Tight Margins Research Articles

Taking a Fresh View of Riser Margin for Deepwater Wells Potentially Boosts Safety

This article, written by Editorial Manager Adam Wilson, contains highlights of paper OTC 22889, ’A Step Change in Safety: Drilling Deepwater Wells With Riser Margin,’ by Robert Ziegler, SPE, Petronas, prepared for the 2012 Offshore Technology Conference, Houston, 30 April-3 May. The paper has not been peer reviewed. Riser margins were abandoned when fluid columns in risers became too long with increasing water depth accessed when floating drilling units with subsea blowout preventers (BOPs) moved to deep water. Removing risers in disconnect events means wells go underbalanced and rely on BOPs to contain wellbore pressure. With the advent of a simple retrofit dual-gradient system based on partially evacuating the riser by pumping mud returns back to surface from an outlet in the riser, riser margin in the form of an overbalanced well can be reintroduced in many cases. Setting the Scene Deepwater drilling has a multitude of unique challenges. Water depth: Cold temperatures combine with long fluid columns with high pressures at the seabed most often sitting squarely in the hydrate-formation zone. Ocean forces put mechanical stresses on the riser system. Perhaps most challenging, a highly complex hydraulic system, the subsea BOP, must be operated remotely in a very hostile environment. Deepwater depositional environment: This leads in most cases to a very tight margin between formation strength and pore pressure. Existing emergency procedures: In the case of a loss of position of the rig, a complex sequence of disconnecting from the BOP must be initiated. The BOP also needs to be closed before the lower marine riser package is disconnected and must reliably seal the wellbore because, by removing the riser, the well becomes underbalanced because primary well control by mud weight is lost. Status Quo The solutions that the industry has embarked on to address these challenges have often been overly complex evolutionary developments instead of clean-sheet designs, leading to high costs and an unavoidable increase of mechanical failure modes. The best example for this approach is the current generation of subsea BOPs. In their functionality, these devices remain close to the original patent in 1929; but, today, they are very large, complex, and heavy (350 tons) devices that require an enormous amount of maintenance and testing. Even if a BOP is closed on an inflow in time so the flow is entirely contained below the BOP, circulating out this kick by an established “driller’s method” very often proves to be difficult if not impossible. This is mainly related to two factors. One is the risk of hydrate formation. The moment gas and free water are mixed in the BOP area, hydrates will form. The second factor is the narrow margin between fracture gradient and pore pressure. Very often, the formation is not able to support the backpressure created by the choke line friction, and circulation without losses can never be established.

Superiority of a Real-Time Planning Technique Over Image Guided Radiation Therapy for the Treatment of Primary Prostate Cancers

Image-Guided Radiation Therapy (IGRT) increases the precision and accuracy of external beam radiation therapy and provides a safer delivery of higher, more curative levels of radiation dose. However, when significant changes to internal anatomy occur, IGRT alone will not be able to compensate for the dose degradation that may occur from using the original IMRT plan. A real-time planning (RTP) or adaptive planning technique would enable the continued use of tight margins with the assurance of full target coverage and efficient normal tissue sparing.

Image guidance for post-prostatectomy radiotherapy: Are we missing the mark?

56 Background: Image-guided radiation therapy (IGRT) has been widely adopted for both definitive and post-operative prostate radiotherapy. In the postoperative setting, numerous studies of prostate bed motion have recommended tight planning margins (<10mm) if IGRT is used daily. The purpose of this analysis is to determine the effect of IGRT on the efficacy and toxicity of post-operative prostate radiotherapy. Methods: Between 1998 and 2010, 286 patients received radiation therapy after prostatectomy at Duke. Recurrent disease following radiation therapy was defined as PSA >0.2 ng/ml and rising or initiation of salvage ADT. CTCAE v 4.0 and the RTOG/LENT late morbidity scores were used to grade acute and late toxicities. Risk for biochemical failure and late Grade 2+ GI toxicity were compared between IGRT (N = 113) and non-IGRT (N = 173) patients using multivariable adjusted Cox regression controlling for age, treatment technique (3D vs IMRT), radiation dose, androgen suppression, pathologic Gleason Score, margin status, pathologic stage, and pre-radiotherapy PSA level. Results: The median margin size for patients with IGRT was 7mm (IQR 6-10mm) and 15mm (IQR 7-15mm) for those without IGRT (p < 0.001). Median follow up was 21 months (IQR 15-33 mo) for patients with IGRT and 49 months (IQR 30-73 mo) for those without IGRT (p < 0.001). On multivariate analysis, patients treated with IGRT had a greater risk of progression versus non-daily imaging (HR = 2.51, p < 0.001), as did patients who received salvage versus adjuvant radiotherapy (HR = 2.41, p = 0.005). Higher pathologic Gleason Score (HR = 1.96, p = 0.026) and pathologic stage (HR = 1.93, p = 0.003) conferred increased risk of progression, while positive margin status was protective (HR = 0.53, p = 0.002). Age, radiation dose, androgen suppression, and treatment technique did not affect biochemical outcome (p > 0.1). There were no differences in acute or late GI toxicity according to treatment technique or use of IGRT (both p > 0.1). Conclusions: The use of IGRT was associated with increased biochemical recurrence for patients receiving post-operative prostate radiotherapy. For these patients, we recommend using treatment margins of at least 10mm to address subclinical disease and organ motion.

