M. Lee

Involvement of CCAAT/enhancer-binding protein α in haptoglobin gene expression by all-trans-retinoic acid

Several acute-phase plasma proteins, including haptoglobin (Hp), are induced in the liver in response to inflammation. Recently, we found that Hp gene expression is up-regulated by all-trans-retinoic acid (ATRA) in the extrahepatic monocytic cell line, THP-1. To investigate the molecular mechanism underlying ATRA-induced Hp gene expression, we analyzed the induction of transcription factor CCAAT/enhancer-binding protein (C/EBP) isoforms in ATRA-stimulated THP-1 cells and their binding to the Hp promoter. Western blot analysis showed that treatment with ATRA increased C/EBPalpha and beta expression, but decreased that of C/EBPdelta. Electrophoretic mobility shift and supershift assays demonstrated that only C/EBPalpha of the C/EBP isoforms bound to the C/EBP DNA-binding sites in the Hp promoter. Furthermore, when ATRA-dependent Hp induction was inhibited by sodium butyrate or auranofin, induction of C/EBPalpha, but not C/EBPbeta, was also diminished. These results suggest that C/EBPalpha is involved in the activation of Hp gene expression by ATRA in human monocytic cells.

SU-F-T-314: Estimation of Dose Distributions with Different Types of Breast Implants in Various Radiation Treatment Techniques for Breast Cancer

PURPOSE This study investigates the effects of different kinds and designs of commercialized breast implants on the dose distributions in breast cancer radiotherapy under a variety of conditions. METHODS The dose for the clinical conventional tangential irradiation, Intensity Modulated Radiation Therapy (IMRT), volumetric modulated arc therapy (VMAT) breast plans was measured using radiochromic films and stimulated luminescence dosimeter (OSLD). The radiochromic film was used as an integrating dosimeter, while the OSLDs were used for real-time dosimetry to isolate the contribution of dose from individual segment. The films were placed at various slices in the Rando phantom and between the body and breast surface OSLDs were used to measure skin dose at 18 positions spaced on the two (right/left) breast. The implant breast was placed on the left side and the phantom breast was remained on the right side. Each treatment technique was performed on different size of the breasts and different shape of the breast implant. The PTV dose was prescribed 50.4 Gy and V47.88≥95%. RESULTS In different shapes of the breast implant, because of the shadow formed extensive around the breast implant, dose variation was relatively higher that of prescribed dose. As the PTV was delineated on the whole breast, maximum 5% dose error and average 3% difference was observed averagely. VMAT techniques largely decrease the contiguous hot spot in the skin by an average of 25% compared with IMRT. The both IMRT and VMAT techniques resulted in lower doses to normal critical structures than tangential plans for nearly all dose analyzation. CONCLUSION Compared to the other technique, IMRT reduced radiation dose exposure to normal tissues and maintained reasonable target homogeneity and for the same target coverage, VMAT can reduce the skin dose in all the regions of the body.

SU-E-T-280: Reconstructed Rectal Wall Dose Map-Based Verification of Rectal Dose Sparing Effect According to Rectum Definition Methods and Dose Perturbation by Air Cavity in Endo-Rectal Balloon

PURPOSE Dosimetric effect and discrepancy according to the rectum definition methods and dose perturbation by air cavity in an endo-rectal balloon (ERB) were verified using rectal-wall (Rwall) dose maps considering systematic errors in dose optimization and calculation accuracy in intensity-modulated radiation treatment (IMRT) for prostate cancer patients. METHODS When the inflated ERB having average diameter of 4.5 cm and air volume of 100 cc is used for patient, Rwall doses were predicted by pencil-beam convolution (PBC), anisotropic analytic algorithm (AAA), and AcurosXB (AXB) with material assignment function. The errors of dose optimization and calculation by separating air cavity from the whole rectum (Rwhole) were verified with measured rectal doses. The Rwall doses affected by the dose perturbation of air cavity were evaluated using a featured rectal phantom allowing insert of rolled-up gafchromic films and glass rod detectors placed along the rectum perimeter. Inner and outer Rwall doses were verified with reconstructed predicted rectal wall dose maps. Dose errors and extent at dose levels were evaluated with estimated rectal toxicity. RESULTS While AXB showed insignificant difference of target dose coverage, Rwall doses underestimated by up to 20% in dose optimization for the Rwhole than Rwall at all dose range except for the maximum dose. As dose optimization for Rwall was applied, the Rwall doses presented dose error less than 3% between dose calculation algorithm except for overestimation of maximum rectal dose up to 5% in PBC. Dose optimization for Rwhole caused dose difference of Rwall especially at intermediate doses. CONCLUSION Dose optimization for Rwall could be suggested for more accurate prediction of rectal wall dose prediction and dose perturbation effect by air cavity in IMRT for prostate cancer. This research was supported by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) (Grant No. 200900420).

TU‐E‐141‐06: Estimation of Dose Distributions with the Dental Artifact Correction in Radiation Treatment Plans for Head‐And‐Neck Cancers

PURPOSE Metal artifacts generated by dental implants cause dose discrepancy in intensity-modulated radiation therapy (IMRT) of head-and-neck cancer cases due to the inaccurate predicted doses. To determine the effective metal artifact reduction (MAR) method presenting minimum dose errors with delivered dose, dosimetric impact of different MAR methods were evaluated in radiation treatment plans. METHODS MAR was implemented using Euler elastic and curvature based sinogram inpainting (EECSI) algorithm, volume clustering with Hounsfield unit (HU) overriding (VCU), and multimodal image-based correction (MIC). When delivered doses were calculated on the corrected computed tomography (CT) images by employing the same plan parameters in the reference IMRT plan (Planref), dose errors were analyzed with dose-volume histograms (DVHs), monitor unit, and dose conformity of target volumes. Dosimetric impacts were also estimated using the biophysical evaluation parameters in three oropharyngeal patients. RESULTS Optimized fluence in the Planref resulted in overdose up to 5% in the salivary glands and spinal cords on the corrected CT images, while the overdose in target volumes increased tumor control probability of 3-7%. Target doses in peripheral regions affected by the surrounded dark pixels were deformed and decreased conformity. The DVHs of organs at risk (OAR) and target volumes also showed the 5-8% volume gap in the prescription dose range. As the efficient MAR is employed into the head-and-neck IMRT plans, more accurate predicted doses of primary structures would be achieved, even if the dose differences of each MAR method are small less than 2-3%. CONCLUSION EEECSI and VCU were useful methods to reduce the metal artifacts and to predict more accurate delivered doses. Since dental artifacts cause dose variation in peripheral region of target volumes and OAR, dose calculation on corrected CT images using efficient MAR techniques and dose verification would be encouraged in head-and-neck IMRT plans.