Three-dimensional dose reconstruction-based pretreatment dosimetric verification in volumetric modulated arc therapy for prostate cancer

Purpose@#We performed three-dimensional (3D) dose reconstruction-based pretreatment verification to evaluate gamma analysis acceptance criteria in volumetric modulated arc therapy (VMAT) for prostate cancer. @*Materials and Methods@#Pretreatment verification for 28 VMAT plans for prostate cancer was performed using the COMPASS system with a dolphin detector. The 3D reconstructed dose distribution of the treatment planning system calculation (TC) was compared with that of COMPASS independent calculation (CC) and COMPASS reconstruction from the dolphin detector measurement (CR). Gamma results (gamma failure rate and average gamma value [GFR and γAvg]) and dose-volume histogram (DVH) deviations, 98%, 2% and mean dose-volume difference (DD98%, DD2% and DDmean), were evaluated. Gamma analyses were performed with two acceptance criteria, 2%/2 mm and 3%/3 mm. @*Results@#The GFR in 2%/2 mm criteria were less than 8%, and those in 3%/3 mm criteria were less than 1% for all structures in comparisons between TC, CC, and CR. In the comparison between TC and CR, GFR and γAvg in 2%/2 mm criteria were significantly higher than those in 3%/3 mm criteria. The DVH deviations were within 2%, except for DDmean (%) for rectum and bladder. @*Conclusions@#The 3%/3 mm criteria were not strict enough to identify any discrepancies between planned and measured doses, and DVH deviations were less than 2% in most parameters. Therefore, gamma criteria of 2%/2 mm and DVH related parameters could be a useful tool for pretreatment verification for VMAT in prostate cancer.

Calculation of Energy Spectra for Electron Beam of Medical Linear Accelerator Using GEANT4 / 의학물리

The energy spectra for electron beam of medical linear accelerator were calculated using a GEANT4 Medical Linac 2 example code. The incident electron mean energy were 6, 9, 12, 16, 20 MeV. This code was designed to calculate electron beam energy spectra according to material, thickness and location of electron scattering foil affecting electron beam characteristic. Lead, Copper, Aluminum and Gold were used for scattering foil. The energy distribution for electron and photon were analyzed by changing position of scattering foil in the head of linear accelerator. The effect of electron scattering foil on energy spectra which is basic data of simulation for medical linear accelerator were presented. The calculated results would be used in design of medical accelerator head.

Neutron Generation from a 24 MV Medical Linac / 의학물리

The energy spectra and dose calculations were performed for secondary neutrons from a 24 MV LINAC using MCNPX code (V2, 4, 0). The energy spectra for neutrons and photons emitted from the LINAC head, and absorbed dose to water were calculated in water phantom. The absorbed doses calculated with Monte Carlo were 0.66~0.35 mGy/photon Gy at the surface to d=5 cm, and calculated with interaction data was 0.52 mGy/photon Gy at the depth of electron equilibrium in water. We have shown that this work can be applied to dose estimation of neutrons from high energy LINAC through the comparison of our results with other results.

Investigation of Study Items for the Patterns of Care Study in the Radiotherapy of Laryngeal Cancer: Preliminary Results / 대한방사선종양학회지

PURPOSE: In order to develop the national guide-lines for the standardization of radiotherapy we are planning to establish a web-based, on-line data-base system for laryngeal cancer. As a first step this study was performed to accumulate the basic clinical information of laryngeal cancer and to determine the items needed for the data-base system. MATERIALS AND METHODS: We analyzed the clinical data of patients who were treated under the diagnosis of laryngeal cancer from January 1998 through December 1999 in the South-west area of Korea. Eligibility criteria of the patients are as follows: 18 years or older, currently diagnosed with primary epithelial carcinoma of larynx, and no history of previous treatments for another cancers and the other laryngeal diseases. The items were developed and filled out by radiation oncologist who are members of Korean Southwest Radiation Oncology Group. SPSS v10.0 software was used for statistical analysis. RESULTS: Data of forty-five patients were collected. Age distribution of patients ranged from 28 to 88 years (median, 61). Laryngeal cancer occurred predominantly in males (10:1 sex ratio). Twenty-eight patients (62%) had primary cancers in the glottis and 17 (38%) in the supraglottis. Most of them were diagnosed pathologically as squamous cell carcinoma (44/45, 98%). Twenty-four of 28 glottic cancer patients (86%) had AJCC (American Joint Committee on Cancer) stage I/II, but 50% (8/16) had in supraglottic cancer patients (p=0.02). Most patients (89%) had the symptom of hoarseness. Indirect laryngoscopy was done in all patients and direct laryngoscopy was performed in 43 (98%) patients. Twenty-one of 28 (75%) glottic cancer cases and 6 of 17 (35%) supraglottic cancer cases were treated with radiation alone, respectively. The combined treatment of surgery and radiation was used in 5 (18%) glottic and 8 (47%) supraglottic patients. Chemotherapy and radiation was used in 2 (7%) glottic and 3 (18%) supraglottic patients. There was no statistically significant difference in the use of combined modality treatments between glottic and supraglottic cancers (p=0.20). In all patients, 6 MV X-ray was used with conventional fractionation. The fraction size was 2 Gy in 80% of glottic cancer patients compared with 1.8 Gy in 59% of the patients with supraglottic cancers. The mean total dose delivered to primary lesions were 65.98 Gy and 70.15 Gy in glottic and supraglottic patients treated, respectively, with radiation alone. Based on the collected data, 12 modules with 90 items were developed for the study of the patterns of care in laryngeal cancer. CONCLUSION: The study items for laryngeal cancer were developed. In the near future, a web system will be established based on the items investigated, and then a nation-wide analysis on laryngeal cancer will be processed for the standardization and optimization of radiotherapy.

