Heterogeneity-corrected vs -uncorrected critical structure maximum point doses in breast balloon brachytherapy

Recent studies have reported potentially clinically meaningful dose differences when heterogeneity correction is used in breast balloon brachytherapy. In this study, we report on the relationship between heterogeneity-corrected and -uncorrected doses for 2 commonly used plan evaluation metrics: maximum point dose to skin surface and maximum point dose to ribs. Maximum point doses to skin surface and ribs were calculated using TG-43 and Varian Acuros for 20 patients treated with breast balloon brachytherapy. The results were plotted against each other and fit with a zero-intercept line. Max skin dose (Acuros) = max skin dose (TG-43) ? 0.930 (R² = 0.995). The average magnitude of difference from this relationship was 1.1% (max 2.8%). Max rib dose (Acuros) = max rib dose (TG-43) ? 0.955 (R² = 0.9995). The average magnitude of difference from this relationship was 0.7% (max 1.6%). Heterogeneity-corrected maximum point doses to the skin surface and ribs were proportional to TG-43-calculated doses. The average deviation from proportionality was 1%. The proportional relationship suggests that a different metric other than maximum point dose may be needed to obtain a clinical advantage from heterogeneity correction. Alternatively, if maximum point dose continues to be used in recommended limits while incorporating heterogeneity correction, institutions without this capability may be able to accurately estimate these doses by use of a scaling factor.     

Late chest wall toxicity after MammoSite breast brachytherapy

PurposeAccelerated partial breast irradiation (APBI) with the MammoSite^® breast brachytherapy (MBB) system is being investigated as an alternative to whole breast radiation in breast conservation therapy (BCT) at multiple centers worldwide. The newness of MBB means a complete understanding of long-term toxicity, particularly involving the chest wall, has yet to be completely articulated. We report the first pathologic rib fractures associated with MBB and dosimetric analysis of the original treatment plans.Methods and MaterialsAs part of ongoing quality assurance, we reviewed the records of 129 sequential patients who underwent MBB for breast cancer and identified those who subsequently had clinically significant and radiographically documented rib fracture(s) involving the ipsilateral chest wall. Equivalent tolerance doses yielding a 5% and 50% risk of rib toxicity within 5 years from treatment with 10 fractions (as with MBB) were previously calculated using the linear quadratic equation based on 2 Gy per fraction treatments delivered to one-third of the rib volume (TD5/5 = 37 Gy; TD50/5 = 44 Gy). The original radiation therapy plans were evaluated vis-à-vis the plane films or PET/CT images documenting the osseous abnormalities and presenting complaints to find the specific fractured ribs. The specific effected ribs were contoured on the planning CT in “bone windows” using the Nucletron MicroSelectron-classic V2 (Nucletron B.V., Veenendaal, The Netherlands) for this analysis and the original patient treatments. With these datasets, we determined the dose–volume characteristics of the effected ribs including maximal dose encompassing the entire rib on one CT slice, V_20Gy, V_30Gy, V_37Gy, V_44Gy , D₅₀, D₂₅, and D₅ (the mean dose to 50%, 25%, and 5% of the rib).ResultsBetween May 2002 and August 2007, three of 105 patients with a minimum of 6-months follow-up who underwent adjuvant APBI by MBB were found to have a total of five treatment-related rib fractures. The average dose–volume characteristics from the original plans were as follows: D₅₀ = 22.1 Gy, D₂₅ = 32.2 Gy, D₅ = 41.6 Gy, max dose to 1 cc = 34.8, D_max (to 0.1 cc) = 45.6 Gy, V₂₀ Gy = 57.4%, V₃₀ Gy = 30.8%, V₃₇ Gy = 15.9%, V₄₄ Gy = 6.6%, and max dose through rib = 35.8 Gy. Two patients sustained two rib fractures and 1 patient had a single rib fracture. Four of five fractures occurred in postmenopausal patients and two of five fractures occurred in a patient with a history of osteoporosis and exposure to adjuvant chemotherapy.ConclusionsFractures occurred in ribs with V₃₇ Gy and V₄₄ Gy each well below 33%. As long-term toxicity data accrue from APBI series, the traditional models for estimating the biologic equivalent dose may benefit from refinements that specifically address the unique radiobiologic and physical properties intrinsic to high-dose-rate brachytherapy for breast conservation therapy.     

