Hyun Do Huh

Development of a 3D optical scanner for evaluating patient-specific dose distributions.

PURPOSE This paper describes the hardware and software characteristics of a 3D optical scanner (P3DS) developed in-house. The P3DS consists of an LED light source, diffuse screen, step motor, CCD camera, and scanner management software with 3D reconstructed software. MATERIALS AND METHOD We performed optical simulation, 2D and 3D reconstruction image testing, and pre-clinical testing for the P3DS. We developed the optical scanner with three key characteristics in mind. First, we developed a continuous scanning method to expand possible clinical applications. Second, we manufactured a collimator to improve image quality by reducing scattering from the light source. Third, we developed an optical scanner with changeable camera positioning to enable acquisition of optimal images according to the size of the gel dosimeter. RESULTS We confirmed ray-tracing in P3DS with optic simulation and found that 2D projection and 3D reconstructed images were qualitatively similar to the phantom images. For pre-clinical tests, the dose distribution and profile showed good agreement among RTP, optical CT, and external beam radiotherapy film data for the axial and coronal views. The P3DS has shown that it can scan and reconstruct for evaluation of the gel dosimeter within 1 min. We confirmed that the P3DS system is a useful tool for the measurement of 3D dose distributions for 3D radiation therapy QA. Further experiments are needed to investigate quantitative analysis for 3D dose distribution.

Construction of a High-quality Voxel Model VKH-Man Using Serially Sectioned Images from Visible Korean Human Project in Korea

In this study, a high-quality voxel model of a Korean adult male was constructed using the Visible Korean Human (VKH) project’s serially sectioned anatomical images. The VKH images are transverse color photographs obtained from the serial sectioning of an adult Korean male cadaver (164 cm, 55 kg) at 0.2 mm intervals. A total of 28 organs and tissues were segmented with the color photographic images. The height and weight of the constructed voxel model, VKH-Man, is 164 cm and 59.6 kg, respectively. The voxel resolution of the model is 1.875 mm × 1.875 mm × 2 mm. The developed model was implemented into a Monte Carlo particle transport simulation code, MCNPX, to calculate the organ and tissue doses and, thereby, the effective doses, and the calculated values were compared with the values obtained from other computational models (KTMAN-2, VIP-Man, and ICRP-74).

Statistical Process Control Analysis for Patient Quality Assurance of Intensity Modulated Radiation Therapy

This study applied statistical process control to set and verify the quality assurances (QA) tolerance standard for our hospital’s characteristics with the criteria standards that are applied to all the treatment sites with this analysis. Gamma test factor of delivery quality assurances (DQA) was based on 3%/3 mm. Head and neck, breast, prostate cases of intensity modulated radiation therapy (IMRT) or volumetric arc radiation therapy (VMAT) were selected for the analysis of the QA treatment sites. The numbers of data used in the analysis were 73 and 68 for head and neck patients. Prostate and breast were 49 and 152 by MapCHECK and ArcCHECK respectively. Cp value of head and neck and prostate QA were above 1.0, Cpml is 1.53 and 1.71 respectively, which is close to the target value of 100%. Cpml value of breast (IMRT) was 1.67, data values are close to the target value of 95%. But value of was 0.90, which means that the data values are widely distributed. Cp and Cpml of breast VMAT QA were respectively 1.07 and 2.10. This suggests that the VMAT QA has better process capability than the IMRT QA. Consequently, we should pay more attention to planning and QA before treatment for breast Radiotherapy.

Erratum to: Branch length similarity entropy-based descriptors for shape representation (Journal of the Korean Physical Society, (2017), 71, 10, (727-732), 10.3938/jkps.71.593)

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SU‐E‐J‐54: Dosimetric Evaluation of Amplitude‐Based Gating in Volumetric Modulated Arc Therapy (VMAT)

PURPOSE The purpose of this work is to evaluate the dosimetric influence in the gated volumetric modulated arc therapy. METHODS This study is performed in three liver cancer patients. Execution of 4D CT simulation and plan deliveries on one-dimensional respiratory motion phantom were based on patients respiratory trace data sets. We chose the regular and irregular respiratory amplitude patterns among the patient respiratory-gated treatment log file. Dose distributions were evaluated using EBT3 film by comparing the gated delivery with static delivery. RESULTS The presented results of static measured and calculated dose distributions showed good agreement with gamma-index passing rates above 97% for 3%/3 m dose accuracy/distance-to-agreement criteria. In regular respiratory amplitude pattern, the results of two in three patients evaluated gamma-index passing rates above 92% except for another patient who was evaluated of 87.16%. Patients whose plans had the largest percentage failing the gamma statistics exhibited irregular respiratory amplitude pattern that evaluated less than 70%. Minimum passing rate was 37.40%. This results showed that the correlation of between sorted 4D CT phase and irregular patient respiratory amplitude pattern may results in considerable dosimetric difference. CONCLUSION The effort to maintain regular patient respiratory amplitude pattern between 4D CT simulation and treatment is the most important in gated volumetric modulated arc therapy.

