Correction of patient positioning errors based on in-line cone beam CTs: clinical implementation and first experiences

BACKGROUND: The purpose of the study was the clinical implementation of a kV cone beam CT (CBCT) for setup correction in radiotherapy. PATIENTS AND METHODS: For evaluation of the setup correction workflow, six tumor patients (lung cancer, sacral chordoma, head-and-neck and paraspinal tumor, and two prostate cancer patients) were selected. All patients were treated with fractionated stereotactic radiotherapy, five of them with intensity modulated radiotherapy (IMRT). For patient fixation, a scotch cast body frame or a vacuum pillow, each in combination with a scotch cast head mask, were used. The imaging equipment, consisting of an x-ray tube and a flat panel imager (FPI), was attached to a Siemens linear accelerator according to the in-line approach, i.e. with the imaging beam mounted opposite to the treatment beam sharing the same isocenter. For dose delivery, the treatment beam has to traverse the FPI which is mounted in the accessory tray below the multi-leaf collimator. For each patient, a predefined number of imaging projections over a range of at least 200 degrees were acquired. The fast reconstruction of the 3D-CBCT dataset was done with an implementation of the Feldkamp-David-Kress (FDK) algorithm. For the registration of the treatment planning CT with the acquired CBCT, an automatic mutual information matcher and manual matching was used. RESULTS AND DISCUSSION: Bony landmarks were easily detected and the table shifts for correction of setup deviations could be automatically calculated in all cases. The image quality was sufficient for a visual comparison of the desired target point with the isocenter visible on the CBCT. Soft tissue contrast was problematic for the prostate of an obese patient, but good in the lung tumor case. The detected maximum setup deviation was 3 mm for patients fixated with the body frame, and 6 mm for patients positioned in the vacuum pillow. Using an action level of 2 mm translational error, a target point correction was carried out in 4 cases. The additional workload of the described workflow compared to a normal treatment fraction led to an extra time of about 10–12 minutes, which can be further reduced by streamlining the different steps. CONCLUSION: The cone beam CT attached to a LINAC allows the acquisition of a CT scan of the patient in treatment position directly before treatment. Its image quality is sufficient for determining target point correction vectors. With the presented workflow, a target point correction within a clinically reasonable time frame is possible. This increases the treatment precision, and potentially the complex patient fixation techniques will become dispensable

Intensity modulated radiotherapy (IMRT) in patients with carcinomas of the paranasal sinuses: clinical benefit for complex shaped target volumes

INTRODUCTION: The aim of the study was to evaluate the clinical outcome of intensity modulated radiotherapy (IMRT) in 46 patients with paranasal sinus tumors with special respect to treatment-related toxicity. PATIENTS AND METHODS: We treated 46 patients with histologically proven tumors of the paranasal sinuses with IMRT. Histological classification included squamous cell carcinoma in 6, adenocarcinoma in 8, adenoidcystic carcinoma in 20 and melanoma in 8 patients, respectively. Six patients had been treated with RT during initial therapy after primary diagnosis, and IMRT was performed for the treatment of tumor progression as re-irradiation. RESULTS: Overall survival rates were 96% at 1 year, 90% at 3 years. Calculated from the initiation of IMRT as primary radiotherapy, survival rates at 1 and 3 years were 95% and 80%. In six patients IMRT was performed as re-irradiation, and survival rate calculated from re-irradiation was 63% at 1 year. Local control rates were 85% at 1, 81% at 2 and 49% at 3 years after primary RT and 50% at 1 year after re-irradiation. Distant metastases-free survival in patients treated with IMRT as primary RT was 83% after 1 and 64% after 3 years. For patients treated as primary irradiation with IMRT, the distant control rate was 83% at 1 year and 0% at 2 years. No severe radiation-induced side-effects could be observed. CONCLUSION: IMRT for tumors of the paranasal sinuses is associated with very good tumor control rates. Treatment-related acute and long-term toxicity can be minimized as compared to historical results with conventional RT

Local radiotherapeutic management of ependymomas with fractionated stereotactic radiotherapy (FSRT)

<p>Abstract</p> <p>Background</p> <p>To assess the role of Fractionated Stereotactic Radiotherapy (FSRT) in the management of ependymomas.</p> <p>Methods</p> <p>From January 1992 to July 2003, FSRT was performed in 19 patients with histologically confirmed ependymomas. The median age was 15 years, 5 patients were younger than 4 years of age.</p> <p>Twelve patients received FSRT as primary postoperative radiotherapy after surgical resection. In 6 patients irradiation of the posterior fossa was performed with a local boost to the tumor bed, and in 4 patients the tumor bed only was irradiated. In 7 patients FSRT was performed as re-irradiation for tumor progression. This patient group was analyzed separately. A median dose of 54 Gy was prescribed in a median fractionation of 5 × 1.8 Gy per week for primary RT using 6 MeV photons with a linear accelerator. For FSRT as re-irradiation, a median dose of 36 Gy was applied. All recurrent tumors were localized within the former RT-field.</p> <p>Results</p> <p>The 5- and 10-year overall survival rates were 77% and 64%, respectively. Patients treated with FSRT for primary irradiation showed an overall survival of 100% and 78% at 3 and 5 years after irradiation of the posterior fossa with a boost to the tumor bed, and a survival rate of 100% at 5 years with RT of the tumor bed only. After re-irradiation with FSRT, survival rates of 83% and 50% at 3-and 5 years, respectively, were obtained.</p> <p>Progression-free survival rates after primary RT as compared to re-irradiation were 64% and 60% at 5 years, respectively.</p> <p>FSRT was well tolerated by all patients and could be completed without interruptions due to side effects. No severe treatment related toxicity > CTC grade 2 for patients treated with FSRT could be observed.</p> <p>Conclusion</p> <p>The present analysis shows that FSRT is well tolerated and highly effective in the management of ependymal tumors. The rate of recurrences, especially at the field border, is not increased as compared to conventional radiotherapy consisting of craniospinal irradiation and a local boost to the posterior fossa.</p