Yasuhiro Osaka

High linear energy transfer carbon radiation effectively kills cultured glioma cells with either mutant or wild-type p53

PURPOSE A mutation in the p53 gene is believed to play an important role in the radioresistance of many cancer cell lines. We studied cytotoxic effects of high linear energy transfer (LET) carbon beams on glioma cell lines with either mutant or wild-type p53. METHODS AND MATERIALS Cell lines U-87 and U-138 expressing wild-type p53 and U-251 and U-373 expressing mutant p53 were used. These cells were irradiated with 290 MeV/u carbon beams generated by the Heavy Ion Medical Accelerator in the National Institute of Radiologic Science or X-rays. A standard colony-forming assay and flow cytometric detection of apoptosis were performed. Cell cycle progression and the expression of p53, p21, and bax proteins were examined. RESULTS High LET carbon radiation was more cytotoxic than low LET X-ray treatment against glioma cells. The effects of the carbon beams were not dependent on the p53 gene status but were reduced by G(1) arrest, which was independent of p21 expression. The expression of bax remained unchanged in all four cell lines. CONCLUSION These results indicate that high LET charged particle radiation can induce cell death in glioma cells more effectively than X-rays and that cell death other than p53-dependent apoptosis may participate in the cytotoxicity of heavy charged particles. Thus, it might prove to be an effective alternative radiotherapy for patients with gliomas harboring mutated p53 gene.

Use of Implanted Markers and Interportal Adjustment With Real-Time Tracking Radiotherapy System to Reduce Intrafraction Prostate Motion

PURPOSE Interportal adjustment was applied to patients with prostate cancer using three fiducial markers and two sets of fluoroscopy in a real-time tumor-tracking radiotherapy (RTRT) system. The incidence of table position adjustment required to keep intrafractional uncertainty within 2.0 mm was investigated in this study. METHODS AND MATERIALS The coordinates of the center of gravity of the three fiducial markers were measured at the start of every portal irradiation in intensity-modulated radiotherapy (IMRT) with seven ports. The table position was adjusted to the planned position if the discrepancy was larger than 2.0 mm in the anterior-posterior (AP), cranial-caudal (CC), or left-right (LR) directions. In total, we analyzed 4,541 observations in 20 patients who received 70 Gy in 30 fractions (7.6 times a day on average). RESULTS The incidence of table position adjustment at 10 minutes from the initial setup of each treatment was 14.2%, 12.3%, and 5.0% of the observations in the AP, CC, and LR directions, respectively. The accumulated incidence of the table position adjustment was significantly higher at 10 minutes than at 2 minutes for AP (p = 0.0033) and CC (p = 0.0110) but not LR (p = 0.4296). An adjustment greater than 5 mm was required at least once in the treatment period in 11 (55%) patients. CONCLUSIONS Interportal adjustment of table position was required in more than 10% of portal irradiations during the 10-minute period after initial setup to maintain treatment accuracy within 2.0 mm.

SU‐FF‐J‐121: Retrospective Analysis of Prostate Cancer Patients with Fiducial Gold Markers Using a Real‐Time Tumor Tracking System

Purpose: The aim of this study was to measure interfraction and intrafraction motion of the prostate during the course of radiation treatment using a real‐time tumortracking system (RTRT‐system) and gold fiducial markers. Method and Materials: Fifty‐five patients underwent implantation with three 2‐mm gold markers in the prostate before IMRTtreatment planningCT scans. Using a RTRT‐system, fluoroscopic images were taken after a) skin‐based patients positioning and b) translational repositioning by moving a couch after a calculation of actual and planned positions of three gold markers. Intrafraction as well as interfraction translation and rotations were analyzed along the three axes (right‐left[RL], cranio‐caudal[CC], antero‐posterior[AP]). Systematic and random errors were computed for these translations and rotations in (a)conventional setup and (b)RTRT setup. To determine adequate margins for these setup, van Herkss formula of (2.5Σ+0.7σ) were used. Results: Without consideration of interfraction errors, prostate treatment would have required average margin of 9.8, 14.3 and 12.5mm (n=1466) about the right‐left(RL), craniao‐caudal(CC), and antero‐posterior(AP) directions, respectively for skin‐based patients positioning. Interfractional random rotation error was 5.9°(systematic error, 8.6°) around RL axis, 3.1°(systematic error, 5.5°) around CC axis, and 5.1°(systematic error, 5.4°) around AP axis. Inclusion of intrafraction movement increases these margins to 11.0, 15.3, and 13.1mm, respectively (n=2905). Intrafractional and inter‐beam adjustment further reduced margins to an average of 2.1, 2.5 and 2.3mm, respectively, based on a threshold of 3mm for each direction. Conclusion: Monitoring and correction of the intrafraction movement for prostate treatment using this system, significant reduction of margins would have achieved. However, the interfraction as well as intrafraction rotations of the prostate should be taken into account for the additional margins because their magnitudes are not negligible. Conflict of Interest: The authors indicated no potential conflicts of interest.