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|Year : 2013 | Volume
| Issue : 3 | Page : 277-281
Frame-based radiosurgery: Is it relevant in the era of IGRT?
Tejinder Kataria1, Deepak Gupta1, KP Karrthick1, Shyam Singh Bisht1, Shikha Goyal1, Ashu Abhishek1, HB Govardhan1, Kuldeep Sharma1, Puneet Pareek1, Aditya Gupta2
1 Division of Radiation Oncology, Medanta Cancer Institute, Gurgaon, Haryana, India
2 Division of Neurosurgery, Medanta Institute of Neurosciences, Medanta The Medicity, Gurgaon, Haryana, India
|Date of Submission||21-Feb-2013|
|Date of Decision||01-Apr-2013|
|Date of Acceptance||11-Jun-2013|
|Date of Web Publication||16-Jul-2013|
Chairperson, Division Radiation Oncology, Medanta Cancer Institute, Medanta the Medicity, Gurgaon, Haryana - 122 001
Source of Support: None, Conflict of Interest: None
Purpose: To assess the setup errors and intrafraction motion in patients treated with frame-based and frameless stereotactic radiosurgery (SRS). Materials and Methods: Ten patients treated with frame-based and six patients treated with frameless radiosurgery were prospectively enrolled in the study. Leksell frame was used for frame-based and a customized uniframe orfit cast for frameless techniques. Cone beam computed tomography (CBCT) scans were taken immediately before and after each treatment to evaluate the positional accuracy and corrections applied with the use of hexapod couch for both groups. Results: The mean translational shifts with frame-based SRS were 1.00 ± 0.30 mm in the lateral direction (X), 0.20 ± 1.20 mm in craniocaudal direction (Y) and -0.10 ± 0.31 mm in the anteroposterior direction (Z). The rotational shifts for frame-based treatments were as follows: roll 0.32 ± 0.70, pitch 0.44 ± 0.66 and yaw 0.20 ± 0.4. For frameless SRS, translational shifts were -0.40 ± 0.90, 1.10 ± 1.10, and 0.50 ± 1.30 mm in X, Y, and Z directions, respectively, and rotational shifts were -0.11 ± 0.78, 0.20 ± 0.44, and 0.29 ± 0.35 in roll, pitch, and yaw, respectively. Intrafraction shifts with frame-based SRS were: X = 0.60 ± 1.80 mm, Y = 0.20 ± 0.60 mm, and Z = 0.00 ± 0.05 mm; and rotational shifts were: roll 0.01 ± 0.27, pitch 0.06 ± 0.15, and yaw 0.01 ± 0.09. For frameless SRS, these were: X = 0.11 ± 0.20 mm, Y = 0.20 ± 0.40 mm, and Z = 0.20 ± 0.20 mm and rotational shifts were: roll 0.09 ± 0.23, pitch 0.00 ± 0.12, and yaw 0.00 ± 0.09. Conclusions: In our experience, set up accuracy of frameless SRS is as good as frame-based SRS. With availability of verification methods such as CBCT and hexapod couch, an accurate and precise treatment delivery is feasible with frameless techniques.
Keywords: Frame-based radiosurgery, frameless radiosurgery, hexapod couch, radiosurgery
|How to cite this article:|
Kataria T, Gupta D, Karrthick K P, Bisht SS, Goyal S, Abhishek A, Govardhan H B, Sharma K, Pareek P, Gupta A. Frame-based radiosurgery: Is it relevant in the era of IGRT?. Neurol India 2013;61:277-81
|How to cite this URL:|
Kataria T, Gupta D, Karrthick K P, Bisht SS, Goyal S, Abhishek A, Govardhan H B, Sharma K, Pareek P, Gupta A. Frame-based radiosurgery: Is it relevant in the era of IGRT?. Neurol India [serial online] 2013 [cited 2019 Aug 19];61:277-81. Available from: http://www.neurologyindia.com/text.asp?2013/61/3/277/115068
| » Introduction|| |
Intracranial stereotactic radiosurgery (SRS) is the three-dimensional treatment of small intracranial targets with radiation in a single fraction. A wide range of brain tumors has been treated with considerable success by SRS. , One of the key elements of radiosurgery is an accurate and reproducible immobilization of the head, as a high dose of radiation is delivered in a single fraction.  Accuracy within 1-2 mm range is necessary since a small uncertainty can compromise the treatment. Traditionally, a rigid frame has been used, albeit with certain limitations such as invasiveness of the frame, limitation of fractionation, and restriction of treatment to sites amenable to frame fixation.
