Effectiveness of fractionated stereotactic radiotherapy for uveal melanoma

PURPOSE: To study the effectiveness and acute side effects of fractionated stereotactic radiation therapy (fSRT) for uveal melanoma. METHODS AND MATERIALS: Between 1999 and 2003, 38 patients (21 male, 17 female) were included in a prospective, nonrandomized clinical trial (mean follow-up of 25 months). A total dose of 50 Gy was given in 5 consecutive days. A blinking light and a camera (to monitor the position of the diseased eye) were fixed to a noninvasive relocatable stereotactic frame. Primary end points were local control, best corrected visual acuity, and toxicity at 3, 6, 12, and 24 months, respectively. RESULTS: After 3 months (38 patients), the local control was 100%; after 12 months (32 patients) and 24 months (15 patients), no recurrences were seen. The best corrected visual acuity declined from a mean of 0.21 at diagnosis to 0.06 2 years after therapy. The acute side effects after 3 months were as follows: conjunctival symptoms (10), loss of lashes or hair (6), visual symptoms (5), fatigue (5), dry eye (1), cataract (1), and pain (4). One eye was enucleated at 2 months after fSRT. CONCLUSIONS: Preliminary results demonstrate that fSRT is an effective and safe treatment modality for uveal melanoma with an excellent local control and mild acute side effects. The follow-up should be prolonged to study both long-term local control and late toxicity.     

A noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy of uveal melanoma

PURPOSE: To introduce a noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy for uveal melanoma. METHODS AND MATERIALS: At the Department of Radiotherapy and Radiobiology, University of Vienna, stereotactic radiotherapy is offered to patients with uveal melanoma considered unsuitable for (106)Ru brachytherapy or local resection. For the present feasibility study, 8 patients were carefully selected according to their ability to fixate a small light source with the diseased eye and whether they had a rather small head to meet the limited geometric space available. A polymethyl methacrylate tube was attached to a stereotactic mask system in craniocaudal orientation supporting a 45 degrees mirror, which was placed in front of the diseased eye. At the other end of the tube, the patient was given a small fixation light, and a small camera was positioned beneath, which was shielded for use during MRI. A computer interface calculated and visualized the spatial difference of the actual and a given reference pupil position, which was defined before CT scanning, during the MRI sequences, and during treatment delivery at the linear accelerator. RESULTS: The described system can be attached to a conventional stereotactic mask system with minor modifications. Because of the large distance between the eye and the fixation light, the optical fixation system was well tolerated by all patients, and a stable position of the eye was obtained. The camera system can be used during CT and MRI without interference. Absorption of the 6-MV photon beam by the mirror and the polymethyl methacrylate tube was negligible. The computer interface designed to determine the pupil position uses an image-processing algorithm that correlates a template of the reference image with the actual image of the eye. Provided sufficient illumination of the pupil, the correlation function showed a pronounced minimum at the reference position. The precision of the algorithm was tested by phantom measurements. For a given 1 mm or 2 mm displacement, the interface reported a mean shift of 0.96 +/- 0.18 mm or 2.07 +/- 0.11 mm, respectively. CONCLUSION: The results of this study demonstrated the feasibility of a new optical fixation system for linear accelerator-based stereotaxis. The artifact-free application of the camera system during image acquisition and irradiation and the use of the computer interface, which automatically monitored eye movements with submillimeter precision, provided large improvements compared with existing techniques. Given well-defined interruption criteria and accelerated image processing, the described system has a high potential to perform automatically gated treatment beam delivery in the near future.     

Patient position reproducibility in fractionated stereotactic radiotherapy: an update after changing dental impression material.

The reproducibility of patient positioning within the Gill-Thomas-Cosman relocatable stereotactic frame was re-evaluated following the substitution of a new, softer, dental impression material for the original hard acrylic compound. The average total displacement for a series of 10 patients was 1.1 mm (+/- 0.6 mm). Rotational discrepancies were small. This technique cannot deliver accurate repositioning in the absence of patient co-operation.     

A linac-based stereotactic irradiation technique of uveal melanoma.

