Hypofractionated stereotactic radiotherapy for medically inoperable stage I non-small cell lung cancer--report on clinical outcome and dose to critical organs

Clinical Evaluation of Fiducial Marker Pre-Planning for Virtual Bronchoscopic Navigation Implantation in Lung Tumour Patients Treated With CyberKnife

Purpose

For the treatment of invisible lung tumours with CyberKnife (CK), fiducial markers (FMs) were implanted as an internal surrogate under virtual bronchoscopic navigation (VBN). This research aims to study the benefits of introducing an additional procedure in assigning the optimal FM positions using a pre-procedure planning system and performing virtual simulation before implantation. The objectives were 1) to reduce the duration of the FM implantation procedure, 2) to reduce the radiation exposure in dose area product (DAP) (dGy*cm²) to patients, and 3) to increase the number of FMs implanted around the tumour.

Methods and Materials

This study is retrospective, single-centre, and observational in nature. A total of 32 patients were divided into two groups. In Group 1, 18 patients underwent conventional VBN FM implantation. In Group 2, 14 patients underwent additional pre-procedure planning and simulation. The steps of pre-procedure planning include 1) importing CT images into the treatment planning system (Eclipse, Varian Medical Systems, Inc.) and delineating five to six FMs in their ideal virtual positions and 2) copying the FM configuration into VBN planning software (LungPoint Bronchus Medical, Inc.) for verification and simulation. Finally, the verified FMs were deployed through VBN with the guidance of the LungPoint planning software.

Results

A total of 162 FMs were implanted among 35 lesions in 32 patients aged from 37 to 92 (median = 66; 16 men and 16 women). Results showed that 1) the average FM insertion time was shortened from 41 min (SD = 2.05) to 23 min (SD = 1.25), p = 0.00; 2) the average absorbed dose of patients in DAP was decreased from 67.4 cGy*cm² (SD = 14.48) to 25.3 cGy*cm² (SD = 3.82), p = 0.01 (1-tailed); and 3) the average number of FMs implanted around the tumour was increased from 4.7 (SD = 0.84) to 5.6 (SD = 0.76), p = 0.00 (1-tailed).

Conclusion

Pre-procedure planning reduces the FM implantation duration from 41.1 to 22.9 min, reduces the radiation exposure in DAP from 67.4 to 25.3 dGy*cm², and increases the number of FMs inserted around the tumour from 4.7 to 5.6.

Evaluation of dose distribution differences from five algorithms implemented in three commercial treatment planning systems for lung SBRT

Early stage lung cancer is increasingly being treated using stereotactic body radiation therapy (SBRT). Several advanced treatment planning algorithms are now available in various commercial treatment planning systems. This work compares the dose distributions calculated for the same treatment plan using, five algorithms, in three different treatment planning systems. All plans were normalized to ensure the prescription dose covers 95% of the planning target volume (PTV). Dose to the planning target volume (PTV) was compared using near-minimum dose (D_98%), near-maximum dose (D_2%) and dose homogeneity, while dose fall-off was compared using D_2cm and R₅₀. Dose to the lung was compared using V_5Gy, V_20Gy and mean lung dose. Statistical analysis shows that dose distributions calculated using Eclipse's Acuros XB and RayStation's Monte Carlo were significantly different from the other dose distributions for the PTV dose parameters investigated. For lung dosimetric parameters, this difference persisted for volumetric modulated arc therapy (VMAT) plans but not for conformal arc plans. While normal tissue complication probability (NTCP) differences were significant for some of the algorithms for VMAT delivery approaches, they were not significantly different for any algorithm for conformal arc plans. All parameters investigated here were within 5% between all algorithms. The results show that, while some small dosimetric differences can be expected around the PTV, the dose distribution to the rest of the treatment area, especially the lungs, should not be clinically-relevant when switching between one of the five algorithms investigated.

Effect of Tumor Location and Dosimetric Predictors for Chest Wall Toxicity in Single-Fraction Stereotactic Body Radiation Therapy for Stage I Non-Small Cell Lung Cancer

PURPOSE

Dosimetric parameters to limit chest wall toxicity (CWT) are not well defined in single-fraction (SF) stereotactic body radiation therapy (SBRT) phase 2 trials. We sought to determine the relationship of tumor location and dosimetric parameters with CWT for SF-SBRT.

METHODS AND MATERIALS

From a prospective registry of 1462 patients, we identified patients treated with 30 Gy or 34 Gy. Gross tumor volume was measured as abutting, ≤1 cm, 1 to 2 cm, or >2 cm from the chest wall. CWT was prospectively graded according to Common Terminology Criteria for Adverse Events version 3.0, with grade 2 requiring medical therapy, grade 3 requiring procedural intervention, and grade 4 being disabling pain. Grade 1 CWT or radiographic rib fracture was not included. Logistic regression analysis was used to identify the parameters associated with CWT and calculate the probability of CWT with dose.

RESULTS

This study included 146 lesions. The median follow-up time was 23.8 months. The 5-year local control, distant metastasis, and overall survival rates were 91.8%, 19.2%, and 28.7%, respectively. Grade 2 to 4 CWT was 30.6% for lesions abutting the chest wall, 8.2% for ≤1 cm from the chest wall, 3.8% for 1 to 2 cm from the chest wall, and 5.7% for >2 cm from the chest wall. Grade ≥3 CWT was 1.4%. Tumor abutment (odds ratio [OR]: 6.5; P = .0005), body mass index (OR: 1.1; P = .02), rib D1cc (OR: 1.01/Gy; P = .03), chest wall D1cc (OR: 1.08/Gy; P = .03), and chest wall D5cc (OR: 1.10/Gy; P = .01) were significant predictors for CWT on univariate analysis. Tumor abutment was significant for CWT (OR: 7.5; P = .007) on multivariate analysis. The probability of CWT was 15% with chest wall D5cc at 27.2 Gy and rib D1cc at 30.2 Gy.

CONCLUSIONS

The rate of CWT with SF-SBRT is similar to the rates published for fractionated SBRT, with most CWT being low grade. Tumor location relative to the chest wall is not a contraindication to SF-SBRT, but the rates increase significantly with abutment. Rib D1cc and chest wall D1cc and D5cc may be used as predictors of CWT.

Short-term outcomes and clinical efficacy of stereotactic body radiation therapy (SBRT) in treatment of adrenal gland metastases from lung cancer

Background

To assess the efficacy and safety of stereotactic body radiation therapy (SBRT) in the management of adrenal gland metastases (AGMs) from lung cancer. Moreover, it is the first two-institutional experience and the largest-to-date study to report the safety and efficacy of SBRT for inoperable AGM from lung cancer.

