治療中コーンビーム断層画像と医療用加速器の動作記録を用いた4次元線量分布計算

学位の種別:課程博士University of Tokyo(東京大学

Evaluation of heterogeneity dose distributions for Stereotactic Radiotherapy (SRT): comparison of commercially available Monte Carlo dose calculation with other algorithms

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to compare dose distributions from three different algorithms with the x-ray Voxel Monte Carlo (XVMC) calculations, in actual computed tomography (CT) scans for use in stereotactic radiotherapy (SRT) of small lung cancers.</p> <p>Methods</p> <p>Slow CT scan of 20 patients was performed and the internal target volume (ITV) was delineated on Pinnacle³. All plans were first calculated with a scatter homogeneous mode (SHM) which is compatible with Clarkson algorithm using Pinnacle³treatment planning system (TPS). The planned dose was 48 Gy in 4 fractions. In a second step, the CT images, structures and beam data were exported to other treatment planning systems (TPSs). Collapsed cone convolution (CCC) from Pinnacle³, superposition (SP) from XiO, and XVMC from Monaco were used for recalculating. The dose distributions and the Dose Volume Histograms (DVHs) were compared with each other.</p> <p>Results</p> <p>The phantom test revealed that all algorithms could reproduce the measured data within 1% except for the SHM with inhomogeneous phantom. For the patient study, the SHM greatly overestimated the isocenter (IC) doses and the minimal dose received by 95% of the PTV (PTV95) compared to XVMC. The differences in mean doses were 2.96 Gy (6.17%) for IC and 5.02 Gy (11.18%) for PTV95. The DVH's and dose distributions with CCC and SP were in agreement with those obtained by XVMC. The average differences in IC doses between CCC and XVMC, and SP and XVMC were -1.14% (p = 0.17), and -2.67% (p = 0.0036), respectively.</p> <p>Conclusions</p> <p>Our work clearly confirms that the actual practice of relying solely on a Clarkson algorithm may be inappropriate for SRT planning. Meanwhile, CCC and SP were close to XVMC simulations and actual dose distributions obtained in lung SRT.</p

DEVELOPMNT OF 3D Does Verification System for Scanned Ion Beam AT HIMAC

A 3D dose imaging system has been developedfor a project of a new cancer treatement with 3D pencil beam scanning at HIMAC. This system provides the dose measurements easily and rapidly. This system consists of a water tank, fluoresecent screen and charge-coupled device, set at isocentor. The fluorescent screen is directlly attached to the downstream side of water tank. One of great advantages of this system is to obtain 2D dose map at once, by correcting LET-dependent quenching. The proced to verify 3D dose distribution is based on the 2D dose measurement of slice-by-slice under a water depth. We will present the measurement result of 3D dose distribution by the prposed method ,and its comparison withthat by theionization chamber.EPAC 2008 (11th European Particle Accelerator Conference

Patient specific QA of scanning beam carbon ion radiotherapy with rotating gantry for choroidal melanoma in clinical trial

The QST hospital has successfully treated more than 200 patients with choroidal melanoma by broad beam carbon ion radiotherapy (CIRT) with a compensator and a patient-specific collimator since 2001. We decided in 2017 to use scanning carbon ion beam with a rotating gantry for this treatment owing to its flexibilities of dose conformation and beam direction, and then its clinical trial started in April, 2018.In our facility, a commercial 2D ionization chamber array had been employed to verify the 2D dose distribution for any patient specific QA. [1] However, the target volume in choroidal melanoma treatment is typically so small that the 2D array is not appropriate to the verification tool of 2D dose distribution due to its low spatial resolution. Thus, in this clinical trial, we applied new method to the patient specific QA. The method consists of two dosimetric verifications by measurements of depth dose distribution with the Bragg peak chamber and lateral dose distributions at three different depths with the pinpoint chambers, and a verification of beam position at each beam spot with the existing beam position monitor (multi-wire proportional chamber). This method was successfully applied to patient specific QAs for 44 treatment beams of all 22 patients received scanning CIRT for choroidal melanoma in this clinical trial until July, 2019. Here, we provide the summary of the QA results and introduce the current QA procedure based on this clinical trial. [1] T. Furukawa et al., Med. Phys., 40, 121707 (2013).The 59th Annual Conference of the Particle Therapy Co-Operative Group (PTCOG59

Stereotactic Body Radiotherapy for Small Lung Tumors in the University of Tokyo Hospital

Our work on stereotactic body radiation therapy (SBRT) for primary and metastatic lung tumors will be described. The eligibility criteria for SBRT, our previous SBRT method, the definition of target volume, heterogeneity correction, the position adjustment using four-dimensional cone-beam computed tomography (4D CBCT) immediately before SBRT, volumetric modulated arc therapy (VMAT) method for SBRT, verifying of tumor position within internal target volume (ITV) using in-treatment 4D-CBCT during VMAT-SBRT, shortening of treatment time using flattening-filter-free (FFF) techniques, delivery of 4D dose calculation for lung-VMAT patients using in-treatment CBCT and LINAC log data with agility multileaf collimator, and SBRT method for centrally located lung tumors in our institution will be shown. In our institution, these efforts have been made with the goal of raising the local control rate and decreasing adverse effects after SBRT

DEVELOPMENT OF 3D DOSE VERIFICATION SYSTEM FOR SCANNED ION BEAM AT HIMAC

A 3D (three-dimensional) dose verification system has been developed as a part of new project involving 3D pencil beam scanning at HIMAC (Heavy Ion Medical Accelerator in Chiba). This system provides the easy and rapid dose measurements. It consists of a water column, a scintillator and a charge-coupled device, set at isocentor. The scinillator is directly attached to the downstream side of the water column. One of the great advantages of this system is to obtain 2D dose map at once, by correcting LET-dependent quenching. Quenching is corrected by measurement slice-by-slice, of a certain water depth. We present the results of 3D dose measurement and comparison with the ionization chamber measurement

Effect of asymmetric lateral beam spread of a pencil beam and oscillation of spot position on fluence distribution for particle pencil beam scanning

A pencil beam scanning system for carbon ion radiotherapy has operated at National Institute of Radiological Sciences (NIRS) in Japan since 2011. The pencil beam scanning system makes conformal dose distribution to a target by superposition of a pencil beam. Then it is required to accurately irradiate the pencil beam with 2-dimensional Gaussian distribution with symmetric variance in the lateral direction to a planned spot position. However, the actual lateral beam spread of the pencil beam is slightly different and the actual beam irradiation position is also slightly different from the planned spot position. The different lateral beam spread and the different beam irradiation position are suppressed to the acceptance level in the beam commissioning process to remain the uniformity of dose distribution. However, the range of the acceptance level has been unclear and determined experimentally. The purpose of this study is to objectively determine the acceptance level about the symmetry of the lateral beam spread of the pencil beam and the accuracy of the beam irradiation position. We calculated a fluence distribution by superposing the individual pencil beam with asymmetric variances in the lateral direction and/or with oscillation of the beam irradiation position. We changed the difference of the lateral beam spread and the amplitude of the oscillation and studied the effect of these variations on the fluence distribution. We present the calculation results and summarize the acceptance level about the symmetry of the pencil beam spread and the accuracy of the beam irradiation position.54th Annual Conference of the Particle Therapy Co-Operative Group (PTCOG54