Delivered Radiation Dose Research Articles

WE‐E‐332‐02: Dosimetric Characterization of a Cone Beam O‐Arm Imaging System

Purpose: The O‐arm is a cone beam imaging system designed primarily to support orthopedic surgery as well as for image‐guided and vascular surgery. Using a gantry that can be opened or closed, the O‐arm can function as a 2D fluoroscopy device or collect 3D volumetric imaging data like a CT system. Our clinical applications of the O‐arm in spine surgical procedures, assessment of pedicle screw position, kyphoplasty procedures, and etc show that the O‐arm 3D mode provides enhanced imaging information in the surgical procedure compared to radiographs or fluoroscopy alone. However, the radiation dose of the O‐arm has remained uninvestigated. This study is to investigate patient dose and scatter radiation from an O‐arm and compare the results to those from a CT scanner and a conventional C‐arm. Method and Materials: The patient dose was measured using a 0.6 cc Farmer ion chamber and 30 cm long CT head and body phantoms. Scatter radiation was measured at several locations around the O‐arm, at 1m, 2m and 3m distances from the iso‐center of the O‐arm, in both the 2D fluoroscopic mode and the 3D mode with a Radcal 10×5−180 pancake ion chamber using a 30 cm long CTDI body phantom as the source of scatter. The same measurements were made for an OEC C‐arm and a 64 slice CT scanner, respectively. Results: The results show that under identical technical conditions and with the same scan length, the O‐arm 3D mode delivers radiation dose to patients and scatter dose to personnel that is comparable to that of the 64 slice CT scanner. The O‐arm 2D mode produces similar scatter radiation as a conventional GE OEC fluoroscopic C‐arm system. Conclusion: Our study demonstrated that the O‐arm had comparable radiation dose to patients and radiologists as CT and C‐arm systems.

SU‐GG‐T‐157: Commission of 2.5 Mm ModuLeaf MLC for Stereotactic Radiation Therapy

Purpose: Improvements of MLC technology in radiotherapy, including smaller leaf sizes, allow greater accuracy in delivering radiation doses to the target with better conformality. For example, the high ablative doses used in hypo‐fractionated stereotactic body radiotherapy (SBRT) require high precision in dose delivery, thus high precision in commissioning the MLC system to verifiy MLC accuracy. The purpose of this study was to evaluate the procedure and challenges in the commissioning and application of 2.5‐mm small‐leaf MLC. Method and Materials: Siemens' newly‐developed Moduleaf MLC (MMLC) with 2.5mm leaf‐size was commissioned for SBRT. Step‐by‐step QA and application procedures for SBRT commission guidelines were followed. Error tolerance and QA results were analyzed through the entire commission process from beam data preparation, to treatment planning system commission, to treatment plan verification. The commission was divided into 3 phases: mechanical commission, software commission, and comprehensive commission. Isocenter accuracy was assured for mechanical precision. For software commission, the effect of small field factor was analyzed. In comprehensive phase, a single field and a head‐and‐neck case were tested with the QA standard. Results: The commission and clinical implementation of 2.5mm MMLC were described in this study, with provided guidelines for QA procedures from beam data collection and modeling to treatment planning methodology. The accuracy of the MLC mechanic isocenter was within 0.2 mm. At the same time, the treatment modalities with or without the flatten filter were compared, and they were consistent to each other except for the dose‐rate effect. Different MMLC clinical protocols, from SBRT to head‐and‐neck and intracranial treatments, have been suggested. Conclusion: After strictly following the physical QA requirements, we successfully commissioned the new mounted‐on 2.5mm MMLC for SRS/SBRT. In the follow‐up studies, clinical applications with MMLC will be further compared to other on‐site SRS systems, including Gamma‐Knife, and Tomotherapy system.

