Microdosimetric calculation of penumbra for biological dose in wobbled carbon-ion beams with Monte Carlo Method.

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.

Multi-institutional analysis of early glottic cancer from 2000 to 2005.

BACKGROUND: The purpose of this study is to analyze the outcome of patients with early glottic cancer (GC) treated with radiotherapy (RT) with or without chemotherapy at 10 institutions in the Tokai District, Japan. METHODS: Ten institutions combined data from 279 patients with T1-T2 GC treated with RT with or without chemotherapy between 2000 and 2005. The overall survival rate, disease-specific survival rate, and local control rate were evaluated in 270 patients, except for incomplete cases due to issues such as discontinuation, using the method of Kaplan-Meier and compared using the log-rank test. Results were considered statistically significant at the level of p < 0.05. RESULTS: For 122 patients, the tumors were classified as T1a, while 64 patients had T1b tumors, and 84 patients had T2 tumors. In three cases of T1 tumors, the subtype was unknown. Combined chemoradiotherapy (CRT) was administered during each stage, and various chemotherapy drugs and regimens were used. The median follow-up period was 55.4 months. The 5-year LC rates for T1a, Tb, and T2 tumors in all patients were 87.9%, 82.7%, and 74.1%, respectively. The difference between T1a and T2 was statistically significant (p = 0.016). The 5-year LC rates for T1a, Tb, and T2 with CRT were 92.7%, 78.6%, and 80.7%, respectively, while the rates with radiation alone were 86.5%, 83.8%, and 64.4%, respectively. The difference between CRT and RT alone was not statistically significant in each stage. CONCLUSIONS: In this survey, CRT was performed for early GC at most institutions in clinical practice. Our data showed no statistical difference in the LC rates between CRT and RT alone in each stage. However, there was a tendency for the LCRs of the CRT group to be more favorable than those of the RT group in the T2-stage.

[Dosimetric perturbation due to scattered rays released by a gold marker used for tumor tracking in external radiotherapy].

Image-guided radiation therapy using a gold marker-based tumor tracking technique provides precise patient setup and monitoring. However, the marker consists of high-Z material, and the resulting scattered rays tend to have adverse effects on the dose distribution of radiotherapy. The purpose of this study was to evaluate the dosimetric perturbation due to the use of a gold marker for radiotherapy in the lungs. The relative dose distributions were compared with film measurement, Monte Carlo simulation, and XiO calculation with the multi grid superposition algorithm using two types of virtual lung phantoms, which were composed of tough water phantoms, tough lung phantoms, cork boards, and a 2.0-mm-diameter gold ball. No dose increase and decrease in the vicinity of the gold ball was seen in the XiO calculations, although it was seen in the film measurements and the Monte Carlo simulation. The dose perturbation due to a gold marker cannot be evaluated using XiO calculation with the superposition algorithm when the tumor is near a gold marker (especially within 0.5 cm). To rule out the presence of such dose perturbations due to a gold marker, the distance between the gold marker and the tumor must therefore be greater than 0.5 cm.

Clinical usefulness of a newly developed body surface navigation and monitoring system in radiotherapy.

