Chie Kurokawa

The dosimetric impact of respiratory breast movement and daily setup error on tangential whole breast irradiation using conventional wedge, field-in-field and irregular surface compensator techniques

To evaluate the dosimetric impact of respiratory breast motion and daily setup error on whole breast irradiation (WBI) using three irradiation techniques; conventional wedge (CW), field-in-field (FIF) and irregular surface compensator (ISC). WBI was planned for 16 breast cancer patients. The dose indices for evaluated clinical target volume (CTVevl), lung, and body were evaluated. For the anterior-posterior (AP) respiratory motion and setup error of a single fraction, the isocenter was moved according to a sine function, and the dose indices were averaged over one period. Furthermore, the dose indices were weighted according to setup error frequencies that have a normal distribution to model systematic and random setup error for the entire treatment course. In all irradiation techniques, AP movement has a significant impact on dose distribution. CTVevlD95 (the minimum relative dose that covers 95 % volume) and V95 (the relative volume receiving 95 % of the prescribed dose) were observed to significantly decrease from the original ISC plan when simulated for the entire treatment course. In contrast, the D95, V95 and dose homogeneity index did not significantly differ from those of the original plans for FIF and CW. With regard to lung dose, the effect of motion was very similar among all three techniques. The dosimetric impact of AP respiratory breast motion and setup error was largest for the ISC technique, and the second greatest effect was observed with the FIF technique. However, these variations are relatively small.

Comparison of total MU and segment areas in VMAT and step-and-shoot IMRT plans

We compared treatment plans for volumetric intensity-modulated arc therapy (VMAT) and step-and-shoot intensity-modulated radiation therapy (IMRT) in terms of their monitor unit (MU) and segment area at each control point to investigate the difference between the two methods. We investigated three sites: prostate (three cases), head and neck (three cases), and pleura (two cases). We used the total MU and the MU weighted average of segment area (MWSA) in each plan to compare VMAT and IMRT plans. VMAT plans tended to have a larger MWSA and a lower total MU than did IMRT plans in all sites, although there was little difference between dose indices in either irradiation technique. We conclude that VMAT is a better treatment technique due to its higher MU efficiency caused by the larger segment area.

Contribution from 3 α‐Condensed States to the Triple‐Alpha Reaction

The α‐condensed state in nuclear systems has been proposed by Tohsaki et al. and has given rise to interesting discussions. The Hoyle state of 12C has been studied as the most typical example of such an α‐condensed state. A new resonant 03+ state (Er = 1.66 MeV, Γ = 1.48 MeV) is predicted as an excited α‐condensed state in addition to the second 0+ state of the Hoyle state by calculations of the 3 α orthogonality condition model (3 α OCM) using the complex scaling method. Based on this result, the breakup strengths of the inversion reaction for sequential (8Be+α→12C+γ) and direct (α+α+α→12C+γ) processes are calculated. It is discussed that a large reaction strength calculated recently by Ogata et al. in non‐resonant energies is considered as a contribution from the excited 03+ state.

Study of Resonance States in a Coupled-Channel System with the Jost Function Method Applying the Orthogonality Condition Model

To study resonant and virtual states in a wide variety of nuclear systems, we develop the Jost function method (JFM) for treating systems having non-local potentials. In the case that the Pauli principle for nucleons between clusters is treated by applying the orthogonality condition model (OCM) to the JFM, the pseudo-potential of the OCM can be considered one of the non-local potentials. As examples to demonstrate the applicability of our method, we apply it to a 1 6 O+α single-channel system and also a 9 Li+n coupled-channel system. We also treat a 1 6 O+n single-channel system with a knock-on exchange kernel to confirm that our method is applicable in more general cases having non-local potentials.