Methods

In this retrospective study, 30 patients (27 males, 3 females) with 32 AGMs were treated by SBRT from October 2006 to June 2016. Of these, 11 patients were treated with the intent of controlling all known metastatic sites and 19 for palliation of bulky AGMs. Follow-up was performed every 3 months for evaluations of efficacy and safety. Factors predictive of overall survival (OS) and local control (LC) were identified with univariate and then multivariate analysis.

Results

Median follow-up time was 10.7 months (2.9–96.4 months). The complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD) rates were 23.3%, 33.3%, 33.3% and 16.7% respectively. The 6-month, 1, and 2-year LC rates were 96.9%, 96.9%, and 72.7% respectively. Additionally, the 6-month, 1, and 2-year OS rates were 85.6%, 58.1%, and 54.0% respectively while 6-month, 1, and 2-year progression free survival (PFS) rates were 39.5%, 24.6%, and 8.2%, respectively. All the patients with cancer-induced pain (8 with abdominal pain and 6 with lumbar back pain) had significant alleviations after SBRT. The treatment was well tolerated with only 1 patient reporting grade-3 diarrhoea. No predictors of OS and LC were found after multivariate analysis, while it was demonstrated that biologic equivalent dose (BED₁₀, α/β = 10) ≥85.5Gy (P = 0.007) and gross tumor volume < 30 ml (P = 0.003) correlated with LC only after univariate analysis.

Conclusion

SBRT is a safe and effective treatment modality in the management of AGMs from lung cancer with high LC rates and acceptable toxicity.

Dosimetric differences between local failure and local controlled non-small cell lung cancer patients treated with stereotactic body radiotherapy: A matched-pair study

INTRODUCTION

Concerns were raised about the accuracy of pencil beam (PB) calculation and potential underdosing of medically inoperable non-small cell lung cancer (NSCLC) treated with stereotactic body radiation therapy (SBRT). From our institutional series, we designed a matched-pair study where each local failure and controlled patient was matched based upon several clinical factors, to investigate the dose difference between the matched-pair.

METHODS

Eighteen pairs of NSCLC patients, treated with 50 Gy in five fractions, were selected. These patients were matched based on treatment intent, tumour size, histology and clinical follow-up. All PB calculated clinical plans were retrospectively recalculated with a MC algorithm. The D₉₉ and D_Mean of the gross tumour volume (GTV) and D₉₅ and D_Mean of the planning tumour volume (PTV) from PB and Monte Carlo (MC) calculation were compared between local failures and controls using the Mann-Whitney test.

RESULTS

The mean PB calculated D95 of PTV was 50.4 Gy for both failures and controls (P = 0.85), indicating no planning differences between the groups. From MC calculations, the mean (±SD) of GTV D₉₉ , GTV D_Mean , PTV D₉₅ , PTV D_Mean were 47.6 ± 2.6/46.3 ± 2.4, 50.4 ± 2.1/49.8 ± 1.6, 44.4 ± 2.7/43.6 ± 3.1, 48.7 ± 2.4/48.2 ± 2.4 Gy for failure/controlled groups, respectively, and there was no significant difference between two groups (all P > 0.1). The dose differences between MC and PB calculations were in agreement with other literatures and there was no significant difference between two groups.

CONCLUSIONS

While PB algorithms may overestimate tumour doses relative to MC algorithms, our matched-pair study did not find dose differences between local failure and local controlled cases.

Comparison of particle beam therapy and stereotactic body radiotherapy for early stage non-small cell lung cancer: A systematic review and hypothesis-generating meta-analysis

PURPOSE

To assess hypo-fractionated particle beam therapy (PBT)'s efficacy relative to that of photon stereotactic body radiotherapy (SBRT) for early stage (ES) non-small cell lung cancer (NSCLC).

METHODS

Eligible studies were identified through extensive searches of the PubMed, Medline, Google-scholar, and Cochrane library databases from 2000 to 2016. Original English publications of ES NSCLC were included. A meta-analysis was performed to compare the survival outcome, toxicity profile, and patterns of failure following each treatment.

RESULTS

72 SBRT studies and 9 hypo-fractionated PBT studies (mostly single-arm) were included. PBT was associated with improved overall survival (OS; p=0.005) and progression-free survival (PFS; p=0.01) in the univariate meta-analysis. The OS benefit did not reach its statistical significance after inclusion of operability into the final multivariate meta-analysis (p=0.11); while the 3-year local control (LC) still favored PBT (p=0.03).

CONCLUSION

Although hypo-fractionated PBT may lead to additional clinical benefit when compared with photon SBRT, no statistically significant survival benefit from PBT over SBRT was observed in the treatment of ES NSCLC in this hypothesis-generating meta-analysis after adjusting for potential confounding variables.

Consequences of Referral Time and Volume Doubling Time in Inoperable Patients With Early Stage Lung Cancer

BACKGROUND

Inoperable patients with early stage lung cancer are referred late. The purpose was to calculate the referral time and the volume doubling time (VDT), and to investigate its consequence with regard to staging and survival in 117 inoperable patients with early stage lung cancer treated with stereotactic body radiotherapy.

MATERIALS AND METHODS

Tumor VDT was calculated using the modified Schwartz formula of exponential growth model and was on the basis of volumes measured on initial diagnostic computed tomography (CT) scans and the planning CT scan. VDT was defined as fast (<100 days), moderate (100-249 days), slow (250-399 days), and no growth (≥400 days). The referral time is the time between the diagnostic CT scan and the radiotherapy planning CT scan.

RESULTS

The median referral time was 86 days. The VDT was fast in 53 patients [45%] of tumors. No significant difference in VDT was found between different tumor or patient characteristics. Patients with T1 tumors that progressed to T2 had a significant worse median survival (P = .01). The overall survival at 5 years according to VDT was 21% for fast-growing tumors, 19% for moderate growth, 31% for slow, and 46% for no growth.

CONCLUSION

The median referral time was almost 3 months. VDT was considered as fast in almost half of tumors examined. This resulted in significant growth and upstaging in 35% of the tumors, with a significant worse survival if T1 tumors progressed to T2 tumors. Therefore, medically inoperable patients should also be offered a fast workup and referral.

Robotic Radiosurgery for Adrenal Gland Metastases

Introduction

The purpose of this study was to investigate the safety and efficacy of CyberKnife (CK) robotic radiosurgery for treatment of adrenal metastases.

