Wedge Filters Research Articles

Assessment of Radiation Dose from Radioactive Wedge Filters during High-Energy X-Ray Therapy

This paper evaluated the amount of radiation generated by wedge filters during radiation therapy using a high-energy linear accelerator, and the dose to the worker during wedge replacement. After 10-MV photon beam was irradiated with wedge filter, the wedge was removed from the linear accelerator, and the dose rate and energy spectrum were measured. The initial measurement was approximately 1 uSv/h, and the radiation level was reduced to 0.3 uSv/h after 6 min. The effective half-life derived from the dose rate measurement was approximately 3.5 min, and the influence of AI-28 was about 53%. From the energy spectrum measurements, a peak of 1,799 keV was measured for AI-28, while the peak for Co-58 was not measured in the control room. The peaks for Au-106 and Cd-105 were found only measurement was done without wedge removement from the linear accelerator. The additional doses received by the radiation worker during wedge replacement were estimated to be 0.08−0.4 mSv per year.

Penumbral Dose Characteristics of Physical and Virtual Wedge Profiles

Purpose: Both physical and virtual wedges are used in radiotherapy to get uniform and desired dose distribution in clinical setting. All linear accelerators of different venders have computer controlled dynamic wedges called virtual wedge filters. Penumbra is one of the important photon beam characteristics needed to be understood in radiation therapy at the time of commissioning of Treatment Planning system (TPS) as well as applying various treatment planning algorithms in clinical applications. In this study we measured the dose profiles of open field, physical wedges (PW) and virtual wedges (VW) for energies (6 MV & 15 MV), various field sizes (10 × 10, 15 × 15 & 20 × 20 cm2), depths (dmax, 10 cm, 20 cm) and wedge angles (15°, 30°, 45° and 60°). From beam profile we calculated the penumbral width for open and wedged fields. The study was carried out on Siemens ONCOR IMRT Plus linear accelerator. The obtained penumbral width of PW and VW of all wedge angles was subtracted from the penumbral width of open field. The deviations in penumbral width were compared and statistically analyzed as a function of energy, depth, field size and wedge angles. Material and Method: The penumbral width was measured using IBA CC13 ion chamber in IBA Blue phantom (a 3D water phantom). The source to surface distance (SSD) during our study was kept 100cm and measurement was taken for 10 × 10, 15 × 15, 20 × 20 cm2 field sizes and for 15°, 30°, 45°, 60° wedges. These measurements were taken for both 6 MV and 15 MV photon energies. Virtual wedge profiles were acquired using LDA-99 linear detector array (IBA, Germany). The deviations in penumbral width for both PW and VW were calculated by subtracting the penumbral width from open field penumbral width in gun direction (in-plane) and deviation in VW penumbral width, and were obtained by subtracting the open field penumbral width in left-right direction (cross-plane) direction. The measured deviations were plotted for both PW and VW. Statistics on the measured deviations was performed by using SPSS Version 15. Results & Conclusion: The results of one way ANOVA (Analysis of Variance) show that the deviations are significant with energy and the deviations are higher in lower energy than higher energy. The deviations increase as depth increases, the deviations are also significant with depth. The deviations increase with field sizes; the deviations as a function of field size are highly significant. The deviations are higher in PW than VW but the deviations with wedge type are in-significant. As wedge angle increases, deviations also increase and the effect of wedge angle is highly significant on deviations.

P34. Configuration, validation and evaluation of the dose calculation algorithm Acuros XB

