Fractionated perioperative high dose rate brachytherapy using a tissue equivalent bendy applicator

Intraoperative radiation techniques allow an additional local dose in areas at high-risk for local failure. With brachytherapy techniques, perioperative radiation can be fractionated. Fractionated treatment might offer an interesting alternative to a single dose, both to increase the therapeutic ratio and to protect late reacting tissues at risk. The dose distribution for brachytherapy applicators can be optimized using spacer materials. In this prospective study a new tissue equivalent bendy applicator (TEBA) that can remain in situ for several days is introduced, and the feasibility of fractionated perioperative high dose rate (HDR) brachytherapy is examined. 31 patients with different tumours (soft tissue sarcoma, Ewings sarcoma, rectal cancer, and locally infiltrating diseases) were treated. The TEBA was applied, depending on resection status and intraoperative findings. Planning was based on digitized radiographs and CT scans. Perioperative HDR brachytherapy was performed using an individual treatment schedule. In 29 patients perioperative radiation was given and in 26 cases fractionated brachytherapy application was possible. TEBA application time varied from 1 day to 11 days. During this time between 1 and 8 fractions were given with total doses from 10 Gy to 25 Gy. Fractionated perioperative brachytherapy with this technique is feasible and adequate. Further studies will show whether fractionated perioperative treatment using the TEBA technique fulfils its theoretical advantages over single dose intraoperative radiotherapy by decreased late toxicity and increased local tumour control.     

利用3D打印颅脑辐射等效体模进行个性化适形放疗的剂量验证

目的 建立利用3D打印颅脑辐射等效体模对患者进行个性化放疗剂量验证的方法,为三维适形放射治疗安全提供一种可靠的剂量保证手段。方法 采集两例患者（患者1和患者2）的CT图像数据,基于患者1的图像数据,重建其颅骨与脑组织,制作颅脑体模,验证颅骨与脑组织的等效材料。基于患者2的图像数据,根据3D图像重建并选用组织等效材料重建完全的头颅结构,采用3D打印技术制作全头颅体模。通过对目标区域插入电离室剂量仪并行放射治疗方案,获得头颅体模病灶部的剂量,验证和校准实际放疗计划的安全性。结果 对所获两个体模分别进行DR、CT成像,颅脑体模的等效骨骼与患者1骨骼的X射线灰度值差异为13 721,颅脑体模的等效脑组织与患者1的脑组织的CT值差异为35~40 HU,全头颅体模等效颞肌与患者2的颞肌组织的CT值差异为18~28 HU,影像数据表明体模材质的辐射等效性与人体组织近似,并且等效剂量分布符合常规治疗范围,体模的剂量验证可以有效验证放疗计划系统的准确性。结论 基于3D打印和组织等效技术所设计的个性化放疗体模,可应用于个性化放射治疗验证。体模制作方法简单快速,个性化程度高,为三维适形放射治疗安全提供一种可靠的剂量保证手段。     

Interfractional fluctuation of rectal dose in high dose rate brachytherapy for prostate cancer

Purpose The aim of the study was to explore the cause of the difference in the maximal rectal dose between the first and second high dose rate (HDR) brachytherapy applications by comparing the thickness of the anterior rectal wall. Materials and methods The rectal dose and the thickness of the anterior rectal wall were analyzed in 26 patients with prostate cancer. After undergoing external beam radiation treatment with a total isocenter dose of 50 Gy, they were treated with HDR brachytherapy of 7.5 Gy/fraction, two fractions daily. The interval between the first HDR brachytherapy session and the second was 5 h. The rectal doses were directly surveyed during irradiation of the HDR brachytherapy. Thickening of the anterior rectal wall was measured at the same level by axial computed tomography scans obtained before the first and second HDR brachytherapy applications. Results The maximal surveyed rectal doses during the first and second HDR brachytherapy applications were 188 ± 51 cGy and 220 ± 35 cGy, respectively (P < 0.01). The fluctuation ratio exceeded 1 in each case. The thickness of the anterior rectal wall before the first and second HDR brachytherapy applications was 18.78 ± 4.34 mm and 14.95 ± 4.09 mm (P < 0.01), respectively. The fluctuation difference exceeded 0 in each case. Conclusion The different rectal dose is attributable to thinning of the anterior rectal wall. The total rectal dose is within the range of doses at risk of exerting a toxic effect on the rectum.     

