Purpose: To develop and evaluate a new four-dimensional image-guided radiotherapy system, which enables precise setup, real-time tumor tracking, and pursuit irradiation.Methods and Materials: The system has an innovative gimbaled X-ray head that enables small-angle (+/- 2.4 degrees) rotations (pan and tilt) along the two orthogonal gimbals. This design provides for both accurate beam positioning at the isocenter by actively compensating for mechanical distortion and quick pursuit of the target. The X-ray head is composed of an ultralight C-band linear accelerator and a multileaf collimator. The gimbaled X-ray head is mounted on a rigid O-ring structure with an on-board imaging subsystem composed of two sets of kilovoltage X-ray tubes and flat panel detectors, which provides a pair of radiographs, cone beam computed tomography images useful for image guided setup, and real-time fluoroscopic monitoring for pursuit irradiation.Results: The root mean square accuracy of the static beam positioning was 0.1 mm for 360 degrees of O-ring rotation. The dynamic beam response and positioning accuracy was +/- 0.6 mm for a 0.75 Hz, 40-mm stroke and +/- 0.4 mm for a 2.0 Hz, 8-mm stroke. The quality of the images was encouraging for using the tomography-based setup. Fluoroscopic images were sufficient for monitoring and tracking lung tumors.Conclusions: Key functions and capabilities of our new system are very promising for precise image-guided setup and for tracking and pursuit irradiation of a moving target. (c) 2006 Elsevier Inc.

A nationwide survey was performed to investigate quality assurance (QA) for photon external radiotherapy. It was carried out by mailing questionnaires to 737 radiotherapy facilities. Six hundred and twenty eight questionnaires were returned, and 603 answers (including 38 answers from 60Co facilities) were available for analysis. At 565 X-ray treatment facilities, only 68 facilities (12%) treated more than 40 patients per day. The 356 facilities (63%) treated less than 20 patients per day. In this survey we examined following itemes: 1) number of radiation oncologists and radiotherapy technologists (RTT) each facility, 2) individuals responsible for QA, 3) ratio of conducting periodic check for basic QA items, and 4) Ratio of verifying monitor unit (MU) calculation. This survey shows that QA is not satisfactory at most of Japanese radiotherapy facilities.

本線量統一グループは,放 射線治療の線量評価 に関わる現状における問題点 として,(1)小 照射野 ビームのための標準データの収集,測 定マニュア ルの作成,(2)小 線源治療用のイリジュームー192の 線源強度の測定法の検討,お よびその トレサー ビ リテイの確立,(3)線 量評価の精度向上,(4)外 部 放射線照射における各種体積,線 量の検討のサブ グループを設け,そ れぞれの活動を行って きた. これら全ての研究は進展段階にあるが,そ の現状 を報告する1). (1)の研究テーマについては,前 物理研究グループ (代表者:平 岡 武)の 継続研究であ り,そ の 研究要約 を定位放射線照射の線量評価として以 下の研究成果に報告する. (2)の研究テーマに関しては,平 成9,10年 度はそ の基礎調査 を主に行い,そ の研究成果 として平 成12年3月 に 「放射線治療における小線源の吸 収線量の標準測定法」 日本医学物理学会編,通 商産業研究社 として発行 した.な お,本 研究 テーマに関 しては平成11,12年 度の研究成果 と して報告する. (3)の研究 テーマについては,放 射線治療計画の QA/QCに ついて検討 し,現 在全国で使用 され ている放射線治療計画装置の現状をアンケー ト 調査 した2)-4).その研究要約を以下の研究成果 に報告する.ま た,外 部照射吸収線量の標準測

Several approximation methods for photon beam dose calculations have been developed by many researchers. Although the currently used methods of radiation dose calculation are practical, it is recognized that these methods are not accurate enough when 3-dimensional anatomic information of shape and atomic content have to be considered. In this paper, we will briefly review the most commonly used dose calculation algomithms and report the results that evaluated the accuracy of does computations using these algorithms. The accuracy is compared with both calculations and measurements on beam central axis for cobalt-60 gamma-rays and 10MV photon beams for various geometries and field sizes. The equivalent TAR method gives good agreement between measured and calculated dose for heterogeneous three layered phantom configurations irradiated by 10MV photon beams. The power law TAR method is also good for cobalt-60 gamma-rays when the extent of the lung-equivalent material heterogeneity is larger than the area of the beamn. The ratio TAR method which doesn't take into account the scattered radiation is inadequate in heterogeneous medium.

