Extracranial Stereotactic Radioablation *

Final results of a phase II trial for stereotactic body radiation therapy for patients with inoperable liver metastases from colorectal cancer

PURPOSE

To evaluate the feasibility and efficacy of stereotactic body radiation therapy (SBRT) in the treatment of colorectal liver metastases.

METHODS

Forty-two patients with inoperable colorectal liver metastases not amenable to radiofrequency ablation (RFA) were treated with SBRT for a total number of 52 lesions. All patients received a total dose of 75 Gy in 3 consecutive fractions. Mean size of the lesions was 3.5 cm (range 1.1-5.4). Toxicity was classified according to the Common Toxicity Criteria version 3.0.

RESULTS

Median follow-up was 24 (range 4-47) months. The progression in field was observed in 5 lesions. Twenty-four months actuarial local control (LC) rate was 91 %. Median overall survival (OS) was 29.2 ± 3.7 months. Actuarial OS rate at 24 months was 65 %. Median progression-free survival was 12.0 ± 4.2 months; 24 months actuarial rate was 35 %. No patients experienced radiation-induced liver disease or grade ≥3 toxicity.

CONCLUSIONS

SBRT represents a feasible alternative for the treatment of colorectal liver metastases not amenable to surgery or other ablative treatments in selected patients, showing optimal LC and promising survival rate.

Clinical outcomes of CyberKnife stereotactic body radiotherapy for peripheral stage I non-small cell lung cancer

The aim of this study was to evaluate the clinical outcome of CyberKnife stereotactic body radiotherapy (SBRT) for patients with stage I non-small cell lung cancer (NSCLC). Fifty patients with peripheral stage I NSCLC who refused surgery or were medically inoperable were treated with 48-60 Gy (median dose: 57 Gy) in three divided doses. Histopathology was available in 86% of patients. Thirty patients had a T1 tumor, and 20 patients had T2 tumors. More than 95% of the target volume was covered by the 72% isodose surface. Fiducials were implanted in or near the tumors in all patients to track tumor movement and breathing patterns. The median follow-up time was 35 months (3-45 months). Based on computed tomography scans, 40 patients achieved complete remission, six patients achieved partial remission, two patients exhibited stable disease, and two patients had progressive disease. The local control rate (CR + PR) was 92%, and the 2-year disease control rate (CR + PR + SD) was 96%. Overall survival for the whole group was 86% at 1 year and 74% at 2 years. Grade III toxicity occurred in two patients (4%) after marker placement. Treatment-related late grade III toxicity occurred in five patients (10%). Toxicities greater than grade III were not observed. CyberKnife SBRT achieves a high rate of local control and long-term curative effect with acceptable toxicity for patients with inoperable stage I NSCLC. However, long-term follow-up is necessary to evaluate survival and late toxicity.

Combination of stereotactic ablative body radiation with targeted therapies

Recent advances allow safe and effective delivery of ablative doses of radiation with stereotactic precision to tumours, resulting in very high levels of tumour control. Parallel advances in the understanding of tumour biology enable delivery of systemic drugs that selectively antagonise biological pathways in the tumour and surrounding microenvironment. Data is emerging that these treatments have synergistic effects that might further increase therapeutic efficacy, and they are therefore being increasingly used in combination, primarily in metastatic or recurrent disease. In this Review we summarise the biological rationale and clinical data for both sterotactic ablative radiotherapy (SABR) and targeted therapies, and the emerging experience with combination of these treatments. We describe potential pathways of cooperation in both tumour and normal tissue between SABR and targeted drugs, and, because fatal toxicities have been reported, we outline clinical precautions.

Volumetric modulated arc therapy for lung stereotactic radiation therapy can achieve high local control rates

Purpose

The aim of this study was to report the outcome of primary or metastatic lung cancer patients undergoing volumetric modulated arc therapy for stereotactic body radiation therapy (VMAT-SBRT).

Methods and materials

From October 2010 to December 2013, consecutive 67 lung cancer patients received single-arc VMAT-SBRT using an Elekta-synergy system. All patients were treated with an abdominal compressor. The gross tumor volumes were contoured on 10 respiratory phases computed tomography (CT) datasets from 4-dimensional (4D) CT and merged into internal target volumes (ITVs). The planning target volume (PTV) margin was isotropically taken as 5 mm. Treatment was performed with a D95 prescription of 50 Gy (43 cases) or 55 Gy (12 cases) in 4 fractions for peripheral tumor or 56 Gy in 7 fractions (12 cases) for central tumor.

Results

Among the 67 patients, the median age was 73 years (range, 59–95 years). Of the patients, male was 72% and female 28%. The median Karnofsky performance status was 90-100% in 39 cases (58%) and 80-90% in 20 cases (30%). The median follow-up was 267 days (range, 40–1162 days). Tissue diagnosis was performed in 41 patients (61%). There were T1 primary lung tumor in 42 patients (T1a in 28 patients, T1b in 14 patients), T2 in 6 patients, three T3 in 3 patients, and metastatic lung tumor in 16 patients. The median mean lung dose was 6.87 Gy (range, 2.5-15 Gy). Six patients (9%) developed radiation pneumonitis required by steroid administration. Actuarial local control rate were 100% and 100% at 1 year, 92% and 75% at 2 years, and 92% and 75% at 3 years in primary and metastatic lung cancer, respectively (p = 0.59). Overall survival rate was 83% and 84% at 1 year, 76% and 53% at 2 years, and 46% and 20% at 3 years in primary and metastatic lung cancer, respectively (p = 0.12).

Conclusions

Use of VMAT-based delivery of SBRT in primary in metastatic lung tumors demonstrates high local control rates and low risk of normal tissue complications.

