Daily online adaptive magnetic resonance image (MRI) guided stereotactic body radiation therapy for primary renal cell cancer

Stereotactic body radiotherapy (SBRT) has demonstrated promising outcomes for patients with early-stage, medically inoperable, primary renal cell carcinoma (RCC) in large multi-institutional studies and prospective clinical trials. The traditional approach used in these studies consisted of a CT-based planning approach for target and organ-at-risk (OAR) volume delineation, treatment planning, and daily treatment delivery. Alternatively, MRI-based approaches using daily online adaptive radiotherapy have multiple advantages to improve treatment outcomes: (1) more accurate delineation of the target volume and OAR volumes with improved soft tissue visualization; (2) gated beam delivery with biofeedback from the patient; and (3) potential for daily plan adaptation due to changes in anatomy to improve target coverage, reduce dose to OARs, or both. The workflow, treatment planning principles, and aspects of treatment delivery specific to this technology are outlined using a case example of a patient with an early-stage RCC of the right kidney treated with MRI-guided SBRT using daily adaptive treatment to a dose of 42 Gy in 3 fractions.     

Characterization of the Transmission of the Elekta Stereotactic Body Frame (ESBF) and Accounting for it During Treatment Planning

The purpose of this study was to measure the transmission of the Elekta Stereotactic Body Frame (ESBF) and treatment table, to calculate the transmission of the frame in the Eclipse Treatment Planning System (TPS) using analytical anisotropic algorithm (AAA), and to demonstrate a simple method of accounting for this transmission in treatment planning. A solid water body phantom was imaged inside the ESBF and planned with multiple 3D-CRT fields using AAA using both 6-MV and 16-MV energies. In the first set of plans, the frame and table were included in the “Body” contour and, therefore, used in the dose calculations. In the second set of plans, the frame and the table were not included in the “Body” contour and, therefore, were not incorporated in the calculations. The latter simulated a setup in which there was no frame or table. Eclipse TPS will only incorporate data from the CT set in calculations, if it is included in the “Body” contour. The plans were treated under two conditions: one with the phantom in the ESBF and one without the frame on a specially designed table. This table allows all the beams to enter the phantom without passing through any attenuating material (i.e., table or frame). Transmission of the frame and table was determined by the ratio of the measurements with the frame and table to the measurements without them. To validate the accuracy of the calculation model, plans with homogeneous phantom and a heterogeneous plan were compared with the measurements. The transmission of the frame varies from 89–94% depending on the angle of the beams and whether they also intercept the table. The AAA algorithm calculated the transmission of the frame and table to within 2% of the measurements for all gantry angles. Validation results showed that AAA can calculate the dose to the target to within 2% of the measured value. The attenuation caused by the ESBF must be accounted for in the planning process. For Eclipse, the frame should be contoured and included in all calculations. This can be done easily and accurately.     

Definition of stereotactic body radiotherapy

This report from the Stereotactic Radiotherapy Working Group of the German Society of Radiation Oncology (Deutschen Gesellschaft für Radioonkologie, DEGRO) provides a definition of stereotactic body radiotherapy (SBRT) that agrees with that of other international societies. SBRT is defined as a method of external beam radiotherapy (EBRT) that accurately delivers a high irradiation dose to an extracranial target in one or few treatment fractions. Detailed recommendations concerning the principles and practice of SBRT for early stage non-small cell lung cancer (NSCLC) are given. These cover the entire treatment process; from patient selection, staging, treatment planning and delivery to follow-up. SBRT was identified as the method of choice when compared to best supportive care (BSC), conventionally fractionated radiotherapy and radiofrequency ablation. Based on current evidence, SBRT appears to be on a par with sublobar resection and is an effective treatment option in operable patients who refuse lobectomy.     

Image-Guided Stereotactic Spine Radiosurgery on a Conventional Linear Accelerator

Stereotactic radiosurgery for spinal metastasis consists of a high radiation dose delivered to the tumor in 1 to 5 fractions. Due to the high radiation dose in a single or fewer treatments, the precision of tumor localization and dose delivery is of great concern. Many groups have published their experiences of spinal radiosurgery with the use of CyberKnife System (Accuray Inc.). In this study, we report in detail our approach to stereotactic spine radiosurgery (SSRS) using a conventional linear accelerator (Varian Trilogy), utilizing the features of kilovolt on-board imaging (kV-OBI) and cone beam computed tomography (CBCT) for image guidance. We present our experience in various aspects of the SSRS procedure, including patient simulation and immobilization, intensity-modulated radiation treatment (IMRT) planning and beam selection, portal dosimetry for patient planning quality assurance (QA), and the use of image guidance in tumor localization prior to and during treatment delivery.     

