High dose-rate brachytherapy source position quality assurance using radiochromic film.

Traditionally, radiographic film has been used to verify high-dose-rate brachytherapy source position accuracy by co-registering autoradiographic and diagnostic images of the associated applicator. Filmless PACS-based clinics that do not have access to radiographic film and wet developers may have trouble performing this quality assurance test in a simple and practical manner. We describe an alternative method for quality assurance using radiochromic-type film. In addition to being easy and practical to use, radiochromic film has some advantages in comparison with traditional radiographic film when used for HDR brachytherapy quality assurance.     

Verification of brachytherapy dosimetry with radiochromic film.

The aim of this work is to empirically validate the optimized dose distribution calculated by the Nucletron Brachytherapy Planning System (v. 13.3) at a distance of 1.0 cm from a stepping source of high-dose-rate-iridium 192 (192Ir). The longitudinal dose distribution at 1.0 cm from a straight pathway of multiple-source positions is measured using radiochromic film and compared with the planning system's calculated results. The optical density of the exposed films was determined with a modified Scanditronix film scanner, and the film was calibrated with 192Ir using manually calculated exposure times. A calibration equation was used to convert scanner output to dose. Our results illustrate the significance of exacting geometry in the experimental setup due to the inverse square law and the small distances involved. The dose distribution calculated by the Nucletron Brachytherapy Planning System (v. 13.3), at a distance of 1.0 cm, is validated to within +/-4% of the measured dose distribution. The advantages and limitations of radiochromic film as a dosimetry tool are also addressed in this work.     

神经介入手术中患者峰值皮肤剂量水平研究

目的 获得神经介入手术中患者峰值皮肤剂量数据（PSD）,评估患者确定性效应发生风险。方法 使用Gafchromic XR RV3胶片采集北京市某三级甲等医院神经介入手术患者的峰值皮肤剂量,主要研究血管栓塞术、血管成形术、血管造影术等3种常见的神经介入手术。使用Epson Expression 10000XL扫描仪扫描胶片,利用ImageJ和Film QA Pro^TM 2014软件测量和分析胶片。结果 共采集49例神经介入手术患者的峰值皮肤剂量数据,包括血管栓塞术23例、血管成形术14例、血管造影术12例。PSD ≥ 2 Gy患者20例,其中血管栓塞术15例,血管成形术5例。血管造影术患者的PSD均<2 Gy。部分神经介入手术患者的峰值皮肤剂量超过国际放射防护委员会（ICRP）第118号报告中的确定性效应剂量阈值。结论 神经介入手术存在发生确定性效应的风险,建议针对风险较高的患者进行随访观察,及时了解其辐射损伤情况和后续诊治。     

A comparison of HDR near source dosimetry using a treatment planning system,Monte Carlo simulation,and radiochromic film

This study aimed to investigate the high-dose rate Iridium-192 brachytherapy, including near source dosimetry, of a catheter-based applicator from 0.5 mm to 1 cm along the transverse axis. Radiochromic film and Monte Carlo (MC) simulation were used to generate absolute dose for the catheter-based applicator. Results from radiochromic film and MC simulation were compared directly to the treatment planning system (TPS) based on the American Association of Physicists in Medicine Updated Task Group 43 (TG-43U1) dose calculation formalism. The difference between dose measured using radiochromic film along the transverse plane at 0.5 mm from the surface and the predicted dose by the TPS was 24%±13%. The dose difference between the MC simulation along the transverse plane at 0.5 mm from the surface and the predicted dose by the TPS was 22.1%±3%. For distances from 1.5 mm to 1 cm from the surface, radiochromic film and MC simulation agreed with TPS within an uncertainty of 3%. The TPS under-predicts the dose at the surface of the applicator, i.e., 0.5 mm from the catheter surface, as compared to the measured and MC simulation predicted dose. MC simulation results demonstrated that 15% of this error is due to neglecting the beta particles and discrete electrons emanating from the sources and not considered by the TPS, and 7% of the difference was due to the photon alone, potentially due to the differences in MC dose modeling, photon spectrum, scoring techniques, and effect of the presence of the catheter and the air gap. Beyond 1 mm from the surface, the TPS dose algorithm agrees with the experimental and MC data within 3%.     