Measurements for dose distribution with a photo-stimulated luminescence dosimeter sheet

Dose distributions for photon beam were measured using a Photo-Stimulated Luminescence Dosimeter (PSLD) sheet, which has 18 × 24 cm2 dimension and 0.2 mm thickness. Its density and effective atomic number are 1.0 g/cm3 and 7.6, respectively. The read out was performed by blue LED lights for 20 seconds, which was much shorter than the readout time for TLD. The percent depth dose and dose profile were obtained as smooth curve after the calibration and it reproduced the measurements with ionization chamber, except for the tail region in the dose profile. We demonstrated the measurement of the prostate VMAT dose distribution also. The result reproduces the calculation by treatment planning system (TPS) qualitatively. It is shown that the PSLD sheet has the potential to measure the dose distribution.

[Impact of the Infrared Monitor Signal Pattern on Accuracy of Target Imaging in 4-dimensional Cone-beam Computed Tomography].

To realize the high precision radiotherapy, localized radiation field of the moving target is very important, and visualization of a temporal location of the target can help to improve the accuracy of the target localization. However, conditions of the breathing and the patients own motion differ from the situation of the treatment planning. Therefore, positions of the tumor are affected by these changes. In this study, we implemented a method to reconstruct target motions obtained with the 4D CBCT using the sorted projection data according to the phase and displacement of the extracorporeal infrared monitor signal, and evaluated the proposed method with a moving phantom. In this method, motion cycles and positions of the marker were sorted to reconstruct the image, and evaluated the image quality affected by changes in the cycle, phase, and positions of the marker. As a result, we realized the visualization of the moving target using the sorted projection data according to the infrared monitor signal. This method was based on the projection binning, in which the signal of the infrared monitor was surrogate of the tumor motion. Thus, further major efforts are needed to ensure the accuracy of the infrared monitor signal.

Visualization of a target positions using the 4 dimensional cone-beam CT image reconstruction with the extracorporeal infrared monitor

To determine the accurate radiation dose for a specific small volume of tissue, confirmation of the temporal location of a target position is very important. The temporal location of the target can help improve the accuracy of target localization. A kilovoltage cone-beam computed tomography (CBCT) system mounted on a linear accelerator can verify the target on each treatment day, but this system requires a long data acquisition time; therefore, reconstructed images are affected by motion. In this study, we implemented a method to reconstruct target motions obtained by a four-dimensional CBCT using sorted projection data according to the phase and displacement of the extracorporeal infrared monitor signal. We evaluated the effect of reconstruction methods on image quality using a moving phantom and respiratory signals of an actual patient. We modified the relationship between the motion cycle and positions of the marker and projection data and evaluated the effect on image quality. Moreover, the effect of target motions in patients on the quality of reconstructed images was investigated. The results of the experiments showed that phase binning and displacement binning reduced the blurring of the reconstructed image. The quality of the reconstructed images was significantly affected by the amplitude as well as the inhalation and exhalation slopes of the marker signal. The missing number of projections in the displacement binning method was caused by non-linearity of breathing pattern. This method was based on projection binning, in which the signal of the infrared monitor served as the surrogate of tumor motion. Therefore, further major efforts are needed to ensure the accuracy of the infrared monitor signal.

SU-E-T-465: Dose Calculation Method for Dynamic Tumor Tracking Using a Gimbal-Mounted Linac

PURPOSE Dynamic tumor tracking using the gimbal-mounted linac (Vero4DRT, Mitsubishi Heavy Industries, Ltd., Japan) has been available when respiratory motion is significant. The irradiation accuracy of the dynamic tumor tracking has been reported to be excellent. In addition to the irradiation accuracy, a fast and accurate dose calculation algorithm is needed to validate the dose distribution in the presence of respiratory motion because the multiple phases of it have to be considered. A modification of dose calculation algorithm is necessary for the gimbal-mounted linac due to the degrees of freedom of gimbal swing. The dose calculation algorithm for the gimbal motion was implemented using the linear transformation between coordinate systems. METHODS The linear transformation matrices between the coordinate systems with and without gimbal swings were constructed using the combination of translation and rotation matrices. The coordinate system where the radiation source is at the origin and the beam axis along the z axis was adopted. The transformation can be divided into the translation from the radiation source to the gimbal rotation center, the two rotations around the center relating to the gimbal swings, and the translation from the gimbal center to the radiation source. After operating the transformation matrix to the phantom or patient image, the dose calculation can be performed as the no gimbal swing. The algorithm was implemented in the treatment planning system, PlanUNC (University of North Carolina, NC). The convolution/superposition algorithm was used. The dose calculations with and without gimbal swings were performed for the 3 × 3 cm2 field with the grid size of 5 mm. RESULTS The calculation time was about 3 minutes per beam. No significant additional time due to the gimbal swing was observed. CONCLUSIONS The dose calculation algorithm for the finite gimbal swing was implemented. The calculation time was moderate.