Purpose The purpose of this study is to implement dosimetric data libraries in a dose calculation algorithm Acuros XB (developed by Varian) in a treatment planning system, to validate the libraries and evaluate the performances of the algorithm with several tests in order to be used in the radiotherapy department. Materials and Methods Acuros XB (AXB) is implanted in the Eclipse TPS Version 10. The methodology used is that of the ESTRO booklet n°7 for the calculation of dose and monitor units (MU) with several levels of tests (level 1, 2 and 3 for static techniques, non-IMRT photon beams and one test with RapidArc technique). Level 1 tests assess AXB in simple configurations (square, rectangular fields) in absolute and relative dose, level 2 tests verify the accuracy consideration of beams modifiers (wedge filters, asymmetric fields), Level 3 tests, using the quality index methodology assess the modeling of the dose distribution with heterogeneity and scatter dose (small complex fields, thin central block) for 6 and 15 MV. Finally a test assesses AXB performances in a complex configuration (small fields, variation of dose rate, MLC movement) with the RapidArc technique. Dose calculations made by AXB on the Eclipse TPS are comparing to measurements which are the references in the same conditions. The tolerances fixed are those presented in the reports of the ESTRO 7 (static techniques, non-IMRT) and ESTRO 9 (IMRT and RapidArc). Main Results and Discussion The calculations made by AXB are in agreement with the measurements for all tests level. Some differences are observed, their number is nevertheless low. Differences between the calculations and measurements are observed at the interface water–air interface; however, they are less important than those observed in AAA and PBC. Conclusion and Discussion Acuros XB models and calculates accurately the dose in simple configurations, with modifiers beams, and with the presence of heterogeneities for static irradiation techniques, and also with a more complex configuration with the RapidArc technique. Acuros XB can be used as a dose calculation algorithm in the Eclipse TPS at the radiotherapy department of the Institut Curie Paris.

Characterization of Al2O3 optically stimulated luminescence films for 2D dosimetry using a 6 MV photon beam

This work evaluates the dosimetric properties of newly developed optically stimulated luminescence (OSL) films, fabricated with either Al2O3:C or Al2O3:C,Mg, using a prototype laser scanning reader, a developed image reconstruction algorithm, and a 6 MV therapeutic photon beam. Packages containing OSL films (Al2O3:C and Al2O3:C,Mg) and a radiochromic film (Gafchromic EBT3) were irradiated using a 6 MV photon beam using different doses, field sizes, with and without wedge filter. Dependence on film orientation of the OSL system was also tested. Diode-array (MapCHECK) and ionization chamber measurements were performed for comparison. The OSLD film doses agreed with the MapCHECK and ionization chamber data within the experimental uncertainties (<2% at 1.5 Gy). The system background and minimum detectable dose (MDD) were <0.5 mGy, and the dose response was approximately linear from the MDD up to a few grays (the linearity correction was <10% up to ~2–4 Gy), with no saturation up to 30 Gy. The dose profiles agreed with those obtained using EBT3 films (analyzed using the triple channel method) in the high dose regions of the images. In the low dose regions, the dose profiles from the OSLD films were more reproducible than those from the EBT3 films. We also demonstrated that the OSL film data are independent on scan orientation and field size over the investigated range. The results demonstrate the potential of OSLD films for 2D dosimetry, particularly for the characterization of small fields, due to their wide dynamic range, linear response, resolution and dosimetric properties. The negligible background and potential simple calibration make these OSLD films suitable for remote audits. The characterization presented here may motivate further commercial development of a 2D dosimetry system based on the OSL from Al2O3:C or Al2O3:C,Mg.

Radiation treatment of patients with cardiac pacemaker: Wedge type effect estimation

Introduction An increasing number of pacemaker patients are receiving radiotherapy in various sites in our department. The need hence arises to accurately determine the radiation burden of pacemaker devices for radiotherapy patients, given the limited tolerance of such devices reported by manufacturers and select the best treatment parameters during the design of their treatment plan. Purpose This study aims to investigate the dependence of pacemaker dose on the type of wedge filter implemented in the radiotherapy machine, comparing the effect of dynamic wedges of various angles to the effect of the universal motorized wedge. Materials and methods In this study two different linear accelerators were used. All measurements were performed with 6 MV photon beams, at a range of distances from the field centre, for wedged and open beams. Dose was measured for dynamic wedges 15°, 30°, 45° and 60° and corresponding motorized wedge angles, for various wedge orientations. Moreover, the above estimated doses were compared with the data from two different treatment planning systems. Results The effect of the wedge filter can elevate the pacemaker dose significantly compared to that of an open field. Comparing the wedge designs measured in this study, the use of a dynamic wedge decreases the pacemaker burden. The pacemaker estimated dose from treatment planning systems diverged from the measured values. Conclusion This study provides data about the pacemaker exposure for different wedge systems. Furthermore, the treatment planning system’s dose estimation errors can not be neglected.