Stereotactic body radiotherapy

Extracranial stereotactic body radiotherapy (SBRT) has been developed and refined over the last 25 years as a means to precisely deliver ablative doses of hypofractionated radiotherapy to small targets located outside of the cranial vault. SBRT has armed the radiation oncologist with a therapeutic approach that allows for intensification of both dose delivered and fractionation regimen employed. As a consequence, tumor control rates have improved to levels that previously have been associated only with surgical resection. Several prospective phase I and II studies have evaluated the use of SBRT for non-small cell lung cancer (NSCLC), liver tumors, and spinal metastases. This article will give an overview of SBRT and evidence for its use in the most common sites of disease for which it is employed today.

Altered fractionation schedules in radiation treatment: a review

Conventionally fractionated radiotherapy is delivered in 1.8- to 2.0-Gy fractions. With increases in understanding of radiation and tumor biology, various alterations of radiotherapy schedules have been tested in clinical trials and are now regarded by some as standard treatment options. Hyperfractionation is delivered through a greater number of smaller treatment doses. Accelerated fractionation decreases the amount of time over which radiotherapy is delivered typically by increasing the number of treatments per day. Hypofractionation decreases the number of fractions delivered by increasing daily treatment doses. Furthermore, many of these schedules have been tested with concurrent chemotherapy regimens. In this review, we summarize the major clinical studies that have been conducted on altered fractionation in various disease sites.

Stereotactic body radiation therapy for post-pulmonary lobectomy isolated lung metastasis of thoracic tumor: survival and side effects

BACKGROUND

Stereotactic body radiation therapy (SBRT) has emerged as an alternative treatment for patients with early stage non-small cell lung cancer (NSCLC) or metastatic pulmonary tumors. However, for isolated lung metastasis (ILM) of thoracic malignances after pulmonary lobectomy, reported outcomes of SBRT have been limited. This study evaluates the role of SBRT in the treatment of such patients.

METHODS

A retrospective search of the SBRT database was conducted in three hospitals. The parameters analyzed in the treated patients were local control, progression-free survival (PFS), overall survival (OS), and the treatment-related side-effects.

RESULTS

In total, 23 patients with single ILM after pulmonary lobectomy treated with SBRT were identified and the median follow-up time was 14 months (range: 6.0-47.0 months). Local recurrences were observed in two patients during follow-up and the 1-year local control rate was 91.3%. Median PFS and OS for the studied cohort were 10.0 months [95% confidence interval (CI) 5.1-14.9 months] and 21.0 months (95% CI 11.4-30.6 months), respectively. Acute radiation pneumonitis (RP) of grade 2 or worse was observed in five (21.7%) and three (13.0%) patients, respectively. Other treatment-related toxicities included chest wall pain in one patient (4.3%) and acute esophagitis in two patients (8.7%). By Pearson correlation analysis, the planning target volume (PTV) volume and the volume of the ipsilateral lung exposed to a minimum dose of 5 Gy (IpV5) were significantly related to the acute RP of grade 2 or worse in present study (p < 0.05). The optimal thresholds of the PTV and IpV5 to predict RP of acute grade 2 or worse RP were 59 cm3 and 51% respectively, according to the receiver-operating characteristics curve analysis, with sensitivity/specificity of 75.0%/80.0% and 62.5%/80.0%.

CONCLUSIONS

SBRT for post-lobectomy ILM was effective and well tolerated. The major reason for disease progression was distant failure but not local recurrence. The PTV and IpV5 are potential predictors of acute RP of grade 2 or higher and should be considered in treatment planning for such patients.

Stereotactic body radiation therapy (SBRT) for lung cancer patients previously treated with conventional radiotherapy: a review

Lung cancer continues to be one of the most prevalent malignancies worldwide and is the leading cause of death in both men and women. Presently, local control rates are quite poor. Improvements in imaging and radiation treatment delivery systems however have provided radiation oncologists with new tools to better target these tumors. Stereotactic body radiation therapy (SBRT) is one such technique that has shown efficacy as upfront treatment for lung cancer. In addition, more recent studies have demonstrated some effectiveness in recurrent tumors in prior irradiated fields as well. This review summarizes seven recent studies of re-irradiation with SBRT in patients with thoracic recurrences treated previously with conventionally fractionated radiation therapy. Combined, 140 patients were included. The median initial thoracic radiation doses ranged from 50-87.5 Gy and median re-irradiation dose ranged from 40-80 Gy. Local control rates varied from 65-92%. Re-irradiation was well tolerated with few grade 4 and 5 complications (observed in one study). Currently, based on these published reports, re-irradiation with SBRT appears feasible for in-field thoracic recurrences, though caution must be taken in all cases of retreatment.

Feasibility study of stereotactic body radiotherapy for peripheral lung tumors with a maximum dose of 100 Gy in five fractions and a heterogeneous dose distribution in the planning target volume

We evaluated toxicity and outcomes for patients with peripheral lung tumors treated with stereotactic body radiation therapy (SBRT) in a dose-escalation and dose-convergence study. A total of 15 patients were enrolled. SBRT was performed with 60 Gy in 5 fractions (fr.) prescribed to the 60% isodose line of maximum dose, which was 100 Gy in 5 fr., covering the planning target volume (PTV) surface (60 Gy/5 fr. - (60%-isodose)) using dynamic conformal multiple arc therapy (DCMAT). The primary endpoint was radiation pneumonitis (RP) ≥ Grade 2 within 6 months. Toxicities were graded according to the Common Terminology Criteria for Adverse Events, version 4.0. Using dose-volumetric analysis, the trial regimen of 60 Gy/5 fr. - (60%-isodose) was compared with our institutional conventional regimen of 50 Gy/5 fr. - (80%-isodose). The enrolled consecutive patients had either a solitary peripheral tumor or two ipsilateral tumors. The median follow-up duration was 22.0 (12.0-27.0) months. After 6 months post-SBRT, the respective number of RP Grade 0, 1 and 2 cases was 5, 9 and 1. In the Grade 2 RP patient, the image showed an organizing pneumonia pattern at 6.0 months post-SBRT. No other toxicity was found. At last follow-up, there was no evidence of recurrence of the treated tumors. The target volumes of 60 Gy/ 5 fr. - (60%-isodose) were irradiated with a significantly higher dose than those of 50 Gy/5 fr. - (80%-isodose), while the former dosimetric parameters of normal lung were almost equivalent to the latter. SBRT with 60 Gy/5 fr. - (60%-isodose) using DCMAT allowed the delivery of very high and convergent doses to peripheral lung tumors with feasibility in the acute and subacute phases. Further follow-up is required to assess for late toxicity.