PURPOSE: To describe a stereotactic irradiation technique for uveal melanomas performed at a linac, based on a non-invasive eye fixation and eye monitoring system. METHODS: For eye immobilization a light source system is integrated in a standard stereotactic mask system in front of the healthy eye: During treatment preparation (computed tomography/magnetic resonance imaging) as well as for treatment delivery, patients are instructed to gaze at the fixation light source. A mini-video camera monitors the pupil center position of the diseased eye. For treatment planning and beam delivery standard stereotactic radiotherapy equipment is used. If the pupil center deviation from a predefined 'zero-position' exceeds 1 mm (for more than 2 s), treatment delivery is interrupted. Between 1996 and 1999 60 patients with uveal melanomas, where (i) tumor height exceeded 7 mm, or (ii) tumor height was more than 3 mm, and the central tumor distance to the optic disc and/or the macula was less than 3 mm, have been treated. A total dose of 60 or 70 Gy has been given in 5 fractions within 10 days. RESULTS: The repositioning accuracy in the mask system is 0.47+/-0.36 mm in rostral-occipital direction, 0.75+/-0.52 mm laterally, and 1.12+/-0.96 mm in vertical direction. An eye movement analysis performed for 23 patients shows a pupil center deviation from the 'zero' position<1 mm in 91% of all cases investigated. In a theoretical analysis, pupil center deviations are correlated with GTV 'movements'. For a pupil center deviation of 1 mm (rotation of the globe of 5 degrees ) the GTV is still encompassed by the 80% isodose in 94%. CONCLUSION: For treatments of uveal melanomas, linac-based stereotactic radiotherapy combined with a non-invasive eye immobilization and monitoring system represents a feasible, accurate and reproducible method. Besides considerable technical requirements, the complexity of the treatment technique demands an interdisciplinary team continuously dedicated to this task.     

Accuracy of a relocatable stereotactic radiotherapy head frame evaluated by use of a depth helmet

In high precision radiotherapy, the more accurately the patient can be relocated, the smaller the clinical to planning target volume margin can be, with reduction in the volume of normal tissue irradiated. The Gill-Thomas-Cosman (GTC) relocatable stereotactic head frame provides immobilization of the patient which is highly reproducible. A depth helmet and measuring probe were used to confirm the accuracy of relocation of 31 patients treated in the GTC frame. The measurements were processed in a spreadsheet developed to calculate the size of the patient's displacement as a vector. Twenty-seven patients received fractionated stereotactically-guided conformal radiotherapy, and 4 single fraction stereotactic radiosurgery, amounting to 564 measurement episodes. The accuracy was extremely good, and considerably more accurate than standard thermoplastic head shells. Ninety-two percent of the displacement vectors were less than 2 mm, and 97% less than 2.5 mm. Considering each dimension separately, the largest mean displacement was 0.4 mm in the superior-inferior direction. Accuracy was constant through a fractionated course for most patients, but prediction based on measurements from the first few fractions was not reliable. Results were dependent on patient selection, with worse reproducibility in patients with neurological deficits, or difficulty cooperating. The depth helmet measurements detected a loosened mouth bite in one patient and allowed repositioning to be verified without the need for the simulator. Total treatment time, including use of the depth helmet to verify treatment position, is quicker (mean 15.7 min) than using portal films. The depth helmet, used in conjunction with the vector displacement spreadsheet, provides a simple way to define the CTV-PTV margin. For fractionated stereotactic radiotherapy we use a 3 mm CTV-PTV margin. This system could assist technology transfer to centres starting stereotactic radiotherapy using the GTC frame.     

LINAC based stereotactic radiotherapy of uveal melanoma: 4 years clinical experience.

PURPOSE: To study local tumor control and radiogenic side effects after fractionated LINAC based stereotactic radiotherapy for selected uveal melanoma. PATIENTS AND METHODS: Between June 1997 and March 2001, 90 patients suffering from uveal melanoma were treated at a LINAC with 6 MV. The head was immobilized with a modified stereotactic frame system (BrainLAB). For stabilization of the eye position a light source was integrated into the mask system in front of the healthy or the diseased eye. A mini-video camera was used for on-line eye movement control. Tumors included in the study were either located unfavorably with respect to macula and optical disc (<3 mm distance) or presented with a thickness >7 mm. Median tumor volume was 305+/-234 mm3 (range 70-1430 mm3), and mean tumor height was 5.4+/-2.3 mm (range 2.7-15.9 mm). Total doses of 70 (single dose 14 Gy @ 80% isodose) or 60 Gy (single dose 12 Gy @ 80% isodose) were applied in five fractions within 10 days. The first fractionation results in total dose (TD) (2 Gy) of 175 Gy for tumor and 238 Gy for normal tissue, corresponding values for the second fractionation schedule are 135 and 180 Gy, respectively. RESULTS: After a median follow-up of 20 months (range 1-48 months) local control was achieved in 98% (n=88). The mean relative tumor reductions were 24, 27, and 37% after 12, 24 and 36 months. Three patients (3.3%) developed metastases. Secondary enucleation was performed in seven patients (7.7%). Long term side effects were retinopathy (25.5%), cataract (18.9%), optic neuropathy (20%), and secondary neovascular glaucoma (8.8%). CONCLUSION: Fractionated LINAC based stereotactic photon beam therapy in conjunction with a dedicated eye movement control system is a highly effective method to treat unfavorably located uveal melanoma. Total doses of 60 Gy (single dose 12 Gy) are considered to be sufficient to achieve good local tumor control.     

