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Current dosimetry protocols specify an effective point of measurement (EPOM) shift of 0.6r for a cylindrical ionization chamber in photon beams. However, prior studies have reported that this shift was excessively large. The objective of this study was to experimentally evaluate the EPOM shifts in photon beams for cylindrical ionization chambers, which are widely used in clinical practice, and thus determine the appropriate EPOM shift. A microdiamond detector, which is a semiconductor detector with a small sensitive volume, was used as a reference detector, and the EPOM shifts of 11 types of cylindrical ionization chambers were evaluated at 6 MV and 10 MV. The depth shift from the percent depth dose (PDD) of the reference detector to that of the evaluated chamber was calculated using the least-squares method and was defined as the EPOM shift. The EPOM shift of the 10 MV condition was slightly larger than that of the 6 MV condition. However, because this trend was not observed for all chambers, the results of the two energies were averaged, and the EPOM shifts were determined to be 0.33r-0.43r (± 0.05) for 10 types of ionization chambers, and 0.03r (± 0.03) for the A1SL chamber. The shifts for all ionization chambers were smaller than 0.6r, indicating that the recommended EPOM shifts were overestimated and the absorbed dose was underestimated at the calibration depth. Hence, the appropriate EPOM shift of the 10 types of ionization chambers was 0.4r (the geometric center of the A1SL chamber), with a dose uncertainty of 0.05%.

Purpose: We developed an x-ray-opaque-marker (XOM) system with inserted fiducial markers for patient-specific quality assurance (QA) in CyberKnife (Accuray) and a general-purpose linear accelerator (linac). The XOM system can be easily inserted or removed from the existing patient-specific QA phantom. Our study aimed to assess the utility of the XOM system by evaluating the recognition accuracy of the phantom position error and estimating the dose perturbation around a marker. Methods: The recognition accuracy of the phantom position error was evaluated by comparing the known error values of the phantom position with the values measured by matching the images with target locating system (TLS; Accuray) and on-board imager (OBI; Varian). The dose perturbation was evaluated for 6 and 10 MV single-photon beams through experimental measurements and Monte Carlo simulations. Results: The root mean squares (RMSs) of the residual position errors for the recognition accuracy evaluation in translations were 0.07 mm with TLS and 0.30 mm with OBI, and those in rotations were 0.13° with TLS and 0.15° with OBI. The dose perturbation was observed within 1.5 mm for 6 MV and 2.0 mm for 10 MV from the marker. Conclusions: Sufficient recognition accuracy of the phantom position error was achieved using our system. It is unnecessary to consider the dose perturbation in actual patient-specific QA. We concluded that the XOM system can be utilized to ensure quantitative and accurate phantom positioning in patient-specific QA with CyberKnife and a general-purpose linac.

This study aimed to evaluate changes in the deformation of the entrance window on a phantom for a horizontal beam geometry with a window thickness of 5 mm. The window deformation over time was measured using a dial indicator for 12 h after water filling. The window deformation was in the range of 0.17-0.37 mm among the three phantoms. The change in deformation over time was found to be 0.06 mm or less 12 h after filling the phantom. For off-center measurements, the maximum difference in variation among the five points in each of the three phantoms was 0.12, 0.11, and 0.07 mm. The window deformation on the phantom for a horizontal beam geometry with the window thickness of 5 mm was considered almost negligible when appropriately used. However, it is important to control the quality of the phantom according to the usage conditions.

We aim to evaluate the basic characteristics of SRS MapCHECK (SRSMC) for CyberKnife (CK) and establish a dose verification system using SRSMC for the tumor-tracking irradiation for CK. The field size and angular dependence of SRSMC were evaluated for basic characterization. The output factors (OPFs) and absolute doses measured by SRSMC were compared with those measured using microDiamond and microchamber detectors and those calculated by the treatment planning system (TPS). The angular dependence was evaluated by comparing the SRSMC with a microchamber. The tumor-tracking dose verification system consists of SRSMC and a moving platform. The doses measured using SRSMC were compared with the doses measured using a microchamber and radiochromic film. The OPFs and absolute doses of SRSMC were within ±3.0% error for almost all field sizes, and the angular dependence was within ±2.0% for all incidence angles. The absolute dose errors between SRSMC and TPS tended to increase when the field size was smaller than 10 mm. The absolute doses of the tumor-tracking irradiation measured using SRSMC and those measured using a microchamber agreed within 1.0%, and the gamma pass rates of SRSMC in comparison with those of the radiochromic film were greater than 95%. The basic characteristics of SRSMC for CK presented acceptable results for clinical use. The results of the tumor-tracking dose verification system realized using SRSMC were equivalent to those of conventional methods, and this system is expected to contribute toward improving the efficiency of quality control in many facilities.

Purpose We developed a novel and simple method to measure the source positions in applicators directly for high-dose-rate (HDR) brachytherapy based on Cherenkov emission imaging, and evaluated the performance. Methods The light emission from plastic applicators used in cervical cancer treatments, irradiated by an 192 Ir γ-ray source, was captured using a charge-coupled device camera. Moreover, we attached plastics of different shapes, including tapes, tubes, and plates to a metal applicator, to use as screens for the Cherenkov imaging. We determined the source positions and dwell intervals from the light profiles along with the applicator and compared these with preset values and dummy marker measurements. Results The source positions and dwell intervals measured from the light images were comparable to the dummy marker measurements and preset values. The distance from the applicator tip to the first source positions agreed with the dummy marker measurements within 0.2 mm for the plastic tandem. The dwell intervals measured using the Cherenkov method agreed with the preset values within 0.6 mm. The distances measured with three plastic types on the metal applicator also agreed with the dummy marker measurements within 0.2 mm. The dwell intervals measured using the plastic tape agreed with the preset values within 0.7 mm. Conclusions The proposed method should be suitable for rapid and easy quality assurance (QA) investigations in HDR brachytherapy, as it enables source position using a single image. The method allows for real-time, filmless measurements of the source positions to be obtained and is useful for rapid feedback in QA procedures.

