Clinicopathologic Analysis of Microscopic Extension in Lung Adenocarcinoma: Defining Clinical Target Volume for Radiotherapy

Experimental Examination of Conventional, Semi-Automatic, and Automatic Volumetry Tools for Segmentation of Pulmonary Nodules in a Phantom Study

The aim of this study is to examine the precision of semi-automatic, conventional and automatic volumetry tools for pulmonary nodules in chest CT with phantom N1 LUNGMAN. The phantom is a life-size anatomical chest model with pulmonary nodules representing solid and subsolid metastases. Gross tumor volumes (GTVis) were contoured using various approaches: manually (0); as a means of semi-automated, conventional contouring with (I) adaptive-brush function; (II) flood-fill function; and (III) image-thresholding function. Furthermore, a deep-learning algorithm for automatic contouring was applied (IV). An intermodality comparison of the above-mentioned strategies for contouring GTVis was performed. For the mean GTVref (standard deviation (SD)), the interquartile range (IQR)) was 0.68 mL (0.33; 0.34-1.1). GTV segmentation was distributed as follows: (I) 0.61 mL (0.27; 0.36-0.92); (II) 0.41 mL (0.28; 0.23-0.63); (III) 0.65 mL (0.35; 0.32-0.90); and (IV) 0.61 mL (0.29; 0.33-0.95). GTVref was found to be significantly correlated with GTVis (I) p < 0.001, r = 0.989 (III) p = 0.001, r = 0.916, and (IV) p < 0.001, r = 0.986, but not with (II) p = 0.091, r = 0.595. The Sørensen-Dice indices for the semi-automatic tools were 0.74 (I), 0.57 (II) and 0.71 (III). For the semi-automatic, conventional segmentation tools evaluated, the adaptive-brush function (I) performed closest to the reference standard (0). The automatic deep learning tool (IV) showed high performance for auto-segmentation and was close to the reference standard. For high precision radiation therapy, visual control, and, where necessary, manual correction, are mandatory for all evaluated tools.

Radiomics nomogram integrating intratumoural and peritumoural features to predict lymph node metastasis and prognosis in clinical stage IA non-small cell lung cancer: a two-centre study

AIM

To investigate the value of a radiomics nomogram integrating intratumoural and peritumoural features in predicting lymph node metastasis and overall survival (OS) in patients with clinical stage IA non-small-cell lung cancer (NSCLC).

MATERIALS AND METHODS

This study retrospectively enrolled 199 patients (training cohort: 71 patients from Affiliated Tumour Hospital of Nantong University; internal validation cohort: 46 patients from Affiliated Tumour Hospital of Nantong University; external validation cohort: 82 patients from the public database). CT radiomics models were constructed based on four volumes of interest: gross tumour volume (GTV), gross and 3 mm peritumoural volume (GPTV₃), gross and 6 mm peritumoural volume (GPTV₆), and gross and 9 mm peritumoural volume (GPTV₉). The optimal radiomics signature was further combined with independent clinical predictors to develop a nomogram. Univariable and multivariable Cox regression analysis were applied to determine the relationship between factors and OS.

RESULTS

GPTV₆ radiomics yielded better performance than GTV, GPTV₃, and, GPTV₉ radiomics in the training (area under the curve [AUC], 0.81), internal validation (AUC, 0.79), and external validation cohorts (AUC, 0.71), respectively. The nomogram integrating GPTV₆ radiomics and spiculation improved predictive ability, with AUCs of 0.85, 0.80, and 0.74 in three cohorts, respectively. Pathological lymph node metastasis, nomogram-predicted lymph node metastasis, and pleural indentation were independent risk predictors of OS (p<0.05).

CONCLUSIONS

The nomogram integrating GPTV₆ radiomics features and independent clinical predictors performed well in predicting lymph node metastasis and prognosis in patients with clinical stage IA NSCLC.

Optimal Clinical Target Volume of Radiotherapy Based on Microscopic Extension around the Primary Gross Tumor in Non-Small-Cell Lung Cancer: A Systematic Review

A crucial issue in radical radiation therapy for non-small-cell lung cancer is how to define the clinical target volume (CTV). Although the scope of microscopic extension (ME) and microscopic proximal bronchial extension (PBE) from a primary tumor should be considered when defining the CTV, there has been limited research on ME and PBE. Therefore, we conducted this systematic review. The PubMed, ICHUSHI (Japanese database), and Cochrane Library databases were searched, and 816 articles were initially retrieved. After primary and secondary screenings, eight articles were ultimately selected. The results of this systematic review suggest the importance of a 0 mm margin in stereotactic radiotherapy for early-stage cancer and a 5–8 mm margin in curative irradiation for locally advanced cancer. Regarding PBE, this review yielded the conclusion that it is appropriate to consider the addition of an approximately 15 mm margin from the bronchial vasculature. Although there were few articles with a high level of evidence, this systematic review enabled us to collate results from previous studies and to provide recommendations, to some extent, regarding the CTV margin in the current clinical environment, where high-precision radiation therapy, such as image-guided radiotherapy and intensity-modulated radiotherapy, is predominant.

Multi-institutional phase II study on the safety and efficacy of dynamic tumor tracking-stereotactic body radiotherapy for lung tumors

BACKGROUND AND PURPOSE

This study aimed to evaluate the safety and efficacy of dynamic tumor tracking-stereotactic body radiotherapy (DTT-SBRT) for lung tumors.

MATERIALS AND METHODS

Patients with cStage I primary lung cancer or metastatic lung cancer with an expected range of respiratory motion of ≥10 mm were eligible for the study. The prescribed dose was 50 Gy in four fractions. A gimbal-mounted linac was used for DTT-SBRT delivery. The primary endpoint was local control at 2 years.

RESULTS

Forty-eight patients from four institutions were enrolled in this study. Forty-two patients had primary non-small-cell lung cancer, and six had metastatic lung tumors. DTT-SBRT was delivered for 47 lesions in 47 patients with a median treatment time of 28 min per fraction. The median respiratory motion during the treatment was 13.7 mm (range: 4.5-28.1 mm). The motion-encompassing method was applied for the one remaining patient due to the poor correlation between the abdominal wall and tumor movement. The median follow-up period was 32.3 months, and the local control at 2 years was 95.2% (lower limit of the one-sided 85% confidence interval [CI]: 90.3%). The overall survival and progression-free survival at 2 years were 79.2% (95% CI: 64.7%-88.2%) and 75.0% (95% CI: 60.2%-85.0%), respectively. Grade 3 toxicity was observed in one patient (2.1%) with radiation pneumonitis. Grade 4 or 5 toxicity was not observed.

CONCLUSION

DTT-SBRT achieved excellent local control with low incidences of severe toxicities in lung tumors with respiratory motion.

Radial Data Mining to Identify Density-Dose Interactions That Predict Distant Failure Following SABR

Purpose

Lower dose outside the planned treatment area in lung stereotactic radiotherapy has been linked to increased risk of distant metastasis (DM) possibly due to underdosage of microscopic disease (MDE). Independently, tumour density on pretreatment computed tomography (CT) has been linked to risk of MDE. No studies have investigated the interaction between imaging biomarkers and incidental dose. The interaction would showcase whether the impact of dose on outcome is dependent on imaging and, hence, if imaging could inform which patients require dose escalation outside the gross tumour volume (GTV). We propose an image-based data mining methodology to investigate density-dose interactions radially from the GTV to predict DM with no a priori assumption on location.

