Résumé
Objective:Proton pencil beam (PB) dose calculation can achieve rapid dose calculation, whereas it is inaccurate due to the approximation in dealing with inhomogeneities. Monte Carlo (MC) dose calculation is recognized as the most accurate method, but it is extremely time consuming. The aim of this study was to apply deep-learning methods to improve the accuracy of PB dose calculation by learning the difference between the MC and PB dose distribution.Methods:A model which could convert the PB dose into the MC dose in lung cancer patients treated with intensity-modulated proton therapy (IMPT) was established based on the Hierarchically Densely Connected U-Net (HD U-Net) network. PB dose and CT images were used as model input to predict the MC dose for IMPT. The beam dose and CT images of 27 non-small cell lung cancer patients were preprocessed to the same angle and normalized, and then used as model input. The accuracy of the model was evaluated by comparing the mean square error and γ passing rate (1 mm/1%) results between the predicted dose and MC dose.Results:The predicted dose showed good agreement with MC dose. Using the 1 mm/1% criteria, the average γ passing rate (voxels receiving more than 10% of maximum MC dose) between the predicted and MC doses reached (92.8±3.4)% for the test patients. The average dose prediction time for test patients was (6.72±2.26) s.Conclusion:A deep-learning model that can accurately predict the MC dose based on the PB dose and CT images is successfully developed, which can be used as an efficient and practical tool to improve the accuracy of PB dose calculation for IMPT in lung cancer patients.
Résumé
Compared with intensity-modulated photon therapy, intensity-modulated proton therapy has significant dose advantages. However,the dose gradient of proton Bragg peak is relatively high,and the proton therapy is likely to be affected by range uncertainties,setup uncertainties and antonymic changes,etc. The difference between the planning dose and actual dose caused by respiratory motion hinders the widespread use of intensity-modulated proton therapy in thoracic cancers. In this paper,research progress on the effect of respiratory motion on intensity-modulated proton therapy and how to reduce the effect were summarized,aiming to provide reference for clinicians and researchers.
Résumé
Objective To evaluate the safety and efficacy of proton and carbon-ion radiotherapy (RT) for stage Ⅰ non-small cell lung cancer (NSCLC) with pencil beam scanning technique.Methods From August 2014 to December 2015,10 patients with stage Ⅰ NSCLC who were inoperable or refused surgery were treated by proton +/-carbon-ion RT.Primary lesions were irradiated using 2-4 portals with 45-degree beams.A total dose of 50-70 GyE/10 fractions,60-64 GyE/15-16 fractions,and 66-72 GyE/22-24 fractions were administered to patients based on tumor location (4 peripheral,3 middle,and 3 central lesions,respectively).Results At the last follow-up in December 2016 with the median follow-up of 18.1 (11.9-28.1) months,local control was found in all patients per CT or PET/CT scanning(6 complete response,3 partial response,and 1 stable disease).However,2 patients with local control (1 partial response and 1 stable disease) experienced a distant failure at 8.7 and 24.9 months after RT,respectively.There was no RT-related Grade 3-5 toxicity in all patients.Grade 2 toxicities were only found in 2 patients (acute skin reaction and leucopenia,respectively).At 1,3-5 months after RT,the pulmonary function tests showed a slightly increase in FVC,FEV1 and DLCO-sb compared with those before RT without statistical significance (P ＞ 0.05).Conclusions The particle RT using pencil beam scanning technique was safe,and yielded encouraging outcome for patients with stage I NSCLC who were inoperable or refused surgery.Further follow-up and prospective clinical studies are warranted in the future.