Measurements of three-dimensional (3D) dose distribution of electron-beams in water are important for high-energy electron beams from medical linear accelerators (LINAC). Although ionization chambers are commonly used for this purpose, measurements take a long time for precise 3D dose distribution. To solve the problem, we tried the measurements of the 3D dose distributions using a scintillator plate combined with a mirror. After we placed a 1 mm thick plastic scintillator plate at the upper inside of a black box, a water phantom was set above the plastic scintillator plate outside the black box, and electron beam was irradiated to the water phantom from the upper side. The attenuated electron-beam by the water in the phantom was detected by the plastic scintillator plate and the scintillation image was formed in the plate. The image was reflected by a surface mirror set below the plastic scintillator plate and detected by a cooled charge coupled device (CCD) camera from the side. We changed the depths of the water in the phantom, obtained the scintillation images, and calculated a 3D scintillation image using the measured images. Measurements were made for 9 MeV and 12 MeV electron-beams using the imaging system. From the images, we could successfully form 3D scintillation images. The depth profiles measured from the 3D images showed almost identical distribution with those calculated by the planning system within the difference of 5%. The lateral profiles also showed almost identical within the difference of the widths less than 2.5 mm. We conclude that the proposed method is promising for 3D dose distribution measurements of electron-beams.

Purpose Medical physicists use a suitable detector connected to an electrometer to measure radiotherapy beams. Each detector and electrometer has a lifetime (due to physical deterioration of detector components and electrical characteristic deterioration in electronic electrometer components), long‐term stability [according to IEC 60731:2011, ≤0.5% (reference‐class dosimeter)], and calibration frequency [according to Muir et al. (J Appl Clin Med Phys. 2017; 18:182‐190), generally 2 years]; thus, physicists should check the electrometer and detector separately. However, to the best of our knowledge, only one study (Blad et al., Phys Med Biol. 1998; 43:2385–2391) has reported checking the electrometer independently from the detector. The present study conducts performance checks on electrometers separately from the detector in clinical settings, using an electrometer equipped with a direct current (DC) generator (EMF 521R) capable of injecting DC (effective range: ±20 pA to ±20 nA) into itself or another electrometer. Methods First, to check the nonlinearity of the generated currents from ±20 pA to ±20 nA, charges generated from the DC generator were measured with the EMF 521R electrometer. Next, six reference‐class electrometers classified according to IEC 60731:2011 were checked for repeatability at a current of ±20 pA or a minimum effective indicated value meeting IEC 60731:2011, as well as for nonlinearity within the current range from ±20 pA to ±20 nA. Results The nonlinearities for the measured currents were less than ±0.05%. The repeatability for the six electrometers was < 0.1%. While the nonlinearity of one electrometer reached up to 0.22% at a current of –20 pA, all six electrometers displayed nonlinearities of less than ±0.1% at currents of ±100 pA or higher. Conclusions This work suggests that it is possible to check the nonlinearity and repeatability of clinical electrometers with DCs above the ±30 pA level using a DC generator in a clinic.

Purpose Equipment refurbishment was performed to remove the beam-hardening filter (BHF) from the CyberKnife system (CK). This study aimed to confirm the change in the beam characteristics between the conventional CK (present-BHF CK) and CK after the BHF was removed (absent-BHF CK) and evaluate the impact of BHF removal on the beam quality correction factors kQ. Methods The experimental measurements of the beam characteristics of the present- and absent-BHF CKs were compared. The CKs were modeled using Monte Carlo simulations (MCs). The energy fluence spectra were calculated using MCs. Finally, kQ were estimated by combining the MC results and analytic calculations based on the TRS-398 and TRS-483 approaches. Results All gamma values for percent depth doses and beam profiles between each CK were less than 0.5 following the 3%/1 mm criteria. The percentage differences for tissue-phantom ratios at depths of 20 and 10 cm and percentage depth doses at 10 cm between each CK were −1.20% and −0.97%, respectively. The MC results demonstrated that the photon energy fluence spectrum of the absent-BHF CK was softer than that of the present-BHF CK. The kQ values for the absent-BHF CK were in agreement within 0.02% with those for the present-BHF CK. Conclusions The photon energy fluence spectrum was softened by the removal of BHF. However, no remarkable impact was observed for the measured beam characteristics and kQ. Therefore, the previous findings of the kQ values for the present-BHF CK can be directly used for the absent-BHF CK.

Purpose: Phantoms for horizontal beam geometry can avoid issues in vertical-beam geometry, such as change in chamber depth due to evaporation, and defining the origin at the water surface. However, their thin entrance windows would deform when these phantoms are filled, which can change the chamber depth, as pointed out by The International Atomic Energy Agency (IAEA) TRS-398. Cur- rently, few reports (Arib et al., J Appl Clin Med Phys. 2006; 7:55–64, and Kinoshita et al., Rep Pract Oncol Radiother. 2018; 23:199–206) are available with practical data on window deformation. There- fore, we investigated the influence of entrance window deformation on chamber depths in water phantoms and the measurements in various beam modalities. Methods: To examine widely used phantoms and phantoms with different characteristics, three phantom types were investigated (the number of phantoms investigated appears in parentheses): PTW—type 41023 (2), Qualita—QWP-04 (2), and IBA—WP34 (2). Prior to the investigation, these phantoms were stored for acclimatization in a room for approximately 10 h under the following two conditions: (a) room temperature: 21 ???? 2°C; (b) room temperature: 27 ???? 2°C. Using a dial indica- tor, the centers of the windows were monitored every 30 min for 12 h immediately after the phan- toms were filled, in a treatment room at the room temperature of 21 ???? 2°C. Results: Immediately after the phantoms were filled, the window deformation ranged from ????0.07 (inward-deformation) to 0.3 mm (outward deformation) among the six phantoms, in comparison with empty phantom windows. For 12 h after the phantoms were filled, the change in the deformation was up to 0.23 mm, but typically less than 0.15 mm. Conclusions: Reference dosimetry in photon, electron, and proton beams would not be influenced significantly by these window behaviors, whereas the window deformation has a slight impact on those heavy ion beams.