Image-Guided Radiotherapy-On Center Stage

Linear accelerator-based radiotherapy, an actor on the therapeutic anticancer stage for the past 50 years, acts indiscriminately of cancer cell types and cell surface markers. Both cancer and normal cells sustain potentially lethal DNA damage, with normal cells often repairing radiation-induced damage quickly after exposure [2]. Today, local control of cancer may happen through use of radiation treatment portals depositing radiation dose that use narrow margins around a cancer target. This is done all in an effort to spare healthy normal tissues from intolerant radiation dose. To provide tight radiation dose margins requires high mechanical accuracy of linear accelerators and even better accuracy in patient positioning. There is an unmet need for radiotherapy technology that assists in accurate patient positioning prior to radiation delivery. Up-to-now, this need has been met by image-guided radiotherapy. With new celebrity-like buzz surrounding emerging novel radiotherapy platforms, radiation oncologists and medical physicists must screen each radiotherapy platform’s overall technologic portfolio. Critical to a platform’s performance is its linear accelerator treatment isocenter. The treatment isocenter is the ideal isocenter point about which all linear accelerator motions occur. Also, the treatment isocenter references all images used in image-guided radiotherapy. Perhaps most compelling, it is the position that informs algorithms calculating radiation dose prescription and resultant radiation dosimetry. While the treatment isocenter is optimal, in actual radiation delivery, a radiation isocenter serves as the focal point for linear accelerator movements. Rather than being a point in space like the treatment isocenter, the radiation isocenter is thought of as a small sphere in space. The radiation isocenter deviates, on a small scale in all directions, from the treatment isocenter based on positional uncertainties of the mechanical gantry, collimator, and couch rotation [3]. The coincidence of the treatment isocenter and radiation isocenter in clinical practice is limited ideally to ± one millimeter for stereotactic radiosurgery and ± two millimeters for intensity modulated radiation therapy [3]. Novel radiotherapy platforms delivering conventional or ablative (>7 Gy per fraction) radiation by integrated robotics and finetuned microleaf collimators must be held to even greater accuracy in radiation isocenter alignment. Imagine image-guided radiotherapy platforms that allow for intrafraction and interfraction compensation for cancer target movement as a consequence of physiologic change in organ size, shape, and motions due to respiration, heartbeat, swallowing, and differential rectal and bladder fillings.

Implementation of a generic concurrent engineering environment framework for boatbuilding

Boatbuilding is a growth market with global competition and tight profit margins. Concurrent engineering is not presently prevalent within the boatbuilding industry and yet this is a technique that has found much success in other industries. A methodology has, therefore, been developed to aid design in the leisure boatbuilding industry. This environment uses collaborative engineering and automated communication to aid the passing of direct communication between all members of the design team. This paper determines the characteristics of importance within boatbuilding and relates these to a framework concurrent engineering environment aimed specifically at this industry. The current work focuses on the structural and production subsystems in an attempt to improve design for production. The use of concurrent engineering tools has been highlighted with an example.