A non-invasive, relocatable stereotactic frame for fractionated radiotherapy and multiple imaging.

A non-invasive relocatable stereotactic frame has been developed for fractionated stereotactic external beam radiotherapy (SRT) by linear accelerator. Fixation is via the upper dentition and tests of repositioning have shown mean antero-posterior and lateral displacements of 1.0 mm. The relocatable frame allows accurate 3-dimensional target localisation by CT, MRI, PET and cerebral angiography and precise isocentric positioning for radiotherapy. This method of immobilisation is ideal for fractionated SRT as well as for other techniques requiring high precision localisation and treatment delivery.     

Modification of Gill-Thomas-Cosman frame for extracranial head-and-neck stereotactic radiotherapy

PURPOSE: A modification of a commercially available, noninvasive, relocatable, stereotactic Gill-Thomas-Cosman (GTC) head frame is presented for treatment of extracranial lesions of the head and neck, base of the skull, and inferior nasopharyngeal region. METHODS AND MATERIALS: Skull-based and nasopharyngeal lesions cannot be treated with the GTC frame because it obstructs the beam path. To treat those lesions, the GTC frame was modified without compromising the integrity, flexibility, or use of the treatment software. The modification uses a set of aluminum extension rods of variable lengths and bevels to support a modified dental plate. The extension rods allow the dental tray and attached GTC frame to be lowered so that the more inferior regions may be treated. Ten patients underwent CT with the modified frame and CT localizer. For some patients, MRI was acquired without the frame. Image fusion of MRI and CT scans was used to delineate the target volume, and planning was done with the existing software for proper treatment. RESULTS: The modification of the GTC frame has been successful in imaging, planning, and extending the treatment domain for the base of the skull, nasopharyngeal regions, and other superior lesions of the head and neck. The reproducibility of the modified frame and the patient localization helmet technique was identical to that of the unmodified frame. CONCLUSION: The modification of the GTC frame is simple and accurate. It provides flexibility in treating an extended range of the base of the skull, nasopharyngeal region, and other superior lesions of the head and neck that otherwise could not be treated with the GTC frame.     

Image-guided radiotherapy for liver cancer using respiratory-correlated computed tomography and cone-beam computed tomography

PURPOSE: To evaluate a novel four-dimensional (4D) image-guided radiotherapy (IGRT) technique in stereotactic body RT for liver tumors. METHODS AND MATERIALS: For 11 patients with 13 intrahepatic tumors, a respiratory-correlated 4D computed tomography (CT) scan was acquired at treatment planning. The target was defined using CT series reconstructed at end-inhalation and end-exhalation. The liver was delineated on these two CT series and served as a reference for image guidance. A cone-beam CT scan was acquired after patient positioning; the blurred diaphragm dome was interpreted as a probability density function showing the motion range of the liver. Manual contour matching of the liver structures from the planning 4D CT scan with the cone-beam CT scan was performed. Inter- and intrafractional uncertainties of target position and motion range were evaluated, and interobserver variability of the 4D-IGRT technique was tested. RESULTS: The workflow of 4D-IGRT was successfully practiced in all patients. The absolute error in the liver position and error in relation to the bony anatomy was 8 +/- 4 mm and 5 +/- 2 mm (three-dimensional vector), respectively. Margins of 4-6 mm were calculated for compensation of the intrafractional drifts of the liver. The motion range of the diaphragm dome was reproducible within 5 mm for 11 of 13 lesions, and the interobserver variability of the 4D-IGRT technique was small (standard deviation, 1.5 mm). In 4 patients, the position of the intrahepatic lesion was directly verified using a mobile in-room CT scanner after application of intravenous contrast. CONCLUSION: The results of our study have shown that 4D image guidance using liver contour matching between respiratory-correlated CT and cone-beam CT scans increased the accuracy compared with stereotactic positioning and compared with IGRT without consideration of breathing motion.     

