This is a report of the symposium entitled “How do we overcome recent radiotherapy accidents?” which was held at the 17th JASTRO Annual Scientific Meeting, Chiba, November, 2004. Eleven accidents of radiotherapy institutions were publicly reported from 2001 through 2004, and 8 of these directly affected patients. At the same time as the first accident happened in 2001, the Intersociety Council of Medical Physics was established and began its action, to search for the cause and to protect against similar accidents at other institutions. Of these, 7 out of 8 accidents were related to updated radiotherapy treatment planning (RTP) system, 4 were due to errors at the acceptance and commissioning of the new RTP system, and one was due to misunderstanding of rules about the delivery dose and not enough mutual communication between a physician and a technologist. The recent activities to maintain and to improve the quality assurance/quality control of radiotherapy are also described

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The laboratory mouse is hailed as holding the experimental key to the human genome. Working on mouse models allows the manipulation of each and every gene to determine their functions, and this will give us detailed insights into many aspects of human disease as well as basic human biology. We have reviewed mouse models for the researches of genetic factors related to radiation-induced normal tissue reaction to learn the possible predictive markers or the mechanism of severe side effects on humans after radiotherapy. Several investigators have reported the important molecules, such as TGF-beta, MnSOD, and CD44, related to radiosensitivity through experiments using several murine stains. The murine model is useful for correlating genetic factor analysis and radiosensitivity, and offers a potential experimental pathway for understanding inter-individual differences in radiosensitivity.

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Purpose: To assess treatment results of radiation therapy for Stage I esophageal cancer.
Materials and Methods: Ninety-one patients with Stage I esophageal cancer received definitive radiation therapy without chemotherapy between 1991 and 2000. There were 28 patients with the depth of m1-2, 30 with m3-sm1, 30 with sm2-3 and 3 unknown. Endoscopic mucosal resection (EMR) was performed in 59 patients before radiotherapy. Twenty-seven patients were treated with high-dose-rate brachytherapy (HDRBT) alone, 56 with combined external radiation therapy (ERT) and HDRBT and 8 with ERT alone.
Results: The 5y-overall survival rate and the cause-specific survival rate were 61% and 83%, respectively. The 5y-overall survival rates for the patients with the depth of m1-2, m3-sm1 and sm2-3 were 81%, 67% and 35%. The cause-specific survival rates were 100%, 81% and 63%. Twenty-nine patients (32%) experienced a recurrence (esophagus; 22, regional LN; 4, both esophagus and LN; 2 and unknown; 1). The failure rates were 29% of m1-2, 23% of m3-sm1 and 47% of sm2-3. Ten of 24 esophageal recurrences were metachronous multiple cancers. Fourteen patients were salvaged and most of salvaged recurrences were detected in the early stage.
Conclusions: For the setting of the radiation field, metachronous multiple esophageal cancer should be considered. Chemoradiotherapy should be investigated for submucosal cancer. Longer and careful follow-up is important to find recurrences in the early stage.

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The Japan Society of Medical Physics Task Group published a new high-energy photon and electron dosimetry protocol in 2002. This protocol is based on the use of an ion chamber having a ⁶⁰Co absorbed-dose to water calibration coefficient, N^60Co_D,W, which is calculated from a ⁶⁰Co exposure calibration coefficient, N_c. This is different from the American Association of Physicists in Medicine Task Group 51 protocol and the International Atomic Energy Agency Technical Report Series No. 398 protocol, which are based on N^60Co_D,W that are calibrated by a sealed water or graphite calorimeter. The purpose of this study is to present the comparison in N_c and N^60Co_D,W between the Kyushu Regional Center (Kyushu) that is the third-order standard in Japan and the National Research Council Canada (NRCC) that is the primary standard in Canada. The N^60Co_D,Wvalues at Kyushu are calculated from N_c while the values at NRCC are calibrated by a sealed water calorimeter. The ratios between the Kyushu and NRCC calibration coefficients were 0.9965±0.0023 and 0.9991±0.0013 in the case of N_c and N^60Co_D,W, respectively. These differences are within the uncertainty in both standards.