A novel restricted single-isocenter stereotactic body radiotherapy (RESIST) method for synchronous multiple lung lesions to minimize setup uncertainties

Treating multiple lung lesions synchronously using a single-isocenter volumetric modulated arc therapy (VMAT) stereotactic body radiation therapy (SBRT) plan can improve treatment efficiency and patient compliance. However, due to set up uncertainty, aligning multiple lung tumors on a single daily cone beam CT (CBCT) image has shown clinically unacceptable loss of target(s) coverage. Herein, we propose a Restricted Single-Isocenter Stereotactic Body Radiotherapy (RESIST), an alternative treatment that mitigates patient setup uncertainties. Twenty-one patients with two lung lesions were treated with single-isocenter VMAT-SBRT using a 6MV-FFF beam to 54 Gy in 3 fractions (n = 7) or 50 Gy in 5 fractions (n = 14) prescribed to 70-80% isodose line. To minimize setup uncertainties, each plan was re-planned using the RESIST method, utilizing a single-isocenter placed at the patient's mediastinum. It allows for an individual plan to be created for each tumor, using the first plan as the base-dose for the second plan, while still allowing both tumors to be treated in the same session. The technique uses novel features in Eclipse, including dynamic conformal arc (DCA)-based dose and aperture shape controller before each VMAT optimization. RESIST plans provided better target dose conformity (p < 0.001) and gradient indices (p < 0.001) and lower dose to adjacent critical organs. Using RESIST to treat synchronous lung lesions with VMAT-SBRT significantly reduces plan complexity as demonstrated by smaller beam modulation factors (p < 0.001), without unreasonably increasing treatment time. RESIST reduces the chance of a geometric miss due by allowing CBCT matching of one tumor at a time. Placement of isocenter at the mediastinum avoids potential patient/gantry collisions, provides greater flexibility of noncoplanar arcs and eliminates the need for multiple couch movements during CBCT imaging. Efficacy of RESIST has been demonstrated for two lesions and can potentially be used for more lesions. Clinical implementation of this technique is ongoing.     

Image-Guided Stereotactic Body Radiotherapy for Lung Tumors Using BodyLoc With Tomotherapy: Clinical Implementation and Set-Up Accuracy

We investigated the use of a BodyLoc immobilization and stereotactic localization device combined with TomoTherapy megavoltage CT (MVCT) in lung stereotactic body radiotherapy (SBRT) to reduce set-up uncertainty and treatment time. Eight patients treated with 3–5 fractions of SBRT were retrospectively analyzed. A BodyLoc localizer was used in both CT simulation for localization and the initial patient treatment set-up. Patients were immobilized with a vacuum cushion on the back and a thermoplastic body cast on the anterior body. Pretreatment MVCT from the TomoTherapy unit was fused with the planning kilovoltage CT (KVCT) before each fraction of treatment to determine interfractional set-up error. The comparison of two MVCTs during a fraction of treatment resulted in the intrafractional uncertainty of the treatment. A total of 224 target isocenter shifts were analyzed to assess these inter- and intrafractional tumor motions. We found that for interfractional shifts, the mean set-up errors and standard deviations were –1.1 ± 2.8 mm, –2.5 ± 8.7 mm, and 4.1 ± 2.6 mm, for lateral, longitudinal, and vertical variation, respectively; the mean setup rotational variation was –0.3 ± 0.7°; and the maximum motion was 13.5 mm in the longitudinal direction. For intrafractional shifts, the mean set-up errors and standard deviations were –0.1 ± 0.7 mm, –0.3 ± 2.0 mm, and 0.5 ± 1.1 mm for the lateral, longitudinal, and vertical shifts, respectively; the mean rotational variation was 0.1 ± 0.2°; and the maximum motion was 3.8 mm in the longitudinal direction. There was no correlation among patient characteristics, set-up uncertainties, and isocenter shifts, and the interfractional set-up uncertainties were larger than the intrafractional isocenter shift. The results of this study suggested that image-guided stereotactic body radiotherapy using the BodyLoc immobilization system with TomoTherapy can improve treatment accuracy.     

