A Randomized Phase 2 Study Comparing 2 Stereotactic Body Radiation Therapy Schedules for Medically Inoperable Patients With Stage I Peripheral Non-Small Cell Lung Cancer: NRG Oncology RTOG 0915 (NCCTG N0927)

The value of brachytherapy in the age of advanced external beam radiotherapy: a review of the literature in terms of dosimetry

Brachytherapy (BT) has long been used for successful treatment of various tumour entities, including prostate, breast and gynaecological cancer. However, particularly due to advances in modern external beam techniques such as intensity-modulated radiotherapy (IMRT), volume modulated arc therapy (VMAT) and stereotactic body radiotherapy (SBRT), there are concerns about its future. Based on a comprehensive literature review, this article aims to summarize the role of BT in cancer treatment and highlight its particular dosimetric advantages. The authors conclude that image-guided BT supported by inverse dose planning will successfully compete with high-tech EBRT in the future and continue to serve as a valuable modality for cancer treatment.

The new SRS/FSRT technique HyperArc for benign brain lesions: a dosimetric analysis

To evaluate the potential benefit of HyperArc (HA) fractionated stereotactic radiotherapy (FSRT) for the benign brain lesion. Sixteen patients with a single deep-seated, centrally located benign brain lesion treated by CyberKnife (CK, G4 cone-based model) were enrolled. Treatment plans for HA with two different optimization algorithms (SRS NTO and ALDO) and coplanar RapidArc (RA) were generated for each patient to meet the corresponding treatment plan criteria. These four FSRT treatment plans were divided into two groups—the homogeneous delivery group (HA-SRS NTO and coplanar RA) and the inhomogeneous delivery group (HA-ALDO and cone-based CK)—to compare for dosimetric outcomes. For homogeneous delivery, the brain V5, V12, and V24 and the mean brainstem dose were significantly lower with the HA-SRS NTO plans than with the coplanar RA plans. The conformity index, high and intermediate dose spillage, and gradient radius were significantly better with the HA-SRS NTO plans than with the coplanar RA plans. For inhomogeneous delivery, the HA-ALDO exhibited superior PTV coverage levels to the cone-based CK plans. Almost all the doses delivered to organs at risk and dose distribution metrics were significantly better with the HA-ALDO plans than with the cone-based CK plans. Good dosimetric distribution makes HA an attractive FSRT technique for the treatment of benign brain lesions.

A novel CRT-IMRT-combined (Co-CRIM) planning technique for peripheral lung stereotactic body radiotherapy in pinnacle treatment planning system

Objectives

This study attempts to explore a novel peripheral lung stereotactic body radiotherapy (SBRT) planning technique that can balance the pros and cons of three‐dimensional conformal radiotherapy (CRT) and intensity‐modulated radiation therapy (IMRT) / volumetric modulated arc therapy (VMAT).

Methods

Treatment plans were retrospectively designed based on CRT, IMRT, VMAT, and the proposed CRT‐IMRT‐combined (Co‐CRIM) techniques using Pinnacle treatment planning system (TPS) for 20 peripheral lung cancer patients. Co‐CRIM used an inverse optimization algorithm available in Pinnacle TPS. To develop a Co‐CRIM plan, the number of segments in each field was limited to one, the minimum segment area was set to the internal target volume (ITV), and the minimum monitor units (MU) of the segment was the quotient of fractional dose divided by twice the number of total fields. The performance of Co‐CRIM was then compared with other techniques.

Results

For conformity index (CI), Co‐CRIM performed comparably to IMRT/VMAT but better than CRT. For gradient index (GI), Co‐CRIM was similar to IMRT/VMAT or CRT. For heterogeneity index (HI), Co‐CRIM was comparable to IMRT/VMAT, higher than CRT. The dosimetric results of spinal cord and lung with Co‐CRIM were better than CRT, comparable to IMRT, but inferior to VMAT. The MU resulted from Co‐CRIM was lower than IMRT/VMAT but higher than CRT. For plan verification γ passing rate, Co‐CRIM was higher than IMRT/VMAT, comparable to CRT. For planning time, Co‐CRIM was shorter than CRT or VMAT but similar to IMRT.

Conclusions

The proposed Co‐CRIM technique on Pinnacle TPS is an effective planning technique for peripheral lung SBRT.

Impact of tumor size and location on lung dose difference between stereotactic body radiation therapy techniques for non-small cell lung cancer

Background

To evaluate the lung dose differences between three‐dimensional conformal radiotherapy (3D‐CRT) and intensity‐modulated radiation therapy (IMRT) techniques for lung stereotactic body radiation therapy (SBRT) and the correlations with tumor characteristics, such as size and location.

Methods

Dosimetric comparisons between the two SBRT techniques in high‐ and low‐ to intermediate‐dose regions were retrospectively performed using four planning indices and lung‐dose parameters in 31 lung tumors. The magnitude of differences in these parameters was analyzed with relation to the planning target volume (PTV) and location‐related parameters.

Results

The absolute differences between the two techniques in lung‐dose parameters were small in both ipsilateral and bilateral lungs. The dosimetric differences were mainly correlated with the PTV rather than location‐related parameters, with positive and negative correlations with the high‐dose and intermediate‐dose parameters, respectively. The distances from the ipsilateral lung centroid to the PTV center were not correlated with the differences in any of the lung‐dose parameters. Additionally, the negative correlations with the MLD and V20 differences disappeared after applying a more rapid dose fall‐off in the IMRT plans for tumors with small PTVs of ≤15 cc.

Conclusions

Lung dose differences between the 3D‐CRT and IMRT techniques for lung SBRT were mainly correlated with the PTV rather than location‐related parameters. Together with the dosimetric benefit in high‐dose lung regions of IMRT for larger tumors, the relative increases in the MLD and V20 for small‐sized tumors could be reduced by applying a more rapid dose fall‐off outside the PTV.

Clinical Outcome of CT-Guided Stereotactic Ablative Brachytherapy for Unresectable Early Non-Small Cell Lung Cancer: A Retrospective, Multicenter Study

Objective

To analyze the efficacy and safety of low dose rate stereotactic ablative brachytherapy (L-SABT) for treatment of unresectable early-stage non-small cell lung cancer (NSCLC).

Methods

Data of patients with early-stage NSCLC who received CT-guided L-SABT (radioactive I-125 seeds implantation) at eight different centers from December 2010 to August 2020 were retrospectively analyzed. Treatment efficacy and complications were evaluated.

Results

A total of 99 patients were included in this study. Median follow-up duration was 46.3 months (6.1-119.3 months). The 1-year, 3-year, and 5-year local control rates were 89.1%, 77.5%, and 75.7%, respectively. The 1-year, 3-year, and 5-year overall survival rates were 96.7%, 70.1%, and 54.4%, respectively. Treatment failure occurred in 38.4% of patients. Local/regional recurrence, distant metastasis, and recurrence combined with metastasis accounted for 15.1%, 12.1%, and 11.1%, respectively. Pneumothorax occurred in 47 patients (47.5%) with 19 cases (19.2%) needing closed drainage. The only radiation-related adverse reaction was two cases of grade 2 radiation pneumonia. KPS 80-100, T1, the lesion was located in the left lobe, GTV D90 ≥150 Gy and the distance between the lesion and chest wall was < 1 cm, were associated with better local control (all P < 0.05); on multivariate analysis KPS, GTV D90, and the distance between the lesion and chest wall were independent prognostic factors for local control (all P < 0.05). KPS 80-100, T1, GTV D90 ≥150 Gy, and the distance between the lesion and chest wall was < 1 cm were also associated with better survival (all P < 0.05); on multivariate analysis KPS, T stage, and GTV D90 were independent prognostic factors for survival (all P < 0.05). The incidence of pneumothorax in patients with lesions <1 cm and ≥1cm from the chest wall was 33.3% and 56.7%, respectively, and the differences were statistically significant (P = 0.026).

Conclusion

L-SABT showed acceptable efficacy in the treatment of unresectable early-stage NSCLC. But the incidence of pneumothorax is high. For patients with T1 stage and lesions <1 cm from the chest wall, it may have better efficacy. Prescription dose greater than 150 Gy may bring better results.

Radiation Therapy in Non-Small-Cell Lung Cancer

The management of non-small-cell lung cancer (NSCLC) varies according to stage. Surgical resection is reserved for operable patients with early-stage NSCLC, while high-dose target radiation-stereotactic body radiation therapy (SBRT)-is reserved for patients whose comorbidities prohibit them from a major surgical procedure. The treatment of locally advanced NSCLC (LA-NSCLC) is stratified according to resectability. Those with resectable disease may require additional treatments such as chemotherapy and radiation, while patients with unresectable disease will require definitive chemoradiation therapy with adjuvant durvalumab. Patients with limited metastatic disease benefit from the combination of SBRT and systemic therapy.

Ten-Year Experience in Implementing Single-Fraction Lung SBRT for Medically Inoperable Early-Stage Lung Cancer

PURPOSE

To review 10 years of using single-fraction lung stereotactic body radiation therapy (SF-SBRT) for medically inoperable peripheral early-stage lung cancer.

METHODS AND MATERIALS

An institutional review board-approved prospective lung SBRT data registry was surveyed until the end of December 2019 for all patients receiving SF-SBRT with minimum 6-month follow-up. Doses used were either 34 Gy or 30 Gy. Outcomes of interest included rates of local failure and overall survival (OS), as well as treatment-related toxicity graded per Common Terminology Criteria for Adverse Events version 3.0.

RESULTS

A total of 229 patients met the study criteria. Patient characteristics included female sex (55%); median age, 74.6 years (range, 47-94); and median Karnofsky Performance Status 80 (range, 50-100). Tumor characteristics included median diameter, 1.6 cm (range, 0.7-4.1); median positron emission tomography standardized uptake value maximum 6.1 (range, 0.8-24.3); and 63.6% of patients biopsied. SF-SBRT dose was 34 Gy in 72.1% cases and 30 Gy in 27.9%, with patient and tumor characteristics balanced between cohorts. Overall median follow-up times for 30 Gy and 34 Gy were 36.7 and 17.2 months, respectively (P < .0001). At analysis, 55.9% patients were alive. Two (0.9%) patients developed grade 3 toxicities, and none had grade 4/5 toxicities. Grades 1 to 2 pneumonitis and chest wall toxicity were seen in 7% and 12.7% patients, respectively. Median overall survival was 44.1 months. Rates of 2-year local, nodal, and distant failure were 7.3%, 9.4%, and 12.2%, respectively. There were no significant differences in outcomes by dose.

CONCLUSIONS

This is the largest institutional series to date reporting on SF-SBRT outcomes for medically inoperable peripheral early-stage lung cancer and the first to report on a decade's experience in implementing this schedule. Outcomes from this analysis are comparable to published results from 2 randomized trials and validate the use of this schedule in routine practice. In the absence of phase 3 trials, this study should encourage increased use of SF-SBRT for inoperable tumors.

Dosimetric benefits of dynamic conformal arc therapy-combined with active breath-hold in lung stereotactic body radiotherapy

To test the hypothesis that dynamic conformal arc therapy (DCAT) in Monaco, compared with volumetric modulated arc therapy (VMAT), maintains plan quality with higher delivery efficiency for lung stereotactic body radiotherapy (SBRT) and to investigate dosimetric benefits of DCAT with active breath-hold (DCAT+ABH), compared with free-breathing (DCAT+FB) for varying tumor sizes and motions. Fifty DCAT plans were used for lung SBRT. Randomly selected 17 DCAT plans were evaluated with respect to the retrospectively generated volumetric modulated arc therapy (VMAT) plans. The maximum dose at 2 cm from planning target volume (PTV) in any direction (D2cm/Rx), the ratio of 50% prescription isodose volume to the PTV (R50%), conformity index (CI), the lung volume receiving ≥20 Gy (V20), and monitor unit (MU) were evaluated. A t-test was used to evaluate the difference of plan quality between DCAT and VMAT. Internal target volume (ITV)/integrated-gross target volume (GTV) attributed by intra-fraction motion and lung V20 were stratified for DCAT+ABH and DCAT+FB across varying GTVs. DCAT maintained plan quality (p = 0.154 for D2cm/Rx, p = 0.089 for R50%, p = 0.064 for CI, and p = 0.780 for lung V20) while reducing MUs up to 30% (p <0.001) from 2748 MU (VMAT) to 1868 MU (DCAT). DCAT+ABH, compared to DCAT+FB, reduced tumor motion, resulting in 19% volume reduction of PTV and 60% reduction in lung V20, on average. The difference in lung V20 between DCAT+ABH and DCAT+FB increased as the target size increased. The DCAT is a favorable approach compared with VMAT. These results support the utility of DCAT as a routine planning platform for lung SBRT, especially when utilized with respiratory motion management using the ABH.

Markerless 3D tumor tracking during single-fraction free-breathing 10MV flattening-filter-free stereotactic lung radiotherapy

BACKGROUND AND PURPOSE

Positional verification during single fraction lung SBRT could increase confidence and reduce the chance of geographic miss. As planar 2DkV imaging during VMAT irradiation is already available on current linear accelerators, markerless tracking based on these images could offer widely available and low-cost verification. We evaluated treatment delivery data and template matching and triangulation for 3D-positional verification during free-breathing, single fraction (34 Gy), 10 MV flattening-filter-free VMAT lung SBRT.

METHODS AND MATERIALS

Tumor tracking based on kV imaging at 7 frames/second was performed during irradiation in 6 consecutive patients (7 lesions). Tumor characteristics, tracking ability, comparison of tracking displacements with CBCT-based shifts, tumor position relative to the PTV margin, and treatment times are reported.

RESULTS

For all 7 lesions combined, 3D tumor position could be determined for, on average, 71% (51-84%) of the total irradiation time. Visually estimated tracked and automated match +/- manually-corrected CBCT-derived displacements generally agreed within 1 mm. During the tracked period, the longitudinal, lateral and vertical position of the tumor was within a 5 mm/3 mm PTV margin 95.5/85.3% of the time. The PTV was derived from the ITV including all tumor motion. The total time from first set-up imaging to end of the last arc was 18.3-31.4 min (mean = 23.4, SD = 4.1).

CONCLUSION

3D positional verification during irradiation of small lung targets with limited motion, was feasible. However, tumor position could not be determined for on average 29% of the time. Improvements are needed. Margin reduction may be feasible. Imaging and delivery of a single 34 Gy fraction was fast.

Evolution of systemic therapy for stages I-III non-metastatic non-small-cell lung cancer

The treatment goal for patients with early-stage lung cancer is cure. Multidisciplinary discussions of surgical resectability and medical operability determine the modality of definitive local treatment (surgery or radiotherapy) and the associated systemic therapies to further improve the likelihood of cure. Trial evidence supports cisplatin-based adjuvant therapy either after surgical resection or concurrently with radiotherapy. Consensus guidelines support neoadjuvant chemotherapy in lieu of adjuvant chemotherapy and carboplatin-based regimens for patients who are ineligible for cisplatin. The incorporation of newer agents, now standard for patients with stage IV lung cancer, into the curative therapy paradigm has lagged owing to inefficient trial designs, the lengthy follow-up needed to assess survival end points and a developmental focus on the advanced-stage disease setting. Surrogate end points, such as pathological response, are being studied and might shorten trial durations. In 2018, the anti-PD-L1 antibody durvalumab was approved for patients with stage III lung cancer after concurrent chemoradiotherapy. Since then, the study of targeted therapies and immunotherapies in patients with early-stage lung cancer has rapidly expanded. In this Review, we present the current considerations in the treatment of patients with early-stage lung cancer and explore the current and future state of clinical research to develop systemic therapies for non-metastatic lung cancer.

Evolution of systemic therapy for stages I-III non-metastatic non-small-cell lung cancer

The treatment goal for patients with early-stage lung cancer is cure. Multidisciplinary discussions of surgical resectability and medical operability determine the modality of definitive local treatment (surgery or radiotherapy) and the associated systemic therapies to further improve the likelihood of cure. Trial evidence supports cisplatin-based adjuvant therapy either after surgical resection or concurrently with radiotherapy. Consensus guidelines support neoadjuvant chemotherapy in lieu of adjuvant chemotherapy and carboplatin-based regimens for patients who are ineligible for cisplatin. The incorporation of newer agents, now standard for patients with stage IV lung cancer, into the curative therapy paradigm has lagged owing to inefficient trial designs, the lengthy follow-up needed to assess survival end points and a developmental focus on the advanced-stage disease setting. Surrogate end points, such as pathological response, are being studied and might shorten trial durations. In 2018, the anti-PD-L1 antibody durvalumab was approved for patients with stage III lung cancer after concurrent chemoradiotherapy. Since then, the study of targeted therapies and immunotherapies in patients with early-stage lung cancer has rapidly expanded. In this Review, we present the current considerations in the treatment of patients with early-stage lung cancer and explore the current and future state of clinical research to develop systemic therapies for non-metastatic lung cancer.

Implementation of Single-Fraction Lung Stereotactic Ablative Radiotherapy in a Multicenter Provincial Cancer Program During the COVID-19 Pandemic

Background During the novel coronavirus disease 2019 (COVID-19) pandemic, cancer centers considered shortened courses of radiotherapy to minimize the risk of infectious exposure of patients and staff members. Amidst a pandemic, the process of implementing new treatment approaches can be particularly challenging in larger institutions with multiple treatment centers. We describe the implementation of single-fraction (SF) lung stereotactic ablative radiotherapy (SABR) in a multicenter provincial cancer program. Materials and Methods British Columbia, Canada has a provincial cancer program with six geographically distributed radiotherapy centers serving a population of 5.1 million, over 944,735 square kilometers. In March 2020, provincial mitigation strategies were developed in case of reduced access to radiotherapy due to the COVID-19 pandemic. SF lung SABR was identified by the provincial lung radiation oncology group as a mitigation measure supported by high-quality randomized evidence that could provide comparable outcomes and toxicity to existing fractionated SABR protocols. A working group consisting of radiation oncologists and medical physicists reviewed the medical literature and drafted consensus guidelines that were reviewed by a group of center representatives as a component of provincial lung radiotherapy mitigation strategic planning. Individual centers were encouraged to implement SF lung SABR as their resources and staffing would allow. Centers were then surveyed about barriers to implementation. Results On March 24, 2020, a working group was created and consensus guidelines for SF lung SABR were drafted. The final version was approved and distributed by the working group on March 26, 2020. The provincial lung radiotherapy mitigation strategy group adopted the guidelines for implementation on April 1, 2020. Implementation was completed at the first center on April 27, 2020. Barriers to implementation were identified at five of six centers. Two centers in regions with disproportionately high COVID-19 cases described inadequate staffing as a barrier to implementation. One center encountered delays due to pre-scheduled commissioning of new treatment techniques. Three centers cited competing priorities as reasons for delay. As of May 2021, two centers had active SF lung SABR programs in place, three centers were in the process of implementation, and one center had no immediate plans for implementation due to ongoing resource issues. Conclusion SF lung SABR was adopted by a provincial cancer program within weeks of conception through rapid communication during the development of COVID-19 pandemic mitigation strategies for radiotherapy. Although consensus guidelines were written and approved in an expedited timeframe, the completion of implementation by individual centers was variable due to differences in resource allocation and staffing among the centers. Strong organizational structures and early identification of potential barriers may improve the efficiency of implementing new treatment initiatives in large multicenter radiotherapy programs.

Estimating the tolerance of brachial plexus to hypofractionated stereotactic body radiotherapy: a modelling-based approach from clinical experience

BACKGROUND

Brachial plexopathy is a potentially serious complication from stereotactic body radiation therapy (SBRT) that has not been widely studied. Therefore, we compared datasets from two different institutions and generated a brachial plexus dose-response model, to quantify what dose constraints would be needed to minimize the effect on normal tissue while still enabling potent therapy for the tumor.

METHODS

Two published SBRT datasets were pooled and modeled from patients at Indiana University and the Richard L. Roudebush Veterans Administration Medical Center from 1998 to 2007, as well as the Karolinska Institute from 2008 to 2013. All patients in both studies were treated with SBRT for apically located lung tumors localized superior to the aortic arch. Toxicities were graded according to Common Terminology Criteria for Adverse Events, and a probit dose response model was created with maximum likelihood parameter fitting.

RESULTS

This analysis includes a total of 89 brachial plexus maximum point dose (Dmax) values from both institutions. Among the 14 patients who developed brachial plexopathy, the most common complications were grade 2, comprising 7 patients. The median follow-up was 30 months (range 6.1-72.2) in the Karolinska dataset, and the Indiana dataset had a median of 13 months (range 1-71). Both studies had a median range of 3 fractions, but in the Indiana dataset, 9 patients were treated in 4 fractions, and the paper did not differentiate between the two, so our analysis is considered to be in 3-4 fractions, one of the main limitations. The probit model showed that the risk of brachial plexopathy with Dmax of 26 Gy in 3-4 fractions is 10%, and 50% with Dmax of 70 Gy in 3-4 fractions.

CONCLUSIONS

This analysis is only a preliminary result because more details are needed as well as additional comprehensive datasets from a much broader cross-section of clinical practices. When more institutions join the QUANTEC and HyTEC methodology of reporting sufficient details to enable data pooling, our field will finally reach an improved understanding of human dose tolerance.

Clinical verification of treatment planning dose calculation in lung SBRT with GATE Monte Carlo simulation code

PURPOSE

This study aims to use GATE/Geant4 simulation code to evaluate the performance of dose calculations with Anisotropic Analytical Algorithm (AAA) in the context of lung SBRT for complex treatments considering images of patients.

METHODS

Four cases of non-small cell lung cancer treated with SBRT were selected for this study. Irradiation plans were created with AAA and recalculated end to end using Monte Carlo (MC) method maintaining field configurations identical to the original plans. Each treatment plan was evaluated in terms of PTV and organs at risk (OARs) using dose-volume histograms (DVH). Dosimetric parameters obtained from DVHs were used to compare AAA and MC.

RESULTS

The comparison between the AAA and MC DVH using gamma analysis with the passing criteria of 3%/3% showed an average passing rate of more than 90% for the PTV structure and 97% for the OARs. Tightening the criteria to 2%/2% showed a reduction in the average passing rate of the PTV to 86%. The agreement between the AAA and MC dose calculations for PTV dosimetric parameters (V₁₀₀; V₉₀; Homogeneity index; maximum, minimum and mean dose; CI_Paddick and D_2cm) was within 18.4%. For OARs, the biggest differences were observed in the spinal cord and the great vessels.

CONCLUSIONS

In general, we did not find significant differences between AAA and MC. The results indicate that AAA could be used in complex SBRT cases that involve a larger number of small treatment fields in the presence of tissue heterogeneities.

Impact of dose to lung outside the planning target volume on distant metastasis or progression after SBRT for early-stage non-small cell lung cancer

Mean dose (EQD2) to 3-cm shell of lung surrounding the PTV was evaluated for association with distant metastasis and PFS after SBRT for stage I NSCLC. Dose was uniformly above previously determined threshold and metastasis was uncommon. An association between outcomes and mean EQD2 could not be confirmed or refuted.

Dosimetric Impact of Acuros XB Dose-to-Water and Dose-to-Medium Reporting Modes on Lung Stereotactic Body Radiation Therapy and Its Dependency on Structure Composition

Purpose

Our purpose was to assess the dosimetric effect of switching from the analytical anisotropic algorithm (AAA) to Acuros XB (AXB), with dose-to-medium (Dm) and dose-to-water (Dw) reporting modes, in lung stereotactic body radiation therapy patients and determine whether planning-target-volume (PTV) dose prescriptions and organ-at-risk constraints should be modified under these circumstances.

Methods and Materials

We included 54 lung stereotactic body radiation therapy patients. We delineated the PTV, the ipsilateral lung, the contralateral lung, the heart, the spinal cord, the esophagus, the trachea, proximal bronchi, the ribs, and the great vessels. We performed dose calculations with AAA and AXB, then compared clinically relevant dose-volume parameters. Paired t tests were used to analyze differences of means. We propose a method, based on the composition of the involved structures, for predicting differences between AXB Dw and Dm calculations.

Results

The largest difference between the algorithms was 4%. Mean dose differences between AXB Dm and AXB Dw depended on the average composition of the volumes. Compared with AXB, AAA underestimated all PTV dose-volume parameters (-0.7 Gy to -0.1 Gy) except for gradient index, which was significantly higher (4%). It also underestimated V₅ of the contralateral lung (-0.3%). Significant differences in near-maximum doses (D₂) to the ribs were observed between AXB Dm and AAA (1.7%) and between AXB Dw and AAA (-1.6%). AAA-calculated D₂ was slightly higher in the remaining organs at risk.

Conclusions

Differences between AXB and AAA are below the threshold of clinical detectability (5%) for most patients. For a small subgroup, the difference in maximum doses to the ribs between AXB Dw and AXB Dm may be clinically significant. The differences in dose volume parameters between AXB Dw and AXB Dm can be predicted with reference to structure composition.

Intrinsic detector sensitivity analysis as a tool to characterize ArcCHECK and EPID sensitivity to variations in delivery for lung SBRT VMAT plans

PURPOSE

To investigate intrinsic sensitivity of an electronic portal imaging device (EPID) and the ArcCHECK detector and to use this in assessing their performance in detecting delivery variations for lung SBRT VMAT. The effect of detector spatial resolution and dose matrix interpolation on the gamma pass rate was also considered.

MATERIALS AND METHODS

Fifteen patients' lung SBRT VMAT plans were used. Delivery variations (errors) were introduced by modifying collimator angles, multi-leaf collimator (MLC) field sizes and MLC field shifts by ±5, ±2, and ±1 degrees or mm (investigating 103 plans in total). EPID and ArcCHECK measured signals with introduced variations were compared to measured signals without variations (baseline), using OmniPro-I'mRT software and gamma criteria of 3%/3 mm, 2%/2 mm, 2%/1 mm, and 1%/1 mm, to test each system's basic performance. The measurement sampling resolution for each was also changed to 1 mm and results compared to those with the default detector system resolution.

RESULTS

Intrinsic detector sensitivity analysis, that is, comparing measurement to baseline measurement, rather than measurement to plan, demonstrated the intrinsic constraints of each detector and indicated the limiting performance that users might expect. Changes in the gamma pass rates for ArcCHECK, for a given introduced error, were affected only by dose difference (DD %) criteria. However, the EPID showed only slight changes when changing DD%, but greater effects when changing distance-to-agreement criteria. This is pertinent for lung SBRT where the minimum dose to the target will drop dramatically with geometric errors. Detector resolution and dose matrix interpolation have an impact on the gamma results for these SBRT plans and can lead to false positives or negatives in error detection if not understood.

CONCLUSION

The intrinsic sensitivity approach may help in the selection of more meaningful gamma criteria and the choice of optimal QA device for site-specific dose verification.

Stereotactic body radiotherapy for synchronous early stage non-small cell lung cancer

INTRODUCTION

In patients with non-small cell lung cancer (NSCLC) who present with multiple pulmonary nodules, it is often difficult to distinguish metastatic disease from synchronous primary lung cancers (SPLC). We sought to evaluate clinical outcomes after stereotactic body radiotherapy (SBRT) alone to synchronous primary lesions.

MATERIAL AND METHODS

Patients with synchronous AJCC 8^th Edition Stage IA-IIA NSCLC and treated with stereotactic body radiation therapy (SBRT) to all lesions between 2009-2018 were reviewed. SPLC was defined as patients having received two courses of SBRT within 180 days for treatment of separate early stage tumors. In total, 36 patients with 73 lesions were included. Overall survival (OS), progression-free survival (PFS), cumulative incidence of local failure (LF), and regional/distant failure (R/DF) were estimated and compared with a control cohort of solitary early stage NSCLC patients.

RESULTS

Median PFS was 38.8 months (95% CI 14.3-not reached [NR]); 3-year PFS rates were 50.6% (35.6-72.1). Median OS was 45.9 months (95% CI: 35.9-NR); 3-year OS was 63.0% (47.4-83.8). Three-year cumulative incidence of LF and R/DF was 6.6% (3.7-13.9) and 35.7% (19.3-52.1), respectively. Patients with SPLC were compared to a control group (n = 272) of patients treated for a solitary early stage NSCLC. There was no statistically significant difference in PFS (p = .91) or OS (p = .43). Evaluation of the patterns of failure showed a trend for worse cumulative incidence of R/DF in SPLC patients as compared to solitary early stage NSCLC (p = .06).

CONCLUSION

SBRT alone to multiple lung tumors with SPLC results in comparable PFS, OS, and LF rates to a cohort of patients treated for solitary early stage NSCLC. Those with SPLC had non-significantly higher R/DF. Patients with SPLC should be followed closely for failure and possible salvage therapy.

Long-Term Outcomes From a Phase 2 Trial of Radiofrequency Ablation Combined With External Beam Radiation Therapy for Patients With Inoperable Non-Small Cell Lung Cancer

PURPOSE

Long-term outcomes after external beam radiation therapy (EBRT) and radiofrequency ablation (RFA) for medically inoperable early-stage non-small cell lung cancer (NSCLC) are not well known.

METHODS AND MATERIALS

Patients with medically inoperable early-stage NSCLC were enrolled in a prospective single-arm, phase 2 study between June 2007 and October 2008 and were treated with RFA followed by EBRT. Radiation was delivered using hypofractionated radiation therapy (HFRT; 70.2 Gy in 26 fractions) or stereotactic body radiation therapy (54 Gy in 3 fractions).

RESULTS

Twelve patients were evaluable; 10 patients were treated with HFRT. The cumulative incidence of local progression at 5 years was 16.7% (95% confidence interval [CI], 0-37.8). Median progression-free survival was 37.8 months (95% CI, 11.1 to not reached) and median overall survival was 53.6 months (95% CI, 21.0 to not reached). There were no mortalities within 30 days after RFA and no grade ≥4 toxicity.

CONCLUSIONS

The combination of RFA with EBRT appears feasible with favorable long-term local control. However, because SBRT alone has similar or better rates of control, we do not recommend routine combined RFA and EBRT.

Combination of Bempegaldesleukin and Anti-CTLA-4 Prevents Metastatic Dissemination After Primary Resection or Radiotherapy in a Preclinical Model of Non-Small Cell Lung Cancer

Surgical resection or hypo-fractionated radiation therapy (RT) in early-stage non-small cell lung cancer (NSCLC) achieves local tumor control, but metastatic relapse remains a challenge. We hypothesized that immunotherapy with anti-CTLA-4 and bempegaldesleukin (BEMPEG; NKTR-214), a CD122-preferential IL2 pathway agonist, after primary tumor RT or resection would reduce metastases in a syngeneic murine NSCLC model. Mice bearing Lewis Lung Carcinoma (LLC) tumors were treated with combinations of BEMPEG, anti-CTLA-4, and primary tumor treatment (surgical resection or RT). Primary tumor size, mouse survival, and metastatic disease at the time of death were assessed. Flow cytometry, qRT-PCR, and cytokine analyses were performed on tumor specimens. All mice treated with RT or surgical resection of primary tumor alone succumbed to metastatic disease, and all mice treated with BEMPEG and/or anti-CTLA-4 succumbed to primary tumor local progression. The combination of primary tumor RT or resection and BEMPEG and anti-CTLA-4 reduced spontaneous metastasis and improved survival without any noted toxicity. Flow cytometric immunoprofiling of primary tumors revealed increased CD8 T and NK cells and decreased T-regulatory cells with the combination of BEMPEG, anti-CTLA-4, and RT compared to RT alone. Increased expression of genes associated with tumor cell immune susceptibility, immune cell recruitment, and cytotoxic T lymphocyte activation were observed in tumors of mice treated with BEMPEG, anti-CTLA-4, and RT. The combination of BEMPEG and anti-CTLA-4 with primary tumor RT or resection enabled effective control of local and metastatic disease in a preclinical murine NSCLC model. This therapeutic combination has important translational potential for patients with early-stage NSCLC and other cancers.

Hypofractionation in Early Stage Non-Small Cell Lung Cancer

Radiation treatment of early stage nonsmall cell lung cancer has evolved over the past 2 decades to progressively more hypofractionated treatment courses. Results comparable to surgical resection are seen with stereotactic body radiotherapy, which is now the standard of care for medically inoperable patients, and a treatment option for operable patients as well. Understanding of the optimal radiation dose and fractionation are evolving, especially for central tumors which have higher treatment toxicity than peripheral tumors.

Stereotactic ablative radiotherapy as single treatment for early stage non-small cell lung cancer: A single institution analysis

BACKGROUND

Stereotactic ablative radiotherapy (SABR) is the current standard-of-care in cases of inoperable early stage non-small cell lung cancer (ES-NSCLC). This study aimed to assess the survival outcomes and recurrence patterns after SABR for ES-NSCLC in a hospital setting.

METHODS

A single-institution retrospective study was performed which included 109 patients who had undergone SABR. The main study endpoints were overall survival (OS), cancer specific survival (CSS), local recurrence-free survival (LRFS), regional recurrence free survival (RRFS) and distant metastasis-free survival (DMFS). Univariate and multivariate analysis were conducted to explore the potential factors which might be related to patient survival.

RESULTS

A total of 109 patients were enrolled into the study. Median follow-up was 44 months (range: 2-93 months). (i) Recurrence results: Among 45 patients with recurrence, 30 patients (28%) had distant metastasis (DM), 17 patients (16%) had local recurrence (LR), 10 patients (9%) had regional recurrence (RR) of lymph nodes and two patients (2%) had second primary lung cancer (SPLC). (ii) Survival results: Median OS, CSS, PFS was 78 months, 78 and 40 months. Two-year OS, CSS, PFS, LRFS, RRFS and DMFS was 84.7%, 87.1%, 69.2%, 86.8%, 92.7% and 78.0%, respectively. Four-year OS, CSS, PFS, LRFS, RRFS and DMFS was 55.6%, 60.7%, 37.3%, 76.3%, 88.4% and 59.4%, respectively. (iii) Univariate and multivariate analyses indicated that age was a prognostic factor of CSS in patients aged <75 years (P = 0.04 HR 2.12 95% confidence interval [CI]: 1.04-4.33).

CONCLUSIONS

Although high survival rates can be achieved in ES-NSCLC patients treated with SABR, using SABR on its own may not be enough. Prolonged surveillance and adjuvant therapy is therefore needed.

An analytical expression for R50% dependent on PTV surface area and volume: A cranial SRS comparison

The intermediate dose spill for a stereotactic radiosurgery (SRS) plan can be quantified with the metric R50%, defined as the 50% isodose cloud volume (V_IDC50% ) divided by the volume of the planning target volume (PTV). By coupling sound physical principles with the basic definition of R50%, we derive an analytical expression for R50% for a spherical PTV. Our analytical expression depends on three quantities: the surface area of PTV (SA_PTV ), the volume of PTV (V_PTV ), and the distance of dose drop-off to 50% (Δr). The value of ∆r was obtained from a simple set of cranial phantom plan calculations. We generate values from our analytical expression for R50% (R50%_Analytic ) and compare the values to clinical R50% values (R50%_Clinical ) extracted from a previously published SRS data set that spans the V_PTV range from 0.15 to 50.1 cm³ . R50%_Analytic is smaller than R50%_Clinical in all cases by an average of 15% ± 7%, and the general trend of R50%_Clinical vs V_PTV is reflected in the same trend of R50%_Analytic . This comparison suggests that R50%_Analytic could represent a theoretical lower limit for the clinical SRS data; further investigation is required to confirm this. R50%_Analytic could provide useful guidance for what might be achievable in SRS planning.

Risk of target coverage loss for stereotactic body radiotherapy treatment of synchronous lung lesions via single-isocenter volumetric modulated arc therapy

Treating multiple lung lesions synchronously via single‐isocenter volumetric modulated arc therapy (VMAT) stereotactic body radiation therapy (SBRT) improves treatment efficiency and patient compliance. However, aligning multiple lung tumors accurately on single pretreatment cone beam CTs (CBCTs) can be problematic. Tumors misaligned could lead to target coverage loss. To quantify this potential target coverage loss due to small, clinically realistic setup errors, a novel simulation method was developed. This method was used on 26 previously treated patients with two metastatic lung lesions. Patients were treated with 4D CT‐based, highly conformal noncoplanar VMAT plans (clinical VMAT) with 6MV‐flattening filter free (FFF) beam using AcurosXB dose calculation algorithm with heterogeneity corrections. A single isocenter was placed approximately between the lesions to improve patient convenience and clinic workflow. Average isocenter to tumor distance was 5.9 cm. Prescription dose was 54 Gy/50 Gy in 3/5 fractions. For comparison, a plan summation (simulated VMAT) was executed utilizing randomly simulated, clinically relevant setup errors, obtained from pretreatment setup, per treatment fraction, in Eclipse treatment planning system for each of the six degrees of freedom within ± 5.0 mm and ± 2°. Simulations yielded average deviations of 27.4% (up to 72% loss) (P < 0.001) from planned target coverage when treating multiple lung lesions using a single‐isocenter plan. The largest deviations from planned coverage and desired biological effective dose (BED10, with α/β = 10 Gy) were seen for the smallest targets (<10 cc), some of which received < 100 Gy BED10. Patient misalignment resulted in substantial decrease in conformity and increase in the gradient index, violating major characteristics of SBRT. Statistically insignificant differences were seen for normal tissue dose. Although, clinical follow‐up of these patients is ongoing, the authors recommend an alternative treatment planning strategy to minimize the probability of a geometric miss when treating small lung lesions synchronously with single‐isocenter VMAT SBRT plans.

Cleaning the dose falloff in lung SBRT plan

PURPOSE

To investigate a planning technique that can possibly reduce low-to-intermediate dose spillage (measured by R50%, D2cm values) in lung SBRT plans.

MATERIALS AND METHODS

Dose falloff outside the target was studied retrospectively in 102 SBRT VMAT plans of lung tumor. Plans having R50% and/or D2cm higher than recommended tolerances in RTOG protocols 0813 and 0915 were replanned with new optimization constraints using novel shell structures and novel constraints. Violations in the RTOG R50% value can be rectified with a dose constraint to a novel shell structure ("OptiForR50"). The construction of structure OptiForR50% and the novel optimization criteria translate the RTOG goals for R50% into direct inputs for the optimizer. Violations in the D2cm can be rectified using constraints on a 0.5 cm thick shell structure with inner surface 2cm from the PTV surface. Wilcoxon signed-rank test was used to compare differences in dose conformity, volume of hot spots, R50%, D2cm of the target in addition to the OAR doses. A two-sided P-value of 0.05 was used to assess statistical significance.

RESULTS

Among 102 lung SBRT plans with PTV sizes ranging from 5 to 179 cc, 32 plans with violations in R50% or D2cm were reoptimized. The mean reduction in R50% (4.68 vs 3.89) and D2cm (56.49 vs 52.51) was statistically significant both having P < 0.01. Target conformity index, volume of 105% isodose contour outside PTV, normal lung V20, and mean dose to heart and aorta were significantly lowered with P < 0.05.

CONCLUSION

The novel planning methodology using multiple shells including the novel OptiForR50 shell with precisely calculated dimensions and optimizer constraints lead to significantly lower values of R50% and D2cm and lower dose spillage in lung SBRT plans. All plans were successfully brought into the zone of no RTOG violations.

Robust Optimization of SBRT Planning for Patients With Early Stage Non-Small Cell Lung Cancer

Purpose:

Setup uncertainty is a known challenge for stereotactic body radiotherapy planning. Using the internal target volume-based robust optimization was proposed as a more accurate way than the conventional planning target volume-based optimization when considering the robustness criteria. In this study, we aim to investigate the feasibility of internal target volume-based robust optimization in stereotactic body radiotherapy planning using 4-dimensional computed tomography and develop a novel dose–volume histogram band width metric to quantitatively evaluate robustness.

Method and Materials:

A total of 50 patients with early stage non-small cell lung cancer, who underwent stereotactic body radiotherapy, were retrospectively selected. Each of the 50 patients had 2 stereotactic body radiotherapy plans: one with the conventional planning target volume-based optimization and the other with patient-specific robustly optimized internal target volume and with a uniform 5 mm setup error. These were compared with the planning target volume-based optimization method based on both plan quality and robustness. The quality was evaluated using dosimetric parameters and radiobiology parameters, such as high-dose spillage (V_90%RX, conformity index), intermediate-dose spillage (dose falloff products), low-dose spillage (normal tissue: V_50%RX), and lung tissue complication probability. The robustness was evaluated under a uniform 3 to 5 mm setup errors with a novel proposed metric: dose–volume histogram band width.

Results:

When compared with planning target volume-based optimization plans, the internal target volume-based robust optimization plans have better conformity of internal target volume coverage (conformity index: 1.17 vs 1.27, P < .001), intermediate-dose spillage (dose falloff product: 129 vs 167, P < .001), low-dose spillage in normal tissue (V_50%RX: 0.8% vs 1.5%, P < .05), and lower risk of radiation pneumonitis (lung tissue complication probability: 4.2% vs 5.5%, P < .001). For the robustness, dose–volume histogram band width analysis shows that the average values in internal target volume, D_95%, D_98%, and D_99%, of internal target volume-based robust optimization are smaller than that of planning target volume-based optimization (unit cGy) under 3-, 4-, and 5-mm setup uncertainties (3-mm setup uncertainty: 42 vs 73 cGy; 4-mm setup uncertainty: 88 vs 176 cGy; 5-mm setup uncertainty: 229 vs 490 cGy), which might indicate that internal target volume-based robust optimization harbored a greater robustness regardless of the setup errors.

Conclusions:

Internal target volume-based robust optimization may have clinical potential in offering better plan quality in both target and organs at risk and lower risk of radiation pneumonitis. In addition, the proposed internal target volume-based robust optimization may demonstrate robustness regardless of different setup uncertainties in the stereotactic body radiotherapy planning.

Registration:

Retrospective study with local ethics committee approval.

Anti-tumor efficacy of CKD-516 in combination with radiation in xenograft mouse model of lung squamous cell carcinoma

BACKGROUND

Hypoxic tumors are known to be highly resistant to radiotherapy and cause poor prognosis in non-small cell lung cancer (NSCLC) patients. CKD-516, a novel vascular disrupting agent (VDA), mainly affects blood vessels in the central area of the tumor and blocks tubulin polymerization, thereby destroying the aberrant tumor vasculature with a rapid decrease in blood, resulting in rapid tumor cell death. Therefore, we evaluated the anti-tumor efficacy of CKD-516 in combination with irradiation (IR) and examined tumor necrosis, delayed tumor growth, and expression of proteins involved in hypoxia and angiogenesis in this study.

METHODS

A xenograft mouse model of lung squamous cell carcinoma was established, and the tumor was exposed to IR 5 days per week. CKD-516 was administered with two treatment schedules (day 1 or days 1 and 5) 1 h after IR. After treatment, tumor tissues were stained with hematoxylin and eosin, and pimonidazole. HIF-1α, Glut-1, VEGF, CD31, and Ki-67 expression levels were evaluated using immunohistochemical staining.

RESULTS

Short-term treatment with IR alone and CKD-516 + IR (d1) significantly reduced tumor volume (p = 0.006 and p = 0.048, respectively). Treatment with CKD-516 + IR (d1 and d1, 5) resulted in a marked reduction in the number of blood vessels (p < 0.005). More specifically, CKD-516 + IR (d1) caused the most extensive tumor necrosis, which resulted in a significantly large hypoxic area (p = 0.02) and decreased HIF-1α, Glut-1, VEGF, and Ki-67 expression. Long-term administration of CKD-516 + IR reduced tumor volume and delayed tumor growth. This combination also greatly reduced the number of blood vessels (p = 0.0006) and significantly enhanced tumor necrosis (p = 0.004). CKD-516 + IR significantly increased HIF-1α expression (p = 0.0047), but significantly reduced VEGF expression (p = 0.0046).

CONCLUSIONS

Taken together, our data show that when used in combination, CKD-516 and IR can significantly enhance anti-tumor efficacy compared to monotherapy in lung cancer xenograft mice.

Technical Note: Comparison of the internal target volume (ITV) contours and dose calculations on 4DCT, average CBCT, and 4DCBCT imaging for lung stereotactic body radiation therapy (SBRT)

PURPOSE

To investigate the differences between internal target volumes (ITVs) contoured on the simulation 4DCT and daily 4DCBCT images for lung cancer patients treated with stereotactic body radiotherapy (SBRT) and determine the dose delivered on 4D planning technique.

METHODS

For nine patients, 4DCBCTs were acquired before each fraction to assess tumor motion. An ITV was contoured on each phase of the 4DCBCT and a union of the 10 ITVs was used to create a composite ITV. Another ITV was drawn on the average 3DCBCT (avgCBCT) to compare with current clinical practice. The Dice coefficient, Hausdorff distance, and center of mass (COM) were averaged over four fractions to compare the ITVs contoured on the 4DCT, avgCBCT, and 4DCBCT for each patient. Planning was done on the average CT, and using the online registration, plans were calculated on each phase of the 4DCBCT and on the avgCBCT. Plan dose calculations were tested by measuring ion chamber dose in the CIRS lung phantom.

RESULTS

The Dice coefficients were similar for all three comparisons: avgCBCT-to-4DCBCT (0.7 ± 0.1), 4DCT-to-avgCBCT (0.7 ± 0.1), and 4DCT-to-4DCBCT (0.7 ± 0.1); while the mean COM differences were also comparable (2.6 ± 2.2mm, 2.3 ± 1.4mm, and 3.1 ± 1.1mm, respectively). The Hausdorff distances for the comparisons with 4DCBCT (8.2 ± 2.9mm and 8.1 ± 3.2mm) were larger than the comparison without (6.5 ± 2.5mm). The differences in ITV D95% between the treatment plan and avgCBCT calculations were 4.3 ± 3.0% and -0.5 ± 4.6%, between treatment plan and 4DCBCT plans, respectively, while the ITV V100% coverages were 99.0 ± 1.9% and 93.1 ± 8.0% for avgCBCT and 4DCBCT, respectively.

CONCLUSION

There is great potential for 4DCBCT to evaluate the extent of tumor motion before treatment, but image quality challenges the clinician to consistently delineate lung target volumes.

Normal lung tissue complication probability in MR-Linac and conventional radiotherapy

Purpose

To study normal lung tissue (NLT) complications in magnetic resonance (MR) image based linac and conventional radiotherapy (RT) techniques.

Materials and Methods

The Geant4 toolkit was used to simulate a 6 MV photon beam. A homogenous magnetic field of 1.5 Tesla (T) was applied in both perpendicular and parallel directions relative to the radiation beam.Analysis of the NLT complications was assessed according to the normal lung tissue complication probability (NTCP), the mean lung dose (MLD), and percentage of the lung volume receiving doses greater than 20 Gy (V₂₀), using a sample set of CT images generated from a commercially available 4D-XCAT digital phantom.

Results

The results show that the MLD and V₂₀ were lower for MR-linac RT. The largest reduction of MLD and V₂₀ for MR-linac RT configurations were 5 Gy and 29.3%, respectively.

Conclusion

MR-linac RT may result in lower NLT complications when compared to conventional RT.

Low Rates of Chest Wall Toxicity When Individualizing the Planning Target Volume Margin in Patients With Early Stage Lung Cancer Treated With Stereotactic Body Radiation Therapy

PURPOSE

Chest wall (CW) toxicity is a potentially debilitating complication of stereotactic body radiation therapy for non-small cell lung cancer, occurring in 10% to 40% of patients. Smaller tumor-to-CW distance has been identified as a risk factor for CW toxicity. We report our experience with individualizing the planning target volume (PTV) along the CW in an effort to reduce the volume of this organ at risk receiving 30 Gy to 50 Gy.

METHODS AND MATERIALS

We performed an institutional review board-approved retrospective analysis of patients with stage I (T1-2aN0M0) non-small cell lung cancer who received stereotactic body radiation therapy between June 2009 and July 2016. Four-dimensional computed tomography was used for treatment planning. A uniform 5-mm expansion of the internal target volume was generated for the PTV. Areas of overlap with the CW were removed from the PTV. Treatment was delivered with cone beam computed tomography guidance. CW toxicity was assessed per the Common Terminology Criteria for Adverse Events, version 5. Descriptive statistics were used to analyze outcomes.

RESULTS

The median follow-up time was 36.8 months. A total of 260 tumors were treated in 225 patients. 225 tumors in 203 patients were peripheral. The internal target volumes for 143 tumors (63.6%) were located within 5 mm of the CW. The median total dose was 48 Gy (range, 42-60 Gy) in 4 fractions (range, 3-5 fractions). The overall rate of grade 1 to 2 CW toxicity was 2.2%, and 2.8% for tumors located within 5 mm of the CW. There were no grade 3/4 cases and no increase in local recurrences with the use of a truncated PTV with a 3-year local control of 92.1% (95% confidence interval, 87.4%-96.8%).

CONCLUSIONS

Truncation of the PTV margin along the CW resulted in a marked reduction of CW toxicity for tumors in close proximity to the CW, with only a 2.8% rate of grade 1 to 2 CW toxicity. Despite PTV reduction, there was no appreciable increase in local failures. A multi-institutional validation of this technique is needed before general incorporation into clinical practice.

Higher Dose Volumes May Be Better for Evaluating Radiation Pneumonitis in Lung Proton Therapy Patients Compared With Traditional Photon-Based Dose Constraints

Purpose

The dosimetric parameters used clinically to reduce the likelihood of radiation pneumonitis (RP) for lung cancer radiation therapy have traditionally been V20Gy ≤ 30% to 35% and mean lung dose ≤ 20 to 23 Gy; however, these parameters are derived based on studies from photon therapy. The purpose of this study is to evaluate whether such dosimetric predictors for RP are applicable for locally advanced non-small cell lung cancer (LA-NSCLC) patients treated with proton therapy.

Methods and Materials

In the study, 160 (78 photon, 82 proton) patients with LA-NSCLC treated with chemoradiotherapy between 2011 and 2016 were retrospectively identified. Forty (20 photon, 20 proton) patients exhibited grade ≥2 RP after therapy. Dose volume histograms for the uninvolved lung were extracted for each patient. The percent lung volumes receiving above various dose levels were obtained in addition to V20Gy and D_mean. These dosimetric parameters and patient characteristics were evaluated with univariate and multivariate logistic regression tests. Receiver operating characteristic curves were generated to obtain the optimal dosimetric constraints through analyzing RP and non-RP sensitivity and specificity values.

Results

The multivariate analysis showed V40Gy and D_mean to be statistically significant for proton and photon patients, respectively. V35Gy to V50Gy were strongly correlated to V40Gy for proton patients. Based on the receiver operating characteristic curves, V35Gy to V50Gy had the highest area under the curve compared with other dose levels for proton patients. A potential dosimetric constraint for RP predictor in proton patients is V40Gy ≤ 23%.

Conclusions

In addition to V20Gy and D_mean, the lung volume receiving higher doses, such as V40Gy, may be used as an additional indicator for RP in LA-NSCLC patients treated with proton therapy.

4D CT analysis of organs at risk (OARs) in stereotactic radiotherapy

Internal organs at risk volumes (IRV) represent the propagation of organs at risk (OARs) in 4DCT. Sixty consecutive patients that underwent 4DCT for thoracic stereotactic radiotherapy were analyzed and IRVs for heart, trachea, esophagus, bronchial tree, great vessels, and spinal cord were calculated. IRVs were then tested for the respect of dose constraints. IRVs were significantly bigger than standard OARs (p-value <0.001 for all the IRVs). IRVs that did not respect the dose constraints were, respectively, 7/60 (11.7%) for Heart IRV, 6/60 (10%) for Esophagus IRV, 11/60 (18.3%) for Trachea IRV, 16/60 (26.6%) for Bronchial Tree and 0/60 (0%) for great vessel and spinal cord IRV. In the subset of central targets, the percentage of plans that can be unacceptable taking into consideration OARs motion reaches 42%. The correlation of IRVs with clinical parameters and toxicity deserves future investigations in prospective trials.

An analytical expression for R50% dependent on PTV surface area and volume: a lung SBRT comparison

In stereotactic body radiation therapy (SBRT), R50% is a common metric for intermediate dose spill and is defined in RTOG 0915 as the ratio of 50% isodose cloud volume (IDC50%) to the planning target volume (PTV). By coupling sound physical principles with the basic definition of intermediate dose spill, we derive an exact analytical expression for R50% for the case of a spherical volume. This expression for R50% depends on three quantities: the surface area of PTV (SA_PTV), the volume of PTV (V_PTV), and the dose gradient Δr. Validity of our analytical expression for R50% was confirmed via direct comparison to peer‐reviewed, multi‐institutional, diverse clinical data. The comparison of our R50% values computed from our analytical expression to the clinical data yielded an average percent difference of 3.8 ± 4.5%.

Five- Versus Ten-Fraction Regimens of Stereotactic Body Radiation Therapy for Primary and Metastatic NSCLC

INTRODUCTION

At our institution, stereotactic body radiotherapy (SBRT) has commonly been prescribed with 50 Gy in 5 fractions and in select cases, 50 Gy in 10 fractions. We sought to evaluate the impact of these 2 fractionation schedules on local control and survival outcomes.

METHODS

We reviewed patients treated with SBRT with 50 Gy/5 fraction or 50 Gy/10 fraction for early-stage non-small cell lung cancer (NSCLC) and metastatic NSCLC. Cumulative incidence of local failure (LF) was estimated using competing risk methodology. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method only for patients with stage I disease.

RESULTS

Of the 353 lesions, 300 (85%) were treated with 50 Gy in 5 fractions and 53 (15%) with 10 fractions. LFs at 3 years were 6.5% and 23.9% and Kaplan-Meier estimate of median time to LF was 17.5 months and 26.2 months, respectively. Multivariable analysis revealed increasing planning target volume (hazard ratio 1.01, P = .04) as an independent predictor of increased LF, but tumor size, ultracentral location, and 10 fractions were not. Among patients with stage I NSCLC (n = 298), overall median PFS was 35.6 months and median OS was 42.4 months. There was no difference in PFS or OS between the 2 treatment regimens for patients with stage I NSCLC. Low rates of grade 3+ toxicity were observed, with 1 patient experiencing grade 3 pneumonitis after a 5-fraction regimen of SBRT.

CONCLUSION

Dose-fractionation schemes with BED₁₀ ≥ 100 Gy provide superior local control and should be offered when meeting commonly accepted constraints. If those regimens appear unsafe, 50 Gy in 10 fractions may provide acceptable compromise between tumor control and safety with relatively durable control, and minimal negative impact on long-term survival.

GOECP/SEOR clinical recommendations for lung cancer radiotherapy during the COVID-19 pandemic

The coronavirus disease 2019 crisis has had a major and highly complex impact on the clinical practice of radiation oncology worldwide. Spain is one of the countries hardest hit by the virus, with devastating consequences. There is an urgent need to share experiences and offer guidance on decision-making with regard to the indications and standards for radiation therapy in the treatment of lung cancer. In the present article, the Oncological Group for the Study of Lung Cancer of the Spanish Society of Radiation Oncology reviews the literature and establishes a series of consensus-based recommendations for the treatment of patients with lung cancer in different clinical scenarios during the present pandemic.

Scatter imaging during lung stereotactic body radiation therapy characterized with phantom studies

By collecting photons scattered out of the therapy beam, scatter imaging creates images of the treated volume. Two phantoms were used to assess the possible application of scatter imaging for markerless tracking of lung tumors during stereotactic body radiation therapy (SBRT) treatment. A scatter-imaging camera was assembled with a CsI flat-panel detector and a 5 mm diameter pinhole collimator. Scatter images were collected during the irradiation of phantoms with megavoltage photons. To assess scatter image quality, spherical phantom lung tumors of 2.1-2.8 cm diameters were placed inside a static, anthropomorphic phantom. To show the efficacy of the technique with a moving target (3 cm diameter), the position of a simulated tumor was tracked in scatter images during sinusoidal motion (15 mm amplitude, 0.25 Hz frequency) in a dynamic lung phantom in open-field, dynamic conformal arc (DCA), and volumetric modulated arc therapy (VMAT) deliveries. Anatomical features are identifiable on static phantom scatter images collected with 10 MU of delivered dose (2.1 cm diameter lung tumor contrast-to-noise ratio of 4.4). The contrast-to-noise ratio increases with tumor size and delivered dose. During dynamic motion, the position of the 3.0 cm diameter lung tumor was identified with a root-mean-square error of 0.8, 1.2, and 2.9 mm for open field (0.3 s frame integration), DCA (0.5 s), and VMAT (0.5 s), respectively. Based on phantom studies, scatter imaging is a potential technique for markerless lung tumor tracking during SBRT without additional imaging dose. Quality scatter images may be collected at low, clinically relevant doses (10 MU). Scatter images are capable of sub-millimeter tracking precision, but modulation decreases accuracy.

Reduced Fractionation in Lung Cancer Patients Treated with Curative-intent Radiotherapy during the COVID-19 Pandemic

Patients treated with curative-intent lung radiotherapy are in the group at highest risk of severe complications and death from COVID-19. There is therefore an urgent need to reduce the risks associated with multiple hospital visits and their anti-cancer treatment. One recommendation is to consider alternative dose-fractionation schedules or radiotherapy techniques. This would also increase radiotherapy service capacity for operable patients with stage I-III lung cancer, who might be unable to have surgery during the pandemic. Here we identify reduced-fractionation for curative-intent radiotherapy regimes in lung cancer, from a literature search carried out between 20/03/2020 and 30/03/2020 as well as published and unpublished audits of hypofractionated regimes from UK centres. Evidence, practical considerations and limitations are discussed for early-stage NSCLC, stage III NSCLC, early-stage and locally advanced SCLC. We recommend discussion of this guidance document with other specialist lung MDT members to disseminate the potential changes to radiotherapy practices that could be made to reduce pressure on other departments such as thoracic surgery. It is also a crucial part of the consent process to ensure that the risks and benefits of undergoing cancer treatment during the COVID-19 pandemic and the uncertainties surrounding toxicity from reduced fractionation have been adequately discussed with patients. Furthermore, centres should document all deviations from standard protocols, and we urge all colleagues, where possible, to join national/international data collection initiatives (such as COVID-RT Lung) aimed at recording the impact of the COVID-19 pandemic on lung cancer treatment and outcomes.

SBRT combined with PD-1/PD-L1 inhibitors in NSCLC treatment: a focus on the mechanisms, advances, and future challenges

Immune checkpoint inhibitors targeting programmed cell death 1 (PD-1), programmed cell death ligand-1 (PD-L1), and others have shown potent clinical efficacy and have revolutionized the treatment protocols of a broad spectrum of tumor types, especially non–small-cell lung cancer (NSCLC). Despite the substantial optimism of treatment with PD-1/PD-L1 inhibitors, there is still a large proportion of patients with advanced NSCLC who are resistant to the inhibitors. Preclinical and clinical trials have demonstrated that radiotherapy can induce a systemic antitumor immune response and have a great potential to sensitize refractory “cold” tumors to immunotherapy. Stereotactic body radiation therapy (SBRT), as a novel radiotherapy modality that delivers higher doses to smaller target lesions, has shown favorable antitumor effects with significantly improved local and distant control as well as better survival benefits in various solid tumors. Notably, research has revealed that SBRT is superior to conventional radiotherapy, possibly because of its more powerful immune activation effects. Thus, PD-1/PD-L1 inhibitors combined with SBRT instead of conventional radiotherapy might be more promising to fight against NSCLC, further achieving more favorable survival outcomes. In this review, we focus on the underlying mechanisms and recent advances of SBRT combined with PD-1/PD-L1 inhibitors with an emphasis on some future challenges and directions that warrant further investigation.

A physically meaningful relationship between R50% and PTV surface area in lung SBRT

Purpose

We propose a novel understanding of two characteristics of the planning target volume (PTV) that affect the intermediate‐dose spill in lung stereotactic body radiation therapy (SBRT) as measured by R50%. This phantom model research investigates two characteristics of the PTV that have a marked effect on the value of R50%: the mean dose deposited within the PTV (D_av) and the surface area of the PTV (SA_PTV).

Methods

Using a phantom model provided by a CT of the IROC Thorax‐Lung Phantom® (IROC Houston QA Center, Houston, TX) and Eclipse® Treatment Planning System (Varian Medical Systems, Palo Alto, CA), we investigate the two characteristics for spherical and cylindrical PTVs. A total of 135 plans with tightly controlled PTV characteristics are employed. A lower bound for R50% (R50%min_∆r) is derived and clearly establishes a relationship between R50% and SA_PTV that has not been fully appreciated previously.

Results

The study of PTV D_av revealed a local minimum for R50% as a function of the PTV D_av at D_av ≈ 110% of Rx dose. As PTV D_av increases above this local minimum, R50% increases; while for PTV D_av less than this local minimum, the R50% value also increases. The study of PTV surface area (SA_PTV) demonstrated that as the SA_PTV increases, the R50% increases if the PTV volume stays the same. The SA_PTV result is predicted by the theoretical investigation that yields the R50% lower bound, R50%min_∆r.

Conclusions

This research has identified two characteristics of the PTV that have a marked influence on R50%: PTV D_av and SA_PTV. These characteristics have not been clearly articulated in the vast body of previous research in SBRT. These results could help explain plans that cannot meet the RTOG criteria for R50%. With further development, these concepts could be extended to provide additional guidance for creating acceptable SBRT plans.

Single-Fraction Stereotactic Body Radiation Therapy: A Paradigm During the Coronavirus Disease 2019 (COVID-19) Pandemic and Beyond?

PURPOSE

Owing to the coronavirus disease 2019 (COVID-19) pandemic, radiation oncology departments have adopted various strategies to deliver radiation therapy safely and efficiently while minimizing the risk of severe acute respiratory syndrome coronavirus-2 transmission among patients and health care providers. One practical strategy is to deliver stereotactic body radiation therapy (SBRT) in a single fraction, which has been well established for treating bone metastases, although it has been infrequently used for other extracranial sites.

METHODS AND MATERIALS

A PubMed search of published articles in English related to single-fraction SBRT was performed. A critical review was performed of the articles that described clinical outcomes of single-fraction SBRT for treatment of primary extracranial cancers and oligometastatic extraspinal disease.

RESULTS

Single-fraction SBRT for peripheral early-stage non-small cell lung cancer is supported by randomized data and is strongly endorsed during the COVID-19 pandemic by the European Society for Radiotherapy and Oncology-American Society for Radiation Oncology practice guidelines. Prospective and retrospective studies supporting a single-fraction regimen are limited, although outcomes are promising for renal cell carcinoma, liver metastases, and adrenal metastases. Data are immature for primary prostate cancer and demonstrate excess late toxicity in primary pancreatic cancer.

CONCLUSIONS

Single-fraction SBRT should be strongly considered for peripheral early-stage non-small cell lung cancer during the COVID-19 pandemic to mitigate the potentially severe consequences of severe acute respiratory syndrome coronavirus-2 transmission. Although single-fraction SBRT is promising for the definitive treatment of other primary or oligometastatic cancers, multi-fraction SBRT should be the preferred regimen owing to the need for additional prospective evaluation to determine long-term efficacy and safety.

Multi-institutional analysis of stereotactic body radiotherapy for sarcoma pulmonary metastases: High rates of local control with favorable toxicity

BACKGROUND/OBJECTIVES

Oligometastatic sarcoma pulmonary metastases (PM's) are traditionally treated with resection and/or chemotherapy. We hypothesize that stereotactic body radiotherapy (SBRT) is an effective, safe alternative to surgery that can achieve excellent local control (LC) with a favorable toxicity profile.

METHODS

Patients treated with SBRT for sarcoma PM's from 2011 to 2016 at Massachusetts General Hospital and the University of Pennsylvania were included. Median dose was 50 Gy. Patients underwent computed tomography (CT) or positron emission tomography/CT Q3 months post-SBRT.

RESULTS

44 patients with 56 separate PM's were treated with SBRT. Median age was 59 (range 19-82). 82% received prior chemotherapy, 66% had prior pulmonary resections (range, 1-5 resections), and 32% received prior thoracic radiotherapy. Median lesion size was 2.0 cm (range, 0.5-8.1 cm). Median follow-up was 16 months and 25 months for patients alive at last follow-up. Overall survival at 12 and 24 months was 74% (95% confidence interval [CI], 67%-81%) and 46% (95% CI, 38%-55%). LC at 12 and 24 months was 96% (95% CI, 93%-98%) and 90% (95% CI, 84%-96%). LC and overall survival did not differ based on age, gender, histology, fractionation, lesion location, or size (P > .05). Three developed Common Terminology Criteria for Adverse Events version 4 grade-2 chest-wall toxicities; one had grade-2 pneumonitis.

CONCLUSIONS

In the first multi-institutional series on SBRT for sarcoma PM's, SBRT has excellent LC and is well-tolerated. SBRT should be considered as an alternative/complement to resection.

Reduced Margin Stereotactic Body Radiation Therapy for Early Stage Non-Small Cell Lung Cancers

Purpose

Our study reports the clinical outcomes of patients treated with 5-mm isotropic margin, fiducial-guided stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer (NSCLC). We also sought to assess the effect of histological subtype on local control.

Methods

We retrospectively reviewed the charts of all patients treated with SBRT for NSCLC between 2007 and 2017 at our institution. All patients who had implanted fiducial markers, planning target volume (PTV) margins of 5 mm or less, early stage disease (T1-T2, N0), and at least one follow-up CT were included in this analysis. Estimates of local control were generated using the Kaplan-Meier method, and differences between survival curves were assessed using the log-rank test.

Results

A total of 152 patients met the inclusion criteria for this analysis, with a median follow-up of 27.9 months. Patients received 54 Gy in three fractions for peripheral tumors and 48-52.5 Gy in four to five fractions for central tumors. NSCLC histology was adenocarcinoma in 69 (45.4%) cases, squamous cell carcinoma in 65 (42.8%) cases, and other or non-subtyped in 18 (11.8%) cases. Across the entire cohort, the two-year estimate of local control was 95.1%. When histology was considered, the two-year estimate of local control among patients with adenocarcinoma was 95.6% as compared with 85.0% for patients with other subtypes (p=0.044).

Conclusions

Fiducial-guided, isotropic 5-mm PTV margin for thoracic SBRT did not compromise local control compared with historical standards. In this series, patients with adenocarcinoma experienced improved local control compared with squamous cell carcinoma.

Clinical Outcomes and Predictors of Lung Toxicity After Multiple Courses of Lung Stereotactic Body Radiotherapy for Early-Stage Non-Small Cell Lung Cancer

BACKGROUND

The clinical outcomes of multicourse lung stereotactic body radiotherapy (SBRT) have yet to be validated in a prospective study, and there are a lack of data on allowable composite dosimetry.

PATIENTS AND METHODS

Forty-four patients underwent multicourse lung SBRT for recurrent or metachronous NSCLC. The median biologically effective dose (BED₁₀) for the first course and subsequent courses were 132 and 100 Gy, respectively. Patient and treatment characteristics were evaluated to determine the correlation with the development of radiation pneumonitis (RP).

RESULTS

The local control rate was 91%. A total of 13.6% developed a grade 2+ RP, and 4.5% developed a grade 3+ RP, including one grade 5. On univariable analysis, multiple composite dosimetric factors (V₅ [proportion of lung structure receiving at least 5 Gy], V₁₀, V₂₀, V₄₀, and mean lung dose) were correlated with the development of RP. When comprised of the first and second course of SBRT, a composite lung V₅ of < 30% and > 50% was associated with a 0 and 75% incidence of grade 2+ RP, respectively. We identified no significant correlation on multivariable analysis but observed a strong trend between composite lung V₅ and the development of grade 2+ RP (hazard ratio, 1.157; P = .058). Evaluation of multiple clinical factors also identified a significant correlation between the timing of repeat lung SBRT and the development of grade 2+ RP after the second course (P = .0028).

CONCLUSION

Subsequent courses of lung SBRT, prescribed to a median BED₁₀ of 100 Gy, can provide a high rate of local control with a 4.5% incidence of grade 3+ toxicity. Composite lung V₅ and the timing of the second course of lung SBRT may be correlated to the development of RP.

Salvage Stereotactic Body Radiation Therapy for Isolated Local Recurrence After Primary Surgical Resection of Non-small-cell Lung Cancer

INTRODUCTION

We sought to evaluate the safety and efficacy of stereotactic body radiation therapy (SBRT) as salvage treatment for local recurrence after prior surgical resection for non-small-cell lung cancer (NSCLC).

MATERIALS AND METHODS

We surveyed our prospective lung SBRT registry for patients who received salvage SBRT (sSBRT) for local recurrence after previous resection of a primary NSCLC. Following sSBRT, local control, distant metastases, overall survival, and treatment-related toxicity were evaluated.

RESULTS

From 2004 to 2017, 48 patients met inclusion criteria. At initial surgery, 44 (83%) patients had stage I to II disease, and surgical approaches were 47.9% wedge resection, 4.2% segmentectomy, 43.8% lobectomy, and 4.2% bilobectomy. The median time to local recurrence after surgery was 26.4 months, and 36 (75%) recurrences were biopsy-proven. Surgical salvage was not possible owing to un-resectability or underlying comorbidities in 45 (93.8%) patients. Most (68.8%) patients received 50 Gy in 5 fractions. The median follow-up after sSBRT was 22.6 months (range, 3.8-108.8 months). Eight (16.7%) patients experienced local or lobar failure, and 9 (19.1%) patients had nodal failure at a median of 12.5 months (range, 2-66.1 months). Nineteen (39.6%) patients failed distantly at a median of 11.4 months. The median overall survival after sSBRT was 29.3 months. A total of 72.9% of patients experienced no toxicity after sSBRT. Three (6.3%) patients developed grade III toxicity (cough, atelectasis, or soft tissue necrosis) following sSBRT.

CONCLUSIONS

Similar to SBRT for primary early stage NSCLC, sSBRT for local relapse following surgical resection of NSCLC offers high rates of local control with limited toxicity. Distant failure remains the primary pattern of failure.

Optimizing lung cancer radiation treatment worldwide in COVID-19 outbreak

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Lung Cancer patients are at high risk for COVID-19 infection.

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All steps should be taken to protect patients and the healthcare workforce.

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Shortened RT overall treatment time is an important consideration during the COVID-19 pandemic.

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Twelve recommendations in the use of RT are proposed by an international panel.

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The proposed recommendations require urgent consideration during this pandemic.

COVID-19 has spread around the planet, sending billions of people into lockdown as health services struggle to cope. Meanwhile in Asia, where the disease began, the spread continues, in China it seems for now to have passed its peak. Italy, Spain, France, UK, and the US have been the countries more affected in terms of deaths. The coronavirus is more dangerous to the elderly and those with certain pre-existing medical conditions which is precisely the profile of lung cancer patients. Essential cancer services should be delivered but all steps should be taken to protect patients and the health workforce from infection with COVID-19. This presents a major challenge to radiotherapy (RT) departments worldwide. An international panel with expertise in the management of lung cancer in high-volume comprehensive centres has come together to share its experience on COVID-19 preparedness to deliver optimal care in such exceptional circumstances. A comprehensive systematic review of the literature through a PubMed search was undertaken. Twelve recommendations including, among others, the consideration of shorter courses, delays, and the omission of RT for lung cancer are proposed by the panel. In summary, we recommend the screening of every single person accessing the treatment room, the consideration of hypofractionation and to delay postoperative RT for non-small cell lung cancer, to avoid twice-daily treatments and delay or deliver prophylactic cranial irradiation during radio(chemo)therapy for limited-stage small cell lung cancer, review image guided RT images for suspicious image findings, and the use of single-fraction RT for the palliative treatment of stage IV lung cancer patients. Given that lung cancer is one of the most common and severe pathologies in radiation oncology departments, the following recommendations require particularly urgent consideration. The decision-making paths strongly depend on locally available resources, and a tailored approach should be used to attend lung cancer patients during this pandemic.