Measurements of dose distribution in water are important for high-energy electron beams from medical linear accelerators (LINAC). Although ionization chambers are commonly used for this purpose, measurements take a relatively long time, especially to obtain data for two- or three-dimensional dose distributions. To solve the problem, we tried imaging of produced light in water during irradiations of high energy electron-beams from LINAC. We placed a water phantom on a table of a LINAC system, and images of produced light in water were measured with a high-sensitivity cooled charge coupled device (CCD) camera during electron-beam irradiations of the water phantom. Measurements were made for different energies and doses of electron beams. We also measured the light spectra of the images by changing optical filters, to observe the difference of the images with respect to the wavelengths and to confirm the source of the optical light. In all irradiations of different energies and doses of electron-beams, we could obtain clear images of produced light in water. From the optical images, although the depth profiles were significantly smaller in shallow part of water, the ranges of the beams could be estimated within 1.7 mm difference with those calculated by the planning system. The lateral profiles and widths derived from the images of produced light were almost identical to those calculated by the planning system; the difference of the width was less than 2.3 mm. The light spectra of the images of produced light of water showed similar distribution to that of the Cerenkov-light although the distribution was slightly steeper. There was not a significant difference observed in the depth profiles between different wave lengths of light. The imaging of produced light in water during electron-beam irradiations has potential to be used for lateral profiles measurements, range and width estimations.

Pretreatment intensity-modulated radiotherapy quality assurance is performed using simple rectangular or cylindrical phantoms; thus, the dosimetric errors caused by complex patient-specific anatomy are absent in the evaluation objects. In this study, we construct a system for generating patient-specific three-dimensional (3D)-printed phantoms for radiotherapy dosimetry. An anthropomorphic head phantom containing the bone and hollow of the paranasal sinus is scanned by computed tomography (CT). Based on surface rendering data, a patient-specific phantom is formed using a fused-deposition-modeling-based 3D printer, with a polylactic acid filament as the printing material. Radiophotoluminescence glass dosimeters can be inserted in the 3D-printed phantom. The phantom shape, CT value, and absorbed doses are compared between the actual and 3D-printed phantoms. The shape difference between the actual and printed phantoms is less than 1 mm except in the bottom surface region. The average CT value of the infill region in the 3D-printed phantom is −6 ± 18 Hounsfield units (HU) and that of the vertical shell region is 126 ± 18 HU. When the same plans were irradiated, the dose differences were generally less than 2%. These results demonstrate the feasibility of the 3D-printed phantom for artificial in vivo dosimetry in radiotherapy quality assurance.

Measurements of dose distribution are important for high energy X-ray beam from linear accelerators (LINAC) for quality assessment (QA) of the system. Although ionization chambers are commonly used for this purpose, measurements need relatively long time to obtain the data especially for the two- or three-dimensional dose distributions. To solve the problem, we conducted optical imaging of water during irradiations of high energy X-ray beam from a LINAC. We placed a water phantom set on a table with a LINAC system, and optical images of water were measured with a high-sensitivity cooled charge coupled device (CCD) camera during X-ray beam irradiations to the water phantom from the upper side. Measurements were made for different energies and doses of X-ray beams. We also measured dynamic images while moving the multi-leaf collimators of the LINAC system to evaluate the performance for more practical condition. Then we measured the light spectra of the optical images of water for X-ray beam by changing the optical filters. In all irradiations of different energies and doses of X-ray beam, we could obtain clear optical images in water. The lateral profiles of the images were almost identical to those calculated by planning system. However the depth profiles were slightly smaller at the deeper area. We obtained dynamic images while moving the multi-leaf collimators. The light spectrum of the image during X-ray beam irradiation was similar to that of the Cerenkov-light. There was not a significant difference in the depth profiles between different wave lengths of light. Optical imaging of water during irradiations of X-ray beam has a potential to be used for the lateral profile of the beams. Also it might be useful to estimate the depth profiles with slight under estimations at deeper areas. Dynamic optical imaging while moving the multi-leaf collimators during irradiation of X-ray were possible.

The American Association of Physicists in Medicine (AAPM) Working Group on TG‐51 published an Addendum to the AAPM's TG‐51 protocol (Addendum to TG‐51) in 2014, and the Japan Society of Medical Physics (JSMP) published a new dosimetry protocol JSMP 12 in 2012. In this study, we compared the absorbed dose to water determined at the reference depth for high‐energy photon beams following the recommendations given in AAPM TG‐51 and the Addendum to TG‐51, IAEA TRS‐398, and JSMP 12. This study was performed using measurements with flattened photon beams with nominal energies of 6 and 10 MV. Three widely used ionization chambers with different compositions, Exradin A12, PTW 30013, and IBA FC65‐P, were employed. Fully corrected charge readings obtained for the three chambers according to AAPM TG‐51 and the Addendum to TG‐51, which included the correction for the radiation beam profile (P rp), showed variations of 0.2% and 0.3% at 6 and 10 MV, respectively, from the readings corresponding to IAEA TRS‐398 and JSMP 12. The values for the beam quality conversion factor k Q obtained according to the three protocols agreed within 0.5%; the only exception was a 0.6% difference between the results obtained at 10 MV for Exradin A12 according to IAEA TRS‐398 and AAPM TG‐51 and the Addendum to TG‐51. Consequently, the values for the absorbed dose to water obtained for the three protocols agreed within 0.4%; the only exception was a 0.6% difference between the values obtained at 10 MV for PTW 30013 according to AAPM TG‐51 and the Addendum to TG‐51, and JSMP 12. While the difference in the absorbed dose to water determined by the three protocols depends on the kQ and P rp values, the absorbed dose to water obtained according to the three protocols agrees within the relative uncertainties for the three protocols.

