J Chung

Apoptotic death of photoreceptors in the streptozotocin-induced diabetic rat retina

Aims/hypothesisNeurodegenerative changes in the diabetic retina occurring before diabetic retinopathy could be inevitable by the altered energy (glucose) metabolism, in the sense that dynamic image-processing activity of the retinal neurons is exclusively dependent on glucose. We therefore investigated the morphological changes in the neural retina, including neuronal cell death, of a streptozotocin-induced model of diabetes.MethodsStreptozotocin was intravenously injected. Rats were maintained hyperglycaemic without insulin treatment for 1 week and 4, 8, 12, and 24 weeks, respectively. Diabetic retinas were processed for histology, electron microscopy, and immunohistochemistry using the TUNEL method.ResultsA slight reduction in the thickness of the inner retina was observed throughout the diabetic retinas and a remarkable reduction was seen in the outer nuclear layer 24 weeks after the onset of diabetes. The post-synaptic processes of horizontal cells in the deep invaginations of the photoreceptors showed degeneration changes from 1 week onwards. A few necrotic ganglion cells were observed after 4 weeks. At 12 weeks, some amacrine cells and a few horizontal cells showed necrotic features. Three to seven cellular layers in the outer nuclear layer and nerve terminals, rolled by the fine processes of the Müller cells near the somata of the degenerated ganglion cells, were apparent at 24 weeks. Apoptosis appeared in a few photoreceptor cells at 4 weeks, and the number of apoptotic photoreceptors increased thereafter.Conclusion/interpretationThese findings suggest that the visual loss associated with diabetic retinopathy could be attributed to an early phase of substantial photoreceptor loss, in addition to later microangiopathy.

Estimation of Coronary Flow Velocity Reserve Using Transthoracic Doppler Echocardiography and Cold Pressor Test Might Be Useful for Detecting of Patients with Variant Angina

Purpose: The cold pressor test (CPT) has been used to detect variant angina, but its sensitivity in predicting vasospasm is low. The aim of this study was to determine whether estimates of the coronary flow velocity reserve (CFVR) in the distal left anterior descending coronary artery (dLAD) using transthoracic echocardiography (TTE) and CPT are useful tool to predict variant angina. Methods: 65 patients (mean age = 52 ± 10 years; male:female = 41:24) who had normal coronary artery on angiography and underwent acetylcholine provocation test were enrolled and divided into the spasm group (n = 31) and the no spasm group (n = 34). During CPT, the peak (PDV) and mean diastolic flow velocity (MDV) of the dLAD were estimated using TTE with a high‐frequency transducer, and electrocardiography, blood pressures, heart rate, and symptoms were monitored every 30 seconds. CPT%PDV and CPT%MDV were defined as the percentage changes in PDV and MDV during CPT, respectively. Results: CPT%PDV was 4.99 ± 23.62% in the spasm group and 52.75 ± 24.78% in the no spasm group (P < 0.001). CPT%MDV was 6.83 ± 23.81% in the spasm group and 50.22 ± 27.83% in the no spasm group (P < 0.001). CPT%PDV<31.1% had a sensitivity of 93.5% and a specificity of 82.4% in predicting variant angina (95% confidence interval [CI]: 0.939–0.979, P < 0.001). CPT%MDV<30.55% had a sensitivity of 90% and a specificity of 76.5% in predicting variant angina (95% CI: 0.884–0.950, P < 0.001). Conclusion: The measurement of changes in the coronary flow velocity of the dLAD using TTE and CPT might be useful for the estimation of endothelial dysfunction in patients with variant angina. (ECHOCARDIOGRAPHY 2010;27:435‐441)

SU-E-T-800: Verification of Acurose XB Dose Calculation Algorithm at Air Cavity-Tissue Interface Using Film Measurement for Small Fields of 6-MV Flattening Filter-Free Beams