Superiority of a Real-time Planning Technique Over Image Guided Radiation Therapy for the Treatment of Primary Prostate Cancers

Image-Guided Radiation Therapy (IGRT) increases the precision and accuracy of external beam radiation therapy and provides a safer delivery of higher, more curative levels of radiation dose. However, when significant changes to internal anatomy occur, IGRT alone will not be able to compensate for the dose degradation that may occur from using the original IMRT plan. A real-time planning (RTP) or adaptive planning technique would enable the continued use of tight margins with the assurance of full target coverage and efficient normal tissue sparing. In its current stage, the adaptive planning technique requires a physician to manually redraw the involved structures before each treatment. These day-to-day contouring variations could potentially be significant and thus overestimate the superiority of the newly created adaptive IMRT plan. A total of 60 CT scans were used during the course of IMRT treatment of 6 prostate cancer patients. An in-room diagnostic CT-on-Rails was used for the purposes of performing daily IGRT in conjunction with an adaptive IMRT planning technique. While the data was analyzed for the standard purposes of IGRT, a brand new optimized IMRT plan was created based on a new set of structures drawn by the on-call physician. This resulting plan was then compared to the initial IMRT plan or “recalculated plan” which was copied onto the new data set and recalculated with the daily IGRT implemented shifts. The RTP plan consistently showed at least equal effectiveness in target coverage and normal-tissue sparing as the initial IMRT recalculated plan. In 25% of the cases, greater rectal sparing was seen in the RTP plan with the largest single case reducing V50 by 40% and V60 by 50%. The most frequent anomalies seen in this study, however, were target coverage of the prostate and PTV. While the RTP plan maintained minimum prescription dose coverage of 97% to the prostate, the recalculated IMRT plan's minimum dose routinely fell below 95%, and in 20% of the cases, it dropped below 90%. In terms of PTV minimum coverage, the recalculated IMRT plan showed consistent dose degradation with 90% of the cases falling below 90% of the prescribed dose. Daily changes of the internal anatomy warrant the need for RTP. To our knowledge, we are one of the first to implement this technique in our daily clinical practice on a consistent basis. RTP possesses the ability to treat other cancer sites besides the prostate and its full potential maybe realized once better and faster auto-segmentation programs are available to minimize manual contouring variability.

Influence of Rotational Setup Error on Tumor Shift in Bony Anatomy Matching Measured with Pulmonary Point Registration in Stereotactic Body Radiotherapy for Early Lung Cancer

To examine the correlation between the patient rotational error measured with pulmonary point registration and tumor shift after bony anatomy matching in stereotactic body radiotherapy for lung cancer. Twenty-six patients with lung cancer who underwent stereotactic body radiotherapy were the subjects. On 104 cone-beam computed tomography measurements performed prior to radiation delivery, rotational setup errors were measured with point registration using pulmonary structures. Translational registration using bony anatomy matching was done and the three-dimensional vector of tumor displacement was measured retrospectively. Correlation among the three-dimensional vector and rotational error and vertebra-tumor distance was investigated quantitatively. The median and maximum rotational errors of the roll, pitch and yaw were 0.8, 0.9 and 0.5, and 6.0, 4.5 and 2.5, respectively. Bony anatomy matching resulted in a 0.2-1.6 cm three-dimensional vector of tumor shift. The shift became larger as the vertebra-tumor distance increased. Multiple regression analysis for the three-dimensional vector indicated that in the case of bony anatomy matching, tumor shifts of 5 and 10 mm were expected for vertebra-tumor distances of 4.46 and 14.1 cm, respectively. Using pulmonary point registration, it was found that the rotational setup error influences the tumor shift. Bony anatomy matching is not appropriate for hypofractionated stereotactic body radiotherapy with a tight margin.

Sci-Fri PM: Delivery - 02: CT image guidance strategies for dose-adaptive IMRT of the prostate.

On-line CT imaging in the radiotherapy room has become the norm for targeted intensity-modulated radiotherapy (IMRT), enabling precise adjustments of the daily patient setup based on soft tissue visualization. Corrections for plasticity of the anatomy and dose deformation are within technological reach but will require more on-line resources. We have developed a computer model that allows exploration of "what if" scenarios for assessing the benefits of Image Guidance strategies in terms of the multi-fraction dose distribution and DVH metrics (Target D95 and rectum V70). In this work we report on changes in anatomy and resultant dose distribution as observed in 35 daily megavoltage CT (MVCT) scans of the pelvis during prostate therapy for 13 patients. Our goal is to assess the effectiveness and efficiency of various adaptive strategies involving imaging schedule with and without dose re-planning of 5-field IMRT with 18 MV x-rays. Our research questions are: To what extent do radiation dose distributions delivered to individual patients (in vivo) diverge from the planned dose distributions (in silico)? Is there a robust schedule of CT image guidance, with or without dose re-planning that will mitigate discrepancies? For prostate IMRT, we conclude that image guidance schedule can be relaxed when generous GTV margins (10/7mm) are used. Tighter margins (isotropic 5 mm) reduce the dose to the rectum as expected. However, daily re-planning may be required to maintain adequate target coverage as planned when tighter margins are used.

