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Purpose: In our proton beam therapy center, we use imaging plates (IP) for dose verification of field matching in irradiation (called patch-field technique). In this study, a polymer gel dosimeter, which can perform three- dimensional dose distribution measurement, was used as a new tool for the verification of the patch field irradiation method corresponding to the rectangular irradiation., Method: The results of measurements of the PAGAT gel dosimeter to irradiate to two rectangular fields called as patch irradiation fields, which were created using the treatment planning system, were evaluated and compared to the results of IP and plan in profiles near the boundary of two fields., Result: In the case of no gap between the two fields, the relative dose using the gel dosimeter was 10.1% higher compared to that measured with the IP in the midpoint of two fields. In case of overlap (called hot region), the result of gels was 6.3% higher than that of IP. In the case of space (called cold region), the result of gels was 14.9% higher than that of IP. The results of the difference between gel and plan in the midpoint of two fields were 14.2% (no gap), -5.0% (hot), and 10.5% (cold)., Conclusion: We found that the gel dosimeter was a 3-D dosimetric tool and possibility method for dose verification of patch fields. In this study, the results were preliminary and included several error factors. In the future, it is necessary to develop a dosimeter with improved and more precise measurements.

Treatment planning systems with highly accurate dose calculation algorithms such as Monte-Carlo method and linear Boltzmann transport equation are becoming popular thanks to a development of the computer technology. These algorithms use new concepts, dose-to-medium and dose-to-water. However, introducing these concepts can cause confusion in clinical sites. Basic knowledges about Monte-Carlo simulation and other corresponding algorithms were explained in this article such as the principles, the parameters and words of caution.

1 H-MRS (proton magnetic resonance spectroscopy) is a method for analyzing material components using the difference of the frequency (chemical shift) in magnetic resonance. 1 H-MRS for human body is able to diagnose the clinical conditions by non-invasive analysis of materials in organs. However, the mechanical limitations and complexity in analyses prevented it from becoming popular as MRI (magnetic resonance imaging). Recently, an ideal environment for 1 H-MRS is commonly available such as stronger magnetic field and improved software, yet we still lack common knowledges about 1 H-MRS which makes whom plans to start it difficult. In this article, the principle, tips, clinical applications and spectrum evaluations were explained focusing on novice users.

Conversion from CT value to density is essential to a radiation treatment planning system. Generally CT value is converted to the electron density in photon therapy. In the energy range of therapeutic photon, interactions between photons and materials are dominated with Compton scattering which the cross-section depends on the electron density. The dose distribution is obtained by calculating TERMA and kernel using electron density where TERMA is the energy transferred from primary photons and kernel is a volume considering spread electrons. Recently, a new method was introduced which uses the physical density. This method is expected to be faster and more accurate than that using the electron density. As for particle therapy, dose can be calculated with CT-to-stopping power conversion since the stopping power depends on the electron density. CT-to-stopping power conversion table is also called as CT-to-water-equivalent range and is an essential concept for the particle therapy.

Although measurement and management of angiographic entrance skin dose (ESD) are deemed extremely important, accurate determination of maximum ESD and its location is generally difficult because of the dependence on therapeutic technique and position. Following our development of body-mounted gear bearing radiophotoluminescence glass dosimeter (RPLD) arrays for direct measurement of ESD in cranial and cardiovascular angiography and interventional radiology (IVR), our focus next turned to the limited number of facilities equipped to read RPLD outputs and the need for methods to effectively provide feedback to clinical facilities. As described here, we first constructed an RPLD reading facility capable of sending and receiving RPLDs by post, offering the potential to enable utilization of the developed gear at all hospitals in Japan that perform angiography and IVR. We next developed specialized web-based system to generate dose maps from RPLD dose data, thereby enabling any facility to perform trial system analysis, evaluation, and implementation; and investigated the results and related problems.

Polymer gels can be used as tissue equivalent dosimeters, and polymer gel dosimetry can be employed without perturbation of the radiation field. In this study, polymer gel dosimetry was used for small circular irradiation fields 10-30 mm in diameter using a radiation planning system. The irradiated gels were compared with planned data for a 50% dose width of 6 Gy dose maximum, and for the dose difference between gels and planned data over an 80% dose maximum area. The present study investigated magnetic resonance imaging (MRI) conditions based on an optimal dose-R2 calibration curve. The average difference between the full width half maximum of the 50% dose width between gels and planned data was 11%. The average dose difference over 80% of the dose was 5.6%. Optimal dose-R2 calibration curves were acquired using images with echo times of 30 and 60 ms. For cases of larger thicknesses and an increasing number of averages, the coefficients of variance of the curves were smaller than under other conditions. Compared to other traditional dosimetric tools, polymer gels have the advantage of providing three-dimensional dosimetric data. An arbitrary profile from the gel's data can be compared with the profile of the planned data. In the future, new gel dosimeters will be needed that demonstrate improved dose evaluation under 1 Gy and stability in high dose areas.

