Radiosurgical System Research Articles

Proctitis following stereotactic body radiation therapy for prostate cancer.

BackgroundProctitis after radiation therapy for prostate cancer remains an ongoing clinical challenge and critical quality of life issue. SBRT could minimize rectal toxicity by reducing the volume of rectum receiving high radiation doses and offers the potential radiobiologic benefits of hypofractionation. This study sought to evaluate the incidence and severity of proctitis following SBRT for prostate cancer.MethodsBetween February 2008 and July 2011, 269 men with clinically localized prostate cancer were treated definitively with SBRT monotherapy at Georgetown University Hospital. All patients were treated to 35-36.25Gy in 5 fractions delivered with the CyberKnife Radiosurgical System (Accuray). Rectal bleeding was recorded and scored using the CTCAE v.4. Telangiectasias were graded using the Vienna Rectoscopy Score (VRS). Proctitis was assessed via the Bowel domain of the Expanded Prostate Index Composite (EPIC)-26 at baseline and at 1, 3, 6, 9, 12, 18 and 24 months post-SBRT.ResultsThe median age was 69 years with a median prostate volume of 39 cc. The median follow-up was 3.9 years with a minimum follow-up of two years. The 2-year actuarial incidence of late rectal bleeding ≥ grade 2 was 1.5%. Endoscopy revealed VRS Grade 2 rectal telangiectasias in 11% of patients. All proctitis symptoms increased at one month post-SBRT but returned to near-baseline with longer follow-up. The most bothersome symptoms were bowel urgency and frequency. At one month post-SBRT, 11.2% and 8.5% of patients reported a moderate to big problem with bowel urgency and frequency, respectively. The EPIC bowel summary scores declined transiently at 1 month and experienced a second, more protracted decline between 6 months and 18 months before returning to near-baseline at two years post-SBRT. Prior to treatment, 4.1% of men felt their bowel function was a moderate to big problem which increased to 11.5% one month post-SBRT but returned to near-baseline at two years post-SBRT.ConclusionsIn this single institution cohort, the rate and severity of proctitis observed following SBRT is low. QOL decreased on follow-up; however, our results compare favorably to those reported for patients treated with alternative radiation modalities. Future prospective randomized studies are needed to confirm these observations.

Patient-reported outcomes following stereotactic body radiation therapy for clinically localized prostate cancer

BackgroundStereotactic body radiation therapy (SBRT) delivers high doses of radiation to the prostate while minimizing radiation to adjacent normal tissues. Large fraction sizes may increase the risk of functional decrements. Treatment-related bother may be more important to a patient than treatment-related dysfunction. This study reports on patient-reported outcomes following SBRT for clinically localized prostate cancer.MethodsBetween August 2007 and July 2011, 228 consecutive hormone-naïve patients with clinically localized prostate cancer were treated with 35–36.25 Gy SBRT delivered using the CyberKnife Radiosurgical System (Accuray) in 5 fractions. Quality of life was assessed using the American Urological Association Symptom Score (AUA) and the Expanded Prostate Cancer Index Composite (EPIC)-26. Urinary symptom flare was defined as an AUA score 15 or more with an increase of 5 or more points above baseline 6 months after treatment.Results228 patients (88 low-, 126 intermediate- and 14 high-risk) at a median age of 69 (44–90) years received SBRT with a minimum follow-up of 24 months. EPIC urinary and bowel summary scores declined transiently at 1 month and experienced a second, more protracted decline between 9 months and 18 months before returning to near baseline 2 years post-SBRT. 14.5% of patients experienced late urinary symptom flare following treatment. Patients who experienced urinary symptom flare had poorer bowel quality of life following SBRT. EPIC scores for urinary bother declined transiently, first at 1 month and again at 12 months, before approaching pre-treatment scores by 2 years. Bowel bother showed a similar pattern, but the second decline was smaller and lasted 9 months to 18 months. EPIC sexual summary and bother scores progressively declined over the 2 years following SBRT without recovery.ConclusionsIn the first 2 years, the impact of SBRT on urination and defecation was minimal. Transient late increases in urinary and bowel dysfunction and bother were observed. However, urinary and bowel function and bother recovered to near baseline by 2 years post-SBRT. Sexual dysfunction and bother steadily increased following treatment without recovery. SBRT for clinically localized prostate cancer was well tolerated with treatment-related dysfunction and bother comparable to conventionally fractionated radiation therapy or brachytherapy.

