Factors affecting the accuracy of respiratory tracking of the image-guided robotic radiosurgery system.

PURPOSE: To analyze the factors affecting the tracking accuracy of the CyberKnife Synchrony Respiratory Tracking System (SRTS). MATERIALS AND METHODS: A dynamic motion phantom (motion phantom) reproduced the respiratory motions of each patient treated with the SRTS using a ball as the target. CyberKnife tracked the ball using the SRTS, and this process was recorded by a video camera mounted on the linear accelerator head. The tracking error was evaluated from the images captured by the video camera. Multiple regression analysis was used to identify factors affecting tracking accuracy from 91 cases. RESULTS: The median tracking error was 1.9 mm (range 0.9-5.3 mm). Four factors affected the tracking accuracy: the average absolute amplitude of the tumor motion in the cranio-caudal (CC) direction (p = 0.007), average position gap due to the phase shift between the internal tumor and external marker positions in the CC direction (p < 0.001), and average velocity of the tumor in the CC (p < 0.001) and anterior-posterior directions (p = 0.033). CONCLUSION: We identified factors that affected tracking accuracy. This information may assist the identification of suitable margins that should be added to each patient's clinical target volume.

A phase I/II study on stereotactic body radiotherapy with real-time tumor tracking using CyberKnife based on the Monte Carlo algorithm for lung tumors.

BACKGROUND: In this phase I/II study, we assessed the safety and initial efficacy of stereotactic body radiotherapy (SBRT) for lung tumors with real-time tumor tracking using CyberKnife based on the Monte Carlo algorithm. METHODS: Study subjects had histologically confirmed primary non-small-cell lung cancer staged as T1a-T2aN0M0 and pulmonary oligometastasis. The primary endpoint was the incidence of Grade ≥3 radiation pneumonitis (RP) within 180 days of the start of SBRT. The secondary endpoint was local control and overall survival rates. Five patients were initially enrolled at level 1 [50 Gy/4 fractions (Fr)]; during the observation period, level 0 (45 Gy/4 Fr) was opened. The dose was escalated to the next level when grade ≥3 RP was observed in 0 out of 5 or 1 out of 10 patients. Virtual quality assurance planning was performed for 60 Gy/4 Fr; however, dose constraints for the organs at risk did not appear to be within acceptable ranges. Therefore, level 2 (55 Gy/4 Fr) was regarded as the upper limit. After the recommended dose (RD) was established, 15 additional patients were enrolled at the RD. The prescribed dose was normalized at the 95% volume border of the planning target volume based on the Monte Carlo algorithm. RESULTS: Between September 2011 and September 2015, 40 patients (primary 30; metastasis 10) were enrolled. Five patients were enrolled at level 0, 15 at level 1, and 20 at level 2. Only one grade 3 RP was observed at level 1. Two-year local control and overall survival rates were 98 and 81%, respectively. CONCLUSION: The RD was 55 Gy/4 Fr. SBRT with real-time tumor tracking using CyberKnife based on the Monte Carlo algorithm was tolerated well and appeared to be effective for solitary lung tumors.

Re-irradiation of recurrent anaplastic ependymoma using radiosurgery or fractionated stereotactic radiotherapy.

PURPOSE: Recurrent ependymomas were retreated with stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT). The efficacy, toxicities, and differences between SRS and FSRT were analyzed. METHODS: Eight patients with recurrent ependymomas fulfilling the criteria described below were evaluated. Inclusion criteria were: (1) the patient had previously undergone surgery and conventional radiotherapy as first-line treatment; (2) targets were located in or adjacent to the eloquent area or were deep-seated; and (3) the previously irradiated volume overlapped the target lesion. RESULTS: FSRT was delivered to 18 lesions, SRS to 20 lesions. A median follow-up period was 23 months. The local control rate was 76 % at 3 years. No significant differences in local control were observed due to tumor size or fractionation schedule. Lesions receiving >25 Gy/5 fr or 21 Gy/3 fr did not recur within 1 year, whereas no dose-response relationship was observed in those treated with SRS. No grade ≥2 toxicity was observed. CONCLUSION: Our treatment protocol provided an acceptable LC rate and minimal toxicities. Because local recurrence of tumors may result in patient death, a minimum dose of 21 Gy/3 fr or 25 Gy/5 fr or higher may be most suitable for treatment of these cases.