SU‐E‐T‐23: Evaluation of Inherent Dose‐Uncertainty for VMAT Using a Dose‐Uncertainty Model

Purpose: To investigate the dose‐uncertainty, which can occur during treatment planning and dose delivery in volumetric modulated arc therapy (VMAT), by generalizing the dose‐uncertainty model. Methods: QA plans for prostate cancer patient treated with VMAT were created for a water phantom (40×40×20 cm3) using Pinnacle3 radiation treatment planning (RTP) system (Philips Radiation Oncology Systems, WI). The plans were exported as DICOM RT dose files from RTP, and the files were processed using an in‐house program to obtain the dose‐uncertainty map. Inherent uncertainty of dose calculation (IU) was evaluated in this study. The IU considered was originated from the error of dose in a high‐dose gradient region caused by finite size of the calculation grid and the finite size of the detector system during RTP commissioning. The IU was calculated for each control point and was summed up to obtain total IU for each VMAT plan. Results: Dose‐uncertainty distribution on the isocenter plane in the axial slice was investigated. Comparing with a dose‐uncertainty distribution of a prostate IMRT plan, which was evaluated by other group, dose‐uncertainty distribution of VMAT plan spread out around the target, because beams entered from all directions over 360 degrees. The maximum IU, which was around 10 % of the prescribed dose, appeared the boundary between the target and the OARs (bladder and rectum). Conclusion: In this study, dose distribution with the inherent dose‐uncertainty was evaluated using the dose‐uncertainty model generalized for VMAT, and applied to VMAT plans for prostate cancer patients. IU of VMAT spread out around the target if compared with that of IMRT plan. The maximum dose‐uncertainty was found in the boundary between the target and OARs and was about 10 % of prescribed dose. This work was supported by JSPS KAKENHI Grant Number 23791449

SU‐E‐T‐119: Characteristics of TLD and PSLD Films for Photon and Electron Dose Measurements

PURPOSE To evaluate the feature of our tissue-equivalent Thermoluminescense and Photoluminescense films for dose distribution measurements of photon and electron, and proton beams. METHODS Thermal and light fading, repeatability, and dose linearity (dose proportionality) were evaluated for our tissue-equivalent Thermoluminescense (TLD) and Photo-Stimulated luminescense (PSLD) films, which has 18 × 40 cm2 dimension and 0.09 mm thickness. These effects were examined at room temperature and under fluorescent light after irradiation by 6 MV photon. Three-dimensional dose distributions for photon, electron, and proton beams were also measured. Before the measurements of dose distributions, the irradiation was done to calibrate the response of each film. The readout was performed by 180 oC for TLD and blue LED lights for PSLD films, and generated light was detected with a CCD camera which has 1024 × 1024 pixels (FLIML 1001E-2, Finger Lakes Instrument). RESULTS After the irradiation, the fading of signals was 1-5% in one hour. It was observed that the variation for 10 sequent dose measurements at 200 cGy using 6 MV photons was less than 5%. Dose profiles for photon and electrons were obtained as smooth curve after the calibration. For photon measurements, PDDs with the TLD films well reproduced the results with ionization chamber, except for the surface region. The measured dose with TLD at surface is around 15%, which is lower more than 30% comparing to the dose with ionization chamber. Although obtained electron PDDs with TLD showed good agreement with that of ionization chamber, PDDs with PSLD showed slightly deviations from the chamber due to the contamination of high Z material. CONCLUSION The characteristics of TLD and PSLD films were evaluated in order to make precise measurements. It is shown that they have the potential to measure the 3D dose distribution including low dose at surface. This work was supported by JSPS KAKENHI Grant Number 23791450.