In this study, we developed an isocenter verification device for use in proton therapy. Radiation and mechanical isocenters were verified for treatment equipment including room lasers, a digital radiography system and the beam axis of a rotational gantry. The special feature of this device is its ability to correlate the position of the three isocenters in one measurement and thus improve accuracy compared to the conventional method using three separate devices. The reproducibility of the method and the fluctuation of the position of the beam axis isocenter were both investigated using this device for almost a year. Monthly measurements of the isocenter position were acquired for two gantries and it was found that the fluctuation was +/- 0.10mm for the up-to-down direction and +/- 0.16mm for the right-to-left direction in Gantry 1 and was +/-0.14mm for the up-to-down direction and +/-0.18mm for the right-to-left direction in Gantry 2. We could be measured with a repeatability of +/-0.18 mm or less by using developed device for the relative positional relationship between each isocenters. Because we can confirm results in approximately 30 minutes, we can perform a quality control after a clinical practice.

In a linear accelerator (linac) that operates at greater than an accelerating energy of 10 MV, neutrons are generated by a photonuclear reaction and the head section of the linac becomes radioactive. The purpose of this research is to obtain data for ensuring the safety of linac decommissioning and upgrading. The decommissioned linac investigated in this study was a Clinac 2100 C/D (Varian) installed in April 1999. Its total time of use was 2757.7 h (equivalent to 496,386 Gy). The dosage for its last three months of use was 7213.67 Gy. After being allowed to sit for a 7-day cooling period, the apparatus was disassembled and the parts of the gantry head portion were removed. The ambient dose equivalent rates, H*(10), (microSv/h) from the removed parts were measured in air, at a location with low background, by using a gamma ray scintillation survey meter. The target was also analyzed with an HP-Ge semiconductor detector, in order to identify the nuclides responsible for the observed radiation. On day 7 after the last use of the linac, the ambient dose equivalent rates, H*(10), (microSv/h) in air at the surface of all parts, except the target and the beryllium window, were within the limit of normal background radiation. The measured value (microSv/h) for the beryllium window decreased to within the background limit on day 10. The measured value (microSv/h) of the target decreased to about 1.5 times the background on day 19. At a distance of 10 cm, all the parts were within the background limit after the initial 7-day cooling period. In the analysis of the target with the HP-Ge semiconductor detector, peaks at 125, 333, 352, 356, 426, 511, 583, 609, 689, 811, 835, 911, 969, 1091, 1099, 1120, 1173, 1238, 1292, 1333, 1461 and 1764keV were detected on day 23. Seven months after the linac was last used, peaks were detected at 352, 511, 583, 609, 835, 911, 969, 1120, 1173, 1238, 1333, 1461 and 1764 keV. From these results, the natural radioactive nuclides can be assigned as 40K, 208Tl, 214Pb, 214Bi and 228Ac; the short half-life nuclides can be assigned as 59Fe, 58Co, 185W and 196Au; and the long half-life nuclides can be assigned as 54Mn and 60Co. These results show that photonuclear activation of parts is important in regard to clearance. Currently, there are no regulations that specify criteria for evaluating radioactivation. Such criteria are needed to establish suitable protocols for the clearance of radioactivated materials.

In Proton Medical Research Center (PMRC), we have performed the respiration-gated irradiation for treating the tumor in the body trunk. In the conventional method, patients must hold their expiration during CT scanning. The phase of holding expiration is different from the end-expiration phase. This results in difference of anatomical location in the body between CT scanning and the respiration-gated irradiation. For the sake of highly-accurate irradiation, a respiration gated CT scanning system is introduced. In case of natural respiration, it has been difficult to achieve the gated CT scanning because a stable period of end-expiratory is not so long as CT scanning time (1 second in our case). In this study, we developed a guided respiration method, which leads a patient to maintain the end-expiratory phase during required time. The respiration gated CT scanning is performed by using this. The phase of the acquired CT image can be approximated to that of respiration-gated irradiation.