Methods

Dose and density were quantified in 1-mm annuli around the GTV for 199 patients with early-stage lung cancer treated with 60 Gy in 5 fractions. Each annulus was summarised by three density and three dose parameters. For parameter combinations, Cox regressions were performed including a dose-density interaction in independent annuli. Heatmaps were created that described improvement in DM prediction due to the interaction. Regions of significant improvement were identified and studied in overall outcome models.

Results

Dose-density interactions were identified that significantly improved prediction for over 50% of bootstrap resamples. Dose and density parameters were not significant when the interaction was omitted. Tumour density variance and high peritumour density were associated with DM for patients with more cold spots (less than 30-Gy EQD2) and non-uniform dose about 3 cm outside of the GTV. Associations identified were independent of the mean GTV dose.

Conclusions

Patients with high tumour variance and peritumour density have increased risk of DM if there is a low and non-uniform dose outside the GTV. The dose regions are independent of tumour dose, suggesting that incidental dose may play an important role in controlling occult disease. Understanding such interactions is key to identifying patients who will benefit from dose-escalation. The methodology presented allowed spatial dose-density interactions to be studied at the exploratory stage for the first time. This could accelerate the clinical implementation of imaging biomarkers by demonstrating the impact of incidental dose for tumours of varying characteristics in routine data.

Evaluation of Microscopic Tumour Extension in Localized Stage Non-Small-Cell Lung Cancer for Stereotactic Radiotherapy Planning

Background: Stereotactic radiotherapy for localised stage non-small-cell lung carcinoma (NSCLC) is an alternative indication for patients who are inoperable or refuse surgery. A study showed that the microscopic tumour extension (ME) of NSCLC varied according to the histological type, which allowed us to deduce adapted margins for the clinical target volume (CTV). However, to date, no study has been able to define the most relevant margins for patients with stage 1 tumours. Methods: We performed a retrospective analysis including patients with adenocarcinoma (ADC) or squamous cell carcinoma (SCC) of localised stage T1N0 or T2aN0 who underwent surgery. The ME was measured from this boundary. The profile of the type of tumour spread was also evaluated. Results: The margin required to cover the ME of a localised NSCLC with a 95% probability is 4.4 mm and 2.9 mm for SCC and ADC, respectively. A significant difference in the maximum distance of the ME between the tumour-infiltrating lymphocytes (TILs), 0−10% and 50−90% (p < 0.05), was noted for SCC. There was a significant difference in the maximum ME distance based on whether the patient had chronic obstructive pulmonary disease (COPD) (p = 0.011) for ADC. Multivariate analysis showed a statistically significant relationship between the maximum microextension distance and size with the shrinkage coefficient. Conclusion: This study definitively demonstrated that the ME depends on the pathology subtype of NSCLC. According to International Commission on Radiation Units and Measurements (ICRU) reports, 50, 62 and 83 CTV margins, proposed by these results, should be added to the GTV (Gross tumour volume). When stereotactic body radiation therapy is used, this approach should be considered in conjunction with the dataset and other margins to be applied.

The Clinical Outcomes, Prognostic Factors and Nomogram Models for Primary Lung Cancer Patients Treated With Stereotactic Body Radiation Therapy

PURPOSE

Stereotactic body radiation therapy (SBRT) is a standard treatment for early primary lung cancer patients. However, there are few simple models for predicting the clinical outcomes of these patients. Our study analyzed the clinical outcomes, identified the prognostic factors, and developed prediction nomogram models for these patients.

MATERIALS AND METHODS

We retrospectively analyzed 114 patients with primary lung cancer treated with SBRT from 2012 to 2020 at our institutions and assessed patient's clinical outcomes and levels of toxicity. Kaplan-Meier analysis with a log-rank test was used to generate the survival curve. The cut-off values of continuous factors were calculated with the X-tile tool. Potential independent prognostic factors for clinical outcomes were explored using cox regression analysis. Nomograms for clinical outcomes prediction were established with identified factors and assessed by calibration curves.

RESULTS

The median overall survival (OS) was 40.6 months, with 3-year OS, local recurrence free survival (LRFS), distant disease-free survival (DDFS) and progression free survival (PFS) of 56.3%, 61.3%, 72.9% and 35.8%, respectively, with grade 3 or higher toxicity rate of 7%. The cox regression analysis revealed that the clinical stage, immobilization device, and the prescription dose covering 95% of the target area (D95) were independent prognostic factors associated with OS. Moreover, the clinical stage, and immobilization device were independent prognostic factors of LRFS and PFS. The smoking status, hemoglobin (Hb) and immobilization device were significant prognostic factors for DDFS. The nomograms and calibration curves incorporating the above factors indicated good predictive accuracy.

CONCLUSIONS

SBRT is effective and safe for primary lung cancer. The prognostic factors associated with OS, LRFS, DDFS and PFS are proposed, and the nomograms we proposed are suitable for clinical outcomes prediction.

Improving the accuracy of prognosis for clinical stage I solid lung adenocarcinoma by radiomics models covering tumor per se and peritumoral changes on CT

OBJECTIVES

To assess methods to improve the accuracy of prognosis for clinical stage I solid lung adenocarcinoma using radiomics based on different volumes of interests (VOIs).

METHODS

This retrospective study included patients with postoperative clinical stage I solid lung adenocarcinoma from two hospitals, center 1 and center 2. Three databases were generated: dataset A (training set from center 1), dataset B (internal test set from center 1), and dataset C (external validation test from center 2). Disease-free survival (DFS) data were collected. CT radiomics models were constructed based on four VOIs: gross tumor volume (GTV), 3 mm external to the tumor border (peritumoral volume [PTV]_0~+3), 6 mm crossing tumor border (PTV_-3~+3), and 6 mm external to the tumor border (PTV_0~+6). The area under the receiver operating characteristic curve (AUC) was used to compare the model accuracies.

RESULTS

A total of 334 patients were included (204 and 130 from centers 1 and 2). The model using PTV_-3~+3 (AUC 0.81 [95% confidence interval {CI}: 0.75, 0.94], 0.81 [0.63, 0.90] for datasets B and C) outperformed the other three models, GTV (0.73 [0.58, 0.81], 0.73 [0.58, 0.83]), PTV_0~+3 (0.76 [0.52, 0.87], 0.75 [0.60, 0.83]), and PTV_0~+6 (0.72 [0.60, 0.81], 0.69 [0.59, 0.81]), in datasets B and C, all p < 0.05.

CONCLUSIONS

A radiomics model based on a VOI of 6 mm crossing tumor border more accurately predicts prognosis of clinical stage I solid lung adenocarcinoma than that based on VOIs including overall tumor or external rims of 3 mm and 6 mm.

KEY POINTS

• Radiomics is a useful approach to improve the accuracy of prognosis for stage I solid adenocarcinoma. • The radiomics model based on VOIs that includes 3 mm within and external to the tumor border (peritumoral volume [PTV]_-3~+3) outperformed models that included either only the tumor itself or those that only included the peritumoral volume.

Size and Predictive Factors of Microscopic Tumor Extension in Locally Advanced Non-Small Cell Lung Cancer

PURPOSE

Radiation therapy for locally advanced non-small cell lung cancer (NSCLC) should treat the whole tumor, including its microscopic extensions, and protect adjacent organs at risk as much as possible. The aim of our study is to evaluate the size of microscopic tumor extension (MEmax) in NSCLC, and search for potential predictive factors.