Intensity-modulated Radiotherapy in the Treatment of Breast Cancer

Intensity-modulated radiotherapy (IMRT) is a newer method of radiotherapy that uses beams with multiple intensity levels for any single beam, allowing concave dose distributions and tighter margins than those possible using conventional radiotherapy. IMRT is ideal for treating complex treatment volumes and avoiding close proximity organs at risk that may be dose limiting and provides increased tumour control through an escalated dose and reduces normal tissue complications through organ at risk sparing. Given the potential advantages of IMRT and the availability of IMRT-enabled treatment planning systems and linear accelerators, IMRT has been introduced in a number of disease sites. This systematic review examined the evidence for IMRT in the treatment of breast cancer to quantify the potential benefits of this new technology and to make recommendations for radiation treatment programmes considering adopting this technique. Providing that avoidance of acute adverse effects associated with radiation is an outcome of interest, then IMRT is recommended over tangential radiotherapy after breast-conserving surgery, based on a review of six published reports including 2012 patients. There were insufficient data to recommend IMRT over standard tangential radiotherapy for reasons of oncological outcomes or late toxicity. Future research should focus on studies with longer follow-up and provide data on late toxicity and disease recurrence rates.

TU-E-BRB-05: Impact of Interfractional Tumor Motion on Respiratory Gated Stereotactic Body Radiation Therapy for Lung Tumors.

To investigate the impact of interfractional tumor motion on dose delivery of gated lung SBRT. 4DCT scan for five lung patient was performed without breathing control at simulation and prior to each treatment. Gated treatment plans were performed on the end-exhale (50% phase) simulation CT with a 30% duty cycle. ITV was created by combining the GTVs at 40%, 50% and 60% phases. PTV was created by adding a 5 mm uniform margin to the ITV. All plans were normalized such that 60 Gy (3 fractions) was prescribed to the 85% isodose line. To calculate the accumulated dose over the treatment course, the original plan parameters were copied to the 40%, 50% and 60% CTs obtained prior to each treatment. In order to eliminate the effect of setup error to dose delivery, treatment isocenters at each fraction were determined by aligning the tumors on the slow CTs obtained prior to each treatment to that on the slow simulation CT. Doses recalculated on the 40% and 60% CTs at each fraction were warped through deformable CT image registration to their corresponding 50% CT to compose the 4D dose at that fraction. Those fractional 4D doses were warped to the 50% simulation CT to compose the accumulated 4D dose over the treatment course. The minimum tumor doses over the treatment course were 59.9, 45.1, 68.9, 41.9 and 47.8 Gy respectively. Tumor V60s were 99.7, 92.2, 100, 97.2 and 93.0% respectively. The corresponding mean lung doses were 3.8, 6.4, 3.7, 4.4 and 3.7 Gy respectively. Change in tumor motion pattern over the treatment course results in tumor underdosing. Tight margins are normally used in lung SBRT. Therefore monitoring of the reproducibility of interfractional tumor motion is critical to the success of dose delivery.

SU-E-J-122: Quantification of Respiratory-Induced Pancreatic Head Tumor Rotation and Deformation Using 4DCT and Fiducial Markers.

