Stenting of an endograft limb in its acute occlusion after endovascular intervention for an abdominal aortic aneurysm. / Stentirovanie branshi stent-grafta pri ee ostroi okkliuzii posle éndovaskuliarnogo vmeshatel'stva po povodu anevrizmy briushnoi aorty.

Endovascular abdominal aortic aneurysm repair (EVAR) has recently become an operation of choice in the presence of clinical, anatomic and organizational conditions for implantation of a stent graft. However, like any other operation, EVAR bears the risk of various complications. Due to low frequency of EVAR, the problem concerning appropriate policy of managing patients presenting with such types of complications may be difficult. Thrombosis of a stent graft's components is encountered more often compared with "open" prosthetic repair of the abdominal aorta. This complication more frequently requires interventions in the scope of femoro-femoral bypass grafting. Attempts of thrombextraction may lead to disconnection of a stent graft's modules and to embolic complications. Presented herein is a clinical case report wherein proceeding from objective examination and laboratory instrumental studies, namely angiography, we chose a policy of endovascular intervention (stenting) for thrombosis of a stent graft's limb. At 2 years of follow up the patient is currently in a satisfactory condition, as confirmed by the findings of MSCT angiography two years after the intervention.

[Mitomycin C after endoscopic endonasal dacryocystorhinostomy]. / Primenenie mitomitsina-S pri éndoskopicheskoi éndonazal'noi dakriotsistorinostomii.

Mitomycin-C (MMC) is the most frequently used agent for prevention of excessive scarring at the osteotomy site after endoscopic endonasal dacryocystorhinostomy (EEDCR), which, however, being applied during the final stage of the surgery, shows questionable effectiveness. AIM: to evaluate the effectiveness of a new administration route of mitomycin C in EEDCR. MATERIAL AND METHODS: The study included 86 patients (95 cases) in the age range of 62.3±9 years with primary acquired nasolacrimal duct obstruction. All patients underwent P.J. Wormald modification of EEDCR and were further divided into 2 groups. In group 1, MMC was injected into the nasal cavity and lacrimal sac mucosa, while in group 2 it was applied locally according to the standard procedure. To measure tissue concentrations of MMC, mucosal biopsies were taken in patients of Group 1. Systemic absorption of MMC was studied through blood samples in both groups. Clinical efficacy was assessed in 14±5 months after surgery. RESULTS: immediately after injection, the average tissue concentration of mitomicyn C in patients of Group 1, was 390±10 µg/g and 30 minutes later - 120±20 µg/g. No mitomycin C was found in Day 1 tissue samples and in any of the blood samples. Positive clinical results were reported in 97.9% of cases from Group 1 and in 87.2% of cases from Group 2. CONCLUSION: The method of injecting MMC during the final stage of EEDCR has proved clinically effective and safe and can be recommended for use in clinical practice.

Automatic landmark generation for deformable image registration evaluation for 4D CT images of lung.

Deformable image registration (DIR) has become a common tool in medical imaging across both diagnostic and treatment specialties, but the methods used offer varying levels of accuracy. Evaluation of DIR is commonly performed using manually selected landmarks, which is subjective, tedious and time consuming. We propose a semi-automated method that saves time and provides accuracy comparable to manual selection. Three landmarking methods including manual (with two independent observers), scale invariant feature transform (SIFT), and SIFT with manual editing (SIFT-M) were tested on 10 thoracic 4DCT image studies corresponding to the 0% and 50% phases of respiration. Results of each method were evaluated against a gold standard (GS) landmark set comparing both mean and proximal landmark displacements. The proximal method compares the local deformation magnitude between a test landmark pair and the closest GS pair. Statistical analysis was done using an intra class correlation (ICC) between test and GS displacement values. The creation time per landmark pair was 22, 34, 2.3, and 4.3 s for observers 1 and 2, SIFT, and SIFT-M methods respectively. Across 20 lungs from the 10 CT studies, the ICC values between the GS and observer 1 and 2, SIFT, and SIFT-M methods were 0.85, 0.85, 0.84, and 0.82 for mean lung deformation, and 0.97, 0.98, 0.91, and 0.96 for proximal landmark deformation, respectively. SIFT and SIFT-M methods have an accuracy that is comparable to manual methods when tested against a GS landmark set while saving 90% of the time. The number and distribution of landmarks significantly affected the analysis as manifested by the different results for mean deformation and proximal landmark deformation methods. Automatic landmark methods offer a promising alternative to manual landmarking, if the quantity, quality and distribution of landmarks can be optimized for the intended application.