立体定向放射治疗在妇科肿瘤中的应用进展

立体定向放射治疗（SBRT）是近年来兴起的放疗新技术,该技术的优点在于它能够在控制正常组织剂量的前提下提高肿瘤组织的剂量。SBRT在妇科肿瘤中的应用主要集中在盆腔复发灶、腹主动脉旁转移淋巴结、远处转移灶的局部治疗,可获得良好的局部控制,甚至一些患者有长期无病生存的可能。尽管SBRT有严格的剂量限制,但放疗后野内复发灶治疗后出现严重不良反应的概率较高。SBRT可以作为局部晚期宫颈癌体外放疗结束后,因某些因素而无法实施后装治疗的替代治疗。     

Clinical outcome of stereotactic body radiotherapy of 54 Gy in nine fractions for patients with localized lung tumor using a custom-made immobilization system

Purpose The aim of this study was to investigate the clinical outcome of stereotactic body radiotherapy (SBRT) of 54 Gy in nine fractions for patients with localized lung tumor using a custom-made immobilization system. Methods and materials The subjects were 19 patients who had localized lung tumor (11 primaries, 8 metastases) between May 2003 and October 2005. Treatment was conducted on 19 lung tumors by fixed multiple noncoplanar conformal beams with a standard linear accelerator. The isocentric dose was 54 Gy in nine fractions. The median overall treatment time was 15 days (range 11–22 days). All patients were immobilized by a thermo-shell and a custom-made headrest during the treatment. Results The crude local tumor control rate was 95% during the follow-up of 9.4–39.5 (median 17.7) months. In-field recurrence was noted in only one patient at the last follow-up. The Kaplan-Meier overall survival rate at 2 years was 89.5%. Grade 1 radiation pneumonia and grade 1 radiation fibrosis were observed in 12 of the 19 patients. Treatment-related severe early and late complications were not observed in this series. Conclusion The stereotactic body radiotherapy of 54 Gy in nine fractions achieved acceptable tumor control without any severe complications. The results suggest that SBRT can be one of the alternatives for patients with localized lung tumors. Part of this work was presented at the 65th annual meeting of the Japan Radiological Society, April 2006     

Radiation injury of the lung after stereotactic body radiation therapy (SBRT) for lung cancer: A timeline and pattern of CT changes

Stereotactic body radiation therapy (SBRT) is a new radiotherapy treatment method that has been applied to the treatment of Stage I lung cancers in medically inoperable patients, with excellent clinical results. SBRT allows the delivery of a very high radiation dose to the target volume, while minimizing the dose to the adjacent normal tissues. As a consequence, CT findings after SBRT have different appearance, geographic extent and progression timeline compared to those following conventional radiation therapy for lung cancer. In particular, SBRT-induced changes are limited to the “shell” of normal tissue outside the tumor and have a complex shape. When SBRT-induced CT changes have a consolidation/mass-like appearance, the differentiation from tumor recurrence can be very difficult. An understanding of SBRT technique as it relates to the development of SBRT-induced lung injury and familiarity with the full spectrum of CT manifestations are important to facilitate diagnosis and management of lung cancer patients treated with this newly emerging radiotherapy method.     

Helical Tomotherapy-Based STAT Stereotactic Body Radiation Therapy: Dosimetric Evaluation for a Real-Time SBRT Treatment Planning and Delivery Program