Measurement and Monte Carlo Simulation of 6 MV X-rays for Small Radiation Fields / 대한방사선종양학회지

PURPOSE: In order to obtain basic data for treatment plan in radiosurgery, we measured small fields of 6 MV X-rays and compared the measured data with our Monte Carlo simulations for the small fields. MATERIALS AND METHODS: The small fields of 1.0, 2.0 and 3.0 cm in diameter were used in this study. Percentage depth dose (PDD) and beam profiles of those fields were measured and calculated. A small semiconductor detector, water phantoms, and a remote control system were used for the measurement. Monte Carlo simulations were performed using the EGS4 code with the input data prepared for the energy distribution of 6 MV X-rays, beam divergence, circular fields and the geometry of the water phantoms. RESULTS: In the case of PDD values, the calculated values were lower than the measured values for all fields and depths, with the differences being 0.3 to 5.7% at the depths of 2.0 to 20.0 cm and 0.0 to 8.9% at the surface regions. As a result of the analysis of beam profiles for all field sizes at a depth of 10cm in water phantom, the measured 90% dose widths were in good agreement with the calculated values, however, the calculated penumbra radii were 0.1 cm shorter than measured values. CONCLUSION: The measured PDDs and beam profiles agreement with the Monte Carlo calculations approximately. However, it is different when it comes to calculations in the area of phantom surface and penumbra because the Monte Carlo calculations were performed under the simplified geometries. Therefore, we have to study how to include the actual geometries and more precise data for the field area in Monte Carlo calculations. The Monte Carlo calculations will be used as a useful tool for the very complicated conditions in measurement and verification.

Dose Calculation for the Buchler Remote Afterloading System / 대한치료방사선과학회지

PURPOSE: The dose calculation program for the Buchler type remote afterloading system was developed. This program also can be used to calculate dose for various sealed sources. METHODS AND MATERIALS: We determined the source length and distribution by dividing the program disk to 72 points. The dose rate for the each program disk and source was calculated. The dose rate table for the xy coordinate was established. The dose rate for the interesting points of the patient were calculated by using this table. We also made isodose curve from this calculations. RESULTS: The storage size for the dose rate table were increased.But the calculation of the dose rate for the patient were carried out rapidly. So we could get real time calculation. CONCLUSION: By using this program, we could calculate the dose rate for the various oints of the patient quickly and accurately. This program will be useful for the treatment with various linear sources.

A Study on the Simulation and the measurement of 6 MeV Electron Beam / 대한치료방사선과학회지

PURPOSE: We compared the calculated percent depth dose curves of 6 MeV electron beam to that of measured to evaluate the usefulness of Monte-Carlo simulation method in radiation physics. MATERIALS AND METHODS: The radiation dose values of 6 MeV electron beam using EGS4 code with one million histories in water were compared values that were measured form the depth dose curve of electron beam irradiated by medical accelerator ML6M. The central exis dose values were calculated according the changing field size, such as 5 X 5, 10 X 10, 15 X 15, 20 X 20 cm2. RESULTS: The value calculated showed a very similar shape to depth dose curve. The calculated and measured value of Dmax at 10 X 10cm2 cone is 15mm and 14mm respectively. The calculated value of the surface radiation dose rate is 65.52% and measured one is 76.94%. The surface radiation dose rate has vaied from 64.43% to 66.99. The calculated values of Dmax are in the range between 15mm and 18mm. The calculated value was fitted well with measured value around the Dmax area, excluding build up range and below the 90% depth dose area. CONCLUSION: This result suggested that the calculation of dose value can be replace the direct measurement of the dose for radiation therapy. Also, EGS4 may be a very convenient program to assess the effect of radiation dose using by personal computers.

Calibration and Radiation Survey of High Dose Rate Remote Afterloading System / 대한치료방사선과학회지

High Dose Rate Remote Afterloading system was installed at Wonkwang Universi-ty Hospital in January 1994. In this report, the calibration of a Gammamed 12-i High Dose Rate Remote Afterloading system and the radiation survey around the facility after design and construct a shieding room are discussed. The radiation survey of the facility indicates that the use of ordinary concrete shielding of existing room will provide adequate shielding. Also, the methodologies for performing source calibra-tion are presented.