion plan, both using 2%/2 mm criteria with a 10% threshold. The results of 2 representative clinical applications showed that online qualitative analysis of carbon-ion plans for prostate cancer could identify changes in patient soft tissue position relative to the planned CT, CTV, and critical organs at risk before treatment. Offline quantitative analysis could quantify dose changes in patients undergoing treatment. In the prostate cancer original plan for prostate cancer, the relative volume of CTV receiving 95% (V 95%) of the prescribed dose was 100%, which were 97.63% and 99.91% before different fractions of treatment, respectively. For the bladder and rectum, V 95% was 3.00% and 3.80%, which were changed to 0.75% and 12.36% for one session of treatment, and 2.76% and 3.08% for another session of treatment, aligning with the results of online qualitative analysis. In the original plan for breast cancer, tumor bed CTV and breast CTV V 95% were 99.93% and 99.93%, which were 100.00% and 99.57% for one session of treatment and 92.32% and 93.13% for another session of treatment, triggering re-planning. The re-planned results were improved to 99.82% and 99.93%. Conclusions:IRCT can be applied to IGRT and ART in proton and heavy-ion radiotherapy, enabling accurate patient positioning verification and adjustment, as well as online anatomical qualitative analysis and offline dose quantitative analysis.

Objective:To develop and validate a structure for broadening the Bragg peak to improve the efficiency and conformality of particle radiotherapy.Methods:Techniques of random stacking and regular stacking were employed to fabricate the mesh-stacked porous structure (MPS). In each layer of the grid, the thickness, line width and spacing were set at 0.1 mm, 0.1 mm and 0.5 mm, respectively, resulting in a total size of 10 cm ×10 cm. Monte Carlo code FLUKA was performed to simulate the transportation of 196 MeV/u carbon ion beam and a 105 MeV proton beam through the MPS. Dose distribution, fluence homogeneity, and modulation stability of the modulated beams were evaluated. Moreover, the modulation effect of MPS in clinical radiotherapy plans for nasopharyngeal carcinoma (63 Gy in 21 fractions), lung cancer (77 Gy in 22 fractions) and prostate cancer (70.4 Gy in 16 fractions) was also evaluated, respectively.Results:The MPS was capable of broadening the Bragg peak width by 1.73 mm for proton beams and 2.95 mm for carbon ion beams. For different entrance positions, regular stacking of more than 10 layers could reduce the modulation power difference of MPS to within 5%. For MPS with 30 layers of regular stacking, the modulated fluence homogeneity could achieve a value of less than 3% by transporting 18 cm distance in air. When comparing to the clinically used ripple filters, MPS reduced the isocenter spot size of proton beams by 0.91 mm. In the comparison study of the treatment plan for nasopharyngeal carcinoma, the use of MPS could shorten the treatment time by 213 s (37%) and reduce the maximum dose to the brainstem by 3.28 Gy (7.5%).Conclusions:MPS effectively broadens the Bragg peak of particle beams and improves the efficiency of clinical radiotherapy. Regularly stacked MPS demonstrates robust modulation stability, and the modulated beam achieves relatively well fluence homogeneity, making it a promising clinical application for closer to the patients and reducing lateral scattering.

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.

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.

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 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 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.