The impact of abdominal compression on outcome in patients treated with stereotactic body radiotherapy for primary lung cancer

The aim of this study was to evaluate the impact of abdominal compression (AC) on outcome in patients treated with stereotactic body radiotherapy (SBRT) for primary lung cancer. We retrospectively reviewed data for 47 patients with histologically proven non-small cell lung cancer and lung tumour motion ≥ 8 mm treated with SBRT. Setup error was corrected based on bony structure. The differences in overall survival (OS), local control (LC) and disease-free survival (DFS) were evaluated to compare patients treated with AC (n = 22) and without AC (n = 25). The median follow-up was 42.6 months (range, 1.4-94.6 months). The differences in the 3-year OS, LC and DFS rate between the two groups were not statistically significant (P = 0.909, 0.209 and 0.639, respectively). However, the largest difference was observed in the LC rate, which was 82.5% (95% CI, 54.9-94.0%) for patients treated without AC and 65.4% (95% CI, 40.2-82.0%) for those treated with AC. After stratifying the patients into prognostic groups based on sex and T-stage, the LC difference increased in the group with an unfavourable prognosis. The present study suggests that AC might be associated with a worse LC rate after SBRT using a bony-structure-based set-up.

Integrating stereotactic body radiation therapy in stage II/III non-small cell lung cancer: is local control important?

Local control for advanced non-small cell lung cancer (NSCLC) remains a significant problem with chemoradiation local failure rates in the chest of 30-50%. Despite attempts at dose escalation with conventional radiation therapy techniques, toxicities limit the amount of radiation that can be delivered. For stage I NSCLC, mounting evidence supports the use of hypofractionated radiation therapy (SBRT) to gain high local control rates with acceptable toxicity. For healthy patients with stage II/III NSCLC, the National Comprehensive Cancer Network guidelines suggest surgery is the preferred standard of care for patients with <N2 nodes or T3 tumors. In select patients who are surgical candidates or have more extensive disease, guidelines may include pre-operative chemoradiation followed by surgery, although this remains controversial and is the subject of a current national clinical trial (RTOG 0839). Dose escalation through conventional radiation therapy planning suggests that we can improve outcomes in stage III patients, but toxicity remains problematic. It follows that with improvements in imaging and delivery of radiotherapy, dose escalation with SBRT incorporation may improve local control in stage II/III NSCLC for medically inoperable patients. The rationale for dose escalation and some of the considerations for incorporation of SBRT dose escalation in stage III lung cancer are reviewed here.

Emergence of stereotactic body radiation therapy and its impact on current and future clinical practice

Stereotactic body radiation therapy (SBRT) is generally a tumor-ablative radiation modality using essential technologies capable of accurately and precisely damaging the target with a high dose while geometrically sparing innocent normal tissues. The intent, conduct, and tissue biology are all dramatically distinct from conventionally fractionated radiotherapy such that new understanding is required for its optimization. It is most practical, tolerable, and tumoricidal in its most potent form treating tumors in the lung and liver. However, it is increasingly being used for tumors adjacent to bowels and nervous tissue, albeit with somewhat less ablative potency. Its strengths include high rates of tumor eradication via a noninvasive, convenient outpatient treatment. Its weakness relates to the possibility of causing difficult-to-manage toxicity (eg, ulceration, stenosis, fibrosis, and even necrosis) that may occur considerably later after treatment, particularly in the vicinity of the body's many tubular structures (eg, organ hila, bowel). However, clinical trials in a variety of organs and sites have shown SBRT to result in good outcomes in properly selected patients. Given its short course, lack of need for recovery, and favorable overall toxicity profile, there is great hope that SBRT will find a prominent place in the treatment of metastatic cancer as a consolidative partner with systemic therapy. With considerable published experience, available required technologies and training, and many patients in need of local therapy, SBRT has found a place in the routine cancer-fighting arsenal.

Optimal schedules of fractionated radiation therapy by way of the greedy principle: biologically-based adaptive boosting

We revisit a long-standing problem of optimization of fractionated radiotherapy and solve it in considerable generality under the following three assumptions only: (1) repopulation of clonogenic cancer cells between radiation exposures follows linear birth-and-death Markov process; (2) clonogenic cancer cells do not interact with each other; and (3) the dose response function s(D) is decreasing and logarithmically concave. Optimal schedules of fractionated radiation identified in this work can be described by the following 'greedy' principle: give the maximum possible dose as soon as possible. This means that upper bounds on the total dose and the dose per fraction reflecting limitations on the damage to normal tissue, along with a lower bound on the time between successive fractions of radiation, determine the optimal radiation schedules completely. Results of this work lead to a new paradigm of dose delivery which we term optimal biologically-based adaptive boosting (OBBAB). It amounts to (a) subdividing the target into regions that are homogeneous with respect to the maximum total dose and maximum dose per fraction allowed by the anatomy and biological properties of the normal tissue within (or adjacent to) the region in question and (b) treating each region with an individual optimal schedule determined by these constraints. The fact that different regions may be treated to different total dose and dose per fraction mean that the number of fractions may also vary between regions. Numerical evidence suggests that OBBAB produces significantly larger tumor control probability than the corresponding conventional treatments.