Treatment of localized prostate cancer using a combination of high dose rate Iridium-192 brachytherapy and external beam irradiation: initial Australian experience

Combination high dose rate brachytherapy (HDRB) and external beam radiation therapy is technically and clinically feasible as definitive treatment for localized prostate cancer. We report the first large Australian experience using this technique of radiation dose escalation in 82 patients with intermediate- and high-risk disease. With a median follow up of 3 years (156 weeks), complications were low and overall prostate-specific antigen progression-free survival was 91% using the American Society for Therapeutic Radiology and Oncology consensus definition. The delivery of hypofractionated radiation through the HDRB component shortens overall treatment time and is both biologically and logistically advantageous. As a radiation boost strategy, HDRB is easy to learn and could be introduced into most facilities with brachytherapy capability.     

Design, construction and evaluation of an anthropomorphic head phantom with realistic susceptibility artifacts

PURPOSE: To design and construct an anthropomorphic head phantom using materials of appropriate magnetic susceptibility and air spaces of realistic dimensions, with the aim of reproducing the susceptibility artifacts found in the human brain. MATERIALS AND METHODS: The phantom is based on a plastic skull filled with MnCl2-doped water. Materials to mimic soft tissue (wax) and bone (plastic skull) were chosen based on mass susceptibility measurements using a superconducting quantum interference device (SQUID) magnetometer. The phantom was designed for and evaluated at 4.7T using field mapping and echo-planar imaging (EPI). RESULTS: The main magnetic field (B0) maps of the phantom resemble those of four volunteers' brains and have similar standard deviations (SDs). Maps of the B0 field gradients in the phantom and real brains are also similar. The phantom has relaxation times close to those of brain tissue at 4.7T. Gradient-echo (GE)-EPI images of the phantom suffer from susceptibility artifacts comparable to those in real heads and at anatomically realistic locations. CONCLUSION: The phantom is a useful tool for evaluating and comparing different susceptibility artifact reduction techniques. The phantom could also be used to test CT-MRI coregistration in the presence of susceptibility artifacts since the water-filled brain cavity is both CT- and MR-visible.     

Standard linear plans in single channel high dose rate brachytherapy: a dosimetric analysis

The use of standard linear plans is proposed for single channel intraluminal High Dose Rate brachytherapy. This technique employs the optimized dwell times derived from a straight line within a curved geometry. Such standardization of the planning procedure ensures expedient delivery of treatment. The 3-D dose distribution resulting from the use of standard linear plans within various curved geometries is investigated. In this study a comparison is made between the dose delivered to the perimeter of the target volume from both standard linear plans and individually optimized plans. Our results demonstrate that the use of a standard linear plan is acceptable in curved geometries, given the current practice of dose and volume specification for high dose rate intraluminal brachytherapy.     

A comparison of the expected costs of high dose rate brachytherapy using Cf versus Ir

A cost analysis to compare high dose rate (HDR) brachytherapy using either californium-252 (²⁵²Cf) or ¹⁹²Ir was performed to determine the prospects of widespread clinical implementation of HDR ²⁵²Cf. Interest in the neutron-emitting ²⁵²Cf radioisotope as a radiotherapy nuclide has undergone a resurgence given recent efforts to fabricate HDR remotely afterloaded sources, and other efforts to create a miniature source for improved accessibility to a variety of anatomic sites. Therefore, HDR ²⁵²Cf brachytherapy may prove to be a potential rival to the use of HDR ¹⁹²Ir remotely afterloaded brachytherapy—the current standard-of-care treatment modality using HDR brachytherapy. Considering the possible improvements in clinical efficacy using HDR ²⁵²Cf brachytherapy and the enormous costs of other high-LET radiation sources, the cost differences between ²⁵²Cf and ¹⁹²Ir may be well-justified.     