Bother following stereotactic body radiation therapy for clinically localized prostate cancer.

195 Background: Stereotactic body radiation therapy (SBRT) delivers high doses of radiation while minimizing radiation to adjacent normal tissues. Large fraction sizes may increase the risk of functional decrements. However, treatment-related bother may be more important to a patient than treatment-related dysfunction. Methods: Between August 2007 and July 2011, 228 hormone-naïve patients with clinically localized prostate cancer were treated with 35-36.25 Gy SBRT delivered using the CyberKnife Radiosurgical System (Accuray) in five fractions. Patients completed the validated Expanded Prostate Cancer Index Composite (EPIC)-26 questionnaire at baseline, one month post-treatment, every three months the first year, then every six months. EPIC scores for bother range from 0 to 100 with lower values representing increased interference or annoyance caused by limitations in function. Results: Two hundred twenty eight patients at a median age of 69 (range, age 44 to 90) received SBRT with a minimum follow-up of 24 months. Urinary bother increased transiently first at one month and again at 12 months before returning to pre-treatment scores at two years: 80.2 (baseline); 68.2 (one month); 79.8 (three months); 78.3 (six months); 74.5 (nine months); 71.1 (12 months); 75.8 (18 months); 78.3 (24 months). Bowel bother followed a similar pattern but with a more protracted late-stage decline: 91.4 (baseline); 76.0 (one month); 87.8 (three months); 88.4 (six months); 85.8 (nine months); 85.7 (12 months); 87.8 (18 months); 90.1 (24 months). Sexual bother progressively worsened over two years: 65.9 (baseline); 64.8 (three months); 63.0 (six months); 63.2 (12 months); 59.0 (18 months); 58.4 (24 months). Conclusions: SBRT for clinically localized prostate cancer was well tolerated. Treatment-related bother was comparable to conventionally fractionated radiation therapy and brachytherapy. Transient late increases in urinary and bowel bother were observed at one year. Sexual bother steadily increased during the first two years following treatment.

Potency preservation following stereotactic body radiation therapy for prostate cancer

BackgroundErectile dysfunction after prostate radiation therapy remains an ongoing challenge and critical quality of life issue. Given the higher dose of radiation per fraction using stereotactic body radiation therapy (SBRT) there is concern that post-SBRT impotency would be higher than conventional radiation therapy approaches. This study sought to evaluate potency preservation and sexual function following SBRT for prostate cancer.MethodsBetween February 2008 and March 2011, 216 men with clinically localized prostate cancer were treated definitively with SBRT monotherapy at Georgetown University Hospital. Potency was defined as the ability to have an erection firm enough for intercourse with or without sexual aids while sexual activity was defined as the ability to have an erection firm enough for masturbation and foreplay. Patients who received androgen deprivation therapy (ADT) were excluded from this study. Ninety-seven hormone-naïve men were identified as being potent at the initiation of therapy and were included in this review. All patients were treated to 35–36.25 Gy in 5 fractions delivered with the CyberKnife Radiosurgical System (Accuray). Prostate specific antigen (PSA) and total testosterone levels were obtained pre-treatment, every 3 months for the first year and every 6 months for the subsequent year. Sexual function was assessed with the Sexual Health Inventory for Men (SHIM), the Expanded Prostate Index Composite (EPIC)-26 and Utilization of Sexual Medication/Device questionnaires at baseline and all follow-up visits.ResultsNinety-seven men (43 low-, 50 intermediate- and 4 high-risk) at a median age of 68 years (range, 48–82 years) received SBRT. The median pre-treatment PSA was 5.9 ng/ml and the minimum follow-up was 24 months. The median pre-treatment total serum testosterone level was 11.4 nmol/L (range, 4.4-27.9 nmol/L). The median baseline SHIM was 22 and 36% of patients utilized sexual aids prior to treatment. Although potency rates declined following treatment: 100% (baseline); 68% (6 months); 62% (12 months); 57% (18 months) and 54.4% (24 months), 78% of previously potent patients had erections sufficient for sexual activity at 24 months post-treatment. Overall sexual aid utilization increased from 36% at baseline to 49% at 24 months. Average EPIC sexual scores showed a slow decline over the first two years following treatment: 77.6 (baseline); 68.7 (6 months); 63.2 (12 months); 61.9 (18 months); 59.3 (24 months). All sexual functions including orgasm declined with time. Prior to treatment, 13.4% of men felt their sexual function was a moderate to big problem which increased to 26.7% two years post treatment. Post-treatment testosterone levels gradually decreased with a median value at two year follow-up of 10.7 nmol/L. However, the average EPIC hormonal scores did not illustrate a statistically significant difference two years post-treatment. Review of the radiation doses to the penile bulb in this study, a potential marker of post-treatment sexual function, revealed that the dose was relatively low and at these low doses the percentage of the penile bulb receiving 29.5 Gy did not correlate with the development of ED.ConclusionsMen undergoing SBRT monotherapy for prostate cancer report sexual outcomes comparable to those reported for conventional radiation modalities within the first 24 months after treatment. Longer follow-up is required to confirm the durability of these findings.