METHODS AND MATERIALS

We retrospectively selected 70 patients treated with postoperative radiation therapy for a NSCLC with N2 nodal status, then 34 additional patients operated for a squamous cell lung cancer with N1 or N2 nodal status. On the digitized slides originating from the resected tumors of these 104 patients, we outlined the border of the tumor, as seen with the naked eye. We then searched for microscopic tumor extension outside of these borders with a magnification as high as 40 × and measured the maximum size of MEmax.

RESULTS

The median MEmax in the whole cohort was 0.85 mm (0-9.95). The MEmax was <5.3 mm in 95% of adenocarcinomas (6.5 mm in the subgroup without neoadjuvant chemotherapy) and <3.5 mm in 95% of squamous cell carcinomas (3.7 mm in the subgroup without neoadjuvant chemotherapy). After multivariate analysis, the factors associated with the size of MEmax were vascular invasion (P = .0002), histologic type, with a wider MEmax for adenocarcinomas in comparison with squamous cell carcinomas (P = .002), tumor size, which was inversely related with the size of MEmax (P = .024), and high blood pressure (P = .03). Macroscopic histologic tumor size was well correlated with both radiologic tumor size on a mediastinal setting computed tomography (correlation coefficient of 0.845) and on a parenchymal setting computed tomography (correlation coefficient of 0.836).

CONCLUSIONS

The clinical target volume margin, accounting for microscopic tumoral extension, could be reduced to 7 mm for adenocarcinomas and 4 mm for squamous cell carcinomas.

A clinicopathologic analysis of microscopic extension in small cell lung cancer and lung adenocarcinoma: Determination of clinical target volume with precise radiotherapy

PURPOSE

The identification of the clinical target volume (CTV) is particularly important in the precise radiotherapy of lung cancer. The purpose of this study was to determine the extension margin from gross tumor volume (GTV) to CTV in primary small cell lung cancer (SCLC) and lung adenocarcinoma (ADC) by microscopic extension (ME).

MATERIAL AND METHODS

The data of 25 cases of SCLC and 29 cases of ADC from August 2015 to August 2020 were analyzed. The measurement of tumor size between preoperative thoracic computed tomography (CT) and postoperative macroscopic specimens was compared, and the ME range of tumor cells was measured under a microscope to determine its correlation with clinical features and pathological manifestations.

RESULTS

A total of 217 slides were examined, corresponding to 103 slides for SCLC and 114 slides for ADC. The radiologic sizes of the tumors in SCLC and ADC were 12.8 and 7.9 mm, respectively (p = 0.09), and the macroscopic sizes were 12.5 and 8.5 mm, respectively (p = 0.07). There was a significant correlation between the radiologic and macroscopic size of the same tumor sample (r = 0.886). Compared with ADC, more SCLC tumor cells infiltrated through vascular or lymphatic dissemination (16% vs. 9%, p = 0.047). The mean ME value was 2.81 mm for SCLC and 2.02 mm for ADC (p = 0.012). To take into account 95% of the ME, a margin of 8 and 7.7 mm must be expanded for SCLC and ADC, respectively. The ME value of the tumor was related to the presence of atelectasis, the location of the tumor, and the Ki-67 cell proliferation index.

CONCLUSION

The GTV of the tumor was contoured according to CT images, which was basically consistent with the actual tumor size. The GTVs of SCLC and ADC should be expanded by 8 and 7.7 mm, respectively, to fully cover the subclinical lesions in 95% of cases.

Toxicity after volumetric modulated arc therapy for lung cancer: a monocentric retrospective study

Background

Intensity-modulated radiotherapy (RT) is now widely implemented and has replaced classical three-dimensional (3D)-RT in many tumor sites, as it allows a better target dose conformity and a better sparing of organs a risk (OAR), at the expense, however, of increasing the volume of low dose to normal tissues. Clinical data on toxicities using volumetric modulated arc therapy (VMAT) in lung cancer remain scarce. We aimed to report both acute (APT) and late (LPT) pulmonary and acute (AET) and late (LET) oesophageal toxicities in such setting.

Methods

All patients treated for a primary lung cancer with VMAT +/- chemotherapy (ChT) in our center from 2014 to 2018 were retrospectively included. Usual clinical, treatment and dosimetric features were collected. Univariate analysis was performed using the receiver operative characteristics approach while multivariate analysis (MVA) relied on logistic regression, calculated with Medcalc 14.8.1.

Results

In total, 167 patients were included, with a median age of 66 years (39-88 years). Median radiation dose was 66 Gy (30-66 Gy); 82% patients received concomitant (32.3%), induction (25.7%) or induction followed by concomitant ChT (24%). After a median follow-up of 14.0 months, the G ≥2 APT, AET, LPT and LET rates were 22.2%, 30.0%, 16.8% and 5.4%, respectively with low grade ≥3 toxicity rates (respectively, 3%, 6.6%, 3% and 0%). On MVA, APT was significantly associated with V30 to the homolateral lung, AET with age, LPT with MEVS while no feature remained significantly correlated with LET.

Conclusions

Low rates of pulmonary and esophageal toxicity were observed in our cohort. Larger prospective studies are needed to confirm these results.

Comparing local control and distant metastasis in NSCLC patients between CyberKnife and conventional SBRT

BACKGROUND AND PURPOSE

Previous literature suggests that the dose proximally outside the PTV could have an impact on the incidence of distant metastasis (DM) after SBRT in stage I NSCLC patients. We investigated this observation (along with local failure) in deliveries made by different treatment modalities: robotic mounted linac SBRT (CyberKnife) vs conventional SBRT (VMAT/CRT).

MATERIALS AND METHODS

This study included 422 stage I NSCLC patients from 2 institutions who received SBRT: 217 treated conventionally and 205 with CyberKnife. The dose behavior outside the PTV of both sub-cohorts were compared by analyzing the mean dose in continuous shells extending 1, 2, 3, …, 100 mm from the PTV. Kaplan-Meier analysis was performed between the two sub-cohorts with respect to DM-free survival and local progression-free survival. A multivariable Cox proportional hazards model was fitted to the combined cohort (n = 422) with respect to DM incidence and local failure.

RESULTS

The shell-averaged dose fall-off beyond the PTV was found to be significantly more modest in CyberKnife plans than in conventional SBRT plans. In a 30 mm shell around the PTV, the mean dose delivered with CyberKnife (38.1 Gy) is significantly larger than with VMAT/CRT (22.8 Gy, p<10^-8). For 95% of CyberKnife plans, this region receives a mean dose larger than the 21 Gy threshold dose discovered in our previous study. In contrast, this occurs for only 75% of VMAT/CRT plans. The DM-free survival of the entire CyberKnife cohort is superior to that of the 25% of VMAT/CRT patients receiving less than the threshold dose (VMAT/CRT_<21Gy), with a hazard ratio of 5.3 (95% CI: 3.0-9.3, p<10^-8). The 2 year DM-free survival rates were 87% (95% CI: 81%-91%) and 44% (95% CI: 28%-58%) for CyberKnife and the below-threshold dose conventional cohorts, respectively. A multivariable analysis of the combined cohort resulted in the confirmation that threshold dose was a significant predictor of DM(HR = 0.28, 95% CI: 0.15-0.55, p<10^-3) when adjusted for other clinical factors. CyberKnife was also found to be superior to the entire VMAT/CRT with respect to local control (HR = 3.44, CI: 1.6-7.3). The 2-year local progression-free survival rates for the CyberKnife cohort and the VMAT/CRT cohort were 96% (95% CI: 92%-98%) and 88% (95% CI: 82%-92%) respectively.