Standard linear plans in single channel high dose rate brachytherapy: a dosimetric analysis

The use of standard linear plans is proposed for single channel intraluminal High Dose Rate brachytherapy. This technique employs the optimized dwell times derived from a straight line within a curved geometry. Such standardization of the planning procedure ensures expedient delivery of treatment. The 3-D dose distribution resulting from the use of standard linear plans within various curved geometries is investigated. In this study a comparison is made between the dose delivered to the perimeter of the target volume from both standard linear plans and individually optimized plans. Our results demonstrate that the use of a standard linear plan is acceptable in curved geometries, given the current practice of dose and volume specification for high dose rate intraluminal brachytherapy.     

Improving coronary artery imaging quality in the high heart rate region and on MDCT using a pulsating cardiac phantom

The multi-sector reconstruction (MSR) algorithm and cardiac half-reconstruction (CHR) algorithm are the main algorithms used in cardiac reconstruction. Analysis of effective temporal resolution (TR) confirmed that optimal rotation speed depends on different heart rates when using MSR. During visualization (3D/MPR image) and quantitative (EF: ejection fraction) evaluations, it was found that image quality and measurement accuracy are well correlated with effective temporal resolution (TR) by the different algorithms. The CHR algorithm resulted in less desirable image quality at TR 250 ms than that from MSR at high heart rates (>75 bpm) in the phantom experiment. We determined that the combination of the MSR algorithm and the optimal selection of gantry rotation speed is important for obtaining high-quality cardiac imaging in the high heart rate region.     

Experience of using MOSFET detectors for dose verification measurements in an end-to-end 192Ir brachytherapy quality assurance system

PurposeEstablishment of an end-to-end system for the brachytherapy (BT) dosimetric chain could be valuable in clinical quality assurance. Here, the development of such a system using MOSFET (metal oxide semiconductor field effect transistor) detectors and experience gained during 2 years of use are reported with focus on the performance of the MOSFET detectors.Methods and MaterialsA bolus phantom was constructed with two implants, mimicking prostate and head & neck treatments, using steel needles and plastic catheters to guide the ¹⁹²Ir source and house the MOSFET detectors. The phantom was taken through the BT treatment chain from image acquisition to dose evaluation. During the 2-year evaluation-period, delivered doses were verified a total of 56 times using MOSFET detectors which had been calibrated in an external ⁶⁰Co beam. An initial experimental investigation on beam quality differences between ¹⁹²Ir and ⁶⁰Co is reported.ResultsThe standard deviation in repeated MOSFET measurements was below 3% in the six measurement points with dose levels above 2 Gy. MOSFET measurements overestimated treatment planning system doses by 2–7%. Distance-dependent experimental beam quality correction factors derived in a phantom of similar size as that used for end-to-end tests applied on a time-resolved measurement improved the agreement.ConclusionsMOSFET detectors provide values stable over time and function well for use as detectors for end-to-end quality assurance purposes in ¹⁹²Ir BT. Beam quality correction factors should address not only distance from source but also phantom dimensions.     

Three-dimensional brain phantom containing bone and grey matter structures with a realistic head contour

Introduction

A physical 3-dimensional phantom that simulates PET/SPECT images of static regional cerebral blood flow in grey matter with a realistic head contour has been developed. This study examined the feasibility of using this phantom for evaluating PET/SPECT images.

Methods

The phantom was constructed using a transparent, hydrophobic photo-curable polymer with a laser-modelling technique. The phantom was designed to contain the grey matter, the skull, and the trachea spaces filled with a radioactive solution, a bone-equivalent solution of K₂HPO₄, and air, respectively. The grey matter and bone compartments were designed to establish the connectivity. A series of experiments was performed to confirm the accuracy and reproducibility of the phantom using X-ray CT, SPECT, and PET.