What type of patients with lesions of the pancreas and spine are suitable candidates for treatment with the CyberKnife robotic radiosurgical system?

AbstractMaterials & methodsA systematic literature review was conducted to critically examine patient selection for patients undergoing stereotactic body radiotherapy (SBRT) to the spine and pancreas on the CyberKnife robotic radiosurgical system (CK). Online databases were searched and data was collected and ranked using a system from the Scottish Intercollegiate Guideline Network. The quality of the evidence analysed was insufficient to generate universal recommendations. However, the conclusions reached do help to demonstrate the safety and efficacy of CK treatment to both pancreatic and spinal patients.ResultsExcellent local control rates and minimal acute toxicity were reported within the spinal literature with uncertainties remaining with regard to the precise tolerance of the spinal cord and the reliability of current toxicity prediction methods. For pancreatic patients prognosis remains dismal due to the tendency for patients to present with advanced or inoperable disease. Combinations of CK SBRT and Gemcitabine chemotherapy are given though regimes vary and overall survival is not extended due to the rapid onset of distant metastases. New chemotherapy agents are required as well as better means of predicting response to treatment.ConclusionNo randomised controlled trials or meta-analyses were identified in the review and these are required in order to generate universal guidelines

Dosimetric comparison of Stereotactic body radiotherapy and Intensity modulated radiotherapy to deliver hypofractionated radiotherapy in organ confined prostate cancer

We compared the dose conformity, homogeneity, dose to organs at risk, and remaining volume at risk of two radiotherapy techniques --stereotactic body radiotherapy and intensity-modulated radiotherapy (IMRT) to deliver hypofractionated radiotherapy in organ-confined prostate cancer. Eleven successive patients treated on the CyberKnife stereotactic robotic radiosurgical system were taken up for this study. The CT images, including the structures contoured, were imported through DICOM RT from the Multiplan (Accuray Inc., Sunnyvale, CA, USA) treatment planning system to the Plato Sunrise treatment planning system (Nucletron, The Netherlands) for creating IMRT treatment plans on the Linac. Treatment planning was done for five fractions, each fraction prescribed to a dose of 7.25 Gy to the planning target volume. Dose volume histograms were generated for the CyberKnife and Linac treatments for comparison. As per our protocol, a plan was considered adequate if at least 95% of planning target volume received the prescribed dose and satisfied the following constraints: a) volume of the rectum receiving 36Gy (V36) to < 1cc and b) volume of the bladder receiving 37Gy (V37) to < 10cc. Both the treatment techniques plans resulted in adequate planning target volume coverage (p value for D95, D90, D5, and V100% was 0.402, 0.97, 0.013, and 0.012, respectively). CyberKnife plans were more conformal (p value 0.001). Remaining volume at risk dose was significantly less in all CyberKnife plans at [V100% (p=0.01), V95% (p=.004), V90% (p=.001), V80% (p=0.02), V70 (p=0.03), V40% (p=0.021), and V30% (p=0.001)] dose levels. The mean dose to rectum was lower in the CyberKnife plans (The p value for V100%, V80%, V50% and V30% dose levels was 0.02, 0.0001, 0.0002, and 0.12, respectively). Categories: Radiation Oncology, Urology

Pilot study of the delivery of microcollimated pars plana external beam radiation in porcine eyes: 270-day analysis.