CONCLUSIONS

In standard-of-care CyberKnife treatments, dose distributions that aid distant control are achieved 95% of the time. Although similar doses could be physically achieved by conventional SBRT, this is not always the case with current prescription practices, resulting in worse DM outcomes for 25% of conventional SBRT patients. Furthermore, CyberKnife was found to provide superior local control compared to VMAT/CRT.

Peritumoral radiomics features predict distant metastasis in locally advanced NSCLC

Purpose

Radiomics provides quantitative tissue heterogeneity profiling and is an exciting approach to developing imaging biomarkers in the context of precision medicine. Normal-appearing parenchymal tissues surrounding primary tumors can harbor microscopic disease that leads to increased risk of distant metastasis (DM). This study assesses whether computed-tomography (CT) imaging features of such peritumoral tissues can predict DM in locally advanced non-small cell lung cancer (NSCLC).

Material and methods

200 NSCLC patients of histological adenocarcinoma were included in this study. The investigated lung tissues were tumor rim, defined to be 3mm of tumor and parenchymal tissue on either side of the tumor border and the exterior region extended from 3 to 9mm outside of the tumor. Fifteen stable radiomic features were extracted and evaluated from each of these regions on pre-treatment CT images. For comparison, features from expert-delineated tumor contours were similarly prepared. The patient cohort was separated into training and validation datasets for prognostic power evaluation. Both univariable and multivariable analyses were performed for each region using concordance index (CI).

Results

Univariable analysis reveals that six out of fifteen tumor rim features were significantly prognostic of DM (p-value < 0.05), as were ten features from the visible tumor, and only one of the exterior features was. Multivariablely, a rim radiomic signature achieved the highest prognostic performance in the independent validation sub-cohort (CI = 0.64, p-value = 2.4×10⁻⁵) significantly over a multivariable clinical model (CI = 0.53), a visible tumor radiomics model (CI = 0.59), or an exterior tissue model (CI = 0.55). Furthermore, patient stratification by the combined rim signature and clinical predictor led to a significant improvement on the clinical predictor alone and also outperformed stratification using the combined tumor signature and clinical predictor.

Conclusions

We identified peritumoral rim radiomic features significantly associated with DM. This study demonstrated that peritumoral imaging characteristics may provide additional valuable information over the visible tumor features for patient risk stratification due to cancer metastasis.

Association of Target Volume Margins With Locoregional Control and Acute Toxicities for Non-small cell lung cancer Treated With Concurrent Chemoradiation Therapy

PURPOSE

This study aimed to investigate the association between target volume margins and clinical outcomes for patients with inoperable non-small cell lung cancer (NSCLC) treated with concurrent chemoradiation therapy.

METHODS AND MATERIALS

We reviewed the records of 82 patients with inoperable NSCLC treated between 2009 and 2016 with concurrent chemoradiation. All patients received positron emission tomography-based treatment planning, 4-dimensional computed tomography simulation to define an internal target volume, and daily cone beam computed tomography. We quantified variations in target volume margins with a margin deviation index (MDI), calculated as the percentage change in equivalent uniform dose between the original planning target volume (PTV) and a standard reference PTV 10 mm beyond the original gross tumor volume, consistent with the minimum margins mandated by recent NSCLC trials. Greater MDIs equated to smaller effective target volume margins. We dichotomized patients by the upper tercile MDI value (5.8%). Endpoints included time to locoregional progression and time to grade ≥ 3 radiation esophagitis (RE3) or radiation pneumonitis (RP3), modelled with the Fine-Gray method.

RESULTS

Median follow-up was 37.8 months (range, 5.9-58.1 months). Larger MDIs correlated with smaller clinical target volume (CTV) + PTV margins, larger gross tumor volumes, later treatment year, and intensity modulated radiation therapy use. The risk of locoregional progression did not differ for MDI ≥5.8% versus <5.8% (adjusted hazard ratio: 0.88; P = .76), but the risk of RE3 or RP3 was decreased for MDI ≥5.8% (adjusted hazard ratio: 0.27; P = .027). Patients with MDI ≥5.8% were treated with smaller CTV + PTV margins (median, 5.6 vs 8 mm; P < .0001) and a marginally lower volume of esophagus receiving ≥50 Gy (median, 31.1% vs 35.3%; P = .069).

CONCLUSIONS

Smaller margins were used for larger tumors but were not associated with an increase in locoregional failures. Additional studies could clarify whether smaller margins, when used alongside modern radiation therapy techniques, decrease treatment-related toxicity for inoperable NSCLC.

How Histopathologic Tumor Extent and Patterns of Recurrence Data Inform the Development of Radiation Therapy Treatment Volumes in Solid Malignancies

The ability to deliver highly conformal radiation therapy using intensity-modulated radiation therapy and particle therapy provides for new opportunities to improve patient outcomes by reducing treatment-related morbidities following radiation therapy. By reducing the volume of normal tissue exposed to radiation therapy (RT), while also allowing for the opportunity to escalate the dose of RT delivered to the tumor, use of conformal RT delivery should also provide the possibility of expanding the therapeutic index of radiotherapy. However, the ability to safely and confidently deliver conformal RT is largely dependent on our ability to clearly define the clinical target volume for radiation therapy, which requires an in-depth knowledge of histopathologic extent of different tumor types, as well as patterns of recurrence data. In this article, we provide a comprehensive review of the histopathologic and radiographic data that provide the basis for evidence-based guidelines for clinical tumor volume delineation.

Dosimetric Analysis of Microscopic Disease in SBRT for Lung Cancers

Objective:

The objective of this study is to theoretically and experimentally evaluate the dosimetry in the microscopic disease regions surrounding the tumor under stereotactic body radiation therapy of lung cancer.

Methods:

For simplicity, the tumor was considered moving along 1 dimension with a periodic function. The probability distribution function of the tumor position was generated according to the motion pattern and was used to estimate the delivered dose in the microscopic disease region. An experimental measurement was conducted to validate both the estimated dose with a probability function and the calculated dose from 4-dimensional computed tomography data using a dynamic thorax phantom. Four tumor motion patterns were simulated with cos⁴(x) and sin(x), each with 2 different amplitudes: 10 mm and 5 mm. A 7-field conformal plan was created for treatment delivery. Both films (EBT2) and optically stimulated luminescence detectors were inserted in and around the target of the phantom to measure the delivered doses. Dose differences were evaluated using gamma analysis with 3%/3 mm.

Results:

The average gamma index between measured doses using film and calculated doses using average intensity projection simulation computed tomography was 80.8% ± 0.9%. In contrast, between measured doses using film and calculated doses accumulated from 10 sets of 4-dimensional computed tomography data, it was 98.7% ± 0.6%. The measured doses using optically stimulated luminescence detectors matched very well (within 5% of the measurement uncertainty) with the theoretically calculated doses using probability distribution function at the corresponding position. Respiratory movement caused inadvertent irradiation exposure, with 70% to 80% of the dose line wrapped around the 10 mm region outside the target.

Conclusion:

The use of static dose calculation in the treatment planning system could substantially underestimate the actual delivered dose in the microscopic disease region for a moving target. The margin for microscopic disease may be substantially reduced or even eliminated for lung stereotactic body radiation therapy.