In radiotherapy, setup precision has great influence on the therapeutic effect. In addition, body movements during the irradiation and physical alternations during the treatment period might cause deviation from the planned irradiation dosage distribution. Both of these factors could undesirably influence the dose absorbed by the target. In order to solve these problems, we developed the "body surface navigation and monitoring system" (hereafter referred to as "Navi-system"). The purpose of this study is to review the precision of the Navi-system as well as its usefulness in clinical radiotherapy. The Navi-system consists of a LED projector, a CCD camera, and a personal computer (PC). The LED projector projects 19 stripes on the patient's body and the CCD camera captures these stripes. The processed image of these stripes in color can be displayed on the PC monitor along with the patient's body surface image, and the digitalized results can be also displayed on the same monitor. The Navi-system calculates the height of the body contour and the transverse height centroid for the 19 levels and compares them with the reference data to display the results on the monitor on a real-time basis. These results are always replaced with new data after they are used for display; so, if the results need to be recorded, such recording commands should be given to the computer. 1) Evaluating the accuracy of the body surface height measurement: from the relationship between actual height changes and calculated height changes with torso surface by the Navi-system, for the height changes from 0.0 mm to ± 10.0mm, the changes show the underestimation of 1.0-1.5 mm and for ± 11.0mm to ± 20.0 mm, the underestimation of 1.5-3.0 mm. 2) Evaluating the accuracy of the transverse height centroid measurement: displacement of the inclined flat panel to the right by 5.0 mm, 10.0 mm, 15.0 mm and 20.0 mm showed the transverse height centroid calculated by the Navi-system for 0.024 ± 0.007 line/pair (mean ± SD), 0.045 ± 0.006 line/pair, 0.066 ± 0.006 line/pair and 0.089 ± 0.007 line/pair, respectively. Also, displacement of the inclined flat panel to the left by 5.0 mm, 10.0 mm, 15.0mm and 20.0 mm showed the transverse height centroid calculated by the Navi-system for 0.015 ± 0.007 line/pair (mean ± SD), 0.034 ± 0.007 line/pair, 0.053 ± 0.008 line/pair and 0.071 ± 0.007 line/pair, respectively. 3) Clinical usefulness of the Navi-system: on using the Navi-system, the frequency of radiotherapy replanning increased from 5.2% to 21.8%, especially in pelvic or abdominal irradiation. We developed a new navigation system for the purpose of compensating for the weakness of MVCT, CBCT and other systems, as well as for having a screening function. This Navi-system can monitor the patient continuously and measure change in height of the patient's body surface from the basic plane, in real time. It can also show the results both qualitatively and quantitatively on the PC monitor.

Dose-volume comparison of proton radiotherapy and stereotactic body radiotherapy for non-small-cell lung cancer.

PURPOSE: This study designed photon and proton treatment plans for patients treated with hypofractionated proton radiotherapy (PT) at the Southern Tohoku Proton Therapy Center (STPTC). We then calculated dosimetric parameters and compared results with simulated treatment plans for stereotactic body radiotherapy (SBRT), using dose--volume histograms to clearly explain differences in dose distributions between PT and SBRT. METHODS AND MATERIALS: Twenty-one patients with stage I non-small-cell lung cancer (stage IA, n = 15 patients; stage IB, n = 6 patients) were studied. All tumors were located in the peripheral lung, and total dose was 66 Gray equivalents (GyE) (6.6 GyE/fraction). For treatment planning, beam incidence for proton beam technique was restricted to two to three directions for PT, and seven or eight noncoplanar beams were manually selected for SBRT to achieve optimal planning target volume (PTV) coverage and minimal dose to organs at risk. RESULTS: Regarding lung tissues, mean dose, V5, V10, V13, V15, and V20 values were 4.6 Gy, 13.2%, 11.4%, 10.6%, 10.1%, and 9.1%, respectively, for PT, whereas those values were 7.8 Gy, 32.0%, 21.8%, 17.4%, 15.3%, and 11.4%, respectively, for SBRT with a prescribed dose of 66 Gy. Pearson product moment correlation coefficients between PTV and dose--volume parameters of V5, V10, V15, and V20 were 0.45, 0.52, 0.58, and 0.63, respectively, for PT, compared to 0.52, 0.45, 0.71, and 0.74, respectively, for SBRT. CONCLUSIONS: Correlations between dose--volume parameters of the lung and PTV were observed and may indicate that PT is more advantageous than SBRT when treating a tumor with a relatively large PTV or several tumors.

Combined chemoradiotherapy for early glottic cancer in clinical practice in Japan: analysis of 10 institutions.