Résumé
Objective To investigate the dosimetric performance of two algorithms for correcting the presence of tissue inhomogeneities,the finite site pencil beam (FSPB) and X-ray voxel Monte Carlo (XVMC) plans were implemented in the MONACO system,with the accuracy of application to clinic treatment of two algorithms were evaluated.Methods In a non-uniform artificial anthropomorphic phantom,regular open fields and intensity modulation radiated therapy (IMRT) plans of the MONACO were measured by using calibrated EBT2 films,and the dose accuracy of the two kinds of plans was analyzed by comparing the planned and measured plane dose.Results In an anthropomorphic phantom,the deviations between the calculated values by XVMC and the measured values by films were less than ± 2％.While the deviations of FSPB values between calculation and measurements was within ± 3％,except at the condition of 15 MV,10 cm ×2 cm field,the dose error in lung was up to 6.51％.The verification of individual IMRT beams based on films showed that the pass rates of calculation by XVMC and FSPB were larger than 90％ with γ criterion of 3％/3 mm and 4％/4 mm,respectively.At 3％/3 mm,the pass rates of FSPB were in the range of 80％-90％.At the same time,the pass rates of all individual fields were higher than 90％.Conclusions The accuracy of dose calculation of XVMC is better than that of FSPB when being in multi-segments and non-uniform media.The error of algorithm can be controlled within ±3％,for the calculation by XVMC.And the dose deficiency of PTV arising from algorithm can be avoided.
Résumé
Objective To compare the dosimetric differences between pencil beam convolution (PBC) and anisotropic analytical algorithm (AAA) in Eclipse treatment planning system for intensitymodulated radiotherapy (IMRT) planning of lung cancer patients and dosimetric verification.Methods 10 IMRT plans of lung cancer patients were calculated using the PBC and AAA and the differences of dosimetric parameter were analyzed according to dose-volume histogram of planning target volume (PTV),lung and spinal cord.The verification measurements were performed on an inhomogeneous thorax phantom using a pinpoint ionization chamber.The agreement between calculated and measured doses was determined.The paired t test was used to compare the results.Results Compared with PBC,the AAA predicted higher maximum PTV dose (t =-4.03,P =0.010),lower minimum PTV dose (t =5.09,P =0.040),and a reduction of the volume of PTV covered by the prescribed dose.The AAA also predicted slightly increases than the PBC algorithm in the mean dose to the lung and the V20 as well as the maximum dose to the spinal cord,and the differences were statistically significant (t =-3.99,-2.79,-5.46,P =0.010,0.038,0.003).In the verification measurements,the agreement between the AAA and measurement was within 2％and superior to the PBC algorithm on isocenter (t =-3.82,P =0.012).Conclusions For IMRT treatment planning of lung cancer,the PBC algorithm overestimates the dose to the PTV and underestimates the dose to the lung and the spinal cord,so the AAA for treating planning in which the tissue inhomogeneous such as lung is present is recommended.
Résumé
ObjectiveTo compare the calculation precision of the collapsed cone convolution (CCC) algorithm and pencil beam convolution (PBC) algorithm in TPS in heterogeneous tissue.Methods We made two virtual lung phantoms,one is single field phantom,In this case the photon beam incident into the phantom,the other is the two fields phantom and a cubic'tumor' was placed in the centre of the phantom.two opposite photon beams incident into the phantom.We calculated the dose of the'tumor' and the lung with the CCC and PBC algorithm.We compared the results in both case with if obtained from Monte Carlo (MC) method.ResultsIn the single field phantom,the photon beam incident from the high-density tissue to the low-density lung equivalent tissue,compared with the result of MC algorithm PBC algorithm overestimated the lung equivalent tissue dose (t =3.90,P =0.012) and the result of CCC algorithm is close to it ( t =2.25,P =0.087 ).In the two fields phantom,tumor boundary dose calculated by CCC algorithm and the MC algorithm are lower than that of the PBC algorithm (t =2.43,3.18,P =0.038,0.011 ),and the difference increase when the field size decrease, the beam energy increase and the density of the inhomogeneity decrease.ConclusionsWe had better use the CCC algorithm when calculating the dose of the tumor surrounded by low-density tissue or the tumor behind the low-density tissue,such as the lung cancer,esophageal cancer etc.