Method for data analysis in different institutions: example of image guidance of prostate cancer patients.

Multi-institutional collaborations allow for more information to be analyzed but the data from different sources may vary in the subgroup sizes and/or conditions of measuring. Rigorous statistical analysis is required for pooling the data in a larger set. Careful comparison of all the components of the data acquisition is indispensable: identical conditions allow for enlargement of the database with improved statistical analysis, clearly defined differences provide opportunity for establishing a better practice. The optimal sequence of required normality, asymptotic normality, and independence tests is proposed. An example of analysis of six subgroups of position corrections in three directions obtained during image guidance procedures for 216 prostate cancer patients from two institutions is presented.

Evaluation of inter-fraction prostate motion using kilovoltage cone beam computed tomography during radiotherapy.

AIMS: The success of delivering the prescribed radiation dose to the prostate while sparing adjacent sensitive tissues is largely dependent on the ability to accurately target the prostate during treatment. Kilovoltage cone beam computed tomography (CBCT) imaging can be used to monitor and compensate for inter-fraction prostate motion, but this procedure increases treatment session time and adds incidental radiation dose to the patient. We carried out a retrospective study of CBCT data to evaluate the systematic and random correction shifts of the prostate with respect to bones and external marks. MATERIALS AND METHODS: A total of 449 daily CBCT studies from 17 patients undergoing intensity-modulated radiotherapy (IMRT) for localised prostate cancer were analysed. The difference between patient set-up correction shifts applied by radiation therapists (via matching prostate position in CBCT and planning computed tomography) and shifts obtained by matching bony anatomy in the same studies was used as a measure of the daily inter-fraction internal prostate motion. RESULTS: The average systematic and random shifts in prostate positions, calculated over all fractions versus only 10 fractions, were not found to be significantly different. DISCUSSION: The measured prostate shifts with respect to bony anatomy and external marks after the first 10 imaging sessions were shown to provide adequate predictive power for defining patient-specific margins in future fractions without a need for ongoing computed tomography imaging. Different options for CBCT imaging schedule are proposed that will reduce the treatment session time and imaging dose to radiotherapy patients while ensuring appropriate prostate cover and normal tissue sparing.

Effect of lateral target motion on image registration accuracy in CT-guided helical tomotherapy: a phantom study.

Optimisation of imaging modes for kilovoltage CT (kVCT) used for treatment planning and megavoltage CT (MVCT) image guidance used in ungated helical tomotherapy was investigated for laterally moving targets. Computed tomography images of the QUASAR Respiratory Motion Phantom were acquired without target motion and for lateral motion of the target, with 2-cm peak-to-peak amplitude and a period of 4 s. Reference kVCT images were obtained using a 16-slice CT scanner in standard fast helical CT mode, untagged average CT mode and various post-processed 4D-CT modes (0% phase, average and maximum intensity projection). Three sets of MVCT images with different inter-slice spacings of were obtained on a Hi-Art tomotherapy system with the phantom displaced by a known offset position. Eight radiation therapists performed co-registration of MVCT obtained with 2-, 4- and 6-mm slice spacing and kVCT studies independently for all 15 CT imaging combinations. In the investigated case, the untagged average kVCT and 4-mm slice spacing for the MVCT yielded more accurate registration in the transverse plane. The average residual uncertainty of this combination of imaging procedures was 0.61 +/- 0.16 mm in the longitudinal direction, 0.45 +/- 0.14 mm in the anterior-posterior direction and insignificant in the lateral direction. Manual registration of MVCT-kVCT study pairs is necessary to account for a target in significant lateral motion with respect to bony structures.

Evaluation of megavoltage CT imaging protocols in patients with lung cancer.

