Jung-in Kim

Photon energy-modulated radiotherapy: Monte Carlo simulation and treatment planning study

PURPOSE To demonstrate the feasibility of photon energy-modulated radiotherapy during beam-on time. METHODS A cylindrical device made of aluminum was conceptually proposed as an energy modulator. The frame of the device was connected with 20 tubes through which mercury could be injected or drained to adjust the thickness of mercury along the beam axis. In Monte Carlo (MC) simulations, a flattening filter of 6 or 10 MV linac was replaced with the device. The thickness of mercury inside the device varied from 0 to 40 mm at the field sizes of 5 × 5 cm(2) (FS5), 10 × 10 cm(2) (FS10), and 20 × 20 cm(2) (FS20). At least 5 billion histories were followed for each simulation to create phase space files at 100 cm source to surface distance (SSD). In-water beam data were acquired by additional MC simulations using the above phase space files. A treatment planning system (TPS) was commissioned to generate a virtual machine using the MC-generated beam data. Intensity modulated radiation therapy (IMRT) plans for six clinical cases were generated using conventional 6 MV, 6 MV flattening filter free, and energy-modulated photon beams of the virtual machine. RESULTS As increasing the thickness of mercury, Percentage depth doses (PDD) of modulated 6 and 10 MV after the depth of dose maximum were continuously increased. The amount of PDD increase at the depth of 10 and 20 cm for modulated 6 MV was 4.8% and 5.2% at FS5, 3.9% and 5.0% at FS10 and 3.2%-4.9% at FS20 as increasing the thickness of mercury from 0 to 20 mm. The same for modulated 10 MV was 4.5% and 5.0% at FS5, 3.8% and 4.7% at FS10 and 4.1% and 4.8% at FS20 as increasing the thickness of mercury from 0 to 25 mm. The outputs of modulated 6 MV with 20 mm mercury and of modulated 10 MV with 25 mm mercury were reduced into 30%, and 56% of conventional linac, respectively. The energy-modulated IMRT plans had less integral doses than 6 MV IMRT or 6 MV flattening filter free plans for tumors located in the periphery while maintaining the similar quality of target coverage, homogeneity, and conformity. CONCLUSIONS The MC study for the designed energy modulator demonstrated the feasibility of energy-modulated photon beams available during beam-on time. The planning study showed an advantage of energy-and intensity modulated radiotherapy in terms of integral dose without sacrificing any quality of IMRT plan.

A comparative planning study for lung SABR between tri-Co-60 magnetic resonance image guided radiation therapy system and volumetric modulated arc therapy

BACKGROUND AND PURPOSE To compare the plan quality of tri-(60)Co magnetic-resonance image-guided radiation therapy (IGRT) to that of volumetric modulated arc therapy (VMAT) for lung stereotactic ablative radiotherapy (SABR). MATERIALS AND METHODS A total of 22 patients with lung tumors located in the lower lobe were selected retrospectively. For each patient, VMAT plans with linac and intensity-modulated radiation therapy (IMRT) plans with the tri-(60)Co system were generated with prescription doses of 60Gy (daily dose=15Gy). For both plan types, identical CT image sets and structures were used, with the exception of planning target volumes (PTV). The PTV for VMAT was generated from the internal target volume (ITV) while the PTV for the tri-(60)Co system was generated from the gross tumor volume (GTV). Clinically relevant dose-volumetric parameters were calculated and analyzed. RESULTS The average PTV volumes of tri-(60)Co plans and VMAT plans were 10.5±12.3cc vs. 27.2±23.5cc, respectively (p<0.001). The maximum and mean doses to PTVs were 64.0±2.6Gy vs. 62.5±0.9Gy (p=0.005) and 61.4±1.7Gy vs. 60.0±0.5Gy (p<0.001), respectively. The conformity and homogeneity indices were 1.89±0.38 vs. 1.01±0.40 (p<0.001) and 0.06±0.02 vs. 0.04±0.00 (p<0.001), respectively. No considerable differences for organs at risk (OARs) were observed between tri-(60)Co plans and VMAT plans. In terms of target conformity, integral dose and lung mean dose, the plan quality of tri-(60)Co plans was inferior to that of VMAT plans when the PTV volumes of tri-(60)Co plans were less than 10cc. However, all treatment plans of tri-(60)Co system were clinically acceptable. CONCLUSION For lung SABR, the quality of ITV-based VMAT plans was better than that of GTV-based tri-(60)Co plans especially when the PTV volumes of the tri-(60)Co plans were less than 10cc. If the breathing pattern of a patient is reproducible, VMAT is considered the optimal option for lung SABR, otherwise the tri-(60)Co IGRT should be considered due to the ability to monitor tumor motion during treatment.