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Purpose: To report on the design and implementation of a database system that provides access to radiotherapy (RT) data for the purpose of data analysis in a clinical trial of carbon ion radiotherapy at National Institute of Radiological Sciences.
Methods and Materials: The data stored in this system are patient treatment planning and record data including non-volumetric data of character and numerical type (1), and 2D or 3D volumetric data sets of CT images, target and organ contours, apertures and range compensators, dose distributions and simulation radiographs (2). Two subsystems were prepared for the respective data types. One is a therapy information database that stores non-volumetric data (1), which can be accessed with client applications working on personal computers (PCs). Another is a DICOM RT archive that stores volumetric data sets (2) as DICOM RT data objects. The archive allows on-line data access with a developed application, RT viewer that works on PCs. Queried data sets can be displayed and downloaded as DICOM files or AAPM/RTOG Data Exchange format files. All the data sets are loaded into the system on-line daily at a specified time.
Results: The system has operated for over two years and during this period we repaired and improved the applications. Presently it operates stably and it has been loaded with the data sets of more than 2000 patients treated since 1994. User applications are described with some examples.
Conclusion: The system enables users to analyze the therapy data for evaluation of treatment results. It provides volumetric data in portable format for further image-based analyses.

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Purpose: Radiotherapy is an important therapeutic tool for malignant tumors in the head and neck and thoracic region. However, radiotherapy has also been known to cause acute mucositis and esophagitis during the early phase of treatment, for which there is no cure to date. A mixture of mucosal protective steroids has been shown to be beneficial in patients with these symptoms receiving radiotherapy alone. The purpose of this study was to examine the efficacy of this agent to treat the mucositis that accompanies chemoradiotherapy. Moreover, the differences between the curative effects were examined retrospectively, according to the region irradiated.
Materials and Methods: Radiotherapy was administered to the head and neck, and thoracic region, and the steroid mixture was prescribed for patients in the radiotherapy alone and chemoradiotherapy groups that exhibited acute radiation-induced mucositis symptoms. We then evaluated daily food consumption, total serum-protein value, serum-albumin value and body weight of the radiation-induced mucositis patients that were treated with the mixture. Moreover, we also examined the efficacy in patients undergoing irradiation of the oral cavity, and of the esophagus (which did not entail irradiation of the oral cavity).
Results: 214 patients treated with the steroid mixture in this study had no treatment-related adverse events. In comparison between the radiotherapy alone and chemoradiotherapy groups, no significant differences were observed for daily food consumption. However, differences were observed for daily food consumption between the groups undergoing irradiation of the oral cavity and irradiation of the esophagus (p=0.0008). In the group experiencing irradiation of the mouth, decreased ability to swallow and digest food associated with the primary disease was also observed. Total serum-protein values, serum-albumin values and body weight exhibited a slight decrease despite the onset of radiation-induced mucositis, compared with the values before radiotherapy. The radiation-induced mucositis did not lead to the cessation of radiotherapy in any patient.
Conclusion: The mixture of mucosal protective drugs was considered to be a safe and efficacious drug for more severe mucositis in the chemoradiotherapy group, which was comparable to that seen in the radiotherapy-alone group.

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Background and Purpose: To create better dose distributions we devised a novel optimization algorithm named the Attraction-Repulsion Model (ARM) which is based on Gauss's law.
Methods: When we used ARM for optimization of dose distribution, all optimization grid points have some attribution and generate attraction or repulsion depending on the dose or dose rate. For each optimization grid point, attraction is defined as the force generated to increase the dose or dose rate; repulsion is defined as the force to decrease the dose or dose rate. We assumed the high dose rate brachytherapy, in which we can change the dwell time. Twenty-five dwell positions were set at each 2.5 mm interval in a straight catheter. (1) 25 dose points were points at 1 cm distance from the catheter; (2) 25 dose points were on an oblique line in which the nearest position was located at 0.8 cm from the catheter and the farthest at 1.2 cm. Optimization was done by ARM, Geometric Optimization (GO) and Dose Point Optimization (DP) to make the dose points to be the same dose.
Results: Using ARM for optimization, at the first condition, the maximum dose was 1.015, the minimum was 0.988 and the standard deviation was 0.006; at the second condition, the maximum dose was 1.017, the minimum was 0.977 and the standard deviation was 0.007. Optimized by DP allowing for negative dwell time, all of points were 1.000. But DP not allowing for the negative dwell time, the solutions became worse. When they are optimized by GO, 25 dwell times were the same at two conditions, because the positions of the dose points do not give influence for the dwell time in GO. The feedback functions used in ARM are compatible with cost functions of Simulated Annealing (SA).
Conclusions: We devised the Attraction-Repulsion Model for the optimization of dose distribution in radiotherapy. We obtained good solutions in 2 dimensional simple models by using the ARM.

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