Evaluation of Dose Uncertainty to the Target Associated With Real-Time Tracking Intensity-Modulated Radiation Therapy Using the CyberKnife Synchrony System.

We investigated the dose uncertainty caused by errors in real-time tracking intensity-modulated radiation therapy (IMRT) using the CyberKnife Synchrony Respiratory Tracking System (SRTS). Twenty lung tumors that had been treated with non-IMRT real-time tracking using CyberKnife SRTS were used for this study. After validating the tracking error in each case, we did 40 IMRT planning using 8 different collimator sizes for the 20 patients. The collimator size was determined for each planning target volume (PTV); smaller ones were one-half, and larger ones three-quarters, of the PTV diameter. The planned dose was 45 Gy in 4 fractions prescribed at 95% volume border of the PTV. Thereafter, the tracking error in each case was substituted into calculation software developed in house and randomly added in the setting of each beam. The IMRT planning incorporating tracking errors was simulated 1000 times, and various dose data on the clinical target volume (CTV) were compared with the original data. The same simulation was carried out by changing the fraction number from 1 to 6 in each IMRT plan. Finally, a total of 240 000 plans were analyzed. With 4 fractions, the change in the CTV maximum and minimum doses was within 3.0% (median) for each collimator. The change in D99 and D95 was within 2.0%. With decreases in the fraction number, the CTV coverage rate and the minimum dose decreased and varied greatly. The accuracy of real-time tracking IMRT delivered in 4 fractions using CyberKnife SRTS was considered to be clinically acceptable.

Pituitary metastases: current practice in Japan.

OBJECT: With advancement of cancer treatment and development of neuroimaging techniques, contemporary clinical pictures of pituitary metastases (PMs) must have changed from past reports. The goal of this paper was to elucidate the clinical features of PMs and current clinical practice related to those lesions. In this retrospective study, questionnaires were sent to 87 physicians who had treated PMs in Japan. RESULTS: Between 1995 and 2010, 201 patients with PMs were treated by the participating physicians. The diagnosis of PM was histologically verified in 69 patients (34.3%). In the other 132 patients (65.7%), the PM was diagnosed by their physicians based on neuroimaging findings and clinical courses. The most frequent primary tumor was lung (36.8%), followed by breast (22.9%) and kidney (7.0%) cancer. The average interval between diagnosis of primary cancer and detection of PM was 2.8 ± 3.9 (SD) years. Major symptoms at diagnosis were visual disturbance in 30.3%, diabetes insipidus in 27.4%, fatigue in 25.4%, headache in 20.4%, and double vision in 17.4%. Major neuroimaging features were mass lesion in the pituitary stalk (63.3%), constriction of tumor at the diaphragmatic hiatus (44.7%), hypothalamic mass lesion (17.4%), and hyperintensity in the optic tract (11.4%). Surgical treatment was performed in 26.9% of patients, and 74.6% had radiation therapy; 80.0% of patients who underwent radiotherapy had stereotactic radiotherapy. The median survival time was 12.9 months in total. Contributing factors for good prognosis calculated by Cox proportional hazard analysis were younger age, late metastasis to the pituitary gland, smaller PM size, and radiation therapy. The Kaplan-Meier survival was significantly better in patients with breast cancer and renal cell cancer than in those with lung cancer. CONCLUSIONS: At the time of this writing, approximately 60% (120/201) of PMs had been treated by stereotactic radiation therapy in Japan. The median survival time was much longer than that reported in past series. To confirm the changes of clinical features and medical practice, a prospective and population-based survey is mandatory.

Development of system using beam's eye view images to measure respiratory motion tracking errors in image-guided robotic radiosurgery system.

