Correlating Dose Variables with Local Tumor Control in Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer: A Modeling Study on 1500 Individual Treatments

Impact of Maximum Point Dose Within the Planning Target Volume on Local Control of Nonsmall Cell Lung Cancer Treated With Stereotactic Body Radiotherapy

BACKGROUND

No consensus exists on the maximum dose delivered to the planning target volume (PTV) in the delivery of stereotactic body radiotherapy (SBRT) for primary lung cancer. We investigated whether higher biologically effective doses (BED) within the PTV were associated with improved tumor control.

METHODS

We reviewed patients with early-stage, node-negative nonsmall cell lung cancer who received curative-intent SBRT between 2005 and 2018. We calculated the maximum BED (maxBED) within the PTV for all patients, analyzing outcomes using the cumulative incidence method and Fine-Gray test statistics to assess prognostic impact.

RESULTS

We analyzed 171 patients (median age, 70.2; range, 43 to 90 y) with 181 lung nodules. Median follow-up was 2.7 years (range, 0.1 to 12 y) for all patients and 4.2 years (range, 0.2 to 8.4 y) for living patients. Median maximum tumor diameter was 1.9 cm (range, 0.7 to 5.6 cm). Patients received a prescription of 48 or 50 Gy in 4 or 5 fractions, respectively, except for one who received 60 Gy in 5 fractions. Median maxBED was 120 Gy (range, 101 to 171 Gy). There was no difference in the 3-year local control (LC) rate among patients treated with a maxBED<120 Gy versus ≥120 Gy ( P =0.83).

CONCLUSIONS

No significant differences in LC were observed between patients with early-stage nonsmall cell lung cancer treated with SBRT in 4 or 5 fractions with a maxBED≥120 Gy. However, a higher maxBED trended toward improved LC rates, suggesting a maxBED threshold greater than 120 Gy may be needed to improve LC rates.

Treatment planning and delivery practice of lung SBRT: Results of the 2022 ESTRO physics survey

BACKGROUND AND PURPOSE

The use of Stereotactic Body Radiation Therapy (SBRT) in lung cancer is increasing. However, there is no consensus on the most appropriate treatment planning and delivery practice for lung SBRT. To gauge the range of practice, quantify its variability and identify where consensus might be achieved, ESTRO surveyed the medical physics community.

MATERIALS AND METHODS

An online survey was distributed to ESTRO's physicist membership in 2022, covering experience, dose and fractionation, target delineation, dose calculation and planning practice, imaging protocols, and quality assurance.

RESULTS

Two-hundred and forty-four unique answers were collected after data cleaning. Most respondents were from Europe the majority of which had more than 5 years' experience in SBRT. The large majority of respondents deliver lung SBRT with the VMAT technique on C-arm Linear Accelerators (Linacs) employing daily pre-treatment CBCT imaging. A broad spectrum of fractionation schemes were reported, alongside an equally wide range of dose prescription protocols. A clear preference was noted for prescribing to 95% or greater of the PTV. Several issues emerged regarding the dose calculation algorithm: 22% did not state it while 24% neglected to specify the conditions under which the dose was calculated. Contouring was usually performed on Maximum or Average Intensity Projection images while dose was mainly computed on the latter. No clear indications emerged for plan homogeneity, complexity, and conformity assessment. Approximately 40% of the responders participated in inter-centre credentialing of SBRT in the last five years. Substantial differences emerged between high and low experience centres, with the latter employing less accurate algorithms and older equipment.

CONCLUSION

The survey revealed an evident heterogeneity in numerous aspects of the clinical implementation of lung SBRT treatments. International guidelines and codes of practice might promote harmonisation.

Multicentric development and evaluation of [18F]FDG PET/CT and CT radiomic models to predict regional and/or distant recurrence in early-stage non-small cell lung cancer treated by stereotactic body radiation therapy

PURPOSE

To develop machine learning models to predict regional and/or distant recurrence in patients with early-stage non-small cell lung cancer (ES-NSCLC) after stereotactic body radiation therapy (SBRT) using [18F]FDG PET/CT and CT radiomics combined with clinical and dosimetric parameters.

METHODS

We retrospectively collected 464 patients (60% for training and 40% for testing) from University Hospital of Liège and 63 patients from University Hospital of Brest (external testing set) with ES-NSCLC treated with SBRT between 2010 and 2020 and who had undergone pretreatment [18F]FDG PET/CT and planning CT. Radiomic features were extracted using the PyRadiomics toolbox®. The ComBat harmonization method was applied to reduce the batch effect between centers. Clinical, radiomic, and combined models were trained and tested using a neural network approach to predict regional and/or distant recurrence.

RESULTS

In the training (n = 273) and testing sets (n = 191 and n = 63), the clinical model achieved moderate performances to predict regional and/or distant recurrence with C-statistics from 0.53 to 0.59 (95% CI, 0.41, 0.67). The radiomic (original_firstorder_Entropy, original_gldm_LowGrayLevelEmphasis and original_glcm_DifferenceAverage) model achieved higher predictive ability in the training set and kept the same performance in the testing sets, with C-statistics from 0.70 to 0.78 (95% CI, 0.63, 0.88) while the combined model performs moderately well with C-statistics from 0.50 to 0.62 (95% CI, 0.37, 0.69).

CONCLUSION

Radiomic features extracted from pre-SBRT analog and digital [18F]FDG PET/CT outperform clinical parameters in the prediction of regional and/or distant recurrence and to discuss an adjuvant systemic treatment in ES-NSCLC. Prospective validation of our models should now be carried out.

Dosimetric Analysis of Proximal Bronchial Tree Subsegments to Assess The Risk of Severe Toxicity After Stereotactic Body Radiation Therapy of Ultra-central Lung Tumors

•Stereotactic body radiation therapy (SBRT) for ultra-central lung tumors is associated with high toxicity rates.•To evaluate differences in radiosensitivity within the proximal bronchial tree (PBT), the PBT was sub-segmented into seven anatomical sections.•A risk-adapted SBRT regimen of EQD2_10 = 54.4 Gy in 8 or 10 fractions results in excellent local control and low rates of severe toxicity.•Data from a recent meta-analysis, the NORDIC Hilus trial and dosimetric data from this study were combined to create a NTCP model.•A dose threshold of EQD2_3 = 100 Gy to the PBT or any of its subsegments is expected to result in low rates of severe bronchial toxicity.

MR-guided stereotactic radiotherapy of infra-diaphragmatic oligometastases: Evaluation of toxicity and dosimetric parameters

BACKGROUND AND PURPOSE

The SOFT trial is a prospective, multicenter, phase 2 trial investigating magnetic resonance (MR)-guided stereotactic ablative radiotherapy (SABR) for abdominal, soft tissue metastases in patients with oligometastatic disease (OMD) (clinicaltrials.gov ID NCT04407897). We present the primary endpoint analysis of 1-year treatment-related toxicity (TRAE).

MATERIALS AND METHODS

Patients with up to five oligometastases from non-hematological cancers were eligible for inclusion. A risk-adapted strategy prioritized fixed organs at risk (OAR) constraints over target coverage. Fractionation schemes were 45-67.5 Gy in 3-8 fractions. The primary endpoint was grade ≥ 4 TRAE within 12 months post-SABR. The association between the risk of gastrointestinal (GI) toxicity and clinical and dosimetric parameters was tested using a normal tissue complication probability model.

RESULTS

We included 121 patients with 147 oligometastatic targets, mainly located in the liver (41 %), lymph nodes (35 %), or adrenal glands (14 %). Nearly half of all targets (48 %, n = 71) were within 10 mm of a radiosensitive OAR. No grade 4 or 5 TRAEs, 3.5 % grade 3 TRAEs, and 43.7 % grade 2 TRAEs were reported within the first year of follow-up. We found a significant association between grade ≥ 2 GI toxicity and the parameters GI OAR D0.1cc, D1cc, and D20cc.