Magnetic resonance imaging in precision radiation therapy for lung cancer

Radiotherapy remains the cornerstone of curative treatment for inoperable locally advanced lung cancer, given concomitantly with platinum-based chemotherapy. With poor overall survival, research efforts continue to explore whether integration of advanced radiation techniques will assist safe treatment intensification with the potential for improving outcomes. One advance is the integration of magnetic resonance imaging (MRI) in the treatment pathway, providing anatomical and functional information with excellent soft tissue contrast without exposure of the patient to radiation. MRI may complement or improve the diagnostic staging accuracy of F-18 fluorodeoxyglucose position emission tomography and computerized tomography imaging, particularly in assessing local tumour invasion and is also effective for identification of nodal and distant metastatic disease. Incorporating anatomical MRI sequences into lung radiotherapy treatment planning is a novel application and may improve target volume and organs at risk delineation reproducibility. Furthermore, functional MRI may facilitate dose painting for heterogeneous target volumes and prediction of normal tissue toxicity to guide adaptive strategies. MRI sequences are rapidly developing and although the issue of intra-thoracic motion has historically hindered the quality of MRI due to the effect of motion, progress is being made in this field. Four-dimensional MRI has the potential to complement or supersede 4D CT and 4D F-18-FDG PET, by providing superior spatial resolution. A number of MR-guided radiotherapy delivery units are now available, combining a radiotherapy delivery machine (linear accelerator or cobalt-60 unit) with MRI at varying magnetic field strengths. This novel hybrid technology is evolving with many technical challenges to overcome. It is anticipated that the clinical benefits of MR-guided radiotherapy will be derived from the ability to adapt treatment on the fly for each fraction and in real-time, using 'beam-on' imaging. The lung tumour site group of the Atlantic MR-Linac consortium is working to generate a challenging MR-guided adaptive workflow for multi-institution treatment intensification trials in this patient group.

The clinical target volume in lung, head-and-neck, and esophageal cancer: Lessons from pathological measurement and recurrence analysis

Radiotherapy research has achieved remarkable progress in target volume definition. Advances in medical imaging facilitate more precise localization of the gross tumor volume, alongside a more detailed understanding of the geometric uncertainties associated with treatment delivery that has enabled robust safety margins to be customized to the specific treatment scenario at hand. By contrast, the clinical target volume, meant to encompass gross tumor, as well as, adjacent sub-clinical disease, has evolved very little. It is more often defined by clinician experience and institutional convention than on a patient-specific basis. This disparity arises from the inherent invisibility of sub-clinical disease in current medical imaging. Its incidence and expanse can only be ascertained via indirect means. This article reviews two such strategies: histopathological measurements on resection specimen and analyses of locoregional recurrences after radiotherapy.

Radio(chemo)therapy in locally advanced nonsmall cell lung cancer

Definitive radiochemotherapy is the standard treatment for many patients with locally advanced nonsmall cell lung cancer (NSCLC). Treatment outcomes have improved over the last decades. Several treatment regimens have been shown effective and safe. This review summarises the results of significant studies between 1996 and 2015 on concomitant and sequential radiochemotherapy regimens and radiation dose per fraction. Beside therapy regimens, optimised radiotherapy planning is indispensable to improve outcome and minimise radiation-induced toxicity. An insight into the rationale of radiotherapy planning for stage III NSCLC is also provided.

Concomitant radiochemotherapy is an established standard treatment for locally advanced nonsmall cell lung cancerhttp://ow.ly/TTkkc

Histologic Subtype in Core Lung Biopsies of Early-Stage Lung Adenocarcinoma is a Prognostic Factor for Treatment Response and Failure Patterns After Stereotactic Body Radiation Therapy

PURPOSE

Stereotactic body radiation therapy (SBRT) has emerged as an effective treatment for early-stage lung cancer. The histologic subtype of surgically resected lung adenocarcinoma is recognized as a prognostic factor, with the presence of solid or micropapillary patterns predicting poor outcomes. We describe the outcomes after SBRT for early-stage lung adenocarcinoma stratified by histologic subtype.

METHODS AND MATERIALS

We identified 119 consecutive patients (124 lesions) with stage I to IIA lung adenocarcinoma who had undergone definitive SBRT at our institution from August 2008 to August 2015 and had undergone core biopsy. Histologic subtyping was performed according to the 2015 World Health Organization classification. Of the 124 tumors, 37 (30%) were a high-risk subtype, defined as containing a component of solid and/or micropapillary pattern. The cumulative incidences of local, nodal, regional, and distant failure were compared between the high-risk and non-high-risk adenocarcinoma subtypes using Gray's test, and multivariable-adjusted hazard ratios (HRs) were estimated from propensity score-weighted Cox regression models.

RESULTS

The median follow-up for the entire cohort was 17 months and for surviving patients was 21 months. The 1-year cumulative incidence of and adjusted HR for local, nodal, regional, and distant failure in high-risk versus non-high-risk lesions was 7.3% versus 2.7% (HR 16.8; 95% confidence interval [CI] 3.5-81.4), 14.8% versus 2.6% (HR 3.8; 95% CI 0.95-15.0), 4.0% versus 1.2% (HR 20.9; 95% CI 2.3-192.3), and 22.7% versus 3.6% (HR 6.9; 95% CI 2.2-21.1), respectively. No significant difference was seen with regard to overall survival.

CONCLUSIONS

The outcomes after SBRT for early-stage adenocarcinoma of the lung correlate highly with histologic subtype, with micropapillary and solid tumors portending significantly higher rates of locoregional and metastatic progression. In this context, the histologic subtype determined from core biopsies is a prognostic factor and could have important implications for patient selection, adjuvant treatment, biopsy methods, and clinical trial design.

An assessment of cone beam CT in the adaptive radiotherapy planning process for non-small-cell lung cancer patients

OBJECTIVE

To investigate the potential use of cone beam CT (CBCT) in adaptive radiotherapy (ART) planning process for non-small-cell lung cancer (NSCLC).

METHODS

17 retrospective patients with NSCLC Stage T1-T4, who had completed a course of radiotherapy with weekly CBCT imaging were selected for the study. The patients had been delineated and planned for three-dimensional (3D) conformal treatment (prescription: 55 Gy in 20 fractions) based on free-breathing four-dimensional CT data. Of these initial 17 patients, 12 had full quantitative data on gross tumour volume (GTV) position and volume throughout treatment. GTV delineation was carried out on weekly CBCT by a clinical oncologist. For each patient, mean percentage change in GTV and centre of mass (COM) displacement (based on 3D vectors) were calculated throughout treatment. Volume overlap between GTVs was calculated. Correlation of the COM displacement and planning GTV (pGTV) was assessed. A linear mixed model with patients as random effects was fitted to the data to assess potential benefit from using ART for these patients.

RESULTS

Comparison of CBCT-based GTV acquired prior to Fraction 1 (cbctGTV1) to pGTV showed mean 20 ± 19% volume increase using a related sample Wilcoxon signed rank test p = 0.04. Correlation was identified between volume reductions and dose delivered (beta = -0.003, p < 0.001)-a highly statistically significant association. Compared with cbctGTV1, the mean ratios ± standard deviation were cbctGTV2, 0.93 ± 0.08; cbctGTV3, 0.84 ± 0.12; and cbctGTV4, 0.75 ± 0.14. The dice similarity coefficient was 0.81 ± 0.14, 0.78 ± 0.17, 0.73 ± 0.19, respectively. The COM was consistent throughout treatment (mean 0.35 ± 0.24 cm). A fitted model predicts that a mean change of 30% volume relative to cbctGTV1 occurs at a dose of approximately 50 Gy.