Methods

We performed a retrospective analysis of 23 patients with adrenal metastases who had been treated with CK between October 2006 and December 2015. Fifteen patients received chemotherapy prior to radiosurgery, all patients underwent computer tomography (CT) fluoroscopically guided percutaneous placement of one to three gold fiducials into the adrenal gland. Nineteen patients were selected for single-fraction radiosurgery with a median dose of 22 Gy, four patients were treated in three fractions with a median dose of 13.5 Gy.

Results

Median follow-up time was 23.6 months. Four patients (17%) experienced local relapse during the evaluation period with a mean time of 19 months to tumor progression. The actuarial local tumor control rate was 95% after one year and 81% after two years. Three of the four patients with local recurrence were retreated with CK radiosurgery. Dynamic tumor tracking enabled accurate treatment with correlation errors less than 2 mm, despite extensive respiration-induced target motion up to 22 mm. Apart from nausea directly after treatment in five patients, we observed no early or late treatment-related side effects.

Conclusions

Single fraction robotic radiosurgery for adrenal gland metastases is a safe and effective treatment option for patients who are not eligible for surgical resection.

Effect of image-guided hypofractionated stereotactic radiotherapy on peripheral non-small-cell lung cancer

The objective of this study was to compare the effects of image-guided hypofractionated radiotherapy and conventional fractionated radiotherapy on non-small-cell lung cancer (NSCLC). Fifty stage- and age-matched cases with NSCLC were randomly divided into two groups (A and B). There were 23 cases in group A and 27 cases in group B. Image-guided radiotherapy (IGRT) and stereotactic radiotherapy were conjugately applied to the patients in group A. Group A patients underwent hypofractionated radiotherapy (6–8 Gy/time) three times per week, with a total dose of 64–66 Gy; group B received conventional fractionated radiotherapy, with a total dose of 68–70 Gy five times per week. In group A, 1-year and 2-year local failure survival rate and 1-year local failure-free survival rate were significantly higher than in group B (P<0.05). The local failure rate (P<0.05) and distant metastasis rate (P>0.05) were lower in group A than in group B. The overall survival rate of group A was significantly higher than that of group B (P=0.03), and the survival rate at 1 year was 87% vs 63%, (P<0.05). The median survival time of group A was longer than that of group B. There was no significant difference in the incidence of complications between the two groups (P>0.05). Compared with conventional fractionated radiation therapy, image-guided hypofractionated stereotactic radiotherapy in NSCLC received better treatment efficacy and showed good tolerability.

Lung deformations and radiation-induced regional lung collapse in patients treated with stereotactic body radiation therapy

PURPOSE

To differentiate radiation-induced fibrosis from regional lung collapse outside of the high dose region in patients treated with stereotactic body radiation therapy (SBRT) for lung tumors.

METHODS

Lung deformation maps were computed from pre-treatment and post-treatment computed tomography (CT) scans using a point-to-point translation method. Fifty anatomical landmarks inside the lung (vessel or airway branches) were matched on planning and follow-up scans for the computation process. Two methods using the deformation maps were developed to differentiate regional lung collapse from fibrosis: vector field and Jacobian methods. A total of 40 planning and follow-ups CT scans were analyzed for 20 lung SBRT patients.

RESULTS

Regional lung collapse was detected in 15 patients (75%) using the vector field method, in ten patients (50%) using the Jacobian method, and in 12 patients (60%) by radiologists. In terms of sensitivity and specificity the Jacobian method performed better. Only weak correlations were observed between the dose to the proximal airways and the occurrence of regional lung collapse.

CONCLUSIONS

The authors presented and evaluated two novel methods using anatomical lung deformations to investigate lung collapse and fibrosis caused by SBRT treatment. Differentiation of these distinct physiological mechanisms beyond what is usually labeled "fibrosis" is necessary for accurate modeling of lung SBRT-induced injuries. With the help of better models, it becomes possible to expand the therapeutic benefits of SBRT to a larger population of lung patients with large or centrally located tumors that were previously considered ineligible.

A design of a DICOM-RT-based tool box for nonrigid 4D dose calculation

The study was aimed to introduce a design of a DICOM-RT-based tool box to facilitate 4D dose calculation based on deformable voxel-dose registration. The computational structure and the calculation algorithm of the tool box were explicitly discussed in the study. The tool box was written in MATLAB in conjunction with CERR. It consists of five main functions which allow a) importation of DICOM-RT-based 3D dose plan, b) deformable image registration, c) tracking voxel doses along breathing cycle, d) presentation of temporal dose distribution at different time phase, and e) derivation of 4D dose. The efficacy of using the tool box for clinical application had been verified with nine clinical cases on retrospective-study basis. The logistic and the robustness of the tool box were tested with 27 applications and the results were shown successful with no computational errors encountered. In the study, the accumulated dose coverage as a function of planning CT taken at end-inhale, end-exhale, and mean tumor position were assessed. The results indicated that the majority of the cases (67%) achieved maximum target coverage, while the planning CT was taken at the temporal mean tumor position and 56% at the end-exhale position. The comparable results to the literature imply that the studied tool box can be reliable for 4D dose calculation. The authors suggest that, with proper application, 4D dose calculation using deformable registration can provide better dose evaluation for treatment with moving target.

Dose differences in intensity-modulated radiotherapy plans calculated with pencil beam and Monte Carlo for lung SBRT

For patients with medically inoperable early‐stage non‐small cell lung cancer (NSCLC) treated with stereotactic body radiation therapy, early treatment plans were based on a simpler dose calculation algorithm, the pencil beam (PB) calculation. Because these patients had the longest treatment follow‐up, identifying dose differences between the PB calculated dose and Monte Carlo calculated dose is clinically important for understanding of treatment outcomes. Previous studies found significant dose differences between the PB dose calculation and more accurate dose calculation algorithms, such as convolution‐based or Monte Carlo (MC), mostly for three‐dimensional conformal radiotherapy (3D CRT) plans. The aim of this study is to investigate whether these observed dose differences also exist for intensity‐modulated radiotherapy (IMRT) plans for both centrally and peripherally located tumors. Seventy patients (35 central and 35 peripheral) were retrospectively selected for this study. The clinical IMRT plans that were initially calculated with the PB algorithm were recalculated with the MC algorithm. Among these paired plans, dosimetric parameters were compared for the targets and critical organs. When compared to MC calculation, PB calculation overestimated doses to the planning target volumes (PTVs) of central and peripheral tumors with different magnitudes. The doses to 95% of the central and peripheral PTVs were overestimated by 9.7%±5.6% and 12.0%±7.3%, respectively. This dose overestimation did not affect doses to the critical organs, such as the spinal cord and lung. In conclusion, for NSCLC treated with IMRT, dose differences between the PB and MC calculations were different from that of 3D CRT. No significant dose differences in critical organs were observed between the two calculations.