To quantify pancreatic head tumor rotation and deformation due to the respiration using 4DCT and fiducial markers. This study included seventeen pancreatic head tumor patients who were treated with gated SBRT using Novalis system in our institution. Each patient had two 5-mm-long fiducial markers placed in pancreatic head approximately 2 cm apart for the gating treatment. All patients had 4DCT scans of 3mm-slice thickness using a CT scanner (SENSATION, SIEMENS) under free breathing condition to create the internal target volume (ITV). The respiratory curve was generated through a pressure sensor placed on the patient's abdomen. The 4DCT image data sets were binned into 8 phases: 0% inhale (end of exhale), 25% inhale, 50% inhale, 75% inhale, 100% inhale (end of inhale), 75% exhale, 50% exhale, and 25% exhale. The fiducial markers were contoured on each phase of 4DCT images, and the 3D coordinates (x,y,z) of centroid of the fiducial marker were recorded. The distance between two markers was calculated for each phase, and its variation on eight phases indicated the pancreatic head deformation. The orientation change of the two markers on eight phases indicated the pancreatic head rotation. Student t-test was performed for the statistical analysis. Pancreatic head rotation and deformation were observed through the breathing cycle. The largest rotation and deformation happened to the course from 0% inhale to 100% inahle. The rotation was 8.0±6.2 degree ranging from 2 to 20 degree. The deformation was 2.0±2.4 mm ranging from 0 to 6.6 mm. Both were statistically significant with p<10-4 for rotation and p=0.0033 for deformation. The 4DCT images showed significant pancreatic head rotation and deformation due to respiration, and both rotation and deformation were highly variable between patients. For patients receiving SBRT with tight margin, rotation and deformation need to be considered, and individualized margin may be necessary.

SU-E-T-422: Lung SBRT Using Cyberknife: Technique and Treatment Outcome.

At East Carolina University, we have been treating primary and secondary lung cancers with Cyberknife stereotactic body radiotherapy (CK- SBRT) since February 2009. Till October 2011, we have treated a total of 79 patients (83 sites). In this study, we present our experience in CK-SBRT and clinical outcome of the treated patients. Of the 79 patients, 43 were female; age of the whole patient population ranged 33.2-89.7yrs (median=73.2yrs). Patients treated for primary lung cancer (n=57) had severe chronic obstructive pulmonary disease (COPD) and were not surgical candidates. Cyberknife robotic system with tracking techniques (Synchrony=52, XsiteLung=22, XsightSpine=5) were used. Majority of the patient (n=52) had multiple gold fiducials placed (1-6 placed; 1-4 tracked per patient) either percutaneously or bronchoscopically. CT images were used for dosimetric planning, by medical physicists, using Cyberknife MultiPlan software. Prescription doses were 25Gy-55Gy in 3-5 fractions (mean=48.2Gy, median=50Gy); doses were prescribed mainly to 80% isodoseline (range=75-96%, mean=81.4%). PTV margin varied from 0-7mm (mean±SD=3.2±1.4mm), based on the tumor locations; breathing patterns and cancer type. Dosimetric coverage of GTV and PTV were (mean±SD): 97.8±5% and 94.7±6.9%, respectively. The treatment response was assessed using either a CT or a PET scan or both. The median follow up was 13.1months (range 0.3-31.9 months). Overall response rate was 98.8% (CR=73.5%). Local failure free survival at one year was 84% for primary (n=57), 76% for recurrent (n=16) lung cancer and 100% for metastatic (n=10) tumors. The toxicity rate was low with one patient reported to have chest wall pain and one patient developed grade 3-4 radiation pneumonitis. In most of the cases tight PTV margins were used. Since the prescriptions were at 80% isodeose line with more than 94% PTV coverage, the treatment outcome appeared reasonable. Further study relating PTV margin, dosimetric coverage, and treatment outcome is in progress.

Demand Side Response: Challenges &amp; Opportunities for providing equilibrium in the UK electricity market

UK Electricity thermal generation is creaking at the seams. A large amount of coal and oil fuelled generation has and is retiring due to age and environmental legislation including the European Union Large Combustion Plant Directive. Furthermore, challenging economics for gas fuelled generation has resulted in few new power plants being built and in fact many being mothballed, including units only two years old, until the business case for their operation becomes more favourable. The resulting decline in capacity and generator availability has lead to very tight capacity margins – the difference between electricity supply and demand levels, which can make National Grid's role – the UK's Transmission System Operator (TSO) – in matching generation and demand quite challenging. Indeed, spare electricity power production in the electricity system is predicted to fall to only 2% by 2015, increasing the risks of blackouts across the UK, should an unforeseen operational issue arise or the UK experience a cold winter. Demand Side Response (DSR) could provide an important contribution to managing security of supply and cutting energy consumption. It offers a cheaper and greener alternative to building new generating capacity and could make a meaningful contribution towards security of supply. This study provides a brief overview of the recent developments on the growing DSR market in the UK. Fast acting, clean flexible load is a unique asset which currently is virtually untapped in the UK. With the emerging regulatory support in the UK and across Europe, this is a valuable commodity which can potentially meet the pressures of peak electricity demand while giving businesses security over their power supply needs. The role of the Demand Response Aggregator (DRA) using an Automated Demand Response (ADR) platform to draw on flexible loads across many sites in a coordinated and automated fashion has been discussed. Furthermore, the relationship between the DRA and ADR Technology Solution Provider in establishing a new business to provide aggregated demand response (load adjustment; down and up) as a service to distribution network operators, TSOs, and wholesale Traders have been explored.

