Dosimetric measurement of scattered radiation for simulated head and neck radiotherapy with homemade oral phantom.

During radiotherapy for head and neck tumours, the oral cavity and cheek area would be inevitably exposed to high energy radiation; thus, the material surface of the teeth, dental restorations with high atomic number, or alloy prosthodontics would generate backscatter electrons that cause the buccal mucosa adjacent to these materials to receive localized high dose enhancement, which primarily leads to side effects or oral mucositis. Based on the size of the adult oral cavity, this study aimed to use acrylic resin to create an oral phantom with two grooves on the left and right sides for placement of three molars. Moreover, the distance between the inner cheek and the side surface of the teeth could be accurately adjusted every 1 mm from 0 to 5 mm. This enhanced the dose in the buccal mucosa during head and neck radiotherapy and made the distribution measurement of the radiation dose simple and feasible at different depths (0-5 mm). Meanwhile, the study employed the film type optically stimulated luminescent dosimeter with a thickness of 0.3 mm to measure the absorbed dose inside the buccal mucosa to reduce the dose interference from radiotherapy. The study fixed three real molars in a row located at the left side of the phantom and employed 6 MV photons and intensity-modulated radiotherapy (IMRT) to treat and simulate oral cancer and measure the attenuation of the molar's backscatter dose from 0 to 5 mm in an up beam direction. The result showed that, in every 3 mm, the phantom had attenuated the enhancement of backscatter dose <3%. The irradiation dose enhancement in a single direction was twice higher than that through IMRT 7 field treatment. These measurement results were consistent with the results of previous studies.

Evaluating the Radiation From Accidental Exposure During a Nondestructive Testing Event.

Industrial radiography is a common nondestructive testing (NDT) method used in various industries. An investigation was conducted for a 1999 incident in Taiwan where two workers (Operators A and B) were accidently exposed to an unshielded Ir source while conducting industrial radiography. Operators A and B experienced acute close-range radiation exposure to a source of Ir for 3 h at a strength of 2.33 × 10 Bq. The health of mammary glands, bone marrow, thyroid glands, eyes, and genital organs of these two workers after radiation exposure was examined. Subsequently, Operator A experienced severe radiation injury, including tissue necrosis and keratinization in the fingers, chromosomal abnormalities, reduced blood cell count, diffuse hyperplasia of the thyroid gland, opaque spots in the crystalline lens, and related radiation effects. The results showed that the left index finger and thumb, eyes, and gonads of Operator A were exposed to a radiation dose of about 369-1,070, 23.1-67.4, 2.4-5.3, and 4.2-11.6 Gy, respectively. Effective dose for Operator A was estimated to range from 6.9 to 18.9 Sv. The left fingers, thumb, eyes, and gonads of Operator B were exposed to a radiation dose of 184.9-646.2, 11.8-40.7, 0.49-3.33, and 0.72-7.18 Gy, respectively, and his effective dose was between 2.5 and 11.5 Sv. This accident indicated a major flaw in the control and regulation of radiation safety for conducting NDT industrial radiography in 1999; however, similar problems still exist. Modifications of the Ionizing Radiation Protection Act in Taiwan are suggested in this study to regulate the management of NDT industries, continually educate the NDT workers in radiation safety, and enact notification provisions for medical care systems toward acute radiation exposure events.

Investigation of photoneutron dose equivalent from high-energy photons in radiotherapy.

Spatial distribution of photoneutron dose equivalent during radiotherapy at different beam size, depth, and distance from a 15 MV linear accelerator was investigated with bubble detectors in a water phantom. The photoneutron dose equivalent was mainly from fast neutrons, and decreased with distance at a fixed field and with depth. Besides, photoneutron dose equivalent was slightly affected by beam size due to the variation of tungsten area exposed in the beam direction and photoneutrons occurred at the jaws. Fast photoneutron dose equivalent of shallow critical organs was represented still considerably outside the beam size.

Three-dimensional conformal radiation therapy for unresectable hepatocellular carcinoma patients who had failed with or were unsuited for transcatheter arterial chemoembolization.

