Extracranial Stereotactic Radioablation *

A single-institution study of stereotactic body radiotherapy for patients with unresectable visceral pulmonary or hepatic oligometastases

Purpose

The purpose of this study is to evaluate the feasibility, efficacy and toxicity of SBRT for treatment of unresectable hepatic or lung metastases regardless of their primary tumor site for patients who received prior systemic chemotherapy.

Methods and materials

Between July 2007 and June 2010, 90 patients were treated with the CyberKnife® SBRT system for hepatic or pulmonary metastatic lesions. Medical records were retrospectively reviewed. The endpoints of this study were local control, overall survival (OS), disease-free survival (DFS), local relapse free-survival (LRFS), and treatment toxicity.

Results

A total of 113 liver and 26 lung metastatic lesions in 52 men (58%) and 38 women (42%) were treated. Median follow-up was 17 months. Median age at treatment was 65 years (range, 23–84 years). Primary cancers were 63 GI, three lung, eight breast, four melanoma, three neuro-endocrine tumors, and three sarcomas. Median diameter of the lesions was 28 mm (range, 7–110 mm) for liver and 12.5 mm (range, 5–63.5 mm) for lung. Local control rates at 1 and 2 years were 84.5% and 66.1%, respectively. Two-year overall survival rate was 70% (95% CI: 55–81%). The 1 and 2-year disease-free survival rates were 27% (95% CI: 18–37%) and 10% (95% CI: 4–20%), respectively. Median duration of disease-free survival was 6.7 months (95% CI: 5.1–9.5 months). Observed toxicities included grade 1–3 acute toxicities. One grade 3 and no grade 4 toxicity were reported.

Conclusion

High-dose SBRT for metastatic lesions is both feasible and effective with high local control rates. Overall survival is comparable with other available techniques. Treatment is well tolerated with low toxicity rates. It could represent an interesting treatment option for oligometastatic patients not amenable to surgery, even when patients had been pre-treated with chemotherapy.

Summary

Stereotactic body radiotherapy (SBRT) has previously been successfully used in the treatment of metastatic lesions. It could be considered as a curative option for oligometastatic patients. This retrospective study involved 90 patients, designed to test potential effectiveness of SBRT in the treatment of oligometastases irrespective of primary. Results suggest SBRT could be an effective treatment extending patients’ life span. This treatment appears to be more effective when used prior to multiple systemic treatment regimens.

Dosimetric evaluation of the impacts of different heterogeneity correction algorithms on target doses in stereotactic body radiation therapy for lung tumors

Heterogeneity correction algorithms can have a large impact on the dose distributions of stereotactic body radiation therapy (SBRT) for lung tumors. Treatment plans of 20 patients who underwent SBRT for lung tumors with the prescribed dose of 48 Gy in four fractions at the isocenter were reviewed retrospectively and recalculated with different heterogeneity correction algorithms: the pencil beam convolution algorithm with a Batho power-law correction (BPL) in Eclipse, the radiological path length algorithm (RPL), and the X-ray Voxel Monte Carlo algorithm (XVMC) in iPlan. The doses at the periphery (minimum dose and D95) of the planning target volume (PTV) were compared using the same monitor units among the three heterogeneity correction algorithms, and the monitor units were compared between two methods of dose prescription, that is, an isocenter dose prescription (IC prescription) and dose-volume based prescription (D95 prescription). Mean values of the dose at the periphery of the PTV were significantly lower with XVMC than with BPL using the same monitor units (P < 0.001). In addition, under IC prescription using BPL, RPL and XVMC, the ratios of mean values of monitor units were 1, 0.959 and 0.986, respectively. Under D95 prescription, they were 1, 0.937 and 1.088, respectively. These observations indicated that the application of XVMC under D95 prescription results in an increase in the actually delivered dose by 8.8% on average compared with the application of BPL. The appropriateness of switching heterogeneity correction algorithms and dose prescription methods should be carefully validated from a clinical viewpoint.

Clinical and dosimetric predictors of radiation pneumonitis in a large series of patients treated with stereotactic body radiation therapy to the lung

PURPOSE

To report clinical and dosimetric factors predictive of radiation pneumonitis (RP) in patients receiving lung stereotactic body radiation therapy (SBRT) from a series of 240 patients.

METHODS AND MATERIALS

Of the 297 isocenters treating 263 patients, 240 patients (n=263 isocenters) had evaluable information regarding RP. Age, gender, current smoking status and pack-years, O2 use, Charlson Comorbidity Index, prior lung radiation therapy (yes/no), dose/fractionation, V5, V13, V20, Vprescription, mean lung dose, planning target volume (PTV), total lung volume, and PTV/lung volume ratio were recorded.

RESULTS

Twenty-nine patients (11.0%) developed symptomatic pneumonitis (26 grade 2, 3 grade 3). The mean V20 was 6.5% (range, 0.4%-20.2%), and the average mean lung dose was 5.03 Gy (0.547-12.2 Gy). In univariable analysis female gender (P=.0257) and Charlson Comorbidity index (P=.0366) were significantly predictive of RP. Among dosimetric parameters, V5 (P=.0186), V13 (P=.0438), and Vprescription (where dose=60 Gy) (P=.0128) were significant. There was only a trend toward significance for V20 (P=.0610). Planning target volume/normal lung volume ratio was highly significant (P=.0024). In multivariable analysis the clinical factors of female gender, pack-years smoking, and larger gross internal tumor volume and PTV were predictive (P=.0094, .0312, .0364, and .052, respectively), but no dosimetric factors were significant.