SU‐GG‐J‐159: Radiation Dose Estimates for in Vivo MicroCT Studies

Purpose: Repeated scans of microCT can deliver radiation dose levels that can perturb the biological response of an animal model. The purpose of this study is to determine if a simple phantom having dimensions that approximate the size of a typical mouse can be substituted for the animal model for radiation dose measurements of microCT scans. Method and Materials: Phantom measurements of radiation dose were performed with a hollow water‐filled acrylic cylinder (OD: 25.4 mm, ID: 19.0 mm) and a lithium fluoride TLD in a PVC pouch immersed in the water compartment of the phantom. CT was performed using a microCT system (X‐O™, Gamma Medica‐Ideas, Northridge, CA) with an x‐ray source of two settings, 75 kVp/0.325 mA and 60 kVp/0.530 mA which are typical for in vivo studies. CT data were acquired using 512 projections over 120 seconds of continuous x‐ray exposure. For comparison, a TLD placed within the thorax of a euthanized mouse (∼30 g) was exposed using the same x‐ray techniques as the phantom. A total of 4 TLDs (one each with two x‐ray settings for the phantom and animal measurements) were read using a Harshaw 6600 TLD reader with correction factors applied for 60–75 kVp x‐ray. Results: The TLD measurements produced dose measurements of 3.645 and 4.255 cGy in the cylindrical phantom, and 4.137 and 4.690 cGy in the euthanized animal, for x‐ray techniques of 75 kVp/0.325 mA and 60 kVp/0.530 mA, respectively. The readings obtained from the phantom measurements were 9–12% lower than those obtained from the animal. Conclusion: The radiation dose measurements using TLDs in the mouse‐sized cylindrical phantom were in a good agreement with the dose measurements in the euthanized animal. This phantom, in combination with TLDs, potentially is a useful tool for estimating radiation dose for serial in vivo studies with microCT.

Radiographic Response to Yttrium-90 Radioembolization in Anterior Versus Posterior Liver Segments

The purpose of our study was to determine if preferential radiographic tumor response occurs in tumors located in posterior versus anterior liver segments following radioembolization with yttrium-90 glass microspheres. One hundred thirty-seven patients with chemorefractory liver metastases of various primaries were treated with yttrium-90 glass microspheres. Of these, a subset analysis was performed on 89 patients who underwent 101 whole-right-lobe infusions to liver segments V, VI, VII, and VIII. Pre- and posttreatment imaging included either triphasic contrast material-enhanced CT or gadolinium-enhanced MRI. Responses to treatment were compared in anterior versus posterior right lobe lesions using both RECIST and WHO criteria. Statistical comparative studies were conducted in 42 patients with both anterior and posterior segment lesions using the paired-sample t-test. Pearson correlation was used to determine the relationship between pretreatment tumor size and posttreatment tumor response. Median administered activity, delivered radiation dose, and treatment volume were 2.3 GBq, 118.2 Gy, and 1,072 cm(3), respectively. Differences between the pretreatment tumor size of anterior and posterior liver segments were not statistically significant (p = 0.7981). Differences in tumor response between anterior and posterior liver segments were not statistically significant using WHO criteria (p = 0.8557). A statistically significant correlation did not exist between pretreatment tumor size and posttreatment tumor response (r = 0.0554, p = 0.4434). On imaging follow-up using WHO criteria, for anterior and posterior regions of the liver, (1) response rates were 50% (PR = 50%) and 45% (CR = 9%, PR = 36%), and (2) mean changes in tumor size were -41% and -40%. In conclusion, this study did not find evidence of preferential radiographic tumor response in posterior versus anterior liver segments treated with yttrium-90 glass microspheres.

Influence of the SURLAS applicator on radiation dose distributions during simultaneous thermoradiotherapy with helical tomotherapy

Simultaneous thermoradiotherapy has been shown to maximize the effect of hyperthermia as a radiation sensitizer in cancer treatment. Here we follow our previous work on feasibility of thermoradiotherapy with the scanning ultrasound reflector linear array system (SURLAS) and TomoTherapy® Hi⋅Art® treatment system, and investigate the influence of the SURLAS hyperthermia applicator on delivered radiation dose with the TomoTherapy. A radiation treatment plan was calculated and the treatment was delivered to a phantom with SURLAS on top simulating the likely clinical setup. Proper positioning of the SURLAS was assisted with a magnetic position-and-orientation tracking device (POTD) and was verified with megavoltage-computed tomography. The delivered dose was measured with an ionization chamber (point measurement) and a radiographic film (2D dose distributions). The planned and delivered point dose data agreed within 0.61% ± 0.63%. Planar dose data agreed within a dose difference of ⩽3% of the maximum dose, and a distance-to-dose-agreement of ⩽1 mm. The susceptibility of the delivered radiation dose on correct SURLAS positioning was studied as well. The largest dose discrepancy was measured for a position for which a maximum number of radiation beams intersected the incorrectly positioned SURLAS within one TomoTherapy gantry rotation. The point dose disagreed by 6.14% ± 0.52%, and 2.25% of pixels of the 2D dose distribution did not pass the 3% dose difference/1 mm distance-to-dose-agreement criteria. Our study showed that correct positioning of the SURLAS applicator had an influence on the delivered radiation dose. Delivered and planned dose distributions were in an excellent agreement when SURLAS was positioned according to the treatment plan. Moving the applicator from its planned position was found to cause a modification of delivered dose distributions. A precise and reproducible positioning of the applicator was assured with a POTD.