The potential role of respiratory motion management and image guidance in the reduction of severe toxicities following stereotactic ablative radiation therapy for patients with centrally located early stage non-small cell lung cancer or lung metastases

Image guidance allows delivery of very high doses of radiation over a few fractions, known as stereotactic ablative radiotherapy (SABR). This treatment is associated with excellent outcome for early stage non-small cell lung cancer and metastases to the lungs. In the delivery of SABR, central location constantly poses a challenge due to the difficulty of adequately sparing critical thoracic structures that are immediately adjacent to the tumor if an ablative dose of radiation is to be delivered to the tumor target. As of current, various respiratory motion management and image guidance strategies can be used to ensure accurate tumor target localization prior and/or during daily treatment, which allows for maximal and safe reduction of set up margins. The incorporation of both may lead to the most optimal normal tissue sparing and the most accurate SABR delivery. Here, the clinical outcome, treatment related toxicities, and the pertinent respiratory motion management/image guidance strategies reported in the current literature on SABR for central lung tumors are reviewed.

Recent advances in radiotherapy for thoracic tumours

Radiation Oncology technology has continued to advance at a rapid rate and is bringing significant benefits to patients. This review outlines some of the advances in technology and radiotherapy treatment of thoracic cancers including brachytherapy, stereotactic radiotherapy, tomotherapy and intensity modulated radiotherapy. The importance of functional imaging with PET and management of movement are highlighted. Most of the discussion relates to non-small cell lung cancer but management of mesothelioma and small cell lung cancer are also covered. This technology has substantial benefits to patients in terms of decreasing toxicity both in the short and longer term.

Design, development of water tank-type lung phantom and dosimetric verification in institutions participating in a phase I study of stereotactic body radiation therapy in patients with T2N0M0 non-small cell lung cancer: Japan Clinical Oncology Group trial (JCOG0702)

A domestic multicenter phase I study of stereotactic body radiotherapy (SBRT) for T2N0M0 non-small cell lung cancer in inoperable patients or elderly patients who refused surgery was initiated as the Japan Clinical Oncology Group trial (JCOG0702) in Japan. Prior to the clinical study, the accuracy of dose calculation in radiation treatment-planning systems was surveyed in participating institutions, and differences in the irradiating dose between the institutions were investigated. We developed a water tank-type lung phantom appropriate for verification of the exposure dose in lung SBRT. Using this water tank-type lung phantom, the dose calculated in the radiation treatment-planning system and the measured dose using a free air ionization chamber and dosimetric film were compared in a visiting survey of the seven institutions participating in the clinical study. In all participating institutions, differences between the calculated and the measured dose in the irradiation plan were as follows: the accuracy of the absolute dose in the center of the simulated tumor measured using a free air ionization chamber was within 2%, the mean gamma value was ≤ 0.47 on gamma analysis following the local dose criteria, and the pass rate was >87% for 3%/3 mm from measurement of dose distribution with dosimetric film. These findings confirmed the accuracy of delivery doses in the institutions participating in the clinical study, so that a study with integration of the institutions could be initiated.

Delayed esophageal perforation from stereotactic body radiation therapy for locally recurrent central nonsmall cell lung cancer

Stereotactic body radiation therapy (SBRT) is a novel form of external beam radiation therapy. It is used to treat early and locally recurrent nonsmall cell lung cancer (NSLC) in medically inoperable patients. It uses high dose, hypofractionated radiotherapy, with targeting of the tumor by precise spatial localization, thus minimizing injury to surrounding tissues. It can be safely used to ablate NSLC in both central and peripheral locations. We present two cases of delayed esophageal perforation after SBRT for locally recurrent central NSLC. The perforations occurred several months after the therapy. They were treated with covered esophageal stents, with mortality, due to the perforation in one of the patients. SBRT should be judiciously used to ablate centrally located NSLC and patients who develop episodes of esophagitis during or after SBRT, need to be closely followed with endoscopy to look for esophageal ulcerations. These ulcers should be closely followed for healing as these may degenerate into full thickness perforations several months after SBRT.

No clinically significant changes in pulmonary function following stereotactic body radiation therapy for early- stage peripheral non-small cell lung cancer: an analysis of RTOG 0236

PURPOSE

To investigate pulmonary function test (PFT) results and arterial blood gas changes (complete PFT) following stereotactic body radiation therapy (SBRT) and to see whether baseline PFT correlates with lung toxicity and overall survival in medically inoperable patients receiving SBRT for early stage, peripheral, non-small cell lung cancer (NSCLC).

METHODS AND MATERIALS

During the 2-year follow-up, PFT data were collected for patients with T1-T2N0M0 peripheral NSCLC who received effectively 18 Gy × 3 in a phase 2 North American multicenter study (Radiation Therapy Oncology Group [RTOG] protocol 0236). Pulmonary toxicity was graded by using the RTOG SBRT pulmonary toxicity scale. Paired Wilcoxon signed rank test, logistic regression model, and Kaplan-Meier method were used for statistical analysis.

RESULTS

At 2 years, mean percentage predicted forced expiratory volume in the first second and diffusing capacity for carbon monoxide declines were 5.8% and 6.3%, respectively, with minimal changes in arterial blood gases and no significant decline in oxygen saturation. Baseline PFT was not predictive of any pulmonary toxicity following SBRT. Whole-lung V5 (the percentage of normal lung tissue receiving 5 Gy), V10, V20, and mean dose to the whole lung were almost identical between patients who developed pneumonitis and patients who were pneumonitis-free. Poor baseline PFT did not predict decreased overall survival. Patients with poor baseline PFT as the reason for medical inoperability had higher median and overall survival rates than patients with normal baseline PFT values but with cardiac morbidity.

CONCLUSIONS

Poor baseline PFT did not appear to predict pulmonary toxicity or decreased overall survival after SBRT in this medically inoperable population. Poor baseline PFT alone should not be used to exclude patients with early stage lung cancer from treatment with SBRT.

A radiation oncologist's and thoracic surgeon's view on the role of stereotactic ablative radiotherapy for operable lung cancer

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 using prospective multi-institutional trials. We review and update the evidence for use of stereotactic ablative radiotherapy in medically inoperable patients with stage I lung cancer, and its possible extension of use to operable patients, from the perspectives of an experienced radiation oncologist and a thoracic surgeon.