CONCLUSIONS

Rate of symptomatic RP was 11%. Our mean lung dose was <600 cGy in most cases and V20<10%. In univariable analysis, dosimetric factors were predictive, while tumor size (or tumor/lung volume ratio) played a role in multivariable and univariable and analysis, respectively.

[Oligometastatic disease, a new concept: stereotactic irradiation for lung metastases. Literature review]

Metastatic lung disease has long been the preserve of systemic treatments, local treatments being considered in a purely palliative intention. Several studies have objectified benefit to the local treatment of metastases, especially oligometastases. Surgery then took an important place in this setting, but the development of techniques for stereotactic radiotherapy on the one hand and the refusal or contraindication for surgery on the other hand led authors to conduct studies in this direction. This literature review describes the realization of stereotactic radiotherapy in treating pulmonary oligometastases and evaluates criteria for the selection of patients who would benefit. A comparison between the results of different studies on this technique allowed to show its effectiveness for local control, overall survival and tolerance. Stereotactic radiotherapy has emerged as a viable alternative, effective and well tolerated with local control rates comparable to that obtained by surgery (74 to 100%). Quality of life after stereotactic radiotherapy should be in a near future an important parameter to support this therapeutic choice, and needs to be precisely assessed.

American College of Surgeons Oncology Group Z4099/Radiation Therapy Oncology Group 1021: a randomized study of sublobar resection compared with stereotactic body radiotherapy for high-risk stage I non-small cell lung cancer

During the past decade, tremendous interest has arisen in the use of nonoperative therapies for patients with non-small cell lung cancer. Of these therapies, stereotactic body radiotherapy has become established as an effective modality for treating peripheral cancer in medically inoperable patients. Toxicity is low, and the treatment is effective, with excellent local control rates. Several investigators have suggested that stereotactic body radiotherapy could be effective for high-risk operable patients (usually treated with sublobar resection) and even perhaps for standard-risk operable patients (usually treated with lobectomy); however, this is less accepted. A direct comparison of stereotactic body radiotherapy and sublobar resection is difficult for a number of reasons. These include different definitions of recurrence, different populations of patients in these studies (with those undergoing stereotactic body radiotherapy tending to be the medically inoperable group), and different methods of classifying morbidity in the surgical and radiation oncology studies. Imaging follow-up has also not been standardized among the studies. Thus, a randomized study is necessary and timely. Investigators from the American College of Surgeons Oncology Group and the Radiation Therapy and Oncology Group have collaborated to develop a phase III randomized study comparing stereotactic body radiotherapy and sublobar resection (with or without brachytherapy) for high-risk operable patients with non-small cell lung cancer. This study (American College of Surgeons Oncology Group Z4099/Radiation Therapy Oncology Group 1021) has recently opened for accrual. It is hoped that this will help to better define the role of these therapies for patients with non-small cell lung cancer.

Positioning accuracy for lung stereotactic body radiotherapy patients determined by on-treatment cone-beam CT imaging

Stereotactic body radiotherapy for early stage non-small cell lung cancer is an emerging treatment option in the UK. Since relatively few high-dose ablative fractions are delivered to a small target volume, the consequences of a geometric miss are potentially severe. This paper presents the results of treatment delivery set-up data collected using Elekta Synergy (Elekta, Crawley, UK) cone-beam CT imaging for 17 patients immobilised using the Bodyfix system (Medical Intelligence, Schwabmuenchen, Germany). Images were acquired on the linear accelerator at initial patient treatment set-up, following any position correction adjustments, and post-treatment. These were matched to the localisation CT scan using the Elekta XVI software. In total, 71 fractions were analysed for patient set-up errors. The mean vector error at initial set-up was calculated as 5.3 ± 2.7 mm, which was significantly reduced to 1.4 ± 0.7 mm following image guided correction. Post-treatment the corresponding value was 2.1 ± 1.2 mm. The use of the Bodyfix abdominal compression plate on 5 patients to reduce the range of tumour excursion during respiration produced mean longitudinal set-up corrections of -4.4 ± 4.5 mm compared with -0.7 ± 2.6 mm without compression for the remaining 12 patients. The use of abdominal compression led to a greater variation in set-up errors and a shift in the mean value.

Dosimetric impact of a frame-based strategy in stereotactic radiotherapy of lung tumors

INTRODUCTION

Technological innovations have taken stereotactic body radiotherapy (SBRT) from frame-based strategies to image-guided strategies. In this study, cone beam computed tomography (CBCT) images acquired prior to SBRT of patients with lung tumors was used to study the dosimetric impact of a pure frame-based strategy.

MATERIAL AND METHODS

Thirty patients with inoperable lung tumors were retrospectively analyzed. All patients had received CBCT-guided SBRT with 3 fractions of 15 Gy to the planning target volume (PTV) margin including immobilization in a stereotactic body frame (SBF). Using the set-up corrections from the co-registration of the CBCT with the planning CT, all individual dose plans were recalculated with an isocenter position equal to the initial set-up position. Dose Volume Histogram (DVH) parameters of the recalculated dose plans were then analyzed.

RESULTS

The simulated plans showed that 88% of all fractions resulted in minimum 14.5 Gy to the internal target volume (ITV). For the simulated summed treatment (3 fractions per patient), 83% of the patients would minimum receive the prescription dose (45 Gy) to 100% of the ITV and all except one would receive the prescription dose to more than 90% of the ITV.

CONCLUSIONS

SBRT including SBF, but without image guidance, results in appropriate dose coverage in most cases, using the current margins. With image guidance, margins for SBRT of lung tumors could possibly be reduced.