Radiologic-anatomic correlation of thoracic vertebrae and rib shadows in chest digital radiograph

The purpose of this study was to provide an introduction to parsing the radiologic appearance of thoracic vertebrae and ribs. In the study, the radiologic-anatomic correlation technique was applied to promote further understanding of normal chest radiographs. The thoracic vertebrae and ribs of chest radiographs were compared with each macroscopic radiologic and computed tomography (CT) image. The rib parsed the linear shadow of the body of the rib. The macroscopic and radiologic images of thoracic vertebrae and ribs were evaluated to explain their normal radiologic findings. The results of such correlation were summarized as follows: 1) The lamina of the vertebral arch was visualized due to anterior rotation of the upper thoracic vertebrae. 2) The density ratio of the thoracic-vertebrae shadow was almost the same in the vertebral body and vertebral arch. 3) The linear shadow superimposed on the rib corresponded to the inferior margin of the rib. The radiologic-anatomic correlation technique was useful to evaluate normal radiologic findings, and the study was useful to radiological technologists.     

多层螺旋CT在肋骨微细骨折诊断中的应用价值

目的 探讨多层螺旋CT薄层重建及曲面重组技术在诊断肋骨微细骨折中的实用价值。方法 对38例临床怀疑肋骨骨折而常规X线平片显示阴性的病例，应用多层螺旋CT扫描并行薄层重建及曲面重组观察。由CT室3组医师分别对常规5mm层厚、1mm层厚横断图像及曲面重组图像进行分析。结果 （1）3组医师应用1mm层厚横断图像及曲面重组图像均确诊26例59根肋骨骨折，另12例未见骨折。3组医师对常规5mm层厚图像的肋骨骨折诊断准确度分别为86．4％、89．8％、94．9％。（2）26例肋骨骨折中单纯左侧肋骨骨折12例、右侧肋骨骨折11例，双侧肋骨骨折3例。（3）按骨折程度分为完全性肋骨骨折18根和不完全性肋骨骨折41根。在18根完全性肋骨骨折中断端错位均不超过2个皮质宽度。结论 不完全性肋骨骨折及无明显移位的完全性肋骨骨折应用X线平片准确诊断困难，薄层重建及曲面重组技术可及时、准确诊断不同程度的肋骨骨折，曲面重组图像清晰、直观地完整显示了肋骨结构及肋骨骨折的位置、形态及程度。     

Utility of CT scan for the diagnosis of chest wall tuberculosis

The objective of this study was to determine the utility of CT scan findings for the diagnosis of chest wall tuberculosis, excluding the spine. We reviewed 15 patients (13 Africans and 2 Indians) with chest wall tuberculosis, retrospectively. The radiologic examination consisted of a plain X-ray and a CT scan of the chest for each patient. The site of disease was the rib in 13 patients or the body of the sternum in 2 patients. One rib was involved in 11 patients, 2 contiguous ribs (one site) in 2 patients, and bilateral disease (two sites) was observed in the remaining patient. The 14 rib sites involved the posterior arc or costovertebral joint in 11 cases, the anterior arc in 2 cases, and the anterior and middle arc in 1 case. The CT scan findings were an abscess (n = 14) or a soft tissue mass (n = 2), osteolytic lesions (n = 13), periosteal reaction (n = 10), and sequestrum (n = 14). Bone sclerosis was observed only in 3 cases of rib involvement. The association of a soft tissue abscess, an osteolytic lesion, and sequestrum, especially in immigrants to France, suggests chest wall tuberculosis on CT scan. Received: 22 October 1998; Revision received: 11 January 1999; Accepted: 8 February 1999     

De novo placement of button gastrostomy catheters in an adult population: experience in 53 patients