Stereotactic body radiation therapy (SBRT) treatments have high-dose gradients and even slight patient misalignment from the simulation to treatment could lead to target underdosing or organ at risk (OAR) overdosing. Daily real-time SBRT treatment planning could minimize the risk of geographic miss. As an initial step toward determining the clinical feasibility of developing real-time SBRT treatment planning, we determined the calculation time of helical TomoTherapy–based STAT radiation therapy (RT) treatment plans for simple liver, lung, and spine SBRT treatments to assess whether the planning process was fast enough for practical clinical implementation. Representative SBRT planning target volumes for hypothetical liver, peripheral lung, and thoracic spine lesions and adjacent OARs were contoured onto a planning computed tomography scan (CT) of an anthropomorphic phantom. Treatment plans were generated using both STAT RT “full scatter” and conventional helical TomoTherapy “beamlet” algorithms. Optimized plans were compared with respect to conformality index (CI), heterogeneity index (HI), and maximum dose to regional OARs to determine clinical equivalence and the number of required STAT RT optimization iterations and calculation times were determined. The liver and lung dosimetry for the STAT RT and standard planning algorithms were clinically and statistically equivalent. For the liver lesions, “full scatter” and “beamlet” algorithms showed a CI of 1.04 and 1.04 and HI of 1.03 and 1.03, respectively. For the lung lesions, “full scatter” and “beamlet” algorithms showed a CI of 1.05 and 1.03 and HI of 1.05and 1.05, respectively. For spine lesions, “full scatter” and “beamlet” algorithms showed a CI of 1.15 and 1.14 and HI of 1.22 and 1.14, respectively. There was no difference between treatment algorithms with respect to maximum doses to the OARs. The STAT RT iteration time with current treatment planning systems is 45 sec, and the treatment planning required 3 iterations or 135 sec for STAT RT liver and lung SBRT plans and 7 iterations or 315 sec for STAT RT spine SBRT plans. Helical TomoTherapy–based STAT RT treatment planning with the “full scatter” algorithm provides levels of dosimetric conformality, heterogeneity, and OAR avoidance for SBRT treatments that are clinically equivalent to those generated with the Helical TomoTherapy “beamlet” algorithm. STAT RT calculation times for simple SBRT treatments are fast enough to warrant further investigation into their potential incorporation into an SBRT program with daily real-time planning. Development of methods for accurate target and OAR determination on megavoltage computed tomography scans incorporating high-resolution diagnostic image co-registration software and CT detector–based exit dose measurement for quality assurance are necessary to build a real-time SBRT planning and delivery program.     

Clinical outcome of stereotactic body radiotherapy of 54 Gy in nine fractions for patients with localized lung tumor using a custom-made immobilization system

Purpose

The aim of this study was to investigate the clinical outcome of stereotactic body radiotherapy (SBRT) of 54?Gy in nine fractions for patients with localized lung tumor using a custom-made immobilization system.

Methods and materials

The subjects were 19 patients who had localized lung tumor (11 primaries, 8 metastases) between May 2003 and October 2005. Treatment was conducted on 19 lung tumors by fixed multiple noncoplanar conformal beams with a standard linear accelerator. The isocentric dose was 54?Gy in nine fractions. The median overall treatment time was 15 days (range 11–22 days). All patients were immobilized by a thermo-shell and a custom-made headrest during the treatment.

Results

The crude local tumor control rate was 95% during the follow-up of 9.4–39.5 (median 17.7) months. In-field recurrence was noted in only one patient at the last follow-up. The Kaplan-Meier overall survival rate at 2 years was 89.5%. Grade 1 radiation pneumonia and grade 1 radiation fibrosis were observed in 12 of the 19 patients. Treatment-related severe early and late complications were not observed in this series.

Conclusion

The stereotactic body radiotherapy of 54?Gy in nine fractions achieved acceptable tumor control without any severe complications. The results suggest that SBRT can be one of the alternatives for patients with localized lung tumors.

     

Characterization of differences in calculated and actual measured skin doses to canine limbs during stereotactic radiosurgery using Gafchromic film