Dosimetric comparison of robotic and conventional linac-based stereotactic lung irradiation in early-stage lung cancer

We aimed to compare dosimetric characteristics of conventional linear accerator-based treatment plans to those created using the robotic CyberKnife® (CK) treatment planning system for patients with early-stage lung cancer. Eight early-stage lung cancer patients treated with stereotactic body radiotherapy (SBRT) using a conventional linac-based (LIN) system were included in this study. New treatment plans were created for the patients with the CK treatment planning system in order to compare the two platforms' dosimetric characteristics. Planning computed tomographies (CT) were obtained in three phases: free-breathing, full exhalation and inhalation. The three GTVs were then added together for internal target volume (ITV) with LIN, whereas no ITV was used for CK. Planning target volumes (PTV) were constituted by adding 5-mm margin to GTV and ITV. Treatment plan was 54 Gy in three fractions. Five-field, seven-field, and dynamic-conformal arc planning techniques were used in LIN plans. Plans were compared according to dose heterogenity (D(max)-maximum dose), volume of 54 Gy (V54) and 27 Gy isodose (V27), conformity index (CI(54) and CI(27)) and lung volumes. PTVs were significantly smaller in CK plans (p=0.012). D(max) was significantly lower in ARC plans (p=0.01). Among all plans, CK had significantly tightest isodose shell received 54 Gy and 27 Gy (p=0.0001). Among LIN plans, V54 was significantly (p=0.03) smaller in ARC plans; but no difference was observed for V27 values. LIN plans have better plan quality (CI(27) and CI(54)) than CK. No statistically significant difference was observed for lung volumes. CK plans had superior V54 and V27 values compared to LIN plans due to smaller PTV. LIN plans had better CI(27) and CI(54) values. Advantages of LIN treatment were no neccessity for fiducial marker use, which may cause pneumothorax, and significantly shorter beam-on treatment times. Both CK and LIN methods are suitable for lung SBRT.

Analysis of the optimum internal margin for respiratory-gated radiotherapy using end-expiratory phase assessments using a motion phantom

We aimed to optimize internal margin (IM) determination for respiratory‐gated radiotherapy using end‐expiratory phase assessments using a motion phantom. Four‐dimensional computed tomography (4D CT) data were acquired using a GE LightSpeed RT CT scanner, a respiratory‐gating system, and a motion phantom designed to move sinusoidally. To analyze the accuracy of 4D CT temporal resolution, a 25.4 mm diameter sphere was inserted into the motion phantom, and we measured the differences in sphere diameters between static and end‐exhalation phase images. In addition, the IM obtained from the maximum intensity projection within the gating window (MIPGW) image was compared to theoretical value. Cranial–caudal motion displacement ranged from 5.0 to 30.0 mm, and the respiratory period ranged from 2.0 to 6.0 sec. Differences in sphere diameters between static and end‐exhalation phase images ranged from 0.37 to 4.6 mm, with 5.0 ‐mm and 30 mm target displacements, respectively. Differences between the IM obtained from the MIPGW and the theoretical values ranged from 1.12 to 6.23 mm with 5.0 mm and 30 mm target displacements, respectively. These differences increased in proportion to the target velocity due to a motion artifact generated during tube rotation. In this study, the IMs obtained using the MIPGW image were overestimated in all cases. We therefore propose that the internal target volume (ITV) for respiratory‐gated radiotherapy should be determined by adding the calculated value to the end‐exhalation phase image. We also demonstrate a methodology for subtracting motion artifacts from the ITV using a motion phantom.

PACS numbers: 87.53.Kn, 87.55.Gh, 87.56.jk

CyberKnife with Tumor Tracking: An Effective Treatment for High-Risk Surgical Patients with Stage I Non-Small Cell Lung Cancer

Published data suggests that wedge resection for stage I non-small cell lung cancer (NSCLC) is associated with improved overall survival compared to stereotactic body radiation therapy. We report CyberKnife outcomes for high-risk surgical patients with biopsy-proven stage I NSCLC. PET/CT imaging was completed for staging. Three-to-five gold fiducial markers were implanted in or near tumors to serve as targeting references. Gross tumor volumes (GTVs) were contoured using lung windows; the margins were expanded by 5 mm to establish the planning treatment volume (PTV). Treatment plans were designed using a mean of 156 pencil beams. Doses delivered to the PTV ranged from 42 to 60 Gy in three fractions. The 30 Gy isodose contour extended at least 1 cm from the GTV to eradicate microscopic disease. Treatments were delivered using the CyberKnife system with tumor tracking. Examination and PET/CT imaging occurred at 3 month follow-up intervals. Forty patients (median age 76) with a median maximum tumor diameter of 2.6 cm (range, 1.4-5.0 cm) and a mean post-bronchodilator percent predicted forced expiratory volume in 1 s (FEV1) of 57% (range, 21-111%) were treated. A median dose of 48 Gy was delivered to the PTV over 3-13 days (median, 7 days). The 30 Gy isodose contour extended a mean 1.9 cm from the GTV. At a median 44 months (range, 12-72 months) follow-up, the 3 year Kaplan-Meier locoregional control and overall survival estimates compare favorably with contemporary wedge resection outcomes at 91 and 75%, respectively. CyberKnife is an effective treatment approach for stage I NSCLC that is similar to wedge resection, eradicating tumors with 1-2 cm margins in order to preserve lung function. Prospective randomized trials comparing CyberKnife with wedge resection are necessary to confirm equivalence.

Failure mode and effect analysis for delivery of lung stereotactic body radiation therapy

PURPOSE

To improve the quality and safety of our practice of stereotactic body radiation therapy (SBRT), we analyzed the process following the failure mode and effects analysis (FMEA) method.