PURPOSE: To investigate the feasibility of primary button gastrostomy insertion with the aid of T-fastener gastropexy. MATERIALS AND METHODS: Fifty-three consecutive patients (33 men, 20 women; mean age, 63.4 years) referred for percutaneous radiologic gastrostomy (PRG) underwent primary button gastrostomy insertion over an 18-month period in two centers. Nine of the patients (17%) were referred after failed endoscopic gastrostomy and 44 (83%) were primarily referred for PRG. Indications for gastrostomy included esophageal/head and neck malignancy (n = 33) and neurologic disorders (n = 20). Gastropexy with three or four T-fasteners was performed in all patients and angioplasty balloon catheters (6 mm x 40 mm) were used to measure tract length and dilate the tract. An 18-F dilator was used for final tract dilation. Button gastrostomy catheters with retention balloons were inserted in all patients. Patient follow-up was performed by the department of dietetics, which contacted patients on a weekly basis. RESULTS: Primary button gastrostomy insertion was successful in 52 of 53 patients (98%). The mean gastrostomy button catheter survival was 13.3 weeks (range, 1-28 weeks). No episodes of button occlusion occurred. Since the beginning of this study, 33 patients (63%) have had their gastrostomy buttons replaced. The reasons for button replacement include burst retention balloons (n = 27; 52%), dislodgment of the catheter (n = 4; 8%), and continuing pain/discomfort at the gastrostomy site (n = 2; 4%). CONCLUSION: Button-type gastrostomy catheters can be placed de novo by interventional radiologists without the need for a mature tract, provided a T-fastener gastropexy is used. The balloon retention button devices are not compromised by occlusion but do tend to become dislodged.     

Mesenchymal hamartoma of the chest wall: radiologic manifestations with emphasis on cross-sectional imaging and histopathologic comparison.

PURPOSE: To describe the imaging features of chest wall mesenchymal hamartoma with emphasis on cross-sectional imaging and comparison with histopathologic results. MATERIALS AND METHODS: For 14 mesenchymal hamartomas of the chest wall in 12 children, radiologic studies (computed tomographic [CT] scans [n = 14], radiographs [n = 11], magnetic resonance [MR] images [n = 9], and bone scintigraphic images [n = 1]) were reviewed by four radiologists with consensus agreement. Clinical history was reviewed for patient demographics and symptoms at presentation. Radiologic studies were evaluated for lesion location, size, number of affected ribs, cortical irregularity or erosion, presence and type of matrix mineralization, lung hyperaeration adjacent to the lesion, degree and homogeneity of radionuclide uptake, and intrinsic characteristics on CT and MR images. RESULTS: Patients included seven male and five female children. Nine patients (75%) were younger than 1 year. Five patients had a chest wall mass; in the remaining seven, the lesion was discovered incidentally. All 14 lesions arose from ribs, 11 were located posteriorly, and 11 affected multiple contiguous ribs. Two patients had multifocal disease, each with two discrete lesions. Radiography in all cases revealed a large expansile rib lesion and an associated extrapleural soft-tissue mass, suggesting an aggressive process. Mineralization was seen in seven (64%) lesions at radiography and in 14 (100%) lesions at CT. Hemorrhagic cavities (secondary aneurysmal bone cyst [ABC] regions) were common, seen in nine (64%) lesions at CT and in four (80%) of five lesions imaged with T2-weighted MR imaging. CONCLUSION: Mesenchymal hamartoma of the chest wall may be recognized by its characteristic occurrence in infancy and cross-sectional imaging features of mineralization and hemorrhagic cystic (secondary ABC) components.     

多层螺旋CT初查漏诊肋骨骨折30例分析

目的 通过对胸部外伤初查CT漏诊肋骨骨折的病例分析,探讨轴位像和容积再现(VR)图像在肋骨骨折的诊断价值及其局限性.方法 搜集我院2016年7月至2019年10月初查CT漏诊的肋骨骨折30例(共39根),采用16层螺旋CT胸部扫描,层厚为5.0 mm或7.5 mm,由2位中级以上诊断医师对轴位像和VR图像采用双盲法分析...     