用胶片法对心脏介入程序中患者峰值皮肤剂量测量研究

目的 采用胶片法对进行心血管介入手术中患者所受峰值皮肤剂量（PSD）进行测量研究,包括冠状动脉血管造影术（CA）和经皮穿刺腔内冠状动脉成形术（PTCA）。方法 选用Gafchromic XR-RV3胶片在两家医院进行患者峰值皮肤剂量的测量。手术时将胶片放在患者身下的诊视床上。记录手术中监视器上显示的kV、mA、透视时间、剂量面积乘积（DAP）、参考点累积剂量等相关信息。采用Epson V750平板扫描仪对胶片进行分析扫描及分析,选用FilmQA软件分别测量图像的红、绿、蓝三色通道的像素值,使用红通道数据计算患者的 PSD。对PSD与设备显示参数进行相关分析,对相关的变量进行多元线性回归分析。结果 共测量CA手术26例,CA+PTCA手术19例。CA手术中,透视时间最高为17.62 min,累积剂量和DAP最大分别为1 498.50 mGy和109.68 Gy ·cm²,PSD最大为361.20 mGy。CA+PTCA手术中,曝光时间最长为64.48 min,累积剂量和DAP最大分别为6 976.20 mGy和5 336.00 Gy ·cm²,17例患者的PSD在1 Gy以内,1例患者PSD在1~2 Gy之间,1例患者PSD超出了发生皮肤损伤2 Gy的阈值,达到了2 195.70 mGy。CA程序中,患者PSD与DAP相关（R²=0.815,P<0.05）,CA+PTCA程序中,患者PSD与累积剂量相关（R²=0.916,P<0.05）。结论 心脏介入放射学程序中部分患者的PSD会超出ICRP建议的发生皮肤确定性效应的2 Gy阈值。DSA设备上显示的剂量相关的参数,只能粗略估算患者PSD的大小。使用XR-RV3胶片精确测量介入手术中患者的峰值皮肤剂量是一种非常快捷、有效的方法。     

Dosimetry of a sonolucent material for an ultrasound-compatible gynecologic high-dose-rate brachytherapy cylinder using Monte Carlo simulation and radiochromic film

Purposehe purpose of this study was to study the dosimetric characterization of sonolucent material “TPX” to be used toward gynecologic high-dose-rate brachytherapy treatments using ultrasound-compatible cylinders in non–model-based dose calculation workflows.MethodsMonte Carlo simulations were performed using EGSnrc application egs_brachy in cylinders of polymethylpentene (TPX) plastic, water, and PMMA. Simulations were performed of five 192Ir sources placed longitudinally in ～3.7 cm diameter, 5.0 cm length cylinders (matching physical cylinders used in film measurements). TPX and PMMA dose distributions and percentage depth dose curves were compared relative to water.Film measurements were performed to validate egs_brachy simulations. TPX and PMMA cylinders were placed in a water tank using 3D-printed supports to position film radially and touching the surface of the cylinders. The same five 192Ir dwell positions were delivered as simulated in egs_brachy.ResultsThe egs_brachy and film percentage depth doses agreed within film uncertainties. The egs_brachy relative dose difference between TPX and water was (0.74 ± 0.09)% and between PMMA and water was (-0.79 ± 0.09)% over the dose scoring phantom. Dose differences for TPX and PMMA relative to water were less than ± 1% within 5 cm of the cylinder surface.ConclusionsIn a solid sonolucent sheath of TPX, the dosimetric differences are comparable with PMMA and other applicator materials in clinical use. No additional uncertainty to dose calculation is introduced when treating through TPX cylinders compared with current applicator materials, and therefore, it is acceptable to perform gynecologic brachytherapy treatments with a sonolucent sheath inserted during radiation delivery.     