Objective. To determine the dose response and toxicity threshold of micro-collimated X-rays delivered to porcine maculae by a stereotactic radiosurgical system after 270 days. Methods. Twelve eyes of six Yucatan mini-swine were randomized to receive up to 90 Gy to the retina, using an office-based trans-pars plana delivery system. To determine the safety profile of this radiation delivery, ophthalmic examination, fundus photography, fluorescein angiography (FA), and spectral domain optical coherence tomography (SD-OCT) were obtained at multiple time points up to 270 days post treatment. Results. No abnormalities were noted on external examination. Cataracts were noted in 4 of 12 eyes. Dose and time-dependent changes were noted on fundus examination, FA, ICG and SD-OCT. No significant abnormalities were seen in the control, 16 Gy or 24 Gy groups using any modality. Histopathology revealed a dose response effect with no discernable lesions in the 16 Gy group. Conclusion. The X-ray delivery system precisely targets the porcine retina in vivo with little effect on surrounding structures. No ophthalmic or intracranial adverse effects were noted at clinically relevant doses at 270 days following radiation delivery.

Pilot Study of the Delivery of Microcollimated Pars Plana External Beam Radiation in Porcine Eyes

To investigate the effects of a novel stereotactic radiosurgical system for pars plana delivery of microcollimated x-rays to the retina and determine the retinal radiological dose response and toxicity threshold in a pig model. The x-rays were delivered through the pars plana to the maculae of Yucatan miniswine to verify the targeting and safety of a cornea-scleral, stabilized, office-based delivery system. Twelve eyes were randomized to receive 0, 16, 24, 42, 60, or 90 Gy in a single dose to the retina. Eye examinations, fundus photography, fluorescein angiography, and spectral-domain optical coherence tomography were obtained at days 7, 30, 60, and 90. Indocyanine green angiography was done at day 90. Through day 90 interim analysis, no abnormalities of external structures were noted. A small cortical lens opacity was noted in the 60-Gy group. Fundus evaluation revealed no abnormalities at 16 or 24 Gy. Beginning at day 30, circular pale retinal lesions with sharp margins were noted in the maculae of the eyes that received 42, 60, and 90 Gy. Higher-dose lesions showed late staining on fluorescein angiography, choroidal hypoperfusion on indocyanine green angiography, and defined photoreceptor loss and retinal thinning on spectral-domain optical coherence tomography. Transscleral stereotactic radiation dosing of porcine eyes demonstrates no apparent clinical abnormalities in doses less than 24 Gy. Doses of 42 Gy or higher led to focal choroidal and retinal damage within the target area. Radiation can induce small-blood vessel closure and thereby has therapeutic potential in neovascular diseases such as age-related macular degeneration.

CyberKnife® enhanced conventionally fractionated chemoradiation for high grade glioma in close proximity to critical structures

IntroductionWith conventional radiation technique alone, it is difficult to deliver radical treatment (≥ 60 Gy) to gliomas that are close to critical structures without incurring the risk of late radiation induced complications. Temozolomide-related improvements in high-grade glioma survival have placed a higher premium on optimal radiation therapy delivery. We investigated the safety and efficacy of utilizing highly conformal and precise CyberKnife radiotherapy to enhance conventional radiotherapy in the treatment of high grade glioma.MethodsBetween January 2002 and January 2009, 24 patients with good performance status and high-grade gliomas in close proximity to critical structures (i.e. eyes, optic nerves, optic chiasm and brainstem) were treated with the CyberKnife. All patients received conventional radiation therapy following tumor resection, with a median dose of 50 Gy (range: 40 - 50.4 Gy). Subsequently, an additional dose of 10 Gy was delivered in 5 successive 2 Gy daily fractions utilizing the CyberKnife® image-guided radiosurgical system. The majority of patients (88%) received concurrent and/or adjuvant Temozolmide.ResultsDuring CyberKnife treatments, the mean number of radiation beams utilized was 173 and the mean number of verification images was 58. Among the 24 patients, the mean clinical treatment volume was 174 cc, the mean prescription isodose line was 73% and the mean percent target coverage was 94%. At a median follow-up of 23 months for the glioblastoma multiforme cohort, the median survival was 18 months and the two-year survival rate was 37%. At a median follow-up of 63 months for the anaplastic glioma cohort, the median survival has not been reached and the 4-year survival rate was 71%. There have been no severe late complications referable to this radiation regimen in these patients.ConclusionWe utilized fractionated CyberKnife radiotherapy as an adjunct to conventional radiation to improve the targeting accuracy of high-grade glioma radiation treatment. This technique was safe, effective and allowed for optimal dose-delivery in our patients. The value of image-guided radiation therapy for the treatment of high-grade gliomas deserves further study.