PACS number: 87.53.Ly

A new index comparable to BED for evaluating the biological efficacy of hypofractionated radiotherapy schemes on early stage non-small cell lung cancer: analysis of data from the literature

BACKGROUND AND PURPOSE

Hypofractionated radiotherapy has been the principal curative treatment option for early stage NSCLC patients who are medically inoperable or those who refuse surgery and achieved favorable clinical outcomes. Evidence demonstrated that the linear quadratic model widely used in normally fractionated radiotherapy cannot work well to fit outcome data by use of BED to predict the effect of hypofractionation schemes. New models and the related metrics need to be developed to quantify the effect of high-dose ablative regimens for early stage NSCLC.

PATIENTS AND METHODS

Trials using hypofractionated radiotherapy without chemotherapy to treat early stage (T1 or T2N0M0) primary NSCLC and providing information on patient numbers, age, T stage and local control rates were eligible. The endpoint was local relapse and the covariates analyzed were total radiotherapy dose, dose per fraction or combinations of the two parameters, treatment duration, T stage and median age of patients within the trial. The model used was a multivariate logistic regression.

RESULTS

19 trials were included (767 patients) in which 90 patients suffered local relapse. Only total dose × dose per fraction (D × d) and stage T had statistically significant effect on local control. Smaller T stage (p=0.000) and increasing D × d (p=0.006) were associated with improved probability of local control. In contrast, BED10 had no significant impact on local control, which probably indicated that D × d might be a more effective metric than BED10 to predict tumor control rate and assess the efficacy of the large dose fractionation schemes for early stage NSCLC.

CONCLUSIONS

BED was not an ideal metric to estimate the effect of the schemes of high-dose ablative radiotherapy for early stage NSCLC, and total dose × fraction dose could be considered as a comparable index, though the result need to be further validated.

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.

Treating adrenal tumors in 26 patients with CyberKnife: a mono-institutional experience

Background

CyberKnife (CK) is a novel stereotactic radiosurgery system for treating tumors in any part of the body. It is a non-invasive or minimally invasive tumor treatment modality that can deliver high doses of spatially precise radiation and minimize exposure to neighboring healthy tissues or vital organs. The purpose of this study was to investigate the safety and efficacy of CK in the treatment of adrenal tumors.

Methods and Results

We performed a retrospective analysis of 26 patients with adrenal tumors who had been treated with CK in the radiotherapy center of our hospital between March 2009 and March 2012. Eight patients had primary adrenal tumors and 18 patients had metastatic adrenal tumors. In addition to CK, 4 patients received chemotherapy and 2 patients received immunotherapy. The average tumor volume was 72.1 cm³ and the prescribed radiation dosage ranged from 30 to 50 Gy and was fractionated 3 to 5 times with a 58% to 80% isodose line. Abdominal CT was performed between 1 to 3 months after the CK treatment to evaluate the short-term efficacy with follow-up examinations once every 3 months. Three patients had complete remission, 12 patients had partial remission, 5 patients had stable disease, and 6 patients had progressive illness. The effective rate of pain relief was 93.8% and the disease control rate was 77% with a median overall survival of 17 months and a median progression-free survival of 14 months. Treatment Related toxicity was well-tolerated, but preventative measure need to be taken for radiation enteritis.

Conclusions

CK is safe and effective for treating adrenal tumors with few adverse reactions. Nonetheless, its long-term effects requires further follow-up.

Stereotactic radiotherapy (SABR) for the treatment of primary non-small cell lung cancer; systematic review and comparison with a surgical cohort

BACKGROUND AND PURPOSE

To assess the efficacy of stereotactic ablative radiotherapy (SABR) for the treatment of non-small cell lung cancer (NSCLC) through a systematic review of all relevant publications from 2006 to the present compared to controls treated with surgery. In the absence of Grade I evidence, the objective outcome data should form the basis for planning future studies and commissioning SABR services.

MATERIALS AND METHODS

Standard systematic review methodology extracting patient and disease characteristics, treatment and outcome data from published articles reporting patient data from populations of 20 or more Stage I NSCLC patients treated with SABR with a median follow up of minimum of 1 year. The individual outcome measures were corrected for stage and summary weighted outcome data were compared to outcome data from a large International Association for the Study of Lung Cancer (IASLC) cohort matched for stage of disease with survival as the principal endpoint and local control (local progression free survival - local PFS) as the secondary endpoint.

RESULTS

Forty-five reports containing 3771 patients treated with SABR for NSCLC were identified that fulfilled the selection criteria; both survival and staging data were reported in 3171 patients. The 2 year survival of the 3201 patients with localized stage I NSCLC treated with SABR was 70% (95% CI: 67-72%) with a 2 year local control of 91% (95% CI: 90-93%). This was compared to a 68% (95% CI: 66-70) 2 year survival of 2038 stage I patients treated with surgery. There was no survival or local PFS difference with different radiotherapy technologies used for SABR.

CONCLUSIONS

Systematic review of a large cohort of patients with stage I NSCLC treated with SABR suggests that survival outcome in the short and medium term is equivalent to surgery for this population of patients regardless of co-morbidity. As selection bias cannot be assessed from the published reports and treatment related morbidity data are limited, a direct comparison between the two treatment approaches should be a priority. In the meantime, SABR can be offered to stage I patients with NSCLC as an alternative to surgery.