Stereotactic radiotherapy for pulmonary metastases

The most common treatment of pulmonary metastasis for solid tumors employs systemic chemotherapy, hormonal therapy, or biologic agents. Some series have suggested that aggressive surgical resection of pulmonary metastasis may improve patient outcomes in terms of quality of life and overall survival. Recently, data from clinical trials and retrospective series support the use of aggressive local control with high conformal dose radiotherapy (stereotactic body radiation therapy) in patients with limited metastases or oligometastases. Further evidence suggests that these patients represent a distinct clinical and biological class of patients. This review focuses on the role of ablative doses of radiotherapy in the treatment of pulmonary metastases. Specifically we discuss the rationale, treatment delivery, and local control that have led to the ongoing randomized clinical trials attempting to demonstrate a benefit over the current palliative standard of care.

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.

Clinical introduction of Monte Carlo treatment planning for lung stereotactic body radiotherapy

The purpose of this study was to investigate the impact of Monte Carlo (MC) calculations and optimized dose definitions in stereotactic body radiotherapy (SBRT) for lung cancer patients. We used a retrospective patient review and basic virtual phantom to determine dose prescriptions. Fifty-three patients underwent SBRT. A basic virtual phantom had a gross tumor volume (GTV) of 10.0 mm with equivalent water density of 1.0 g/cm3, which was surrounded by equivalent lung surrounding the GTV of 0.25 g/cm3. D95 of the planning target volume (PTV) and D99 of the GTV were evaluated with different GTV sizes (5.0 to 30.0 mm) and different lung densities (0.05 to 0.45 g/cm3). Prescribed dose was defined as 95% of the PTV should receive 100% of the dose (48 Gy/4 fractions) using pencil beam (PB) calculation and recalculated using MC calculation. In the patient study, average doses to the D95 of the PTV and D99 of the GTV using the MC calculation plan were 19.9% and 10.2% lower than those by the PB calculation plan, respectively. In the phantom study, decreased doses to the D95 of the PTV and D99 of the GTV using the MC calculation plan were accompanied with changes GTV size from 30.0to 5.0 mm, which was decreased from 8.4% to 19.6% for the PTV and from 17.4%to 27.5% for the GTV. Similar results were seen with changes in lung density from 0.45 to 0.05 g/cm3, with doses to the D95 of the PTV and D99 of the GTV were decreased from 12.8% to 59.0% and from 7.6% to 44.8%, respectively. The decrease in dose to the PTV with MC calculation was strongly dependent on lung density. We suggest that dose definition to the GTV for lung cancer SBRT be optimized using MC calculation. Our current clinical protocol for lung SBRT is based on a prescribed dose of 44 Gy in 4 fractions to the GTV using MC calculation.

Lung

The lungs are particularly sensitive to RT, and are often the primary dose-limiting structure during thoracic therapy.

The alveolar/capillary units and pneumocytes within the alveoli appear to be particularly sensitive to RT.

Hypoxia may be important in the underlying physiology of RT-associated lung injury.

The cytokine transforming growth factor-beta (TGF-β), plays an important role in the development of RT-induced fibrosis.

The histopathological changes observed in the lung after RT are broadly characterized as diffuse alveolar damage.

The interaction between pre-treatment PFTs and the risk of symptomatic lung injury is complex. Similarly, the link between changes in PFTs and the development of symptoms is uncertain.

The incidence of symptomatic lung injury increases with increase in most dosimetric parameters. The mean lung dose (MLD) and V20 have been the most-often considered parameters. MLD might be a preferable metric since it considers the entire 3D dose distribution.

Radiation to the lower lobes appears to be more often associated with clinical symptoms than is radiation to the upper lobes. This might be related to incidental cardiac irradiation. In pre-clinical models, there appears to be a complex interaction between lung and heart irradiation.

TGF-β has been suggested in several studies to predict for RT-induced lung injury, but the data are still somewhat inconsistent.

Oral prednisone (Salinas and Winterbauer 1995), typically 40–60 mg daily for 1–2 weeks with a slow taper, is usually effective in treating pneumonitis. There are no widely accepted treatments for fibrosis.

A number of chemotherapeutic agents have been suggested to be associated with a range of pulmonary toxicities.

Dosimetric comparison of patient setup strategies in stereotactic body radiation therapy for lung cancer

PURPOSE

In this work, the authors retrospectively compared the accumulated dose over the treatment course for stereotactic body radiation therapy (SBRT) of lung cancer for three patient setup strategies.

METHODS

Ten patients who underwent lung SBRT were selected for this study. At each fraction, patients were immobilized using a vacuum cushion and were CT scanned. Treatment plans were performed on the simulation CT. The planning target volume (PTV) was created by adding a 5-mm uniform margin to the internal target volume derived from the 4DCT. All plans were normalized such that 99% of the PTV received 60 Gy. The plan parameters were copied onto the daily CT images for dose recalculation under three setup scenarios: skin marker, bony structure, and soft tissue based alignments. The accumulated dose was calculated by summing the dose at each fraction along the trajectory of a voxel over the treatment course through deformable image registration of each CT with the planning CT. The accumulated doses were analyzed for the comparison of setup accuracy.

RESULTS

The tumor volume receiving 60 Gy was 91.7 ± 17.9%, 74.1 ± 39.1%, and 99.6 ± 1.3% for setup using skin marks, bony structures, and soft tissue, respectively. The isodose line covering 100% of the GTV was 55.5 ± 7.1, 42.1 ± 16.0, and 64.3 ± 7.1 Gy, respectively. The corresponding average biologically effective dose of the tumor was 237.3 ± 29.4, 207.4 ± 61.2, and 258.3 ± 17.7 Gy, respectively. The differences in lung biologically effective dose, mean dose, and V20 between the setup scenarios were insignificant.

CONCLUSIONS

The authors' results suggest that skin marks and bony structure are insufficient for aligning patients in lung SBRT. Soft tissue based alignment is needed to match the prescribed dose delivered to the tumors.