Quantification of prostate and seminal vesicle interfraction variation during IMRT

PURPOSE: To quantify the interfraction variability in prostate and seminal vesicle (SV) positions during a course of intensity-modulated radiotherapy (IMRT) using an integrated computed tomography (CT)-linear accelerator system and to assess the impact of rectal and bladder volume changes. METHODS AND MATERIALS: We studied 15 patients who had undergone IMRT for prostate carcinoma. Patients had one pretreatment planning CT scan followed by three in-room CT scans per week using a CT-on-rails system. The prostate, bladder, rectum, and pelvic bony anatomy were contoured in 369 CT scans. Using the planning CT scan as a reference, the volumetric and positional changes were analyzed in the subsequent CT scans. RESULTS: For all 15 patients, the mean systematic internal prostate and SV variation was 0.1 +/- 4.1 mm and 1.2 +/- 7.3 mm in the anteroposterior axis, -0.5 +/- 2.9 mm and -0.7 +/- 4.5 mm in the superoinferior axis, and 0.2 +/- 0.9 mm and -0.9 +/- 1.9 mm in the lateral axis, respectively. The mean magnitude of the three-dimensional displacement vector was 4.6 +/- 3.5 mm for the prostate and 7.6 +/- 4.7 mm for the SVs. The rectal and bladder volume changes during treatment correlated with the anterior and superior displacement of the prostate and SVs. CONCLUSION: The dominant prostate and SV variations occurred in the anteroposterior and superoinferior directions. The systematic prostate and SV variation between the treatment planning CT and daily therapy as a result of the rectal and bladder volume changes emphasizes the need for daily directed target localization and/or immobilization techniques.     

The TALON removable head frame system for stereotactic radiosurgery/radiotherapy: measurement of the repositioning accuracy

PURPOSE: To present the TALON removable head frame system as an immobilization device for single-fraction intensity-modulated stereotactic radiosurgery (IMRS) and fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT); and to evaluate the repositioning accuracy by measurement of anatomic landmark coordinates in repeated computed tomography (CT) examinations. METHODS AND MATERIALS: Nine patients treated by fractionated stereotactic intensity-modulated radiotherapy underwent repeated CTs during their treatment courses. We evaluated anatomic landmark coordinates in a total of 26 repeat CT data sets and respective x, y, and z shifts relative to their positions in the nine treatment-planning reference CTs. An iterative optimization algorithm was employed using a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomic landmark measurements relative to the original image set. This allowed for the calculation of the x, y, and z components of translation of the target isocenter for each repeat CT. In addition to absolute target isocenter translation, the magnitude (sum vector) of isocenter motion and the patient/target rotation about the three principal axes were calculated. RESULTS: Anatomic landmark analysis over a treatment course of 6 weeks revealed a mean target isocenter translation of 0.95 +/- 0.55, 0.58 +/- 0.46, and 0.51 +/- 0.38 mm in x, y, and z directions, respectively. The mean magnitude of isocenter translation was 1.38 +/- 0.48 mm. The 95% confidence interval ([CI], mean translation plus two standard deviations) for repeated isocenter setup accuracy over the 6-week period was 2.34 mm. Average rotations about the x, y, and z axes were 0.41 +/- 0.36, 0.29 +/- 0.25, and 0.18 +/- 0.15 degrees, respectively. Analysis of the accuracy of the first repeated setup control, representative of single-fraction stereotactic radiosurgery situations, resulted in a mean target isocenter translation in the x, y, and z directions of 0.52 +/- 0.38, 0.56 +/- 0.30, and 0.46 +/- 0.25 mm, respectively. The mean magnitude of isocenter translation was 0.99 +/- 0.28 mm. The 95% confidence interval for these radiosurgery situations was 1.55 mm. Average rotations at first repeated setup control about the x, y, and z axes were 0.24 +/- 0.19, 0.19 +/- 0.17, and 0.19 +/- 0.12 degrees, respectively. CONCLUSION: The TALON relocatable head frame was seen to be well suited for immobilization and repositioning of single-fraction stereotactic radiosurgery treatments. Because of its unique removable design, the system was also seen to provide excellent repeat immobilization and alignment for fractionated stereotactic applications. The exceptional accuracy for the single-fraction stereotactic radiosurgical application of the system was seen to deteriorate only slightly over a 6-week fractionated stereotactic treatment course.     