Determination of an Effective Wedge Angle by Combination of Two Arbitrary Universal Wedge Fields in Radiation Therapy of Cancer Patients with Megavoltage Photon Beams.

Wedge filters are commonly used in radiation oncology for eliminating hot spots and creating a uniform dose distribution in optimizing isodose curves in the target volume for clinical aspects. These are some limited standard physical wedges (15°, 30°, 45°, 60°),or creating an arbitrary wedge angle, like motorized wedge or dynamic wedge,... The new formulation is presented by the combination of wedge fields for determining an arbitrary effective wedge angles. The isodose curves also are derived for these wedges. we performed the dosimetry of Varian Clinac 2100C/D with Scanditronix Wellhofer water blue phantom, CU500E, OmniPro - Accept software and 0.13cc ionization chamber for 6Mv photon beam in depth of 10cm (reference depth) for universal physical wedges (15°, 30°, 45°, and 60°) and reference field 10x10cm2. By combining the isodose curve standard wedge fields with compatible weighting dose for each field, the effective isodose curve is calculated for any wedge angle. The relation between a given effective wedge angle and the weighting of each combining wedge fields was derived. A good agreement was found between the measured and calculated wedge angles and the maximum deviation did not exceed 3°. The difference between the measured and calculated data decreased when the combined wedge angles were closer. The results are in agreement with the motorized single wedge appliance in the literature. This technique showed that the effective wedge angle that is obtained from this method is adequate for clinical applications and the motorized wedge formalism is a special case of this consideration.

In vivo skin dose measurement in breast conformal radiotherapy.

Aim of the studyAccurate skin dose assessment is necessary during breast radiotherapy to assure that the skin dose is below the tolerance level and is sufficient to prevent tumour recurrence. The aim of the current study is to measure the skin dose and to evaluate the geometrical/anatomical parameters that affect it.Material and methodsForty patients were simulated by TIGRT treatment planning system and treated with two tangential fields of 6 MV photon beam. Wedge filters were used to homogenise dose distribution for 11 patients. Skin dose was measured by thermoluminescent dosimeters (TLD-100) and the effects of beam incident angle, thickness of irradiated region, and beam entry separation on the skin dose were analysed.ResultsAverage skin dose in treatment course of 50 Gy to the clinical target volume (CTV) was 36.65 Gy. The corresponding dose values for patients who were treated with and without wedge filter were 35.65 and 37.20 Gy, respectively. It was determined that the beam angle affected the average skin dose while the thickness of the irradiated region and the beam entry separation did not affect dose. Since the skin dose measured in this study was lower than the amount required to prevent tumour recurrence, application of bolus material in part of the treatment course is suggested for post-mastectomy advanced breast radiotherapy. It is more important when wedge filters are applied to homogenize dose distribution.

Visual Outcomes of Parapapillary Uveal Melanomas Following Proton Beam Therapy

In parapapillary melanoma patients, radiation-induced optic complications are frequent and visual acuity is often compromised. We investigated dose-effect relationships for the optic nerve with respect to visual acuity after proton therapy. Of 5205 patients treated between 1991 and 2014, those treated using computed tomography (CT)-based planning to 52 Gy (prescribed dose, not accounting for relative biologic effectiveness correction of 1.1) in 4 fractions, with minimal 6-month follow-up and documented initial and last visual acuity, were included. Deterioration of ≥0.3 logMAR between initial and last visual acuity results was reported. A total of 865 consecutive patients were included. Median follow-up was 69 months, mean age was 61.7 years, tumor abutted the papilla in 35.1% of patients, and tumor-to-fovea distance was ≤3 mm in 74.2% of patients. Five-year relapse-free survival rate was 92.7%. Visual acuity was ≥20/200 in 72.6% of patients initially and 47.2% at last follow-up. A wedge filter was used in 47.8% of the patients, with a positive impact on vision and no impact on relapse. Glaucoma, radiation-induced optic neuropathy, maculopathy were reported in 17.9%, 47.5%, and 33.6% of patients, respectively. On multivariate analysis, age, diabetes, thickness, initial visual acuity and percentage of macula receiving 26 Gy were predictive of visual acuity. Furthermore, patients irradiated to ≥80% of their papilla had better visual acuity when limiting the 50% (30-Gy) and 20% (12-Gy) isodoses to ≤2 mm and 6 mm of optic nerve length, respectively. A personalized proton therapy plan with optic nerve and macular sparing can be used efficiently with good oncological and functional results in parapapillary melanoma patients.