Accurate calculation of absorbed dose to the skin, especially the superficial and radiosensitive basal cell layer, is difficult for many reasons including, but not limited to, the build-up effect of megavoltage photons, tangential beam effects, mixed energy scatter from support devices, and dose interpolation caused by a finite resolution calculation matrix. Stereotactic body radiotherapy (SBRT) has been developed as an alternative limb salvage treatment option at Colorado State University Veterinary Teaching Hospital for dogs with extremity bone tumors. Optimal dose delivery to the tumor during SBRT treatment can be limited by uncertainty in skin dose calculation. The aim of this study was to characterize the difference between measured and calculated radiation dose by the Varian Eclipse (Varian Medical Systems, Palo Alto, CA) AAA treatment planning algorithm (for 1-mm, 2-mm, and 5-mm calculation voxel dimensions) as a function of distance from the skin surface. The study used Gafchromic EBT film (International Specialty Products, Wayne, NJ), FilmQA analysis software, a limb phantom constructed from plastic water? (fluke Biomedical, Everett, WA) and a canine cadaver forelimb. The limb phantom was exposed to 6-MV treatments consisting of a single-beam, a pair of parallel opposed beams, and a 7-beam coplanar treatment plan. The canine forelimb was exposed to the 7-beam coplanar plan. Radiation dose to the forelimb skin at the surface and at depths of 1.65 mm and 1.35 mm below the skin surface were also measured with the Gafchromic film. The calculation algorithm estimated the dose well at depths beyond buildup for all calculation voxel sizes. The calculation algorithm underestimated the dose in portions of the buildup region of tissue for all comparisons, with the most significant differences observed in the 5-mm calculation voxel and the least difference in the 1-mm voxel. Results indicate a significant difference between measured and calculated data extending to average depths of 2.5 mm, 3.4 mm, and 10 mm for the 1-mm, 2-mm, and 5-mm dimension calculation matrices, respectively. These results emphasize the importance of selecting as small a treatment planning software calculation matrix dimension as is practically possible and of taking a conservative approach for skin treatment planning objectives. One suggested conservative approach is accomplished by defining the skin organ as the outermost 2–3 mm of the body such that the high dose tail of the skin organ dose-volume histogram curve represents dose on the deep side of the skin where the algorithm is more accurate.     

Simple and effective immobilization for radiation treatment of choroidal melanoma

At our institution, patients diagnosed with choroidal melanoma requiring external beam radiation therapy are treated with two 6 MV volumetric-modulated arcs delivering 50 Gy over 5 daily fractions. The patient is immobilized using an Orfit head and neck mask and is directed to look at a light emitting diode (LED) during CT simulation and treatment to minimize eye movement. Patient positioning is checked with cone beam computed tomography (CBCT) daily. Translational and rotational displacements greater than 1 mm or 1° off the planned isocenter position are corrected using a Hexapod couch. The aim of this study is to verify that the mask system provides adequate immobilization and to verify our 2-mm planning target volume (PTV) margins are sufficient. Residual displacements provided by pretreatment verification and post-treatment CBCT data sets were used to assess the impact of patient mobility during treatment on the reconstructed delivered dose to the target and organs at risk. The PTV margin calculated using van Herk's method¹ was used to assess patient motion plus other factors that affect treatment position, such as kV-MV isocenter coincidence. Patient position variations were small and were shown to not cause significant dose variations between the planned and reconstructed dose to the target and organs at risk. The PTV margin analysis showed patient translational motion alone required a PTV margin of 1 mm. Given other factors that affect treatment delivery accuracy, a 2-mm PTV margin was shown to be sufficient for treatment of 95% of our patients with 100% of dose delivered to the GTV. The mask immobilization with LED focus is robust and we showed a 2-mm PTV margin is adequate with this technique.     

Stereotactic radiotherapy in the liver hilum

Background

A basis for future trials with stereotactic body radiotherapy (SBRT) for tumors of the liver hilum should be established. Thus, dosage concepts, planning processes, and dose constraints as well as technical innovations are summarized in this contribution.

Methods

On the background of our own data, the current literature was reviewed. The use of SBRT in the most common tumors of the liver hilum (pancreatic cancer and Klatskin tumors) was investigated. Dose constraints were calculated in 2?Gy standard fractionation doses.

Results

A total of 8?pilot or phase?I/II studies about SBRT in the liver hilum were identified. In recent years, the SBRT technique has developed very quickly from classical stereotactic body frame radiotherapy to IGRT techniques including gating and tracking systems. In the studies using classical body frame technique, patients experienced considerable toxicities (duodenal ulcer/perforation) as compared to tolerable side effects in IGRT studies (<10% grade 3 and 4 toxicities). Dose constraints for duodenum, liver, kidneys, colon, and spinal cord were derived from the investigated studies. Survival and local tumor control data are very heterogeneous: median survival in these patients with locally advanced pancreatic or Klatskin tumors ranges between 5 and 32?months. Excellent local tumor control rates of about 80% over 24?months were achieved using SBRT.