Dose calculation differences between Monte Carlo and pencil beam depend on the tumor locations and volumes for lung stereotactic body radiation therapy

Stereotactic body radiation therapy (SBRT) has been increasingly used as an efficacious treatment modality for early-stage non-small cell lung cancer. The accuracy of dose calculations is compromised due to the presence of inhomogeneity. For the purpose of a consistent prescription, radiation doses were calculated without heterogeneity correction in several RTOG trials. For patients participating in these trials, recalculations of the planned doses with more accurate dose methods could provide better correlations between the treatment outcomes and the planned doses. Using a Monte Carlo (MC) dose calculation algorithm as a gold standard, we compared the recalculated doses with the MC algorithm to the original pencil beam (PB) calculations for our institutional clinical lung SBRT plans. The focus of this comparison is to investigate the volume and location dependence on the differences between the two dose calculations. Thirty-one clinical plans that followed RTOG and other protocol guidelines were retrospectively investigated in this study. Dosimetric parameters, such as D1, D95, and D99 for the PTV and D1 for organs at risk, were compared between two calculations. Correlations of mean lung dose and V20 of lungs between two calculations were investigated. Significant dependence on tumor size and location was observed from the comparisons between the two dose calculation methods. When comparing the PB calculations without heterogeneity correction to the MC calculations with heterogeneity correction, we found that in terms of D95 of PTV: (1) the two calculations resulted in similar D95 for edge tumors with volumes greater than 25.1 cc; (2) an average overestimation of 5% in PB calculations for edge tumors with volumes less than 25.1 cc; and (3) an average overestimation of 9% or underestimation of 3% in PB calculations for island tumors with volumes smaller or greater than 22.6 cc, respectively. With heterogeneity correction, the PB calculations resulted in an average reduction of 23.8% and 15.3% in the D95 for the PTV for island and edge lesions, respectively, when compared to the MC calculations. For organs at risks, very small differences were found among all the comparisons. Excellent correlations for mean dose and V20 of lungs were observed between the two calculations. This study demonstrated that using a single scaling factor may be overly simplified when accounting for the effects of heterogeneity correction. Accurate dose calculations, such as the Monte Carlo algorithms, are highly recommended to understand dose responses in lung SBRT.

Long-term clinical experience of high-dose ablative lung radiotherapy: high pre-treatment [18F]fluorodeoxyglucose-positron emission tomography maximal standardized uptake value of the primary tumor adversely affects treatment outcome

PURPOSE

The aim of this study was to report the long-term clinical experience with lung stereotactic ablative radiotherapy (SABR).

METHODS

Between April 2004 and December 2011, 58 of 92 consecutive lung SABR cases were treated with a curative purpose and were eligible for inclusion. Forty patients were treated for primary lung cancer, and eighteen were treated for locally confined recurrent tumors. The majority of the cases were medically inoperable (65.5%). A median five fractions with a total dose of 30-60Gy were prescribed to the planned target volume. We routinely performed an image-guided respiratory gating technique or four-dimensional computed tomography to minimize set-up errors and accurately determine target volumes.

RESULTS

The median follow-up was 23.8 (range, 1.5-77.2) months. The median age of the entire cohort was 73 (range, 48-90) years. The median gross tumor volume and maximal tumor diameter were 20 (range, 0.5-189.7) ml and 2.2 (range, 0.7-5.9) cm, respectively. The two-year local control (LC) rate was 92.1%, and the major pattern of failure was distant metastasis (25.9%). A high pre-treatment maximal standardized uptake value (mSUV) of the primary tumor significantly and adversely affected LC, local relapse-free survival, distant metastasis-free survival, cause-specific survival and overall survival. The toxicity rates (≥grade 2) were 34.5% and 35% for the central and peripheral tumors, respectively, and one grade 5 toxic event (death due to massive hemoptysis) occurred in a centrally located tumor at 16.7 months post-SABR.

CONCLUSIONS

Lung SABR remains an effective and safe local treatment modality. Pre-treatment mSUV may be a helpful parameter to select patients requiring higher radiation doses and adjuvant systemic therapy for lung SABR.

Spine radiosurgery: a dosimetric analysis in 124 patients who received 18 Gy

PURPOSE

To define the safely tolerated doses to organs at risk (OARs) adjacent to the target volume (TV) of spine radiosurgery (SRS) with 18-Gy in a single fraction.

METHODS AND MATERIALS

A total of 124 patient cases with 165 spine metastases were reviewed. An 18-Gy single-fraction regimen was prescribed to the 90% isodose line encompassing the TV. A constraint of 10 Gy to 10% of the spinal cord outlined 6 mm above and below the TV was used. Dosimetric data to OARs were analyzed.

RESULTS

A total of 124 patients (100%) were followed-up, and median follow-up time was 7 months (1-50 months). Symptoms and local control were achieved in 114 patients (92%). Acute Radiation Therapy Oncology Group (RTOG) grade 1 oral mucositis occurred in 11 of 11 (100%) patients at risk for oropharyngeal toxicity after cervical spine treatment. There were no RTOG grade 2-4 acute or late complications. Median TV was 43.2 cc (5.3-175.4 cc) and 90% of the TV received median dose of 19 Gy (17-19.8 Gy). Median (range) of spinal cord maximum dose (Dmax), dose to spinal cord 0.35 cc (Dsc0.35), and cord volume receiving 10 Gy (Vsc10) were 13.8 Gy (5.4-21 Gy), 8.9 Gy (2.6-11.4 Gy) and 0.33 cc (0-1.6 cc), respectively. Other OARs were evaluated when in proximity to the TV. Esophagus (n=58), trachea (n=28), oropharynx (n=11), and kidneys (n=34) received median (range) V10 and V15 of 3.1 cc (0-5.8 cc) and 1.2 cc (0-2.9 cc), 2.8 cc (0-4.9 cc), and 0.8 cc (0-2.1 cc), 3.4 cc (0-6.2 cc) and 1.6 cc (0-3.2 cc), 0.3 cc (0-0.8 cc) and 0.08 cc (0-0.1 cc), respectively.

CONCLUSIONS

Cord Dmax of 14 Gy and D0.35 of 10 Gy are safe dose constraints for 18-Gy single-fraction SRS. Esophagus V10 of 3 cc and V15 of 1 cc, trachea V10 of 3 cc, and V15 of 1 cc, oropharynx V10 of 3.5 cc and V15 of 1.5 cc, kidney V10 of 0.3 cc, and V15 of 0.1 cc are planning guidelines when these OARs are in proximity to the TV.

Optimising stereotactic body radiotherapy for non-small cell lung cancer with volumetric intensity-modulated arc therapy--a planning study

AIMS

The potential advantages of stereotactic body radiotherapy (SBRT) for early stage non-small cell lung cancer (NSCLC) over conventional fractionated radiotherapy include a higher biological effective dose, a reduction in accelerated repopulation, greater patient convenience and reduced demand on radiotherapy resources. Before introducing SBRT in our department, a review of planning and delivery was undertaken, starting with an assessment of optimum beam number and arrangement.

MATERIALS AND METHODS

Radiotherapy planning computed tomography scans for five patients previously treated for T1 peripheral NSCLC were selected. In each the contoured tumour had planning target volume (PTV) margins of 1cm in all directions. Forward-planned three-field coplanar and non-coplanar plans and a seven-field coplanar plan were produced and optimised. In-house inverse-planning software (AutoBeam) was used to generate three-, five-, seven- and nine-field coplanar and non-coplanar plans and two volumetric intensity-modulated arc therapy (VMAT) plans. The resulting V(20), V(11), PTV(90), PTV(95) and mean lung dose were compared.