Effect of fiber structure on dialysate flow profile and hollow-fiber hemodialyzer reliability: CT perfusion study.

Background Uniform dialysate distributions in hollow-fiber hemodialyzers facilitate effective solute removal, and the fiber structure inside hemodialyzers plays a significant role in determining dialysate flow distribution and dialysis efficiency. The authors analyzed the effects of undulated fibers on dialysate flow profiles and hemodialyzer reliability using a perfusion CT technique. Method Using a multi-detector row CT unit, perfusion studies were performed on two different types of hemodialyzers: (A) straight fiber configuration; (B) undulated fiber configuration (wavy-shaped fibers). Deconvolution theory was used for image processing to derive dialysate flows, dialysate volumes, and mean transit time distributions. Three-dimensional perfusion maps for the two types of hemodialyzers were reconstructed using high resolution images and these parameters were compared at hemodialyzer midsections. Results Dialysate maldistributions were observed in both types of hemodialyzer. However, dialysate flow distributions were more uniform in the undulated-fiber hemodialyzer, whereas more complex flow distributions developed in straight-fiber hemodialyzer. Reliability as determined using intraclass correlation coefficients was markedly higher for the hemodialyzer containing undulated fiber (0.968 vs. 0.496 for type A and type B, respectively). Conclusions The undulated-fiber type was found to have more uniform, consistent dialysate flow profiles. It is believed that this type of hemodialyzer will be found helpful for measurement and prescription of the delivered hemodialysis dose due to its better consistency.

14C Level At Mt Chiak and Mt Kyeryong in Korea

We have observed Delta (super 14) C concentrations in the northern hemisphere temperate region in the bomb pulse period, using cross-dated tree ring samples. The tree-ring samples were taken from one 70-year-old and two 50-year-old red pines (Pinus densiflora) on Mt Chiak, Korea and from a 50-year-old red pine (Pinus densiflora) on Mt Kyeryong, Korea. Twenty-two tree-ring samples from four red pines ranging from 1950 to 2000 AD were pretreated to obtain holo-cellulose, combusted to CO (sub 2) by an element analyzer (EA) and converted to graphite for Delta (super 14) C measurement using the accelerator mass spectrometry (AMS) facility at Seoul National University. Our results for Delta (super 14) C showed good agreement with those measured by other researchers at similar latitudes. The observed steady decrease of Delta (super 14) C from 1965 to 2000 AD is described by a single exponential function with a lifetime tau = 15.99+ or -0.43 yr. This lifetime is similar to that of the high-latitude region in Europe.

Gamma-index method sensitivity for gauging plan delivery accuracy of volumetric modulated arc therapy

PURPOSE The aim of this study was to investigate the sensitivity of the gamma-index method according to various gamma criteria for volumetric modulated arc therapy (VMAT). METHODS Twenty head and neck (HN) and twenty prostate VMAT plans were retrospectively selected for this study. Both global and local 2D gamma evaluations were performed with criteria of 3%/3 mm, 2%/2 mm, 1%/2 mm and 2%/1 mm. In this study, the global and local gamma-index calculated the differences in doses relative to the maximum dose and the dose at the current measurement point, respectively. Using log files acquired during delivery, the differences in parameters at every control point between the VMAT plans and the log files were acquired. The differences in dose-volumetric parameters between reconstructed VMAT plans using the log files and the original VMAT plans were calculated. The Spearmans rank correlation coefficients (rs) were calculated between the passing rates and those differences. RESULTS Considerable correlations with statistical significances were observed between global 1%/2 mm, local 1%/2 mm and local 2%/1 mm and the MLC position differences (rs = -0.712, -0.628 and -0.581). The numbers of rs values with statistical significance between the passing rates and the changes in dose-volumetric parameters were largest in global 2%/2 mm (n = 16), global 2%/1 mm (n = 15) and local 2%/1 mm (n = 13) criteria. CONCLUSION Local gamma-index method with 2%/1 mm generally showed higher sensitivity to detect deviations between a VMAT plan and the delivery of the VMAT plan.