Surface and superficial dose dosimetric verification for postmastectomy radiotherapy

In patients given postmastectomy radiotherapy (PMRT), the chest wall is a very thin layer of soft tissue with a low-density lung tissue behind. Chest wall treated in this situation with a high-energy photon beam presents a high dosimetric uncertainty region for both calculation and measurement. The purpose of this study was to measure and to evaluate the surface and superficial doses for patients requiring PMRT with different treatment techniques. An elliptic cylinder cork and superflab boluses were used to simulate the lung and the chest wall, respectively. Sets of computed tomography (CT) images with different chest wall thicknesses were acquired for the study phantom. Hypothetical clinical target volumes (CTVs) were outlined and modified to fit a margin of 1–3 mm, depending on the chest wall thickness, away from the surface for the sets of CT images. The planning target volume (PTV) was initially created by expanding an isotropic 3-mm margin from the CTV, and then a margin of 3 mm was shrunk from the phantom surface to avoid artifact-driven results in the beam-let intensity. Treatment techniques using a pair of tangential wedged fields (TWFs) and 4-field intensity-modulated radiation therapy (IMRT) were designed with a prescribed fraction dose (D_p) of 180 cGy. Superficial dose profiles around the phantom circumference at depths of 0, 1, 2, 3, and 5 mm were obtained for each treatment technique using radiochromic external beam therapy (EBT) films. EBT film exhibits good characteristics for dose measurements in the buildup region. Underdoses at the median and lateral regions of the TWF plans were shown. The dose profiles at shallow depths for the TWF plans show a dose buildup about 3 mm at the median and lateral tangential incident regions with a surface dose of about 52% of D_p. The dose was gradually increased toward the most obliquely tangential angle with a maximum dose of about 118% of D_p. Dose profiles were more uniform in the PTV region for the 4-F IMRT plans. Most of the PTV region had doses >94% of D_p at depths >1 mm. The mean surface dose was about 65% of D_p for the 4-F IMRT plans. The maximum dose for the 4-F IMRT plans was <118.4% of D_p. The application of added bolus has to consider the treatment technique, tumor coverage, and possible skin reactions. For PMRT, if the chest surface and wall are treated adequately, at least 3 mm bolus should be added to the chest wall when tangential beams and 6-MV photon energy are arranged. However, when the surface and superficial regions are not high-risk areas, an IMRT plan with tangential beams and 6-MV photon energy can provide uniform dose distributions within the PTV, spare the skin reaction, and deliver sufficient doses to the chest wall at depths >1 mm.     

DR双能减影的肋骨成像与胸部成像的对比研究

目的 探讨双能减影对肋骨病变的诊断价值。方法 收集200例病人行胸部数字化X线摄影（DR）双能减影,对双能减影后胸廓的肋骨像与胸部的肋骨像进行对比分析,采用5阶法行ROC曲线解析。结果 200例中肋骨钙化50例,肋骨破坏7例,肋骨骨折22例。双能减影的胸廓肋骨像的ROC曲线解析参数（Az=0.9367）,大于胸部肋骨像的解析参数（Az=0.6830）。结论 胸部DR双能减影对肋骨病变及膈下肋显示明显优于胸部的肋骨像。     

Experience with dilatation of tight esophageal stenoses using a balloon catheter

The dilatation of oesophageal stenoses with balloon catheters was made in 38 patients with 44 stenoses of different origin. The most frequent stenosis was localized in oesophagogastric or oesophagocolic anastomosis after oesophagectomy, postcorrosive stenoses an those after reflux oesophagitis. The stenoses were mostly of filiform type, the diameter being 1-3 mm (79%) less frequently 4-7 mm (21%). It became possible to dilate 37 stenoses up to 10 to 20 mm, four stenoses to 22 mm. In only three cases the stenosis was dilated to less than 10 mm. In six patients it proved necessary to repeat the dilatation within one to six-month intervals. The dilatation failed to give positive in one case.     