Optimization of normalized prescription isodose selection for stereotactic body radiation therapy: conventional vs robotic linac

PURPOSE

Although modern technology has allowed for target dose escalation by minimizing normal tissue dose, the dose delivered to a tumor and surrounding tissues still depends largely on the inherent characteristics of the radiation delivery platform. This work aims to determine the optimal prescription isodose line that minimizes normal tissue irradiation for stereotactic body radiation therapy (SBRT) for a conventional linear accelerator and a robotic delivery platform.

METHODS

Spherical targets with diameters of 10, 20, and 30 mm were constructed in the lungs and liver of a computer based digital torso phantom which simulates respiratory and cardiac motion. Normal tissue contours included normal lung, normal liver, and a concentric 10 mm shell of normal tissue extending from the spherical target surface. For linac planning, noncoplanar, nonopposing three dimensional (3D) conformal beams were designed, and variable prescription isodose lines were achieved by varying the MLC block margin. For CyberKnife planning, variable prescription isodose lines were achieved by inverse planning. True 4D dose calculations were used for the moving target and surrounding tissue based on each of ten phases of a 4D CT dataset. Doses of 60 Gy in three fractions were prescribed to cover 95% of the target tumor. Commonly used conformality, dosimetric, and radiobiological indices for lung and liver SBRT were used to compare different plans and determine the optimally prescribed isodose line for each treatment platform.

RESULTS

For linac plans, the average optimal prescription isodose line based on all indices evaluated occurred between 59% and 69% for lung tumors and between 67% and 77% for liver tumors depending on the tumor size. CyberKnife plans had average optimal prescription isodose lines occurring between 40% and 48% for lung tumors and between 41% and 42% depending on the tumor size. However, prescription isodose lines under 50% are not advised to prevent large heterogeneous dose distributions within the target.

CONCLUSIONS

The choice of prescription isodose line was shown to have a significant impact on parameters commonly used as constraints for lung and liver SBRT treatment planning for both linac-based and CyberKnife delivery platforms. By methodically choosing the prescription isodose line, normal tissue toxicities from SBRT may be reduced.

The RSSearch™ Registry: patterns of care and outcomes research on patients treated with stereotactic radiosurgery and stereotactic body radiotherapy

BACKGROUND

The RSSearch™ Registry is a multi-institutional, observational, ongoing registry established to standardize data collection from patients treated with stereotactic radiosurgery (SRS) and/or stereotactic body radiotherapy (SBRT). This report describes the design, patient demographics, lesion characteristics, and SRS/SBRT treatment patterns in RSSearch™. Illustrative patient-related outcomes are also presented for two common treatment sites--brain metastases and liver metastases.

MATERIALS AND METHODS

Thirty-nine US centers participated in RSSearch™. Patients screened for SRS/SBRT were eligible to be enrolled. Descriptive analyses were performed to assess patient characteristics, physician treatment practices, and clinical outcomes. Kaplan-Meier analysis was used to determine overall survival (OS), local progression-free (LPFS), and distant disease-free survival (DDFS).

RESULTS

From January, 2008-January, 2013, 11,457 patients were enrolled. The median age was 67 years (range 7-100 years); 51% male and 49% female. Forty-six percent had no prior treatment, 22% had received chemotherapy, 19% radiation therapy and 17% surgery. There were 11,820 lesions from 65 treatment locations; 54% extracranial and 46% intracranial. The most common treatment locations were brain/cranial nerve/spinal cord, lung, prostate and liver. Metastatic lesions accounted for the majority of cases (41.6%), followed by primary malignant (32.9%), benign (10.9%), recurrent (9.4%), and functional diseases (4.3%). SRS/SBRT was used with a curative intent in 39.8% and palliative care in 44.8% of cases. The median dose for all lesions was 30 Gy (range < 1-96.7 Gy) delivered in a median number of 3 fractions. The median dose for lesions in the brain/cranial nerve/spinal cord, lung, liver, pancreas and prostate was 24, 54, 45, 29 and 36.25 Gy, respectively. In a subset analysis of 799 patients with 952 brain metastases, median OS was 8 months. For patients with a Karnofsky performance score (KPS) > 70, OS was 11 months vs. 4 months for KPS ≤ 70. Six-month and 12-month local control was 79% and 61%, respectively for patients with KPS ≤ 70, and 85% and 74%, respectively for patients with KPS > 70. In a second subset analysis including 174 patients with 204 liver metastases, median OS was 22 months. At 1-year, LPFS and DDFS rates were 74% and 53%, respectively.

LPFS CONCLUSION

This study demonstrates that collective patterns of care and outcomes research for SRS/SBRT can be performed and reported from data entered by users in a common database. The RSSearch™ dataset represents SRS/SBRT practices in a real world setting, providing a useful resource for expanding knowledge of SRS/SBRT treatment patterns and outcomes and generating robust hypotheses for randomized clinical studies.

What would be the most appropriate α/β ratio in the setting of stereotactic body radiation therapy for early stage non-small cell lung cancer

We hypothesize that the correlation between the radiation dose expressed as the biologically effective dose (BED) and the clinical endpoints will correlate better as the value of the α/β ratio is increased to >10 Gy, which theoretically minimizes the overestimation of the dose potency associated with the linear quadratic (LQ) formula in the setting of stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer (NSCLC). A search was conducted in the PubMed electronic databases in August 2011. In the studies analyzed, increasing the α/β ratio is associated with an increase in the strength of the correlation between isocenter BED and local control, especially in the studies with median followup of ≥24 months, for which Spearman's correlation coefficients of 0.74-0.76 were achieved for α/β of 20 Gy, 30 Gy, and 50 Gy (P =  0.007-0.008). A trend toward statistical significance was observed for the correlation of isocenter BED and the 2-year overall survival when an α/β of 20 Gy was used approached statistical significance (P = 0.073). Our results suggest that an α/β > 10 Gy may be more appropriate for the prediction of dose response in the setting of lung SBRT.