Conclusion

Despite a few negative results, SBRT seems to be a promising technique in the treatment of tumors of the liver hilum. Highest precision in diagnostics, positioning, and irradiation as well as strict dose constraints should be applied to keep target volumes as small as possible and side effects tolerable.     

Immobilization in stereotactic radiotherapy: the head and neck localizer frame.

Stereotactic radiotherapy refers to multiple daily fractions of radiation, over days or weeks of treatment, with the patient in a relocatable stereotactic frame. The linear accelerator-based, couch-mounted system from Radionics utilizes the Gill-Thomas-Cosman (GTC) frame and the new Tarbell-Loeffler-Cosman (TLC) pediatric frame for accurate positioning reproducibility. Radionics has now made available the Head and Neck Localizer (HNL) frame to be used with its XPlan treatment planning system and the mini multileaf collimator (MMLC). This will extend the overall capability of stereotactic radiotherapy to the treatment of head and neck cancers. However, with no data available on the HNL frame, a study is being undertaken to assess the accuracy in patient position reproducibility using the frame. This report provides the preliminary findings of comparing depth-helmet readings with radiographic data, together with recommended modifications to the frame.     

Avoidance sectors to reduce dosimetric impact of an irreproducible pannus on setup uncertainty in prostate SBRT VMAT: A case study

This work investigates whether the use of an avoidance sector in a two-arc volumetric modulated arc therapy (VMAT) prostate stereotactic body radiotherapy (SBRT) plan reduces dosimetric variations due to an irreproducible pannus. A morbidly obese patient with favorable-risk prostate cancer elected treatment with SBRT. The patient was treated with the avoidance arcs across the pannus to eliminate reproducibility issues created by daily pannus variability in set up. For post-treatment assessment, the case was planned using Varian Eclipse? treatment planning system (TPS) with two VMAT arcs with and without 100° avoidance sectors across the pannus. The dose was re-calculated using the external body contour from four daily treatment cone-beam computer tomography scans, and on two virtual body contours created by expanding the pannus region of the external contour by 5 and 10 mm. Dose differences between planned and re-calculated rectal wall mean dose and the V_24Gy were numerically larger in the absence of the avoidance sector for all fractions and for both simulated pannus variations, with maximum changes of 2.6% and 1.3%. Maximum point dose variations in the PTV, CTV, rectum, bladder, and femoral heads were 105 cGy or less for all cases, with and without the avoidance sector. The use of an avoidance sector across this large, asymmetrical pannus did not inhibit achieving dose constraints and provided a reduction in dose variability which was nominal in this case for 10 mm variations. Avoidance sectors can be safely implemented in cases with obvious reproducibility concerns in the setting of prostate VMAT SBRT.     

Optimization and quality assurance of an image-guided radiation therapy system for intensity-modulated radiation therapy radiotherapy

To develop a quality assurance (QA) of XVI cone beam system (XVIcbs) for its optimal imaging-guided radiotherapy (IGRT) implementation, and to construe prostate tumor margin required for intensity-modulated radiation therapy (IMRT) if IGRT is unavailable. XVIcbs spatial accuracy was explored with a humanoid phantom; isodose conformity to lesion target with a rice phantom housing a soap as target; image resolution with a diagnostic phantom; and exposure validation with a Radcal ion chamber. To optimize XVIcbs, rotation flexmap on coincidency between gantry rotational axis and that of XVI cone beam scan was investigated. Theoretic correlation to image quality of XVIcbs rotational axis stability was elaborately studied. Comprehensive QA of IGRT using XVIcbs has initially been explored and then implemented on our general IMRT treatments, and on special IMRT radiotherapies such as head and neck (H and N), stereotactic radiation therapy (SRT), stereotactic radiosurgery (SRS), and stereotactic body radiotherapy (SBRT). Fifteen examples of prostate setup accounted for 350 IGRT cone beam system were analyzed. IGRT accuracy results were in agreement ± 1 mm. Flexmap 0.25 mm met the manufacturer's specification. Films confirmed isodose coincidence with target (soap) via XVIcbs, otherwise not. Superficial doses were measured from 7.2–2.5 cGy for anatomic diameters 15–33 cm, respectively. Image quality was susceptible to rotational stability or patient movement. IGRT using XVIcbs on general IMRT treatments such as prostate, SRT, SRS, and SBRT for setup accuracy were verified; and subsequently coordinate shifts corrections were recorded. The 350 prostate IGRT coordinate shifts modeled to Gaussian distributions show central peaks deviated off the isocenter by 0.6 ± 3.0 mm, 0.5 ± 4.5 mm in the X(RL)- and Z(SI)-coordinates, respectively; and 2.0 ± 3.0 mm in the Y(AP)-coordinate as a result of belly and bladder capacity variations. Sixty-eight percent of confidence was within ± 4.5 mm coordinates shifting. IGRT using XVIcbs is critical to IMRT for prostate and H and N, especially SRT, SRS, and SBRT. To optimize this modality of IGRT, a vigilant QA program is indispensable. Prostate IGRT reveals treatment accuracy as subject to coordinates' adjustments; otherwise a 4.5-mm margin is required to allow for full dose coverage of the clinical target volume, notwithstanding toxicity to normal tissues.     