CONCLUSION

In this phase II study of MR-guided SABR of oligometastases in the infra-diaphragmatic region, we found a low incidence of toxicity despite half of the lesions being within 10 mm of a radiosensitive OAR. GI OAR D0.1cc, D1cc, and D20cc were associated with grade ≥ 2 GI toxicity.

Predictive clinical and dosimetric parameters for risk of relapse in early-stage non-small cell lung cancer treated by SBRT: A large single institution experience

Purpose

To evaluate the impact of dosimetric parameters on efficacy of stereotactic body radiation therapy (SBRT) in early-stage non-small cell lung cancer (ES-NSCLC), using Hypofractionated Treatment Effects in the Clinic (HyTEC) reporting standards.

Methods

From April 2010 to December 2020, 497 patients who received SBRT for ES-NSCLC at the University Hospital of Liège were retrospectively enrolled. A total dose of 40 to 60 Gy in 3-5 fractions (72-180 Gy biologically effective dose with an α/β ratio of 10 (BED10)) was prescribed to the 80 % isodose line of the PTV. Potential clinical and dosimetric predictors of recurrence, overall survival (OS) and disease specific survival (DSS) were evaluated using univariate and multivariate analyses.

Results

After a median follow-up of 32 months (range 3-143 months), the local control and disease-free survival (DFS) rates at 3 years were 91 % (95 % CI: 90 %-93 %) and 75 % (95 % CI: 73 %-77 %), respectively. The median OS was 41.6 months and the median DSS was not reached. On multivariate analysis, a higher gross tumor volume (GTV) Dmax (BED10) (cut-off 198 Gy) and a larger percent of the GTV receiving ≥110 % of the prescribed dose were predictive of a better local control, only GTV volume was correlated with DSS and no parameter was correlated with OS and regional or distant recurrences.

Conclusion

Lung SBRT for ES-NSCLC in 3 to 5 fractions resulted in high local control rates. A higher percent of GTV receiving ≥110 % of the prescribed dose and a higher GTV Dmax (BED10) seem to allow a better local control.

Deep Learning-Guided Dosimetry for Mitigating Local Failure of Patients With Non-Small Cell Lung Cancer Receiving Stereotactic Body Radiation Therapy

PURPOSE

Non-small cell lung cancer (NSCLC) stereotactic body radiation therapy with 50 Gy/5 fractions is sometimes considered controversial, as the nominal biologically effective dose (BED) of 100 Gy is felt by some to be insufficient for long-term local control of some lesions. In this study, we analyzed such patients using explainable deep learning techniques and consequently proposed appropriate treatment planning criteria. These novel criteria could help planners achieve optimized treatment plans for maximal local control.

METHODS AND MATERIALS

A total of 535 patients treated with 50 Gy/5 fractions were used to develop a novel deep learning local response model. A multimodality approach, incorporating computed tomography images, 3-dimensional dose distribution, and patient demographics, combined with a discrete-time survival model, was applied to predict time to failure and the probability of local control. Subsequently, an integrated gradient-weighted class activation mapping method was used to identify the most significant dose-volume metrics predictive of local failure and their optimal cut-points.

RESULTS

The model was cross-validated, showing an acceptable performance (c-index: 0.72, 95% CI, 0.68-0.75); the testing c-index was 0.69. The model's spatial attention was concentrated mostly in the tumors' periphery (planning target volume [PTV] - internal gross target volume [IGTV]) region. Statistically significant dose-volume metrics in improved local control were BED Dnear-min ≥ 103.8 Gy in IGTV (hazard ratio [HR], 0.31; 95% CI, 015-0.63), V104 ≥ 98% in IGTV (HR, 0.30; 95% CI, 0.15-0.60), gEUD ≥ 103.8 Gy in PTV-IGTV (HR, 0.25; 95% CI, 0.12-0.50), and Dmean ≥ 104.5 Gy in PTV-IGTV (HR, 0.25; 95% CI, 0.12-0.51).

CONCLUSIONS

Deep learning-identified dose-volume metrics have shown significant prognostic power (log-rank, P = .003) and could be used as additional actionable criteria for treatment planning in NSCLC stereotactic body radiation therapy patients receiving 50 Gy in 5 fractions. Although our data do not confirm or refute that a significantly higher BED for the prescription dose is necessary for tumor control in NSCLC, it might be clinically effective to escalate the nominal prescribed dose from BED 100 to 105 Gy.

Outcome of conventional radiotherapy in small centrally located tumours or lymph nodes: minimal toxicity, remarkable survival but challenging loco-regional control

BACKGROUND

In peripheral lung tumours, stereotactic body radiotherapy (SBRT) is superior to conventional RT. SBRT has also shown high loco-regional control (LC) in centrally located tumours, but there is a high risk of severe toxicity. The STRICTSTARLung trial (NCT05354596) examines if risk-adapted SBRT for central tumours is feasible. In this study, we examined overall survival (OS), Disease-free survival (DSF), LC, and toxicity in patients with central tumours that could have been candidates for SBRT but received conventional RT.

MATERIAL AND METHODS

Retrospectively, we evaluated 49 lung cancer patients that between 2008 and 2021 received RT (60-70Gy in 2 Gy fractions) for a solitary tumour or lymph node with a diameter <5cm located <2cm from the bronchial tree, oesophagus, aorta or heart. All tumours were pathologically verified; 30 were primary lung tumours (T1b-T4) and 19 were solitary lymph nodes (T0N1-N2). Chemotherapy was administered as concomitant (29) or sequential (4). OS and LC were analysed using Kaplan Meier. Cox proportional hazards model for OS and disease-free survival (DFS) was performed including tumour volume, histology, sex, T- vs N-site and chemotherapy. Toxicity was scored.

RESULTS

In 42 patients, the tumour was located <1 cm to mediastinum. Median follow-up time was 44 months (range: 7-123). The median OS was 51 months. OS at 1-, 3- and 5-year was 88% (SE:5), 59% (SE:7) and 50% (SE:8). Loco-regional recurrences occurred in 16 patients resulting in 1-, and 3-year LC rates of 77% (SE:6) and 64% (SE:8). The majority occurred within 3 years after RT. Only stage showed significant impact on OS and DFS. No patients experienced grade 4-5 toxicity. Seven patients developed grade 3 toxicity (5 oesophageal stenosis, 2 pneumonitis).

CONCLUSION

Conventional RT for patients with small central lung tumours or solitary lymph nodes is feasible. Median OS was 51 months, and toxicity was low with no grade 4-5 events.

Individualized Stereotactic Ablative Radiotherapy for Lung Tumors: The iSABR Phase 2 Nonrandomized Controlled Trial

Importance

Stereotactic ablative radiotherapy (SABR) is used for treating lung tumors but can cause toxic effects, including life-threatening damage to central structures. Retrospective data suggested that small tumors up to 10 cm3 in volume can be well controlled with a biologically effective dose less than 100 Gy.

Objective

To assess whether individualizing lung SABR dose and fractionation by tumor size, location, and histological characteristics may be associated with local tumor control.

Design, Setting, and Participants

This nonrandomized controlled trial (the iSABR trial, so named for individualized SABR) was a phase 2 multicenter trial enrolling participants from November 15, 2011, to December 5, 2018, at academic medical centers in the US and Japan. Data were analyzed from December 9, 2020, to May 10, 2023. Patients were enrolled in 3 groups according to cancer type: initial diagnosis of non-small cell lung cancer (NSCLC) with an American Joint Committee on Cancer 7th edition T1-3N0M0 tumor (group 1), a T1-3N0M0 new primary NSCLC with a history of prior NSCLC or multiple NSCLCs (group 2), or lung metastases from NSCLC or another solid tumor (group 3).