Purpose: To verify the dose accuracy of Acuros XB (AXB) dose calculation algorithm at air-tissue interface using inhomogeneous phantom for 6-MV flattening filter-free (FFF) beams. Methods: An inhomogeneous phantom included air cavity was manufactured for verifying dose accuracy at the air-tissue interface. The phantom was composed with 1 and 3 cm thickness of air cavity. To evaluate the central axis doses (CAD) and dose profiles of the interface, the dose calculations were performed for 3 × 3 and 4 × 4 cm2 fields of 6 MV FFF beams with AAA and AXB in Eclipse treatment plainning system. Measurements in this region were performed with Gafchromic film. The root mean square errors (RMSE) were analyzed with calculated and measured dose profile. Dose profiles were divided into inner-dose profile (>80%) and penumbra (20% to 80%) region for evaluating RMSE. To quantify the distribution difference, gamma evaluation was used and determined the agreement with 3%/3mm criteria. Results: The percentage differences (%Diffs) between measured and calculated CAD in the interface, AXB shows more agreement than AAA. The %Diffs were increased with increasing the thickness of air cavity size and it is similar for both algorithms. In RMSEs of inner-profile, AXB was more accurate than AAA. The difference was up to 6 times due to overestimation by AAA. RMSEs of penumbra appeared to high difference for increasing the measurement depth. Gamma agreement also presented that the passing rates decreased in penumbra. Conclusion: This study demonstrated that the dose calculation with AXB shows more accurate than with AAA for the air-tissue interface. The 2D dose distributions with AXB for both inner-profile and penumbra showed better agreement than with AAA relative to variation of the measurement depths and air cavity sizes.

SU‐GG‐T‐168: Comparison of Target Coverage and Organs at Risk Dose between Simultaneous Integrated Boost Whole Field IMRT and a Junctioned IMRT with Conventional Radiotherapy Field in Treatment of Nasopharyngeal Carcinoma

We have retrospectively investigated 20 nasopharyngeal carcinoma patients treated in our institution between March 2007 and August 2009 was reviewed. We used simultaneous integrated boost whole field intensity modulated radiotherapy to treat the entire planning target volume in the head and neck cancer. For comparison with the jounctioned intensity modulated radiotherapy technique, treatment plans were each replanned using jounctioned intensity modulated radiotherapy technique at 6 MV. The effect on target coverage and sparing of organs at risk, including laryngeal sparing in the optimal whole field intensity modulated radiotherapy plan was compared with that achieved using a jounctioned intensity modulated radiotherapy technique. The mean larynxdose was 25.2 Gy in the whole sis intensity modulated radiotherapy. and 19.8 ar in the jounctioned intensity modulated radiotherapy. With comparison between whole field intensity modulated radiotherapy and jounctioned intensity modulated radiotherapy technique, it demonstrated that larynxdose in the whole field intensity modulated radiotherapy technique was increased to that achieved with jounctioned intensity modulated radiotherapy and conventional anterior neck field. However, if applying strong dose constraint on larynx and using the pseudo volume to enforce a steep dose fall‐off immediately outside the target, the simultaneous integrated boost whole field intensity modulated radiotherapy technique led to larynxdose comparable to that achieved with jounctioned intensity modulated radiotherapy. Therefore, in our current practice we use the simultaneous integrated boost whole field intensity modulated radiotherapy technique which does not have the problem of setup error at match line for treatment of nasopharyngeal carcinoma.

SU‐FF‐T‐199: Development of Customized QA Program to Generate 2D Dose Map with High Resolution for IMRT Plans Using 120 Leaf DMLC