Welche Faktoren beeinflussen die Reproduzierbarkeit der Patientenlagerung in der täglichen Bestrahlungsroutine?

Aim

Factors which influence the accuracy of the field application during daily irradiation routine are not well known. The aim of this prospective analysis was to determine the significance of these factors on the occurrence of field misadjustments in irradiation without immobilization and to evaluate their clinical relevance

Patients and Method s

Fifty-three patients received external cobalt-60 beam irradiation without fixation. Once weekly portal images of all treatment fields were carried out. In addition to objective patient data (age, weight. height, general condition, irradiation indication), the psychological situation of the patient during treatment (anxiety, restlessness, pain) and work circumstances of the medical staff during treatment were evaluated once weekly. The distance of clearly visible anatomic structures to the field borders of the portal images were measured and the deviation to the corresponding simulator images was calculated. Patient data were correlated to the number of field misadjustments (deviation larger than 1 cm).

Results

Patients whose condition is generally poor and patients being treated palliatively, patients with feeling of anxiety, restlessness or pain during simulation or irradiation and heavy patients (90 kg and more) were more often misadjusted. The number of field misadjustments increased with the stress of the medical staff.

Conclusions

The problem of reproducibility of external beam irradiation without fixation in palliative treatment is of clinical relevance. Effective analgesic therapy and a comfortable and painfree patient set-up reduce misadjustments. In curative treatment, immobilization techniques should be used.     

Dynamic targeting image-guided radiotherapy.

Volumetric imaging and planning for 3-dimensional (3D) conformal radiotherapy and intensity-modulated radiotherapy (IMRT) have highlighted the need to the oncology community to better understand the geometric uncertainties inherent in the radiotherapy delivery process, including setup error (interfraction) as well as organ motion during treatment (intrafraction). This has ushered in the development of emerging technologies and clinical processes, collectively referred to as image-guided radiotherapy (IGRT). The goal of IGRT is to provide the tools needed to manage both inter- and intrafraction motion to improve the accuracy of treatment delivery. Like IMRT, IGRT is a process involving all steps in the radiotherapy treatment process, including patient immobilization, computed tomography (CT) simulation, treatment planning, plan verification, patient setup verification and correction, delivery, and quality assurance. The technology and capability of the Dynamic Targeting IGRT system developed by Varian Medical Systems is presented. The core of this system is a Clinac or Trilogy accelerator equipped with a gantry-mounted imaging system known as the On-Board Imager (OBI). This includes a kilovoltage (kV) x-ray source, an amorphous silicon kV digital image detector, and 2 robotic arms that independently position the kV source and imager orthogonal to the treatment beam. A similar robotic arm positions the PortalVision megavoltage (MV) portal digital image detector, allowing both to be used in concert. The system is designed to support a variety of imaging modalities. The following applications and how they fit in the overall clinical process are described: kV and MV planar radiographic imaging for patient repositioning, kV volumetric cone beam CT imaging for patient repositioning, and kV planar fluoroscopic imaging for gating verification. Achieving image-guided motion management throughout the radiation oncology process requires not just a single product, but a suite of integrated products to manipulate all patient data, including images, efficiently and effectively.