Résumé
The pencil beam convolution (PBC) algorithms in radiation treatment planning system have been widely used to calculate the radiation dose. A new photon dose calculation algorithm, referred to as the anisotropic analytical algorithm (AAA), was released for use by the Varian medical system. The aim of this paper was to investigate the difference in dose calculation between the AAA and PBC algorithm using the intensity modulated radiation therapy (IMRT) plan for lung cancer cases that were inhomogeneous in the low density. We quantitatively analyzed the differences in dose using the eclipse planning system (Varian Medical System, Palo Alto, CA) and I'mRT matirxx (IBA, Schwarzenbruck, Germany) equipment to compare the gamma evaluation. 11 patients with lung cancer at various sites were used in this study. We also used the TLD-100 (LiF) to measure the differences in dose between the calculated dose and measured dose in the Alderson Rando phantom. The maximum, mean, minimum dose for the normal tissue did not change significantly. But the volume of the PTV covered by the 95% isodose curve was decreased by 6% in the lung due to the difference in the algorithms. The difference dose between the calculated dose by the PBC algorithms and AAA algorithms and the measured dose with TLD-100 (LiF) in the Alderson Rando phantom was -4.6% and -2.7% respectively. Based on the results of this study, the treatment plan calculated using the AAA algorithms is more accurate in lung sites with a low density when compared to the treatment plan calculated using the PBC algorithms.
Sujets)
Humains , Poumon , Tumeurs du poumonRésumé
The purpose of this study is to evaluate the variation of radiation dose distribution for liver tumor located in liver dome and for the interest organs(normal liver, kidney, stomach) with the pencil beam convolution (PBC) algorithm versus anisotropic Analyticalal algorithm (AAA) of the Varian Eclipse treatment planning system, The target volumes from 20 liver cancer patients were used to create treatment plans. Treatment plans for 10 patients were performed in Stereotactic Body Radiation Therapy (SBRT) plan and others were performed in 3 Dimensional Conformal Radiation Therapy (3DCRT) plan. dose calculation was recalculated by AAA algorithm after dose calculation was performed by PBC algorithm for 20 patients. Plans were optimized to 100% of the PTV by the Prescription Isodose in Dose Calculation with the PBC algorithm. Plans were recalculated with the AAA, retaining identical beam arrangements, monitor units, field weighting and collimator condition. In this study, Total PTV was to be statistically significant (SRS: p=0.018, 3DCRT: p=0.006) between PBC and AAA algorithm. and in the case of PTV, ITV in liver dome, plans for 3DCRT were to be statistically significant respectively (p=0.013, p=0.024). normal liver and kidney were to be statistically significant (p=0.009, p=0.037). For the predictive index of dose variation, CVF ratio was to be statistically significant for PTV in the liver dome versus PTV (SRS r=0.684, 3DCRT r=0.732, p<0.01) and CVF ratio for Tumor size was to be statistically significant (SRS r=-0.193, p=0.017, 3DCRT r=0.237, p=0.023).
Sujets)
Humains , Rein , Foie , Tumeurs du foie , Composés organothiophosphorés , Caractéristiques de la population , OrdonnancesRésumé
Less execution of the electron arc treatment could in large part be attributed to the lack of an adequate planning system. Unlike most linear accelerators providing the electron arc mode, no commercial planning systems for the electron arc plan are available at this time. In this work, with the expectation that an easily accessible planning system could promote electron arc therapy, a commercial planning system was commissioned and evaluated for the electron arc plan. For the electron arc plan with use of a Varian 21-EX, Pinnacle3 (ver. 7.4f), with an electron pencil beam algorithm, was commissioned in which the arc consisted of multiple static fields with a fixed beam opening. Film dosimetry and point measurements were executed for the evaluation of the computation. Beam modeling was not satisfactory with the calculation of lateral profiles. Contrary to good agreement within 1% of the calculated and measured depth profiles, the calculated lateral profiles showed underestimation compared with measurements, such that the distance-to-agreement (DTA) was 5.1 mm at a 50% dose level for 6 MeV and 6.7 mm for 12 MeV with similar results for the measured depths. Point and film measurements for the humanoid phantom revealed that the delivered dose was more than the calculation by approximately 10%. The electron arc plan, based on the pencil beam algorithm, provides qualitative information for the dose distribution. Dose verification before the treatment should be mandatory.
Sujets)
Électrons , Dosimétrie photographique , Accélérateurs de particulesRésumé
Generally,pencil beam kernels for photon beam calculation are obtained through Monte Carlo calculations.In this paper,a pencil beam model is set up with a method of deconvolution from measured broad beam profiles.These profiles are usually available in a radiotherapy planning system.Furthermore,this method is applied to computing dose distributions at different sizes.Comparisons with measurements show that the accuracy of the calculated dose distributions fits well in a1%error interval in high dose gradient regions.