Experimental validation of the filtering approach for dose monitoring in proton therapy at low energy

The higher physical selectivity of proton therapy demands higher accuracy in monitoring of the delivered dose, especially when the target volume is located next to critical organs and a fractionated therapy is applied. A method to verify a treatment plan and to ensure the high quality of the hadrontherapy is to use Positron Emission Tomography (PET), which takes advantage of the nuclear reactions between protons and nuclei in the tissue during irradiation producing β +-emitting isotopes. Unfortunately, the PET image is not directly proportional to the delivered radiation dose distribution; this is the reason why, at the present time, the verification of depth dose profiles with PET techniques is limited to a comparison between the measured activity and the one predicted for the planned treatment by a Monte Carlo model. In this paper we test the feasibility of a different scheme, which permits to reconstruct the expected PET signal from the planned radiation dose distribution along beam direction in a simpler and more direct way. The considered filter model, based on the description of the PET image as a convolution of the dose distribution with a filter function, has already demonstrated its potential applicability to beam energies above 70 MeV. Our experimental investigation provides support to the possibility of extending the same approach to the lower energy range ([40, 70] MeV), in the perspective of its clinical application in eye proton therapy.

Preoperative Treatment Combining Capecitabine with Radiation Therapy in Rectal Cancer: A GERCOR Phase II Study

Objective(s): To assess efficacy and tolerability of preoperative capecitabine chemoradiation in rectal cancer. Methods: Patients received radiotherapy 45 Gy in 25 fractions over 5 weeks and capecitabine 825 mg/m² twice daily throughout radiotherapy. Surgery was performed 5–7 weeks after radiotherapy. The primary endpoint was pathological complete response, secondary endpoints were downstaging and tolerability. Results: Fifty-one patients were enrolled in a phase II study, median age 62 years (range 35–78). Sixty-three percent of tumours involved the lower third of the rectum, 45% were fixed. The median delivered radiotherapy dose was 44.8 Gy (range 39.6–45.0 Gy) over 33–49 days. The treatment-related grade 3 adverse events were diarrhoea (12%), skin reactions (8%) and asthenia (8%), with no grade 4 toxicity. Fifty patients underwent surgery (29 conservative) and 1 patient refused. The pathological complete response rate was 20% and a further 10% of patients had minimal residual disease. Additional tumour downstaging was seen in 28% of patients and the sphincter preservation rate was 58%. Conclusions: Preoperative capecitabine chemoradiation is well tolerated and its efficacy supports further exploration, both as a single agent and as part of new therapeutic strategies.

The Role of mTOR Inhibition in Augmenting Radiation Induced Autophagy

Radiation affects both tumor and normal tissues, limiting the total delivered radiation dose. Therefore, novel ways to exploit molecular targets and improve the therapeutic ratio are continually being investigated. Autophagy plays an important role in cancer cell death decisions, particularly in solid tumors. This is counterbalanced by its function in cellular energy preservation. Recent studies have attempted to exploit autophagy in order to improve therapeutic ratio. However, direct inhibition of autophagy has been demonstrated to promote cancer cell death or survival dependent on cell type and condition. The mammalian target of rapamycin (mTOR) also regulates autophagy, as well as cell survival and proliferation pathways. Therefore, inhibition at this level of signaling would represent an excellent therapeutic target as it would limit cell growth, decrease cell proliferation, and boost autophagocytosis. Current investigations of mTOR inhibitors in combination with radiation appear to potentiate radiation's ability to induce autophagy. Further studies are necessary to fully elucidate which tumors have the most robust induction of autophagy in response to mTOR inhibition and radiation.