Variations in the Dose Profiles of Physical and Virtual Wedge Filters of ONCOR Linear Accelerator

PurposeIn this study, we measured the dose profiles of physical wedges (PWs) and virtual wedges (VW) for photon energies (6 MV and 15 MV), various field sizes (10 × 10, 15 × 15, and 20 × 20 cm2), depths (dmax, 10 cm, 20 cm), and wedge angles (15°, 30°, 45°, and 60°). This study was performed using a Siemens ONCOR IMRT Plus linear accelerator. The acquired dose profiles of PW and VW were compared and statistically analyzed. Materials and MethodsThe dose profiles were measured using IBA CC13 ion chamber in IBA Blue phantom (a three-dimensional water phantom). The source-to-surface distance was kept 100 cm and measurements were taken for 10 × 10, 15 × 15, and 20 × 20 cm2 field sizes and for 15°, 30°, 45°, and 60° PWs. These measurements were taken for both 6 MV and 15 MV photon energies. VW profiles were obtained using LDA-99 linear detector array (IBA, Germany). The percent off-axis dose difference between PW and VW profiles were calculated, analyzed, and plotted. Statistics on the measured data was applied using SPSS version 13. Results and ConclusionThe percent dose difference between PW and VW beam profiles were calculated at different off-axis positions. These dose variations increased in the wedge direction (toe region), but were negligible in the nonwedge direction. The results of one-way analysis of variance show that the dose variation between PW and VW are significant with off-axis positions, wedge angles, and depth, but are statistically nonsignificant with energy and field sizes. These variations could produce abnormal doses, especially in large field sizes and wedge angles in clinical applications, which could be avoided by understanding the behavior of wedge profiles and comparing the calculated (from treatment planning system) and measured (actual) doses.

선형가속기의 선량율에 따른 쐐기필터의 선량분포

This study is aimed at assessing whether dynamic wedge filters are appropriate to be used instead of physical wedge filters. The X-ray energy generated from linear accelerator is commercialize 6 MV and 10 MV. 15°, 30°, 45°, and 60° of physical wedge filter was irradiated by dose rate 100, 200, 300, 400, 500, and 600 MU/min for each angle and for comparison with a dynamic wedge filter, irradiate 96 times under the same conditions. The measurement conditions are as 100 ㎝ source-film distance and 10 × 10 ㎝ irradiated surface. A developed film was scanned and analyzed after a calibration through a dose analysis program and the dose rate was compared after calculating the standard deviation. Dynamic wedge filters make dose, scattered rays and treatment time reduced and very useful due to less irradiated doses to patients. The errors at each dose rate under the same conditions were irrelevant. Thus, treatment based on a high dose rate depending on the patient is expected to be feasible. Keyword : radiation therapy, linear accelerator, wedge filter, dynamic wedge filter, physical wedge filter

유방암 수술기법에 따른 방사선치료계획 기법의 선택

Techniques, using physical wedge filter and using dynamic wedge filter and FIF(Field in Field) and ISCT(Irregular Surface Compensating Technique), have been developed according to progress of radiation therapy of breast cancer. Measurement of dose was done to judge the usefulness of technique using three cases, non tissue loss after breast conserving operating and tissue loss after breast conserving operating and mastectomy. Dose indexes of breast tissue, CI (Conformity Index), HI (Homogeneity Index) and QOC (Quality of Coverage), dose index of skin, or dose indexes of lung, volume of 50 percent dose and 20 percent dose were estimated and compared. Using dynamic wedge filter is useful plan at non tissue loss allowing for high dose of lung. FIF and ISCT are useful plan at tissue loss. ISCT is useful plan at mastectomy. Henceforth, we need to apply to valid plan and body type and thorax size.