Containing 80% tungsten by weight, tungsten functional paper (TFP) is a radiation-shielding material that is lightweight, flexible, disposable, and easy to cut. Through experimental measurements and Monte Carlo simulations, we investigated the feasibility of using TFP as a bolus in electron beam radiotherapy. Commercial boluses of thickness 5 and 10 mm and from one to nine layers of TFPs (0.3–2.7 mm) were positioned on the surface of water-equivalent phantoms. The percentage depth dose curves and transverse dose profiles were measured using a 9-MeV electron beam from a clinical linear accelerator. Normalized to the value at the depth of maximum dose without bolus, the relative doses at the phantom surface for no bolus, 5-mm bolus, 10-mm bolus, 1 TFP, 3 TFPs, 6 TFPs, and 9 TFPs were 78%, 88%, 92%, 84%, 92%, 102%, and 112%, respectively; the therapeutic depths corresponding to a 90% dose level were 29.1 mm, 22.7 mm, 17.7 mm, 26.6 mm, 23.2 mm, 19.3 mm, and 15.8 mm, respectively. The TFP contributed to increased skin dose and provided dose uniformity within the target volume. However, it also resulted in increased lateral constriction and penumbra width. The results of Monte Carlo simulation produced similar trends as the experimental measurements. Our findings suggest that using TFP as a novel thin and flexible skin bolus for electron beam radiotherapy is feasible.

Purpose In the previous treatment planning system (TPS) for CyberKnife (CK), multileaf collimator (MLC)-based treatment plans could be created only by using the finite-size pencil beam (FSPB) algorithm. Recently, a new TPS, including the FSPB with lateral scaling option (FSPB+) and Monte Carlo (MC) algorithms, was developed. In this study, we performed basic and clinical end-to-end evaluations for MLC-based CK tumor-tracking radiotherapy using the MC, FSPB+, and FSPB. Methods Water- and lung-equivalent slab phantoms were combined to obtain the percentage depth dose (PDD) and off-center ratio (OCR). The CK M6 system and Precision TPS were employed, and PDDs and OCRs calculated by the MC, FSPB+, and FSPB were compared with the measured doses obtained for 30.8 × 30.8 mm2 and 60.0 × 61.6 mm2 fields. A lung motion phantom was used for clinical evaluation and MLC-based treatment plans were created using the MC. The doses were subsequently recalculated using the FSPB+ and FSPB, while maintaining the irradiation parameters. The calculated doses were compared with the doses measured using a microchamber (for target doses) or a radiochromic film (for dose profiles). The dose volume histogram (DVH) indices were compared for all plans. Results In homogeneous and inhomogeneous phantom geometries, the PDDs calculated by the MC and FSPB+ agreed with the measurements within ±2.0% for the region between the surface and a depth of 250 mm, whereas the doses calculated by the FSPB in the lung-equivalent phantom region were noticeably higher than the measurements, and the maximum dose differences were 6.1% and 4.4% for the 30.8 × 30.8 mm2 and 60.0 × 61.6 mm2 fields, respectively. The maximum distance to agreement values of the MC, FSPB+, and FSPB at the penumbra regions of OCRs were 1.0, 0.6, and 1.1 mm, respectively, but the best agreement was obtained between the MC-calculated curve and measurements at the boundary of the water- and lung-equivalent slabs, compared with those of the FSPB+ and FSPB. For clinical evaluations using the lung motion phantom, under the static motion condition, the dose errors measured by the microchamber were -1.0%, -1.9%, and 8.8% for MC, FSPB+, and FSPB, respectively; their gamma pass rates for the 3%/2 mm criterion comparing to film measurement were 98.4%, 87.6%, and 31.4% respectively. Under respiratory motion conditions, there was no noticeable decline in the gamma pass rates. In the DVH indices, for most of the gross tumor volume and planning target volume, significant differences were observed between the MC and FSPB, and between the FSPB+ and FSPB. Furthermore, significant differences were observed for lung Dmean , V15 Gy , and V20 Gy between the MC, FSPB+, and FSPB. Conclusions The results indicate that the doses calculated using the MC and FSPB+ differed remarkably in inhomogeneous regions, compared with the FSPB. Because the MC was the most consistent with the measurements, it is recommended for final dose calculations in inhomogeneous regions such as the lung. Furthermore, the sufficient accuracy of dose delivery using MLC-based tumor-tracking radiotherapy by CK was demonstrated for clinical implementation.

The aim of this study is to investigate the dosimetric uncertainty of stochastic noise and the post-irradiation density growth for reflective-type radiochromic film to obtain the appropriate dose from the exactly controlled film density. Film pieces were irradiated with 6-MV photon beams ranging from 0 to 400 cGy. The pixel values (PVs) of these films were obtained using a flatbed scanner at elapsed times of 1 min to 120 h between the end of irradiation and the film scan. The means and standard deviations (SDs) of the PVs were calculated. The SDs of the converted dose scale, usd, and the dose increases resulting from the PV increases per ±29 min at each elapsed time, utime, were computed. The combined dose uncertainties from these two factors, uc, were then calculated. A sharp increase in the PV occurred within the first 3 h after irradiation, and a slight increase continued from 3 h to 120 h. usd was independent of post-irradiation elapsed time. Sharp decreases in utime were obtained within 1 h after irradiation, and slight decreases in utime were observed from 1 to 24 h after irradiation. uc first decreased 1 h after irradiation and remained constant afterward. Assuming that the post-irradiation elapsed times of all of the related measurements are synchronized within ±29 min, the elapsed time should be at least 1 h in our system. It is important to optimize the scanning protocol for each institution with consideration of the required measurement uncertainty and acceptable latency time.