SU‐GG‐T‐537: Dosimetric Effect of Residual Tumor Motion in Phase and Amplitude‐Based Gated Lung Stereotactic Body Radiotherapy

Purpose To evaluate dosimetric effect of residual tumor motion in lung Stereotactic Body Radiotherapy(SBRT) with two gating methods using external markers: amplitude‐(AG) and phase‐based(PG). Methods and Materials The 3D tumor motion data were obtained from the treatment logs of 6 lung patients with various target size, each treated with 3 fractions of SBRT using Cyberknife Robotic Radiosurgical System and Synchrony™(Accuray, Sunnyvale CA). Amplitude and phase‐based gating treatments were simulated with a gating window of 5 mm. Planning target volume(PTV) was defined as physician‐contoured clinical target volume(CTV) surrounded by isotropic 5 mm margin. Each patient was prescribed with 60Gy/3fractions prescribed to 80% isodose line which covered at least 95% of the PTV. In order to reconstruct the dose with motion, the multileaf collimator(MLC) leave positions at each segment were resorted according to the residual tumor motion. The newly created MLC file was imported back to treatment planning system(Eclipse™; Varian Medical Systems, Palo Alto, CA) for dose recalculation. Results In either AG or PG, with a 5‐mm margin, CTV coverage is not affected as much as PTV. With residual tumor motion constrained within gating window(5 mm), both gating methods result in an insignificant decrease(&lt;1%) in dose coverage on PTVs and CTVs. With baseline shift(2–10 mm), the residual motion during PG has higher probability of excursion outside gating window. The PTV D95 decreases by 9–14% with PG and 5–9% with AG. Overall, AG appears to offer greater target dose coverage compared to PG, however at the expense of reduction of the duty cycle. Compared with PG, AG increases the fractional treatment time by up to 46%, which may be undesirable in gated lung SBRT treatments. Conclusion The ideal gating method for lung SBRT requires further investigation and optimization but may be individualized dependent on the empirical pattern of motion observed in each case.

The Targeting Accuracy of the CyberKnife as Measured with EBT2 film inside a Ball-Cube-II film Cassette and Head Phantom

Introduction: The CyberKnife (Accuray, Inc., Sunnyvale, California, USA) is an image-guided radiosurgical system which utilizes a compact 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgery. The total system error of the CyberKnife system, as measured with an anthropomorphic head phantom containing a film holder, has been previously reported to be submillimetric. In making these prior accuracy measurements, the Ball-Cube-I was used. However, a new design, the Ball-Cube-II, which uses a different kind of pre-cut films, has recently become available. In this study, we investigate the use of this device for measuring the total system accuracy of the CyberKnife. Methods: The Ball-Cube-II film cassette is a radiosurgical quality assurance (QA) tool. Similar to the existing Ball-Cube-I design, the Ball-Cube-II holds two pieces of notched radiochromic (www.gafchromic.com) film that are placed orthogonally within the film cassette. There are holes and pins in the film Ball-Cube-II cassette and holes in the EBT2 film, allowing the film to fit tightly, thus minimizing movement of the film with respect to the film cassette. The ball cube is then placed within an anthropomorphic phantom. The method for determining the localization accuracy of the CyberKnife System is similar for both film cube designs. More specifically, the spatial coordinates for the centroid of the planned dose distribution is compared with the centroid of the dose actually delivered. Results: Using the Ball-Cube-I with MD-55 film, and the head phantom, the total accuracy measured was 0.34 +/- 0.17 mm. While using the ball-cube II with EBT2 film, the total accuracy measured was 0.45 +/- 0.09 mm. Conclusions: The ball-cube-II restricts movement of the film inside the film cube, and thereby reduces the uncertainty of film placement within the cube. This design has the potential to more precisely determine the accuracy of the CyberKnife system. The accuracy of the CyberKnife using film cube with the head phantom was measured to be between 0.34 and 0.45 mm.