Results

The total weight was 1997 ± 2 g excluding the inner liquid, and volumes were 563 ± 1 and 306 ± 2 mL, corresponding to the grey matter and bone compartments, respectively. The apparent attenuation coefficient averaged over the whole brain was 0.168 ± 0.006 cm^?1 for Tc-99 m, which was consistent with the previously reported value for humans (0.168 ± 0.010 cm^?1). Air bubbles were well removed from both grey-matter and bone compartments, as confirmed by X-ray CT. The phantom was well adapted to experiments using PET and SPECT devices.

Conclusion

The 3-dimensional brain phantom constructed in this study may be of use for evaluating the adequacy of SPECT/PET reconstruction software programs.     

Improving 3D PET imaging by restoration: a phantom study.

The main objective of our work is to improve 3D PET imaging. Compared with 2D PET, 3D PET imaging has slightly worse axial resolution and a significantly higher contribution of scatter and randoms, but 3D PET has much better sensitivity than 2D PET imaging. A Jaszczak deluxe phantom was acquired in 3D mode on our GE Advance PET system. Activity of 333 MBq of 18F was uniformly distributed. Prior to the emission scan, blank and transmission scans had been acquired. They were used for attenuation correction. The duration of the emission scan was 20 min, transmission 10 min, and blank 20 min. Standard FBP reconstruction software provided by the vendor was used to obtain slice images. Point spread function was also acquired in a 21 cm diameter cylinder phantom filled with water 6.0 cm from the center and used to create restoration filters. Two restoration filters were applied, medium and sharp. Results showed significant improvement in resolution, contrast and detectability of the cold rods. The artifacts outside the phantom were also significantly reduced. For 11.1 mm rods, average contrast was 0.49+/-0.02 in the original image, 0.52+/-0.04 in the medium restored image, and in the sharply restored image 0.75+/-0.05. For 7.9 mm rods, average contrast was 0.07+/-0.01 in the original image, 0.21+/-0.03 in the medium restored image, and 0.50+/-0.04 in the sharply restored image. The amount of noise in the uniform slices, measured as the coefficient of variation (COV), was 5.5, 7.1 and 10.8% in the original image and in the images restored with medium and sharp filters, respectively. In conclusion, restoration can significantly improve the resolution and contrast of 3D PET imaging.     

Detectability of small and flat polyps in MDCT colonography using 2D and 3D imaging tools: results from a phantom study

OBJECTIVE: The objective of this phantom study was to determine the performance of MDCT colonography for the detection of small polyps under ideal imaging conditions and to determine the added value of 3D imaging when used as an adjunct to 2D imaging. MATERIALS AND METHODS: Thirty-six polypoid and 39 flat polyps (44 lesions, 2-5 mm; 31 lesions, 6-8 mm) were placed in three explanted segments of a thoroughly cleaned porcine colon (overall length, 4.5 m) that was distended with air and submerged in a water phantom. MDCT data sets with 4 x 1 mm collimation and 6-mm table feed were reconstructed every 0.7 mm with 1.25-mm effective slice width. The data were reviewed by three radiologists using 2D images in all three projections and with 3D volume-rendered images available as an adjunct to the 2D images. RESULTS: Additional 3D as a problem-solving tool significantly increased the overall sensitivity (96% vs 90%), decreased the total number of false-positive calls (n = 9 vs n = 5), and increased the diagnostic confidence level (p < 0.03) compared with 2D images alone. Small polyps less than or equal to 5 mm (89% vs 95%, p = 0.004) and flat polyps (82% vs 94%, p = 0.001) especially benefited from 3D. Sensitivity was generally higher for polypoid than for flat polyps (99% vs 94%, p = 0.041). CONCLUSION: Under phantom conditions, simulating an ideal clinical setup, MDCT colonography is not limited by spatial resolution and detects polyps less than or equal to 5 mm in size with high sensitivity and specificity. Additional 3D image tools improve diagnostic accuracy and reviewer confidence, especially for the detection of flat and small polyps.     