Metal dental restoration materials cause dose enhancement upstream and dose disturbance downstream of the high‐density inhomogeneous regions in which these materials are used. In this study, we evaluated the impact of a dental metallic crown (DMC) on intensity‐modulated radiotherapy (IMRT) and volumetric‐modulated arc therapy (VMAT) for head and neck cancer. Additionally, the possibility of sparing the oral mucosa from dose enhancement using an individual intraoral mouthpiece was evaluated. An experimental oral phantom was designed to verify the dosimetric impact of a DMC. We evaluated the effect on single beam, parallel opposing beam, arc beam, IMRT, and VMAT treatment plans. To evaluate the utility of a 3‐mm‐thick intraoral mouthpiece, the doses across the mouthpiece were measured. For single beam irradiation, the measured doses at the entrance and exit planes of the DMC were 51% higher and 21% lower than the calculated dose by the treatment planning system, respectively. The maximum dose enhancements were 22% and 46% for parallel opposing beams and the 90° arc rotation beam, respectively. For IMRT and VMAT, the measured doses adjacent to the DMC were 12.2%±6.3% (mean±1.96 SD) and 12.7%±2.5% higher than the calculated doses, respectively. With regard to the performance of the intraoral mouthpiece for the IMRT and VMAT cases, the disagreement between measured and calculated doses at the outermost surface of the mouthpieces were −2.0%, and 2.0%, respectively. Dose enhancements caused by DMC‐mediated radiation scattering occurred during IMRT and VMAT. Because it is difficult to accurately estimate the dose perturbations, careful consideration is necessary when planning head and neck cancer treatments in patients with DMCs. To spare the oral mucosa from dose enhancement, the use of an individual intraoral mouthpiece should be considered. PACS numbers: 87.55.km, 87.55.N‐, 87.55.Qr

The relative response of an alanine dosimeter to electron beams was evaluated using Co-60 gamma rays as a reference to establish an output dose-evaluation service. Alanine dosimeters were irradiated with 16-MeV electron beams and Co-60 gamma rays. For electron-beam irradiation, to ensure minimum dose gradient in alanine pellets, a thin holder with a different arrangement and material from a holder used in Co-60 gamma irradiation was employed. Monte Carlo simulations were conducted for electron beams from 12 MeV to 18 MeV to calculate the relative response and compare them with the experimental results. A correction factor for the acrylic holder was also calculated. The experimental relative response was 0.990. The experimental value agreed with the relative responses obtained by Monte Carlo calculations. The calculations with the electron beams of different energies showed that the response of the alanine dosimeter did not depend on the energy of the electron beams. The correction factor of the acrylic holder was approximately 1.004 for any incident energy. The dose of high-energy electron beams by the alanine dosimeter can be measured more easily using the relative response rather than the direct dose measurement from a calibration curve of electron beams.

Determination of absorbed dose distributions in phantoms in X-ray beams of high energy medical linear accelerators (LINAC) is important for quality control checks of the system. Although optical imaging of water during irradiations of X-ray beams from a LINAC is a promising method, depth dose profiles showed underestimation in deeper parts of the water mainly probably because of the angular dependency of Cerenkov-light produced in water. To solve the problem, the authors added vitamin B2 to water and obtained optical images with a high-sensitivity cooled charge coupled device (CCD) camera during X-ray beams irradiations. Then, the depth and lateral distributions of these optical images were evaluated and compared with those of the dose planning system. The depth dose profiles of vitamin B2 water were similar to those calculated by the dose planning system, although there was dependency on the vitamin B2 concentrations. The lateral profiles of the optical images of vitamin B2 water were slightly smoother than those of the dose planning system at the edge of the distribution. With the measured light spectra of the vitamin B2 water, it was confirmed that the Cerenkov-light was converted to longer wavelength of light by the addition of vitamin B2. The authors conclude that vitamin B2 water has a potential to be a promising material to reduce the difference from those of dose planning system for determining the depth dose profiles.

Background Uncertainty in the calibration of high-energy radiation sources is dependent on user and equipment type. Aim We evaluated the uncertainty in the positioning of a cylindrical chamber at a reference depth for reference dosimetry of high-energy photon beams and the resulting uncertainty in the chamber readings for 6- and 10-MV photon beams. The aim was to investigate major contributions to the positioning uncertainty to reduce the uncertainty in calibration for external photon beam radiotherapy. Materials and methods The following phantoms were used: DoseView 1D, WP1D, 1D SCANNER, and QWP-07 as one-dimensional (1D) phantoms for a vertical-beam geometry; GRI-7632 as a phantom for a fixed waterproofing sleeve; and PTW type 41023 and QWP-04 as 1D phantoms for a horizontal-beam geometry. The uncertainties were analyzed as per the Guide to the Expression of Uncertainty in Measurement. Results The positioning and resultant uncertainties in chamber readings ranged from 0.22 to 0.35 mm and 0.12–0.25%, respectively, among the phantoms (using a coverage factor k = 1 in both cases). The major contributions to positioning uncertainty are: definition of the origin for phantoms among users for the 1D phantoms for a vertical-beam geometry, water level adjustment among users for the phantom for a fixed waterproofing sleeve, phantom window deformation, and non-water material of the window for the 1D phantoms for a horizontal-beam geometry. Conclusion The positioning and resultant uncertainties in chamber readings exhibited minor differences among the seven phantoms. The major components of these uncertainties differed among the phantom types investigated.

