Single-Fraction Stereotactic Ablative Body Radiotherapy for Primary and Extracranial Oligometastatic Cancers

Stereotactic ablative body radiotherapy (SABR) consists of delivering high doses of ionising radiation, typically across three to eight fractions with high precision and conformity. SABR has become increasingly commonplace throughout the last quarter of a century and is offered for the treatment of various primary and metastatic tumour types. Delivering SABR in a single fraction has arisen as an appealing possibility for several reasons. These include fewer hospital visits, greater patient convenience, improved sustainability and lower costs. However, these factors must be balanced against considerations such as toxicity, side-effects and, most importantly, progression-free and overall survival. In this review we seek to analyse the results of studies looking at the efficacy of single-fraction SABR for lung, prostate, renal and pancreas primary tumours, as well as oligometastases. The tumour type to be most widely treated with single-fraction SABR is lung, but its remit continues to expand. We also look at the biological rationale underpinning SABR and how this can be extended to single-fraction regimens. Finally, we turn our attention towards the future directions of SABR and specifically single-fraction regimens. These include the possibility of combining SABR with immunotherapy and technological advances in the field, which could serve to expand the scope of SABR. We conclude by summarising the current clinical studies of single-fraction SABR.

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.

Long-Term Clinical Results of MR-Guided Stereotactic Body Radiotherapy of Liver Metastases

(1) Background: Magnetic-resonance (MR)-guided stereotactic body radiotherapy (SBRT) allows for ablative, non-invasive treatment of liver metastases. However, long-term clinical outcome data are missing. (2) Methods: Patients received MR-guided SBRT with a MRIdian Linac between January 2019 and October 2021 and were part of an ongoing prospective observational registry. Local hepatic control (LHC), distant hepatic control (DHC), progression free survival (PFS) and overall survival (OS) were estimated with the Kaplan-Meier method. Toxicity was documented according to CTCAE (v.5.0). (3) Results: Forty patients were treated for a total of 54 liver metastases (56% with online plan adaptation). Median prescribed dose was 50 Gy in five fractions equal to a biologically effective dose (BED) (alpha/beta = 10 Gy) of 100 Gy. At 1 and 2 years, LHC was 98% and 75%, DHC was 34% and 15%, PFS was 21% and 5% and OS was 83% and 57%. Two-year LHC was higher in case of BED > 100 Gy (100% vs. 57%; log-rank p = 0.04). Acute grade 1 and 2 toxicity (mostly nausea) occurred in 26% and 7% of the patients, with no grade ≥ 3 event. (4) Conclusions: To our knowledge, this is the largest cohort of MR-guided liver SBRT. Long-term local control was promising and underscores the aim of achieving >100 Gy BED. Nonetheless, distant tumor control remains challenging.

Targeting Stereotactic Body Radiotherapy on Metabolic PET- and Immuno-PET-Positive Vertebral Metastases

(1) Background: Stereotactic body radiotherapy (SBRT) for vertebral metastases (VM) allows the delivery of high radiation doses to tumors while sparing the spinal cord. We report a new approach to clinical target volume (CTV) delineation based on anti-carcinoembryonic antigen (CEA) positron emission tomography (pretargeted immuno-PET; “iPET”) in patients with metastatic breast cancer (BC) or medullary thyroid cancer (MTC). (2) Methods: All patients underwent iPET, spine magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET-CT) using ¹⁸F-deoxyglucose (FDG) for BC or ¹⁸F-dihydroxy-phenylalanine (F-DOPA) for MTC. Vertebrae locations and vertebral segments of lesions were recorded and the impact on CTV delineation was evaluated. (3) Results: Forty-six VM eligible for SBRT following iPET were evaluated in eight patients (five BC, three MTC). Eighty-one vertebral segments were detected using MRI, 26 with FDG or F-DOPA PET/CT, and 70 using iPET. iPET was able to detect more lesions than MRI for vertebral bodies (44 vs. 34). iPET-based delineation modified MRI-based CTV in 70% (32/46) of cases. (4) Conclusion: iPET allows a precise mapping of affected VM segments, and adds complementary information to MRI in the definition of candidate volumes for VM SBRT. iPET may facilitate determining target volumes for treatment with stereotactic body radiotherapy in metastatic vertebral disease.

The multidisciplinary management of oligometastases from colorectal cancer: a narrative review

In the United States of America, almost 150,000 people are estimated to be diagnosed with colorectal cancer in 2020 and up to 35% of those are expected to present with oligometastatic disease. The term 'oligometastasis' was first used in 1995, however surgical literature describing liver resection for colorectal cancer dates back to the 1940s. Five-year survival rates of up to 42% with surgery alone for solitary lesions are reported. Modern trials have demonstrated median overall survival rates of over 80 months for patients with colorectal liver metastases treated with perioperative chemotherapy. Colorectal liver metastases have accordingly been described as 'proof of concept' for the oligometastatic theory.