Predicting Isocenter Shift due to Prostate Motion and Selecting Patient Specific Posterior Margin for IGRT of Prostate

Purposes/Objective: Image-Guided Radiation Therapy has been shown to significantly decrease setup errors and correct for organ motions (by patient repositioning, referred to as shift here), thus allowing the use of a tight treatment margin. The objective of the present work is to show that our evidenced-based patient positioning technique (isocenter shift) can effectively reduce the overall setup error for the majority of prostate patients. Methods and Materials: We reviewed and analyzed the pre-treatment CT scans of 87 prostate patients treated from 2005-2007. Each patient received 10-15 image-guided fractions in the first phase of the treatment course. By systematically analyzed the imaging data and comparing to the planning CT, the isocenter positioning in both the left-right and anterior-posterior directions in the second phase of the treatment course can be predicted, along with the selection of a patient specific posterior margin. Results: For 90% of the patients, the isocenter correction can be predicted to within 95% confidence. 90% of the patients in the study have a posterior margin in the range 5-8 mm for the second phase of treatment. The outliers in the frequency distributions of the iso-shifts for both the left-right and anterior-posterior directions seems to indicate that more frequent image-guided sessions are required in order to improve the setup accuracy. Conclusions: An adequate number of image-guided treatments provide a semi-pattern recognition approach for patient repositioning. This, together with the inclusion of a quasi-adaptive margin can accommodate the daily variance of the prostate positions and affords a 95% confidence limit for tumor coverage. Our evidence-based method can effectively reduce the systematic setup error which potentially could modify the cumulative dose distribution. The use of adaptive strategy as proposed in this work reduces the overall setup error.

Motion-compensated estimation of delivered dose during external beam radiation therapy: Implementation in Philips’ Pinnacle3treatment planning system

Recent research efforts investigating dose escalation techniques for three-dimensional conformal radiation therapy (3D CRT) and intensity modulated radiation therapy (IMRT) have demonstrated great benefit when high-dose hypofractionated treatment schemes are implemented. The use of these paradigms emphasizes the importance of smaller treatment margins to avoid high dose to surrounding normal tissue or organs at risk (OARs). However, tighter margins may lead to underdosage of the target due to the presence of organ motion. It is important to characterize organ motion and possibly account for it during treatment delivery. The need for real-time localization of dynamic targets has encouraged the use and development of more continuous motion monitoring systems such as kilo-voltage/fluoroscopic imaging, electromagnetic tracking, and optical monitoring systems. This paper presents the implementation of an algorithm to quantify translational and rotational interfractional and intrafractional prostate motion and compute the dosimetric effects of these motion patterns. The estimated delivered dose is compared with the static plan dose to evaluate the success of delivering the plan in the presence of prostate motion. The method is implemented on a commercial treatment planning system (Pinnacle(3), Philips Radiation Oncology Systems, Philips Healthcare) and is termed delivered dose investigational tool (DiDIT). The DiDIT implementation in Pinnacle(3) is validated by comparisons with previously published results. Finally, different workflows are discussed with respect to the potential use of this tool in clinical treatment planning. The DiDIT dose estimation process took approximately 5-20 min (depending on the number of fractions analyzed) on a Pinnacle(3) 9.100 research version running on a Dell M90 system (Dell, Inc., Round Rock, TX, USA) equipped with an Intel Core 2 Duo processor (Intel Corporation, Santa Clara, CA, USA). The DiDIT implementation in Pinnacle(3) was found to be in agreement with previously published results, on the basis of the percent dose difference (PDD). This metric was also utilized to compare plan dose versus delivered dose, for prostate targets in three clinically acceptable treatment plans. This paper presents results from the implementation of an algorithm on a commercially available treatment planning system that quantifies the dosimetric effects of interfractional and intrafractional motion in external beam radiation therapy (EBRT) of prostate cancer. The implementation of this algorithm within a commercial treatment planning system such as Pinnacle(3) enables easy deployment in the existing clinical workflow. The results of the PDD tests validate the implementation of the DiDIT algorithm in Pinnacle(3), in comparison with previously published results.