The aim of this work is to optimize an additional collimator in a beam delivery system to reduce neutron exposure to patients in passive carbon-ion therapy. All studies were performed by Monte Carlo simulation assuming the beam delivery system at Heavy-Ion Medical Accelerator in Chiba. We calculated the neutron ambient dose equivalent at patient positions with an additional collimator, and optimized the position, aperture size and material of the collimator to reduce the neutron ambient dose equivalent. The collimator located 125 and 470 cm upstream from the isocenter could reduce the dose equivalent near the isocenter by 35%, while the collimator located 813 cm upstream from the isocenter was ineffective. As for the material of the collimator, iron and nickel could conduct reduction slightly better than aluminum and polymethyl methacrylate. The additional collimator is an effective method for the reduction of the neutron ambient dose equivalent near the isocenter.

A novel method is proposed to measure NO in breath. Breath NO is a useful diagnostic measure for asthma patients. Due to the low water solubility of NO, existing wet chemical NO measurements are conducted on NO(2) after removal of pre-existing NO(2) and conversion of NO to NO(2). In contrast, this study utilizes direct measurement of NO by wet chemistry. Gaseous NO was collected into an aqueous phase by a honeycomb-patterned microchannel scrubber and reacted with diaminofluorescein-2 (DAF-2). Fluorescence of the product was measured using a miniature detector, comprising a blue light-emitting diode (LED) and a photodiode. The response intensity was found to dramatically increase following addition of NO(2) into the absorbing solution or air sample. By optimizing the conditions, the sensitivity obtained was sufficient to measure parts per billion by volume levels of NO continuously. The system was applied to real analysis of NO in breath, and the effect of coexisting compounds was investigated. The proposed system could successfully measure breath NO.

The purpose of this study is to calculate correction factors for plastic water (PW) and plastic water diagnostic-therapy (PWDT) phantoms in clinical photon and electron beamdosimetry using the EGSnrc Monte Carlo code system. A water-to-plastic ionization conversion factor k p l for PW and PWDT was computed for several commonly used Farmer-type ionization chambers with different wall materials in the range of 4–18 MV photonbeams. For electron beams, a depth-scaling factor c p l and a chamber-dependent fluence correction factor h p l for both phantoms were also calculated in combination with NACP-02 and Roos plane-parallel ionization chambers in the range of 4–18 MeV. The h p l values for the plane-parallel chambers were evaluated from the electron fluence correction factor ϕ p l w and wall correction factors P wall , w and P wall , p l for a combination of water or plastic materials. The calculated k p l and h p l values were verified by comparison with the measured values. A set of k p l values computed for the Farmer-type chambers was equal to unity within 0.5% for PW and PWDT in photonbeams. The k p l values also agreed within their combined uncertainty with the measured data. For electron beams, the c p l values computed for PW and PWDT were from 0.998 to 1.000 and from 0.992 to 0.997, respectively, in the range of 4–18 MeV. The ϕ p l w values for PW and PWDT were from 0.998 to 1.001 and from 1.004 to 1.001, respectively, at a reference depth in the range of 4–18 MeV. The difference in P wall between water and plastic materials for the plane-parallel chambers was 0.8% at a maximum. Finally, h p l values evaluated for plastic materials were equal to unity within 0.6% for NACP-02 and Roos chambers. The h p l values also agreed within their combined uncertainty with the measured data. The absorbed dose to water from ionization chamber measurements in PW and PWDT plastic materials corresponds to that in water within 1%. Both phantoms can thus be used as a substitute for water for photon and electron dosimetry.

This article describes the procedures for correction of the modulator thickness and commissioning of the XiO treatment planning system (TPS) for modulator-based intensity modulated radiation therapy (M-IMRT). This modulator manufacturing system adopts a method in which the modulator is milled using a floor-type computer-aided numerical control milling machine (CNC-mill) with modulator data calculated by XiO TPS. XiO TPS uses only effective attenuation coefficients (EAC) for modulator thickness calculation. This article describes a modified method for assessing modulator thickness. A two-dimensional linear attenuation array was used to correct the modulator thickness calculated by XiO. Narrow-beam geometry was used for measuring the linear attenuation coefficient (LAC) at off-axis positions (OAP) for varying brass thicknesses. An equation for the two-dimensional LAC ratio (2D-LACR) can be used to calculate the corrected modulator thickness. It is assumed that the broad beam EAC of a small field varies with the brass thickness and the OAP distance in the same way as that of LACR, so the two-dimensional EAC (2D-EAC) is equal to the EAC corrected using the LACR. The dose distribution was evaluated for three geometric patterns and one clinical case on low energy x ray (4 MV) with a large field size (20 x 20 cm2). The results using the proposed correction method of modulator thickness showed a good agreement between the measured dose distributions and the dose distributions calculated by TPS with the correction. Hence, the method is effective to improve the accuracy of M-IMRT in XiO TPS. An important problem for the brass modulator is the milling condition, such as the drill diameter and the cutting pitch size. It is necessary to improve the accuracy of M-IMRT for the "softening" and "hardening" effects of the beam to be considered in dose calculation in patients and the modulator profile design.

Fine particulate and phase pure barium titanate with its average particle size as small as 120 nm and its tetragonality as high as 1.0085 was obtained by adding bovine serum albumin (BSA) to the reactant mixture comprising fine particulate BaCO3 and TiO2. In the presence of BSA, BaCO3 decomposed at substantially lower temperatures as a consequence of coordination of BSA preferentially to the ligand field of Ba. Elimination of remaining free carbon by increasing oxygen partial pressure under flowing air was one of the technical key issues of the high crystallinity and sinterability of the product.