Rib fractures in athletes

Rib fractures are the most common serious injury of the chest. They occur most commonly in the middle and lower ribs with blunt trauma, and also with direct force to a small area of the chest wall and violent muscle contractions. Diagnosis is generally not difficult. The athlete should have a chest x-ray to confirm the diagnosis. Differential diagnosis includes severe rib contusion, costochondral separations, muscle strains and pneumothorax. If no internal problems exist, treatment consists of ice, NSAIDs, analgesics and a rib belt or tape. Healing should be well on its way before a return to sports. Fractures of the first 4 ribs or the last 2 ribs, multiple fractures and flail segments are less benign than other fractures, and may result in injury to surrounding structures. First rib and floating rib fractures are uniquely athletic fractures; they are avulsion fractures caused by a sudden vigorous contraction in different directions of pull.     

Skin dose estimation using virtual structures for Contura Multi-Lumen Balloon breast brachytherapy

PurposeTo propose a workflow that uses ultrasound (US)-measured skin–balloon distances and virtual structure creations in the treatment planning system to evaluate the maximum skin dose for patients treated with Contura Multi-Lumen Balloon applicators.Methods and MaterialsTwenty-three patients were analyzed in this study. CT and US were used to investigate the interfractional skin–balloon distance variations. Virtual structures were created on the planning CT to predict the maximum skin doses. Fitted curves and its equation can be obtained from the skin–balloon distance vs. maximum skin dose plot using virtual structure information. The fidelity of US-measured skin distance and the skin dose prediction using virtual structures were assessed.ResultsThe differences between CT- and US-measured skin–balloon distances values had an average of −0.5 ± 1.1 mm (95% confidence interval [CI] = −1.0 to 0.1 mm). Using virtual structure created on CT, the average difference between the predicted and the actual dose overlay maximum skin dose was −1.7% (95% CI = −3.0 to −0.4%). Furthermore, when applying the US-measured skin distance values in the virtual structure trendline equation, the differences between predicted and actual maximum skin dose had an average of 0.7 ± 6.4% (95% CI = −2.3% to 3.7%).ConclusionsIt is possible to use US to observe interfraction skin–balloon distance variation to replace CT acquisition. With the proposed workflow, based on the creation of virtual structures defined on the planning CT- and US-measured skin–balloon distances, the maximum skin doses can be reasonably estimated.     

Chest wall invasion by lung cancer: limitations of CT evaluation

Thirty-three patients with peripheral pulmonary malignancies contiguous with a pleural surface were evaluated for chest wall invasion by computed tomography (CT). CT criteria included pleural thickening adjacent to the tumor, encroachment on or increased density of the extrapleural fat, asymmetry of the extrapleural soft tissues adjacent to the tumor, apparent mass invading the chest wall, and rib destruction. The CT scans were classified as positive, negative, or equivocal for invasion, and a decision matrix was constructed comparing CT results with pathologic data. The sensitivity of CT was 38%, specificity was 40%, and accuracy was 39% for evaluation of invasion if equivocal CT results were counted as radiologic errors. CT scanning has low accuracy in assessing chest wall invasion in patients with peripheral lung cancers.     

Tesio catheter: radiologically guided placement, mechanical performance, and adequacy of delivered dialysis

PURPOSE: Tunneled catheters are an alternative means of vascular access for patients in need of hemodialysis who cannot undergo dialysis through a surgical shunt. This study was undertaken to evaluate the performance of the Tesio dialysis catheter. MATERIALS AND METHODS: A prospective study of the Tesio catheter was performed. Follow-up data regarding catheter function and adequacy of dialysis were obtained from nine hemodialysis facilities. RESULTS: Seventy-nine Tesio catheters were placed in 71 patients. Immediate technical success was 99% (78 of 79 catheters). The procedure complication rate was 9% (seven catheters). Only two complications required intervention: one fatal air embolism and one chest wall hematoma. Sixty-seven catheters in 60 patients were followed up for a total of 4,367 catheter days. Overall, catheter-related infection occurred in 9% (six of 67 catheters). Primary catheter patency was 87% at 1 week, 82% at 1 month, 72% at 3 months, and 66% at 6 months. Mean blood flow was 286 mL/min immediately after insertion, 301 mL/min at 3 months, and 306 mL/min at 6 months. Adequate dialysis dose as reflected by a urea reduction ratio of 60 or more or a urea kinetic modeling, or Kt/V, value of 1.2 or more was observed on at least one occasion for 74% and 76% of catheters, respectively. CONCLUSION: The Tesio catheter is a reasonable means of vascular access for patients who undergo dialysis but are not candidates for surgical shunt placement.     