CONCLUSION

Using a 30% reduction in volume, ART would not be of benefit for all radiotherapy-alone-treated patients with NSCLC assessed in this study. For individual patients and patients with atelectasis, CBCT imaging was able to identify volume change.

ADVANCES IN KNOWLEDGE

For patients treated with 55 Gy in 20 fractions, target volume changes throughout treatment have been demonstrated using CBCT and can be used to highlight patients who may benefit from ART.

Tumor Spread through Air Spaces is an Important Pattern of Invasion and Impacts the Frequency and Location of Recurrences after Limited Resection for Small Stage I Lung Adenocarcinomas

INTRODUCTION

Tumor invasion in lung adenocarcinoma is defined as infiltration of stroma, blood vessels, or pleura. Based on observation of tumor spread through air spaces (STAS), we considered whether this could represent new patterns of invasion and investigated whether it correlated with locoregional versus distant recurrence according to limited resection versus lobectomy.

METHODS

We reviewed resected small (less than or equal to 2 cm) stage I lung adenocarcinomas (n = 411; 1995-2006). Tumor STAS was defined as tumor cells-micropapillary structures, solid nests, or single cells-spreading within air spaces in the lung parenchyma beyond the edge of the main tumor. Competing risks methods were used to estimate risk of disease recurrence and its associations with clinicopathological risk factors.

RESULTS

STAS was observed in 155 cases (38%). In the limited resection group (n = 120), the risk of any recurrence was significantly higher in patients with STAS-positive tumors than that of patients with STAS-negative tumors (5-year cumulative incidence of recurrence, 42.6% versus 10.9%; P < 0.001); the presence of STAS correlated with higher risk of distant (P = 0.035) and locoregional recurrence (P = 0.001). However, in the lobectomy group (n = 291), the presence of STAS was not associated with either any (P = 0.50) or distant recurrence (P = 0.76). In a multivariate analysis, the presence of tumor STAS remained independently associated with the risk of developing recurrence (hazard ratio, 3.08; P = 0.014).

CONCLUSION

The presence of STAS is a significant risk factor of recurrence in small lung adenocarcinomas treated with limited resection. These findings support our proposal that STAS should formally be recognized as a pattern of invasion in lung adenocarcinoma.

Is a Clinical Target Volume (CTV) Necessary in the Treatment of Lung Cancer in the Modern Era Combining 4-D Imaging and Image-guided Radiotherapy (IGRT)?

Objective: We hypothesized that omission of clinical target volumes (CTV) in lung cancer radiotherapy would not compromise control by determining retrospectively if the addition of a CTV would encompass the site of failure.

Methods: Stage II-III patients were treated from 2009-2012 with daily cone-beam imaging and a 5 mm planning target volume (PTV) without a CTV. PTVs were expanded 1 cm and termed CTVretro. Recurrences were scored as 1) within the PTV, 2) within CTVretro, or 3) outside the PTV. Locoregional control (LRC), distant control (DC), progression-free survival (PFS), and overall survival (OS) were estimated.

Result: Among 110 patients, Stage IIIA 57%, IIIB 32%, IIA 4%, and IIB 7%. Eighty-six percent of Stage III patients received chemotherapy. Median dose was 70 Gy (45-74 Gy) and fraction size ranged from 1.5-2.7 Gy. Median follow-up was 12 months, median OS was 22 months (95% CI 19-30 months), and LRC at two years was 69%. Fourteen local and eight regional events were scored with two CTVretro failures equating to a two-year CTV failure-free survival of 98%.

Conclusion: Omission of a 1 cm CTV expansion appears feasible based on only two events among 110 patients and should be considered in radiation planning.

Prognostic nomogram to predict survival after surgery for synchronous multiple lung cancers in multiple lobes

INTRODUCTION

In the absence of metastatic disease, surgery for synchronous non-small-cell lung cancers involving multiple lobes can be curative. However, there currently exists no reliable prognostic instrument for this patient population after surgery. We undertook an analysis to examine the prognostic significance of adenocarcinoma histology and developed a prognostic nomogram.

METHODS

This study was a pooled analysis of six previously reported datasets. Patients without extra-thoracic metastasis who underwent surgical resection of synchronous lung cancers in multiple lobes were included. Those with small cell cancer, carcinoid tumor, or exclusively carcinoma in situ were excluded. A multivariable Cox proportional hazards regression model was fitted to identify independent survival predictors for nomogram development.

RESULTS

Data from 467 patients were analyzed. Adenocarcinoma was a sole histology in 253 patients (54.2%). Those with exclusively adenocarcinoma histology had a better median survival than their counterparts: 67.4 versus 36.2 months, (p < 0.001). Multivariable analysis incorporating histology, sex, age, maximal T-size, highest N-stage, and laterality demonstrated that having exclusively adenocarcinoma histology independently predicted an improved survival: hazard ratio 0.61 (95% confidence interval: 0.48, 0.78). Other favorable survival predictors were N0, T-size less than or equal to 3 cm, bilateral cancers, age less than 70 years, and women sex. The developed nomogram was well calibrated and demonstrated a moderate to good discrimination with a bootstrap-corrected Harrell C-statistic of 0.70.

CONCLUSION

Several unique features among patients with resected synchronous multiple lung cancers, including the presence of exclusively adenocarcinoma histology, are of prognostic significance. A simple nomogram incorporating these factors can be utilized to predict patient survival with acceptable accuracy.

The importance of surrounding tissues and window settings for contouring of moving targets

AIM

The aim of the study was to assess the importance of surrounding tissues for the delineation of moving targets in tissue-specific phantoms and to find optimal settings for lung, soft tissue, and liver tumors.

MATERIALS AND METHODS

Tumor movement was simulated by a water-filled table tennis ball (target volume, TV). Three phantoms were created: corkboards to simulate lung tissue (lung phantom, LunPh), animal fat as fatty soft tissue (fatty tissue phantom, FatPh), and water enhanced with contrast medium as the liver tissue (liver phantom, LivPh). Slow planning three-dimensional compute tomography images (3D-CTs) were acquired with and without phantom movements. One-dimensional tumor movement (1D), three-dimensional tumor movement (3D), as well as a real patient's tumor trajectories were simulated. The TV was contoured using two lung window settings, two soft-tissue window settings, and one liver window setting. The volumes were compared to mathematical calculated values.

RESULTS

TVs were underestimated in all phantoms due to movement. The use of soft-tissue windows in the LivPh led to a significant underestimation of the TV (70.8% of calculated TV). When common window settings [LunPh + 200 HU/-1,000 HU (upper window/lower window threshold); FatPh: + 240 HU/-120 HU; LivPh: + 175 HU/+ 50 HU] were used, the contoured TVs were: LivPh, 84.0%; LunPh, 93.2%, and FatPh, 92.8%. The lower window threshold had a significant impact on the size of the delineated TV, whereas changes of the upper threshold led only to small differences.

CONCLUSION

The decisive factor for window settings is the lower window threshold (for adequate TV delineation in the lung and fatty-soft tissue it should be lower than density values of surrounding tissue). The use of a liver window should be considered.

A block matching-based registration algorithm for localization of locally advanced lung tumors

PURPOSE

To implement and evaluate a block matching-based registration (BMR) algorithm for locally advanced lung tumor localization during image-guided radiotherapy.