Accuracy of single-session extracranial radiotherapy for simple shaped lung tumor or metastasis using fast 3-D CT treatment planning

BACKGROUND: This study is situated in the area of measuring set-up accuracy and time periods of single-session extracranial radiotherapy (SSRT) for simple-shaped targets (e.g., spherical or rotational symmetrical) definitively located in the peripheral lung. METHODS AND MATERIALS: After adaptation of the stereotactic body frame, the patient has to remain in the vacuum pillow during planning computed tomography (CT), fast three-dimensional (3-D) treatment planning, and direct irradiation after verification. Fast preplanning is performed by using virtual simulation software to accelerate the method. RESULTS: In our new procedure, SSRT is applied in approximately 1.5 h. The mean setup accuracy vector was 2.4+/-0.7 mm in the range of 1.34 to 4 mm. Mean intrafractional patient movement in the stereotactic body frame before and after radiation was 0.70 mm+/-0.5 mm and 0.76+/-0.76 mm in the range of 0 to 2.8 mm. Mean time period steps were measured at (1) planning CT with 3-D treatment planning: 76+/-12 min; (2) irradiation and verification: 33+/-7 min; and (3) complete procedure duration: 109+/-11 min (range, 89-169). CONCLUSIONS: The main difference between the positioning technique of SSRT and that of conventional extracranial radiosurgery is the tighter patient fixation, which guarantees minimal patient movement. The main advantages are procedure acceleration and omission of CT simulation. SSRT is a preliminary stage of real-time treatment.     

Cone-beam computed tomography in hypofractionated stereotactic radiotherapy for brain metastases

ABSTRACT: BACKGROUND: To assess interfraction translational and rotational setup errors, in patients treated with image-guided hypofractionated stereotactic radiotherapy, immobilized by a thermoplastic mask and a bite-block and positioned using stereotactic coordinates. METHODS: 37 patients with 47 brain metastases were treated with hypofractionated stererotactic radiotherapy. All patients were immobilized with a combination of a thermoplastic mask and a bite-block fixed to a stereotactic frame support. Daily cone-beam CT scans were acquired for every patient before the treatment session and were matched online with planning CT images, for 3D image registration. The mean value and standard deviation of all translational (X,Y,Z) and rotational errors (thetax, thetay, thetaz) were calculated for the matching results of bone matching algorithm. RESULTS: A total of 194 CBCT scans were analyzed. Mean +/- standard deviation of translational errors (X, Y, Z) were respectively 0.5 +/- 1.6 mm (range -5.7 and 5.9 mm) in X; 0.4 +/- 2.7 mm (range -8.2 and 12.1 mm) in Y; 0.4 +/- 1.9 mm (range -7.0 and 14 mm) in Z; median and 90th percentile were respectively within 0.5 mm and 2.4 mm in X, 0.3 mm and 3.2 mm in Y, 0.3 mm and 2.2 mm in Z. Mean +/- standard deviation of rotational errors (thetax, thetay, thetaz) were respectively 0.0 degrees +/- 1.3 degrees (thetax) (range -6.0 degrees and 3.1 degrees); -0.1 degrees +/- 1.1 degrees (thetay) (range -3.0 degrees and 2.4 degrees); -0.6 degrees +/- 1.4 degrees (thetaz) (range -5.0 degrees and 3.3 degrees). Median and 90th percentile of rotational errors were respectively within 0.1 degrees and 1.4 degrees (thetax), 0.0 degrees and 1.2 degrees (thetay), 0.0 degrees and 0.9 degrees (thetaz). Mean +/- SD of 3D vector was 3.1 +/- 2.1 mm (range 0.3 and 14.9 mm); median and 90th percentile of 3D vector was within 2.7 mm and 5.1 mm. CONCLUSIONS: Hypofractionated stereotactic radiotherapy have the significant limitation of uncertainty in interfraction repeatability of the patient setup; image-guided radiotherapy using cone-beam computed tomography improves the accuracy of the treatment delivery reducing setup uncertainty, giving the possibility of 3-dimensional anatomic informations in the treatment position.     

Noninvasive patient fixation for extracranial stereotactic radiotherapy.