Prospects for microbeam radiation therapy of brain tumours in children to reduce neurological sequelae

Microbeam radiation therapy (MRT), a form of experimental radiosurgery of tumours using multiple parallel, planar, micrometres-wide, synchrotron-generated X-ray beams ('microbeams'), can safely deliver radiation doses to contiguous normal animal tissues that are much higher than the maximum doses tolerated by the same normal tissues of animals or patients from any standard millimetres-wide radiosurgical beam. An array of parallel microbeams, even in doses that cause little damage to radiosensitive developing tissues, for example, the chick chorioallantoic membrane, can inhibit growth or ablate some transplanted malignant tumours in rodents. The cerebella of 100 normal 20 to 38g suckling Sprague-Dawley rat pups and of 13 normal 5 to 12kg weanling Yorkshire piglets were irradiated with an array of parallel, synchrotron-wiggler-generated X-ray microbeams in doses overlapping the MRT-relevant range (about 50-600Gy) using the ID17 wiggler beamline tangential to the 6GeV electron synchrotron ring at the European Synchrotron Radiation Facility in Grenoble, France. Subsequent favourable development of most animals over at least 1 year suggests that MRT might be used to treat children's brain tumours with less risk to the development of the central nervous system than is presently the case when using wider beams.

SU-FF-J-81: Estimation of Dose Variations During Prostate Radiation Treatment Due to Elastic Deformations of Soft Tissues

Objective: The true dose distribution is subject to change due to organ shifts and also deformations. The goal of this work is to estimate the effect of the elastic organ deformations on the dose distribution for the average prostate IMRT treatment. Methods: A prostate patient was surveyed during the radiation treatment (IRB approved). The original treatment plan was created based on the planning CT. On-board cone beam computed tomography (CBCT) images were taken before treatments for the first 5 days and once a week therafter. The prostate, seminal vesicles (SV), bladder and rectum segmented on each CBCT were deformably registered against the planning CT. The analysis was conducted with the help of C++ ITK image registration and segmentation package. Initially, a volume (e.g., prostate and bladder) segmented on the planning CT scan was aligned against corresponding volume on the daily CBCT scan using a translational filter. Then, the aligned volume on CBCT was elastically deformed (Finite Element elastic deformation method), and the computed deformation vector field was used to propagate the true delivered radiation dose distribution to the original CT-based volume of the patient. Results: For the plan with a planning target volume (PTV) defined as a combination of both prostate and SV with a 5-mm margin, the DVH parameters fluctuated as follows (Vx denotes percent volume above x% of the prescription dose): prostate mean V100 76%, mean V95 97%, compared to the original prostate 98.15% and 100%, rectum and bladder mean V50 49% and 75% correspondingly, compared to the original rectum and bladder 50% and 29%. Conclusions: This study shows that some deviations from the planned dose may occur due to elastic distortion of soft tissue geometry. The developed suite of applications can be used to monitor actual delivered dose to the targets and critical structures.

SU-FF-T-339: Pediatric Sarcoma Radiotherapy: Target Coverage and Normal Tissue Sparing in 66 Patients Treated with External-Beam Photon Techniques

Purpose: To investigate the variation in target coverage, normal tissue dosimetry, and treatment planning statistics for pediatric sarcoma patients treated with external-beam radiation therapy (EBRT) and develop a baseline for future comparison of new methods and modalities such as proton and intensity-modulated arc therapy. Methods: From January 2003 to July 2005, 66 pediatric patients (1.4–21.6 years old, median 11.6) with soft-tissue and bone sarcomas were prospectively treated on an institutional phase II protocol using EBRT that included forward planned multi-segment 3-dimensional conformal (FPMS-RT) or inverse-planned intensity-modulated radiation therapy (IMRT) with or without low-dose-rate brachytherapy. Results: Beam arrangement consisted of 2-field (11%), multifield coplanar (49%), and noncoplanar (40%). Fields per fraction averaged 7 (2–19) utilizing 6MV (88%) and 6/15MV (12%) photons. MU per fraction averaged 333 (252 for FPMS-RT and 478 for IMRT). PTV ranged from 35 cm3 to 4657 cm3. Total delivered radiation doses ranged from 41.4Gy to 70.2Gy (median, 50.4Gy). Beam delivery time for each fraction (including inter-field beam-off) averaged 9 minutes (5.2 minutes non-IMRT, 17 minutes IMRT with a range of 7–45 minutes). Median PTV D95 and V95 were, respectively, 93.4% of the prescribed dose and 94.6% of the target volume for the initial phase and 97.8% and 99.2% for a reduced volume phase. The spinal cord dose exceeded 45 Gy and was limited to 52 Gy (<1 c.c.) in 13 out of 36 patients due to tumor involvement or target volume proximity (spinal cord tumors). Conclusions: Improvements in conformity and dose gradient with current methods are still required for challenging paraspinal and head and neck cases. In general, critical organ constraints compromise the delivery of intended high dose to the planned target; however, the inability to achieve CTV coverage (V95>95%) for some patients does not appear to result in significant risk of early local recurrence.