AIM: To conduct a retrospective analysis regarding treatment strategies for early glottic cancer (GC) at ten institutions. PATIENTS AND METHODS: A questionnaire-based survey was used to obtain personal and medical information on patients who started radiation therapy for T1 or T2 GC between January 2000 and December 2005. RESULTS: A total of 279 patients were registered for the survey, of whom 124 patients were classified as T1a, with 65 patients as T1b and 87 patients as T2. The rates of chemoradiotherapy for T1a, T1b and T2 were 24%, 23% and 60%, respectively. A comparison of results for academic and non-academic hospitals showed statistically different rates of combination therapy for T1a (6.9% vs. 39.3%, respectively; p<0.001) and T1b (11.4% vs. 36.6%, respectively; p<0.05) but not for T2 (70.0% vs. 54.4%, respectively; p = 0.158). CONCLUSION: In clinical practice, combined chemoradiotherapy was performed for early GC at most institutions in Tokai District, Japan.

Dose distribution near thin titanium plate for skull fixation irradiated by a 4-MV photon beam.

To investigate the effects of scattered radiation when a thin titanium plate (thickness, 0.05 cm) used for skull fixation in cerebral nerve surgery is irradiated by a 4-MV photon beam. We investigated the dose distribution of radiation inside a phantom that simulates a human head fitted with a thin titanium plate used for post-surgery skull fixation and compared the distribution data measured using detectors, obtained by Monte Carlo (MC) simulations, and calculated using a radiation treatment planning system (TPS). Simulations were shown to accurately represent measured values. The effects of scattered radiation produced by high-Z materials such as titanium are not sufficiently considered currently in TPS dose calculations. Our comparisons show that the dose distribution is affected by scattered radiation around a thin high-Z material. The depth dose is measured and calculated along the central beam axis inside a water phantom with thin titanium plates at various depths. The maximum relative differences between simulation and TPS results on the entrance and exit sides of the plate were 23.1% and - 12.7%, respectively. However, the depth doses do not change in regions deeper than the plate in water. Although titanium is a high-Z material, if the titanium plate used for skull fixation in cerebral nerve surgery is thin, there is a slight change in the dose distribution in regions away from the plate. In addition, we investigated the effects of variation of photon energies, sizes of radiation field and thickness of the plate. When the target to be irradiated is far from the thin titanium plate, the dose differs little from what it would be in the absence of a plate, though the dose escalation existed in front of the metal plate.

Megavoltage photon beam attenuation by carbon fiber couch tops and its prediction using correction factors.

The purpose of this study was to evaluate the effect of megavoltage photon beam attenuation (PBA) by couch tops and to propose a method for correction of PBA. Four series of phantom measurements were carried out. First, PBA by the exact couch top (ECT, Varian) and Imaging Couch Top (ICT, BrainLAB) was evaluated using a water-equivalent phantom. Second, PBA by Type-S system (Med-Tec), ECT and ICT was compared with a spherical phantom. Third, percentage depth dose (PDD) after passing through ICT was measured to compare with control data of PDD. Forth, the gantry angle dependency of PBA by ICT was evaluated. Then, an equation for PBA correction was elaborated and correction factors for PBA at isocenter were obtained. Finally, this method was applied to a patient with hepatoma. PBA of perpendicular beams by ICT was 4.7% on average. With the increase in field size, the measured values became higher. PBA by ICT was greater than that by Type-S system and ECT. PBA increased significantly as the angle of incidence increased, ranging from 4.3% at 180 degrees to 11.2% at 120 degrees . Calculated doses obtained by the equation and correction factors agreed quite well with the measured doses between 120 degrees and 180 degrees of angles of incidence. Also in the patient, PBA by ICT was corrected quite well by the equation and correction factors. In conclusion, PBA and its gantry angle dependency by ICT were observed. This simple method using the equation and correction factors appeared useful to correct the isocenter dose when the PBA effect cannot be corrected by a treatment planning system.

Assessment of spatial uncertainties in the radiotherapy process with the Novalis system.