METHODS

The FMEA was performed by a multidisciplinary team. For each step in the SBRT delivery process, a potential failure occurrence was derived and three factors were assessed: the probability of each occurrence, the severity if the event occurs, and the probability of detection by the treatment team. A rank of 1 to 10 was assigned to each factor, and then the multiplied ranks yielded the relative risks (risk priority numbers). The failure modes with the highest risk priority numbers were then considered to implement process improvement measures.

RESULTS

A total of 28 occurrences were derived, of which nine events scored with significantly high risk priority numbers. The risk priority numbers of the highest ranked events ranged from 20 to 80. These included transcription errors of the stereotactic coordinates and machine failures.

CONCLUSION

Several areas of our SBRT delivery were reconsidered in terms of process improvement, and safety measures, including treatment checklists and a surgical time-out, were added for our practice of gantry-based image-guided SBRT. This study serves as a guide for other users of SBRT to perform FMEA of their own practice.

Inhibition of NF-κB and DNA double-strand break repair by DMAPT sensitizes non-small-cell lung cancers to X-rays

We investigated the efficacy and mechanism of dimethylaminoparthenolide (DMAPT), an NF-κB inhibitor, to sensitize human lung cancer cells to X-ray killing in vitro and in vivo. We tested whether DMAPT increased the effectiveness of single and fractionated X-ray treatment through inhibition of NF-κB and/or DNA double-strand break (DSB) repair. Treatment with DMAPT decreased plating efficiency, inhibited constitutive and radiation-induced NF-κB binding activity, and enhanced radiation-induced cell killing by dose modification factors of 1.8 and 1.4 in vitro. X-ray fractionation demonstrated that DMAPT inhibited split-dose recovery/repair, and neutral DNA comet assays confirmed that DMAPT altered the fast and slow components of X-ray-induced DNA DSB repair. Knockdown of the NF-κB family member p65 by siRNA increased radiation sensitivity and completely inhibited split-dose recovery in a manner very similar to DMAPT treatment. The data suggest a link between inhibition of NF-κB and inhibition of DSB repair by DMAPT that leads to enhancement of X-ray-induced cell killing in vitro in non-small-cell lung cancer cells. Studies of A549 tumor xenografts in nude mice demonstrated that DMAPT enhanced X-ray-induced tumor growth delay in vivo.

MLC tracking for Elekta VMAT: a modelling study

A model has been developed to simulate volumetric modulated arc therapy (VMAT) delivery for Elekta control systems. The model was experimentally validated for static-tumour VMAT delivery and has been applied to the investigation of motion compensation with dynamic multileaf collimator (dMLC) delivery tracking for a series of VMAT lung treatment plans at various control point spacings for five patients. The relative increase in treatment time with dMLC tracking was calculated for four 1D rigid-body motion trajectories, and the effect of the control point spacing, the MLC leaf speed and an increased number of dose levels on the dMLC tracking delivery time evaluated. It has been observed that a faster leaf speed is advantageous for motion trajectories with shorter time periods and larger amplitudes. The accuracy of dMLC tracking was found to increase with a decreased control point spacing and is dependent on the amplitude and time period of the motion trajectory of the target. dMLC tracking is shown to be a promising emerging technology which can confer advantage over breath-hold motion-compensation techniques which more drastically reduce the efficiency of VMAT and are more invasive for the patient.

Role of radiation therapy in the management of renal cell cancer

Renal cell carcinoma (RCC) is traditionally considered to be radioresistant; therefore, conventional radiotherapy (RT) fraction sizes of 1.8 to 2 Gy are thought to have little role in the management of primary RCC, especially for curative disease. In the setting of metastatic RCC, conventionally fractionated RT has been an effective palliative treatment in 50% of patients. Recent technological advances in radiation oncology have led to the clinical implementation of image-guided radiotherapy, allowing biologically potent doses to the tumors intra- and extra-cranially. As predicted by radiobiologic modeling, favorable outcomes have been observed with highly hypofractionated schemes modeled after the experience with intracranial stereotactic radiosurgery (SRS) for RCC brain metastases with reported local control rates averaging 85%. At present, both primary and metastatic RCC tumors may be successfully treated using stereotactic approaches, which utilize steep dose gradients to maximally preserve function and avoid toxicity of adjacent organs including liver, uninvolved kidney, bowel, and spinal cord regions. Future endeavors will combine stereotactic body radiation therapy (SBRT) with novel targeted therapies, such as tyrosine kinase inhibitors and targeted rapamycin (mTOR) inhibitors, to maximize both local and systemic control.

Evaluation of response after stereotactic body radiotherapy for hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is increasing in incidence due to hepatitis C. Stereotactic body radiotherapy (SBRT) is a noninvasive, effective therapy in the management of liver malignancies. The authors evaluated radiological response in 26 patients with HCC treated with SBRT at Indiana University.

METHODS

Between March 2005 and June 2008, 26 patients with HCC who were not surgical candidates were enrolled in a phase 1 to 2 trial. Eligibility criteria included solitary tumors ≤ 6 cm or up to 3 lesions with sum diameters ≤ 6 cm, and well-compensated cirrhosis. All patients had imaging before, at 1 to 3 months, and every 3 to 6 months after SBRT.

RESULTS

Patients received 3 to 5 fractions of SBRT. Median SBRT dose was 42 Gray (Gy) (range: 24-48 Gy). Median follow-up was 13 months. Per Response Evaluation Criteria in Solid Tumors (RECIST), 4 patients had a complete response (CR), 15 had a partial response (PR), and 7 achieved stable disease (SD) at 12 months. One patient with SD experienced progression marginal to the treated area. The overall best response rate (CR + PR) was 73%. In comparison, by European Association for the Study of the Liver (EASL) criteria, 18 of 26 patients had ≥ 50% nonenhancement at 12 months. Thirteen of 18 demonstrated 100% nonenhancement, being > 50% in 5 patients. Kaplan-Meier 1- and 2-year survival estimates were 77% and 60%, respectively.