A set of patient and staff dose data for validation of Monte Carlo calculations in interventional cardiology.

The purpose of this paper is to report a set of experimental values of patient and staff doses in a cardiac catheterisation laboratory using the range of radiographic and geometric parameters from routine clinical practice. The data obtained will be available for validation of Monte Carlo calculations and for training purposes. They will also help optimise radiation protection for patients and staff. Experimental measurements were made with an anthropomorphic phantom, and a monoplane flat detector-based X-ray system was used for interventional cardiology procedures. Standard operational protocols used in clinical practice were applied. Around 1000 patient dose and 5000 staff dose values were measured for different operational conditions (angulations, distances, collimation and wedge filter, magnification, phantom thicknesses, using Copper absorber, etc.). Uncertainties were also estimated. Increase factors of 3-10 for patients and staff doses were measured for the different C-arm angulations.

Measurement and comparison of head scatter factor for 7 MV unflattened (FFF) and 6 MV flattened photon beam using indigenously designed columnar mini phantom

AimTo measure and compare the head scatter factor for 7MV unflattened and 6MV flattened photon beam using a home-made designed mini phantom. BackgroundThe head scatter factor (Sc) is one of the important parameters for MU calculation. There are multiple factors that influence the Sc values, like accelerator head, flattening filter, primary and secondary collimators. Materials and methodsA columnar mini phantom was designed as recommended by AAPM Task Group 74 with high and low atomic number material for measurement of head scatter factors at 10cm and dmax dose water equivalent thickness. ResultsThe Sc values measured with high-Z are higher than the low-Z mini phantoms observed for both 6MV-FB and 7MV-UFB photon energies. Sc values of 7MV-UFB photon beams were smaller than those of the 6MV-FB photon beams (0.6–2.2% (Primus), 0.2–1.4% (Artiste) and 0.6–3.7% (Clinac iX (2300CD))) for field sizes ranging from 10cm×10cm to 40cm×40cm. The SSD had no influence on head scatter for both flattened and unflattened beams. The presence of wedge filters influences the Sc values. The collimator exchange effects showed that the opening of the upper jaw increases Sc irrespective of FF and FFF. ConclusionsThere were significant differences in Sc values measured for 6MV-FB and unflattened 7MV-UFB photon beams over the range of field sizes from 10cm×10cm to 40cm×04cm. Different results were obtained for measurements performed with low-Z and high-Z mini phantoms.

Photonic crystal wedge as a tunable multichannel filter

Abstract Tunable multichannel filtering properties of a one-dimensional photonic crystal wedge constructed from two one-dimensional photonic crystals are demonstrated theoretically. Using the transfer matrix method, it is shown that the filtering properties, including the frequency and number of channels, can be tuned by adjusting the lateral position of the incident beam, the incident angle and the apex angle of the wedge. The angular response of the PC wedge filter is also analyzed.

Scale invariant texture representation based on frequency decomposition and gradient orientation

This paper proposes an effective scale invariant texture representation based on frequency decomposition and gradient orientation. First, the image intensities are decomposed into different orientations by using wedge filters in the frequency domain, and the N-nary coding method is adopted for the vector quantization. Second, the scale invariant gradient orientation is generated by selecting the most stable value of the gradient orientation with different Gaussian scales. Finally, the 2D joint distribution of the two types of local descriptors is used as the representation. The performance was evaluated on texture classification using a nearest neighbor classifier. Simple but not ordinary, our method achieves state of the art classification performance on the KTH-TIPS dataset under the traditional experimental design. Moreover, the main experiments were conducted on the KTH-TIPS and KTH-TIPS2-b datasets with the experimental designs of scale invariance validation. Compared with the methods of basic image features (BIFs) and local energy pattern (LEP), the proposed representation achieves superior performance with much lower dimension of representation.