Effect of dose prescription and block margin on small field treatment planning

AbstractBackground and purpose: We evaluated the effect of block margin on small fields when point dose prescription (ICRU) or isodose line prescription (RTOG) formats are used.Material and methods: A total of 11 clinical SBRT cases, one 4-field prostate case and 2 phantom cases using 0, 0.5 or 1 cm block margins were analysed. Integral dose and target coverage were compared using DVHs and isodose volumes for either isodose line prescription (100% Rx dose to 95% PTV volume) or isocenter point prescription (100% Rx dose to the isocenter) were calculated.Results: Tight planning target margins using isodose line prescription leads to good target coverage but high dose heterogeneity with hot spots possibly exceeding 140% of the prescription dose for small target volumes. As block margin is increased, target coverage converges for the two methods but point dose prescriptions result in better dose homogeneity. For a given block margin, integral doses are consistently larger for isodose line prescription over point prescription, but are similar when block margins are adjusted to produce equal target coverage. As target size increases dose heterogeneity and integral dose differences disappear.Conclusions: For small targets, the ICRU point prescription method can produce comparable PTV coverage to the isodose line prescription method with less dose heterogeneity and comparable integral dose. Reduction of hot spots in potentially normal tissue and reporting clarity makes this internationally recommended prescription standard preferable.

Loop-mediated isothermal amplification (LAMP) assays for the species-specific detection of Eimeria that infect chickens

BackgroundEimeria parasites can cause the disease coccidiosis in poultry and even subclinical infection can incur economic loss. Diagnosis of infection predominantly relies on traditional techniques including lesion scoring and faecal microscopy despite the availability of sensitive molecular assays, largely due to cost and the requirement for specialist equipment. Despite longstanding proven efficacy these traditional techniques demand time and expertise, can be highly subjective and may under-diagnose subclinical disease. Recognition of the tight economic margins prevailing in modern poultry production and the impact of avian coccidiosis on poverty in many parts of the world has highlighted a requirement for a panel of straightforward and sensitive, but cost-effective, Eimeria species-specific diagnostic assays.ResultsLoop-mediated isothermal amplification (LAMP) is an uncomplicated, quick and relatively inexpensive diagnostic tool. In this study we have developed a panel of species-specific LAMP assays targeting the seven Eimeria species that infect the chicken. Each assay has been shown to be genuinely species-specific with the capacity to detect between one and ten eimerian genomes, equivalent to less than a single mature schizont. Development of a simple protocol for template DNA preparation from tissue collected post mortem with no requirement for specialist laboratory equipment supports the use of these assays in routine diagnosis of eimerian infection. Preliminary field testing supports this hypothesis.ConclusionsDevelopment of a panel of sensitive species-specific LAMP assays introduces a valuable new cost-effective tool for use in poultry husbandry.

Stereotactic Body Radiation Therapy for Patients with Heavily Pretreated Liver Metastases and Liver Tumors

Stereotactic body radiation therapy (SBRT) offers better accuracy, tighter margins and higher dose delivery for liver tumors. Initial reports on CyberKnife SBRT for liver have shown promising local control with minimal toxicity for select patients. We present our initial experience in a heavily pretreated group of liver metastases and primary liver tumor patients.

Stereotactic Body Radiation Therapy for Prostate Cancer

Stereotactic body radiation therapy (SBRT) is a promising treatment option for prostate cancer. Hypofractionation regimens, such as SBRT, may be more advantageous compared with conventional regimens because low α:β ratio of prostate cancer has high sensitivity to dose per fraction. In addition, a smaller and tighter margin with SBRT is expected to provide a low toxicity rate without reducing tumor control. The purpose of this article is to examine radiobiological, technical and clinical aspects of SBRT for prostate cancer.

Harnessing Radiation Technology to Improve Survival

Harnessing Radiation Technology to Improve Survival