SU-DD-A2-04: Validation of the Mechanical Systems for a Tomotherapy Hi-Art Unit

Purpose: To validate the accuracy of the table and gantry motion of the Tomotherapy Hi-Art system and to measure the range of table deflection and to assess the impact on dose delivery. Method and Materials: The Tomotherapy Hi-Art system delivers radiation dose to a target using a helical tomotherapy delivery. Because of this fact, the mechanical accuracy of the table speed and gantry rotation speed, which determine the pitch of the delivery, are extremely important. The amount of table sag relative to the treatment plan is also critical. Table speed and gantry speed were measured by attaching a marker with three reflective spheres to both the table top and gantry structure. The position of the markers was monitored with a Polaris infra-red camera system. Measurements were taken for 4 treatments of varying pitch. The table top sag for 0, 150, and 300 pounds weight was measured both at the end of the table and at the isocenter for different table positions. The impact of this on a delivered plan was checked by measuring a plan using film dosimetry with 0, 150, and 300 pounds of added weight. Results: Table speed was verified to be accurate within 0.5%. The average gantry rotation period was found to be within 0.02 seconds of the planned value. The maximum sag at the end of the table ranged from 1.25 to 3.35 cm. The sag at isocenter ranged from 0.5 to 1.4 cm. The results translate to a maximum deflection angle of 1.1 degrees. The resulting films showed a maximum shift in isodose curves of 1 mm in the vertical direction. Conclusion: The mechanical systems on the Tomotherapy unit are capable of producing the planned pitch values with high accuracy. The table deflection while substantial does not significantly affect the accuracy of the delivery.

Three-dimensional computed craniofacial tomography (3D-CT): potential uses and limitations

Abstract Aims To determine the potential uses and limitations of 3D-CT craniofacial imaging in contemporary clinical practice. Methods The relevant historical and contemporary literature was reviewed. Results There would seem to be many potential uses for 3D-CT craniofacial imaging in clinical practice. Significant limitations may, however, relate to the availability and cost of such imaging and the delivered radiation dose. Conclusions With continued research and development, the use of such 3D-CT craniofacial imaging techniques may become appropriate for future orthodontic and clinical diagnostic applications.

Accuracy of two heterogeneity dose calculation algorithms for IMRT in treatment plans designed using an anthropomorphic thorax phantom

With the advent of intensity-modulated radiation therapy (IMRT), the inclusion of heterogeneity corrections is further complicated by the conformal delivery of many small beams forming steep dose gradients. Radiation treatment planning has evolved to take into account even small changes in tissue density so that the dose to tumor can be further optimized. However, different treatment planning systems incorporate different heterogeneity correction algorithms, and it is unclear whether any of these algorithms are superior to others in terms of accurately predicting delivered radiation doses relative to measurement in a clinical setting. The purpose of this study was to determine the accuracy of heterogeneity dose calculations from two widely used IMRT treatment planning systems (Pinnacle and Corvus) against measurement. These two systems handle heterogeneity dose corrections by means of a collapsed-cone convolution superposition algorithm and a finite-size pencil-beam algorithm with one-dimensional depth scaling correction, respectively. Treatment plans were generated by each system using an anthropomorphic thorax phantom, routine clinical lung tumor constraints, and a common prescribed dose. Dose measurements made by thermoluminescent detectors (TLDs) and radiochromic film positioned within the phantom's lung and offset tumor insert were then compared with the calculated values. The collapsed cone convolution superposition dose calculation algorithm provided clinically acceptable results (+/-5% of the normalization dose or 3 mm distance to agreement) in the designed treatment plan and delivery. The pencil-beam algorithm with an effective pathlength correction showed reasonable agreement within the gross tumor volume, overestimated dose within a majority of the planning target volume, and underestimated the extent of the penumbral broadening, yielding only about 60% accuracy when judged by the above criterion. Even judged by a more generous criterion (+/-7% /7 mm), the results were clinically unfavorable (at only about 80% accuracy). To ascertain the dose in heterogeneous regions such as the tumor-lung interface and the peripheral lung dose near the tumor, the superposition convolution algorithm that accounts for lateral scatter and electron transport should be used. The use of the pencil-beam algorithm with only an effective pathlength correction may result in the dose to the target being overestimated. As a result, a full understanding of any treatment planning system's heterogeneity algorithm is required prior to clinical implementation.