PURPOSE: To evaluate the setup accuracy that can be achieved with a novel noninvasive patient fixation technique based on a body cast attached to a recently developed stereotactic body frame during fractionated extracranial stereotactic radiotherapy. METHODS AND MATERIALS: Thirty-one CT studies (> or = 20 slices, thickness: 3 mm) from 5 patients who were immobilized in a body cast attached to a stereotactic body frame for treatment of paramedullary tumors in the thoracic or lumbar spine were evaluated with respect to setup accuracy. The immobilization device consisted of a custom-made wrap-around body cast that extended from the neck to the thighs and a separate head mask, both made from Scotchcast. Each CT study was performed immediately before or after every second or third actual treatment fraction without repositioning the patient between CT and treatment. The stereotactic localization system was mounted and the isocenter as initially located stereotactically was marked with fiducials for each CT study. Deviation of the treated isocenter as compared to the planned position was measured in all three dimensions. RESULTS: The immobilization device can be easily handled, attached to and removed from the stereotactic frame and thus enables treatment of multiple patients with the same stereotactic frame each day. Mean patient movements of 1.6 mm+/-1.2 mm (laterolateral [LL]), 1.4 mm+/-1.0 mm (anterior-posterior [AP]), 2.3 mm+/-1.3 mm (transversal vectorial error [VE]) and < slice thickness = 3 mm (craniocaudal [CC]) were recorded for the targets in the thoracic spine and 1.4 mm+/-1.0 mm (LL), 1.2 mm+/-0.7 mm (AP), 1.8 mm+/-1.2 mm (VE), and < 3 mm (CC) for the lumbar spine. The worst case deviation was 3.9 mm for the first patient with the target in the thoracic spine (in the LL direction). Combining those numbers (mean transversal VE for both locations and maximum CC error of 3 mm), the mean three-dimensional vectorial patient movement and thus the mean overall accuracy can be safely estimated to be < or = 3.6 mm. CONCLUSION: The presented combination of a body cast and head mask system in a rigid stereotactic body frame ensures reliable noninvasive patient fixation for fractionated extracranial stereotactic radiotherapy and may enable dose escalation for less radioresponsive tumors that are near the spinal cord or otherwise critically located while minimizing the risk of late sequelae.     

Is a Single Respiratory Correlated 4D-CT Study Sufficient for Evaluation of Breathing Motion?

PURPOSE: Respiratory correlated computed tomography has been shown to be effective for evaluation of breathing-induced motion of pulmonary tumors. This study investigated whether a single four-dimensional CT study (4D-CT) is representative and sufficient for treatment planning in stereotactic body radiotherapy (SBRT). METHODS AND MATERIALS: Four repeated helical 4D-CT studies were acquired every 10 min for 10 patients with 14 pulmonary metastases. Patients remained immobilized in a stereotactic body frame (SBF) for 30 min; abdominal compression was applied to seven patients. Using amplitude based sorting, eight phases equally distributed over the breathing cycle were reconstructed for each 4D-CT study. Tumor position was defined in a total of 406 CT series and variability of breathing motion and mean tumor position were evaluated. RESULTS: Peak-to-peak tumor motion was 9.9 mm +/- 6.8 mm (mean +/- standard deviation) and 9.0 mm +/- 7.4 mm at time point 0 min (t(0)) and t(30), respectively. In one patient with poor pulmonary function, continuous increase of breathing motion from 17.4 mm at t(0) to 28.3 mm at t(30) was seen. In five and two lesions, respectively, a drift of the mean tumor position greater than 3 mm and 5 mm was observed. A borderline significance was calculated for larger tumor position variability in midventilation phases compared with peak-ventilation phases of the breathing cycle (p = 0.08). CONCLUSION: Treatment planning based on a single 4D-CT study is reliable for the majority of patients. Increased intrafractional uncertainties were seen for patients with poor pulmonary function and with tumors located in the lower lobe.     

Repositioning accuracy of a commercially available double-vacuum whole body immobilization system for stereotactic body radiation therapy