CONCLUSIONS

SBRT is effective therapy for patients with HCC with an overall best response rate (CR + PR) of 73%. Nonenhancement on imaging, a surrogate for ablation, may be a more useful indicator than size reduction in evaluating HCC response to SBRT in the first 6 to 12 months, supporting EASL criteria.

Stereotactic body radiotherapy for multisite extracranial oligometastases: final report of a dose escalation trial in patients with 1 to 5 sites of metastatic disease

BACKGROUND

A subset of patients with metastatic cancer in limited organs may benefit from metastasis-directed therapy. The authors investigated whether patients with limited metastases could be safely treated with metastasis-directed radiotherapy.

METHODS

Patients with 1 to 5 metastatic cancer sites with a life expectancy of >3 months received escalating stereotactic body radiotherapy (SBRT) doses to all known cancer sites. Patients were followed radiographically with CT scans of the chest, abdomen, and pelvis and metabolically with fluorodeoxyglucose-positron emission tomography, 1 month after treatment, and then every 3 months. Acute toxicities were scored using the National Cancer Institute's Common Terminology Criteria for Adverse Events version 3.0, and late toxicities were scored using the Radiation Therapy Oncology Group late toxicity scoring system.

RESULTS

Sixty-one patients with 113 metastases were enrolled from November 2004 to November 2009 on a prospective radiation dose escalation study. Median follow-up was 20.9 months. Patients tolerated treatment well; the maximal tolerated dose was not reached in any cohort. Eleven patients (18.3%) have not progressed. One and 2-year progression-free survival are 33.3% (95% confidence interval [CI], 22.8-46.1) and 22.0% (95% CI, 12.8-34.4); 1-year and 2-year overall survival are 81.5% (95% CI, 71.1-91.1) and 56.7% (95% CI, 43.9-68.9). Seventy-two percent of patients whose tumors progressed did so in limited (1-3) metastatic sites.

CONCLUSIONS

Patients with 1 to 5 metastases can be safely treated to multiple body sites and may benefit from SBRT. Further investigation should focus on patient selection.

Evaluation and treatment of high-risk patients with early-stage lung cancer

Standard therapy for early-stage non-small cell lung cancer is lobectomy for patients who are able to tolerate such surgery. However, the risk of postoperative morbidity is not trivial, with a 30% to 40% incidence of postoperative complications and a 1% to 5% incidence of operative mortality. Some patients, though technically resectable, refuse surgery or are considered medically inoperable because of insufficient respiratory reserve, cardiovascular disease, or general frailty. This group is considered either "high risk" or "medically inoperable."

Feasibility and early clinical assessment of flattening filter free (FFF) based stereotactic body radiotherapy (SBRT) treatments

Purpose

To test feasibility and safety of clinical usage of Flattening Filter Free (FFF) beams for delivering ablative stereotactic body radiation therapy (SBRT) doses to various tumor sites, by means of Varian TrueBeam™ (Varian Medical Systems).

Methods and Materials

Seventy patients were treated with SBRT and FFF: 51 lesions were in the thorax (48 patients),10 in the liver, 9 in isolated abdominal lymph node, adrenal gland or pancreas. Doses ranged from 32 to 75 Gy, depending on the anatomical site and the volume of the lesion to irradiate. Lung lesions were treated with cumulative doses of 32 or 48 Gy, delivered in 4 consecutive fractions. The liver patients were treated in 3 fractions with total dose of 75 Gy. The isolated lymph nodes were irradiated in 6 fractions with doses of 45 Gy. The inclusion criteria were the presence of isolated node, or few lymph nodes in the same lymph node region, in absence of other active sites of cancer disease before the SBRT treatment.

Results

All 70 patients completed the treatment. The minimum follow-up was 3 months. Six cases of acute toxicities were recorded (2 Grade2 and 2 Grade3 in lung and 2 Grade2 in abdomen). No patient experienced acute toxicity greater than Grade3. No other types or grades of toxicities were observed at clinical evaluation visits.

Conclusions

This study showed that, with respect to acute toxicity, SBRT with FFF beams showed to be a feasible technique in 70 consecutive patients with various primary and metastatic lesions in the body.

Stereotactic radiosurgery for lung tumors

Lung cancer remains the most common cause of cancer-related deaths in the United States, and although surgery remains the standard treatment for early-stage tumors, stereotactic radiation is gaining an increasing role as an alternative form of therapy. Initially a form of treatment designed for neurosurgical applications, during the past decade stereotactic radiosurgery (SRS) has gone from a novel treatment for patients deemed to be prohibitive candidates for surgical resection to the point that there is now an international, randomized, multicenter trial to compare SRS to lobectomy in otherwise-healthy patients. This article reviews the history of SRS as applied to lung tumors, summarizes the currently available data on efficacy and toxicity, and describes some of the current controversial aspects of this treatment.

A contemporary review of stereotactic radiotherapy: inherent dosimetric complexities and the potential for detriment

OBJECTIVE

The advantages of highly localised, conformal treatments achievable with stereotactic radiotherapy (SRT) are increasingly being extended to extracranial sites as stereotactic body radiotherapy with advancements in imaging and beam collimation. One of the challenges in stereotactic treatment lies in the significant complexities associated with small field dosimetry and dose calculation. This review provides a comprehensive overview of the complexities associated with stereotactic radiotherapy and the potential for detriment.