RESULTS

Analysis of variance showed non-coplanar plans to have lower V(11) and higher PTV(90) and PTV(95) than coplanar plans. VMAT showed equivalent V(20) and target coverage when compared with the best non-coplanar plans, but with a faster delivery time (2min 8s versus 12min 40s).

CONCLUSIONS

Inverse-planned five-field non-coplanar plans and VMAT improve target coverage while minimising the higher dose to normal lung tissue for SBRT of NSCLC compared with coplanar beam arrangements. VMAT is preferable because of significantly shorter treatment delivery times.

Stereotactic body radiation therapy and 3-dimensional conformal radiotherapy for stage I non-small cell lung cancer: A pooled analysis of biological equivalent dose and local control

PURPOSE

To determine the relationship between tumor control probability (TCP) and biological effective dose (BED) for radiation therapy in medically inoperable stage I non-small cell lung cancer (NSCLC).

METHODS AND MATERIALS

Forty-two studies on 3-dimensional conformal radiation therapy (3D-CRT) and SBRT for stage I NSCLC were reviewed for tumor control (TC), defined as crude local control ≥ 2 years, as a function of BED. For each dose-fractionation schedule, BED was calculated at isocenter using the linear quadratic (LQ) and universal survival curve (USC) models. A scatter plot of TC versus BED was generated and fitted to the standard TCP equation for both models.

RESULTS

A total of 2696 patients were included in this study (SBRT: 1640; 3D-CRT: 1056). Daily fraction size was 1.2-4 Gy (total dose: 48-102.9) with 3D-CRT and 6-26 (total dose: 20-66) with SBRT. Median BED was 118.6 Gy (range, 68.5-320.3) and 95.6 Gy (range, 46.1-178.1) for the LQ and USC models, respectively. According to the LQ model, BED to achieve 50% TC (TCD50) was 61 Gy (95% confidence interval, 50.2-71.1). TCP as a function of BED was sigmoidal, with TCP ≥ 90% achieved with BED ≥ 159 Gy and 124 Gy for the LQ and USC models, respectively.

CONCLUSIONS

Dose-escalation beyond a BED 159 by LQ model likely translates into clinically insignificant gain in TCP but may result in clinically significant toxicity. When delivered with SBRT, BED of 159 Gy corresponds to a total dose of 53 Gy in 3 fractions at the isocenter.

Stereotactic body radiation therapy in non-small-cell lung cancer: linking radiobiological modeling and clinical outcome

For patients with peripheral, early-stage non-small-cell lung cancer, it has been found feasible to deliver 5 or fewer fractions of large doses through stereotactic body radiation therapy (SBRT) without causing severe early or late injury and with impressive tumor control. In this review, we employ radiobiological modeling with the linear quadratic formulation to explore the adequacy of various dose schedules used for tumor control in the lung as supported by clinical evidence, the influence of dose distribution and delivery time on local control, and how to decrease the likelihood of severe toxicity following SBRT. Furthermore, the validity of the linear quadratic formalism in the high dose range of SBRT for lung cancer is explored.

[Preliminary effect of Cyberknife radiosurgery in the treatment of 31 patients with advanced non-small cell lung cancer]

背景与目的

射波刀是近年来新出现的一种立体定向放射治疗技术，具有大剂量、高精度和周围受照射的正常组织或是重要器官的范围小等优点，在治疗非小细胞肺癌（non-small cell lung cancer, NSCLC）方面取得了显著的效果。本研究旨在探讨射波刀（Cyberknife）治疗晚期NSCLC的疗效和安全性。

方法

在2009年3月-2010年3月间，我们应用射波刀治疗31例（34个肿瘤病灶）临床Ⅲ期-Ⅳ期的周围型NSCLC患者，其中Ⅲ期5例，Ⅳ期26例，腺癌15例，鳞癌12例，大细胞癌1例，腺鳞癌2例，不确定NSCLC 1例。28例患者联合了化疗。平均肿瘤体积67.2 cm³，处方总剂量36 Gy-60 Gy，分割2次-5次。等计量线65%-85%。治疗后1-2个月复查胸部CT，观察近期疗效，每3个月随访一次。

结果

2例完全缓解，16例部分缓解，7例稳定，6例进展，总体有效率达58%，疾病控制率为81%。所有患者治疗耐受性良好，最主要的不良反应表现为乏力，无4级或是4级以上的不良反应发生。

结论

射波刀治疗晚期NSCLC安全性好，有较好的近期疗效，不良反应轻，患者易耐受。但是远期疗效有待进一步随访。

Analysis of suitable prescribed isodose line fitting to planning target volume in stereotactic body radiotherapy using dynamic conformal multiple arc therapy

PURPOSE

To assess the most suitable value of a relative prescribed dose in clinical treatment plans of stereotactic body radiotherapy (SBRT) using dynamic conformal multiple arc therapy to treat lung tumors.

METHODS AND MATERIALS

We retrospectively generated alternative SBRT plans for typical examples of 8 patients who had been treated with SBRT for a lung tumor with a prescribed dose of 50 Gy in 5 fractions. The prescribed dose had been defined as 80% of the maximal dose in the planning target volume (PTV) ("the 80% isodose plan"). Alternative 20%-90% isodose plans at 10% intervals were generated (64 plans; 8 plans for each of the 8 patients), and factors related to leaf margins, target volume, normal lung volume, and monitor units were compared using dose-volume histogram analysis.

RESULTS

We could generate all the 64 plans. Compared with the 80% isodose plan, the V20 and mean lung dose (MLD) were both lower in the 60% plan; the V20 was approximately 19% lower (4.72% vs 3.84%) and the MLD was 13% lower (4.0 Gy vs 3.5 Gy). Mean PTV and ITV doses were higher in the lower percentage isodose plans. Compared with the 80% isodose plan, in the 60% isodose plan the mean PTV was 19% higher (56.1 Gy vs 66.8 Gy) and the mean ITV was 30% higher (59.6 Gy vs 77.4 Gy). The mean total monitor units increased more steeply than did the mean homogeneity index. The mean conformity index values in the 60% and 70% isodose plans were less than 1.15.