Currently, megavoltage CT studies in most centres with tomotherapy units are performed prior to every treatment for patient set-up verification and position correction. However, daily imaging adds to the total treatment time, which may cause patient discomfort as well as results in increased imaging dose. In this study, four alternative megavoltage CT imaging protocols (images obtained: during the first five fractions, once per week, alternating fractions and daily on alternative weeks) were evaluated retrospectively using the daily position correction data for 42 patients with lung cancer. The additional uncertainty introduced by using a specific protocol with respect to the daily imaging, or residual uncertainty, was analysed on a patient and population bases. The impact of less frequent imaging schedules on treatment margin calculation was also analysed. Systematic deviations were reduced with increased imaging frequency, while random deviations were largely unaffected. Mean population systematic errors were small for all protocols evaluated. In the protocol showing the greatest error, the treatment margins necessary to accommodate residual errors were 1.2, 1.3 and 1.7 mm larger in the left-right, superior-inferior and anterior-posterior directions, respectively, compared with the margins calculated using the daily imaging data. The increased uncertainty because of the use of less frequent imaging protocols may be acceptable when compared with other sources of uncertainty in lung cancer cases, such as target volume delineation and motion because of respiration. Further work needs to be carried out to establish the impact of increased residual errors on dose distribution.

Optimal slice thickness for cone-beam CT with on-board imager.

PURPOSE: To find the optimal slice thickness (Δτ) setting for patient registration with kilovoltage cone-beam CT (kVCBCT) on the Varian On Board Imager (OBI) system by investigating the relationship of slice thickness to automatic registration accuracy and contrast-to-noise ratio. MATERIALS AND METHOD: Automatic registration was performed on kVCBCT studies of the head and pelvis of a RANDO anthropomorphic phantom. Images were reconstructed with 1.0 ≤ Δτ (mm) ≤ 5.0 at 1.0 mm increments. The phantoms were offset by a known amount, and the suggested shifts were compared to the known shifts by calculating the residual error. A uniform cylindrical phantom with cylindrical inserts of various known CT numbers was scanned with kVCBCT at 1.0 ≤ Δτ (mm) ≤ 5.0 at increments of 0.5 mm. The contrast-to-noise ratios for the inserts were measured at each Δτ. RESULTS: For the planning CT slice thickness used in this study, there was no significant difference in residual error below a threshold equal to the planning CT slice thickness. For Δτ > 3.0 mm, residual error increased for both the head and pelvis phantom studies. The contrast-to-noise ratio is proportional to slice thickness until Δτ = 2.5 mm. Beyond this point, the contrast-to-noise ratio was not affected by Δτ. CONCLUSION: Automatic registration accuracy is greatest when 1.0 ≤ Δτ (mm) ≤ 3.0 is used. Contrast-to-noise ratio is optimal for the 2.5 ≤ Δτ (mm) ≤ 5.0 range. Therefore 2.5 ≤ Δτ (mm) ≤ 3.0 is recommended for kVCBCT patient registration where the planning CT is 3.0 mm.

Schedule for CT image guidance in treating prostate cancer with helical tomotherapy.

The aim of this study was to determine the effect of reducing the number of image guidance sessions and patient-specific target margins on the dose distribution in the treatment of prostate cancer with helical tomotherapy. 20 patients with prostate cancer who were treated with helical tomotherapy using daily megavoltage CT (MVCT) imaging before treatment served as the study population. The average geometric shifts applied for set-up corrections, as a result of co-registration of MVCT and planning kilovoltage CT studies over an increasing number of image guidance sessions, were determined. Simulation of the consequences of various imaging scenarios on the dose distribution was performed for two patients with different patterns of interfraction changes in anatomy. Our analysis of the daily set-up correction shifts for 20 prostate cancer patients suggests that the use of four fractions would result in a population average shift that was within 1 mm of the average obtained from the data accumulated over all daily MVCT sessions. Simulation of a scenario in which imaging sessions are performed at a reduced frequency and the planning target volume margin is adapted provided significantly better sparing of organs at risk, with acceptable reproducibility of dose delivery to the clinical target volume. Our results indicate that four MVCT sessions on helical tomotherapy are sufficient to provide information for the creation of personalised target margins and the establishment of the new reference position that accounts for the systematic error. This simplified approach reduces overall treatment session time and decreases the imaging dose to the patient.