Measuring the Evolution of Mass Density Distribution of Wire Explosion

Wire explosion is the initial stage of the development of wire array Z-pinch load driven by high pulsed current. Based on the pulsed power generator PPG-1 (400 kA/100 ns), the process of 10-μm-W wire explosion at tens of kiloamperes was investigated. The time sequence images of wire explosion were obtained by X-ray backlighting with X-pinch X-ray point source, and the mass density distribution of the exploding wire at a certain time was calibrated by method of grayscale contrast based on a particular step wedge filter. By image processing of the time sequence images of wire explosion, the evolution of mass density distribution of wire explosion was presented.

SU‐E‐CAMPUS‐T‐05: Preliminary Results On a 2D Dosimetry System Based On the Optically Stimulated Luminescence of Al2O3

Purpose:To develop a precise 2D dose mapping technique based on the optically stimulated luminescence (OSL) from Al2O3 films for medical applications.Methods:A 2D laser scanning reader was developed using fast F+‐center (lifetime of &lt;7 ns) and slow F‐center (lifetime of 35 ms) OSL emission from newly developed Al2O3 films (Landauer Inc.). An algorithm was developed to correct images for both material and system properties. Since greater contribution of the F??‐center emission in the recorded signal increases the readout efficiency and robustness of image corrections, Al2O3:C,Mg film samples are being investigated in addition to Al2O3:C samples. Preliminary investigations include exposure of the films to a 6 MV photon beam at 10 cm depth in solid water phantom with an SSD of 100 cm, using a 10 cm × 10 cm flat field or a 4 cm × 4 cm field with a 60° wedge filter. Kodak EDR2 radiographic film and EBT2 Gafchromic film were also exposed for comparison.Results:The results indicate that the algorithm is able to correct images and calculate 2D dose. For the wedge field irradiation, the calculated dose at the center of the field was 0.9 Gy for Al2O3:C and 0.87 Gy for Al2O3:C,Mg, whereas, the delivered dose was 0.95 Gy. A good qualitative agreement of the dose profiles was obtained between the OSL films and EDR2 and EBT2 films. Laboratory tests using a beta source suggest that a large dynamic range (10−2−102 Gy) can be achieved using this technique.Conclusion:A 2D dosimetry system and an in‐house image correction algorithm were developed for 2D film dosimetry in medical applications. The system is in the preliminary stage of development, but the data demonstrates the feasibility of this approach. This work was supported by Landauer, Inc.

Geometrical determinations of IMRT photon pencil-beam path in radiotherapy wedges and limit divergence angle with the Anisotropic Analytic Algorithm (AAA)

Purpose: Static wedge filters (WF) are commonly used in radiation therapy, forward and/or inverse planning. We calculated the exact 2D/3D geometrical pathway of the photon-beam through the usual alloy WF, in order to get a better dose related to the beam intensity attenuation factor(s), after the beam has passed through the WF. The objective was to provide general formulation into the Anisotropic Analytical Algorithm (AAA) model coordinates system (depending on collimator/wedge angles) that also can be applied to other models. Additionally, second purpose of this study was to develop integral formulation for 3D wedge exponential factor with statistical approximations, with introduction for the limit angle/conformal wedge. Methods : The radiotherapy model used to develop this mathematical task is the classical superposition-convolution algorithm, AAA (developed by Ulmer and Harder). We worked with optimal geometrical approximations to make the computational IMRT calculations quicker/reduce the planning-system time. Analytic geometry/computational-techniques to carry out simulations (for standard wedges) are detailed/developed sharply. Integral developments/integral-statistical approximations are explained. Beam-divergence limit Angle for optimal wedge filtration formulas is calculated/sketched, with geometrical approximations. Fundamental trigonometry is used for this purpose. Results: Extent simulation tables for WF of 15o, 30o, 45o, and 60o are shown with errors. As a result, it is possible to determine the best individual treatment dose distribution for each patient. We presented these basic simulations/numerical examples for standard manufacturing WF of straight sloping surface, to check the accuracy/errors of the calculations. Simulations results give low RMS/Relative Error values (formulated) for WF of 15o, 30o, 45o, and 60o. Conclusion : We obtained a series of formulas of analytic geometry for WF that can be applied for any particular dose delivery model. Simulations results gave acceptable trigonometrical approximations/data that can be used for LINAC applications/planning-system software. The integral formulas presented are practical for dose delivery calculations/3D-approximations when using WF/other similar types of beam modification devices. Limit angle formulation and conformal wedge concept was also presented. Cite this article as: Casesnoves F. Geometrical determinations of IMRT photon pencil-beam path in radiotherapy wedges and limit divergence angle with the Anisotropic Analytic Algorithm (AAA). Int J Cancer Ther Oncol 2014; 2 (3):02031. DOI: 10.14319/ijcto.0203.1