Long-term results of pulsed irradiation of skin metastases from breast cancer. Effectiveness and sequelae.

PURPOSE: The concept of pulsed brachytherapy suggested by Brenner and Hall requires an unusual fractionation scheme. Effectiveness and sequelae of this new irradiation method were observed in patients with disseminated cutaneous metastases of breast cancer. PATIENTS AND METHODS: A flexible, reusable skin mold (weight 110 g) was developed for use with a pulsed dose rate (PDR) afterloader. An array of 18 parallel catheters (2 mm diameter) at equal distances of 10 or 12 mm was constructed by fixation of the catheters in a plastic wire mesh. The array is sewn between 2 foam rubber slabs of 5 mm thickness to provide a defined constant distance to the skin. Irradiations are possible up to a maximum field size of 20 x 23.5 cm using a nominal 37 GBq Ir-192 source. Pulses of 1 Gy reference dose at the skin surface are applied at a rate of 1 pulse every 1.2 hours (0.8 Gy per hour). The dose distribution is geometrically optimized to provide a homogeneous skin dose (100% +/- 10%). The 80% dose level lies at 5 mm below the skin surface. Between April 1994 and December 1997, 52 patients suffering from cutaneous metastases at the thoracic wall were treated with 54 fields and total doses of 38 to 50 Gy (median 42 Gy) applying 2 PDR courses with a pause of 4 to 5 weeks. RESULTS: Forty-six patients (48 fields) were eligible for evaluation in June 1998. The median follow-up was 16 months (range 7.1 to 46.2 months). Local control was achieved in 40 out of 48 fields (83%) or 41 of 46 patients (89%), respectively. Moist desquamation occurred in 52% of the patients. Late reactions were judged after a minimum follow-up of 6 months. Thirty-two fields had been previously irradiated with external beam therapy to doses of 40 to 60 Gy. Regardless of whether the skin was preirradiated or not all patients surviving long enough developed telangiectasia within 2 years after PDR irradiation. In preirradiated patients (n = 32) skin contractures and/or skin necrosis occurred in 12% each. In newly irradiated patients (n = 14) no contractures or skin necrosis were observed. CONCLUSIONS: Pulsed brachytherapy is an effective and time-sparing method for the treatment of cutaneous metastases from breast cancer. Skin reactions are comparable to the sequelae of orthovoltage therapy. Two sessions of approximately 20 Gy PDR were tolerated on preirradiated skin without severe sequelae.     

Modeling study for optimization of skin dose for partial breast irradiation using Xoft Axxent electronic brachytherapy applicator

PurposeBalloon brachytherapy with the MammoSite system (Hologic Inc., Bedford, MA) is a widely used approach for accelerated partial breast irradiation. Inherent to this approach, high skin doses can occur if the balloon to skin distance is small. This has been associated with late skin toxicity, particularly telangiectasia. The Xoft Axxent electronic brachytherapy balloon applicator (Xoft, Fremont, CA) is a novel device for accelerated partial breast irradiation. It is unique in that it uses an electronic 50-kV source. This source has a pronounced anisotropy with constriction of isodose distribution at the proximal end of the catheter. This anisotropy can be considered as an advantage to optimize skin dose when the cavity to skin distance is small. In this study, we simulated various balloon-insertion orientations to optimized skin surface dose.MethodsBreast phantoms were constructed of tissue-equivalent material. Xoft Axxent balloon catheters were inserted at a distance of 6 mm from the surface. The catheter was placed at three different catheter to surface orientations: (1) perpendicular to the surface, (2) oblique to the surface (45°), and (3) parallel to the surface. Three-dimensional treatment planning was then performed using Nucletron's Plato planning system (Nucletron, Columbia, MD). Multiple dwell positions were used, and the dose was optimized to the target volume. The target volume was defined as volume from the balloon surface to 1-cm distance from the balloon surface or to the phantom surface (if less then 1 cm from the balloon surface). Target volume coverage was compared between plans using dose–volume histograms. Surface doses were compared using isodose line distribution and surface point doses. Plato planned surface doses were then verified by direct measurement using Landauer Dot InLight dosimeters (Landauer, Glenwood, IL).ResultsExcellent target coverage was obtained for all three catheter orientations with a D₉₅ of ≥95%. Surface dose was lowest for the perpendicular orientation with a calculated dose of 99%. The parallel orientation had the highest surface dose of 164%. The oblique orientation showed intermediate results with a surface dose of 117%. Measured surface doses were reproducible and correlated well with calculated values.ConclusionOptimized Xoft Axxent balloon catheter orientation using source anisotropy and multiple dwell positions can be used to minimize excessive skin dose and yet maintain optimal tumor cavity coverage when the cavity to skin distance is small. This has the potential to decrease skin late effects and improve cosmetic outcome. Further clinical study is warranted.     