In this study, we assessed the geometric accuracy of an automated positioning system in Gamma Knife (GK) surgery. Specifically, we looked at the total spatial uncertainty over the entire treatment range of GK stereotactic radiosurgery (SRS) procedures in both the GK model C and the Perfexion (PFX). An originally-developed phantom and a radiochromic film were used for obtaining actual dose distributions. The phantom, with inserted films on different axial planes (z = 60, 75, 100, 125, 140 mm), sagittal planes (x = 60, 75, 100, 125, 140 mm), and coronal planes (y = 60, 75, 100, 125, 140 mm), was placed on a Leksell skull frame. Computed tomography (CT) was then performed with a stereotactic localizer box attached to the frame, and dose planning was made using the Leksell GammaPlan treatment planning system. The phantom finally received beam delivery using a single shot of a 4-mm collimator helmet. The discrepancy between the planned shot position and the irradiated center position was evaluated by a dedicated film analysis software. The total uncertainty of CT-based GK SRS was less than 1 mm for almost all measured points over the stereotactic space in both the model C and the PFX. In addition, the geometric accuracy of the automated positioning system was estimated to be less than 0.1 mm and equal to 0.5 mm in the central and peripheral areas, respectively. We confirmed that the total spatial uncertainties of both the GK model C and the PFX are acceptable for clinical use.

In carbon-ion radiotherapy, it is important to evaluate the biological dose because the relative biological effectiveness values vary greatly in a patient’s body. The microdosimetric kinetic model (MKM) is a method of estimating the biological effect of radiation by use of microdosimetry. The lateral biological dose distributions were estimated with a modified MKM, in which we considered the overkilling effect in the high linear-energy-transfer region. In this study, we used the Monte Carlo calculation of the Geant4 code to simulate a horizontal port at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. The lateral biological dose distributions calculated by Geant4 were almost flat as the lateral absorbed dose in the flattened area. However, in the penumbra region, the lateral biological dose distributions were sharper than the lateral absorbed dose distributions. Furthermore, the differences between the lateral absorbed dose and biological dose distributions were dependent on the depth for each multi-leaf collimator opening size. We expect that the lateral biological dose distribution presented here will enable high-precision calculations for a treatment-planning system.

We ultrastructually examined the chick yolk sac endodermal epithelium and evaluated our findings in combination with the biochemical analysis of serum and yolk lipoproteins. Twenty-five to 30 nm-sized particles were demonstrated to be a principal element of the extracellular yolk mass and these were determined to be yolk very low density lipoprotein (VLDL). The particles were shown to be taken up by the epithelial cells via coated pits and engulfed by plasma membrane invaginations together with yolk subdroplets, another element of the yolk mass. Through apical vacuoles, the two yolk elements were incorporated into yolk drops, which were identified to be one of the lysosomal structures by a cytochemical procedure using acid phosphatase (AcP)ase activity. During the last week of incubation, which is the final third of the incubation period, the digestion seemed to progress rapidly in the yolk drops, which came to resemble lipolysosomes; lipoprotein production became active as expressed by an enlarged Golgi apparatus. The newly produced lipoprotein particles were electron-lucent and irregular in size (50-120 nm). They were sequestered in secretory vacuoles and secreted from the vascular surface of the epithelial cells. Finally, the particles were thought to be taken into the vitelline circulation as plasma lipoproteins. The major component of lipoprotein in serum was determined to be low density lipoprotein (LDL) and high density lipoprotein (HDL), while cholesterol content was found to increase during incubation. We concluded that endodermal epithelial cells participate the synthesis of plasma LDL and HDL. For this synthesis the cells probably apply lipids and apo-protein generated from yolk VLDL degradation.

The purpose of this study is to calculate correction factors for plastic water (PW) and plastic water diagnostic-therapy (PWDT) phantoms in clinical photon and electron beam dosimetry using the EGSnrc Monte Carlo code system. A water-to-plastic ionization conversion factor k(pl) for PW and PWDT was computed for several commonly used Farmer-type ionization chambers with different wall materials in the range of 4-18 MV photon beams. For electron beams, a depth-scaling factor c(pl) and a chamber-dependent fluence correction factor h(pl) for both phantoms were also calculated in combination with NACP-02 and Roos plane-parallel ionization chambers in the range of 4-18 MeV. The h(pl) values for the plane-parallel chambers were evaluated from the electron fluence correction factor phi(pl)w and wall correction factors P(wall,w) and P(wall,pl) for a combination of water or plastic materials. The calculated k(pl) and h(pl) values were verified by comparison with the measured values. A set of k(pl) values computed for the Farmer-type chambers was equal to unity within 0.5% for PW and PWDT in photon beams. The k(pl) values also agreed within their combined uncertainty with the measured data. For electron beams, the c(pl) values computed for PW and PWDT were from 0.998 to 1.000 and from 0.992 to 0.997, respectively, in the range of 4-18 MeV. The phi(pl)w values for PW and PWDT were from 0.998 to 1.001 and from 1.004 to 1.001, respectively, at a reference depth in the range of 4-18 MeV. The difference in P(wall) between water and plastic materials for the plane-parallel chambers was 0.8% at a maximum. Finally, h(pl) values evaluated for plastic materials were equal to unity within 0.6% for NACP-02 and Roos chambers. The h(pl) values also agreed within their combined uncertainty with the measured data. The absorbed dose to water from ionization chamber measurements in PW and PWDT plastic materials corresponds to that in water within 1%. Both phantoms can thus be used as a substitute for water for photon and electron dosimetry.

