Dosimetric Effects of Intrafractional Organ Motion in Field-in-Field Technique for Whole-Breast Irradiation

Purpose: We evaluated the motion-induced dosimetric effects on the field-in-field (FIF) technique for whole-breast irradiation (WBI) using actual patient organ motion data obtained from cine electronic portal imaging device (cine EPID) images during treatment. Materials and Methods: Ten breast cancer patients who received WBI after breast-conserving surgery were selected. The static FIF (SFIF) plan involved the application of two parallel opposing tangential and boost FIFs. To obtain the amplitude of the internal organ motion during treatment, cine EPID images were acquired five times for each patient. The outside contour of the breast (OCB) and chest wall (CW) contour were tracked using in-house motion analysis software. Intrafractional organ motion was analyzed. The dynamic FIF (DFIF) reflecting intrafractional organ motion incorporated into the SFIF plan was calculated and compared with the SFIF in terms of the dose homogeneity index (DHI90/10) for the target and V20 for the ipsilateral lung. Results: The average motion amplitudes along the X and Y directions were 1.84±1.09 mm and 0.69±0.50 mm for OCB and 1.88±1.07 mm and 1.66±1.49 mm for CW, respectively. The maximum motion amplitudes along the X and Y directions were 5.53 and 2.08 mm for OCB and 5.22 and 6.79 mm for CW, respectively. Significant differences in DHI90/10 values were observed between SFIF and DFIF (0.94 vs 0.95, P<0.05) in statistical analysis. The average V20 for the lung in the DFIF was slightly higher than that of the SFIF in statistical analysis (19.21 vs 19.00, P<0.05). Conclusion: Our findings indicate that the FIF technique can form a safe and effective treatment method for WBI. Regular monitoring using cine EPID images can be effective in reducing motioninduced dosimetric errors.ope

Optimization of Proton CT Detector System and Image Reconstruction Algorithm for On-Line Proton Therapy.

The purposes of this study were to optimize a proton computed tomography system (pCT) for proton range verification and to confirm the pCT image reconstruction algorithm based on projection images generated with optimized parameters. For this purpose, we developed a new pCT scanner using the Geometry and Tracking (GEANT) 4.9.6 simulation toolkit. GEANT4 simulations were performed to optimize the geometric parameters representing the detector thickness and the distance between the detectors for pCT. The system consisted of four silicon strip detectors for particle tracking and a calorimeter to measure the residual energies of the individual protons. The optimized pCT system design was then adjusted to ensure that the solution to a CS-based convex optimization problem would converge to yield the desired pCT images after a reasonable number of iterative corrections. In particular, we used a total variation-based formulation that has been useful in exploiting prior knowledge about the minimal variations of proton attenuation characteristics in the human body. Examinations performed using our CS algorithm showed that high-quality pCT images could be reconstructed using sets of 72 projections within 20 iterations and without any streaks or noise, which can be caused by under-sampling and proton starvation. Moreover, the images yielded by this CS algorithm were found to be of higher quality than those obtained using other reconstruction algorithms. The optimized pCT scanner system demonstrated the potential to perform high-quality pCT during on-line image-guided proton therapy, without increasing the imaging dose, by applying our CS based proton CT reconstruction algorithm. Further, we make our optimized detector system and CS-based proton CT reconstruction algorithm potentially useful in on-line proton therapy.ope

A Numerical Voxel Model for 3D-printed Uncompressed Breast Phantoms

Physical breast phantoms would be useful for the development of a dedicated breast computed tomography (BCT) system and its optimization. While the conventional breast phantoms are available in compressed forms, which are appropriate for the mammography and digital tomosynthesis, however, the BCT requires phantoms in uncompressed forms. Although simple cylindrical plastic phantoms can be used for the development of the BCT system, they will not replace the roles of uncompressed phantoms describing breast anatomies for a better study of the BCT. In this study, we have designed a numerical voxel breast phantom accounting for the random nature of breast anatomies and applied it to the 3D printer to fabricate the uncompressed anthropomorphic breast phantom. The numerical voxel phantom mainly consists of the external skin and internal anatomies, including the ductal networks, the glandular tissues, the Cooper's ligaments, and the adipose tissues. The voxel phantom is then converted into a surface data in the STL file format by using the marching cube algorithm. Using the STL file, we obtain the skin and the glandular tissue from the 3D printer, and then assemble them. The uncompressed breast phantom is completed by filling the remaining space with oil, which mimics the adipose tissues. Since the breast phantom developed in this study is completely software-generated, we can create readily anthropomorphic phantoms accounting for diverse human breast anatomies.ope

Improvement in Sensitivity of Radiochromic 3D Dosimeter Based on Rigid Polyurethane Resin by Incorporating Tartrazine