Intervention

Up to 4 tumors were treated with once-daily SABR. The dose ranged from 25 Gy in 1 fraction for peripheral tumors with a volume of 0 to 10 cm3 to 60 Gy in 8 fractions for central tumors with a volume greater than 30 cm3.

Main outcome

Per-group freedom from local recurrence (same-lobe recurrence) at 1 year, with censoring at time of distant recurrence, death, or loss to follow-up.

Results

In total, 217 unique patients (median [IQR] age, 72 [64-80] years; 129 [59%] male; 150 [69%] current or former smokers) were enrolled (some multiple times). There were 240 treatment courses: 79 in group 1, 82 in group 2, and 79 in group 3. A total of 285 tumors (211 [74%] peripheral and 74 [26%] central) were treated. The most common dose was 25 Gy in 1 fraction (158 tumors). The median (range) follow-up period was 33 (2-109) months, and the median overall survival was 59 (95% CI, 49-82) months. Freedom from local recurrence at 1 year was 97% (90% CI, 91%-99%) for group 1, 94% (90% CI, 87%-97%) for group 2, and 96% (90% CI, 89%-98%) for group 3. Freedom from local recurrence at 5 years ranged from 83% to 93% in the 3 groups. The proportion of patients with grade 3 to 5 toxic effects was low, at 5% (including a single patient [1%] with grade 5 toxic effects).

Conclusions and Relevance

The results of this nonrandomized controlled trial suggest that individualized SABR (iSABR) used to treat lung tumors may allow minimization of treatment dose and is associated with excellent local control. Individualized dosing should be considered for use in future trials.

Trial Registration

ClinicalTrials.gov Identifier: NCT01463423.

A competing risk analysis of the patterns and risk factors of recurrence in early-stage non-small cell lung cancer treated with stereotactic ablative radiotherapy

INTRODUCTION

To assess patterns of recurrence after stereotactic ablative radiotherapy (SABR) in patient ineligible to surgery with early-stage non-small cell lung cancer (ES-NSCLC), report survival and treatment after first recurrence.

METHODS

We performed a retrospective analysis on 1068 patients with ES-NSCLC and 1143 lesions. Between group differences were estimated using competing risk analysis and cause-specific hazard ratios were calculated. Overall survival (OS) after first recurrence was calculated.

RESULTS

Median follow-up was 37.6 months. Univariate analysis demonstrated that ultra-central location was associated with higher risk of regional recurrence (RR) and distant metastasis (DM) (p = 0.004 and 0.01). Central lesions were associated with higher risk of local recurrence (LR) and RR (p < 0.001). Ultra-central lesions were associated with shorter OS (p = 0.002) compared to peripheral lesions. In multivariate analysis, central location was the only factor associated with increased LR and RR risks (p = 0.016 and 0.005). Median OS after first recurrence was 14.8 months. There was no difference in OS after first recurrence between ultra-central, central, and peripheral lesions (p = 0.83). Patients who received a second SABR course had an OS of 51.3 months, compared to 19.5 months with systemic therapy and 8.1 months with supportive care (p < 0.0001).

DISCUSSION

The main prognostic factor for LR and RR risks was central location. Ultra-central and central tumors might benefit from treatment intensification strategies such as dose escalation and/or addition of systemic therapy to improve radiotherapy outcomes. After a first recurrence post SABR, patients with contralateral lung recurrences and those who were eligible to receive a second course of SABR had improved OS.

Predicting cancer relapse following lung stereotactic radiotherapy: an external validation study using real-world evidence

Purpose

For patients receiving lung stereotactic ablative radiotherapy (SABR), evidence suggests that high peritumor density predicts an increased risk of microscopic disease (MDE) and local-regional failure, but only if there is low or heterogenous incidental dose surrounding the tumor (GTV). A data-mining method (Cox-per-radius) has been developed to investigate this dose-density interaction. We apply the method to predict local relapse (LR) and regional failure (RF) in patients with non-small cell lung cancer.

Methods

199 patients treated in a routine setting were collated from a single institution for training, and 76 patients from an external institution for validation. Three density metrics (mean, 90th percentile, standard deviation (SD)) were studied in 1mm annuli between 0.5cm inside and 2cm outside the GTV boundary. Dose SD and fraction of volume receiving less than 30Gy were studied in annuli 0.5-2cm outside the GTV to describe incidental MDE dosage. Heat-maps were created that correlate with changes in LR and RF rates due to the interaction between dose heterogeneity and density at each distance combination. Regions of significant improvement were studied in Cox proportional hazards models, and explored with and without re-fitting in external data. Correlations between the dose component of the interaction and common dose metrics were reported.

Results

Local relapse occurred at a rate of 6.5% in the training cohort, and 18% in the validation cohort, which included larger and more centrally located tumors. High peritumor density in combination with high dose variability (0.5 - 1.6cm) predicts LR. No interactions predicted RF. The LR interaction improved the predictive ability compared to using clinical variables alone (optimism-adjusted C-index; 0.82 vs 0.76). Re-fitting model coefficients in external data confirmed the importance of this interaction (C-index; 0.86 vs 0.76). Dose variability in the 0.5-1.6 cm annular region strongly correlates with heterogeneity inside the target volume (SD; ρ = 0.53 training, ρ = 0.65 validation).

Conclusion

In these real-world cohorts, the combination of relatively high peritumor density and high dose variability predicts increase in LR, but not RF, following lung SABR. This external validation justifies potential use of the model to increase low-dose CTV margins for high-risk patients.

Local Control Correlates with Overall Survival in Radiotherapy for Early-stage Non-small Cell Lung Cancer: A Systematic Review

PURPOSE

Local control (LC) is an important outcome of local cancer therapy, besides overall survival (OS). We conducted a comprehensive literature search to investigate whether a high LC rate contributes to good OS in radiotherapy for early-stage non-small cell lung cancer (ES-NSCLC).

MATERIALS AND METHODS

Studies in patients receiving radiotherapy for peripheral ES-NSCLC, mainly staged as T1-2N0M0 were included for a systematic review. Relevant information was collected including, dose fractionation, T stage, median age, 3-year LC, cancer-specific survival (CSS), disease-free survival (DFS), distant metastasis-free survival (DMFS), and OS. Correlations between outcomes and clinical variables were evaluated.

RESULTS

After screening, 101 data points from 87 studies including 13,435 patients were selected for the quantitative synthesis. Univariate meta-regression analysis revealed that the coefficients between the 3-year LC and 3-year DFS, DMFS, CSS, and OS were 0.753 (95% confidence interval (CI): 0.307-1.199; p<0.001), 0.360 (95% CI: 0.128-0.593; p=0.002), 0.766 (95% CI: 0.489-1.044; p<0.001), and 0.574 (95% CI: 0.275-0.822; p<0.001), respectively. Multivariate analysis revealed that the 3-year LC (coefficient, 0.561; 95% CI: 0.254-0.830; p<0.001) and T1 proportion (coefficient, 0.207; 95% CI: 0.030-0.385; p=0.012) were significantly associated with the 3-year OS and CSS (coefficient for 3-year LC, 0.720; 95% CI: 0.468-0.972; p<0.001 and T1 proportion, 0.002; 95% CI: 0.000-0.003; p=0.012). Toxicities ≥grade 3 were low (3.4%).

CONCLUSIONS

Three-year LC was correlated with three-year OS in patients receiving radiotherapy for ES-NSCLC. A 5% increase in 3-year LC is expected to improve the 3-year CSS and OS rates by 3.8% and 2.8%, respectively.

To fly or not to fly: Stereotactic MR-guided adaptive radiotherapy effectively treats ultracentral lung tumors with favorable long-term outcomes

BACKGROUND

Stereotactic radiotherapy of ultracentral lung tumors (ULT) is challenging as it may cause overdoses to sensitive mediastinal organs with severe complications. We aimed to describe long-term outcomes after stereotactic magnetic resonance (MR)-guided online adaptive radiotherapy (SMART) as an innovative treatment of ULT.