Optimal slice thickness for cone-beam CT with on-board imager

Purpose: To find the optimal slice thickness (Δτ) setting for patient registration with kilovoltage cone-beam CT (kVCBCT) on the Varian On Board Imager (OBI) system by investigating the relationship of slice thickness to automatic registration accuracy and contrast-to-noise ratio. Materials and method: Automatic registration was performed on kVCBCT studies of the head and pelvis of a RANDO anthropomorphic phantom. Images were reconstructed with 1.0 ≤ Δτ (mm) ≤ 5.0 at 1.0 mm increments. The phantoms were offset by a known amount, and the suggested shifts were compared to the known shifts by calculating the residual error. A uniform cylindrical phantom with cylindrical inserts of various known CT numbers was scanned with kVCBCT at 1.0 ≤ Δτ (mm) ≤ 5.0 at increments of 0.5 mm. The contrast-to-noise ratios for the inserts were measured at each Δτ. Results: For the planning CT slice thickness used in this study, there was no significant difference in residual error below a threshold equal to the planning CT slice thickness. For Δτ > 3.0 mm, residual error increased for both the head and pelvis phantom studies. The contrast-to-noise ratio is proportional to slice thickness until Δτ = 2.5 mm. Beyond this point, the contrast-to-noise ratio was not affected by Δτ. Conclusion: Automatic registration accuracy is greatest when 1.0 ≤ Δτ (mm) ≤ 3.0 is used. Contrast-to-noise ratio is optimal for the 2.5 ≤ Δτ (mm) ≤ 5.0 range. Therefore 2.5 ≤ Δτ (mm) ≤ 3.0 is recommended for kVCBCT patient registration where the planning CT is 3.0 mm

Consistency check of planned adaptive option on helical tomotherapy.

This study aims to evaluate a new Planned Adaptive software (TomoTherapy Inc., Madison, WI) of the helical tomotherapy system by retrospective verification and adaptive re-planning of radiation treatment. Four patients with different disease sites (brain, nasal cavity, lungs, prostate) were planned in duplicate using the diagnostic planning kVCT data set and MVCT studies of the first treatment fraction with the same optimization parameters for both plan types. The dosimetric characteristics of minimum, maximum, and mean dose to the targets as well as to organs at risk were compared. Both sets of plans were used for calculation of dose distributions in a water-equivalent phantom. Corresponding measurements of these plans in phantom were carried out with the use of radiographic film and ion chamber. In the case of the lung and prostate cancer patients, changes in dosimetric parameters compared to data generated with the kVCT study alone were less than 2%. Certain changes for the nasal cavity and brain cancer patients were greater than 2%, but they were explained in part by anatomy changes that occurred during the time between kVCT and MVCT studies. The Planned Adaptive software allows for adaptive radiotherapy planning using the MVCT studies obtained by the helical tomotherapy imaging system.

[Optimization of MVCT imaging schedule in prostate cancer treatment using helical tomotherapy]. / Optimisation du processus d'imagerie de haute énergie (MVCT) pour la tomothérapie hélicoïdale des cancers de la prostate.

PURPOSE: Megavoltage CT (MVCT) study on helical tomotherapy permits to verify and correct the patient setup by coregistration with the planning kVCT. This process is time-consuming and our objective is to investigate a possibility of using a smaller number of imaging studies in the case of patients with prostate cancer. PATIENTS AND METHODS: The interfraction shifts of 20 patients (about 700 MVCT studies) treated in our institution have been recorded and analyzed. A new reference position has been calculated as an average of shifts observed during different initial number of fractions imaged. RESULTS: The analysis of the reference position obtained for the set of 20 patients as a function of the number of imaging sessions has shown that MVCT studies during first four fractions are sufficient for the majority of patients. CONCLUSION: Imaging during the first four fractions can be used to determine a reference position for patients with prostate cancer treated on helical tomotherapy. A study on Planned Adaptive (TomoTherapy Inc., Madison, WI, USA) software to evaluate the clinical significance of this scenario is currently in process in our institution.

Sci-Thurs PM: Delivery-07: Evaluation of prospects to use daily megavoltage CT studies for adaptive radiotherapy.