The accuracy of the CyberKnife Synchrony Respiratory Tracking System (SRTS) is considered to be patient-dependent because the SRTS relies on an individual correlation between the internal tumor position (ITP) and the external marker position (EMP), as well as a prediction method to compensate for the delay incurred to adjust the position of the linear accelerator (linac). We aimed to develop a system for obtaining pretreatment statistical measurements of the SRTS tracking error by using beam's eye view (BEV) images, to enable the prediction of the patient-specific accuracy. The respiratory motion data for the ITP and the EMP were derived from cine MR images obtained from 23 patients. The dynamic motion phantom was used to reproduce both the ITP and EMP motions. The CyberKnife was subsequently operated with the SRTS, with a CCD camera mounted on the head of the linac. BEV images from the CCD camera were recorded during the tracking of a ball target by the linac. The tracking error was measured at 15 Hz using in-house software. To assess the precision of the position detection using an MR image, the positions of test tubes (determined from MR images) were compared with their actual positions. To assess the precision of the position detection of the ball, ball positions measured from BEV images were compared with values measured using a Vernier caliper. The SRTS accuracy was evaluated by determining the tracking error that could be identified with a probability of more than 95% (Ep95). The detection precision of the tumor position (determined from cine MR images) was < 0.2 mm. The detection precision of the tracking error when using the BEV images was < 0.2mm. These two detection precisions were derived from our measurement system and were not obtained from the SRTS. The median of Ep95 was found to be 1.5 (range, 1.0-3.5) mm. The difference between the minimum and maximum Ep95 was 2.5mm, indicating that this provides a better means of evaluating patient-specific SRTS accuracy. A suitable margin, based on the predicted patient-specific SRTS accuracy, can be added to the clinical target volume.

Effect of residual patient motion on dose distribution during image-guided robotic radiosurgery for skull tracking based on log file analysis.

PURPOSE: The present study aimed to assess the effect of residual patient motion on dose distribution during intracranial image-guided robotic radiosurgery by analyzing the system log files. MATERIALS AND METHODS: The dosimetric effect was analyzed according to the difference between the original and estimated dose distributions, including targeting error, caused by residual patient motion between two successive image acquisitions. One hundred twenty-eight treatments were analyzed. Forty-two patients were treated using the isocentric plan, and 86 patients were treated using the conformal (non-isocentric) plan. RESULTS: The median distance from the imaging center to the target was 55 mm, and the median interval between the acquisitions of sequential images was 79 s. The median translational residual patient motion was 0.1 mm for each axis, and the rotational residual patient motion was 0.1° for Δpitch and Δroll and 0.2° for Δyaw. The dose error for D 95 was within 1 % in more than 95 % of cases. The maximum dose error for D 10 to D 90 was within 2 %. None of the studied parameters, including the interval between the acquisitions of sequential images, was significantly related to the dosimetric effect. CONCLUSION: The effect of residual patient motion on dose distribution was minimal.

Salvage stereotactic reirradiation using the CyberKnife for the local recurrence of nasal or paranasal carcinoma.

PURPOSE: To evaluate the clinical outcome of stereotactic reirradiation using the CyberKnife system for recurrent nasal or paranasal carcinoma. MATERIALS AND METHODS: From May 2005 to February 2010, 51 patients with local recurrence of nasal or paranasal carcinoma were reirradiated using CyberKnife. Tumor volume ranged from 3.1 to 204.9 ml (median, 33.8). The previous conventional radiotherapy dose ranged from 40 to 70 Gy (median, 60). The median follow-up period for surviving patients was 21 months (range, 12-52). The marginal doses were 20-41.5 Gy in 1-5 fractions (35 Gy). Toxicities were evaluated with the Common Terminology Criteria for Adverse Events version 4.0. RESULTS: The median overall survival and local control periods after reirradiation were 14.5 and 9.5 months, respectively. The 1-year survival and local control rates were 67% and 62%, respectively. Grade 3 or higher adverse events were observed in 23%. Grade 4 dermatitis and soft tissue necrosis were observed in 2 and 1 patients who had received trimodality combination therapy as their previous treatment, respectively. CONCLUSIONS: Salvage stereotactic reirradiation using CyberKnife is feasible and effective for the local recurrence of nasal and paranasal carcinomas. To further improve treatment outcomes, exploration of better planning and dose fractionation, as well as combination chemotherapy would be worthwhile.