Multidetector row CT for imaging the paediatric tracheobronchial tree

The introduction of multidetector row computed tomography (MDCT) scanners has altered the approach to imaging the paediatric thorax. In an environment where the rapid acquisition of CT data allows general hospitals to image children instead of referring them to specialist paediatric centres, it is vital that general radiologists have access to protocols appropriate for paediatric applications. Thus a dramatic reduction in the delivered radiation dose is ensured with optimal contrast bolus delivery and timing, and inappropriate repetition of the scans is avoided. This article focuses on the main principles of volumetric CT imaging that apply generically to all MDCT scanners. We describe the reconstruction techniques for imaging the paediatric thorax and the low-dose protocols used in our institution on a 16-slice detector CT scanner. Examples of the commonest clinical applications are also given.

Brain Metastases from Endometrial Carcinoma: Report of Three Cases and Review of the Literature

Endometrial carcinoma is a rare cause of brain metastases, accounting for less than 1% of all metastatic lesions to the brain. This report aims to review our experience in the treatment of patients with brain metastases from endometrial carcinoma in order to establish the characteristics of these patients and evaluate the results and efficacy of whole-brain radiation therapy as a palliative measure. Three cases of brain metastases from endometrial carcinoma treated with radiotherapy were identified in the files of the Division of Radiotherapy at the A. Businco Regional Oncological Hospital of Cagliari between 1999 and 2005. All patients had brain metastases as the only sign of systemic disease (a single lesion in 2 patients and 2 lesions in 1 patient). Two patients were classified as RTOG RPA class I and 1 patient as class III. Radiotherapy to the brain was delivered after surgical resection in the first 2 patients and as the only method of palliation in the third patient. The delivered radiation dose was 3000 cGy in 10 fractions over 2 weeks in the postoperative setting and 2000 cGy in 5 fractions over 1 week to the patient treated with irradiation alone. The 2 surgically treated patients are alive and well after 16 and 64 months, respectively. The patient treated with palliative intent died 2 months after irradiation. The combination of surgery and postoperative whole-brain irradiation in selected patients with solitary brain metastases from endometrial carcinoma is an effective method of palliation.

Dose-guided radiation therapy with megavoltage cone-beam CT

Recent advances in fractionated external beam radiation therapy have increased our ability to deliver radiation doses that conform more tightly to the tumour volume. The steeper dose gradients delivered in these treatments make it increasingly important to set precisely the positions of the patient and the internal organs. For this reason, considerable research now focuses on methods using three-dimensional images of the patient on the treatment table to adapt either the patient position or the treatment plan, to account for variable organ locations. In this article, we briefly review the different adaptive methods being explored and discuss a proposed dose-guided radiation therapy strategy that adapts the treatment for future fractions to compensate for dosimetric errors from past fractions. The main component of this strategy is a procedure to reconstruct the dose delivered to the patient based on treatment-time portal images and pre-treatment megavoltage cone-beam computed tomography (MV CBCT) images of the patient. We describe the work to date performed to develop our dose reconstruction procedure, including the implementation of a MV CBCT system for clinical use, experiments performed to calibrate MV CBCT for electron density and to use the calibrated MV CBCT for dose calculations, and the dosimetric calibration of the portal imager. We also present an example of a reconstructed patient dose using a preliminary reconstruction program and discuss the technical challenges that remain to full implementation of dose reconstruction and dose-guided therapy.

