Improving interinstitutional and intertechnology consistency of pulmonary SBRT by dose prescription to the mean internal target volume dose.

PURPOSE: Dose, fractionation, normalization and the dose profile inside the target volume vary substantially in pulmonary stereotactic body radiotherapy (SBRT) between different institutions and SBRT technologies. Published planning studies have shown large variations of the mean dose in planning target volume (PTV) and gross tumor volume (GTV) or internal target volume (ITV) when dose prescription is performed to the PTV covering isodose. This planning study investigated whether dose prescription to the mean dose of the ITV improves consistency in pulmonary SBRT dose distributions. MATERIALS AND METHODS: This was a multi-institutional planning study by the German Society of Radiation Oncology (DEGRO) working group Radiosurgery and Stereotactic Radiotherapy. CT images and structures of ITV, PTV and all relevant organs at risk (OAR) for two patients with early stage non-small cell lung cancer (NSCLC) were distributed to all participating institutions. Each institute created a treatment plan with the technique commonly used in the institute for lung SBRT. The specified dose fractionation was 3â€¯× 21.5 Gy normalized to the mean ITV dose. Additional dose objectives for target volumes and OAR were provided. RESULTS: In all, 52 plans from 25 institutions were included in this analysis: 8 robotic radiosurgery (RRS), 34 intensity-modulated (MOD), and 10 3D-conformal (3D) radiation therapy plans. The distribution of the mean dose in the PTV did not differ significantly between the two patients (median 56.9 Gy vs 56.6 Gy). There was only a small difference between the techniques, with RRS having the lowest mean PTV dose with a median of 55.9 Gy followed by MOD plans with 56.7 Gy and 3D plans with 57.4 Gy having the highest. For the different organs at risk no significant difference between the techniques could be found. CONCLUSIONS: This planning study pointed out that multiparameter dose prescription including normalization on the mean ITV dose in combination with detailed objectives for the PTV and ITV achieve consistent dose distributions for peripheral lung tumors in combination with an ITV concept between different delivery techniques and across institutions.

[Radiosurgery and fractionated stereotactic radiotherapy of vestibular schwannoma]. / Radiochirurgie und fraktionierte stereotaktische Radiotherapie des Vestibularisschwannoms.

Management of vestibular schwannoma (VS) should always be interdisciplinary and results better than the natural course. Particularly in small VS, either microsurgical resection or radiosurgery (RS) can be employed. RS is a special method (initially only possible stereotactically) for delivering high-precision radiation from many directions to the target point (the isocenter) in a single high dose. With the development of three different systems-Gamma Knife (Elekta, Stockholm, Sweden), special linear accelerators, and CyberKnife (Accuray, Sunnyvale, CA, USA)-the options were extended to 1-5 fractions for RS and multisession RS (msRS), and to up to 6 weeks of conventional fractionation as stereotactic radiotherapy (SRT). Whereas RS uses high ablative single doses, SRT is based on the well-known radiobiological effects of multiple fractions comprising lower single doses up to a required much higher total dose. Evaluation showed that RS and SRT achieve similarly high rates of tumor control of around 90% and low rates of side effects (1-7%). Therefore, SRT is unnecessary for small but clearly progressing VS, which has made RS a very comfortable, effective treatment option. In addition to SRT, larger VS can be treated comparably effectively with CyberKnife-based msRS. Since modern MRI frequently discovers small VS as "incidental findings", the initial biding strategy (wait and scan) is of particular importance. Only with increasing symptoms and detectable tumor growth is the treatment indication established, at which time the decision for surgery and RS/SRT should be taken interdisciplinary under consideration of the patient's wishes.

Radiosurgery/stereotactic radiotherapy in the therapeutical concept for skull base meningiomas.

OBJECTIVE: Microsurgical resection is still the treatment of choice for skull base meningiomas. But the risk of postoperative neurological deficits is high, and in many of these cases complete tumor removal cannot be achieved. Therefore recurrences are even more probable. Stereotactically guided radiation therapy - radiosurgery (RS) or stereotactic radiotherapy (SRT) - offers an additional or alternate treatment option for those patients. We evaluated local control rates, symptomatology, and toxicity. PATIENTS AND METHODS: 224 patients were treated with stereotactically guided radiation techniques in two departments between 1997 and 2003. 129 of 224 had recurrences after 1 to 3 prior tumor resections and 95 of 224 were treated with SRT/RS alone. 87.9% of cases had benign, 7.8% had atypical and 4.3% had malignant meningiomas. RS was only applied in 11 cases. Tumor volumes ranged from 0.16 ccm to 3.56 ccm. The other 213 patients had larger tumor volumes of up to 135 ccm or a meningioma close to optical structures. Therefore 183 cases were treated with SRT in normal fractions of 1.8-2 Gy in single doses up to 60 Gy. Hypofractionated SRT with single fraction doses of 5 or 4 Gy was applied in 30 cases. Follow-up data were available in 181 skull base meningiomas and the progression-free and overall survival rates, the toxicity and symptomatology were evaluated. RESULTS: The median follow-up was 36 months. The overall survival and the progression-free survival rates for 5 years were 92.9%, and 96.9%, respectively. Two tumor progressions have occurred to date but further follow up is required. Tumor volumes (TV) had shrunk about by 19.7% at 6 months (p<0.0001) and by 23.2% at 12 months (p<0.01) after SRT/RS. In 95.6% the symptoms had improved or were stable. Clinically significant acute toxicity (grade III) was seen in only 1 case (2.7%). Some patients developed late toxicity: 8.8% had grade I, 4.4% had grade II and 1.1% had grade III. No other neurological deficits occurred during follow-up. CONCLUSION: SRT and RS offer an additional or alternative treatment option with a high efficacy and few side effects for the tumor control of skull base meningiomas. An individual and interdisciplinary decision respecting treatment is needed for each patient. In cases of large TV (>4 ccm), tumors adjacent to critical structures (<2 mm) or in high-risk patients the use of SRT offers greater benefits.