A new 3-dimensional (3-D) computation algorithm, "Modified equivalent TMR method", for photon beam dose calculation, considering heterogeneous corrections, has been developed. This algorithm is base on the modified equivalent TAR method that was proposed by Inamura et al. The modified equivalent TAR method was deduced from the equivalent TAR method proposed originally by Sontag and Cunning ham. In addition, reducing the computational time during treatment planning, the concept of quasirandom number suggested by Inamura et al, is adopted for this algorithm. The purpose of this study is to evaluate the accuracy of the dose computations of this new algorithm. The accuracy is compared with both measure and calculated data for Cobalt-60 gamma rays and 10 MV photon beams for various geometries and field sizes on the axis. Weighting factor expressing the relative importance of each volume element in contributing to the scatter dose at the point of calculation, is computed using the three following models that are exponentially approximated as the distance function from the scattering point to the calculation one. 1) "All Scatter model" accounts for the all scattering points. 2) "No Back Scatter model" only takes account of the forward scattered radiation at the calculation point. 3) "Compton Scatter model" takes account for the contributing rate of the scatter dose at the calculating point using the approximation of Klein-Nishina's angular distribution. Using the modified equivalent TMR method, we show that the accuracy of a 3-D dose computation is less than 2% for a homogeneous medium and about 6% for a heterogeneous one. This algorithm is possible for calculating a 3-D dose distribution for short periods of time in actual treatment planning and also for to photon beam applications with more than 6 MV.

A real time CT-linked treatment planning system, called a CT simulator, has been developed. The basic system consists of a CT scanner, a multi-image display component, a treatment planning device with real time visual optimization and a laser beam projecting component. All the components are connected on line and operate simultaneously. The system can be used for 3-D planning and simulation for radiation therapy within a short time. This new CT simulator is a useful 3-D treatment planning system in radiation therapy.

The in vivo effects of buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) biosynthesis, on the cytotoxicity of cyclophosphamide (CYM), cisplatin (CDDP) and bleomycin (BLM), were examined by monitoring the changes of non-protein thiols (NPSH) in normal tissues and in the NFSa fibrosarcoma. We used the lung colony assay as a measure of tumor response and the spleen colony assay as a measure of normal tissue response to CYM. In this study, 5 mmol/kg of BSO was subcutaneously injected four times every 12 hr before administration of the above anti-neoplastic drugs. GSH levels in subcutaneous NFSa tumors decreased to 2% of the control 12 hr after the last administration of BSO, but in the bone marrow, had recovered to 41 %. In the colony assays, BSO increased the anti-cancer effects of the three chemotherapeutic agents, but did not modify the bone marrow suppression by CYM. This finding was a result of the differential response of GSH depletion in the tumor and in the bone marrow. Our study demonstrates that BSO is an effective chemosensitizer of these drugs and may be of therapeutic value when used at an optimal interval.

The effect of single and different split radiation doses with varying rates and time intervals was investigated in an experimental system in vivo using second generation isotransplants of two mouse mammary carcinomas. The changes in the growth delay time (GDT) and tumor control rate (TCR) were analyzed, and explained by a dose dependence of the repair of sublethal radiation damage, reoxygenation and cellular repopulation in the tumors. A direct relationship was found between the size of the first of two dose fractions and the time interval between two exposures at which treatment with split doses is most effective in delaying or preventing tumor growth. Multiple exposures to unequal dose fractions are more effective than to equal fractions with the same total dose.