3D打印个体化模具在子宫内膜癌术后三维后装治疗中的剂量学研究

目的 探讨3D打印个体化模具辅助子宫内膜癌术后三维后装治疗中的剂量学优势。方法 回顾性选取宁波大学附属第一医院21例早期子宫内膜癌术后患者的三维后装治疗计划,利用北京科霖众计划系统,在已实施的个体化模具组基础上,为每位患者设计虚拟单通道柱状施源器计划,所有计划均采用三维逆向模拟退火的算法。比较两组计划靶区90%、98%和100%体积接受的最低剂量(D₉₀、D₉₈、D₁₀₀)以及适形指数(CI)、均匀度(HI)、超剂量体积指数(OI);同时,对比两组危及器官膀胱、直肠、小肠和尿道的0.01、1、2以及5 cm³所接受的最大剂量(D_{0.01 cm³}、D_{1 cm³}、D_{2 cm³}以及D_{5 cm³})差异。结果 两组计划都能满足临床需求。在靶区所受剂量方面,两组计划靶区D₉₀、D₉₈、D₁₀₀没有明显差异,但是个体化模具组靶区剂量的CI、HI均优于单通道组靶区,而靶区OI指数小于单通道计划(t=-3.21、-5.99、6.25,P＜0.05)。在危及器官所受剂量方面,个体化模具组膀胱、直肠、尿道所受剂量D_{1 cm³}、D_{2 cm³}和D_{5 cm³}相比单通道组均有明显降低(t=3.18、3.21、3.77、7.97、8.92、10.92、2.54、3.46、4.28,P＜0.05);小肠由于距离靶区比较远,在两组计划中所受剂量差异不明显(P＞0.05)。结论 3D打印个体化模具在子宫内膜癌术后三维近距离治疗中靶区均匀度、适形指数更优,而且膀胱、直肠、尿道所受剂量更低,具有推广价值。     

A novel end-to-end test for combined dosimetric and geometric treatment verification using a 3D-printed phantom

The dosimetric and geometric accuracy are important components to ensure safe patient treatment in radiation therapy. Therefore, these components must be checked during quality control. This work presents a possible solution for the determination of the geometric isocenter deviation in the entire treatment chain. Additionally, the dose measurement of the established end-to-end test workflow measured in the same procedure as the geometric deviation is described. An in-house designed end-to-end test phantom went through the entire procedure of a standard patient treatment and the dosimetric and geometric accuracy were determined. At 3 linear accelerators (linac), the phantom was positioned either with cone beam computed tomography or with surface guidance. In this position, a Winston-Lutz test was performed and the deviations of the gantry, collimator and couch isocenter measurements to the phantom position were determined. Additionally, a dose measurement in the phantom was performed and compared to the dose predicted in the treatment planning system. To validate the results obtained with the in-house designed phantom, comparative measurements with commercial phantoms were performed. According to the performed end-to-end test, 2 out of the 3 linacs showed isocenter variations larger than 1 mm for collimator and gantry rotations and larger than 2 mm for couch rotations. With an isocenter variation of less than 1 mm for collimator and gantry rotations, 1 linac fulfilled the tolerance for stereotactic treatments without couch rotation. With couch rotation, an isocenter variation of less than 2 mm was detected at this linac, which fulfilled the tolerance for IMRT treatments. The mean dose deviation between measurement and treatment planning system was 1.82% ± 1.03%. The results acquired with the UMM phantom did not show statistically significant deviations to those acquired with relevant other commercial phantoms. The novel end-to-end test procedure allows for a combined dosimetric and geometric treatment evaluation. Besides the commonly performed dose end-to-end test the geometric isocenter deviation within a patient treatment workflow was evaluated and categorized for IMRT or SBRT.