PURPOSE: The purpose of this study was to evaluate the accuracy of a new version of the ExacTrac X-ray (ETX) system with statistical analysis retrospectively in order to determine the tolerance of systematic components of spatial uncertainties with the Novalis system. METHODS AND MATERIALS: Three factors of geometrical accuracy related to the ETX system were evaluated by phantom studies. First, location dependency of the detection ability of the infrared system was evaluated. Second, accuracy of the automated calculation by the image fusion algorithm in the patient registration software was evaluated. Third, deviation of the coordinate scale between the ETX isocenter and the mechanical isocenter was evaluated. From the values of these examinations and clinical experiences, the total spatial uncertainty with the Novalis system was evaluated. RESULTS: As to the location dependency of the detection ability of the infrared system, the detection errors between the actual position and the detected position were 1% in translation shift and 0.1 degrees in rotational angle, respectively. As to the accuracy of patient verification software, the repeatability and the coincidence of the calculation value by image fusion were good when the contrast of the X-ray image was high. The deviation of coordinates between the ETX isocenter and the mechanical isocenter was 0.313 +/- 0.024 mm, in a suitable procedure. CONCLUSIONS: The spatial uncertainty will be less than 2 mm when suitable treatment planning, optimal patient setup, and daily quality assurance for the Novalis system are achieved in the routine workload.

Commissioning of modulator-based IMRT with XiO treatment planning system.

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.

Dosimetric characteristics of a cubic-block-piled compensator for intensity-modulated radiation therapy in the Pinnacle radiotherapy treatment planning system.

We examined the dose distributions generated by Pinnacle3 (Philips Radiation Oncology Systems, Milpitas, CA) for intensity-modulated radiotherapy (IMRT) plans using a cubic-block-piled compensator as the intensity modulator for 4-MV and 10-MV photon beams. The Pinnacle treatment planning system (TPS) uses an algorithm in which only the physical density of the absorber is required for calculating the characteristics of the modulator. The intensity modulator consists of cubic blocks (attenuator) of a tungsten alloy, plus cubic blocks of polyethylene resin foam that fill the spaces between the attenuator blocks and polymethyl methacrylate (PMMA) boards that act as the platform for the modulator. By measuring the transmission for various thicknesses of attenuator and by deriving values for the total physical density of the modulator, we determined the optimal effective density by comparing the curves fitted for the actual transmission data with the transmission calculated by the TPS. Using these effective densities, we examined the accuracy of Pinnacle3 for dose profiles of specific geometric patterns. The levels of consistency between the measurements and the calculations were within a tolerance of 3% of the dose difference and had a 3-mm distance to agreement for the ladder-, stairstep-, and pyramid-shaped test patterns, except in the high dose gradient region. In this modulator assembly, leakage occurred from the slits between the cubic blocks. This leakage was about 1.6% at maximum, and its influence on dose distribution was not crucial. In the TPS, in which physical density was the only usercontrollable parameter, we used the effective density of the absorber deduced from the effective mass attenuation coefficient. We conclude that the intensity modulation compensator system, together with a piled cubic attenuator, is clinically applicable, with an acceptable tolerance level. For the intensity map of the IMRT plan, measurements in treatment fields met 3% and 3-mm criteria, excluding some regions of high gradient, which had a discrepancy of less than 5% and 4 mm.

Visual comparisons between Cherenkov radiation from water and fluorescence from a scintillator.

A system for observing blue light of Cherenkov radiation was constructed using a Co-60 gamma-ray irradiation unit. However, there was some doubt that the observed light was not Cherenkov light, but scintillation. Therefore, the radiation from water was compared with that from a scintillator. The difference between both luminosities was examined using photographs taken in a dark irradiation room with mirrors and a camera. The radiation from the scintillator was much stronger than that from water. The differences between luminosities of the light radiated in the beam direction, at right angles to the beam and in the reverse beam direction were examined for both radiations. The luminosity from water showed very definite anisotropy, while that from the scintillator was almost isotropic. Furthermore, the light radiated in the beam direction from water was the strongest, and the strengths of the light radiated in the three directions from the scintillator were almost equivalent to each other. It was confirmed that the radiation from water irradiated by Co-60 gamma-rays was indeed Cherenkov light. The anisotropy of the radiated Cherenkov light and the isotropy of the scintillation were clearly observed in the photographs.

[Dosimetry with phantom for total body irradiation(TBI)].