Characterization of GaN dosimetry for 6 MV photon beam in clinical conditions

We characterized a recently proposed implantable GaN-based dosimeter in clinical conditions, for its application in external radiotherapy according to ESTRO (European Society for Radiotherapy & Oncology) practical guidelines. Our studies were carried out using a 6 MV photon beam with the dosimeter under test in a water tank or a PMMA phantom. They were focused on evaluating short term and long term reproducibility of measurements, and assessing the effects of parameters such as field size, source-skin distance, use of wedge filter, beam incidence, dose rate, accumulated dose, GaN-induced dose perturbation, air cavities and temperature. The estimated repeatability and reproducibility are better than 0.5% and 2% at 1σ respectively. There are no significant effects of the parameters under our studies, apart from field size and temperature. The field-size dependence is due to over-compensation of the GaN response method of the dosimeter, the resulting errors remain lower than 5% for field sizes up to 10 × 10 cm2. The temperature dependence mainly results from the GaN luminescence properties, and causes the GaN response to decrease steadily when increasing temperature, with a sensitivity of −1.4%/°C. The observed quasi-linear temperature dependence may facilitate the correction to improve the accuracy of measurements.

Chemoradiotherapy for highly advanced gastric cancer.

121 Background: Although the prognosis of early gastric cancer is favorable, the treatment for advanced cases still have difficulty in achieving satisfactory results. Thus, more effective multimodality treatment should be established. Chemoradiotherapy has become a standard treatment for gastric cancer especially as an adjuvant therapy while radiotherapy has been expected as one of the modalities against highly advanced gastric cancer. Methods: Patients with advanced gastric cancer who were treated with chemotherapy of S-1 and cisplatin plus radiation were analyzed retrospectively. Concurrent radiation therapy (5 days/week) at 2 Gy/day was started with chemotherapy and repeated daily on days 1–5, 8–12, 15–19 and 22–26. Irradiation was planned using a computed tomography (CT) simulator for two rectangular portals with a pair of 45-degree wedge filters and was targeted at the primary tumor and surrounding lesions, including lymph nodes. Results: A total 109 patients were treated with chemoradiotherapy between 2002 and 2013 at our institute. The median age was 64 years. Histological type included 45 differentiated and undifferentiated 64 subtypes. The TNM stage before the treatment was diagnosed as IIIA: 11; IIIB: 10; IIIC: 14; IV: 74. Of the 98 evaluable patients, 69 patients had partial responses while no patients had a complete response, resulting in an overall response rate of 70%. Progressive disease (PD) occurred in 2 patients (4%). The most frequent adverse events more than grade 3 were hematologic toxicities, including leukocytopenia (47%), neutropenia (25%), and thrombocytopenia (24%). Non-hematologic toxicities such as general fatigue, renal-related events, and gastrointestinal toxicities were manageable with no treatment-related death. The median survival time was 537 days. Conclusions: While there were disadvantages of radiotherapy including the difficulty of confirming the area of irradiation due to peristaltic movement, risk of perforation and ulceration, recent technological advancement of radiation therapy has enabled pinpoint accuracy in treatment of primary gastric lesions and regional lymph nodes. There has been much anticipation that chemoradiotherapy will be a part of multidisciplinary treatment for advanced cancer.