CYBERKNIFE RADIOSURGERY FOR TRIGEMINAL SCHWANNOMAS

Trigeminal schwannomas (TS) are benign tumors that are managed by surgical resection and/or stereotactic radiosurgery. Most radiosurgical series report results using the gamma knife. The CyberKnife (Accuray, Inc., Sunnyvale, CA) is a frameless, robotic stereotactic radiosurgical system. In this series, we report our experience using the CyberKnife in the treatment of TS. We retrospectively reviewed the medical records and diagnostic imaging in 13 consecutive patients with TS who were treated with the CyberKnife from 2003 to 2007. Seven patients had a previous surgical resection. The mean tumor volume was 6.3 mL (range, 0.39-19.98 mL), and the mean marginal dose was 18.5 Gy. Six of the tumors were treated in a single session. The mean clinical follow-up period was 21.8 months (range, 7-53 months). In this series, the tumor control rate was 100%. The average reduction in tumor volume was 45% (range, 14-98%). A modest improvement in facial pain was noted in 4 of the 6 patients who presented with this symptom. One patient had improvement in facial numbness, and another had improvement in pretreatment headaches. One patient developed jaw weakness and facial dysesthesia, and another patient developed asymptomatic radiation necrosis. Although the length of follow-up is limited, we report our initial experience with CyberKnife treatment of TS. Our results demonstrate tumor control rates and clinical outcomes that parallel those of previous reports using gamma knife radiosurgery; however, long-term follow-up studies are needed.

Frameless Stereotactic Radiosurgery with a Bite-plate: Our Experience with Brain Metastases

Non-invasive frameless stereotactic radiosurgical systems have recently been developed. We report our experience of frameless stereotactic radiosurgery (SRS) with a bite-plate for brain metastases. Between February 2002 and December 2005, 147 patients with brain metastases were treated with C-arm linear accelerator-based SRS and 122 patients were followed up by our institute. An optic tracking system with infrared light-emitting diodes was used for real-time monitoring. A bite-plate with fiducial markers was applied as a first-line method for frameless SRS. Head-ring fixation was used in patients lacking teeth. Lung carcinomas (63%) were the most common primary tumors, followed by breast carcinomas (13%). Ninety patients underwent radiosurgery with a bite-plate and 32 patients underwent fixation of a head ring. Males were significantly more predominant in the head-ring group (26 men and 6 women), compared with the bite-plate group (47 men and 43 women, p < 0.01). The average age (62 years) in the bite-plate group was significantly younger than that (68 years) in the head-ring group (p < 0.01). The median survival time was 12.0 months in the bite-plate group and 8.0 months in the head-ring group (p = 0.0621). Nine patients who had brain metastases in or close to the brain stem were treated with fractionated stereotactic radiotherapy. The frameless stereotactic radiosurgical system with a bite-plate is safe and effective for the treatment of brain metastasis. Elderly male patients sometimes are edentulous and require placement of a head ring for radiosurgery.

The Use of TLD and Gafchromic Film to Assure Submillimeter Accuracy for Image-Guided Radiosurgery

The Cyberknife is an image-guided radiosurgical system. It uses a compact X-band 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgical doses. While routine quality assurance (QA) is essential for any radiosurgery system, QA plays an even more vital role for the Cyberknife system, due to the complexity of the system and the wide range of applications. This paper presents a technique for performing quality assurance using thermoluminescence detectors (TLDs) and Gafchromic films that is intended to be specific for the Cyberknife. However, with minor modification, the proposed method can also be used for QA of other radiosurgery systems. Our initial QA procedure for the CyberKnife utilized a 30 × 30 × 11-cm solid water phantom containing a planar array of slots for 1× 1 × 1-mm TLDs on a 2-mm grid. With the objective of significantly simplifying CyberKnife QA, a new procedure for verification was developed, which uses much fewer TLDs than the prior solid water phantom technique. This new method requires only that the system target dose to the center of a cluster of 7 TLDs. In a prior study with Gafchromic films, conducted at 3 different Cyberknife facilities, the mean clinically relevant error was demonstrated to be 0.7 mm. A similar Gafchromic film analysis replicated these error measurements as part of the present investigation. It cannot be emphasized enough the importance of implementing routine QA to verify the accuracy of any radiosurgery system. Our quality assurance procedure tests the treatment planning system, as well as the entire treatment delivery including the image targeting system and the robot system. Either TLDs or Gafchromic films may be used for QA test of a radiosurgery system. Using both methods for measurement has the advantage independently verifying the accuracy of the system. This approach, which is routinely in used at our institution, has repeatedly confirmed the submillimeter targeting accuracy of our Cyberknife.