Purpose: As a part of patient specific QA for IMRT plans, customized program was developed to evaluate accurate dose distribution of IMRT plans using 120 Leaf dMLC. It is designed to make 2D dose map, where mid‐leaf, inter‐leaf, rounded leaf end transmission dose, tongue and groove (T&G) effects, scattered dose from dMLC as well as primary beam dose were calculated with high resolution (1 mm). Method and Materials: Mid‐leaf, interleaf transmission dose, scattered dose from dMLC were measured by films with various collimatorfield sizes at 6 MV X‐ray on Varian 21Ex. The transmission dose from T&G was calculated using superposition of single slit‐beam kernel extracted from measured open beam profile. The transmission dose from rounded leaf end was calculated along the distance from leaf end. By analyzingMLCsequence file of IMRT plans and measured dosimetric data of dMLC, intensity matrix per segmented MU was produced. 2D kernel profile produced by 1×1 mm2 pencil beam was derived from measured 10×10 cm2 profile by iterative method using line search optimization algorithm. Then primary dose map was reconstructed using superposition‐convolution method with intensity matrix and kernel profile. Extra dose from dMLC per segmented MU was also added to the primary dose map. Results: Reconstructed 2D dose map could explain contributions of primary beam dose, and extra doses resulted from the movement of leaves. The transmission dose from rounded leaf end was increased up to 10% to the total dose when leaves had little motion. Mid‐leaf or interleaf transmission dose also could contribute average 10% to the total dose. Conclusion: Our program can explain unwanted dose distribution due to the movement of dMLC. And it could be expected to be an alternative method instead of film dosimetry, or can be used to complement the drawback of 2D‐array detector with poor resolution.

SU‐GG‐T‐134: Dosimetric Verification of Dose Calculation Algorithms for IMRT Treatment Plan

Purpose: The purpose of this study was to determine the accuracy of dose calculation in penumbra region from two different commercial IMRTtreatment planning systems (TPS). The accuracy of IMRT calculations with a convolution/superposition and a pencil‐beam algorithm was tested using commission data with the modified values from Gaussian fitting approaches the real doses to correct for the spatial response of finite‐sized ionization chamber against measurement. Method and Materials: The IMRT head and neck phantom used in this study was housed in a custom‐designed package for efficient evaluation of the measured doses with different materials and various detectors. The Varian 21EX linear accelerator with 6 MV beam was used. The Pinnacle and the Ecilpse TPSs were calculated based on commissioning data that included beam profiles collected with a 0.125 cm3ionization chamber. We have modified the commissioning data by a Gaussian function of an ionization chamber kernel to the real profile. Dose measurements made by ionization chamber, and glass dosimeter positioned within the phantoms target insert were compared with the calculated doses. Results: The differences for these algorithm results in average PTV doses were within 1.0%. Ionization chamber results showed approximately 1.7% better agreement than the glass dosimeters and the differences between measured and calculated doses were more than 3.0% for both algorithms. However, calculations using these algorithms after it were re‐commissioned from Gaussian fitting gave better agreement with measurements of IMRT field. A main reason of these results was attributed to detector size effects in the commissioning data. Conclusion: These results show that accurately measuring the penumbra region improves the accuracy of the dose calculations predicted by the TPS and thus is important to choose an appreciate detector.

SU‐GG‐T‐233: Development of Glass Dosimeter Postal Dose Intercomparison for High‐Energy Photon Beam

Purpose: The purpose of this study is to evaluate whether the glass dosimeter would be suitable for external dosimetric audit in the radiotherapy. We investigate the methodology of the absorbed dose determination with the glass dosimeter, which requires various correction factors in order to achieve the dosimetric accuracy. Method and Materials: The model GD‐301 glass dosimeter and FGD‐1000 automatic readout system were used. In order to assure dose measurement accuracy, the calibration coefficient and correction factors (non‐linearity dose response, fading, energy dependence and angular dependence) of the glass dosimeter should be determined. We also performed the feasibility test of the glass dosimeter postal dose intercomparison for 8 beams output checks of high photon energy involving 4 centers in Korea. The glass dosimeter results were compared to the measurement obtained with a LiFTLD. Results: The feasibility results can be observed that, the relative deviations of the glass dosimeter were 3.5% smaller than the corresponding TLD values for all photon beams. It is possible that the agreement between the doses obtained with the glass dosimeter and stated doses by participants for following two main reasons: (1) the same dosimetry protocol is used at all participating centers to determine the dose given to the glass dosimeter: (2) the participating centers where the physicists have already experienced from a previous TLD audit program and have sufficient knowledge of the glass dosimeter system. Conclusion: This feasibility study has shown that the new glass dosimeter system has considerable potential to be used for a postal dose audit program. The next step in the glass dosimeter postal program will be the expansion of participating centers. We will investigate the other factors, such as the glass dosimeter holder correction used in this study which might influence the accuracy of determination of absorbed dose from glass dosimeter response.

SU‐FF‐T‐368: Radioprotective Effect of the Bolus On Testicular Dose Following Radiation Therapy

Purpose: To estimate the radioprotective effect of the bolus on testicular radiationdose following radiation therapy for testicular seminoma. Methods and Materials: Testicular dose measurements were performed with thermoluminescent dosimeters(TLDs) between three and seven times on two patients and anthropomorphic phantom. All treatments were taken with L‐shaped fields administered as two parallel‐opposed AP and PA equally weighted fields of 15 MV X‐rays. One fraction of 180 cGy was delivered to the same isocenter with 120 multi‐leaf collimations from a Varian 21EX linear accelerator. In two patients, a round testicle shield device was used to protect the testes during treatment period. To reduce an additional testicular dose, we inserted the bolus (0.5, 1 cm thickness) in the shield device. In phantom, the comparison measurement was performed with and without the shield device added the bolus. Results: The testicular dose ranged from <1 cGy to 6 cGy (range 0.6–3.3%, mean 1.1% of the prescribed dose at the reference point). With only the shield device, the measured dose to the testicles ranged from 1.9–3.2 cGy (mean 2.2 cGy). The absorbed dose was reduced to 1%–2% of the prescribed dose relative to that of without the shield device. Mean testicular dose of the shield device added the bolus was 1.1 cGy (range 0.8–1.4). By using the bolus of 0.5 and 1 cm thickness, 10%–50% of the absorbed dose to testicle decreased. This was due to the reduction of scattered testicular radiationdose by the bolus in shield device. Conclusion: This study observed the shielding benefit of the bolus on testicular dose during radiation treatment with 15 MV X‐rays. Decreasing the undesired irradiation on testicle by using the bolus shoud be pursued in an effort to reduce the genetic risk.

SU‐FF‐T‐02: Comparison of the Dosimetric Properties of Standard MOSFET and MicroMOSFET with Home Made Phantom

Purpose: To evaluate dosimetric properties of a standard MOSFET in comparison with a microMOSFET Method and Materials: We developed the phantoms to perform a calibration and to analyzecharacteristics of standard MOSFET and microMOSFET. The phantoms are made of polystyrene, which have the shape of semi‐sphere with 10cm diameters and flat slab of 30×30cm2 with 1cm thickness. The slab phantom was used for calibration and characterization measurements such as reproducibility, linearity and dose rate dependence. The semi‐sphere phantom was used for angular and directional dependence on the types of MOSFETs. The measurements were conducted at a depth of 1.5cm under 10×10cm2 fields at 100cm SSD for reproducibility, linearity, and dose rate dependence. For calibration and reproducibility, five standard MOSFETs and microMOSFETs were repeatedly irradiated by 200cGy three times. Dose linearity was evaluated in the range of 10 to 600cGy. The effect of dose rate was also investigated by 200cGy from 100 to 600MU/min. For angular and directional dependence, the measurements were performed between 0° and 90° gantry angles, while MOSFETs were placed at the center of semi‐sphere phantom. The 50cGy was irradiated repeatedly three times under same setup. Results: The average calibration factor was 1.1±0.95 for standard MOSFETs and 1.09±0.50 for microMOSFETs. The response of reproducibility in the two types of MOSFETs was found to be maximum 0.5% variation. In linearity, the results showed good linear response with R2 value of 0.997 and 0.999. The angular and directional dependence was found to be within ±2∼5% and ±7∼8%. Conclusion: Standard MOSFET and microMOSFET were compared by the dosimetric characteristics with the home‐made phantom. For linearity, reproducibility and calibration factor, two types of MOSFETs showed similar results. On the other hand, standard MOSFET and microMOSFET were found to be remarkable difference due to its detection area size in angular and directional dependence.