METHODS

This study is based on a comprehensive review of literature accessible via PubMed and other sources, covering stereotactic radiotherapy, small-field dosimetry and dose calculation.

FINDINGS

Several key issues were identified in the literature. They pertain to dose prescription, dose measurement and dose calculation within and beyond the treatment field. Field-edge regions and penumbrae occupy a significant portion of the total field size. Spectral and dosimetric characteristics are difficult to determine and are compounded by effects of tissue inhomogeneity. Measurement of small-fields is made difficult by detector volume averaging and energy response. Available dosimeters are compared, and emphasis is given to gel dosimetry which offers the greatest potential for three-dimensional small-field dosimetry. The limitations of treatment planning system algorithms as applied to small-fields (particularly in the presence of heterogeneities) is explained, and a review of Monte Carlo dose calculation is provided, including simplified treatment planning implementations. Not incorporated into treatment planning, there is evidence that far from the primary field, doses to patients (and corresponding risks of radiocarcinogenesis) from leakage/scatter in SRT are similar to large fields.

CONCLUSIONS

Improved knowledge of dosimetric issues is essential to the accurate measurement and calculation of dose as well as the interpretation and assessment of planned and delivered treatments. This review highlights such issues and the potential benefit that may be gained from Monte Carlo dose calculation and verification via three-dimensional dosimetric methods (such as gel dosimetry) being introduced into routine clinical practice.

Evaluation of treatment response after nonoperative therapy for early-stage non-small cell lung carcinoma

Nonsurgical management of early primary lung cancer has grown tremendously in recent years, and today, available options extend far beyond that of conventional radiation therapy (CRT) to include minimally invasive image-guided delivery of thermal energies, specifically radiofrequency ablation, microwave ablation, and cryoablation, and more conformal stereotactic body radiation therapy. Because the tumor is never resected with these nonoperative interventions, histopathological evaluation of tumor margins for the presence of residual tumor is impossible, and as such, tumor response after each of these therapies is largely based on imaging. To date, computerized tomography and computerized tomography-positron emission tomography remain the most readily available modalities for assessment of therapeutic efficacy, and to this end as detailed within this article, strict imaging survey and familiarity with the expected imaging characteristics of the treated tumor will aid in recognition of unexpected findings, specifically those of incomplete therapy and/or tumor recurrence.

Stereotactic ablative radiation therapy for primary lung tumors

Stereotactic ablative radiotherapy, also known as stereotactic body radiation therapy, has been developed as an innovative therapy for stage I non-small cell lung cancer and has now emerged as a standard treatment option for medically inoperable patients through careful analysis utilizing prospective, multi-institutional trials. This article reviews and updates the evidence for use of stereotactic ablative radiotherapy in medically inoperable patients with stage I lung cancer, its extension of use to medically operable patients, and the toxicities associated with this emerging technique.

Individualized higher dose of 70-75 Gy using five-fraction robotic stereotactic radiotherapy for non-small-cell lung cancer: a feasibility study

OBJECTIVE

To determine whether robotic stereotactic radiotherapy of 70-75 Gy delivered in five fractions results in an improved therapeutic ratio, compared with three fractions, in the treatment of peripheral non-small-cell lung cancer (NSCLC), in which case doses of up to 85 Gy in five fractions may be feasible.

MATERIALS AND METHODS

Between December 2006 and May 2010, 20 patients (9 female, 11 male, aged 65 to 88) were treated using the CyberKnife® Robotic Radiosurgery System for NSCLC with doses ranging from 67 Gy to 75 Gy based on location, histopathological type, grade of histopathological differentiation, tumor diameter/volume, and normal tissue constraints, with the doses being delivered in five fractions over 5 to 8 days. Tumor diameters ranged from 1.5 cm to 3.4 cm (median: 2.5 cm). Patients with Stage I to IV NSCLC were treated, and the results and observations were analyzed for clinical characteristics and outcomes including toxicity. All patients, except one who had refused surgery, had co-morbid conditions that precluded a lobectomy.

RESULTS

Twenty patients were followed every three months by positron emission tomography/computed tomography (PET/CT). Mean follow-up was 23 months (range: four to 58 months). Local control was achieved in all treated tumors. Three patients expired, and three developed new regional metastases, none of which was within the planning target volume (PTV). The remainder of the patients demonstrated no evidence of recurrence or continued growth detectable by PET/CT. There was no toxicity above Grade 1.

CONCLUSIONS

It is feasible to treat peripheral NSCLC with individualized maximal tolerable doses ranging from 67 Gy to 75 Gy in five fractions chosen on the basis of location, histopathological type, grade of histopathological differentiation, tumor diameter/volume, and normal tissue constraints.

Phase I dose-escalation study of stereotactic body radiation therapy for low- and intermediate-risk prostate cancer

PURPOSE

To evaluate the tolerability of escalating doses of stereotactic body radiation therapy in the treatment of localized prostate cancer.

PATIENTS AND METHODS

Eligible patients included those with Gleason score 2 to 6 with prostate-specific antigen (PSA) ≤ 20, Gleason score 7 with PSA ≤ 15, ≤ T2b, prostate size ≤ 60 cm(3), and American Urological Association (AUA) score ≤ 15. Pretreatment preparation required an enema and placement of a rectal balloon. Dose-limiting toxicity (DLT) was defined as grade 3 or worse GI/genitourinary (GU) toxicity by Common Terminology Criteria of Adverse Events (version 3). Patients completed quality-of-life questionnaires at defined intervals.