In frame-based radiosurgery, immobilization of head is usually performed with a rigid stereotactic frame, which is attached to the patient's skull with screws penetrating the skin. This method allows radiosurgical treatment with a single fraction at a high level of precision; however, it is invasive and does not allow fractionated stereotactic irradiation that would be desirable for malignant intracranial tumors as well as for tumors larger than 3.50 cm. In recent times, alternatives to the invasive patient fixation technique such as frameless stereotactic systems, with a positional accuracy in submillimeter range, have been explored. ,,,,, The margin added to the target volume for errors in localization and set up must be small in order to minimize the potential treatment-related complications of SRS.  In this study, we assess the set up errors and intrafraction motion in patients with brain lesions treated with frame-based and frameless SRS.
| » Materials and Methods|| |
A total of 16 patients (10 patients with frame and 6 patients without frame) were consecutively treated with SRS in the division of Radiation Oncology between September 2010 and September 2012.
Treatment planning and verification procedure
After obtaining an informed consent, patients were taken for mould room procedure, where the thermoplastic cast was fabricated for frameless radiosurgery and Leksell frame was affixed for frame-based radiosurgery. For computed tomography (CT) imaging in frame-based SRS, stereotactic CT localizer box was attached to the Leksell frame. The frame was attached to the CT couch with CT adapter. Using leveler, rotation of the frame was adjusted. For frameless SRS, three fine cross-marks on the mask were given to define the reference plane and reference point (position 0 of the 3D-coordinate system). They were marked on the mask with a fine pen (0.50 mm line thickness) using the in-room LASER system of the 64-slice positron emission tomography-CT (PET-CT) scanner (BIOGRAPH -Siemens mCT). After fixation of the system to the CT table, the patient was relocated in the mask or frame. Table adjustments were made with the help of the room LASER system and the inner light LASER of the CT scanner. A continuous CT scan of the whole head (1 mm slice thickness, without superposition of slices, 512 × 512 matrix, pitch of 1) was performed after intravenous injection of 1-1.5 ml per kg body weight of IV contrast material. Radiopaque markers (lead balls, diameter 1 mm) were carefully positioned in the center of the three marked crosses and thus were visible on the CT scan. These three points defined the origin of the 3D-reference coordinate system. After this procedure, patients planned for treatment with the frameless technique was released from the mask. Those planned for frame-based SRS were sent to magnetic resonance imaging (MRI) room, where they underwent contrast-enhanced T1-weighted MRI (26 cm FOV, 512 × 512 pixel size, 1 mm slice interval) using a 1.5 Tesla MRI. Both MRI and CT studies were transferred to the 3D-treatment planning system (Focal sim ver 4.64).
The target volume was identified on the basis of the fused CT and MR images. The gross tumor volume (GTV) was delineated as contrast-enhancing tumor demonstrated on MRI scans. Clinical target volume (CTV) was the same as GTV. Planning target volume (PTV) was generated by geometric expansion of 1-2 mm around GTV. In our patients, radiosurgical dose was under 20 Gy for 18 brain lesions and exceeded 20 Gy for four brain lesions. Doses were prescribed to the 80-90% isodose line normalized to the maximum dose. After contouring, the images and structure sets were sent to CMS Ergo++ R1.7 Planning system to set stereotactic coordinates. Stereotactic transformation (SCT) module read the patient files and set the conditions for transforming CT coordinates to sterotactic coordinates for each of the images. The coordinate transformation was based on the position of the fiducial marker on a stereotactic CT localization frame. The fiducial was digitized manually and fine-tuned automatically to register in each image. Once all the fiducial were registered and saved from the SCT, report window gave the sterotactic coordinates.