CONCLUSIONS

The 60% isodose plan was considered the best plan in this analysis because of the lower comparative dosimetric factors in normal lung tissue (including V20 and MLD) and the higher comparative mean PTV and internal target volume doses achieved, along with good conformity index values. In clinical use, accurate estimation and commissioning should be performed for the dose distribution prior to selecting a plan. Further investigation is warranted to determine whether the calculated dosimetric advantages result in improved outcomes.

Phase I/II study of hypofractioned radiation with three-dimensional conformal radiotherapy for clinical T3-4N0-1M0 stage esophageal carcinoma

Compared to conventional fractionated-dose radiotherapy, high hypofractionated-dose radiotherapy could yield tumoricidal effects. However, few clinical trials of hypofractionated radiotherapy in loco-regionally advanced incurable esophageal cancer at present have yet been performed. The purpose of the current study was to evaluate the efficacy and toxicity of hypofractioned radiation with three-dimensional conformal radiotherapy for clinical T3-4N0-1M0 stage esophageal carcinoma. From September 2003 to December 2005, 45 patients with locally advanced esophageal carcinoma were grouped and received three-dimensional conformal hypofractioned radiotherapy (3D-CRT) whose fractionated dose was gradually increase per group. Radiotherapy was administered to a total dose of from 50 to 54 Gy (fractionated dose of from 3.0 to 6.0 Gy, 3 times weekly), over a 3-4 week period. And patients received 4 cycles chemotherapy. The median follow-up period for survivors was 38 months. Treatment tolerance rate was 78.8% with daily dose of from 3 to 5 Gy. There are 21.2% patients occurring Grade ≥ 3 acute toxicities. But patients couldn't tolerate daily dose of 6 Gy (55.6%). The 1-year, 2-year and 3-year local control rates were 62%, 49% and 39% respectively. And the 1-year, 2-year and 3-year overall survival rates were 34%, 21% and 9% respectively. The median overall survival time was 17 months. At the time of following up, 13 patients (31.0%) had occurred esophageal late complications, with mainly esophageal perforation, hemorrhage or stenosis, including initial stenosis aggravation. Therefore hypofractionated irradiation was thought to be feasible for clinical T3-4N0-1M0 stage esophageal carcinoma. And daily dose of ≤5 Gy was comparatively suitable in hypofractionated irradiation for esophageal carcinoma, and the patients tolerated well. But further research was in need also.

Hypofractionated radiotherapy has the potential for second cancer reduction

Background and Purpose

A model for carcinoma and sarcoma induction was used to study the dependence of carcinogenesis after radiotherapy on fractionation.

Materials and methods

A cancer induction model for radiotherapy doses including fractionation was used to model carcinoma and sarcoma induction after a radiation treatment. For different fractionation schemes the dose response relationships were obtained. Tumor induction was studied as a function of dose per fraction.

Results

If it is assumed that the tumor is treated up to the same biologically equivalent dose it was found that large dose fractions could decrease second cancer induction. The risk decreases approximately linear with increasing fraction size and is more pronounced for sarcoma induction. Carcinoma induction decreases by around 10% per 1 Gy increase in fraction dose. Sarcoma risk is decreased by about 15% per 1 Gy increase in fractionation. It is also found that tissue which is irradiated using large dose fractions to dose levels lower than 10% of the target dose potentially develop less sarcomas when compared to tissues irradiated to all dose levels. This is not observed for carcinoma induction.

Conclusions

It was found that carcinoma as well as sarcoma risk decreases with increasing fractionation dose. The reduction of sarcoma risk is even more pronounced than carcinoma risk. Hypofractionation is potentially beneficial with regard to second cancer induction.

Systemic review of the patterns of failure following stereotactic body radiation therapy in early-stage non-small-cell lung cancer: clinical implications

PURPOSE

To analyze the patterns of failure, the toxicity profile, and the factors influencing efficacy of stereotactic body radiation (SBRT) for early-stage non-small-cell lung cancer (NSCLC).

METHODS AND MATERIALS

A search was based on PubMed electronic databases. All searches were conducted in May, 2009.

RESULTS

The local control ranged from 80% to 100% in most studies with adequate isocentric or peripheral biologically effective dose (BED). Recurrences were associated with increased tumor size. The main pattern of failure after SBRT was distant metastasis. Grades 3-5 toxicity occurred mostly in centrally located tumors, and adjuvant chemotherapy may further decrease all recurrences; possibly translating to a survival benefit in large or centrally located tumors where high BED cannot be safely reached.

CONCLUSION

SBRT is an excellent treatment option for early-stage, and mostly medically inoperable, NSCLC. BED at both the isocenter and the tumor periphery is very important for optimal tumor control; higher doses are required for large (T2) lesions; SBRT for centrally located tumors can be feasible with a much less aggressive dose regimen than 60-66Gy/3 fractions and adjacent critical structures excluded from the target volume; chemotherapy may optimize the clinical outcome in large or centrally located lesions.

A comparison of two stereotactic body radiation fractionation schedules for medically inoperable stage I non-small cell lung cancer: the Cleveland Clinic experience

PURPOSE

To assess the impact of fractionation upon tumor control and toxicity in medically inoperable early stage lung cancer patients treated with stereotactic body radiotherapy.

METHODS

We reviewed 94 consecutive stereotactic body radiotherapy treatments (86 patients) with medically inoperable stage I non-small cell lung cancer receiving either 50 Gy in five fractions (n = 56) or 60 Gy in three fractions (n = 38) from October 2003 to August 2007. Institutional practice was 10 Gy x 5 before March 1, 2006, when it changed to 20 Gy x 3 to conform to Radiation Therapy Oncology Group 0236 unless otherwise dictated clinically.

RESULTS

Median age was 73 years and median Karnofsky performance status 80. A total of 69 lesions were T1, 24 were T2 lung cancer. Median follow-up was 15.3 months. For the 50- and 60-Gy cohorts at 1 year, local control was 97.3% versus 100%, nodal failure 7.3% versus 3.4%, distant metastasis rate 21.8% versus 29.5%, and overall survival 83.1% versus 76.9% (p = 0.68, 0.54, 0.56, and 0.54, respectively). There was no difference in overall survival for patients with histologic (n = 61) compared with radiographic (n = 33) diagnosis. There was no impact of fractionation in the subset of T2 tumors. We observed two cases (2.2%) of clinical grade 2 pneumonitis. Mild late chest wall toxicity (grade 1 or 2) was seen in nine patients (10%) at a median of 8.4 months after treatment and was more common in the 60-Gy group (7 of 38 [18%] versus 2 of 56 [4%], p = 0.028).

CONCLUSIONS

Local control, overall survival, nodal failure, and distant failure were not affected by fractionation. Chest wall toxicity was more common with 60-Gy group.