PURPOSE: To evaluate gross tumor volume (GTV) changes for non-small cell lung cancer (NSCLC) patients using daily megavoltage CT (MVCT) studies acquired before each treatment fraction on helical tomotherapy, and to relate the potential benefit of adaptive image-guided radiotherapy to changes in GTV. METHODS: 17 patients were prescribed 30 fractions of radiotherapy on helical tomotherapy for NSCLC at London Regional Cancer Program from December 2005 to March 2007. The GTV was contoured on the daily MVCT studies of each patient. Adapted plans were created using merged MVCT-kVCT image sets to investigate the advantages of replanning for patients with differing GTV regression characteristics. RESULTS: The average GTV change observed over 30 fractions was -38%, ranging from -12 to -87%. No significant correlation was observed between GTV change and patient's physical or tumor features. The pattern of GTV changes of the 17 patients could be broadly divided into 3 groups with distinctive potential for benefit from adaptive planning. CONCLUSIONS: GTV changes are difficult to predict quantitatively based on patient or tumor characteristics. If changes do occur, there are points in time during the treatment course when it may be appropriate to adapt the plan to improve sparing of normal tissues. If the GTV decreases by greater than 30% at any point in the first twenty fractions of treatment, adaptive planning is appropriate to further improve the therapeutic ratio.

Poster - Thurs Eve-41: Imaging and radiation delivery in helical tomotherapy: Phantom study of a moving target.

Treating lung cancer with radiation therapy by guaranteed delivery of the prescription dose to the target is difficult due to tumour motion. The standard approach to account for motion effects consists of adding a substantial margin to a lesion visible on the CT study. Larger irradiated volume results in increased dose deposition in healthy lung and the potential for patient complications. This investigation focuses on determining the optimal choice of planning CT mode for improved radiation delivery in terms of better target coverage and sparing of healthy organs. Dosimetric measurements were performed on a helical tomotherapy unit. A Quasar® (Modus Medical Devices, London, ON) respiratory phantom was imaged while a polystyrene target moved sinusoidally with a period of 4 s and amplitude of 2 cm. For target moving in superior-inferior and lateral directions, conventional fast-CT image studies were created, as well as maximum intensity projection (MIP) and average intensity projection (AveIP) image studies using four-dimensional CT information. All types of CT studies were used to develop treatment plans with a prescription of 2 Gy per fraction to the target outlined according to the imaged data. Measurements of dose deposition were made in four locations within the moving target using an Exradin A1SL ion chamber. Comparing all results to the dose measured at the centre of the static phantom, the MIP plans overdose the target, the fast-CT results vary from case to case, while the AveIP plans provide consistent dose distribution across the target within 2% of the normalization dose.

Tomotherapy as a tool in image-guided radiation therapy (IGRT): theoretical and technological aspects.

Helical tomotherapy (HT) is a novel treatment approach that combines Intensity-Modulate Radiation Therapy (IMRT) delivery with in-built image guidance using megavoltage (MV) CT scanning. The technique utilises a 6 MV linear accelerator mounted on a CT type ring gantry. The beam is collimated to a fan beam, which is intensity modulated using a binary multileaf collimator (MLC). As the patient advances slowly through the ring gantry, the linac rotates around the patient with a leaf-opening pattern optimised to deliver a highly conformal dose distribution to the target in the helical beam trajectory. The unit also allows the acquisition of MVCT images using the same radiation source detuned to reduce its effective energy to 3.5 MV, making the dose required for imaging less than 3 cGy. This paper discusses the major features of HT and describes the advantages and disadvantages of this approach in the context of the commercial Hi-ART system.

Tomotherapy as a tool in image-guided radiation therapy (IGRT): current clinical experience and outcomes.

Modern radiotherapy is characterised by a better target definition through medical imaging accompanied by significantly improved radiation delivery methods, most notably Intensity-Modulate Radiation Therapy (IMRT). However, the treatment can only be as accurate as the positioning of patients for their daily radiotherapy fraction. It is in this context that a number of imaging modalities - ranging from ultrasound to on-board kilovoltage imaging and computed tomography (CT) - have found their way into the treatment room where they verify accurate patient positioning prior to or even during delivery of radiation. Helical tomotherapy (HT) combines IMRT delivery with in-built image guidance using megavoltage CT scanning. This paper discusses the initial experience of different centres with IGRT using HT illustrated by a number of clinical examples from the installation in London in Ontario, Canada, one of the world's first HT sites. We found that HT allows the delivery of highly conformal radiation dose distributions combined with adequate daily image acquisition. An important feature of this unit is its seamless integration, which also includes a customised inverse treatment planning system and a quality assurance module for individual patients.