EUS-guided fiducial placement for CyberKnife radiotherapy of mediastinal and abdominal malignancies

The CyberKnife frameless image-guided stereotactic radiosurgery system delivers radiation doses to tumors with high precision by use of real-time image guidance. Radiographic markers (or fiducials) implanted at the tumor site are used as reference points by the system to target the radiation beams. Diagnostic and interventional EUS have multiple applications in the multidisciplinary approach to tumors. The goal of this prospective study was to evaluate the safety and feasibility of placing fiducials in mediastinal and intra-abdominal tumors under EUS guidance. Patients were evaluated for EUS-guided fiducial placement. A linear echoendoscope was used to localize the tumor, insert a 19-gauge fine needle in the target area, and place the fiducials through the needle lumen. The position of the fiducials was verified by EUS and by fluoroscopy. Georgetown University Hospital, between February 2005 and August 2005. Thirteen patients scheduled to undergo CyberKnife radiation therapy. EUS-guided fiducial placement was successful in a total of 11 of 13 patients (84.6%). The locations of the tumors were as follows: retrocrural area at the dome of the diaphragm, porta hepatis, gastroesophageal junction, mediastinum, thoracic paraspinal area, and pancreas. A total of 3 to 6 fiducials were placed in each patient. An infectious complication developed in 1 patient within 30 days of the procedure. EUS-guided fiducial placement in lesions of the mediastinum and abdomen is a feasible and safe technique that can be used to mark a tumor site and guide CyberKnife radiation therapy. This new application of interventional EUS further expands the role of EUS in the multidisciplinary approach to the oncology patient.

Novel lung IMRT planning algorithms with nonuniform dose delivery strategy to account for respiratory motion

To effectively deliver radiation dose to lung tumors, respiratory motion has to be considered in treatment planning. In this paper we first present a new lung IMRT planning algorithm, referred as the dose shaping (DS) method, that shapes the dose distribution according to the probability distribution of the tumor over the breathing cycle to account for respiratory motion. In IMRT planning a dose-based convolution method was generally adopted to compensate for random organ motion by performing 4-D dose calculations using a tumor motion probability density function. We modified the CON-DOSE method to a dose volume histogram based convolution method (CON-DVH) that allows nonuniform dose distribution to account for respiratory motion. We implemented the two new planning algorithms on an in-house IMRT planning system that uses the Eclipse (Varian, Palo Alto, CA) planning workstation as the dose calculation engine. The new algorithms were compared with (1) the conventional margin extension approach in which margin is generated based on the extreme positions of the tumor, (2) the dose-based convolution method, and (3) gating with 3 mm residual motion. Dose volume histogram, tumor control probability, normal tissue complication probability, and mean lung dose were calculated and used to evaluate the relative performance of these approaches at the end-exhale phase of the respiratory cycle. We recruited six patients in our treatment planning study. The study demonstrated that the two new methods could significantly reduce the ipsilateral normal lung dose and outperformed the margin extension method and the dose-based convolution method. Compared with the gated approach that has the best performance in the low dose region, the two methods we proposed have similar potential to escalate tumor dose, but could be more efficient because dose is delivered continuously.

Estimation of patient organ doses from CT examinations in Tanzania

Although the use of CT in medical diagnosis delivers radiation doses to patients that are higher than those from other radiological procedures, lack of optimized protocols could be an additional source of increased dose in developing countries. The aims of this study are, first, to determine the magnitude of radiation doses received by selected radiosensitive organs of patients undergoing CT examinations and compare them with other studies, and second, to assess how CT scanning protocols in practice affect patient organ doses. In order to achieve these objectives, patient organ doses from five common CT examinations were obtained from eight hospitals in Tanzania. The patient organ doses were estimated using measurements of CT dose indexes (CTDI), exposure‐related parameters, and the ImPACT spreadsheet based on NRPB conversion factors. A large variation of mean organ doses among hospitals was observed for similar CT examinations. These variations largely originated from different CT scanning protocols used in different hospitals and scanner type. The mean organ doses in this study for the eye lens (for head), thyroid (for chest), breast (for chest), stomach (for abdomen), and ovary (for pelvis) were 63.9 mGy, 12.3 mGy, 26.1 mGy, 35.6 mGy, and 24.0 mGy, respectively. These values were mostly comparable to and slightly higher than the values of organ doses reported from the literature for the United Kingdom, Japan, Germany, Norway, and the Netherlands. It was concluded that patient organ doses could be substantially minimized through careful selection of scanning parameters based on clinical indications of study, patient size, and body region being examined. Additional dose reduction to superficial organs would require the use of shielding materials.PACS numbers: 87.59 Fm; 87.66Jj; 87.52‐g