Assessment of potential jaw-tracking advantage using control point sequences of VMAT planning

This study aims to evaluate the potential jaw‐tracking advantage using control point sequences of volume volumetric‐modulated arc therapy (VMAT) planning. VMAT plans for patients with prostate and head and neck (H&N) cancers were converted into new static arc (SA) plans. The SA plan consisted of a series of static fields at each control point of the VMAT plan. All other machine parameters of the SA plan were perfectly identical to those of the original VMAT plan. The jaw‐tracking static arc (JTSA) plans were generated with fields that closed the jaws of each SA field into the multileaf collimators (MLCs) aperture. The dosimetric advantages of JTSA over SA were evaluated in terms of a dose‐volume histogram (DVH) of organ at risk (OAR) after renormalizing both plans to make the same target coverage. Both plans were delivered to the MatriXX‐based COMPASS system for 3D volume dose verification. The average jaw size reduction of the JTSA along the X direction was 3.1±0.9 cm for prostate patients and 6.9±1.9 cm for H&N patients. For prostate patients, the organs far from the target showed larger sparing (3.7%—8.1% on aver‐age) in JTSA than the organs adjacent to the target (1.1%—1.5%). For the H&N plans, the mean dose reductions for all organs ranged from 4.3% to 11.9%. The dose reductions were more significant in the dose regions of D80,D90, and D95 than the dose regions of D5,D10, and D20 for all patients. Likewise, the deliverability and reproducibility of jaw‐tracking plan were validated. The measured dosimetric advantage of JTSA over SA coincided with the calculated one above. PACS numbers: 87.55.D‐, 87.55.ne

Three-dimensional dialysate flow analysis in a hollow-fiber dialyzer by perfusion computed tomography.

Perfusion computed tomography (PCT) is a means to rapidly and easily evaluate cerebral perfusion in patients presenting with acute stroke symptoms, which provides insights into capillary-level hemodynamics. In this study, we used PCT to analyze the 3-dimensional dialysate flow in a low-flux hemodialyzer equipped with a standard fiber bundle. The dynamic CT studies were performed with 64-channel multi-detector row CT (MDCT) at a dialysate flow rate of 500 ml/min and a 1.0 ml/sec injection rate of contrast agent. Central volume principle was used to calculate hydrodynamic parameters by deconvolution of time-density curves (TDCs). Functional maps of dialysate flow (DF), dialysate volume (DV), and mean transit time (MTT) could quantitatively describe the dialysate flow maldistribution, variations in fiber packing, and perfusion pressure distribution in a hemodialyzer, respectively. PCT by means of analysis was able to overcome the limitations of conventional imaging techniques for analyzing dialysate flow distributions in hollow-fiber dialyzers. Not only local hydrodynamic phenomena at microscopic level but also macroscopic flow behavior of dialysate were visualized quantitatively. Therefore, we concluded that PCT is a quantitative analysis method to provide better insights into hydrodynamics of hollow-fiber dialyzers and is expected to contribute to optimization of artificial kidneys.

Quality of tri-Co-60 MR-IGRT treatment plans in comparison with VMAT treatment plans for spine SABR