CMS Monaco version 3.1 was used for treatment planning. Treatment was delivered to each patient in a single fraction using 6 MV Linear accelerator (Elekta Synergy-S with beam modulator) that has a Hexapod couch for 6D correction.
After a suitable dose plan was devised and approved for treatment, patients were taken for treatment on the same day for patients with frame and within 24-48 hours for patients with thermoplastic mask. Pretreatment Quality Assurance procedures and verification were performed using Standard Imaging A16 slimline microchamber (0.007 cc active volume) with RW slab phantom. They were found in agreement with calculated dose within ±2% accuracy. The patient with the frame or thermoplastic cast assembly was then positioned on the treatment couch in an identical manner as per CT simulation along with the immobilization system and was affixed to the tabletop. On the treatment couch, the isocenter as per CT simulation was adjusted with the help of the in-room LASER system. The setup differences in translational or rotational directions were corrected with help of Hexapod (Hexapod Evo couch top, protocol - kine 118 Table top - iBeamevo.specs Product version - 1.1.12@19924 Elekta). Verification of the isocenter was performed to confirm its correct position. The shift in all three dimensions including translational movements and rotations (roll, pitch, and yaw) were recorded in comparison with isocenter determined on planning CT scan - both bone matching and gray value protocols were used for final matching. The new table position gave the value of deviation in the rotational and translational axes [Figure 1] and [Figure 2].
After cone beam CT (CBCT) verification and correction of both rotational and translational errors with Hexapod, treatment was executed. Another CBCT was taken after completion of the treatment session or mid-treatment (for treatment times longer than 30 minutes) and shifts with respect to the corrected isocenter (rotational and translational) were recorded.
| » Results|| |
Patient characteristics are listed in [Table 1]. Median age was 51 years (range 30-71 years). Thirteen patients had a solitary lesion and one each had 2, 3, and 4 lesions. Most common histology was metastases (n = 7) followed by meningioma (3 patients), schwannoma (n = 2), recurrent glioblastoma (n = 1), acoustic neuroma (n = 1), and arteriovenous malformation (n = 1).
The pretreatment mean translational errors with frame-based SRS were 1.00 mm (SD=0.30) in the lateral direction (X), 0.20 mm (SD = 1.20) in craniocaudal (Y) direction, and -0.10 mm (SD = 0.31) in the anteroposterior direction (Z), and rotational errors were: roll 0.32 degree (SD = 0.70), pitch 0.44 degree (SD = 0.66), and yaw 0.20 degree (SD = 0.40). Intrafraction translational errors with frame-based SRS were: X = 0.60 mm (SD = 1.80), Y = 0.20 mm (SD = 0.60), and Z = 0.00 mm (SD = 0.50) and rotational errors were: roll 0.01 degree (SD = 0.27), pitch = 0.06 degree (SD = −0.15), and yaw = 0.01 degree (SD = 0.09) [Table 2].
|Table 2: Comparison of parameters before and after correction with frame|
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For pretreatment frameless SRS, these shifts were −0.40 mm (SD = 0.90) in the lateral direction, 1.10 mm (SD = 1.10) in craniocaudal direction and −0.50 mm (SD = 1.30) in the anteroposterior direction, and rotational errors were: Roll −0.11 degree (SD = 0.78), pitch 0.20 degree (SD = 0.44), and yaw 0.29 degree (SD = 0.35). For frameless SRS, the shifts were: X =0.10 mm (SD = 0.20), Y = 0.20 mm (SD = 0.40), and Z = 0.20 mm (SD = 0.20) and rotational errors were: roll 0.09 degree (SD = 0.23), pitch 0.00 degree (SD = 0.12), and yaw 0.00 degree (SD = 0.09) [Table 3].
|Table 3: Comparison of parameters before and after correction without frame|
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On comparing translational and rotational variations between frame-based and frameless radiosurgery, the differences were not statistically significant [Table 3] and [Table 4]. Median treatment times for frame-based and frameless radiosurgery (including time for CBCT) were 35 minutes (range, 25-40 minutes) and 30 minutes (range 25-38 minutes), respectively.
