Comparison of the Characteristics of Two Types of Parallel-plate Ionization Chamber Under Small-field Electron Irradiation.

BACKGROUND/AIM: This study compared two types of parallel-plate ionization chamber to clarify the pitfalls of dosimetry in electron radiation therapy. MATERIALS AND METHODS: The ion recombination correction factor and polarity effect correction factor, sensitivity, and percentage depth doses (PDDs) of PPC05 and PPC40 parallel-plate ionization chambers were compared in a small-field electron beam. The output ratios were measured for 4-20 MeV electron beams with field sizes of 10 cm × 10 cm, 6 cm × 6 cm, and 4 cm × 4 cm. Furthermore, the films were placed in water and positioned in the beam with their surface perpendicular to the beam axis, and lateral profiles were obtained for each beam energy and each field. RESULTS: Regarding PDDs, at depths greater than the peak dose, the percentage depth dose for PPC40 was smaller than that for PPC05 in small fields and at beam energies greater than 12 MeV, which could be attributed to the lack of lateral electron equilibrium at small depths and multiple scattering events at large depths. The output ratio of PPC40 was approximately 0.025-0.038, which was lower than that of PPC05 in a 4 cm × 4 cm field. For large fields, the lateral profiles were similar, regardless of the beam energy, however, for small fields, the flatness of the lateral profile was beam energy dependent. CONCLUSION: The PPC05 chamber, which has a smaller ionization volume, is therefore more suitable than the PPC40 chamber for small-field electron dosimetry, in particular at high beam energies.

Effective Control of Brain Metastases Irrespective of Distance from Isocenter in Single-isocenter Multitarget Stereotactic Radiosurgery.

BACKGROUND/AIM: Few previous studies have evaluated the effectiveness of single-isocenter multitarget (SIMT) stereotactic radiosurgery (SRS) in clinical practice. PATIENTS AND METHODS: Gross tumor volumes of 113 metastases in 13 patients were measured by contrast-enhanced magnetic resonance imaging. Prescribed doses were set at 20-24 Gy. Based on tumor reduction rates (TRRs) measured before and after SIMT SRS, tumor shrinkage effect was categorized into four grades; almost disappeared: TRR=1, decreased: 0.3≤TRR<1, stable: -0.2

[Application of Real-time Variable Shape Tungsten Rubber for Nail Radiation Protection in the Total Skin Electron Beam (TSEB) Therapy].

PURPOSE: This study investigated whether real-time variable shape tungsten rubber (STR) could be applied for nail radiation protection in total skin electron beam (TSEB) therapy. METHODS: Simulated finger phantoms were made from syringes filled with physiological saline of volumes 5, 10, 20, and 30 ml (inner diameters of 14.1, 17.0, 21.7, and 25.3 mm, respectively). Gafchromic film was applied to the phantom, and lead (thickness 1-3 mm) or STR (thickness 1-4 mm) with an area of 4´1.5 cm was used to cover the film. A 6 MeV electron beam with an 8 mm acrylic board was then used to irradiate the phantom. The source-surface distance (SSD) was 444 cm, the field size was 36´36 cm at SSD of 100 cm without an electron applicator, and the monitor unit was 2000 MU. The shielding rates were obtained from the dose profiles. RESULTS: The mean values of the shielding rate values for all phantoms were 50.1, 97.6, and 98.7% for 1, 2, and 3 mm of lead, respectively, and -13.6, 53.9, 91.2, and 99.4% for 1, 2, 3, and 4 mm of STR, respectively. CONCLUSION: STR with a thickness of 4 mm had the same shielding properties as lead with a thickness of 3 mm, which was an approximately 100% shielding rate. STR could therefore be used in TSEB therapy instead of lead.

Prediction of radiation pneumonitis using dose-volume histogram parameters with high attenuation in two types of cancer: A retrospective study.

The constraint values of dose-volume histogram (DVH) parameters for radiation pneumonitis (RP) prediction have not been uniform in previous studies. We compared the differences between conventional DVH parameters and DVH parameters with high attenuation volume (HAV) in CT imaging in both esophageal cancer and lung cancer patients to determine the most suitable DVH parameters in predicting RP onset. Seventy-seven and 72 patients who underwent radiation therapy for lung cancer and esophageal cancer, respectively, were retrospectively assessed. RP was valued according to the Common Terminology Criteria for Adverse Events. We quantified HAV with quantitative computed tomography analysis. We compared conventional DVH parameters and DVH parameters with HAV in both groups of patients. Then, the thresholds of DVH parameters that predicted symptomatic RP and the differences in threshold of DVH parameters between lung cancer and esophageal cancer patient groups were compared. The predictive performance of DVH parameters for symptomatic RP was compared using the area under the receiver operating characteristic curve. Mean lung dose, HAV30% (the proportion of the lung with HAV receiving ≥30 Gy), and HAV20% were the top three parameters in lung cancer, while HAV10%, HAV5%, and V10 (the percentage of lung volume receiving 10 Gy or more) were the top three in esophageal cancer. By comparing the differences in the threshold for parameters predicting RP between the two cancers, we saw that HAV30% retained the same value in both cancers. DVH parameters with HAV showed narrow differences in the threshold between the two cancer patient groups compared to conventional DVH parameters. DVH parameters with HAV may have higher commonality than conventional DVH parameters in both patient groups tested.