Optimization of the accelerated partial breast brachytherapy fractionation considering radiation effect on planning target and organs at risk

The same fractionation scheme of accelerated partial breast irradiation (APBI) with brachytherapy is usually applied to APBI patients without considering the radiaton effect on the planning target and organs at risk (OARs) for an individual patient. The purpose of this study is to report the results of optimization of the fractionation scheme by evaluating the radiation effect on target and OARs with a modified linear-quadratic model, universal survival curve (USC), based on dose-volume histograms (DVHs). Ten breast patients treated with multilumen balloon brachytherapy were selected. The minimum skin and chest wall/rib (CW/rib) spacing ranged from 2.5 to 14.3 mm and from 0.5 to 25.0 mm, respectively. The USC model parameters were set as: (1) breast:α = 0.3, β = 0.05; (2) skin: acute reaction α = 0.101, β = 0.009; late reaction α = 0.064, β = 0.029; (3) CW/rib: α = 0.3, β = 0.12. Boundary dose D_t was 6 Gy for both target and OARs. The relation between radiation effects on the target (E_T) and OARs (E_OAR) were plotted for fraction numbers (N) from 1 to 20. If E_T is set at a certain value, the fractionation that results in a minimum E_OAR value corresponds to the optimal fractionation. The results show that the optimal fractionation is different for different OAR damage effects. For most of the patients, N = 2 is best for minimizing skin acute reactions while N = 20 is best for minimizing skin late reactions. N varies from 3 to 20 among patients for minimizing CW/rib toxicity. The determined unique optimal N for treatment delivery was found to vary from 1 to 20 among these 10 patients resulted from balancing the different damage effects considering the spatial dose for a given patient geometry. Optimal fractionation can be achieved for an individual patient by evaluating the radiation effect on tumor and OARs with the USC model based on the patient specific DVHs with APBI brachytherapy.     

Dose perturbation due to catheter materials in high-dose-rate interstitial 192Ir brachytherapy

PurposeCatheters made of either metal or plastic are currently used in brachytherapy treatment to insert radiative sources into patients. However, the radiation dose perturbations due to catheter attenuation are not taken into account in treatment planning. The purpose of this work is to quantify the effects of catheter composition on dose distribution and study their impacts on the overall treatment with high-dose-rate ¹⁹²Ir sources.Methods and MaterialsDose perturbations are first studied in a simplified case consisting of two parallel catheters. The catheter wall is either composed of stainless steel or polyoxymethylene. The attenuations are studied as the distance between the two catheters is varied from 5 to 30 mm. Dose perturbations resulting from irradiation are evaluated with a Monte Carlo GEANT4 dose calculation algorithm. The dose differences are further investigated with seven typical high-dose-rate prostate treatment plans involving 17 catheters.ResultsThe dose differences compared with water in the simplified case reach −4.3 ± 0.1% for stainless steel and 1.7 ± 0.5% for polyoxymethylene at 10 mm above the source when the catheters are separated by a distance of 5 mm. Dose perturbations are reduced in real treatment plans because of the contributions of the many dwell positions. Stainless steel and polyoxymethylene catheters induce on an average a dose difference of −1.3 ± 0.3% and 0.1 ± 0.2%, respectively in the target.ConclusionsThe dose differences reported in this work do not warrant any changes in the clinical procedures.