PATIENTS & METHODS

We analyzed 36 patients that received SMART to 40 tumors between 02/2020 - 08/2021 inside prospective databases. ULT were defined by planning target volume (PTV) overlap with the proximal bronchial tree or esophagus. We calculated Kaplan Meier estimates for overall survival (OS) and progression-free survival (PFS), and competing risk estimates for the incidence of tumor progression and treatment-related toxicities. ULT patients (N = 16) were compared to non-ULT patients (N = 20).

RESULTS

Baseline characteristics were similar between ULT and non-ULT, but ULT were larger (median PTV: ULT 54.7 cm³, non-ULT 19.2 cm³). Median follow-up was 23.6 months. ULT and non-ULT showed a similar OS (2-years: ULT 67%, non-ULT 60%, p = 0.7) and PFS (2-years: ULT 37%, non-ULT 34%, p = 0.73). Progressions occurred mainly at distant sites (2-year incidence of distant progression: ULT 63%, non-ULT 61%, p = 0.77), while local tumor control was favorable (2-year incidence of local progression: ULT 7%, non-ULT 0%, p = 0.22). Treatment of ULT led to significantly more toxicities ≥ grade (G) 2 (ULT: 9 (56%), non-ULT: 1 (5%), p = 0.002). Most toxicities were moderate (G2). Two ULT patients developed high-grade toxicities: 1) esophagitis G3 and bronchial bleeding G4 after VEGF treatment, 2) bronchial bleeding G3. Estimated incidence of high-grade toxicities was 19% (3-48%) in ULT, and no treatment-related death occurred.

CONCLUSION

Our small series supports SMART as potentially effective treatment of ULT. SMART with careful fractionation could reduce severe complications, but treatment of ULT remains a high-risk procedure and needs careful benefit-risk-assessment.

Stereotactic magnetic resonance-guided online adaptive radiotherapy of adrenal metastases combines high ablative doses with optimized sparing of organs at risk

Purpose/Objective

To evaluate the potential of stereotactic magnetic resonance-guided online adaptive radiotherapy (SMART) to fulfill dose recommendations for stereotactic body radiotherapy (SBRT) of adrenal metastases and spare organs at risk (OAR).

Materials and methods

In this subgroup analysis of a prospective registry trial, 22 patients with adrenal metastases were treated on a 0.35 T MR-Linac in 5-12 fractions with fraction doses of 4-10 Gy. Baseline plans were re-calculated to the anatomy of the day. These predicted plans were reoptimized to generate adapted plans. Baseline, predicted and adapted plans were compared with regard to PTV objectives, OAR constraints and published dose recommendations.

Results

The cohort comprised patients with large GTV (median 36.0 cc) and PTV (median 66.6 cc) and predominantly left-sided metastases. 179 of 181 fractions (98.9 %) were adapted because of PTV and/or OAR violations. Predicted plans frequently violated PTV coverage (99.4 %) and adjacent OAR constraints (bowel: 32.9 %, stomach: 32.8 %, duodenum: 10.4 %, kidneys: 10.8 %). In the predicted plans, the volume exposed to the maximum dose was exceeded up to 16-fold in the duodenum and up to 96-fold in the spinal cord. Adapted plans significantly reduced OAR violations by 96.4 % for the bowel, 98.5 % for the stomach, 85.6 % for the duodenum and 83.3 % for the kidneys. Plan adaptation improved PTV coverage from 82.7 ± 8.1 % to 90.6 ± 4.9 % (p < 0.001). Furthermore, recently established target volume thresholds could easily be fulfilled with SMART. No toxicities > grade II occurred.

Conclusion

SMART fulfills established GTV and PTV dose recommendations while simultaneously sparing organs at risk even in a challenging cohort.

Should organs at risk (OARs) be prioritized over target volume coverage in stereotactic ablative radiotherapy (SABR) for oligometastases? a secondary analysis of the population-based phase II SABR-5 trial

BACKGROUND AND PURPOSE

Stereotactic ablative radiotherapy (SABR) for oligometastases may improve survival, however concerns about safety remain. To mitigate risk of toxicity, target coverage was sacrificed to prioritize organs-at-risk (OARs) during SABR planning in the population-based SABR-5 trial. This study evaluated the effect of this practice on dosimetry, local recurrence (LR), and progression-free survival (PFS).

METHODS

This single-arm phase II trial included patients with up to 5 oligometastases between November 2016 and July 2020. Theprotocol-specified planning objective was to cover 95 % of the planning target volume (PTV) with 100 % of the prescribed dose, however PTV coverage was reduced as needed to meet OAR constraints. This trade-off was measured using the coverage compromise index (CCI), computed as minimum dose received by the hottest 99 % of the PTV (D99) divided by the prescription dose. Under-coverage was defined as CCI < 0.90. The potential association between CCI and outcomes was evaluated.

RESULTS

549 lesions from 381 patients were assessed. Mean CCI was 0.88 (95 % confidence interval [CI], 0.86-0.89), and 196 (36 %) lesions were under-covered. The highest mean CCI (0.95; 95 %CI, 0.93-0.97) was in non-spine bone lesions (n = 116), while the lowest mean CCI (0.71; 95 % CI, 0.69-0.73) was in spine lesions (n = 104). On multivariable analysis, under-coverage did not predict for worse LR (HR 0.48, p = 0.37) or PFS (HR 1.24, p = 0.38). Largest lesion diameter, colorectal and 'other' (non-prostate, breast, or lung) primary predicted for worse LR. Largest lesion diameter, synchronous tumor treatment, short disease free interval, state of oligoprogression, initiation or change in systemic treatment, and a high PTV Dmax were significantly associated with PFS.

CONCLUSION

PTV under-coverage was not associated with worse LR or PFS in this large, population-based phase II trial. Combined with low toxicity rates, this study supports the practice of prioritizing OAR constraints during oligometastatic SABR planning.

Dose-effect relationship of stereotactic body radiotherapy in non-small cell lung cancer patients

OBJECTIVE

To establish the dose effect relationship between the dose parameters of stereotactic body radiation therapy (SBRT) for early non-small cell lung cancer (NSCLC) and the local tumor control rate.

MATERIALS AND METHODS

A comprehensive literature search was conducted using PubMed, the Web of Science and the Cochrane databases to determine the articles treated with SBRT in early-stage NSCLC. Original studies with complete prescription dose information, tumor local control rate and other important parameters were screened and reported. Probit model in XLSTAT 2016 was used for regression analysis, and P < 0.05 was set as a statistically significant level.

RESULTS

After literature screening, 22 eligible studies were included in probit model regression analysis, involving 1861 patients. There is no significant dose effect relationship between nominal BED₁₀ and peripheral BED₁₀ versus 3 years local control probability. There were significant dose effect relationships between the center BED₁₀ and the average BED₁₀ versus the 3 years local control probability, with P values are 0.001 and < 0.0001, respectively. According to the results of this model, the 3 years local control rate of 90.5% (87.5-92.1%) and 89.5% (86.7-91.0%) can be expected at the center BED₁₀ of 180 Gy or the average BED₁₀ of 140 Gy, prospectively.

CONCLUSIONS

For NSCLC treated with SBRT, more attention should be paid to the central dose and average dose of PTV. A set of clear definition in the dose prescription should be established to ensure the effectiveness and comparability of treatment.

Dosimetric robustness of lung tumor photon radiotherapy evaluated from multiple event CT imaging

PURPOSE

Intrafractional respiratory motion is a concern for lung tumor radiotherapy but full evaluation of its impact is hampered by the lack of images representing the true motion. This study presents a novel evaluation using free-breathing images acquired over realistic treatment times to study the dosimetric impact of respiratory motion in photon radiotherapy.