Correlation of dose computed using different algorithms with local control following stereotactic ablative radiotherapy (SABR)-based treatment of non-small-cell lung cancer

PURPOSE

To retrospectively compute dose distributions for lung cancer patients treated with SABR, and to correlate dose distributions with outcome using a tumor control probability (TCP) model.

METHODS

Treatment plans for 133 NSCLC patients treated using 12 Gy/fxn × 4 (BED=106 Gy), and planned using a pencil-beam (1D-equivalent-path-length, EPL-1D) algorithm were retrospectively re-calculated using model-based algorithms (including convolution/superposition, Monte Carlo). 4D imaging was performed to manage motion. TCP was computed using the Marsden model and associations between dose and outcome were inferred.

RESULTS

Mean D95 reductions of 20% (max.=33%) were noted with model-based algorithms (relative to EPL-1D) for the smallest tumors (PTV<20 cm(3)), corresponding to actual delivered D95 BEDs of ≈ 60-85 Gy. For larger tumors (PTV>100 cm(3)), D95 reductions were ≈ 10% (BED>100 Gy). Mean lung doses (MLDs) were 15% lower for model-based algorithms for PTVs<20 cm(3). No correlation between tumor size and 2-year local control rate was observed clinically, consistent with TCP calculations, both of which were ≈ 90% across all PTV bins.

CONCLUSION

Results suggest that similar control rates might be achieved for smaller tumors using lower BEDs relative to larger tumors. However, more studies with larger patient cohorts are necessary to confirm this possible finding.

Dosimetric errors during treatment of centrally located lung tumors with stereotactic body radiation therapy: Monte Carlo evaluation of tissue inhomogeneity corrections

Early experience with stereotactic body radiation therapy (SBRT) of centrally located lung tumors indicated increased rate of high-grade toxicity in the lungs. These clinical results were based on treatment plans that were computed using pencil beam-like algorithms and without tissue inhomogeneity corrections. In this study, we evaluated the dosimetric errors in plans with and without inhomogeneity corrections and with planning target volumes (PTVs) that were within the zone of the proximal bronchial tree (BT). For 10 patients, the PTV, lungs, and sections of the BT either inside or within 2cm of the PTV were delineated. Two treatment plans were generated for each patient using the following dose-calculation methods: (1) pencil beam (PB) algorithm without inhomogeneity correction (IC) (PB - IC) and (2) PB with inhomogeneity correction (PB + IC). Both plans had identical beam geometry but different beam segment shapes and monitor units (MU) to achieve similar conformal dose coverage of PTV. To obtain the baseline dose distributions, each plan was recalculated using a Monte Carlo (MC) algorithm by keeping MUs the same in the respective plans. The median maximum dose to the proximal BT and PTV dose coverage in the PB + IC plans were overestimated by 8% and 11%, respectively. However, the median maximum dose to the proximal BT and PTV dose coverage in PB - IC plans were underestimated by 15% and 9%. Similar trends were observed in low-dose regions of the lung within the irradiated volume. Our study indicates that dosimetric bias introduced by unit tissue density plans cannot be characterized as underestimation or overestimation of dose without taking the tumor location into account. This issue should be considered when analyzing clinical toxicity data from early lung SBRT trials that utilized unit tissue density for dose calculations.

Strategies for optimizing the response of cancer and normal tissues to radiation

Approximately 50% of all patients with cancer receive radiation therapy at some point during the course of their treatment, and the majority of these patients are treated with curative intent. Despite recent advances in the planning of radiation treatment and the delivery of image-guided radiation therapy, acute toxicity and potential long-term side effects often limit the ability to deliver a sufficient dose of radiation to control tumours locally. In the past two decades, a better understanding of the hallmarks of cancer and the discovery of specific signalling pathways by which cells respond to radiation have provided new opportunities to design molecularly targeted therapies to increase the therapeutic window of radiation therapy. Here, we review efforts to develop approaches that could improve outcomes with radiation therapy by increasing the probability of tumour cure or by decreasing normal tissue toxicity.

Stereotactic ablative radiotherapy in the UK: current status and developments

Stereotactic ablative radiotherapy (SABR) has developed from the principles and techniques used in the stereotactic radiosurgery treatment of brain metastases. Advances in computer technology, imaging, planning and treatment delivery and evidence from retrospective analysis of single- and multi-institutional early-phase studies have established SABR in the treatment of medically inoperable early lung cancer. Effective multidisciplinary team working is crucial to safe delivery of SABR. The variation in patient selection, radiotherapy planning and delivery techniques has led to a collective approach to SABR implementation across the UK. Centres developing the technique are represented in the UK SABR Consortium, which is supported by the relevant UK professional bodies and represents a platform to develop extracranial SABR across the UK. The uptake of SABR in the UK has been slowed by workforce issues, but at least 15 centres are currently delivering treatment with over 500 patients treated using UK SABR Consortium guidance. A mentoring program is being piloted helping new centres to develop their programs, and over 30 UK centres are expected to be offering SABR treatment by the end of 2014. The use of consistent guidance for patient selection, treatment planning and delivery in the UK gives the opportunity to collect and audit toxicity and outcome across the centres, contributing to the internationally reported SABR experience. Having established this service in the UK, the development of SABR through clinical research is a priority, and with input from the Radiotherapy Trials Quality Assurance Group, the UK is developing a national study program that includes participation in international trials.

Stereotactic body radiotherapy in patients with stage I non-small-cell lung cancer aged 75 years and older: retrospective results from a multicenter consortium

BACKGROUND

This study was a retrospective analysis of elderly patients treated with stereotactic body radiotherapy (SBRT) in the setting of a multi-institutional consortium.