SU‐E‐T‐475: Small Field Dosimetry of Volumetric Modulated Arc Therapy According to a New Dosimetry Formalism

Purpose: To verify small field dosimetry techniques based on the proposed new formalism for reference dosimetry of nonstandard fields [Alfonso et al., Med. Phys. 35, 5179‐5186 (2008)] in volumetric modulated arc therapy field. Methods: For this study, we constructed a cylindrical PMMA phantom including a hole to measure a reference absorbed dose at the center of phantom. We investigated a candidate plan‐class specific reference (pcsr) field using Eclpise 8.6 and the CTimages of home‐made phantom. Four detectors were used for the absorbed dose to water in the pcsr field: Thermoluminescent dosimeter, Glass dosimeter, a diamonddetector and a liquid filled ionization chamber. For determining correction factor between the condition of conventional reference field and pcsr field, three cylindrical ionization chambers of varying volumes were used (a farmer type chamber, a Semiflex chamber and a PinPoint chamber) in pcsr fields by means of one arc and two arc gantry with continuously varying beam aperture, gantry speed and dose rate. Results: We found the correction factors were not different between one fully arc pcsr field and two fully arc pcsr field. For one fully acr pcsr field, the correction factors of each chamber were found in a range of 0.988–0.999, while for two acr pcsr field, they were found in a range of 0.984–0.996. The measurement in each pcsr field found the different within 1.2 %. Conclusions: We investigated two pcsr fields and measured the correction factors using chambers with various volumes. We found that the correction factors were changed according to chambers and pcsr fields. Therefore, in small field and nonstandard field such as VMAT, the correction factor have to be measure using proper pcsr fields and chambers.

Comparison of linac-based fractionated stereotactic radiotherapy and tomotherapy treatment plans for intra-cranial tumors

This study compares and analyzes stereotactic radiotherapy using tomotherapy and linac-based fractionated stereotactic radiotherapy in the treatment of intra-cranial tumors, according to some cases. In this study, linac-based fractionated stereotactic radiotherapy and tomotherapy treatment were administered to five patients diagnosed with intra-cranial cancer in which the dose of 18–20 Gy was applied on 3–5 separate occasions. The tumor dosing was decided by evaluating the inhomogeneous index (II) and conformity index (CI). Also, the radiation-sensitive tissue was evaluated using low dose factors V1, V2, V3, V4, V5, and V10, as well as the non-irradiation ratio volume (NIV). The values of the II for each prescription dose in the linac-based non-coplanar radiotherapy plan and tomotherapy treatment plan were (0.125±0.113) and (0.090±0.180), respectively, and the values of the CI were (0.899±0.149) and (0.917±0.114), respectively. The low dose areas, V1, V2, V3, V4, V5, and V10, in radiation-sensitive tissues in the linac-based non-coplanar radiotherapy plan fell into the ranges 0.3%−95.6%, 0.1%−87.6%, 0.1%−78.8%, 38.8%-69.9%, 26.6%-65.2%, and 4.2%−39.7%, respectively, and the tomotherapy treatment plan had ranges of 13.6%−100%, 3.5%−100%, 0.4%−94.9%, 0.2%−82.2%, 0.1%−78.5%, and 0.3%−46.3%, respectively. Regarding the NIV for each organ, it is possible to obtain similar values except for the irradiation area of the brain stem. The percentages of NIV 10%, NIV20%, and NIV30%for the brain stem in each patient were 15%−99.8%, 33.4%−100%, and 39.8%−100%, respectively, in the fractionated stereotactic treatment plan and 44.2%-96.5%, 77.7%-99.8%, and 87.8%−100%, respectively, in the tomotherapy treatment plan. In order to achieve higher-quality treatment of intra-cranial tumors, treatment plans should be tailored according to the isodose target volume, inhomogeneous index, conformity index, position of the tumor upon fractionated stereotactic radiosurgery, and radiation dosage for radiation-sensitive tissues.

The Feasibility of Goggle Monitor for Respiratory Biofeedback of Patient to Reduce Correlation Error Using Real-Time Tumor Tracking System

The aim of this study was to reduce correlation error using goggle monitor during treatment radisurgery using CyberKnife system. We analyzed the correlation error during treatment radiosurgery without goggle monitor and with using goggle monitor. The correlation error for free breathing was form 0.215 mm to 9. Oil mm. However, using goggle monitor is from 0.239 mm to 8.376 mm. We commended to use goggle monitor which can biofeedback her respiratory cycle and shape to reduced correlation error during treatment radiosurgery

A study on the characteristic of normoxic polymer gel dosimeter according to its composition

In this study, to find the optimal composition of the gel as therapeutic radiation, the amounts of methacrylic acid and gelatin were varied. The polymer gel with various compositions were evaluated for its sensitivity, reproducibility, and accuracy. As the concentration of the gelatine is high, the threshold R2 value increases and the dose response was decreases. As the concentration of the methacrylic acid is high, both the threshold R2 value and the dose response were decrease. As both concentrations of the gelatine and the methacrylic acid is high, the sensitivity to the dose was increases within some range. It was found that the polymer gel composed in this study can be optimized for measuring the therapeutic radiation.

Quality assurance of inhomogeneity correction algorithm in the intensity modulated radiotherapy and dynamic conformal arc radiotherapy using multiple heterogeneous head and neck phantoms

To quantify the differences between heterogeneous dose estimates from the calculation algorithm of 3-D treatment planning systems and dosimetry measurements, radiation was delivered in accordance with IMRT and dynamic conformal arc radiotherapy (DCART) QC procedures using multiple heterogeneous head & neck phantoms. The multiple inhomogeneous head and neck phantoms were constructed by various materials such as water equivalent homogeneous (acryl), air equivalent (cavity), bone equivalent (teflon) materials. The absolute and relative dosimetry were done using pinpoint ionization chamber, film and TLD (Harshaw 100). With custom-written software modules, the measured and calculated dose distributions were superimposed and compared. The point dose measured at the interface between water and air material region shows about 7 % mismatch with the treatment planning system in IMRT. This dose difference is even increased at the interface between bone and water material region reaches up to 18 % under-dose comparative to planned value. Our results suggest that the effectiveness of the imhomogeneity corrections used in IMRT and DCART planning should be evaluated in order to ensure meaningful quality assurance and delivery.