METHODS

Small (1 cm(3)), nonoverlapping image subvolumes ("blocks") were automatically identified on the planning image to cover the tumor surface using a measure of the local intensity gradient. Blocks were independently and automatically registered to the on-treatment image using a rigid transform. To improve speed and robustness, registrations were performed iteratively from coarse to fine image resolution. At each resolution, all block displacements having a near-maximum similarity score were stored. From this list, a single displacement vector for each block was iteratively selected which maximized the consistency of displacement vectors across immediately neighboring blocks. These selected displacements were regularized using a median filter before proceeding to registrations at finer image resolutions. After evaluating all image resolutions, the global rigid transform of the on-treatment image was computed using a Procrustes analysis, providing the couch shift for patient setup correction. This algorithm was evaluated for 18 locally advanced lung cancer patients, each with 4-7 weekly on-treatment computed tomography scans having physician-delineated gross tumor volumes. Volume overlap (VO) and border displacement errors (BDE) were calculated relative to the nominal physician-identified targets to establish residual error after registration.

RESULTS

Implementation of multiresolution registration improved block matching accuracy by 39% compared to registration using only the full resolution images. By also considering multiple potential displacements per block, initial errors were reduced by 65%. Using the final implementation of the BMR algorithm, VO was significantly improved from 77% ± 21% (range: 0%-100%) in the initial bony alignment to 91% ± 8% (range: 56%-100%;p < 0.001). Left-right, anterior-posterior, and superior-inferior systematic BDE were 3.2, 2.4, and 4.4 mm, respectively, with random BDE of 2.4, 2.1, and 2.7 mm. Margins required to include both localization and delineation uncertainties ranged from 5.0 to 11.7 mm, an average of 40% less than required for bony alignment.

CONCLUSIONS

BMR is a promising approach for automatic lung tumor localization. Further evaluation is warranted to assess the accuracy and robustness of BMR against other potential localization strategies.

Thoracoscopic lobectomy as salvage surgery for local recurrence of non-small cell lung cancer after carbon ion radiotherapy in an initially operable patient

Carbon ion radiotherapy (CIRT) for patients with early-stage non-small cell lung cancer (NSCLC) has recently provided favorable local control with very few toxic reactions. Because CIRT for NSCLC has been mostly performed for elderly or inoperable patients, salvage surgery for NSCLC after CIRT has rarely been reported. We describe a case of complete thoracoscopic right upper lobectomy with mediastinal lymphadenectomy performed as salvage surgery for local recurrence of stage IA NSCLC after CIRT in an initially operable patient who had refused surgery 27 months previously. Pleural adhesions caused by CIRT were localized to the pulmonary apex and the central pulmonary structures were intact at the time of the salvage surgery, which allowed us to successfully perform thoracoscopic lobectomy without any complications. Thus, salvage surgery for NSCLC after CIRT may be feasible in an initially operable patient, as CIRT appears to be unlikely to cause any difficulties in the salvage surgery.

Patterns of locoregional failure in stage III non-small cell lung cancer treated with definitive chemoradiation therapy

PURPOSE

Chemoradiation therapy (CRT) is the core treatment of locally advanced non-small cell lung cancer (LA-NSCLC), but potential toxicities limit radiation therapy dose. These toxicities, plus the advent of increasingly conformal radiation therapy, have prioritized target definition and the use of involved-field radiation therapy (IFRT). Published data largely focus on regional rather than local failure patterns. We report our pattern-of-failure experience treating patients with LA-NSCLC with definitive CRT, focusing on both local and regional recurrences with detailed dosimetric analyses of failure location.

METHODS AND MATERIALS

Patients treated between December 2004-2010 were included. Imaging scans from date of failure were fused with the RT-planning CT scan, and recurrent nodes were contoured to determine if the recurrence was in a previously irradiated region, defined as involved nodal recurrence (INR) versus elective nodal recurrence (ENR). Local failures were contoured and identified as in-field, marginal, or out-of-field based on dose received. Actuarial overall survival (OS) and progression-free survival (PFS) were calculated, and the cumulative incidences of local, regional, locoregional, and distant recurrence (CILR, CIRR, CILRR, CIDR) were determined with death as a competing risk.

RESULTS

One hundred five patients were included with a median survival of 21.8 months. The 3-year OS and PFS were 36% and 22%, respectively. The 3 year CILRR, CILR, CIRR, CIDR were 41%, 38%, 40%, and 58%, respectively. Thirty patients failed regionally, but only 7 patients developed an ENR with no concurrent local failure or INR, and only 1 of these patients did not develop distant metastases within 1 month of recurrence. A total of 21 patients (20%) developed an ENR with or without other areas of recurrence.

CONCLUSIONS

Elective regional recurrences rarely occurred as the sole site of failure, despite the use of IFRT. Moreover, the pattern of local failure was entirely in-field. These data strongly support field design focusing on gross nodal and primary disease.

Place of proton radiotherapy in future radiotherapy practice

Proton beam therapy offers potential dosimetric advantages coupled with complexities not currently encompassed in the photon radiotherapy experience. The practice is evolving alongside other developments in oncology, which include higher precision of photon radiotherapy, greater understanding of the biological effect of radiation and its potential modification, and the recognition of new molecular targets with a plethora of agents aimed at affecting biological function. For proton therapy to have an impact on clinical practice requires full examination in rigorous clinical trials comparing proton with best photon therapy. Only the results of present and future studies, showing equivalent, superior, or even potentially worse clinical results will shape their application. The desired goal is to develop personalized treatment strategies of fractionation appropriate for protons potentially combined with targeted agents. We describe the steps in health technology assessment and the potential design of preclinical and clinical trials to define the role of proton therapy in the future.

Current challenges in clinical target volume definition: tumour margins and microscopic extensions

Determination of optimal clinical target volume (CTV) margins around gross tumour volume (GTV) for modern radiotherapy techniques, requiring more precise target definitions, is controversial and complex. Tumour localisation has been greatly improved using molecular imaging integrated with conventional imaging techniques. However, the exact incidence and extent of microscopic disease, to be encompassed by CTV, cannot be visualised by any techniques developed to date and remain uncertain. As a result, the CTV is generally determined by clinicians based on their experience and patients' histopathological data. In this article we review histopathological studies addressing the extent of subclinical disease and its possible correlation with tumour characteristics in various tumour sites. The data have been tabulated to facilitate a comparison between proposed margins by different investigations and with current margins generally accepted for each tumour site. It is concluded that there is a need for further studies to reach a consensus on the optimal CTV pertaining to each tumour site.

Translational and rotational intra- and inter-fractional errors in patient and target position during a short course of frameless stereotactic body radiotherapy

BACKGROUND

Implementation of cone beam computed tomography (CBCT) in frameless stereotactic body radiotherapy (SBRT) of lung tumours enables setup correction based on tumour position. The aim of this study was to compare setup accuracy with daily soft tissue matching to bony anatomy matching and evaluate intra- and inter-fractional translational and rotational errors in patient and target positions.