PATIENTS AND METHODS

Three institutions pooled data on patients aged ≥ 75 years who received SBRT for stage I non-small-cell lung cancer (NSCLC). Forty-seven tumors in 46 patients were analyzed in patients aged 75 to 92 years (median, 82 years). Treatment was delivered during 2007 to 2009, with a median follow-up of 12.4 months. All patients underwent staging positron emission tomography-computed tomography (PET-CT), and 87% of tumors were confirmed by biopsy results. Total doses were 35 to 60 Gy, mainly in 3 to 5 fractions. All tumors were treated using a linear accelerator, with 96% of patients receiving 3-dimensional (3D) conformal RT and 4% undergoing intensity modulated RT (IMRT).

RESULTS

At the time of analysis, the local failure rate was 2% (1 of 47). The regional failure rate was 9% (4 of 47). The distant failure rate was 6% (3 of 47). The combined failure rate was 15% (7 of 47) because 1 patient experienced both regional and distant failure. Among 20 tumors with any acute toxicity, there were no ≥ grade 3 toxicities. Pneumonitis (n = 10) grades 1 (n = 3) and 2 (n = 2) was seen in 15% and 10% of patients, respectively; these data were missing for 25% of patients.

CONCLUSION

SBRT in patients aged ≥ 75 years with stage I NSCLC proved tolerable, with toxicity rates comparable to those in younger patients. Excellent rates of local, regional, and distant control were achieved at a median follow-up of 12.4 months. This patient population represents a rapidly growing segment of the early lung cancer population, and SBRT appears to be a safe and effective treatment option for patients who are not optimal candidates for surgery.

Stereotactic body radiation therapy for stage I non-small-cell lung cancer: a historical overview of clinical studies

Because of difficulties with stabilization, breathing motion and dosimetry, stereotactic body radiotherapy for lung cancer has only been practiced for the past 15 years. However, a large amount of case data has rapidly been accumulated in recent years. Stereotactic body radiotherapy for Stage I non-small-cell lung cancer has been actively investigated in inoperable patients since around 1995, and a number of clinical trials have been undertaken. Early studies from 2001 presented a 3-year local control rate of 94% and a 3-year overall survival rate of 66% for patients receiving 50-60 Gy in 10 fractions. Another study in 2005, using 48 Gy in four fractions, presented a 3-year local control rate of 98% and 3-year overall survival rates of 83% for Stage IA patients and 72% for Stage IB patients. A multi-institutional study showed favorable local control and survival rates in a group receiving a biologically effective dose of 100 Gy. A dose-escalation study in the USA suggested a maximum tolerated dose of 60 Gy in three fractions. A Phase II clinical trial (RTOG0236) followed, with a reported 3-year local control rate of 98% and a 3-year overall survival rate of 56% for patients who received 60 Gy in three fractions. A Japanese Phase II clinical trial (JCOG0403) investigated a dose of 48 Gy in four fractions among 165 Stage IA patients, showing a 3-year survival rate of 76% and a 3-year locally progression-free survival rate of 69% for the operable group. An overview of past clinical trials in stereotactic body radiotherapy for Stage I non-small-cell lung cancer and current issues is presented and discussed.

Hope for progress after 40 years of futility? Novel approaches in the treatment of advanced stage III and IV non-small-cell-lung cancer: Stereotactic body radiation therapy, mediastinal lymphadenectomy, and novel systemic therapy

Non-small-cell lung cancer (NSCLC) remains a leading cause of cancer mortality. The majority of patients present with advanced (stage III-IV) disease. Such patients are treated with a variety of therapies including surgery, radiation, and chemotherapy. Despite decades of work, however, overall survival in this group has been resistant to any substantial improvement. This review briefly details the evolution to the current standard of care for advanced NSCLC, advances in systemic therapy, and novel techniques (stereotactic body radiation therapy [SBRT], and transcervical extended mediastinal lymphadenectomy [TEMLA] or video-assisted mediastinal lymphadenectomy [VAMLA]) that have been used in localized NSCLC. The utility of these techniques in advanced stage therapy and potential methods of combining these novel techniques with systemic therapy to improve survival are discussed.

Is radiofrequency ablation or stereotactic ablative radiotherapy the best treatment for radically treatable primary lung cancer unfit for surgery?

A best evidence topic was constructed according to a structured protocol. The question addressed was whether radiofrequency (RF) offers better results than stereotactic ablative therapy in patients suffering from primary non-small-cell lung cancer (NSCLC) unfit for surgery. Of the 90 papers found using a report search for RF, 5 represented the best evidence to answer this clinical question. Concerning stereotactic ablative therapy, of the 112 papers found, 10 represented the best evidence to answer this clinical question. A manual search of the reference lists permitted us to include seven more articles. The authors, journal, date, country of publication, study type, group studied, relevant outcomes and results of these papers are given. We conclude that, on the whole, the 23 retrieved studies clearly support the use of stereotactic ablative therapy rather than RF in patients suffering from primary NSCLC unfit for surgery. Indeed, stereotactic ablative therapy offered a 5-year local control rate varying between 83 and 89.5%, whereas the local control rate after RF ranges from 58 to 68%, with a short follow-up of ∼18 months. Furthermore, both overall survival and cancer-specific survival were better with stereotactic ablative therapy, with a 3-year overall survival ranging from 38 to 84.7% and the 3-year cancer-specific survival from 64 to 88%, whereas the 3-year OS, only reported in two studies, ranged from 47 to 74% for RF. Moreover, the post-interventional morbidity was superior for RF ranging from 33 to 100% (mainly composed by pneumothorax), whereas radiation pneumonitis and rib fracture, ranging, respectively, from 3 to 38% and 1.6 to 4%, were the primary complications following stereotactic ablative therapy. Hence, the current evidence shows that stereotactic ablative therapy is a safe and effective procedure and should be proposed first to patients suffering from primary NSCLC unfit for surgery. However, the published evidence is quite limited, mainly based on small studies of <100 patients. Moreover, so far there is no blind, prospective control, randomized study comparing these two techniques. Consequently, despite the encouragement of these preliminary results, they must be interpreted with caution.