We evaluated the repositioning accuracy of a commercially available stereotactic whole body immobilization system (BodyFIX, Medical Intelligence, Schwabmuenchen, Germany) in 36 patients treated by hypofractionated stereotactic body radiation therapy. CT data were acquired for positional control of patient and tumor before each fraction of the treatment course. Those control CT datasets were compared with the original treatment planning CT simulation and analyzed with respect to positional misalignment of bony patient anatomy, and the respective position of the treated small lung or liver lesions. We assessed the stereotactic coordinates of distinct bony anatomical landmarks in the original CT and each control dataset. In addition, the target isocenter was recorded in the planning CT simulation dataset. An iterative optimization algorithm was implemented, utilizing a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomical landmark measurements relative to the original treatment planning CT data set. This allowed for the calculation of the x, y and z-components of translation of the patient's body and the target's center-of-mass for each control CT study, as well as rotation about the principal room axes in the respective CT data sets. In addition to absolute patient/target translation, the total magnitude vector of patient and target misalignment was calculated. A clinical assessment determined whether or not the assigned planning target volume safety margins would have provided the desired target coverage. To this end, each control CT study was co-registered with the original treatment planning study using immobilization system related fiducial markers, and the computed isodose calculation was superimposed. In 109 control setup CT scans available for comparison with their respective treatment planning CT simulation study (2-5 per patient, median 3), anatomical landmark analysis revealed a mean bony landmark translation of -0.4 +/- 3.9 (mean +/- SD), -0.1 +/- 1.6 and 0.3 +/- 3.6 mm in x, y and z-directions, respectively. Bony landmark setup deviations along one or more principal axis larger than 5 mm were observed in 32 control CT studies (29.4%). Body rotations about the x-, y- and z-axis were 0.9 +/- 0.7, 0.8 +/- 0.7 and 1.8 +/- 1.6 degrees, respectively. Assuming a rigid body relationship of target and bony anatomy, the mean computed absolute target translation was 2.9 +/- 3.3, 2.3 +/- 2.5 and 3.2 +/- 2.7 mm in x, y and z-directions, respectively. The median and mean magnitude vector of target isocenter displacement was computed to be 4.9 mm, and 5.7 +/- 3.7 mm. Clinical assessment of PTV/target volume coverage revealed 72 (66.1%), 23 (21.1%), and 14 (12.8%), of excellent (100% isodose coverage), good (>90% isodose coverage), and poor GTV/isodose alignment quality (less than 90% isodose coverage to some aspect of the GTV), respectively. Loss of target volume dose coverage was correlated with translations >5 mm along one or more axes (p<0.0001), rotations >3 degrees about the z-axis (p=0.0007) and body mass index >30 (p<0.0001). The analyzed BodyFIX whole body immobilization system performed favorably compared with other stereotactic body immobilization systems for which peer-reviewed repositioning data exist. While the measured variability in patient and target setup provided clinically acceptable setup accuracy in the vast majority of cases, larger setup deviations were occasional observed. Such deviations constitute a potential for partial target underdosing warranting, in our opinion, a pre-delivery positional assessment procedure (e.g., pre-treatment control CT scan).     

Treatment accuracy of fractionated stereotactic radiotherapy.

BACKGROUND AND PURPOSE: To assess the geometric accuracy of the delivery of fractionated stereotactic radiotherapy (FSRT) for brain tumours using the Gill-Thomas-Cosman (GTC) relocatable frame. Accuracy of treatment delivery was measured via portal images acquired with an amorphous silicon based electronic portal imager (EPI). Results were used to assess the existing verification process and to review the current margins used for the expansion of clinical target volume (CTV) to planning target volume (PTV). PATIENTS AND METHODS: Patients were immobilized in a GTC frame. Target volume definition was performed on localization CT and MRI scans and a CTV to PTV margin of 5mm (based on initial experience) was introduced in 3D. A Brown-Roberts-Wells (BRW) fiducial system was used for stereotactic coordinate definition. The existing verification process consisted of an intercomparison of the coordinates of the isocentres and anatomy between the localization and verification CT scans. Treatment was delivered with 6 MV photons using four fixed non-coplanar conformal fields using a multi-leaf collimator. Portal imaging verification consisted of the acquisition of orthogonal images centred through the treatment isocentre. Digitally reconstructed radiographs (DRRs) created from the CT localization scans were used as reference images. Semi-automated matching software was used to quantify set up deviations (displacements and rotations) between reference and portal images. RESULTS: One hundred and twenty six anterior and 123 lateral portal images were available for analysis for set up deviations. For displacements, the total errors in the cranial/caudal direction were shown to have the largest SD's of 1.2 mm, while systematic and random errors reached SD's of 1.0 and 0.7 mm, respectively, in the cranial/caudal direction. The corresponding data for rotational errors (the largest deviation was found in the sagittal plane) was 0.7 degrees SD (total error), 0.5 degrees (systematic) and 0.5 degrees (random). The total 3D displacement was 1.8 mm (mean), 0.8 mm (SD) with a range of 0.3-3.9 mm. CONCLUSIONS: Portal imaging has shown that the existing verification and treatment delivery techniques currently in use result in highly reproducible setups. Random and systematic errors in the treatment planning and delivery chain will always occur, but monitoring and minimising them is an essential component of quality control. Portal imaging provides fast and accurate facility for monitoring patients on treatment and the results of this study have shown that a reduction in CTV to PTV margin from 5 to 4 mm (resulting in a considerable increase in the volume of normal tissue sparing) could be made.     