OBJECTIVE To investigate the plan quality of tri-Co-60 intensity-modulated radiation therapy (IMRT) plans for spine stereotactic ablative radiotherapy (SABR). METHODS A total of 20 patients with spine metastasis were retrospectively selected. For each patient, a tri-Co-60 IMRT plan and a volumetric-modulated arc therapy (VMAT) plan were generated. The spinal cords were defined based on MR images for the tri-Co-60 IMRT, while isotropic 1-mm margins were added to the spinal cords for the VMAT plans. The VMAT plans were generated with 10-MV flattening filter-free photon beams of TrueBeam STx™ (Varian Medical Systems, Palo Alto, CA), while the tri-Co-60 IMRT plans were generated with the ViewRay™ system (ViewRay inc., Cleveland, OH). The initial prescription dose was 18 Gy (1 fraction). If the tolerance dose of the spinal cord was not met, the prescription dose was reduced until the spinal cord tolerance dose was satisfied. RESULTS The mean dose to the target volumes, conformity index and homogeneity index of the VMAT and tri-Co-60 IMRT were 17.8 ± 0.8 vs 13.7 ± 3.9 Gy, 0.85 ± 0.20 vs 1.58 ± 1.29 and 0.09 ± 0.04 vs 0.24 ± 0.19, respectively. The integral doses and beam-on times were 16,570 ± 1768 vs 22,087 ± 2.986 Gy cm3 and 3.95 ± 1.13 vs 48.82 ± 10.44 min, respectively. CONCLUSION The tri-Co-60 IMRT seems inappropriate for spine SABR compared with VMAT. Advances in knowledge: For spine SABR, the tri-Co-60 IMRT is inappropriate owing to the large penumbra, large leaf width and low dose rate of the ViewRay system.

Dosimetric effects of roll rotational setup errors on lung stereotactic ablative radiotherapy using volumetric modulated arc therapy

OBJECTIVE To evaluate the dosimetric effects of roll-rotational setup errors of stereotactic ablative radiotherapy (SABR) for lung cancer using volumetric modulated arc therapy (VMAT). METHODS A total of 23 lung SABR cases were evaluated retrospectively. Each of the planning CT images was intentionally rotated by ±1°, ±2° and ±3°. After that, to simulate the translational couch correction, rotated CT images were moved along the x, y and z axis to match the centroid of the target volume in the rotated CT images with that in the original CT images. The differences in D95% and V100% of the target volume, D0.35cc of spinal cord, D0.35cc and D5cc of oesophagus and V20Gy of lung between the original and the rotated CT images were calculated. RESULTS The average differences in D95% and V100% of target volume, D0.35cc of spinal cord, D0.35cc and D5cc of oesophagus and V20Gy of lung were -0.3% ± 0.4% and -0.7% ± 2.4%, 1.6 ± 27.9 cGy, -1.6 ± 37.6 cGy, 15.9 ± 25.3 cGy and 0.0% ± 0.1%, respectively. The dosimetric changes in organs at risk (OARs) near the target volume were sometimes considerable due to roll-rotational setup errors, despite the translational correction, and those were patient specific. CONCLUSION In the case of coplanar VMAT for lung SABR, dosimetric changes to the target volume due to roll-rotational setup errors could be compensated by translational correction, whereas those to the OARs could not in some cases. ADVANCES IN KNOWLEDGE Roll-rotational setup errors would increase the dose to OARs despite the translational correction.

Correlation analysis between 2D and quasi-3D gamma evaluations for both intensity-modulated radiation therapy and volumetric modulated arc therapy

The aim of this work was to investigate correlations between 2D and quasi-3D gamma passing rates. A total of 20 patients (10 prostate cases and 10 head and neck cases, H&N) were retrospectively selected. For each patient, both intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were generated. For each plan, 2D gamma evaluation with radiochromic films and quasi-3D gamma evaluation with fluence measurements were performed with both 2%/2 mm and 3%/3 mm criteria. Gamma passing rates were grouped together according to delivery techniques and treatment sites. Statistical analyses were performed to examine the correlation between 2D and quasi-3D gamma evaluations. Statistically significant difference was observed between delivery techniques only in the quasi-3D gamma passing rates with 2%/2 mm. Statistically significant differences were observed between treatment sites in the 2D gamma passing rates (differences of less than 8%). No statistically significant correlations were observed between 2D and quasi-3D gamma passing rates except the VMAT group and the group including both IMRT and VMAT with 3%/3 mm (r = 0.564 with p = 0.012 for theVMAT group and r = 0.372 with p = 0.020 for the group including both IMRT and VMAT), however, those were not strong. No strong correlations were observed between 2D and quasi-3D gamma evaluations.