Comprehensive analysis of pulmonary function Test (PFT) changes after stereotactic body radiotherapy (SBRT) for stage I lung cancer in medically inoperable patients

BACKGROUND

To assess for variables predicting pulmonary function test (PFT) changes after stereotactic body radiotherapy (SBRT) for medically inoperable stage I lung cancer.

METHODS

We reviewed 92 consecutive patients undergoing SBRT for stage I lung cancer between February 2004 and August 2007. A total of 102 lesions were treated using prescriptions of 20 Gy x 3 (n = 40), 10 Gy x 5 (n = 56), and 5 Gy x 10 (n = 6). Institutional practice was 10 Gy x 5 before March 1, 2006 before changing to 20 Gy x 3 to conform to RTOG 0236 unless otherwise dictated clinically.

RESULTS

Median pretreatment forced expiratory volume at 1 second (FEV1) was 1.21 liter (50% of predicted) and median diffusion capacity to carbon monoxide (DLCO) was 56.5. There was no significant overall change in PFT's after SBRT. Individual patients experienced both substantial improvements and declines (10% declined at least 14% predicted FEV1% and 19% predicted DLCO). The mean change in FEV1 was -0.05 liter (range, -0.98 to +1.29 liter; p = 0.22) representing -1.88% predicted baseline FEV1 (range, -33 to + 43%; p = 0.62). DLCO declined 2.59% of predicted (range, -37 to +33%; p = 0.27). Conformality index, V5 and V10 were associated with individual patient changes in FEV1% (p = 0.033, p = 0.0036, p = 0.025, respectively), however, correlations were small and overall treatment dose did not predict for changes (p = 0.95). There was no significant difference in FEV1 (p = 0.55) or FEV1% (p = 0.37) changes for central versus peripheral locations. No factors predicted for individual changes in DLCO. Patients with FEV1% below the median of the study population had significantly longer overall survival (p = 0.0065). Although patients dying of cardiac disease died earlier than those dying of other causes, FEV1% below median was not associated with a lower risk of dying of cardiac disease or with lower Charlson comorbidity index.

CONCLUSIONS

(1) SBRT was well tolerated and PFT changes were minimal. (2) Central lesions were safely treated with 50 Gy.

Synchronous monitoring of external/internal respiratory motion: validity of respiration-gated radiotherapy for liver tumors

PURPOSE

Four-dimensional (4D) radiotherapy, in particular respiration gating for the treatment of lung tumors, is gaining popularity. Its utility for other sites, however, has not been investigated fully. The purpose of this study was to see whether 4D therapy is feasible for liver tumors.

MATERIAL AND METHODS

Six patients (five with hepatomas and one with metastatic liver tumor) had a fiducial, gold marker 1.5 mm in diameter implanted in the vicinity of their liver tumors. The inner and external (i.e., upper abdominal wall) respiratory movements were simultaneously recorded using a real-time tumor-tracking radiotherapy system and respiration monitor equipment applied to the mid to upper abdomen.

RESULTS

The fluctuations from the baseline position of liver tumors were small; the mean absolute value was 3.92 +/- 1.94 mm. The mean right-left, anteroposterior, and craniocaudal total movements were 4.19 +/- 2.46, 7.23 +/- 2.96, and 15.98 +/- 6.02 mm, respectively. The phase shift was negligible.

CONCLUSION

Liver tumors may be suitable for respiration-gated radiotherapy, and they may become curable with 4D radiotherapy.

Radiation-induced rib fractures after hypofractionated stereotactic body radiation therapy of non-small cell lung cancer: a dose- and volume-response analysis

BACKGROUND AND PURPOSE

The aim of this study is to analyse the dose-response and the volume-response of radiation-induced rib fractures after hypofractionated stereotactic body radiation therapy (SBRT).

MATERIALS AND METHODS

During the period 1998-2005, 68 patients with medically inoperable stage I non-small cell lung cancer (NSCLC) were treated with hypofractionated SBRT to 45 Gy in 3 fractions. Among the 33 patients with complete treatment records and radiographic follow-up exceeding 15 months (median: 29 months), 13 fractures were found in seven patients. Identifying all ribs receiving at least 21 Gy, 81 ribs (13 with and 68 without fracture) in 26 patients were separately contoured and their dose-volume histograms (DVHs) were obtained. The DVHs were assessed with the mean dose and cut-off models. Maximum likelihood estimation was used to fit dose-response and volume-response curves to each model.

RESULTS

It was possible to quantify the risk of radiation-induced rib fracture using response curves and information contained in the DVHs. Absolute volumes provided better fits than relative volumes and dose-response curves were more suitable than volume-response curves. For the dose given by the 2 cm(3) cut-off volume, D(2 cm(3)), the logistic dose-response curve for three fractions was parameterised by D(50)=49.8 Gy and gamma(50)=2.05. Consequently, for a median follow-up of 29 months, if D(2 cm(3))<3 x 7.0 Gy the risk is close to 0, and the 5% and 50% risks are given by D(2 cm(3))=3 x 9.1 Gy and 3 x 16.6 Gy, respectively.

CONCLUSIONS

In this group of patients, the risk for radiation-induced rib fracture following hypofractionated SBRT was related to the dose to 2 cm(3) of the rib.

Stereotactic radiotherapy with real-time tumor tracking for non-small cell lung cancer: clinical outcome

PURPOSE

To report the clinical outcome of treatment using real-time tumor tracking for 70 patients with inoperable stage I non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

Seventy inoperable patients with peripherally located early-stage NSCLC were treated with 45 or 60 Gy in three fractions using CyberKnife. Pathology was available in 51% of patients. Thirty-nine patients had a T1-tumor and 31 had a T2-tumor. Markers were placed using the vascular, percutaneous intra-, or extra-pulmonary approach, depending on the risk of pneumothorax.

RESULTS

The actuarial 2-year local control rate for patients treated with 60 Gy was 96%, compared to 78% for patients treated with a total dose of 45 Gy (p=0.197). All local recurrences (n=4) occurred in patients with T2-tumors. Overall survival for the whole group at two years was 62% and the cause specific survival was 85%. The median follow-up was 15 months. Grade 3 toxicity occurred in two patients (3%) after marker placement. Treatment-related late grade 3 toxicity occurred in 7 patients (10%). No grade > or = 4 toxicity occurred.

CONCLUSION

Excellent local control of 96% at 1- and 2-years was achieved using 60 Gy in three fractions for NSCLC patients treated with the real-time tumor tracking. Toxicity was low.