Initial clinical experience with frameless radiosurgery for patients with intracranial metastases

Reena Kamath.  IJROBP 2005;61:1467

Sixty-four patients received frameless SRS for intracranial metastatic disease. Minimum follow-up was 6 months with none lost to follow-up. Patients had a median of 2 metastases and a maximum of 4. The median number of isocenters was 2 with median arcs of 10 and median dose of 17.5 Gy. Thirteen patients were treated for progressive/recurrent disease after surgical resection or whole brain radiotherapy (WBRT). Fifty-one patients were treated with frameless SRS as an an adjunct to initial treatment. Of the total treated, 17 were treated with SRS alone, 20 were treated with WBRT plus SRS, 16 were treated with surgical resection plus SRS, and the remaining 11 were treated with surgical resection plus WBRT plus SRS.

Results: With a median actuarial follow-up period of 8.2 months, ultimate local control was 88%. The median time to progression was 8.1 months. The median overall survival was 8.7 months. Of the 17 patients treated with SRS alone, 86% had ultimate local control with mean overall survival of 7.1 months. Of the 13 patients who received surgical resection plus SRS without WBRT as primary treatment, there was 85% ultimate local control with an overall survival of 10.3 months. Three patients treated with initial surgery alone had recurrence treated with SRS 2–3 months after resection. All these patients obtained local control and median survival was >10 months. Of the 13 patients who received WBRT followed by SRS as boost treatment, 92% had local control and mean overall survival was 7.3 months. Of 7 patients who received SRS after recurrence after WBRT, 100% had local control with median survival of 8.2 months. For 8 patients who received surgery followed by WBRT and SRS, local control was 50%; however, ultimate intracranial control was achieved in 7 of 8 patients with repeat SRS and surgical resection. The overall survival in this group of patients was 14.7 months. No patient had a serious (Grade 3 or higher) complication requiring intervention.

Conclusions: Frameless optically guided radiosurgery is less invasive, can be performed as a standard radiotherapy-based simulation procedure, and maintains submillimetric accuracy. Our initial results with frameless SRS for metastatic disease suggest survival times and local control (88%) eqiuvalent to frame-based methodologies. Practical noninvasive delivery makes treatment and potential retreatment to avoid WBRT more feasible.
 

Radiosurgery has rapidly become a standard treatment option for patients with intracranial metastases. Because of this growing role for SRS, it is desirable to consider a noninvasive and facile delivery modality that can easily be performed in the radiation oncology clinic. A recent national cooperative group trial suggests an advantage for WBRT plus SRS vs. WBRT alone. In contrast, some studies have suggested that deletion of surgery for a solitary lesion  or deletion of WBRT. may permit equivalent survival for patients with brain metastases ranging from good to a more grave prognosis. Additionally, several retrospective studies failed to show overall survival differences between patients receiving SRS alone vs. WBRT followed by SRS. Lastly, in a retrospective review by Sneed , it was observed that omission of up-front WBRT did not decrease overall survival in patients treated with SRS alone for newly diagnosed brain metastases (8.2 vs. 8.6 months) even in subsets of patients without extracranial disease or single/multiple lesions.

Our results suggest frameless radiosurgery alone is a reasonable alternative to whole brain radiotherapy with an overall survival of 7.1 month (SRS alone) vs. 7.3 months (SRS with WBRT), confirming the findings of Sneed et al. Whole brain RT may impact the quality of survival by promoting side effects, including hair loss, nausea, vomiting, dementia, and cerebral atrophy, especially for long-term survivors. Others consider that avoidance of WBRT leads to lack of local control and diminished quality. Logically, SRS alone has worse local control compared with SRS plus WBRT; thus, the ability to scan during follow-up and treat prospective small recurrences is an important advantage of this noninvasive technique. As a palliative and noninvasive approach for out of field recurrence, a frameless approach is highly desirable.

In our experience, surgical resection followed by SRS has comparable overall survival and local control rates compared with surgical resection followed by WBRT, suggesting that WBRT may be omitted for a certain subset of patients to avoid long-term neurocognitive deficits (5). In a study comparing patients receiving WBRT alone to surgical resection followed by WBRT, Patchell  found with combination treatment overall survival was 10 months with a local control rate of 89%. In our study, the overall survival and local control rates for patients receiving surgical resection with SRS were 10.3 months and 85%, respectively. Our comparable results suggest WBRT may be omitted in the initial treatment regimen. In another study evaluating patients who received WBRT with SRS instead of surgery, Auchter  observed a similarly increased survival (56 weeks) compared with surgical resection followed by WBRT. This was also confirmed in our study with an overall survival of 14.6 months and ultimate local control of 88% in those treated with surgical resection, WBRT, and SRS combined. Our study also shows SRS is a good salvage option for patients who have recurrent intracranial disease after surgical resection or WBRT; we observed a 100% local control rate for the 10 patients in our study who recurred after initial treatment.

Local control rates in the 80–90% range have been reported in frame-based SRS literature for intracranial metastases . Our 88% ultimate local control rate with frameless SRS suggests frameless SRS is a viable option and provides similar local control for patients with metastases normally treated with frame-based approaches. In this study, accuracy rivals frame-based approaches. Although head ring placement may be perceived as minimally invasive while providing a high degree of accuracy, it may not be optimal as it does cause pain and discomfort. Frameless SRS provides the option of treatment planning and treatment delivery on separate days, which, although not used in our current treatment pattern, may be helpful for many clinics. Patients being treated on the same day have a bite block, CT scan in the morning, and are free until radiosurgery treatment in the afternoon. They no longer require monitoring by staff during the day and may leave the facility until treatment is delivered. The possibility of machine breakdown on a day of radiosurgery is always a concern, and in a frame-based approach might require hospital admission while the machine is repaired. This potential problem is obviated with frameless SRS. The frameless approach also reduces extensive resource utilization, personnel, cost, and complexity of the SRS procedure. There are however, a few conditions that prevent using the frameless SRS approach. Because radiosurgery treatment delivery using conventional techniques (arcing of circular collimators) requires approximately 15 min per isocenter, patients with greater than 4 isocenters are not good candidates owing to patient fatigue resulting from lengthy treatment sessions. While we initially excluded these patients from our series, we later had patients with up to 4 metastases to treat with up to 7 isocenters. This was technically challenging and time-consuming. It may be possible to treat such patients by treating lesions consecutively over several days although we have not done this. Additionally, highly irregular treatment volumes and poor Karnofsky performance status score of patients also prevent optimal use of the frameless SRS technique. In summary, while these early results with frameless SRS are encouraging, further study is needed before routine use of this technique can be recommended.