METHODS

Cine-CT images of 14 patients with lung cancer acquired during eight minutes of free-breathing at three occasions were used to simulate dose tracking of four different planning methods. These methods aimed to deliver 54 Gy in three fractions to D_50% of the target and were denoted as robust 4D (RB4), homogeneous fluence to the ITV (FLU) and an isodose prescription to the ITV with a high central dose (ISD), concurrently renormalized (IRN). Differences in dose coverage probability and homogeneity between the methods were quantified. Correlations between underdosage and attributes regarding the tumor and its motion were investigated.

RESULTS

Despite tumor motion amplitudes being larger than in the 4DCT all but FLU achieved the intended CTV D_50% for the cohort average. For all methods but IRN at least 93% of the patients would have received 95% of the intended dose. No differences in D_50% were found between RB4 and ISD nor IRN. However, RB4 led to better homogeneity.

CONCLUSIONS

Tumor motion in free-breathing not covered by the 4DCT had a small impact on dose. The RB4 is recommended for planning of free-breathing treatments. No factor was found that consistently correlated dose degradation with patient or motion attributes.

Predicting Local Failure after Partial Prostate Re-Irradiation Using a Dosiomic-Based Machine Learning Model

The aim of this study is to predict local failure after partial prostate re-irradiation for the treatment of isolated locally recurrent prostate cancer by using a machine learning classifier based on radiomic features from pre-treatment computed tomography (CT), positron-emission tomography (PET) and biological effective dose distribution (BED) of the radiotherapy plan. The analysis was conducted on a monocentric dataset of 43 patients with evidence of isolated intraprostatic recurrence of prostate cancer after primary external beam radiotherapy. All patients received partial prostate re-irradiation delivered by volumetric modulated arc therapy. The gross tumor volume (GTV) of each patient was manually contoured from planning CT, choline-PET and dose maps. An ensemble machine learning pipeline including unbalanced data correction and feature selection was trained using the radiomic and dosiomic features as input for predicting occurrence of local failure. The model performance was assessed using sensitivity, specificity, accuracy and area under receiver operating characteristic curves of the score function in 10-fold cross validation repeated 100 times. Local failure was observed in 13 patients (30%), with a median time to recurrence of 36.7 months (range = 6.1–102.4 months). A four variables ensemble machine learning model resulted in accuracy of 0.62 and AUC 0.65. According to our results, a dosiomic machine learning classifier can predict local failure after partial prostate re-irradiation.

Relationship between Dose Prescription Methods and Local Control Rate in Stereotactic Body Radiotherapy for Early Stage Non-Small-Cell Lung Cancer: Systematic Review and Meta-Analysis

Variations in dose prescription methods in stereotactic body radiotherapy (SBRT) for early stage non-small-cell lung cancer (ES-NSCLC) make it difficult to properly compare the outcomes of published studies. We conducted a comprehensive search of the published literature to summarize the outcomes by discerning the relationship between local control (LC) and dose prescription sites. We systematically searched PubMed to identify observational studies reporting LC after SBRT for peripheral ES-NSCLC. The correlations between LC and four types of biologically effective doses (BED) were evaluated, which were calculated from nominal, central, and peripheral prescription points and, from those, the average BED. To evaluate information on SBRT for peripheral ES-NSCLC, 188 studies were analyzed. The number of relevant articles increased over time. The use of an inhomogeneity correction was mentioned in less than half of the articles, even among the most recent. To evaluate the relationship between the four BEDs and LC, 33 studies were analyzed. Univariate meta-regression revealed that only the central BED significantly correlated with the 3-year LC of SBRT for ES-NSCLC (p = 0.03). As a limitation, tumor volume, which might affect the results of this study, could not be considered due to a lack of data. In conclusion, the central dose prescription is appropriate for evaluating the correlation between the dose and LC of SBRT for ES-NSCLC. The standardization of SBRT dose prescriptions is desirable.

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.

Adaptive MR-Guided Stereotactic Radiotherapy is Beneficial for Ablative Treatment of Lung Tumors in High-Risk Locations

PURPOSE

To explore the benefit of adaptive magnetic resonance-guided stereotactic body radiotherapy (MRgSBRT) for treatment of lung tumors in different locations with a focus on ultracentral lung tumors (ULT).

PATIENTS & METHODS

A prospective cohort of 21 patients with 23 primary and secondary lung tumors was analyzed. Tumors were located peripherally (N = 10), centrally (N = 2) and ultracentrally (N = 11, planning target volume (PTV) overlap with proximal bronchi, esophagus and/or pulmonary artery). All patients received MRgSBRT with gated dose delivery and risk-adapted fractionation. Before each fraction, the baseline plan was recalculated on the anatomy of the day (predicted plan). Plan adaptation was performed in 154/165 fractions (93.3%). Comparison of dose characteristics between predicted and adapted plans employed descriptive statistics and Bayesian linear multilevel models. The posterior distributions resulting from the Bayesian models are presented by the mean together with the corresponding 95% compatibility interval (CI).

RESULTS

Plan adaptation decreased the proportion of fractions with violated planning objectives from 94% (predicted plans) to 17% (adapted plans). In most cases, inadequate PTV coverage was remedied (predicted: 86%, adapted: 13%), corresponding to a moderate increase of PTV coverage (mean +6.3%, 95% CI: [5.3-7.4%]) and biologically effective PTV doses (BED₁₀) (BED_min: +9.0 Gy [6.7-11.3 Gy], BED_mean: +1.4 Gy [0.8-2.1 Gy]). This benefit was smaller in larger tumors (-0.1%/10 cm³ PTV [-0.2 to -0.02%/10 cm³ PTV]) and ULT (-2.0% [-3.1 to -0.9%]). Occurrence of exceeded maximum doses inside the PTV (predicted: 21%, adapted: 4%) and violations of OAR constraints (predicted: 12%, adapted: 1%, OR: 0.14 [0.04-0.44]) was effectively reduced. OAR constraint violations almost exclusively occurred if the PTV had touched the corresponding OAR in the baseline plan (18/19, 95%).

CONCLUSION

Adaptive MRgSBRT is highly recommendable for ablative treatment of lung tumors whose PTV initially contacts a sensitive OAR, such as ULT. Here, plan adaptation protects the OAR while maintaining best-possible PTV coverage.

Planning benchmark study for SBRT of liver metastases: Results of the DEGRO/DGMP working group stereotactic radiotherapy and radiosurgery

PURPOSE

To investigate, if liver SBRT treatment planning can be harmonized across different treatment planning systems, delivery techniques and institutions by using a specific prescription method and to minimize the knowledge gap concerning inter-system and inter-user differences. To provide best practice guidelines for all used techniques.

METHODS

A multiparametric specification of target dose (GTV_D50%, GTV_D0.1cc, GTV_V90%, PTV_V70%) with a prescription dose of GTV_D50% = 3 × 20 Gy and OAR limits were distributed with CTs and structure sets from three liver metastases patients. Thirty-five institutions provided 132 treatment plans using different irradiation techniques. These plans were first analyzed for target and OAR doses. Four different renormalization methods were performed (PTV_Dmin, PTV_D98%, PTV_D2%, PTV_Dmax). The resulting 660 treatments plans were evaluated regarding target doses in order to study the effect of dose renormalization to different prescription methods. A relative scoring system was used for comparisons.

RESULTS

GTV_D50% prescription can be performed in all systems. Treatment plan harmonization was overall successful with standard deviations for D_max, PTV_D98%, GTV_D98% and PTV_Dmean of 1.6 Gy, 3.3 Gy, 1.9 Gy and 1.5 Gy, respectively. Primary analysis showed 55 major deviations from clinical goals in 132 plans, while in only <20% of deviations GTV/PTV dose was traded for meeting OAR limits. GTV_D50% prescription produced the smallest deviation from target planning objectives and between techniques, followed by the PTV_Dmax, PTV_D98%, PTV_D2% and PTV_Dmin prescription. Deviations were significant for all combinations but for the PTV_Dmax prescription compared with GTV_D50% and PTV_D98%. Based on the various dose prescription methods, all systems significantly differed from each other, while GTV_D50% and PTV_D98% prescription showed the least differences between the systems.

CONCLUSIONS

This study showed the feasibility of harmonizing liver SBRT treatment plans across different treatment planning systems and delivery techniques when a sufficient set of clinical goals is given.

Toxicity and efficacy of stereotactic body radiotherapy for ultra-central lung tumours: a single institution real life experience

OBJECTIVES

The use of stereotactic body radiotherapy (SBRT) to treat ultra-central lung tumours remains more controversial than for peripheral and central tumours. Our objective was to assess toxicities, local control (LC) rate and survival data in patients with ultra-central lung tumours treated with SBRT.

METHODS

We conducted a retrospective and monocentric study about 74 patients with an ultra-central lung tumour, consecutively treated between 2012 and 2018. Ultra-central tumours were defined as tumours whose planning target volume overlapped one of the following organs at risk (OARs): the trachea, right and left main bronchi, intermediate bronchus, lobe bronchi, oesophagus, heart.

RESULTS

Median follow-up was 25 months. Two patients (2.7%) showed Grade 3 toxicity. No Grade 4 or 5 toxicity was observed. 11% of patients experienced primary local relapse. LC rate was 96.7% at 1 year and 87.6% at 2 years. Median progression free survival was 12 months. Median overall survival was 31 months.

CONCLUSION

SBRT for ultra-central tumours remains safe and effective as long as protecting organs at risk is treatment-planning priority.

ADVANCES IN KNOWLEDGE

The present study is one of the rare to describe exclusively ultra-central tumours through real-life observational case reports. Globally, literature analysis reveals a large heterogeneity in ultra-central lung tumours definition, prescribed dose, number of fractions. In our study, patients treated with SBRT for ultra-central lung tumours experienced few Grade 3 toxicities (2.7%) and no Grade 4 or 5 toxicities, due to the highest compliance with dose constraints to OARs. LC remained efficient.

Combining computed tomography and biologically effective dose in radiomics and deep learning improves prediction of tumor response to robotic lung stereotactic body radiation therapy

PURPOSE

The aim of this study is to improve the performance of machine learning (ML) models in predicting response of non-small cell lung cancer (NSCLC) to stereotactic body radiation therapy (SBRT) by integrating image features from pre-treatment computed tomography (CT) with features from the biologically effective dose (BED) distribution.

MATERIALS AND METHODS

Image features, consisting of crafted radiomic features or machine-learned features extracted using a convolutional neural network, were calculated from pre-treatment CT data and from dose distributions converted into BED for 80 NSCLC lesions over 76 patients treated with robotic guided SBRT. ML models using different combinations of features were trained to predict complete or partial response according to response criteria in solid tumors, including radiomics CT (Rad_CT ), radiomics CT and BED (Rad_CT,BED ), deep learning (DL) CT (DL_CT ), and DL CT and BED (DL_CT,BED ). Training of ML included feature selection by neighborhood component analysis followed by ensemble ML using robust boosting. A model was considered as acceptable when the sum of average sensitivity and specificity on test data in repeated cross validations was at least 1.5.

RESULTS

Complete or partial response occurred in 58 out of 80 lesions. The best models to predict the tumor response were those using BED variables, achieving significantly better area under curve (AUC) and accuracy than those using only features from CT, including a Rad_CT,BED model using three radiomic features from BED, which scored an accuracy of 0.799 (95% confidence intervals (0.75-0.85)) and AUC of 0.773 (0.688-0.846), and a DL_CT,BED model also using three variables with an accuracy of 0.798 (0.649-0.829) and AUC of 0.812 (0.755-0.867).

CONCLUSION

According to our results, the inclusion of BED features improves the response prediction of ML models for lung cancer patients undergoing SBRT, regardless of the use of radiomic or DL features.

Improving interinstitutional and intertechnology consistency of pulmonary SBRT by dose prescription to the mean internal target volume dose

Purpose

Dose, fractionation, normalization and the dose profile inside the target volume vary substantially in pulmonary stereotactic body radiotherapy (SBRT) between different institutions and SBRT technologies. Published planning studies have shown large variations of the mean dose in planning target volume (PTV) and gross tumor volume (GTV) or internal target volume (ITV) when dose prescription is performed to the PTV covering isodose. This planning study investigated whether dose prescription to the mean dose of the ITV improves consistency in pulmonary SBRT dose distributions.

Materials and methods

This was a multi-institutional planning study by the German Society of Radiation Oncology (DEGRO) working group Radiosurgery and Stereotactic Radiotherapy. CT images and structures of ITV, PTV and all relevant organs at risk (OAR) for two patients with early stage non-small cell lung cancer (NSCLC) were distributed to all participating institutions. Each institute created a treatment plan with the technique commonly used in the institute for lung SBRT. The specified dose fractionation was 3 × 21.5 Gy normalized to the mean ITV dose. Additional dose objectives for target volumes and OAR were provided.

Results

In all, 52 plans from 25 institutions were included in this analysis: 8 robotic radiosurgery (RRS), 34 intensity-modulated (MOD), and 10 3D-conformal (3D) radiation therapy plans. The distribution of the mean dose in the PTV did not differ significantly between the two patients (median 56.9 Gy vs 56.6 Gy). There was only a small difference between the techniques, with RRS having the lowest mean PTV dose with a median of 55.9 Gy followed by MOD plans with 56.7 Gy and 3D plans with 57.4 Gy having the highest. For the different organs at risk no significant difference between the techniques could be found.

Conclusions

This planning study pointed out that multiparameter dose prescription including normalization on the mean ITV dose in combination with detailed objectives for the PTV and ITV achieve consistent dose distributions for peripheral lung tumors in combination with an ITV concept between different delivery techniques and across institutions.

Supplementary Information

The online version of this article (10.1007/s00066-021-01799-w) contains supplementary material, which is available to authorized users.

Comparison of liver exposure in CT-guided high-dose rate (HDR) interstitial brachytherapy versus SBRT in hepatocellular carcinoma

Background

In unresectable hepatocellular carcinoma several local ablative treatments are available. Among others, radiation based treatments such as stereotactic body radiotherapy (SBRT) and high-dose rate interstitial brachytherapy (HDR BT) have shown good local control rates.

Methods

We conducted a dose comparison between actually performed HDR BT versus virtually planned SBRT to evaluate the respective clinically relevant radiation exposure to uninvolved liver tissue. Moreover, dose coverage and conformity indices were assessed.

Results

Overall, 46 treatment sessions (71 lesions, 38 patients) were evaluated. HDR BT was applied in a single fraction with a dose prescription of 1 × 15 Gy. D98 was 17.9 ± 1.3 Gy, D50 was 41.8 ± 8.1 Gy. The SBRT was planned with a prescribed dose of 3 × 12.5 Gy (65%-Isodose), D98 was 50.7 ± 3.1 Gy, D2 was 57.0 ± 2.3 Gy, and D50 was 55.2 ± 2.3 Gy.

Regarding liver exposure Vliver10Gy_BT was compared to Vliver15.9Gy_SBRT, Vliver16.2Gy_SBRT (EQD2 equivalent doses), and Vliver20Gy_SBRT (clinically relevant dose), all results showed significant differences (p < .001). In a case by case analysis Vliver10Gy_BT was smaller than Vliver20Gy_SBRT in 38/46 cases (83%). Dmean of the liver was significantly smaller in BT compared to SBRT (p < .001).

GTV volume was correlated to the liver exposure and showed an advantage of HDR BT over SBRT in comparison of clinically relevant doses, and for EQD2 equivalent doses. The advantage was more pronounced for greater liver lesions The Conformity Index (CI) was significantly better for BT, while Healthy Tissue Conformity Index (HTCI) and Conformation Number (CN) showed an advantage for SBRT (p < .001).

Conclusion

HDR BT can be advantageous in respect of sparing of normal liver tissue as compared to SBRT, while providing excellent target conformity.

Higher biologically effective dose is associated with improved survival in patients with squamous cell carcinoma of the lung treated with stereotactic body radiation therapy

BACKGROUND

Multiple studies have suggested that patients with early-stage SCC of the lung treated with SBRT are more susceptible to local failure compared to other NSCLC histologies. It is unknown if higher BED leads to improved outcomes in this patient population. We evaluated the effect of "high" BED versus "low" BED SBRT on overall survival (OS) in SCC and non-SCC NSCLC patients.

METHODS

The National Cancer Database was used to identify patients with cT1-2N0M0 NSCLC diagnosed between 2006-2016 treated with 3-5 fraction SBRT. Patients were grouped by BED_high (>150 Gy) and BED_low (≤132 Gy). Univariate and multivariable analysis using Kaplan-Meier and Cox proportional hazards regression modeling were performed. Propensity-score matched analysis with inverse probability of treatment (IPTW) weighting was used to account for selection bias.

RESULTS

We identified 4,717 eligible SCC patients and 8,807 eligible non-SCC NSCLC patients. In SCC patients, BED_high was associated with improved OS in both univariate and multivariate analysis (MVA HR 0.84 95% CI 0.76-0.92, p < 0.001), with estimated IPTW-adjusted 3-year OS of 49% compared to 41% for the BED_low group. In contrast, BED_high was not associated with improved OS compared to BED_low for non-SCC NSCLC patients (MVA HR 0.94 95% CI 0.86-1.04, p = 0.23), with estimated IPTW-adjusted 3-year OS of 54% and 53%, respectively.

CONCLUSIONS

Our analysis suggests that in patients with early-stage NSCLC, SBRT regimens with BED > 150 Gy may confer a survival benefit in patients with SCC histology. Histology-based dose modification should be considered, and prospective validation may be warranted.

Stereotactic Body Radiation Therapy With a High Maximum Dose Improves Local Control, Cancer-Specific Death, and Overall Survival in Peripheral Early-Stage Non-Small Cell Lung Cancer

PURPOSE

We investigated whether delivery of a high biologically effective dose (BED) to primary tumors affects systemic outcomes of cancer-specific death (CSD) and overall survival (OS) rates after stereotactic body radiation therapy (SBRT) in patients with early-stage non-small cell lung cancer (ES-NSCLC).

METHODS AND MATERIALS

Among consecutive ES-NSCLC patients treated with SBRT between 2005 and 2019, we retrospectively identified patients who received a prescription of 50 to 60 Gy in 5 fractions with maximum doses of 62.5 to 100 Gy. Patients were categorized by maximum BED within the planning target volume with a threshold dose of 200 Gy. Outcomes were analyzed in all and matched patients.

RESULTS

Overall, 433 patients were eligible, and 262 and 171 patients were categorized into HighBED and LowBED groups, respectively. After propensity score matching, pairs of 154 patients were selected. Median follow-up times for the HighBED and LowBED groups were 52.3 months (range, 0.8-107.2 months) and 121.6 months (range, 3.0-162.8 months), respectively. The local recurrence rate in the HighBED group was significantly lower than that in the LowBED group (5-year rate, 1.3% and 7.2%; hazard ratio [HR], 0.15; 95% confidence interval [CI], 0.03-0.65; P = .011). Rates of any recurrence and CSD in the HighBED group were significantly lower (5-year any recurrence: 18.1% and 32.1%; HR, 0.52; 95% CI, 0.33-0.83; P = .0058; 5-year CSD: 9.5% and 21.8%; HR, 0.38; 95% CI, 0.20-0.70; P = .002), and OS in the HighBED group was significantly better compared with the LowBED group (5-year rate: 61.7% and 51.8%; HR, 0.71; 95% CI, 0.50-1.00; P = .047).

CONCLUSION

In patients with peripheral ES-NSCLC, SBRT with a high maximum dose may improve not only local control, but also any recurrence, CSD, and OS rates without increased toxicity. Further trials designed to evaluate whether higher intensity SBRT increases local control rates and contributes to improved CSD and OS outcomes are anticipated.

SEOR SBRT-SG survey on SRS/SBRT dose prescription criteria in Spain

AIM

Stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS) are essential tools in radiation oncology. In Spain, the use of these techniques continues to grow as older linear accelerators (linacs) are replaced with modern equipment. However, little is known about inter-centre variability in prescription and dose heterogeneity limits. Consequently, the SBRT-Spanish Task Group (SBRT-SG) of the Spanish Society of Radiation Oncology (SEOR) has undertaken an initiative to assess prescription and homogeneity in SRS/SBRT treatment. In the present study, we surveyed radiation oncology (RO) departments to obtain a realistic overview of prescription methods used for SBRT and SRS treatment in Spain.

METHODS

A brief survey was developed and sent to 34 RO departments in Spain, mostly those who are members of the SEOR SBRT-SG. The survey contained seven questions about the specific prescription mode, dose distribution heterogeneity limits, prescription strategies according to SRS/SBRT type, and the use of IMRT-VMAT (Intensity Modulated Radiation Therapy-Volumetric Modulated Arc Therapy).

RESULTS

Responses were received from 29 centres. Most centres (59%) used the prescription criteria D_95% ≥ 100%. Accepted dose heterogeneity was wide, ranging from 107 to 200%. Most centres used IMRT-VMAT (93%).

CONCLUSIONS

This survey about SRS/SBRT prescription and dose heterogeneity has evidenced substantial inter-centre variability in prescription criteria, particularly for intended and accepted dose heterogeneity. These differences could potentially influence the mean planning target volume dose and its correlation with treatment outcomes. The findings presented here will be used by the SEOR SBRT-SG to develop recommendations for SRS/SBRT dose prescription and heterogeneity.

Hypofractionated radiotherapy for hepatocellular carcinomas adjacent to the gastrointestinal tract

AIM

Decisions regarding therapeutic plans for inoperable patients with hepatocellular carcinoma (HCC) adjacent to the gastrointestinal (GI) tract are challenging because radiofrequency ablation has the potential risk of thermal injury. Moreover, the response rate of transcatheter arterial chemoembolization is relatively low and stereotactic body radiotherapy (SBRT) is believed to be too toxic. We have applied hypofractionated radiotherapy (HFRT) for such lesions. This study investigated the outcomes and toxicities of this treatment.

METHODS

Among consecutive HCC patients treated with radiotherapy with curative intent at our institution between 2015 and 2019, we retrospectively extracted those outside of the indication for SBRT due to exceeding the constraint of the GI tract and who were treated using HFRT with a prescription dose of 42 Gy in 14 fractions and prophylactic proton pump inhibitor administration for 6 months. The oncological outcomes and toxicities were investigated.

RESULTS

A total of 66 patients with 73 lesions were eligible. The median follow-up period was 24.0 months. The local recurrence, intrahepatic recurrence, liver-related death, and overall survival rates at 2 years were 11.3%, 50.6%, 15.9%, and 60.4%, respectively. Six (9.1%) patients experienced Child-Pugh score deterioration ≥2 within 6 months following treatment. Two and one patient developed grades 2 and 3 gastroduodenal bleeding, respectively.

CONCLUSIONS

HFRT can achieve good local control in patients with HCC adjacent to the GI tract, with low GI toxicity incidence. Our study demonstrated that HFRT can be a potentially curative treatment option for lesions.

Automated gross tumor volume contour generation for large-scale analysis of early-stage lung cancer patients planned with 4D-CT

PURPOSE

Patients with early-stage lung cancer undergoing stereotactic ablative radiotherapy receive four-dimensional computed tomography (4D-CT) for treatment planning. Often, an internal gross target volume (iGTV), which approximates the motion envelope of a tumor over the breathing cycle, is delineated without defining a gross tumor volume (GTV). However, the GTV volume and shape are important parameters for prognostic and dose modelling, and there is interest in radiomic features extracted from the GTV and surrounding tissue. We demonstrate and validate a method to generate the GTV from an iGTV contour to aid retrospective analysis on routine data.

METHOD

It is possible to reconstruct the geometry of a tumor with knowledge of tumor motion and the motion envelope formed during respiration. To demonstrate this, the tumor motion path was estimated with local rigid registration, and the iGTV positioned incrementally at stations along the reverse path. It is shown that the tumor volume is the largest set common to the intersection of the iGTV at these positions, hence can be derived. This was implemented for 521 lung lesions on 4D-CT. Eleven patients with a GTV delineation performed by a radiation oncologist on a reference phase (50%) were used for validation. The generated GTV was compared to that delineated by the expert using distance-to-agreement (DTA), volume, and distance between centres of mass. An overall success rate was determined by detecting registration inaccuracy and performing a quality check on the routine iGTV. For successfully generated contours, GTV volume was compared to iGTV volume in a prognostic model for overall survival.

RESULTS

For the validation dataset, DTA mean (0.79 - 1.55 mm) and standard deviation (0.68 - 1.51 mm) were comparable to expected observer variation. Difference in volume was < 5 cm³ , and average difference in position was 1.21 mm. Deviations in shape and position were mainly caused by observer differences in iGTV and GTV interpretation as opposed to algorithm performance. For the complete dataset, an acceptable contour was generated for 94% of patients using statistical and visual assessment to detect failures. Generated GTV volumes improved prognostic model performance over iGTV volumes.

CONCLUSION

A method to generate a GTV from an iGTV and 4D-CT dataset was developed. This method facilitates data analysis of patients with early-stage lung cancer treated in the routine setting, that is, data mining, prognostic modeling, and radiomics. Generation failure detection removes the need for visual assessment of all contours, reducing a time-consuming aspect of big-data analysis. Favorable prognostic performance of generated GTV volumes over iGTV ones demonstrates opportunities to use this methodology for future study.

Pulmonary oligometastases treated by stereotactic body radiation therapy (SBRT): a single institution's experience

Background

To investigate the effect of stereotactic body radiation therapy (SBRT) on pulmonary oligometastases and to analyze the clinical factors and dose parameters affecting local recurrence-free survival (LRFS) and overall survival (OS).

Methods

This study retrospectively enrolled a total of 84 patients (148 lesions) treated in our department from May 2015 to November 2018. Pulmonary oligometastases was defined as up to 5 metastatic lesions in the lung and with both the primary tumor and any extra-thoracic metastases being controlled. Patients receiving a BED₁₀ (biological effective dose, α/β =10) of SBRT ≥75 Gy and a dose/fraction ≥4 Gy were enrolled. The patient group consisted of 52 men (61.9%) and 32 women (38.1%), with a median age 56 years (range, 29-80 years). Median tumor diameter was 1.71cm (range, 1.2-5.0 cm). The BED₁₀ was 75-119 Gy in 4-15 fractions. Univariate and multivariate Cox regression analyses were performed on factors predicting the outcomes.

Results

All patients completed the treatment as planned, and the median follow-up time was 20.3 months. The median OS for the entire group was 34.3 months, with an actuarial 1-, 2-, 3- and 5-year OS of 74.7%, 59.4%, 49.7%, and 36.8%, respectively. Among the 148 lesions in the whole group, 19 (12.8%) lesions had local recurrence (LR). The median LRFS time for all patients was 56.9 months. The LRFS rate was 93.6%, 83.5%, 81.4%, and 76.6% at 1, 2, 3, and 5 years, respectively. No patient developed acute grade 3 or 4 toxicity. On univariate analysis, age ≥63 years old, primary site of colorectal cancer, BED₁₀ <85.2 Gy, pathological type of adenocarcinoma, planning target volume (PTV) min BED₁₀ <76.6 Gy, and gross tumor volume (GTV) ≥8.8 cc, were significantly associated with poorer LRFS. Multivariate analysis showed that age ≥63 years old, primary site of colorectal cancer, and PTV min BED₁₀ <76.6 Gy were significant risk factors affecting LRFS.

Conclusions

SBRT is feasible for pulmonary oligometastasis with favorable local control and minimal toxicity. Multiple dose parameters, instead of a prescription dose only, in combination with clinical parameters, should be considered for optimal local control.

Time of PTV is ending, robust optimization comes next

Continuous improvements have been made in the way to prescribe, record and report dose distributions since the therapeutic use of ionizing radiations. The international commission for radiation units and measurement (ICRU) has provided a common language for physicians and physicists to plan and evaluate their treatments. The PTV concept has been used for more than two decades but is becoming obsolete as the CTV-to-PTV margin creates a static dose cloud that does not properly recapitulate all planning vs. delivery uncertainties. The robust optimization concept has recently emerged to overcome the limitations of the PTV concept. This concept is integrated in the inverse planning process and minimizes deviations to planned dose distribution through integration of uncertainties in the planning objectives. It appears critical to account for the uncertainties that are specific to protons and should be accounted for to better exploit the clinical potential of proton therapy. It may also improve treatment quality particularly in hypofractionated photon plans of mobile tumors and more widely to photon radiotherapy. However, in contrast to the PTV concept, a posteriori evaluation of plan quality, called robust evaluation, using error-based scenarios is still warranted. Robust optimization metrics are warranted. These metrics are necessary to compare PTV-based photon and robustly optimized proton plans in general and in model-based NTCP approaches. Assessment of computational demand and approximations of robust optimization algorithms along with metrics to evaluate plan quality are needed but a step further to better prescribe radiotherapy may has been achieved.

Treatment plan quality during online adaptive re-planning

BACKGROUND

Online adaptive radiotherapy is intended to prevent plan degradation caused by inter-fractional tumor volume and shape changes, but time limitations make online re-planning challenging. The aim of this study was to compare the quality of online-adapted plans to their respective reference treatment plans.

METHODS

Fifty-two patients treated on a ViewRay MRIdian Linac were included in this retrospective study. In total 238 online-adapted plans were analyzed, which were optimized with either changing of the segment weights (n = 85) or full re-optimization (n = 153). Five different treatment sites were evaluated: prostate, abdomen, liver, lung and pelvis. Dosimetric parameters of gross tumor volume (GTV), planning target volume (PTV), 2 cm ring around the PTV and organs at risk (OARs) were considered. The Wilcoxon signed-rank test was used to assess differences between online-adapted and reference treatment plans, p < 0.05 was considered significant.

RESULTS

The average duration of the online adaptation, consisting of contour editing, plan optimization and quality assurance (QA), was 24 ± 6 min. The GTV was slightly larger (average ± SD: 1.9% ± 9.0%) in the adapted plans than in the reference plans (p < 0.001). GTV-D95% exhibited no significant changes when considering all plans, but GTV-D2% increased by 0.40% ± 1.5% on average (p < 0.001). There was a very small yet significant decrease in GTV-coverage for the abdomen plans. The ring Dmean increased on average by 1.0% ± 3.6% considering all plans (p < 0.001). There was a significant reduction of the dose to the rectum of 4.7% ± 16% on average (p < 0.001) for prostate plans.

CONCLUSIONS

Dosimetric quality of online-adapted plans was comparable to reference treatment plans and OAR dose was either comparable or decreased, depending on treatment site. However, dose spillage was slightly increased.