[Characterization of Small Volume Plastic Scintillation Detector].

Some radiation detectors are used for quality assurance and measured to radiation dose for high precision external beam radiotherapy. Recently, plastic scintillation detectors for MeV X-ray measurement are commercially released. The purpose of this study was to evaluate the performance of a commercial plastic scintillation detector with respect to the dose linearity, dose rate dependence, and the output coefficient compared the ionization chamber and the semiconductor detector using each different X-ray energy with or without flattening filter. The result that the dose linearity of each detector showed a linear response in any detectors. Dose rate dependence of plastic scintillation detector was increased when setting dose rate was changed, especially setting to low dose rate. The output coefficient of plastic scintillation detector was equivalent as that of the semiconductor detector even in smallest irradiation field. In conclusion, it was suggested that the plastic scintillation detector is a suitable detector in dose verification measurements for high precision external beam radiotherapy, although we must be with care to low dose rate measurements.

Exclusion of emphysematous lung from dose-volume estimates of risk improves prediction of radiation pneumonitis.

BACKGROUND: The risk factors for radiation pneumonitis (RP) in patients with chronic obstructive pulmonary disease (COPD) are unclear. Mean lung dose (MLD) and percentage of irradiated lung volume are common predictors of RP, but the most accurate dosimetric parameter has not been established. We hypothesized that the total lung volume irradiated without emphysema would influence the onset of RP. METHODS: We retrospectively evaluated 100 patients who received radiotherapy for lung cancer. RP was graded according to the Common Terminology Criteria for Adverse Events (version 4.03). We quantified low attenuation volume (LAV) using quantitative computed tomography analysis. The association between RP and traditional dosimetric parameters including MLD, volume of the lung receiving a dose of ≥2 Gy, ≥ 5 Gy, ≥ 10 Gy, ≥ 20 Gy, and ≥30 Gy, and counterpart measurements of the lung without LAV, were analyzed by logistic regression. We compared each dosimetric parameter for RP using multiple predictive performance measures including area under the receiver operating characteristic curve (AUC) and integrated discrimination improvement (IDI). RESULTS: Of 100 patients, RP of Grades 1, 2, 3, 4, and 5 was diagnosed in 24, 12, 13, 1, and 1 patients, respectively. Compared with traditional dosimetric parameters, counterpart measurements without LAV improved risk prediction of symptomatic RP. The ratio of the lung without LAV receiving ≥30 Gy to the total lung volume without LAV most accurately predicted symptomatic RP (AUC, 0.894; IDI, 0.064). CONCLUSION: Irradiated lung volume without LAV predicted RP more accurately than traditional dosimetric parameters.

[Examination of attenuation correction using low-dose computed tomography].

Attenuation correction is necessary for the reconstruction of SPECT images. One report has mentioned that attenuation correction by X-ray computed tomography (CT) is effective for a non-uniform attenuation body. We examined the effect of attenuation correction on SPECT images by changing the scanning conditions of CT, and evaluated the possibility of attenuation correction by low-dose CT. The phantom was scanned under several X-ray tube conditions varying from 80 kV to 135 kV and from 7.5 mAs to 200 mAs. We obtained equations of attenuation correction based on the Hounsfield Unit (HU) units of each pixel and compared the effects of attenuation correction. The results showed that the equation for attenuation correction under each condition did not vary significantly, and the effects of attenuation correction by the equations did not vary significantly between CT of low dose and that of clinical dose. This result suggest that the attenuation correction obtained by low-dose CT was equal to that obtained by the clinical dose. In conclusion, it seemed that the equation and map of attenuation correction matched with each radionuclide yielded more adequate attenuation correction than conventional methods.

The first trial of phase contrast imaging for digital full-field mammography using a practical molybdenum x-ray tube.

RATIONALE AND OBJECTIVES: The image quality of a newly developed full-field digital phase contrast mammography (PCM) system and of a conventional screen-film (SF) mammography system were compared via images of a phantom and receiver operating characteristic (ROC) analysis of clinical images. METHODS: Magnified (1.75X) PCM images were scanned (sampling rate, 43.75 microm) and then reduced to original-sized, 25-micron pixel images printed on photothermographic film. Along with corresponding SF images, the phantom images were evaluated subjectively, and the clinical images of 38 patients were subjected to ROC analysis of mass and microcalcification. RESULTS: In the image quality of a phantom, the PCM exceeded the SF. In both mass and microcalcification, the ROC analysis Az values of the PCM clinical images surpassed those of the SF images. CONCLUSION: The PCM provides better images than the SF. Clinical trials suggest superior detection of both mass and microcalcification by full-field digital PCM over conventional SF mammography.

[Introduction of manual for the management radioactive medical waste].

Societies concerned with radioactive rays and nuclear medicine have recently highlighted the necessity of managing radioactive medical waste resulting from nuclear medicine examinations. We introduce a manual that we have created and explain its use in decision-making and management practices aimed at the reduction of radioactive medical waste at hospitals that have not yet solved this problem. We hope that our manual will help in reducing this medical waste.