THE LEKSELL GAMMA KNIFE PERFEXION AND COMPARISONS WITH ITS PREDECESSORS

The objective of this study is to introduce a new radiosurgical device, the Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden). Design and performance characteristics are compared with previous models of the gamma knife in a clinical setting. Performance-related features in the design of the new radiosurgical system are described, and the ability to create complex shapes of isodose volumes even with a single isocenter is demonstrated. The concept of "dynamic shaping" of dose distribution is introduced as a means of decreasing the exposure to structures outside the target. Dose plans for the Leksell Gamma Knife Models B, 4C, and Perfexion have been created for target pathologies to illustrate how the software and hardware of the new radiosurgical system can increase treatment quality, decrease treatment time, and increase patient comfort. Radiation doses to critical organs in the rest of the human body are compared. The automated collimator arrangement in the Perfexion makes it possible to produce more complex treatment volumes than with previous models of the gamma knife. This results from the enhanced ability to shape isodose volumes, even for single isocenters. The collimator arrangement and the patient positioning system also allow shorter patient transit times, reducing unwanted radiation exposure during movement between isocenters. The Perfexion exceeds the capabilities of previous gamma knife models in terms of treatment efficiency, conformity, and radiation protection. These qualities enable treatment of larger target volumes, especially close to eloquent areas. Pathologies previously inaccessible in the head and neck are now treatable due to the increased volume of the radiation cavity.

THE LEKSELL GAMMA KNIFE PERFEXION AND COMPARISONS WITH ITS PREDECESSORS

The objective of this study is to introduce a new radiosurgical device, the Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden). Design and performance characteristics are compared with previous models of the gamma knife in a clinical setting. Performance-related features in the design of the new radiosurgical system are described, and the ability to create complex shapes of isodose volumes even with a single isocenter is demonstrated. The concept of "dynamic shaping" of dose distribution is introduced as a means of decreasing the exposure to structures outside the target. Dose plans for the Leksell Gamma Knife Models B, 4C, and Perfexion have been created for target pathologies to illustrate how the software and hardware of the new radiosurgical system can increase treatment quality, decrease treatment time, and increase patient comfort. Radiation doses to critical organs in the rest of the human body are compared. The automated collimator arrangement in the Perfexion makes it possible to produce more complex treatment volumes than with previous models of the gamma knife. This results from the enhanced ability to shape isodose volumes, even for single isocenters. The collimator arrangement and the patient positioning system also allow shorter patient transit times, reducing unwanted radiation exposure during movement between isocenters. The Perfexion exceeds the capabilities of previous gamma knife models in terms of treatment efficiency, conformity, and radiation protection. These qualities enable treatment of larger target volumes, especially close to eloquent areas. Pathologies previously inaccessible in the head and neck are now treatable due to the increased volume of the radiation cavity.

CyberKnife Radiosurgery for Lesions of the Foramen Magnum

The region of the foramen magnum (FM) presents an especially difficult area for therapeutic intervention. Indeed, this location is challenging to access surgically, particularly in the case of intramedullary and anterior lesions. Therefore, the potential for morbidity associated with therapy to the foramen magnum, most frequently in the form of lower cranial nerve deficits, has encouraged the search for methods that can effectively treat lesions of this region while sparing the important neighboring structures. We report our experience in the use of Cyberknife radiosurgery as a treatment option for these lesions. Thirty-five patients (17 men, 18 women; mean age, 51 yr; range, 18-83) with 35 lesions either spanning or approximating the foramen magnum were treated with the CyberKnife radiosurgical system. Histologies were determined either by prior surgery or radiographic criteria and included 25 benign tumors (nine meningiomas, five schwannomas, four neurofibromas, three hemangioblastomas, two ependymomas, one chordomas, and one pilocytic astrocytoma) along with 10 malignant growths (nine metastases and one chondrosarcoma). Twenty-seven (77%) patients presented with at least one sign and/or symptom, while eight (23%) patients were completely asymptomatic. The most common symptoms were headache, limb numbness, and limb/truncal ataxia, all of which were reported by ten (29%) patients. Among cranial neuropathies, CN XII dysfunction was evident in four (11%) patients. The specific fractionation schedule (mean of 1.8 sessions; range, 1-5) was based on the size of the treated lesion. The mean dose utilized was 19 Gy. Radiographic follow-up was obtained for twenty-three (66%) patients. Nine of the twenty-three (39%) were stable in size, ten lesions decreased in size (43%), and four lesions increased in size (17%). In terms of symptom relief, follow-up was collected for twenty-four (69%) patients. Eleven (46%) of these patients experienced no change in their signs or symptoms, while seven (29%) patients experienced improvement. Six (25%) patients witnessed deterioration in their signs and symptoms. Overall, eighteen (75%) patients had their signs and symptoms either stabilize or improve. There were eleven (31%) deaths in our series, eight of which were related to the disease (though not directly related to CyberKnife treatment) and three of which were from unrelated causes. Complications directly related to CyberKnife radiosurgery were noted in four (11%) of the thirty-five patients. These included one case of temporary emesis immediately following treatment, one case of cystic enlargement two months out, and two cases of radiation necrosis (occurring 1.5 yrs and 2.5 yrs out from treatment). Cyberknife radiosurgery can be an effective treatment for many foramen magnum lesions.