Achieving the Relocation Accuracy of Stereotactic Frame-based Cranial Radiotherapy in a Three-point Thermoplastic Shell

AimsTo compare the accuracy of fractionated cranial radiotherapy in a standard three-point thermoplastic shell using daily online correction with accuracy in a Gill–Thomas–Cosman relocatable stereotactic frame.Materials and methodsAll patients undergoing fractionated radiotherapy for benign intracranial tumours between March 2009 and August 2010 were included. Patients were immobilised in the frame with those unable to tolerate it immobilised in the shell. The ExacTrac imaging system was used for verification/correction. Daily online imaging before and after correction was carried out for shell patients and systematic and random population set-up errors calculated. These were compared with frame patients who underwent standard departmental imaging/correction with fractions 1–3 and weekly thereafter. Set-up margins were calculated from population errors.ResultsSystematic and random errors were 0.3–0.7 mm/° before correction and 0.1–0.2 mm/° after correction in all axes in the frame, and 0.6–1.5 mm/° before correction and 0.1–0.4 mm/° after correction in the shell. Isotropic margins required for patient set-up could be reduced from 2 mm to <1 mm in the frame and from 5 mm to <1 mm in the shell.ConclusionSimilar set-up accuracy can be achieved in the standard thermoplastic shell as in a relocatable frame despite less precise immobilisation. The use of daily online correction precludes the need for larger set-up margins.     

Quality assurance in fractionated stereotactic radiotherapy

The recent development of fractionated stereotactic radiotherapy (SRT), which utilises the relocatable Gill-Thomas-Cosman frame (GTC ‘repeat localiser’), requires comprehensive quality assurance (QA). This paper focuses on those QA procedures particularly relevant to fractionated SRT treatments, and which have been derived from the technique used at the Royal Marsden Hospital. They primarily relate to the following: (i) GTC frame fitting, initially in the mould room, and then at each imaging session and treatment fraction; (ii) checking of the linear accelerator beam geometry and alignment lasers; and (iii) setting up of the patient for each fraction of treatment. The precision of the fractionated technique therefore depends on monitoring the GTC frame relocation at each fitting, checking the accuracy of the radiation isocentre of the treatment unit, its coincidence with the patient alignment lasers and the adjustments required to set the patient up accurately. The results of our quality control checks show that setting up to a mean radiation isocentre using precisely set-up alignment lasers can be achievable to within I mm accuracy. When this is combined with a mean GTC frame relocatability of I mm on the patient, a 2-mm allowance between the prescribed isodose surface and the defined target volume is a realistic safety margin for this technique.     

Stereotactic body radiation therapy: evaluation of setup accuracy and targeting methods for a new couch integrated immobilization system

A new stereotactic frame system was designed at Indiana University to utilize the precision motion control of newer accelerator couches and treat obese patients previously untreatable in other frame systems during stereotactic body radiation therapy (SBRT). The repositioning accuracy and target reproducibility of this frame was evaluated in the treatment of both lung and liver tumors. The external coordinate system on the new frame was validated using a phantom system. Translational motions were carried out using couch motors. Five patients were treated with SBRT and twenty-three verification CT scans were acquired. The displacement of the gross tumor volume (GTV) and adjacent vertebral body between the original CT scan and the verification CT scans was determined. The mean setup accuracy for the patient study was less than 5 mm. Mean displacement of the GTV was 3.0 mm (0.0-6.0 mm) in the lateral (x) direction, 4.1 mm (0.0-8.9 mm) in the superior-inferior (y) direction, and 2.6 mm (0.0-10.0 mm) in the cranio-caudal (z) direction. Comparison of vertebral body position showed mean displacement of 2.4 mm (0.0 to 8.0 mm), 1.9 mm (0.0 mm to 2.0 mm), and 0.9 mm (0.0 to 5.0 mm) for the same shift directions. Repositioning could be accurately carried out from an initial reference position using the treatment couch controllers. Adequate set-up accuracy using a frame system capable of accommodating wide girth patients was achieved and was comparable to other published studies for narrower frames. With these results, a 5 mm expansion for PTV margins remains the standard for our institution.