Single and hypofractionated stereotactic radiotherapy with CyberKnife for craniopharyngioma.

Craniopharyngiomas are slow-growing tumors found in the suprasellar region, with especially high incidence in Japanese children. Due to the location, proximity and adhesiveness of the tumor to adjacent critical structures, these tumors remain a significant clinical challenge. The purpose of this study was to evaluate the clinical outcome of single and hypofractionated stereotactic radiotherapy (SRT) with CyberKnife for craniopharyngioma. Forty-three patients (21 men and 22 women; median age 44 years; range 3-85 years) were treated at two institutions. Three cases were treated in a single fraction to a marginal dose of 13-16 Gy. The other 40 cases were treated in 2-5 fractions to a marginal dose of 13-25 Gy. Tumor volumes ranged from 0.09 to 20.8 cm(3) (median 2.0 cm(3)). Toxicities were evaluated with the Common Terminology Criteria for Adverse Events version 4.0. The median follow-up period was 40 months (range 12-92 months). The 3-year overall survival and local control rates were 100 and 85%, respectively. In-field cyst enlargement was observed in 9 patients. These tumors had significantly larger volumes (mean 6.9 cm(3); 95% confidence interval, CI, 2.8-10.9 cm(3)) than the 34 controlled tumors (2.9 cm(3); CI 1.5-4.3 cm(3)) (P = 0.02). Out-field tumor regrowth was observed in 4 patients. No radiation-induced symptomatic visual disorder or brain necrosis was observed. Hypopituitarism was observed in only 1 patient. Single and hypofractionated SRT using CyberKnife produced high tumor control rates with minimal complications. Hypofractionated SRT may be useful for protecting the visual nerve and neuroendocrine function, especially for tumors located near the optic pathways and for large tumors.

Hypofractionated stereotactic radiotherapy with CyberKnife for nonfunctioning pituitary adenoma: high local control with low toxicity.

The aim was to evaluate the clinical outcome of hypofractionated stereotactic radiotherapy (SRT) with CyberKnife for nonfunctioning pituitary adenoma. From October 2000 to March 2009, 100 patients with nonfunctioning pituitary adenoma were treated with hypofractionated SRT. Forty-three patients were male, and 57 were female. The patient's ages ranged from 16 to 82 years (median, 59 years). Five patients were medically inoperable, and 1 refused surgery; the remaining 94 were recurrent cases or those receiving postoperative adjuvant SRT. No patients had a history of previous cranial radiotherapy. Tumor volume ranged from 0.7 to 64.3 mL (median, 5.1 mL). The marginal doses were 17.0 to 21.0 Gy for the 3-fraction schedule and 22.0 to 25.0 Gy for the 5-fraction schedule. Toxicities were evaluated with the Common Terminology Criteria for Adverse Events version 4.0. The median follow-up period for living patients was 33 months (range, 18-118.5 months). The 3-year overall survival and local control rates were 98% and 98%, respectively. In-field and out-field tumor regrowth were observed in 3 and 2 patients, respectively. Transient cyst enlargement occurred in 3 cases. A post-SRT grade 2 visual disorder occurred in 1 patient. Symptomatic post-SRT hypopituitarism was observed in 3 of 74 patients who had not received hormone replacement therapy after surgery. CyberKnife SRT involving 21 Gy in 3 fractions or 25 Gy in 5 fractions is safe and effective for surgical treatment of nonfunctioning pituitary adenoma. Hypofractionated SRT appears useful for protecting the visual nerve and neuroendocrine function, especially for tumors located near the optic pathways and large tumors.