Initial experience in treating lung cancer with helical tomotherapy.

Helical tomotherapy is a new form of image-guided radiation therapy that combines features of a linear accelerator and a helical computed tomography (CT) scanner. Megavoltage CT (MVCT) data allow the verification and correction of patient setup on the couch by comparison and image registration with the kilovoltage CT multi-slice images used for treatment planning. An 84-year-old male patient with Stage III bulky non-small cell lung cancer was treated on a Hi-ART II tomotherapy unit. Daily MVCT imaging was useful for setup corrections and signaled the need to adapt the delivery plan when the patient's anatomy changed significantly.

Comparison of advanced irradiation techniques with photons for benign intracranial tumours.

BACKGROUND AND PURPOSE: The potential benefits and limitations of different radiation techniques (stereotactic arc therapy (SRS/T), intensity modulated radiotherapy (IMRT), helical tomotherapy (HT), Cyberknife and intensity-modulated multiple arc therapy (AMOA)) have been assessed using comparative treatment planning methods on twelve patients presenting with 'benign' brain tumours. MATERIALS AND METHODS: Plans for five acoustic neurinomas, five meningiomas and two pituitary adenomas were computed to generate dose distributions for all modalities using a common CT dataset to delineate planning target volume and organs at risk. RESULTS: HT, AMOA and IMRT resulted superior to SRS/T and Cyberknife for target coverage. For the first group V(95%) ranged from 98% to 100%, minimum dose ranged from 91% to 96% and standard deviation from 0.84% to 1.67%. For organs at risk all techniques respected planning objectives with a tendency of Cyberknife and SRS/T to better spare the brain stem and the healthy brain tissue (e.g., V(20Gy) of 2.0% and 2.3%, respectively, compared to 3.1-5.0% for the other techniques). AMOA is in general preferable to IMRT for all OARs. Conformity index (CI(95)) was better for HT and Cyberknife (both 1.8) and less for AMOA and IMRT (3.9 and 3.0, respectively). CONCLUSION: All techniques provided good OAR sparing and primarily differed in target coverage indices. For the class of tumours investigated in this report, HT, AMOA and IMRT had better target coverage with HT providing the best combination of indeces. Between AMOA and IMRT, target coverage was comparable and, considering organs at risk, AMOA was slightly preferable.

Helical tomotherapy for craniospinal radiation.

Helical tomotherapy (HT) plans for craniospinal radiation were generated for the case of a 4-year-old boy with disseminated ependymoma. The HT plans demonstrated excellent target coverage, homogeneity and organ sparing compared with a conventional linear accelerator based craniospinal radiation plan. On the basis of this case study, further evaluation of HT for craniospinal radiotherapy seems justified.

Verification dosimetry during treatment for helical tomotherapy using radiographic film.

Helical tomotherapy (HT) is a novel radiotherapy treatment modality that allows the delivery of intensity modulated radiation in a rotational fashion. Due to the complexity of the treatment approach, it is desirable to have a simple tool for treatment delivery verification. Radiographic film placed under the patient is exposed to dose from most of the possible beam projections and therefore constitutes a useful in vivo dosimetry record of the whole treatment. Measurements were performed during the initial clinical implementation of HT at the London Regional Cancer Centre on all patients during the first treatment fraction. It was possible to predict the optical density of the film using a dose calculation on a phantom of similar size to the patient. The comparison of expected and delivered dose allows the verification of dose delivery patterns which was found to be particularly useful in the case of treatment interruptions. The absolute dose measured with film differed in general by less than 10% from the expected one despite the fact that no build-up was used on the film. The agreement improved with proximity of the primary target to the location of the film on the treatment couch. Due to the rotational delivery mode, radiographic film was shown to be a useful, cheap and convenient method to verify dose delivery in helical tomotherapy.