BACKGROUND: The purpose of our study was to evaluate the outcome of unresectable hepatocellular carcinoma (HCC) patients, who had either failed with or were unsuited for transcatheter arterial chemoembolization (TACE), treated with three-dimensional conformal radiation therapy (3DCRT) and to determine the prognostic outcome factors. METHODS: From September 1999 to March 2003, 44 patients with unresectable HCC underwent 3DCRT. Thirty-seven patients were male and seven female. Mean age was 62 years, ranging from 34 to 88. Eastern Cooperative Oncology Group (ECOG) performance status was 0 in 10 patients, 1 in 19 patients, and 2 in 15 patients. According to Child-Pugh classification for cirrhosis of the liver, 32 patients were in class A and 12 patients in class B. There were 14 patients with main portal vein thrombosis. Twenty patients had alpha-fetoprotein (AFP) level >400 ng/ml. Tumor size was <5 cm in 16 patients, 5-10 cm in 16 patients, and >10 cm in 12 patients. Thirty-two patients had tumors of confluent type, the remaining patients presented a single hepatic tumor. Serum hepatitis antigen markers were positive for type B in 35 patients and type C in nine patients. Twenty-one patients had Okuda Stage I, 22 patients Stage II, and one patient Stage III. According to the AJCC staging system (5th edition), eight patients were in Stage II (T2N0M0), 19 in Stage IIIA (T3N0M0) and 17 in Stage IVA (T4N0M0). RESULTS: An objective response was observed in 27 of 44 patients, giving a response rate of 61.4%. The survival rates at 1, 2 and 3 years were 60.5%, 40.3% and 32.0%, respectively. In the analysis of prognostic factors, Okuda stage, AJCC stage, portal vein thrombosis, pretreatment AFP level, and total dose of radiotherapy all had significant impact on survival. CONCLUSIONS: 3DCRT induced a substantial tumor response rate of 61.4% with survival rates at 1, 2 and 3 years of 60.5%, 40.3% and 32.0%, respectively, and a median survival time of 15.2 months in patients with unresectable HCC who had either failed with or were unsuited for TACE. The complications are acceptable and can be managed with conservative treatment. Although we do not know whether there is a survival benefit through the use of this treatment, 3DCRT seems to be a practical method of salvage for this subset of patients. Further study is warranted to evaluate the survival of such patients with and without this treatment.

Prognostic factors affecting the outcome of nasopharyngeal carcinoma.

BACKGROUND: The aim of the study is to evaluate patients with nasopharyngeal carcinoma treated with multisegmental intensity-modulated radiotherapy with or without chemotherapy and analyze patient, tumor and treatment characteristics, determining outcome. METHODS: From June 1999 through to April 2003, we treated in our institution 83 patients with nasopharyngeal carcinoma, 70 males and 13 females, their ages ranging from 25 to 85 years (median, 48 years). Nineteen patients had T1 tumors, 35 had T2 tumors, six had T3 tumors and 23 had T4 tumors. Sixty-four patients had cervical lymph node metastasis. Twenty patients were treated with radiation therapy alone and 63 patients with concurrent chemoradiotherapy. Cumulative radiation dose to primary tumor ranged from 70.2 to 77.4 Gy (median, 75.6 Gy). Follow-up ranged from 3 to 41.53 months (median, 17 months). RESULTS: Local complete response was achieved in 81 patients (97.5%). Local failure was observed in two patients, nodal failure in one patient and systemic failure in 14 patients. Overall survival, disease-free survival and disease-specific survival were 83, 84 and 93%, respectively, at 1 year, 82, 74 and 88%, respectively, at 2 years and 82, 61 and 88%, respectively, at 3 years. In univariate analysis, T stage of disease was a significant predictor of disease-free survival favoring those with early-stage (T1 + T2) disease (P = 0.040). Cumulative radiation dose to primary tumor was a significant predictor of disease-specific survival favoring those with >75.6 Gy (P = 0.010). Stage of disease (P = 0.007), N-classification (P = 0.046) and cumulative dose to primary tumor (P = 0.046) were significant prognostic factors for overall survival. CONCLUSIONS: High locoregional control for nasopharyngeal carcinoma was achieved with multisegmental intensity-modulated radiotherapy. Distant metastases are still the main impact on survival. More effective chemotherapy regimens and other systemic agents are needed to decrease the rate of distant metastasis.

Study of induced thermoluminescence in CVD diamond film by low-energy X-rays.

For diamond film the one-hit model that is used to interpret low-energy X-ray thermoluminescence (TL) will require some modifications. After the films were irradiated with a superficial X-ray machine with different peak voltages, a two-compartment model with three parameters, the target size, the microscopic saturation factor and the high-LET saturation factor, was used to more precisely describe the TL response to X-ray with energies down to 10 kV. The microdosimetric distribution was calculated using single-event Monte Carlo code developed by authors together with EEDL cross-section data library. Some mechanistic insight into the physical aspect of radiation interaction with solid detectors can be obtained. The sensitive size in diamond was found to be about 15 nm. The saturation of one group of sublevels combined with the activation of another group of sublevels caused the relative efficiency to have a local minimum near 20 keV. The relative efficiency becomes higher below 10 keV, which is similar to the increasing relative biological effectiveness when the linear energy transfer passing through a biological system increases. The similarity made this material to be a molecular-scale dosimeter in the future.

Indoor light on thermoluminescence of CVD diamond film used as a high-energy photon dosimeter.

The effect of light on polycrystalline diamond film that was produced by chemical vapor deposition and is used as a thermoluminescent dosimeter should be considered, although some researchers have indicated that such an effect was theoretically unlikely to happen. A 15 min exposure to a normal desk light bulb induces significant thermoluminescence (TL) comparable to a 0.5 Gy exposure to high-energy photons. This light-induced TL will be saturated within 2 h. The saturated TL intensity depends on the frequency of the light and the blue light dominates. The TL peak area at a temperature of 605 K is insensitive to light but is sensitive to high-energy photons. Another peak at about 410 K is caused by light only, because the TL from the ionization radiation at the same location is bleached. The effect of light could be easily distinguished by a numerical or an experimental method. Lamps with a green lampshade or pure red lights are suggested for use as indoor light sources. To reduce the effect of light, pre-heating treatment before readout is also suggested.