We investigated the influence of incorporating tartrazine on the dose response characteristics of radiochromic 3D dosimeters based on polyurethane resin. We use three types of polyurethane resins with different Shore hardness values: 30 A, 50 A, and 80 D. PRESAGE dosimeters are fabricated with different chemical components and concentrations. Tartrazine (Yellow No. 5) helps incorporate a yellow dye to fabricate the dosimeter. Elemental composition is analyzed with the Zeff. Three sets of six different PRESAGE dosimeters were fabricated to investigate the effects of incorporating yellow dye on the dose response characteristics of the dosimeter. The dose response curve was obtained by measuring the optical absorbance using a spectrometer and optical density using optical CT, respectively. The energy and dose rate dependences are evaluated for the dosimeter with the highest sensitivity. For the optical density measurement, significant sensitivity enhancements of 36.6% and 32.7% were achieved in polyurethane having a high Shore hardness of 80 D and 50 A by incorporating tartrazine, respectively. The same results were obtained in the optical absorbance measurements. The ratio of the Zeff of the dosimeter with 80 D Shore hardness to water was 1.49. The polyurethane radiochromic dosimeter with a Shore hardness of 80 D showed the highest sensitivity and energy and dose rate independence upon the incorporation of tartrazine.ope

약하게 조영증강된 병변의 유방 전용 CT 영상의 대조도 개선을 위한 적응적 영상 재조정 방법: 팬텀 연구

Purpose Dedicated breast CT is an emerging volumetric X-ray imaging modality for diagnosis that does not require any painful breast compression. To improve the detection rate of weakly enhanced lesions, an adaptive image rescaling (AIR) technique was proposed. Materials and Methods Two disks containing five identical holes and five holes of different diameters were scanned using 60/100 kVp to obtain single-energy CT (SECT), dual-energy CT (DECT), and AIR images. A piece of pork was also scanned as a subclinical trial. The image quality was evaluated using image contrast and contrast-to-noise ratio (CNR). The difference of imaging performances was confirmed using student's t test. Results Total mean image contrast of AIR (0.70) reached 74.5% of that of DECT (0.94) and was higher than that of SECT (0.22) by 318.2%. Total mean CNR of AIR (5.08) was 35.5% of that of SECT (14.30) and was higher than that of DECT (2.28) by 222.8%. A similar trend was observed in the subclinical study. Conclusion The results demonstrated superior image contrast of AIR over SECT, and its higher overall image quality compared to DECT with half the exposure. Therefore, AIR seems to have the potential to improve the detectability of lesions with dedicated breast CT.ope

Carotid-Sparing TomoHelical 3-Dimensional Conformal Radiotherapy for Early Glottic Cancer.

PURPOSE: The purpose of this study was to investigate the dosimetric benefits and treatment efficiency of carotid-sparing TomoHelical 3-dimensional conformal radiotherapy (TH-3DCRT) for early glottic cancer. MATERIALS AND METHODS: Ten early-stage (T1N0M0) glottic squamous cell carcinoma patients were simulated, based on computed tomography scans. Two-field 3DCRT (2F-3DCRT), 3-field intensity-modulated radiation therapy (3F-IMRT), TomoHelical-IMRT (TH-IMRT), and TH-3DCRT plans were generated with a 67.5-Gy total prescription dose to the planning target volume (PTV) for each patient. In order to evaluate the plan quality, dosimetric characteristics were compared in terms of conformity index (CI) and homogeneity index (HI) for PTV, dose to the carotid arteries, and maximum dose to the spinal cord. Treatment planning and delivery times were compared to evaluate treatment efficiency. RESULTS: The median CI was substantially better for the 3F-IMRT (0.65), TH-IMRT (0.64), and TH-3DCRT (0.63) plans, compared to the 2F-3DCRT plan (0.32). PTV HI was slightly better for TH-3DCRT and TH-IMRT (1.05) compared to 2F-3DCRT (1.06) and 3F-IMRT (1.09). TH-3DCRT, 3F-IMRT, and TH-IMRT showed an excellent carotid sparing capability compared to 2F-3DCRT (p < 0.05). For all plans, the maximum dose to the spinal cord was < 45 Gy. The median treatment planning times for 2F-3DCRT (5.85 minutes) and TH-3DCRT (7.10 minutes) were much lower than those for 3F-IMRT (45.48 minutes) and TH-IMRT (35.30 minutes). The delivery times for 2F-3DCRT (2.06 minutes) and 3F-IMRT (2.48 minutes) were slightly lower than those for TH-IMRT (2.90 minutes) and TH-3DCRT (2.86 minutes). CONCLUSION: TH-3DCRT showed excellent carotid-sparing capability, while offering high efficiency and maintaining good PTV coverage.ope

Secondary Neutron Dose Measurement for Proton Line Scanning Therapy

Proton therapy is increasingly being actively used in the treatment of cancer. In contrast to photons, protons have the potential advantage of delivering higher doses to the cancerous tissue and lower doses to the surrounding normal tissue. However, a range shifter is needed to degrade the beam energy in order to apply the pencil beam scanning technique to tumors located close to the minimum range. The secondary neutrons are produced in the beam path including within the patient's body as a result of nuclear interactions. Therefore, unintended side effects may possibly occur. The research related to the secondary neutrons generated during proton therapy has been presented in a variety of studies worldwide, since 2007. In this study, we measured the magnitude of the secondary neutron dose depending on the location of the detector and the use of a range shifter at the beam nozzle of the proton scanning mode, which was recently installed. In addition, the production of secondary neutrons was measured and estimated as a function of the distance between the isocenter and detector. The neutron dose was measured using WENDI-II (Wide Energy Neutron Detection Instruments) and a Plastic Water phantom; a Zebra dosimeter and 4-cm-thick range shifter were also employed as a phantom. In conclusion, we need to consider the secondary neutron dose at proton scanning facilities to employ the range shifter reasonably and effectively.ope

Clinical Application Study of Semi-cylindrical Beam Spoiler for Radiation Treatment of Early-stage Glottic Cancer Patients

Background/aim: The purpose of this study was to determine whether a semi-cylindrical beam spoiler (sCBS) developed herein effectively increases the skin dose in patients with early-stage glottic cancer. Patients and methods: We measured the surface doses for 26 patients who used the sCBS during treatment of early-stage glottic cancer through a parallel-opposed lateral two-field 6 MV photon beam. Measurements were performed by attaching optically stimulated luminescent dosimeters to the left, right, anterior (in-field), inferior, and superior (out-field) sides of the patient. Results: The measured results were 81.8±2.1% (left), 81.0±1.7% (right), and 76.8±2.7% (anterior) in the in-field region compared to prescription doses, with 5.7±1.7% (superior) and 2.7±0.7% (inferior) in the out-field region. Conclusion: sCBS can deliver a suitably ideal surface dose for treatment of early-stage glottic cancer.ope

Leibniz's Notion of Composibility

학위논문 (석사)-- 서울대학교 대학원 : 철학과 서양철학전공, 2016. 2. 이석재.In this thesis, I evaluate the different interpretations of Leibniz's notion of compossibility. Scholars have distinguished two ways to explicate Leibniz's position. On the one hand, proponents of the logical interpretation argue that compossibility implies a logical relation between substances complete concepts. That is, nothing more than the consideration of complete concepts is required. On the other, proponents of the lawful interpretation argue that relations of lawfulness and orderliness are necessary in evaluating compossibility claims. James Messina and Donald Rutherford argue that neither the logical nor lawful interpretation is an adequate account of Leibniz's position, and propose a novel interpretation of compossibility. I argue, however, that this novel interpretation is flawed. Messina and Rutherford's reason for rejecting the lawful interpretation is as much as a reason to reject their interpretation, or so I argue.0. The Problem 1 1. The 'Logical' Approach 3 1.1 Benson Mates' Solution 4 1.2 Nicholas Rescher's Solution 8 1.3 World-Bound Substances 11 2. The 'Lawful' Approach 15 2.1 Bertrand Russell and General Laws 16 2.2 Laws as Facts 20 2.3 Hypothetical Compossibility 22 2.4 Harmony, Compossibility, and Connection 25 3.0 Laws, Independence, and God 32 3.1 The World Apart Doctrine 38 3.2 The Possibility of Spinozism 40 3.3 The Threat of Spinozism 47 3.4 Laws and Final Causes 50 4.0 Conclusion 55 Works Cited 57 국문초록 59Maste

Optimization of treatment planning workflow and tumor coverage during daily adaptive magnetic resonance image guided radiation therapy (MR-IGRT) of pancreatic cancer

BACKGROUND: To simplify the adaptive treatment planning workflow while achieving the optimal tumor-dose coverage in pancreatic cancer patients undergoing daily adaptive magnetic resonance image guided radiation therapy (MR-IGRT). METHODS: In daily adaptive MR-IGRT, the plan objective function constructed during simulation is used for plan re-optimization throughout the course of treatment. In this study, we have constructed the initial objective functions using two methods for 16 pancreatic cancer patients treated with the ViewRay MR-IGRT system: 1) the conventional method that handles the stomach, duodenum, small bowel, and large bowel as separate organs at risk (OARs) and 2) the OAR grouping method. Using OAR grouping, a combined OAR structure that encompasses the portions of these four primary OARs within 3 cm of the planning target volume (PTV) is created. OAR grouping simulation plans were optimized such that the target coverage was comparable to the clinical simulation plan constructed in the conventional manner. In both cases, the initial objective function was then applied to each successive treatment fraction and the plan was re-optimized based on the patient's daily anatomy. OAR grouping plans were compared to conventional plans at each fraction in terms of coverage of the PTV and the optimized PTV (PTV OPT), which is the result of the subtraction of overlapping OAR volumes with an additional margin from the PTV. RESULTS: Plan performance was enhanced across a majority of fractions using OAR grouping. The percentage of the volume of the PTV covered by 95% of the prescribed dose (D95) was improved by an average of 3.87 +/- 4.29% while D95 coverage of the PTV OPT increased by 3.98 +/- 4.97%. Finally, D100 coverage of the PTV demonstrated an average increase of 6.47 +/- 7.16% and a maximum improvement of 20.19%. CONCLUSIONS: In this study, our proposed OAR grouping plans generally outperformed conventional plans, especially when the conventional simulation plan favored or disregarded an OAR through the assignment of distinct weighting parameters relative to the other critical structures. OAR grouping simplifies the MR-IGRT adaptive treatment planning workflow at simulation while demonstrating improved coverage compared to delivered pancreatic cancer treatment plans in daily adaptive radiation therapy.ope