RESULTS

Groups of 15 patients received 45 Gy, 47.5 Gy, and 50 Gy in five fractions (45 total patients). The median follow-up is 30 months (range, 3 to 36 months), 18 months (range, 0 to 30 months), and 12 months (range, 3 to 18 months) for the 45 Gy, 47.5 Gy, and 50 Gy groups, respectively. For all patients, GI grade ≥ 2 and grade ≥ 3 toxicity occurred in 18% and 2%, respectively, and GU grade ≥ 2 and grade ≥ 3 toxicity occurred in 31% and 4%, respectively. Mean AUA scores increased significantly from baseline in the 47.5-Gy dose level (P = .002) as compared with the other dose levels, where mean values returned to baseline. Rectal quality-of-life scores (Expanded Prostate Cancer Index Composite) fell from baseline up to 12 months but trended back at 18 months. In all patients, PSA control is 100% by the nadir + 2 ng/mL failure definition.

CONCLUSION

Dose escalation to 50 Gy has been completed without DLT. A multicenter phase II trial is underway treating patients to 50 Gy in five fractions to further evaluate this experimental therapy.

Dose escalation for non-small cell lung cancer: analysis and modelling of published literature

PURPOSE

To review the published clinical data on non-small cell lung cancer treated with radical radiotherapy to confirm a dose-response relationship as a basis for further dose-escalation trials.

METHODS

Twenty-four published clinical trials were identified, 16 of which - with 29 different standard, hyper- and hypofractionated treatment schedules - were analysed. Prescription doses were converted to biologically-equivalent dose (BED), with a correction for repopulation. Disease-free survival data were corrected for the stage profile of each cohort to allow better comparison of results. We also analysed moderate (grade II and III) lung and oesophageal acute toxicity related to the corrected BED delivered to the tumour.

RESULTS

The clinical data analysed showed good agreement between the observed and modelled disease-free survival at 2 years when compared to the published models of Fenwick (correlation coefficient 0.525, p=0.003) and Martel (correlation coefficient 0.492, p=0.007), indicating a clear tumour dose-response. In the normally fractionated treatments (∼ 2 Gy per fraction), improved disease-free survival was generally observed in the shorter schedules (maximum around 6 weeks). However, the best outcomes were obtained for the hypofractionated schedules. No systematic relationship was seen between prescribed dose and lung or oesophageal acute toxicity, possibly due to dose selection depending on V(20) or MLD in some studies and the diversity of the patients analysed.

CONCLUSIONS

We have demonstrated a dose-response relationship for NSCLC based on clinical data. The clinical data provide a rational basis for selection of dose escalation schedules to be tested in future randomised trials.

Radiographic and metabolic response rates following image-guided stereotactic radiotherapy for lung tumors

PURPOSE

To evaluate radiographic and metabolic response after stereotactic body radiotherapy (SBRT) for early lung tumors.

MATERIALS AND METHODS

Thirty-nine tumors were treated prospectively with SBRT (dose=48-60 Gy, 4-5 Fx). Thirty-six cases were primary NSCLC (T1N0=67%; T2N0=25%); three cases were solitary metastases. Patients were followed using CT and PET at 6, 16, and 52 weeks post-SBRT, with CT follow-up thereafter. RECIST and EORTC criteria were used to evaluate CT and PET responses.

RESULTS

At median follow-up of 9 months (0.4-26), RECIST complete response (CR), partial response (PR), and stable disease (SD) rates were 3%, 43%, 54% at 6 weeks; 15%, 38%, 46% at 16 weeks; 27%, 64%, 9% at 52 weeks. Mean baseline tumor volume was reduced by 46%, 70%, 87%, and 96%, respectively at 6, 16, 52, and 72 weeks. Mean baseline maximum standardized uptake value (SUV) was 8.3 (1.1-20.3) and reduced to 3.4, 3.0, and 3.7 at 6, 16, and 52 weeks after SBRT. EORTC metabolic CR/PR, SD, and progressive disease rates were 67%, 22%, 11% at 6 weeks; 86%, 10%, 3% at 16 weeks; 95%, 5%, 0% at 52 weeks.

CONCLUSIONS

SBRT yields excellent RECIST and EORTC based response. Metabolic response is rapid however radiographic response occurs even after 1-year post treatment.

Dosimetric characterization of an image-guided stereotactic small animal irradiator

Small animal irradiation provides an important tool used by preclinical studies to assess and optimize new treatment strategies such as stereotactic ablative radiotherapy. Characterization of radiation beams that are clinically and geometrically scaled for the small animal model is uniquely challenging for orthovoltage energies and minute field sizes. The irradiator employs a commercial x-ray device (XRAD 320, Precision x-ray, Inc.) with a custom collimation system to produce 1-10 mm diameter beams and a 50 mm reference beam. Absolute calibrations were performed using the AAPM TG-61 methodology. Beam's half-value layer (HVL) and timer error were measured with an ionization chamber. Percent depth dose (PDD), output factors (OFs) and off-axis ratios were measured using radiochromic film, a diode and a pinpoint ionization chamber at 19.76 and 24.76 cm source-to-surface distance (SSD). PDD measurements were also compared with Monte Carlo (MC) simulations. In-air and in-water absolute calibrations for the reference 50 mm diameter collimator at 19.76 cm SSD were measured as 20.96 and 20.79 Gy min(-1), respectively, agreeing within 0.8%. The HVL at 250 kVp and 15 mAs was measured to be 0.45 mm Cu. The reference field PDD MC simulation results agree with measured data within 3.5%. PDD data demonstrate typical increased penetration with increasing field size and SSD. For collimators larger than 5 mm in diameter, OFs measured using film, an ion chamber and a diode were within 3% agreement.