MATERIAL AND METHODS

Fifteen consecutive SBRT patients were included in the study. Vacuum cushions were used for immobilisation. SBRT plans were based on midventilation phase of four-dimensional (4D)-CT or three-dimensional (3D)-CT from PET/CT. Margins of 5 mm in the transversal plane and 10 mm in the cranio-caudal (CC) direction were applied. SBRT was delivered in three fractions within a week. At each fraction, CBCT was performed before and after the treatment. Setup accuracy comparison between soft tissue matching and bony anatomy matching was evaluated on pretreatment CBCTs. From differences in pre- and post-treatment CBCTs, we evaluated the extent of translational and rotational intra-fractional changes in patient position, tumour position and tumour baseline shift. All image registration was rigid with six degrees of freedom.

RESULTS

The median 3D difference between patient position based on bony anatomy matching and soft tissue matching was 3.0 mm (0-8.3 mm). The median 3D intra-fractional change in patient position was 1.4 mm (0-12.2 mm) and 2.2 mm (0-13.2 mm) in tumour position. The median 3D intra-fractional baseline shift was 2.2 mm (0-4.7 mm). With correction of translational errors, the remaining systematic and random errors were approximately 1°.

CONCLUSION

. Soft tissue tumour matching improved precision of treatment delivery in frameless SBRT of lung tumours compared to image guidance using bone matching. The intra-fractional displacement of the target position was affected by both translational and rotational changes in tumour baseline position relative to the bony anatomy and by changes in patient position.

Advances in radiotherapy: from 2D to 4D

Imaging techniques are increasingly integrated into modern radiotherapy (RT). Multimodal imaging is used to define the target for RT planning and imaging technology is also being integrated into linear accelerators, with the purpose to ensure delivery of radiation with high geometric accuracy. The integration of imaging in RT calls for a stronger collaboration between diagnostic radiologists and the professions involved in RT.

Tumor regression and positional changes in non-small cell lung cancer during radical radiotherapy

INTRODUCTION

We have used respiratory-correlated cone beam computed tomography (rcCBCT) imaging to study the volumetric and positional changes that occur throughout the course of radical radiotherapy in non-small cell lung cancer (NSCLC).

METHODS

Tumor volumes and centers of mass were recorded and analyzed on weekly serial rcCBCT images of NSCLC patients treated with radical radiotherapy to a dose ≥45 Gy with concurrent chemotherapy.

RESULTS

Sixty patients with locally advanced NSCLC were included; in 31 patients, the primary tumor was peripheral and thus suitable for contouring. There was a mean percent decrease of 40.2% by fraction 15 and 51.1% by treatment completion. Among all 60 patients, 19 patients (32%) had more than 30% regression by fraction 15 and 25 patients (81%) by treatment completion. Statistically significant tumor migration in at least one direction between the first and the last 2 weeks was demonstrated in 14 of 27 patients. Clinically relevant changes (atelectasis and effusions) were noted in 11 of 29 visually assessed patients.

CONCLUSIONS

Current rcCBCT image quality allows assessment of tumors located more peripherally. Significant tumor regression was documented in the majority of patients. In view of these observations, the suitability of adaptive radiotherapy in radical lung cancer treatment should be further investigated.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Noninvasive evaluation of microscopic tumor extensions using standardized uptake value and metabolic tumor volume in non-small-cell lung cancer

PURPOSE

To prospectively evaluate whether maximal microscopic extensions (MEmax) correlate with maximal standardized uptake value (SUVmax) and metabolic tumor volume (MTV) at 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) images in non-small-cell lung cancer (NSCLC).

METHODS AND MATERIALS

Thirty-nine patients with Stage I-IIIA NSCLC underwent surgery after FDG-PET/CT scanning. SUVmax and MTV were calculated on the PET/CT images. The maximum linear distance from the tumor margin to the farthest extent of the tumor in every dimension was measured at the tumor section. The correlations among MEmax, SUVmax, MTV and other clinical pathologic parameters were analyzed.

RESULTS

MEmax for all patients had a significant correlation with SUVmax (r = 0.777, p = 0.008) and MTV (r = 0.724, p < 0.001). When expressed in terms of the probability of covering ME with respect to a given margin, we suggested that margins of 1.93 mm, 3.90 mm, and 9.60 mm for SUVmax ≤ 5, 5-10, and >10 added to the gross tumor volume would be adequate to cover 95% of ME.

CONCLUSIONS

This study demonstrated that tumors with high SUVmax and MTV have more MEmax and would therefore require more margin expansion from gross tumor volume to clinical target volume. FDG-PET/CT, especially for SUVmax, is promising and effective and merits additional study in noninvasive delimiting of the clinical target volume margin for NSCLC.

Therapeutic implications of molecular imaging with PET in the combined modality treatment of lung cancer

Molecular imaging with PET, and certainly integrated PET-CT, combining functional and anatomical imaging, has many potential advantages over anatomical imaging alone in the combined modality treatment of lung cancer. The aim of the current article is to review the available evidence regarding PET with FDG and other tracers in the combined modality treatment of locally advanced lung cancer. The following topics are addressed: tumor volume definition, outcome prediction and the added value of PET after therapy, and finally its clinical implications and future perspectives. The additional value of FDG-PET in defining the primary tumor volume has been established, mainly in regions with atelectasis or post-treatment effects. Selective nodal irradiation (SNI) of FDG-PET positive nodal stations is the preferred treatment in NSCLC, being safe and leading to decreased normal tissue exposure, providing opportunities for dose escalation. First results in SCLC show similar results. FDG-uptake on the pre-treatment PET scan is of prognostic value. Data on the value of pre-treatment FDG-uptake to predict response to combined modality treatment are conflicting, but the limited data regarding early metabolic response during treatment do show predictive value. The FDG response after radical treatment is of prognostic significance. FDG-PET in the follow-up has potential benefit in NSCLC, while data in SCLC are lacking. Radiotherapy boosting of radioresistant areas identified with FDG-PET is subject of current research. Tracers other than (18)FDG are promising for treatment response assessment and the visualization of intra-tumor heterogeneity, but more research is needed before they can be clinically implemented.

Localization accuracy of the clinical target volume during image-guided radiotherapy of lung cancer

PURPOSE

To evaluate the position and shape of the originally defined clinical target volume (CTV) over the treatment course, and to assess the impact of gross tumor volume (GTV)-based online computed tomography (CT) guidance on CTV localization accuracy.

METHODS AND MATERIALS

Weekly breath-hold CT scans were acquired in 17 patients undergoing radiotherapy. Deformable registration was used to propagate the GTV and CTV from the first weekly CT image to all other weekly CT images. The on-treatment CT scans were registered rigidly to the planning CT scan based on the GTV location to simulate online guidance, and residual error in the CTV centroids and borders was calculated.

RESULTS

The mean GTV after 5 weeks relative to volume at the beginning of treatment was 77% ± 20%, whereas for the prescribed CTV, it was 92% ± 10%. The mean absolute residual error magnitude in the CTV centroid position after a GTV-based localization was 2.9 ± 3.0 mm, and it varied from 0.3 to 20.0 mm over all patients. Residual error of the CTV centroid was associated with GTV regression and anisotropy of regression during treatment (p = 0.02 and p = 0.03, respectively; Spearman rank correlation). A residual error in CTV border position greater than 2 mm was present in 77% of patients and 50% of fractions. Among these fractions, residual error of the CTV borders was 3.5 ± 1.6 mm (left-right), 3.1 ± 0.9 mm (anterior-posterior), and 6.4 ± 7.5 mm (superior-inferior).

CONCLUSIONS

Online guidance based on the visible GTV produces substantial error in CTV localization, particularly for highly regressing tumors. The results of this study will be useful in designing margins for CTV localization or for developing new online CTV localization strategies.