Stereotactic body radiotherapy as salvage treatment for recurrence of non-small cell lung cancer after prior surgery or radiotherapy

Treatment options for thoracic recurrences of non-small cell lung cancer (NSCLC) are limited. Stereotactic body radiation therapy (SBRT) is an emerging, potentially effective technology to manage recurrent NSCLC, although with limited prospective studies. This work reviews the outcomes of patients undergoing salvage SBRT for pulmonary recurrences after prior resection or prior radiotherapy for NSCLC. Following salvage SBRT, after prior external beam radiation (SBRT or conventionally fractionated), the 2-year overall survival (OS) ranged from 37% to 79% in 11 of the studies (397 patients) reviewed here, while the 2-year local control (LC) ranged from 37% to 90% in 6 studies that reported that outcome. Toxicity risks are acceptable albeit with appreciable risks of severe to potentially fatal toxicity, necessitating the need to weigh risks vs. benefits in the re-irradiation setting. There were fewer studies on the use of SBRT after prior resection. Following salvage SBRT, after prior resection, the 2-year OS ranged from 56% to 68% in 4 studies (131 patients) reviewed here, while the 2-year LC ranged from 83% to 100% in 3 of these studies. SBRT in the salvage setting after prior resection appeared to be well-tolerated, with toxicity risks comparable to historical patients treated with SBRT alone (i.e., SBRT without prior resection, which is not reviewed here). The data are limited due to the retrospective nature of published studies (all but 4 with <40 patients), with various clinical scenarios (i.e., original NSCLC stage, prior treatment, location of target amenable to salvage SBRT) and a range of SBRT dosing and techniques. More studies are needed to better understand the tumor control, survival and toxicity of SBRT for salvage therapy of NSCLC patients, as well as the potentially prognostic factors that could affect these outcomes.

Patient reported outcomes following video assisted thoracoscopic (VATS) resection or stereotactic ablative body radiotherapy (SABR) for treatment of non-small cell lung cancer: protocol for an observational pilot study (LiLAC)

BACKGROUND

Lung cancer is increasingly a disease of the elderly and frail population with a median age of 70 years at diagnosis. Therefore, consideration of the impact of interventions on health-related quality of life (HRQOL) and not only absolute survival is especially important. For non-small cell lung cancer (NSCLC), video-assisted thoracoscopic surgery (VATS) has been gaining popularity over the last few decades, replacing traditional open lobectomies. For high-risk patients who are not deemed suitable for surgery, stereotactic ablative body radiotherapy (SABR) provides a potentially curative alternative. However, little is known about how VATS and SABR affect HRQOL measured using patient reported outcome measures (PROMs). The LiLAC study (Life after Lung Cancer) aims to explore HRQOL following intervention with VATS or SABR using validated PROMs and to pilot the use of an online questionnaire system (QTool) in this setting. We hope the results will aid both patients and clinicians in decision making and improve the management of post-intervention problems.

METHODS

In total, 300 patients (150 VATS and 150 SABR) patients will be recruited over the study period. Patients will be approached prior to intervention and asked to complete baseline HRQOL questionnaires. They will be given access to the QTool online system and then in the 12 months following intervention will be asked to complete questionnaires (paper or online) at 4-time points. Answers will available for patients and clinicians to view throughout the study period. Clinical information (age, gender, co-morbidity, current medications and smoking status along with treatment-specific information) will also be collected. Primary outcome will be to detect changes of PROs (HRQOL and patient satisfaction) after VATS lung resections or SABR in early stage lung cancer patients. Secondary outcomes include correlation of patient's clinical data with HRQOL results to identify predictors of poor outcomes and exploration of patient and clinician views on the usefulness of QOL measurements.

DISCUSSION

(I) This first study will primarily compare multiple patients reported outcomes for 12 months after VATS lobectomy and SABR in early stages NSCLC patients. We will explore the acceptability of an online assessment of the HRQOL in NSCLC patients. (II) The study is also focused on the patients' opinion during the shared decision-making process, which has rarely been investigated in surgical lung cancer patients. (III) This is not a randomised trial. As a consequence, inherent cohort selection bias and unknown or unaccounted confounders correlated with the outcome of interest may influence the results of the comparison between the treatment groups. (IV) LILAC is not looking at a direct comparison, but to depict the trajectory of recovery post-treatments and preservation or improvement of the HRQOL. This study has received ethical approval from NRES Yorkshire and the Humber- Leeds East Research Ethics Committee (REC Ref: 16/YH/0407). Results of this study will be shared with participating hospitals and made available to the academic community through submission for publication in international peer-reviewed journals and presentation at relevant national and international conferences.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02882750.

"Old people suffer the ravages of the years": changes of treatments in elderly patients with early stage non-small cell lung cancer

The increase in life expectancy and the spreading of lung cancer screening led to a further rise of newly detected non-small cell lung cancer (NSCLC) cases. Age, per se, should not be considered a contraindication for treatments in fit patients. Early stage NSCLC is more and more treated with minimally invasive surgery. Stereotactic ablative radiation therapy (SABR) has been developed as an innovative therapy for stage I NSCLC and is now considered a standard treatment option for medically inoperable patients or for patient who refuse operation. Preoperative careful functional evaluations either respiratory or cardiovascular, as well as preoperative staging, are mandatory to pose indication for surgery in elderly. On the other hand, all elderly patients with lung cancer should have some form of assessment of physiologic age. As minimally invasive thoracic surgery has reduced the postoperative morbidity and has led to a decrease in the length of hospital stay, lobectomy remains the treatment of choice for early stage NSCLC in elderly patients. Discussion by experienced multidisciplinary team is the best approach to evaluate the advantages/disadvantages of each treatment modality in elderly patients with early-stage NSCLC.