Hypofractionation results in reduced tumor cell kill compared to conventional fractionation for tumors with regions of hypoxia

PURPOSE

Tumor hypoxia has been observed in many human cancers and is associated with treatment failure in radiation therapy. The purpose of this study is to quantify the effect of different radiation fractionation schemes on tumor cell killing, assuming a realistic distribution of tumor oxygenation.

METHODS AND MATERIALS

A probability density function for the partial pressure of oxygen in a tumor cell population is quantified as a function of radial distance from the capillary wall. Corresponding hypoxia reduction factors for cell killing are determined. The surviving fraction of a tumor consisting of maximally resistant cells, cells at intermediate levels of hypoxia, and normoxic cells is calculated as a function of dose per fraction for an equivalent tumor biological effective dose under normoxic conditions.

RESULTS

Increasing hypoxia as a function of distance from blood vessels results in a decrease in tumor cell killing for a typical radiotherapy fractionation scheme by a factor of 10(5) over a distance of 130 μm. For head-and-neck cancer and prostate cancer, the fraction of tumor clonogens killed over a full treatment course decreases by up to a factor of ∼10(3) as the dose per fraction is increased from 2 to 24 Gy and from 2 to 18 Gy, respectively.

CONCLUSIONS

Hypofractionation of a radiotherapy regimen can result in a significant decrease in tumor cell killing compared to standard fractionation as a result of tumor hypoxia. There is a potential for large errors when calculating alternate fractionations using formalisms that do not account for tumor hypoxia.

Stereotactic radiotherapy of primary lung cancer and other targets: results of consultant meeting of the International Atomic Energy Agency

To evaluate the current status of stereotactic body radiotherapy (SBRT) and identify both advantages and disadvantages of its use in developing countries, a meeting composed of consultants of the International Atomic Energy Agency was held in Vienna in November 2006. Owing to continuous developments in the field, the meeting was extended by subsequent discussions and correspondence (2007-2010), which led to the summary presented here. The advantages and disadvantages of SBRT expected to be encountered in developing countries were identified. The definitions, typical treatment courses, and clinical results were presented. Thereafter, minimal methodology/technology requirements for SBRT were evaluated. Finally, characteristics of SBRT for developing countries were recommended. Patients for SBRT should be carefully selected, because single high-dose radiotherapy may cause serious complications in some serial organs at risk. Clinical experiences have been reported in some populations of lung cancer, lung oligometastases, liver cancer, pancreas cancer, and kidney cancer. Despite the disadvantages expected to be experienced in developing countries, SBRT using fewer fractions may be useful in selected patients with various extracranial cancers with favorable outcome and low toxicity.

Multiple breath-hold CBCT for online image guided radiotherapy of lung tumors: simulation with a dynamic phantom and first patient data

BACKGROUND AND PURPOSE

Computer controlled breath-hold effectively reduces organ motion for image-guided precision radiotherapy of lung tumors. However, the acquisition time of 3D cone-beam-CT (CBCT) exceeds maximum breath-hold times. We have developed an approach enabling online verification using CBCT image acquisition with ABC®-based breath-hold.

METHODS

Patient CBCT images were acquired with ABC®-based repeat breath-hold. The clinical situation was also simulated with a Motion Phantom. Reconstruction of patient and phantom images with selection of free-breathing and breath-hold projections only was performed.

RESULTS

CBCT-imaging in repeat breath-hold resulted in a precisely spherical appearance of a tumor-mimicking structure in the phantom. A faint "ghost" structure (free-breathing phases) can be clearly discriminated. Mean percentage of patient breath-hold time was 66%. Reconstruction based on free-breathing-only shows blurring of both tumor and diaphragm, reconstruction based on breath-hold projections only resulted in sharp contours of the same structures. From the phantom experiments, a maximal repositioning error of 1mm in each direction can be estimated.

DISCUSSION AND CONCLUSION

CBCT during repetitive breath hold provides reliable soft-tissue-based positioning. Fast 3D-imaging during one breath-hold is currently under development and has the potential to accelerate clinical linac-based volume imaging.

Chest wall toxicity after stereotactic body radiotherapy for malignant lesions of the lung and liver

PURPOSE

To quantify the frequency of rib fracture and chest wall (CW) pain and identify the dose-volume parameters that predict CW toxicity after stereotactic body radiotherapy (SBRT).

METHODS AND MATERIALS

The records of patients treated with SBRT between 2000 and 2008 were reviewed, and toxicity was scored according to Common Terminology Criteria for Adverse Events v3.0 for pain and rib fracture. Dosimetric data for CW and rib were analyzed and related to the frequency of toxicity. The risks of CW toxicity were then further characterized according to the median effective concentration (EC(50)) dose-response model.

RESULTS

A total of 347 lesions were treated with a median follow-up of 19 months. Frequency of Grade I and higher CW pain and/or fracture for CW vs. non-CW lesions was 21% vs. 4%, respectively (p < 0.0001). A dose of 50 Gy was the cutoff for maximum dose (Dmax) to CW and rib above which there was a significant increase in the frequency of any grade pain and fracture (p = 0.03 and p = 0.025, respectively). Volume of CW receiving 15 Gy - 40 Gy was highly predictive of toxicity (R(2) > 0.9). According to the EC(50) model, 5 cc and 15 cc of CW receiving 40 Gy predict a 10% and 30% risk of CW toxicity, respectively.

CONCLUSION

Adequate tumor coverage remains the primary objective when treating lung or liver lesions with SBRT. To minimize toxicity when treating lesions in close proximity to the CW, Dmax of the CW and/or ribs should remain <50 Gy, and <5 cc of CW should receive ≥ 40 Gy.