Total body irradiation(TBI) is being used as a method of preparation for bone marrow transplantation(BMT). In TBI, the dose calculation is based on dosimetry using a phantom. We measured the basic dose with a phantom using a 10 MV X-rays. We confirmed the accuracy of the dose calculation performed in our facilities and investigated a method of more accurate dosimetry. We measured the variation in dose according to the size of the phantom and the depth using a tough water phantom, and examined the difference in TMR according to SCD, field size, and size of the phantom. Consequently, the dose has been changed regardless of the size of the phantom at larger than 80 x 30 x 30 cm(3), and it is about 1% larger than 30 x 30 x 30 cm(3). Also TMR has changed according to various conditions, including the size of the phantom, field size, and SCD. Therefore, it was found that dosimetry using the 30 x 30 x 30 cm(3) phantom leads to underestimation in dose calculation, and there is no difference in dose between the field size of 151.5 x 160 cm(2) and 151.5 x 80 cm(2). It is also necessary to consider the effect of the vertical size of the phantom.

A method for measuring the dose distribution of the radiotherapy domain using the computed radiography system.

Knowing the dose distribution in a tissue is as important as being able to measure exposure or absorbed dose in radiotherapy. Therefore, we have developed a measurement method for the dose distribution (CR dosimetry) in the phantom based on the imaging plate (IP) of the computed radiography (CR). The IP was applied for the dose measurement as a dosimeter instead of the film used for film dosimetry. The data from the irradiated IP were processed by a personal computer with 10 bits and were depicted as absorbed dose distributions in the phantom. The image of the dose distribution was obtained from the CR system using the DICOM form. The CR dosimetry is an application of CR system currently employed in medical examinations to dosimetry in radiotherapy. A dose distribution can be easily shown by the Dose Distribution Depiction System we developed this time. Moreover, the measurement method is simpler and a result is obtained more quickly compared with film dosimetry.

[Observation of Cherenkov Radiation from Aquarium Irradiated with Co-60 Gamma-rays]

Cherenkov radiation in water at a nuclear power plant is caused by a nuclear fuel rod and is well known generally. If students can observe Cherenkov radiation at school easily, they can be impressed by the fascinating radiation. Moreover the observation may bring about interest in radiological physics profoundly. A few years ago, management of the Co-60 gamma-ray irradiation apparatus was transferred to Nagoya university school of health sciences from the related hospital. Therefore we have examined the system to observe the Cherenkov radiation in water from secondary electrons generated by Co-60 gamma-rays. At first, the Cherenkov radiation in the aquarium was led to the corridor outside the irradiation room using a mirror, and observed directly while avoiding exposure. Secondly photographs of the Cherenkov radiation from various angles were taken under conditions which consisted of several irradiation fields and pass lengths of gamma-rays in water, and were compared with each other. Our method for observing the Cherenkov radiation may be useful enough for students to raise their dedication in radiological physics study.

Evaluation of Linearity for the Radiophotoluminescence Glass Dosimeter Based on Monochromatic X-rays.

Although low energy X-rays have been utilized for mammography, their safety in medical use is a matter of concern. Characteristics of the radiophotoluminescence glass dosimeter, GD-403, consisting of a glass element and filters, were investigated with respect to monochromatic X-rays obtained from a synchrotron radiation for personal monitoring of low energy photons. We focused on low energy X-rays ranging from 8 to 20 keV to study the linearity of the GD-403 response between photon fluence and dose equivalent. The GD-403 was placed on a tough water phantom and irradiated using an 11-15 mm x 0.1-7 mm beam for modulation of the photon fluence. The tough water phantom could be moved through a distance of 110-150 mm with a stepping motor. For the dose equivalent at 1cm depth (H1), 3mm (H3) and 70 &mgr;m (H70), the GD-403 showed sufficient linearities against the photon fluences in the energy regions of 8 to 20 keV, 13 to 20 keV and 13 to 20 keV, respectively. However, H3 and H70 did not provide sufficient linearities in the energy region of 8 to 12 keV. Moreover, we compared the result in this experiment with the value calculated from the absorbed dose of air using the mass absorption coefficient for the X-ray energy ranging from 10 to 20 keV.