CyberKnife® radiosurgery in the treatment of complex skull base tumors: analysis of treatment planning parameters

BackgroundTumors of the skull base pose unique challenges to radiosurgical treatment because of their irregular shapes, proximity to critical structures and variable tumor volumes. In this study, we investigate whether acceptable treatment plans with excellent conformity and homogeneity can be generated for complex skull base tumors using the Cyberknife® radiosurgical system.MethodsAt Georgetown University Hospital from March 2002 through May 2005, the CyberKnife® was used to treat 80 patients with 82 base of skull lesions. Tumors were classified as simple or complex based on their proximity to adjacent critical structures. All planning and treatments were performed by the same radiosurgery team with the goal of minimizing dosage to adjacent critical structures and maximizing target coverage. Treatments were fractionated to allow for safer delivery of radiation to both large tumors and tumors in close proximity to critical structures.ResultsThe CyberKnife® treatment planning system was capable of generating highly conformal and homogeneous plans for complex skull base tumors. The treatment planning parameters did not significantly vary between spherical and non-spherical target volumes. The treatment parameters obtained from the plans of the complex base of skull group, including new conformity index, homogeneity index and percentage tumor coverage, were not significantly different from those of the simple group.ConclusionOur data indicate that CyberKnife® treatment plans with excellent homogeneity, conformity and percent target coverage can be obtained for complex skull base tumors. Longer follow-up will be required to determine the safety and efficacy of fractionated treatment of these lesions with this radiosurgical system.

Accuray CyberKnife® image-guided radiosurgical system

Radiosurgery is the application of radiation therapy in an extremely precise manner. These techniques apply large bioequivalent doses of radiation to a small area in order to destroy tumor cells, while sparing surrounding normal tissues. Radiosurgery has been available for intracranial abnormalities since the 1950s but it has only recently become available to treat tumors outside of the brain and skull base. This article outlines the authors experience with CyberKnife® in the treatment of spinal and spine-associated abnormalities.

Significance of different conformity indices for evaluation of radiosurgery treatment plans for vestibular schwannomas

Object. There are various kinds of conformity parameters currently in use, although several of them are limited and reflect only target volume coverage or normal tissue overdosage. Indices are reviewed with the goal of determining those that are most significant for the evaluation of radiosurgery treatment plans for patients with vestibular schwannoma, based on the authors' experience at the Novalis Shaped Beam Surgery Center. Methods. Fifty-five radiosurgery plans for patients with vestibular schwannomas (VSs) have been evaluated. In this paper the conformation number (CN) and dose-related CN (dCN) are evaluated, and a penalty for underdosed target volumes and overdosed normal tissue is incorporated. A strategy is discussed to apply these indices (CN and dCN) to define the optimal prescription isodose (PI). For a given radiosurgery treatment plan, permitting partial target underdosage may offer an improvement of the CN. Variations of different conformation indices have been calculated for varying prescription levels—for example, an isodose plan. The resulting graph for the CN is discussed in detail to illustrate its use in defining the optimal PI level. For the 55 cases of VSs reported on, the median CNmax result was 0.78. Conclusions. It is possible to achieve highly conformal dose distributions with Novalis radiosurgical system. The CN is the parameter of choice when evaluating radiosurgery treatment plans and scoring possible treatment plans. It takes into account both target underdosage and normal tissue overdosage and offers a valuable scoring parameter while avoiding false-perfect scores.