Accuracy of the convolution/superposition dose calculation algorithm at the condition of electron disequilibrium.

Using Monte Carlo simulation and the convolution/superposition algorithm, this work examines percent depth dose curves of the central axis in an acrylic phantom (20 x 20 x 20 cm(3)) with variously sized air cavities (20 x 20 x 1.0, 20 x 20 x 2.0, 20 x 20 x 3.0, 20 x 20 x 4.0 and 20 x 20 x 4.95 cm(3) for study of longitudinal electron disequilibrium (ED) and 3.6 x3.6 x 4.95, 4.5 x 4.5 x 4.95, 5.4 x 5.4 x 4.95 and 20 x 20 x 4.95 cm(3) for study of lateral ED). Radiochromic film samples are also measured to verify the Monte Carlo results. The Monte Carlo simulation is performed using OMEGA/BEAM and DOSXYZ codes, and the convolution/superposition calculation relies on an ADAC commercial treatment planning system. Underestimating the dose kernel expansion leads to overestimating the dose of what was found in the air cavity of ED using the convolution/superposition algorithm. Consequently, the dose in the rebuild-up region is influenced. The influenced region is on the acrylic phantom surface to a depth of about 0.5 cm. The density scaling method of the convolution/superposition algorithm, applied to heterogeneous media, should be enhanced to account for the over-expansion of the dose kernel in the cavity of ED.

The effect of a metal hip prosthesis on the radiation dose in therapeutic photon beam irradiations.

Prostate and cervical cancer patients are often treated with external X-ray beams of bi-lateral incidence. Such treatment may incur some dose effect that cannot be predicted precisely in commercial treatment planning systems (TPS) for patients having undergone total hip replacement. This study performs a Monte Carlo (MC) simulation and an analytical calculation (convolution superposition algorithm which is implemented in ADAC TPS) of a 6 MV, 5 x 5 cm2 X-ray beam incident into water with the existence of hip prosthesis, e.g. Ti6A14V and CoCrMo alloy. The results indicate that ADAC TPS cannot precisely account for the scatter and backscatter radiation that a metal hip prosthesis causes. For percent depth dose (PDD) curves, the maximum underdosage of ADAC TPS up to 5mm above the interface between dense material and water is 5%, 20% and 27% for PDD(Bone), PDD(Ti) and PDD(Co), respectively. The dose re-buildup, which occurs behind the hip region, becomes more and more obvious for denser medium existed in water. Increasing inhomogeneity also enhances the underdosage of ADAC for greater depth (> 10cm), as the figures of nearly 2% in PDD(Bone), PDD(Ti) and 4-5% in PDD(Co) reveal. Overestimating the attenuated power of high-density non-water material in ADAC TPS causes this underdosage. For dose profiles, no significant differences were found in Profile(Bone) at any depth. Profile(Ti) reveals that MC slightly exceeds ADAC at off-axis position 1.0-2.0 cm. Profile(Co) reveals this more obviously. This finding means that scatter radiation from these denser materials is significant and cannot be predicted precisely in ADAC.

Surface dose with grids in electron beam radiation therapy.

This investigation attempts to solve the problem of the lack of skin-sparing effect in electron radiation therapy and to increase the tolerance of skin to radiation using the grid technique. Electron grid therapy involves the mounting of a Cerrobend grid in the electron cone. Film dosimetry was employed to measure the relative surface dose and the percentage depth dose profile of electron grid portals. Various grid hole diameters (d = 0.45, 1.0, 1.5 cm) and grid hole spacings (s = 0.4, 0.2 cm) were considered for electron beams from 6 to 14 MeV. Experimental results indicate that the electron grid technique can reduce the relative surface dose in electron radiation therapy. Degradations of the relative surface dose depend on the percentage of open area in the grid portal. A proper grid design allows the surface dose to be reduced and the range of nonhomogeneous doses to be limited to a depth at which the target volume can receive a homogeneous dose. The grid technique can lower the surface dose in electron radiation therapy.

Monte Carlo simulation of surface percent depth dose.

This work studied the surface percent depth dose of 6 and 15 MV X-rays, 10 x 10 cm2 and 20 x 20 cm2 fields by Monte Carlo simulation. The OMEGA/BEAM code, an EGS4 user code developed by the NRCC, was used. The linac, Siemens PRIMUS, was accurately modeled according to the ion chamber and CEA film measurement, and the phase space data generated from this linac were collected to simulate dose distribution in water. The water phantom had radius 30 cm and thickness 10 cm. The percent depth doses at zero depth, PDDsurface, for 6 MV X-rays were 13.85 +/- 0.11% and 23.21 +/- 0.20% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively. For 15 MV X-rays, PDDsurface values were 8.83 +/- 0.07% and 18.60 +/- 0.12% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively.