CyberKnife Stereotactic Body Radiation Therapy Research Articles

The efficacy of stereotactic body radiation therapy on huge hepatocellular carcinoma unsuitable for other local modalities.

Background and aimTo evaluate the safety and efficacy of Cyberknife stereotactic body radiation therapy (SBRT) and its effect on survival in patients with unresectable huge hepatocellular carcinoma (HCC) unsuitable of other standard treatment option.MethodsBetween 2009 and 2011, 22 patients with unresectable huge HCC (≧10 cm) were treated with SBRT. dose ranged from 26 Gy to 40 Gy in five fractions. Overall survival (OS) and disease-progression free survival (DPFS) were determined by Kaplan-Meier analysis. Tumor response and toxicities were also assessed.ResultsAfter a median follow-up of 11.5 month (range 2–46 months). The objective response rate was achieved in 86.3% (complete response (CR): 22.7% and partial response (PR): 63.6%). The 1-yr. local control rate was 55.56%. The 1-year OS was 50% and median survival was 11 months (range 2–46 months). In univariate analysis, Child-Pugh stage (p = 0.0056) and SBRT dose (p = 0.0017) were significant factors for survival. However, in multivariate analysis, SBRT dose (p = 0.0072) was the most significant factor, while Child-Pugh stage of borderline significance. (p = 0.0514). Acute toxicities were mild and well tolerated.ConclusionThis study showed that SBRT can be delivered safely to huge HCC and achieved a substantial tumor regression and survival. The results suggest this technique should be considered a salvage treatment. However, local and regional recurrence remain the major cause of failure. Further studies of combination of SBRT and other treatment modalities may be reasonable.

Prostate-Specific Antigen Bounce Following Stereotactic Body Radiation Therapy for Prostate Cancer

Introduction: Prostate-specific antigen (PSA) bounce after brachytherapy has been well-documented. This phenomenon has also been identified in patients undergoing stereotactic body radiation therapy (SBRT). While the parameters that predict PSA bounce have been extensively studied in prostate brachytherapy patients, this study is the first to analyze the clinical and pathologic predictors of PSA bounce in prostate SBRT patients.Materials and Methods: Our institution has maintained a prospective database of patients undergoing SBRT for prostate cancer since 2006. Our study population includes patients between May 2006 and November 2011 who have at least 18 months of follow-up. All patients were treated using the CyberKnife treatment system. The prescription dose was 35–36.25 Gy in five fractions.Results: One hundred twenty patients were included in our study. Median PSA follow-up was 24 months (range 18–78 months). Thirty-four (28%) patients had a PSA bounce. The median time to PSA bounce was 9 months, and the median bounce size was 0.50 ng/mL. On univariate analysis, only younger age (p = 0.011) was shown to be associated with an increased incidence of PSA bounce. Other patient factors, including race, prostate size, prior treatment by hormones, and family history of prostate cancer, did not predict PSA bounces. None of the tumor characteristics studied, including Gleason score, pre-treatment PSA, T-stage, or risk classification by NCCN guidelines, were associated with increased incidence of PSA bounces. Younger age was the only statistically significant predictor of PSA bounce on multivariate analysis (OR = 0.937, p = 0.009).Conclusion: PSA bounce, which has been reported after prostate brachytherapy, is also seen in a significant percentage of patients after CyberKnife SBRT. Close observation rather than biopsy can be considered for these patients. Younger age was the only factor that predicted PSA bounce.

EP-1791: The use of failure mode and effects analysis for risk assessment in Cyberknife stereotactic body radiation therapy.

EP-1791: The use of failure mode and effects analysis for risk assessment in Cyberknife stereotactic body radiation therapy.

SP-0433: Real time prostrate gland motion and deformation during cyberknife stereotactic body radiotherapy

SP-0433: Real time prostrate gland motion and deformation during cyberknife stereotactic body radiotherapy

Excellent Cancer Outcomes Following Patient-adapted Robotic Lung SBRT But a Case for Caution in Idiopathic Pulmonary Fibrosis

The aim of this study is to report outcomes and prognostic factors for early stage non-small cell lung cancer treated with patient-adapted Cyberknife stereotactic body radiotherapy. A retrospective analysis of 150 patients with T1-2N0 non-small cell lung cancer treated with stereotactic body radiotherapy was conducted. An algorithm based on tumor and patient's characteristics was used to orient patients towards soft tissue (Xsight Lung), fiducials or adjacent bone (Xsight Spine) tracking. Median biological effective dose without correction for tissue inhomogeneities was 180 Gy10 for peripheral tumors and 113 Gy10 for central tumors. Median follow-up was 22 months. Actuarial 2 years local control, overall survival and disease-specific survival were respectively 96%, 87% and 95%. Every 1 cm increase in tumor diameter was associated with a relative risk for regional or distant relapse of 2 (95%CI = 1.2-3.6, p = 0.009). With doses ≥132 Gy10 and <132 Gy10, local control was 98% vs. 82% (p = 0.07), disease-specific survival 97% vs. 78% (p = 0.02) and overall survival 93% vs. 76% (p = 0.01), respectively. Better disease-specific survival and a trend for better overall survival was observed for peripheral vs. central tumors (96% vs. 79%, p = 0.05 and 92% vs. 74%, p = 0.08, respectively). A higher Charlson comordibity score (≥4) predicted lower overall survival (79% vs. 98%, p = 0.01). Toxicities included 3 patients with idiopathic pulmonary fibrosis who developed grade 5 pneumonitis and 2 patients with grade 3 pneumonitis. We therefore report excellent local control and disease-specific survival following patient-adapted Cyberknife lung stereotactic body radiotherapy. Although toxicities were in general minimal, patients with pulmonary fibrosis might be at greater risk of severe complications. Small size, peripheral location, dose ≥ 132 Gy10 and a low Charlson co-morbidity score seem to be associated with better outcomes.

Stereotactic Body Radiotherapy in Prostate Cancer: Is Rapidarc a Better Solution than Cyberknife?

AimsThere is increasing interest in stereotactic body radiotherapy (SBRT) for the management of prostate adenocarcinoma, with encouraging initial biological progression-free survival results. However, the limited literature is dominated by the use of the Cyberknife platform. This led to an international phase III study comparing outcomes for Cyberknife SBRT with both surgery and conventionally fractionated intensity-modulated radiotherapy (the PACE study). We aim to compare Cyberknife delivery with Rapidarc, a more widely available treatment platform. Materials and methodsThe scans of six previous prostate radiotherapy patients with a range of prostate sizes were chosen. The clinical target volume was defined as the prostate gland, with 3 mm added for the Cyberknife planning target volume (PTV) and 5 mm for the Rapidarc PTV. Accuray multiplan v. 4.5 was used for planning with delivery on a Cyberknife VSI system v9.5; Varian Eclipse v10 was used for Rapidarc planning with delivery using a Varian 21EX linear accelerator. Both systems attempted to deliver at least 35 Gy to the PTV in five fractions with PTV heterogeneity <12%. ResultsAll organ at risk (OAR) constraints were achieved by both platforms, whereas the Cyberknife failed to achieve the desired PTV homogeneity constraint in two cases. In other OARs without constraints, Cyberknife delivered higher doses. The volume of the 35 Gy isodose was slightly larger with Rapidarc, but conversely at doses <35 Gy normal tissues received higher doses with Cyberknife. The mean planning and delivery time was in favour of Rapidarc. ConclusionsWe have shown that there is no discernible dosimetric advantage to choosing Cyberknife over Rapidarc for SBRT delivery in prostate cancer. Given the significant benefits of Rapidarc in terms of availability, planning and delivery time, the authors suggest that phase III trials of SBRT should include Rapidarc or equivalent rotational delivery platforms.

Improving plan quality and consistency by standardization of dose constraints in prostate cancer patients treated with CyberKnife

Treatment plans for prostate cancer patients undergoing stereotactic body radiation therapy (SBRT) are often challenging due to the proximity of organs at risk. Today, there are no objective criteria to determine whether an optimal treatment plan has been achieved, and physicians rely on their personal experience to evaluate the plan's quality. In this study, we propose a method for determining rectal and bladder dose constraints achievable for a given patient's anatomy. We expect that this method will improve the overall plan quality and consistency, and facilitate comparison of clinical outcomes across different institutions. The 3D proximity of the organs at risk to the target is quantified by means of the expansion‐intersection volume (EIV), which is defined as the intersection volume between the target and the organ at risk expanded by 5 mm. We determine a relationship between EIV and relevant dosimetric parameters, such as the volume of bladder and rectum receiving 75% of the prescription dose (V75%). This relationship can be used to establish institution‐specific criteria to guide the treatment planning and evaluation process.A database of 25 prostate patients treated with CyberKnife SBRT is used to validate this approach. There is a linear correlation between EIV and V75% of bladder and rectum, confirming that the dose delivered to rectum and bladder increases with increasing extension and proximity of these organs to the target. This information can be used during the planning stage to facilitate the plan optimization process, and to standardize plan quality and consistency. We have developed a method for determining customized dose constraints for prostate patients treated with robotic SBRT. Although the results are technology‐specific and based on the experience of a single institution, we expect that the application of this method by other institutions will result in improved standardization of clinical practice.PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.de, 87.55.dk

Quantifying variability of intrafractional target motion in stereotactic body radiotherapy for lung cancers

In lung stereotactic body radiotherapy (SBRT), variability of intrafractional target motion can negate the potential benefits of four‐dimensional (4D) treatment planning that aims to account for the dosimetric impacts of organ motion. This study used tumor motion data obtained from CyberKnife SBRT treatments to quantify the reproducibility of probability motion function (pmf) of 37 lung tumors. The reproducibility of pmf was analyzed with and without subtracting the intrafractional baseline drift from the original motion data. Statistics of intrafractional tumor motion including baseline drift, target motion amplitude and period, were also calculated. The target motion amplitude significantly correlates with variations (1 SD) of motion amplitude and baseline drift. Significant correlation between treatment time and variations (1 SD) of motion amplitude was observed in anterior‐posterior (AP) motion, but not in craniocaudal (CC) and left‐right (LR) motion. The magnitude of AP and LR baseline drifts significantly depend on the treatment time, while the CC baseline drift does not. The reproducibility of pmf as a function of time can be well described by a two‐exponential function with a fast and slow component. The reproducibility of pmf is over 60% for the CC motion and over 50% for the AP and LR motions when baseline variations were subtracted from the original motion data. It decreases to just over 30% for the CC motion and about 20% for the AP and LR motion, otherwise. 4D planning has obvious limitations due to variability of intrafractional target motion. To account for potential risks of overdosing critical organs, it is important to simulate the dosimetric impacts of intra‐ and interfractional baseline drift using population statistics obtained from SBRT treatments.PACS number: 87.55.‐x

SU-E-T-517: Ray Tracing and Mote Carlo Based Dose Computation for Chest Wall and Ribs for Lung Cancer Patients Treated with Cyberknife

Purpose: Chest wall and ribs are considered organs at risk while treating lung tumors adjacent to chest wall. This study was to evaluate the dosimetric differences in chest wall and ribs irradiation for Cyberknife stereotactic body radiation therapy (SBRT) when treatment plans were computed using Ray Tracking Algorithm (RTA) and Monte Carlo Algorithm (MCA). Methods: Twenty eight lung cancer patients who had tumors abutting the chest wall were selected for this study. A uniform 2cm thickness of chest wall and appropriate portions of rib were contoured for evaluating dose distribution using RTA and MCA of Cyberknife MultiPlan software (version‐3.5.2). Treatment plans were first computed using RTA and then were recomputed using MCA without changing the total monitor unit (MU). Range of prescription dose was 50Gy‐60Gy (mean=54.6Gy). Studied dosimetric parameters were maximum point dose and doses to 1cc, 5cc, 10cc, 30cc, 50cc, 70cc, and 100cc of chest wall. Maximum point dose and doses to 1cc, 2cc, 5cc, and 10cc of ribs were also studied. These parameters were considered as clinically more relevant. Results: Dosimetric computation results revealed that RTA overestimated dose to both the chest wall and the ribs for all the studied parameters. Increase of average dose was in the range of 7.5–12.1% (p‐value 0.05), and 10.3–13.4% (p‐value <0.05) for chest wall and ribs, respectively. The lower the volume of interest, the larger was the difference in dose for the two algorithms. Average difference in maximum point dose for chest wall was 11.2% (p‐value <0.001) and that was 13.4% for ribs (p‐value <0.002). Conclusion: As compared to Monte Carlo algorithm, Ray Tracing algorithm significantly overestimates dose to chest wall and ribs. Although treatment planning with Monte Carlo is more involved, it should be used because of accuracy and significant difference in dose distribution in chest wall and ribs.

SU‐E‐T‐432: Dosimetric Computation of Cyberknife SBRT Plans for Treatment of Kidney and Adrenal Gland

Purpose: It is well‐accepted that Monte Carlo algorithm (MCA) methods are superior to Ray‐Tracing algorithm (RTA), i.e., effective path length (EPL), methods for computing radiation dose, especially for structures with heterogeneous tissue compositions. In this study, the differences of dose distribution in target volumes (kidneys and adrenal glands) and adjacent organs at risk (OARs) were evaluated while the treatment plans were computed using MCA and RTA for Cyberknife™ stereotactic body radiotherapy (SBRT). Methods: A total of 14 renal tumor (10 kidney and 4 adrenal gland) patients who had prescriptions in the range of 24Gy–48Gy (mean=42Gy) were selected. Treatment plans were computed using RTA and MCA in Cyberknife MultiPlan™ (version‐3.5.2). First, dose was calculated using RTA and then was recomputed using MCA, keeping total MU the same. Liver, heart, stomach, spleen, bowel, and contralateral kidney were considered as OARs. Dosimetric parameters considered for the target and OARs were minimum dose, mean dose, and maximum point dose. Additionally, dose delivered to 95% and 5% of the target volumes were evaluated. Dose computed with two algorithms were compared and statistically analyzed using two‐tailed t‐tests. Results: This study revealed that differences (average) in mean dose (0.79Gy), maximum dose (2.02Gy), 95% (0.76Gy) and 5% (0.83Gy) of target coverage dose were not statistically significant (p‐value&gt;0.05). Differences in minimum dose (average=0.04–3.75Gy) to OARs exhibited significance (p‐value&lt; 0.05), though differences in minimum dose to target volumes (average=1.14Gy) showed no significant difference (p‐value&gt;0.05). Conclusion: Although Monte‐Carlo is more accurate compared to Ray‐Tracing for dosimetric computation, especially tumors in heterogeneous tissue composition, dose computation and delivery using MCA are quite involved due to additional computational time and associated patient‐specific quality assurance. This study indicated that both RTA and MCA are almost equally effective as dosimetric computation methods for renal tumors, and RTA can be used without compromising dosimetric accuracy.

SU-D-105-01: Patient-Specific Quality Assurance for Monte Carlo-Calculated Lung SBRT On Cyberknife - Is It Necessary?

Purpose: In transitioning from ray-tracing (RT) to Monte Carlo (MC) dose computation algorithm for Cyberknife lung stereotactic body radiotherapy (SBRT), we realized large differences (10–20%) in PTV coverage to heterogeneous target regions which required dosimetric confirmation. Currently, our practice requires an independent second calculation for all plans. MuCheck software (Oncology Data Systems) is used in lieu of physical measurements for RT plans; however, there exists no commercial software for verifying MC plans. We determined all lung SBRT plans should utilize the MC algorithm and initially be confirmed by direct measurements. Methods: Lung treatment plans were first optimized with RT then recalculated using MC for final optimization and high-resolution dose computation. The MC plan was superimposed on a heterogeneous thorax phantom CT (Standard Imaging 91230) using the phantom overlay tool of the MultiPlan 3.5.2 software. Isodose distributions were manually shifted to place the ion chamber (0.053cc Exradin-A1SL) in a suitably homogeneous region within the CTV. The plan was then delivered to the thorax phantom with the ion chamber placed in the mediastinum insert location. Results: This methodology was used for 33 consecutive lung patients receiving Cyberknife SBRT with PTVs ranging from 10.7–185.9cm3. The mean deviation between measured and MC calculated doses was −2.31%±1.66%. The maximum deviation was −4.69%. Acceptable tolerance for patient-specific QA was considered ±5%. Conclusion: The MC algorithm provides improved accuracy over RT for heterogeneous dose calculation, confirmed by direct point measurements. Patient-specific QA using a heterogeneous lung phantom provided an acceptable anthropomorphic approximation of patient plans calculated with MC. Since the QA results establish satisfactory delivery of MC doses, patient-specific plans calculated on a homogeneous phantom comparing RT and MC algorithms may provide a suitable second check without direct measurement. Conversely, many users may continue direct measurement as a second check until commercial MC verification software becomes available.

CyberKnife Stereotactic Body Radiation Therapy for Inoperable Stage II Non-small Cell Lung Cance

CyberKnife Stereotactic Body Radiation Therapy for Inoperable Stage II Non-small Cell Lung Cance

SU-E-T-412: Can Cyberknife SBRT Be an Alternative to Brachytherapy for Cervical Cancer Treatment?

To investigate the effectiveness of stereotactic body radiation therapy (SBRT) with Cyberknife for treatment of squamous cell carcinoma (SCCa) of cervix that are commonly treated with brachytherapy. SCCa of cervix is routinely treated with external beam radiation therapy (EBRT) followed by brachytherapy. Common practice is to use high-dose- rate (HDR) brachytherapy, mainly with Ir-192; however, low-dose-rate (LDR) brachytherapy with Cs-137 is also used. Three of our patients with cervical SCCa who were chosen to have LDR brachytherapy (Cs-137 with tandem and ovoids) could not tolerate the prolonged treatment or applicator placement. All these patients previously received 45Gy (1.8Gy/fratction) from EBRT and well tolerated. Planned LDR treatment dose and time were for patient-1: 42.63Gy in 73.5hr, patient-2: 42.34Gy in 73hr, patient-3: 41.76Gy in 72hr. Delivered LDR dose and time were: 3.75Gy in 6.5hr, OGy in Ohr, and 17.3Gy in 19.8hr, for patient-1, -2 and -3, respectively. Two of the three patients tolerated LDR treatment partially; the second patient could not tolerate the applicator, which required immediate removal after placement. Treatments were completed with Cyberknife SBRT (CK-SBRT)doses of 25Gy, 15Gy and 25Gy for patient-1, -2 and -3, respectively; all had 5Gy/fraction and 3fractions/week. Prescriptions were at 80% isododelines; CTV coverages were 96.6%, 99.9% and 100% for patient-1, -2 and -3, respectively. Till their last follow-up in February 2012, all three patients were doing fine clinically without any evidence of disease; none of these patients had any complications that could be related to CK-SBRT. Appears that CK-SBRT can be a viable treatment alternative to brachytherapy. CK-SBRT may also be more appealing to patients and physicians for a variety of reasons such as out-patient procedure, shorter treatment time, no need for operating room, and no need for applicator insertion and tolerance. However, extensive clinical study is warranted in this regard.

SU-E-T-422: Lung SBRT Using Cyberknife: Technique and Treatment Outcome.

At East Carolina University, we have been treating primary and secondary lung cancers with Cyberknife stereotactic body radiotherapy (CK- SBRT) since February 2009. Till October 2011, we have treated a total of 79 patients (83 sites). In this study, we present our experience in CK-SBRT and clinical outcome of the treated patients. Of the 79 patients, 43 were female; age of the whole patient population ranged 33.2-89.7yrs (median=73.2yrs). Patients treated for primary lung cancer (n=57) had severe chronic obstructive pulmonary disease (COPD) and were not surgical candidates. Cyberknife robotic system with tracking techniques (Synchrony=52, XsiteLung=22, XsightSpine=5) were used. Majority of the patient (n=52) had multiple gold fiducials placed (1-6 placed; 1-4 tracked per patient) either percutaneously or bronchoscopically. CT images were used for dosimetric planning, by medical physicists, using Cyberknife MultiPlan software. Prescription doses were 25Gy-55Gy in 3-5 fractions (mean=48.2Gy, median=50Gy); doses were prescribed mainly to 80% isodoseline (range=75-96%, mean=81.4%). PTV margin varied from 0-7mm (mean±SD=3.2±1.4mm), based on the tumor locations; breathing patterns and cancer type. Dosimetric coverage of GTV and PTV were (mean±SD): 97.8±5% and 94.7±6.9%, respectively. The treatment response was assessed using either a CT or a PET scan or both. The median follow up was 13.1months (range 0.3-31.9 months). Overall response rate was 98.8% (CR=73.5%). Local failure free survival at one year was 84% for primary (n=57), 76% for recurrent (n=16) lung cancer and 100% for metastatic (n=10) tumors. The toxicity rate was low with one patient reported to have chest wall pain and one patient developed grade 3-4 radiation pneumonitis. In most of the cases tight PTV margins were used. Since the prescriptions were at 80% isodeose line with more than 94% PTV coverage, the treatment outcome appeared reasonable. Further study relating PTV margin, dosimetric coverage, and treatment outcome is in progress.

Stereotactic Body Radiation Therapy in Recurrent Hepatocellular Carcinoma

To examine the safety and efficacy of Cyberknife stereotactic body radiation therapy (SBRT) and its effect on survival in patients of recurrent hepatocellular carcinoma (HCC). This was a matched-pair study. From January 2008 to December 2009, 36 patients with 42 lesions of unresectable recurrent HCC were treated with SBRT. The median prescribed dose was 37 Gy (range, 25 to 48 Gy) in 4-5 fractions over 4-5 consecutive working days. Another 138 patients in the historical control group given other or no treatments were selected for matched analyses. The median follow-up time was 14 months for all patients and 20 months for those alive. The 1- and 2-year in-field failure-free rates were 87.6% and 75.1%, respectively. Out-field intrahepatic recurrence was the main cause of failure. The 2-year overall survival (OS) ratewas 64.0%, and median time to progression was 8.0 months. In the multivariable analysis of all 174 patients, SBRT (yes vs. no), tumor size (≤4 cm vs. >4 cm), recurrent stage (stageIIIB/IV vs. I) and Child-Pugh classification (A vs. B/C) were independent prognostic factors for OS. Matched-pair analysis revealed that patients undergoing SBRT had better OS(2-year OS of 72.6% vs. 42.1%, respectively, p = 0.013). Acute toxicities were mild and tolerable. SBRT is a safe and efficacious modality and appears to be well-tolerated at the dose fractionation we have used, and its use correlates with improved survival in this cohort of patients with recurrent unresectable HCC. Out-field recurrence is the major cause of failure. Further studies of combinations of SBRT and systemic therapies may be reasonable.

Virtual HDR SBRT for localized prostate carcinoma: Efficacy and quality-of-life assessment.

45 Background: We designed a CyberKnife (CK) prostate Stereotactic Body Radiotherapy (SBRT) method to recapitulate HDR fractionation and target volume coverage (“Virtual HDR”). We report 4 year efficacy, toxicity and quality of life (QoL) outcomes. Methods: Eligible patients had low- (Gleason &lt; 6, PSA &lt; 10 ng/mL, &lt; T2bN0) or intermediate-risk (Gleason &lt; 6 with PSA 10.01 – 20 ng/mL or Gleason 7 with PSA &lt; 10 ng/mL, &lt; T2bN0) prostate cancer. A dose of 38 Gy/4 fractions was given to &gt; 95% of the PTV; with “HDR-like” bladder, urethral and rectal dose constraints, and “HDR-like” dose escalation in the PTV. Toxicities were assessed using CTCAE3.0 criteria. QoL was assessed using the Expanded Prostate Cancer Index Composite (EPIC). Results: Since July 2006, 59 patients were treated. Two were lost to follow-up and 6 have been followed &lt; 6 months, leaving 51 (32 low- and 19 intermediate-risk) patients for analysis. Median f/u is 42 months (range, 6-60). 4-year actuarial biochemical-disease free survival is 98% (ASTRO, Phoenix). Freedom from local and distant relapse is 100% and 98%. Median baseline PSA of 6.3 ng/mL (range 1.0 – 14.1) decreased to 0.1 ng/mL by 48 months. Acute grade 2 GU and GI toxicity rates were 22% and 4%, respectively (0% Grade 3+). Three (6%) late Grade 3 GU toxicities occurred at 18, 48 and 48 months. No grade 3+ GI toxicity occurred. Late grade 2 GU and GI toxicity rates were 18% and 2%, respectively. Only 2 patients (4%) had ongoing late &gt; grade 2 GU toxicity at last follow-up (0% GI). Mean EPIC urinary and bowel scores decreased at 2 months, with subsequent improvement and stability to 48 months. Mean EPIC sexual scores gradually declined to 48 months. Of patients potent at baseline, 63% were potent at 3 years, including 100% &lt; age 60, 64% age 61-70 and 60% &gt; age 70. Conclusions: To 4 years, HDR-like CK SBRT for low- and intermediate-risk prostate cancer results in a very low PSA nadir and relapse rate, minimal toxicity and a favorable QoL outcome, with an age-dependent potency preservation rate. The occasional occurrence of late grade 3 urethral stricture can likely be reduced by better patient selection (caution re: patients with significant pre-existing uropathy). Acute and late grade 2 GU toxicity usually resolves with conservative management.

Fiducial-free CyberKnife stereotactic body radiation therapy (SBRT) for single vertebral body metastases: acceptable local control and normal tissue tolerance with 5 fraction approach

This retrospective analysis examines the local control and toxicity of five-fraction fiducial-free CyberKnife stereotactic body radiation therapy (SBRT) for single vertebral body (VB) metastases. All patients had favorable performance status (ECOG 0–1), oligometastatic disease, and no prior spine irradiation. A prescribed dose of 30–35 Gy was delivered in five fractions to the planning target volume (PTV) using the CyberKnife with X-sight spine tracking. Suggested maximum spinal cord and esophagus point doses were 30 and 40 Gy, respectively. A median 30 Gy (IQR, 30–35 Gy) dose was delivered to a median prescription isodose line of 70% (IQR, 65–77%) to 20 patients. At 34 months median follow-up (IQR, 25–40 months) for surviving patients, the 1- and 2-year Kaplan–Meier local control estimates were 80 and 73%, respectively. Two of the five local failures were infield in patients who had received irradiation to the gross tumor volume and three were paravertebral failures just outside the PTV in patients with prior corpectomy. No local failures occurred in patients who completed VB radiation alone. The 1- and 2-year Kaplan–Meier overall survival estimates were 80 and 57%, respectively. Most deaths were attributed to metastatic disease; one death was attributed to local recurrence. The mean maximum point doses were 26.4 Gy (SD, 5.1 Gy) to the spinal cord and 29.1 Gy (SD, 8.9 Gy) to the esophagus. Patients receiving maximum esophagus point doses greater than 35 Gy experienced acute dysphagia (Grade I/II). No spinal cord toxicity was documented. Five-fraction fiducial-free CyberKnife SBRT is an acceptable treatment option for newly diagnosed VB metastases with promising local control rates and minimal toxicity despite the close proximity of such tumors to the spinal cord and esophagus. A prospective study aimed at further enhancing local control by targeting the intact VB and escalating the total dose is planned.

Stereotactic Body Radiation Therapy for Patients with Heavily Pretreated Liver Metastases and Liver Tumors

We present our initial experience with CyberKnife stereotactic body radiation therapy (SBRT) in a heavily pretreated group of patients with liver metastases and primary liver tumors. From October 2007 to June 2009, 48 patients were treated at the Philadelphia CyberKnife Center for liver metastases or primary liver tumors. We report on 30 patients with 41 discrete lesions (1–4 tumors per patient) who received an ablative radiation dose (BED ≥ 79.2 Gy10 = 66 Gy EQD2). The treatment goal was to achieve a high SBRT dose to the liver tumor while sparing at least 700 cc of liver from radiation doses above 15 Gy. Twenty-three patients were treated with SBRT for metastatic cancer to the liver; the remainder (n = 7) were primary liver tumors. Eighty-seven percent of patients had prior systemic chemotherapy with a median 24 months from diagnosis to SBRT; 37% had prior liver directed therapy. Local control was assessed for 28 patients (39 tumors) with 4 months or more follow-up. At a median follow-up of 22 months (range, 10–40 months), 14/39 (36%) tumors had documented local failure. A decrease in local failure was found with higher doses of SBRT (p = 0.0237); 55% of tumors receiving a BED ≤ 100 Gy10 (10/18) had local failure compared with 19% receiving a BED > 100 Gy10 (4/21). The 2-year actuarial rate of local control for tumors treated with BED > 100 Gy10 was 75% compared to 38% for those patients treated with BED ≤ 100 Gy10 (p = 0.04). At last follow-up, 22/30 patients (73%) had distant progression of disease. Overall, seven patients remain alive with a median survival of 20 months from treatment and 57 months from diagnosis. To date, no patient experienced persistent or severe adverse effects. Despite the heavy pretreatment of these patients, SBRT was well tolerated with excellent local control rates when adequate doses (BED > 100 Gy10) were used. Median survival was limited secondary to development of further metastatic disease in the majority of patients.

CyberKnife Boost for Patients with Cervical Cancer Unable to Undergo Brachytherapy

Standard radiation therapy for patients undergoing primary chemosensitized radiation for carcinomas of the cervix usually consists of external beam radiation followed by an intracavitary brachytherapy boost. On occasion, the brachytherapy boost cannot be performed due to unfavorable anatomy or because of coexisting medical conditions. We examined the safety and efficacy of using CyberKnife stereotactic body radiotherapy (SBRT) as a boost to the cervix after external beam radiation in those patients unable to have brachytherapy to give a more effective dose to the cervix than with conventional external beam radiation alone. Six consecutive patients with anatomic or medical conditions precluding a tandem and ovoid boost were treated with combined external beam radiation and CyberKnife boost to the cervix. Five patients received 45 Gy to the pelvis with serial intensity-modulated radiation therapy boost to the uterus and cervix to a dose of 61.2 Gy. These five patients received an SBRT boost to the cervix to a dose of 20 Gy in five fractions of 4 Gy each. One patient was treated to the pelvis to a dose of 45 Gy with an external beam boost to the uterus and cervix to a dose of 50.4 Gy. This patient received an SBRT boost to the cervix to a dose of 19.5 Gy in three fractions of 6.5 Gy. Five percent volumes of the bladder and rectum were kept to ≤75 Gy in all patients (i.e., V75 Gy ≤ 5%). All of the patients remain locally controlled with no evidence of disease following treatment. Grade 1 diarrhea occurred in 4/6 patients during the conventional external beam radiation. There has been no grade 3 or 4 rectal or bladder toxicity. There were no toxicities observed following SBRT boost. At a median follow-up of 14 months, CyberKnife radiosurgical boost is well tolerated and efficacious in providing a boost to patients with cervix cancer who are unable to undergo brachytherapy boost. Further follow-up is required to see if these results remain durable.

Temporal compartmental dosing effects for robotic prostate stereotactic body radiotherapy

The rate of dose accumulation within a given area of a target volume tends to vary significantly for non-isocentric delivery systems such as Cyberknife stereotactic body radiotherapy. In this study, we investigated whether intra-target temporal dose distributions produce significant variations in the biological equivalent dose. For the study, time courses of ten patients were reconstructed and calculation of a biologically equivalent uniform dose (EUD) was performed using a formula derived from the linear quadratic model (α/β = 3 for prostate cancer cells). The calculated EUD values obtained for the actual patient treatments were then compared with theoretical EUD values for delivering the same physical dose distribution except that the whole target being irradiated continuously (e.g. large-field ‘dose-bathing’ type of delivery). For all the case, the EUDs for the actual treatment delivery were found to correlate strongly with the EUDs for the large-field delivery: a linear correlation coefficient of R2 = 0.98 was obtained and the average EUD for the actual Cyberknife delivery was somewhat higher (5.0 ± 4.7%) than that for the large-field delivery. However, no statistical significance was detected between the two types of delivery (p = 0.21). We concluded that non-isocentric small-field Cyberknife delivery produced consistent biological dosing that tracked well with the constant-dose-rate, large-field-type delivery for prostate stereotactic body radiotherapy.