Accuracy of measurement of radiochromic film density for high-energy X-rays

Radiochromic film (RC-film) is of great interest as a film-type dosimeter for radiation oncology applications. We present a two-dimensional image-based evaluation of the measurement accuracy of a commercial RC-film product (Gafchromic MD-55-2 film, ISP TECHNOLOGIES, Inc.) by using a commercial Laser Densitometer (Model 1710, Computerized Medical Systems, Inc.) as an optical density imaging system. The coefficient of variation of the density (pixel-value) in one sample was approximately 3% to 11% at 3 Gy or less, and 3% or less at 4 to 60 Gy. Although the coefficient of variation between three samples at the same dose was about 14% at 1 Gy, it decreased as the dose increased, reaching several percent. In 1 to 6 Gy samples, geometric imaging artifacts [interference (moire) patterns] were observed, and it was found that scan-sampling pitch influenced the accuracy of measurement of the density of the sample. To improve the accuracy of density measurement, sufficient knowledge about characteristic features of the density measuring system is essential.     

放射性核素近距离治疗血管再狭窄的现状和进展

自从血管成形术应用于临床,血管再狭窄问题就随之而来,放射性核素血管内近距离治疗己产生富有希望的结果。现综述放射性核素近距离治疗的辐射机制、两种基本操作平台、放射性核素的选择、吸收剂量和剂量率、疗效、副作用和工作人员受照剂量等。     

Evaluation of new methods for removing moire artifact of radiochromic film

An optical interference-pattern, a moire artifact, is produced during the film scanning process using a flatbed scanner. Images with moire artifacts include optical density fluctuations thereby leading to inaccuracy of measurement. In this study, we proposed two methods for removing moire artifacts from radiochromic film and compared dose response and profile as well as image resolution and size between our proposed methods versus the conventional process. The proposed methods could remove the artifacts without impairing dosimetric performance. It is expected that the proposed methods facilitate more accurate film dosimetry with reflective radiochromic films.     

A dosimetric comparison of MammoSite high-dose-rate brachytherapy and Xoft Axxent electronic brachytherapy

PURPOSE: Over 20,000 patients have been treated with partial breast irradiation (PBI) using the MammoSite balloon brachytherapy applicator (IBB). Recently, a new form of balloon-based PBI, Xoft Axxent electronic brachytherapy (KVB), which uses a 50-kV x-ray source, has been introduced. This analysis was undertaken to dosimetrically compare the results of treatment using these two methods of PBI. METHODS AND MATERIALS: The study population consisted of 15 patients previously treated with IBB. The planning CT scans from these 15 patients were used to construct hypothetical treatment plans using the source characteristics of the KVB device. The plans were then compared using the dosimetric parameters discussed below. RESULTS: The mean %V(90) was 99.6% vs. 99.0% (p=nonsignificant [ns]), the mean %V(100) was 96.5% vs. 96.5%, the mean %V(150) was 41.8% vs. 59.4% (p<0.05), the mean %V(200) was 11.3% vs. 32.0% (p<0.05), and the mean %V(300) was 0.4% vs. 6.7% (p<0.05) for the IBB and KVB methods, respectively. The mean ipsilateral breast %V(50) was 19.8% vs. 13.0% (p<0.05), the mean ipsilateral lung %V(30) was 3.7% vs. 1.1% (p<0.05), and the mean heart %V(5) was 59.2% vs. 9.4% (p<0.05) for the IBB and KVB methods, respectively. CONCLUSIONS: The IBB and KVB methods of PBI offer comparable target volume coverage; however, the KVB method is associated with an increased volume of breast tissue in the high-dose regions and a decreased dose to the adjacent normal tissues.     

A comparison of brachytherapy techniques for partial breast irradiation

Accelerated partial breast irradiation has emerged as an important treatment option for select patients with early-stage breast cancer. Numerous techniques for the delivery of accelerated partial breast irradiation have been developed involving both external beam and brachytherapy techniques. Brachytherapy techniques in general have the advantage of directly targeting the tumor bed and are not hampered by the requirement for large planning target volume margins needed with external beam techniques to account for uncertainties in targeting a very mobile organ, easily affected by patient and respiratory motion. We review established brachytherapy techniques and new emerging approaches. Technical considerations, available clinical data, advantages and shortcomings of each technique are reviewed.     

Coronary intravascular brachytherapy for in-stent restenosis: A review of the contemporary literature

Intracoronary stent restenosis (ISR) is a clinically relevant challenge in the modern era. Heterogeneity in patient- and lesion-specific factors can further compound this clinical challenge. Coronary intravascular brachytherapy (IVBT) was the standard therapeutic approach for ISR prior to the advent of drug-eluting stents (DES). Despite prospective data describing the superiority of DES over IVBT for treating de novo ISR, IVBT remains a treatment option for patients with complex disease. The purpose of this review is to evaluate the historical and contemporary literature surrounding IVBT in order to elucidate its role in modern cardiac care and to describe opportunities for future investigations to improve patient selection. Herein, we provide a review of the contemporary literature describing IVBT as a safe and effective treatment option for patients with recurrent, refractory ISR after multilayer DES and no good surgical or mechanical option. Combination therapy with emerging technologies such as DCBs may further increase efficacy.     

A new delivery system to resolve dosimetric issues in intravascular brachytherapy

PurposeRenewed interest is being expressed in intravascular brachytherapy (IVBT). A number of unresolved issues exist in the discipline. Providing a homogeneous and adequate dose to the target remains difficult in IVBT. The guidewire that delivers the device to the target, arterial plaques, and stent struts are all known to reduce the dose delivered to target. The viability and efficacy of a proposed IVBT delivery system designed to resolve the issue of guidewire attenuation is evaluated and compared to that of a popular and commercially available IVBT device.Methods and MaterialsMonte Carlo simulations are conducted to determine distributions of absorbed dose around an existing and proposed IVBT delivery system.ResultsFor the Novoste Beta-Cath 3.5F (TeamBest®), dose in water varies by 10% as a function of angle in the plane perpendicular to the delivery catheter due to off-centering of seeds in the catheter. Dose is reduced by 52% behind a stainless steel guidewire and 64% behind a guidewire, arterial plaque, and stent strut for the Novoste Beta-Cath 3.5F. Dose is not perturbed by the presence of a guidewire for the proposed device and is reduced by 46% by an arterial plaque and stent strut.ConclusionsDose attenuation by guidewire is likely the single greatest source of dose attenuation in IVBT in terms of absolute dose reduction and is greater than previously reported for the Novoste Beta-Cath 3.5F. The Novoste Beta-Cath 3.5F delivers an inhomogeneous dose to target. A delivery system is proposed, which resolves the issue of guidewire attenuation in IVBT and should reduce treatment times.     

Measurement of relative output for 90Sr ophthalmic applicators using radiochromic film.

The treatment of various superficial lesions of the eye has, for many years, been conducted using strontium 90 (90Sr) ophthalmic applicators that have a steep dose gradient near their surface. A new applicator acquired by a treatment facility must have its output compared with that of any older applicators already in use to ensure consistent treatments. These measurements may be done using available dosimeters such as film and thermoluminescent detectors. Our work made use of radiochromic film and a document scanner to perform relative output measurements for 4 different 90Sr ophthalmic applicators acquired from the same manufacturer (Amersham Healthcare, Arlington Heights, IL) over a span of 28 years. Relative outputs were found to vary by < 10% with respect to the manufacturer's values, which is well within the uncertainty limit for absolute output of 20% specified by the manufacturer. The film measurements were verified using thermoluminescent dosimeters. Radiochromic film was also used to obtain a percentage depth dose curve and a 2 dimensional isodose distribution in a plane perpendicular to the active surface for the newest applicator (SIA 20).     