|Table 4: Comparison of parameters with frame and without frame before correction|
Click here to view
| » Discussion|| |
An accurate and reproducible immobilization of head is necessary for delivery of radiosurgery. Traditionally, invasive frame-based techniques have been used for brain SRS. In the past two decades, diverse frameless devices have been developed, such as infrared camera guidance, dental and implanted fiducial markers. ,,,,, For frameless SRS, an important prerequisite is a high degree of accuracy to deliver safe radiation similar to that of invasive frame-based radiosurgery. In our study, we have evaluated the accuracy in terms of both translational and rotational uncertainties for both frame-based and frameless radiosurgery using pretreatment CBCT. Considering the long treatment duration associated with radiosurgery, we also evaluated intrafraction motion by repeating the CBCT midway or after completion of treatment.
The observed shifts for frame-based and frameless SRS have been elaborated in [Table 2], [Table 3], [Table 4] and [Table 5]. Pretreatment, the maximum shift was obtained in craniocaudal direction with a mean of 1.00 mm and maximum rotation in pitch of −0.44 degrees. Ramakrishna et al. found a vertical deviation of 0.50 mm between a frame-based system and the BrainLAB frameless mask.  Similar results have also been reported by Dietmar et al. In these studies, rotational errors were not calculated. However, for detailed analysis of positional accuracy, estimates of translational and rotational errors as well as intrafraction motion are required. Intrafraction motion, as obtained from posttreatment CBCT, was maximum in lateral direction at 0.60 mm and maximum rotation in roll of 0.09 degrees.
|Table 5: Comparison of parameters with frame and without frame after correction|
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Pretreatment mean shifts for frameless radiosurgery in our study were: X = −0.40 mm (SD = 0.90), Y = 1.10 mm (SD = 1.10), Z = -0.50 mm (SD = −1.30), roll -0.11 degree (SD = 0.78), pitch 0.20 degree (SD = 0.44), and yaw 0.29 degree (SD = 0.35). Minniti et al., in their study, reported mean isocenter displacement of 0.12 mm (SD 0.35) in the lateral direction, 0.20 mm (SD 0.40) in the anteroposterior, and 0.40 mm (SD 0.60) in craniocaudal direction.  Wong et al. reported mean and maximum 3D displacements at the isocenter of 0.7 and 2.50 mm, respectively, using a thermoplastic mask.  Similarly, mean 3D target isocenter translation of 1.64 ± 0.84 mm, and a maximum dislocation of 3.39 mm have been reported by Fuss et al. Shifts ranging from 1.3 to 2 mm in X, 0.6-1.80 mm in Y, and 0.9-1.50 mm in Z direction have been shown in other studies. ,,,
Posttreatment shifts in cases of frameless SRS were: X =0.11 mm (SD = 0.20), Y = 0.20 mm (SD = 0.40), Z = 0.20 mm (SD = 0.20), roll 0.09 degree (SD = 0.23), pitch 0.00 degree (SD = 0.12), and yaw 0.00 degree (SD = 0.09). Minniti et al. reported mean measured isocenter displacements of 0.04 mm (SD 0.14) in the lateral direction, 0.06 mm (SD 0.15) in the anteroposterior direction, and 0.08 mm (SD 0.20) in craniocaudal direction. The mean 3D displacement was 0.09 mm (SD 0.28), with a maximum shift of 0.60 mm.  In our study, we repeated CBCT on the treatment couch either midway or following completion of treatment in contrast to Minniti et al.'s study where patients fitted with the mask were transported in a wheelchair from the treatment room to the CT room. This might explain the smaller shifts in our study.
Frame-based SRS has been the preferred standard technique for precise delivery of high dose radiation in brain lesions due to high degree of patient repositioning accuracy. Frameless treatments, in contrast, are assumed to have less reproducibility. In our experience, the setup accuracy of frame-based SRS matches that of fframeless SRS. With recent advances (CBCT and Hexapod), we can determine as well as correct deviations in all six dimensions hence enabling frameless SRS.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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