This article describes the procedures for correction of the modulator thickness and commissioning of the XiO treatment planning system (TPS) for modulator-based intensity modulated radiation therapy (M-IMRT). This modulator manufacturing system adopts a method in which the modulator is milled using a floor-type computer-aided numerical control milling machine (CNC-mill) with modulator data calculated by XiO TPS. XiO TPS uses only effective attenuation coefficients (EAC) for modulator thickness calculation. This article describes a modified method for assessing modulator thickness. A two-dimensional linear attenuation array was used to correct the modulator thickness calculated by XiO. Narrow-beam geometry was used for measuring the linear attenuation coefficient (LAC) at off-axis positions (OAP) for varying brass thicknesses. An equation for the two-dimensional LAC ratio (2D-LACR) can be used to calculate the corrected modulator thickness. It is assumed that the broad beam EAC of a small field varies with the brass thickness and the OAP distance in the same way as that of LACR, so the two-dimensional EAC (2D-EAC) is equal to the EAC corrected using the LACR. The dose distribution was evaluated for three geometric patterns and one clinical case on low energy x ray (4 MV) with a large field size (20 x 20 cm2). The results using the proposed correction method of modulator thickness showed a good agreement between the measured dose distributions and the dose distributions calculated by TPS with the correction. Hence, the method is effective to improve the accuracy of M-IMRT in XiO TPS. An important problem for the brass modulator is the milling condition, such as the drill diameter and the cutting pitch size. It is necessary to improve the accuracy of M-IMRT for the "softening" and "hardening" effects of the beam to be considered in dose calculation in patients and the modulator profile design.

The present report describes the fabrication technique and dosimetry aspects of a desktop numerically controlled milling machine (NC-Mill) based a compensator system that uses lead clay (Shield cray, Reactor Experiments, Inc., U.S.A.). Effective path lengths of patients were determined for CT image sets using the ray-tracing technique and converted to compensator thickness with the equivalent TMR method. Rigid urethane foam was processed with the NC-Mill to produce a mold for filters, and the lead clay was adopted as the compensating material. The dose distribution was measured on the compensating plane of an anthropomorphic phantom and a stair-step PMMA phantom. It was found that the radiation field with inhomogeneous dose was as high as 30%+/-3% with the compensating filters. In addition, when the absorbed dose at the central axis of 52 compensating filters that were used clinically was measured, 75.0% showed an error of less than +/-3%, and 3.8% showed the maximum dose error: >+/-5%. Overall, the present system was capable of producing dose uniformity to within +/-5% for a stair-step phantom, an anthropomorphic phantom, and clinical situations.

Purpose: Intraoperative radiotherapy (IORT) with an electron beam is one of the accelerated partial breast irradiation methods that have recently been used in early-stage breast cancer. A protective acrylic resin-copper disk is inserted between the breast tissue and the pectoralis muscle to minimize the dose received by the posterior structures. However, a problem with this protective disk is that the surgical incision must be larger than the field size because the disk is manufactured from stiff and unyielding materials. The purpose of this study was to assess the applicability of a new tungsten-based functional paper (TFP) as an alternative to the existing protective disk in IORT. Methods: The newly introduced TFP (Toppan Printing Co., Ltd., Tokyo, JP) is anticipated to become a useful device that is lead-free, light, flexible, and easily processed. The radiation shielding performance of TFP was verified by experimental measurements and Monte Carlo (MC) simulations using PHITS code. The doses transmitted through the protective disk or TFP were measured on a Mobetron mobile accelerator. The same geometries were then reproduced, and the dose distributions were simulated by the MC method. Results: The percentages of transmitted dose relative to the absence of the existing protective disk were lower than 2% in both the measurements and MC simulations. In the experimental measurements, the percentages of transmitted dose for a 9 MeV electron beam were 48.1, 2.3, and 0.6% with TFP thicknesses of 1.9, 3.7, and 7.4 mm, respectively. The percentages for a 12 MeV were 76.0, 49.3, 20.0, and 5.5% with TFP thicknesses of 1.9, 3.7, 7.4, and 14.8 mm, respectively. The results of the MC simulation showed a slight dose increase at the incident surface of the TFP caused by backscattered radiation. Conclusion: The results indicate that a small-incision procedure may be possible by the use of TFP.

Purpose: Several clinical reference dosimetry protocols for absorbed-dose to water have recently been published: The American Association of Physicists in Medicine (AAPM) published an Addendum to the AAPM’s TG-51 (Addendum TG-51) in April 2014, and the Japan Society of Medical Physics (JSMP) published the Japan Society of Medical Physics 12 (JSMP12), a clinical reference dosimetry protocol, in September 2012. This investigation compared and evaluated the absorbed-dose to water of high-energy photon beams according to Addendum TG-51, International Atomic Energy Agency Technical Report Series No. 398 (TRS-398), and JSMP12. Methods: Differences in the respective beam quality conversion factors with Addendum TG-51, TRS-398, and JSMP12 were analyzed and the absorbed-dose to water using 6- and 10-MV photon beams was measured according to the protocols recommended in Addendum TG-51, TRS-398, and JSMP12. The measurements were conducted using two Farmer-type ionization chambers, Exradin A12 and PTW 30013. Results: The beam quality conversion factors for both the 6- and 10-MV photon beams with Addendum TG-51 were within 0.6%, in agreement with the beam quality conversion factors with TRS-398 and JSMP12. The Exradin A12 provided an absorbed-dose to water ratio from 1.003 to 1.006 with TRS-398 / Addendum TG-51 and from 1.004 to 1.005 with JSMP 12 / Addendum TG-51, whereas the PTW 30013 provided a ratio of 1.001 with TRS-398 / Addendum TG-51 and a range from 0.997 to 0.999 with JSMP 12 / Addendum TG-51. Conclusion: Despite differences in the beam quality conversion factor, no major differences were seen in the absorbed-dose to water with Addendum TG-51, TRS-398, and JSMP12. However, Addendum TG-51 provides the most recent data for beam quality conversion factors based on Monte Carlo simulation and greater detail for the measurement protocol. Therefore, the absorbed-dose to water measured with Addendum TG-51 is an estimate with less uncertainty.