A polymer-alanine film for measurements of radiation dose distributions

A film dosimeter (0.35 mm thick) composed of polyethylene-vinyl acetate and microcrystalline l-α-alanine has been prepared and investigated with respect to dosimetric properties using electron spin resonance spectroscopy. The useful absorbed dose range is ∼ 25 to 10⁵ Gy and no dose-rate dependence of the response is observed between 1 and 10⁷ Gy s⁻¹ within the dose range up to 50 kGy. With irradiation temperature increasing from 25 to 80°C, the response increases at most by 10%. The response is stable, within experimental uncertainty, at least up to 2500 h after irradiation. The suitability of the polymer-alanine film for measurements of ionizing photon and electron dose distributions is demonstrated.     

Dosimetry for 131Cs and 125I seeds in solid water phantom using radiochromic EBT film

PurposeTo measure the 2D dose distributions with submillimeter resolution for ¹³¹Cs (model CS-1 Rev2) and ¹²⁵I (model 6711) seeds in a Solid Water phantom using radiochromic EBT film for radial distances from 0.06 cm to 5 cm. To determine the TG-43 dosimetry parameters in water by applying Solid Water to liquid water correction factors generated from Monte Carlo simulations.MethodsEach film piece was positioned horizontally above and in close contact with a ¹³¹Cs or ¹²⁵I seed oriented horizontally in a machined groove at the center of a Solid Water phantom, one film at a time. A total of 74 and 50 films were exposed to the ¹³¹Cs and ¹²⁵I seeds, respectively. Different film sizes were utilized to gather data in different distance ranges. The exposure time varied according to the seed air-kerma strength and film size in order to deliver doses in the range covered by the film calibration curve. Small films were exposed for shorter times to assess the near field, while larger films were exposed for longer times in order to assess the far field. For calibration, films were exposed to either 40 kV (M40) or 50 kV (M50) x-rays in air at 100.0 cm SSD with doses ranging from 0.2 Gy to 40 Gy. All experimental, calibration and background films were scanned at a 0.02 cm pixel resolution using a CCD camera-based microdensitometer with a green light source. Data acquisition and scanner uniformity correction were achieved with Microd3 software. Data analysis was performed using ImageJ, FV, IDL and Excel software packages. 2D dose distributions were based on the calibration curve established for 50 kV x-rays. The Solid Water to liquid water medium correction was calculated using the MCNP5 Monte Carlo code. Subsequently, the TG-43 dosimetry parameters in liquid water medium were determined.ResultsValues for the dose-rate constants using EBT film were 1.069±0.036 and 0.923±0.031 cGy U⁻¹ h⁻¹ for ¹³¹Cs and ¹²⁵I seed, respectively. The corresponding values determined using the Monte Carlo method were 1.053±0.014 and 0.924±0.016 cGy U⁻¹ h⁻¹ for ¹³¹Cs and ¹²⁵I seed, respectively. The radial dose functions obtained with EBT film measurements and Monte Carlo simulations were plotted for radial distances up to 5 cm, and agreed within the uncertainty of the two methods. The 2D anisotropy functions obtained with both methods also agreed within their uncertainties.ConclusionEBT film dosimetry in a Solid Water phantom is a viable method for measuring ¹³¹Cs (model CS-1 Rev2) and ¹²⁵I (model 6711) brachytherapy seed dose distributions with submillimeter resolution. With the Solid Water to liquid water correction factors generated from Monte Carlo simulations, the measured TG-43 dosimetry parameters in liquid water for these two seed models were found to be in good agreement with those in the literature.     

Dose evaluation and measurement of the Re liquid-filled balloon in intravascular brachytherapy

We compared the Monte Carlo evaluation and GafChromic MD-55 film experimental measurement of ¹⁸⁸Re liquid-filled balloons in intravascular brachytherapy using two phantoms of 6 mm vascular diameter, a phantom of 4 mm vascular diameter and a phantom of 3 mm vascular diameter. A dose-evaluation interface program was developed and was shown to be capable of quickly providing information such as the necessary ¹⁸⁸Re source irradiation time to deliver a prescribed dose.