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

Brachial plexopathy following stereotactic body radiation therapy in apical lung malignancies: A dosimetric pooled analysis of individual patient data

BACKGROUND AND OBJECTIVES

The aim of this study is to establish dosimetric constraints for the brachial plexus at risk of developing grade ≥ 2 brachial plexopathy in the context of stereotactic body radiation therapy (SBRT).

PATIENTS AND METHODS

Individual patient data from 349 patients with 356 apical lung malignancies who underwent SBRT were extracted from 5 articles. The anatomical brachial plexus was delineated following the guidelines provided in the atlases developed by Hall, et al. and Kong, et al.. Patient characteristics, pertinent SBRT dosimetric parameters, and brachial plexopathy grades (according to CTCAE 4.0 or 5.0) were obtained. Normal tissue complication probability (NTCP) models were used to estimate the risk of developing grade ≥ 2 brachial plexopathy through maximum likelihood parameter fitting.

RESULTS

The prescription dose/fractionation schedules for SBRT ranged from 27 to 60 Gy in 1 to 8 fractions. During a follow-up period spanning from 6 to 113 months, 22 patients (6.3 %) developed grade ≥2 brachial plexopathy (4.3 % grade 2, 2.0 % grade 3); the median time to symptoms onset after SBRT was 8 months (ranged, 3-54 months). NTCP models estimated a 10 % risk of grade ≥2 brachial plexopathy with an anatomic brachial plexus maximum dose (Dmax) of 20.7 Gy, 34.2 Gy, and 42.7 Gy in one, three, and five fractions, respectively. Similarly, the NTCP model estimates the risks of grade ≥2 brachial plexopathy as 10 % for BED Dmax at 192.3 Gy and EQD2 Dmax at 115.4 Gy with an α/β ratio of 3, respectively. Symptom persisted after treatment in nearly half of patients diagnosed with grade ≥2 brachial plexopathy (11/22, 50 %).

CONCLUSIONS

This study establishes dosimetric constraints ranging from 20.7 to 42.7 Gy across 1-5 fractions, aimed at mitigating the risk of developing grade ≥2 brachial plexopathy following SBRT. These findings provide valuable guidance for future ablative SBRT in apical lung malignancies.

Hypofractionated Stereotactic Radiation Therapy Dosimetric Tolerances for the Inferior Aspect of the Brachial Plexus: A Systematic Review

We sought to systematically review and summarize dosimetric factors associated with radiation-induced brachial plexopathy (RIBP) after stereotactic body radiation therapy (SBRT) or hypofractionated image guided radiation therapy (HIGRT). From published studies identified from searches of PubMed and Embase databases, data quantifying risks of RIBP after 1- to 10-fraction SBRT/HIGRT were extracted and summarized. Published studies have reported <10% risks of RIBP with maximum doses (Dmax) to the inferior aspect of the brachial plexus of 32 Gy in 5 fractions and 25 Gy in 3 fractions. For 10-fraction HIGRT, risks of RIBP appear to be low with Dmax < 40 to 50 Gy. For a given dose value, greater risks are anticipated with point volume-based metrics (ie, D0.03-0.035cc: minimum dose to hottest 0.03-0.035 cc) versus Dmax. With SBRT/HIGRT, there were insufficient published data to predict risks of RIBP relative to brachial plexus dose-volume exposure. Minimizing maximum doses and possibly volume exposure of the brachial plexus can reduce risks of RIBP after SBRT/HIGRT. Further study is needed to better understand the effect of volume exposure on the brachial plexus and whether there are location-specific susceptibilities along or within the brachial plexus structure.

Dosimetric analysis of brachial plexopathy after stereotactic body radiotherapy: Significance of organ delineation

OBJECTIVES

Examine the significance of contouring the brachial plexus (BP) for toxicity estimation and select metrics for predicting radiation-induced brachial plexopathy (RIBP) after stereotactic body radiotherapy.

MATERIALS AND METHODS

Patients with planning target volume (PTV) ≤ 2 cm from the BP were eligible. The BP was contoured primarily according to the RTOG 1106 atlas, while subclavian-axillary veins (SAV) were contoured according to RTOG 0236. Apical PTVs were classified as anterior (PTV-A) or posterior (PTV-B) PTVs. Variables predicting grade 2 or higher RIBP (RIBP2) were selected through least absolute shrinkage and selection operator regression and logistic regression.

RESULTS

Among 137 patients with 140 BPs (median follow-up, 32.1 months), 11 experienced RIBP2. For patients with RIBP2, the maximum physical dose to the BP (BP-Dmax) was 46.5 Gy (median; range, 35.7 to 60.7 Gy). Of these patients, 54.5 % (6/11) satisfied the RTOG limits when using SAV delineation; among them, 83.3 % (5/6) had PTV-B. For patients with PTV-B, the maximum physical dose to SAV (SAV-Dmax) was 11.2 Gy (median) lower than BP-Dmax. Maximum and 0.3 cc biologically effective doses to the BP based on the linear-quadratic-linear model (BP-BEDmax LQL and BP-BED0.3cc LQL, α/β = 3) were selected as predictive variables with thresholds of 118 and 73 Gy, respectively.

CONCLUSION

Contouring SAV may significantly underestimate the RIBP2 risk in dosimetry, especially for patients with PTV-B. BP contouring indicated BP-BED0.3cc LQL and BP-BEDmax LQL as potential predictors of RIBP2.

Radiation-induced inferior brachial plexopathy after stereotactic body radiotherapy: Pooled analyses of risks

INTRODUCTION

Radiation-induced brachial plexopathy (RIBP), resulting in symptomatic motor or sensory deficits of the upper extremity, is a risk after exposure of the brachial plexus to therapeutic doses of radiation. We sought to model dosimetric factors associated with risks of RIBP after stereotactic body radiotherapy (SBRT).

METHODS

From a prior systematic review, 4 studies were identified that included individual patient data amenable to normal tissue complication probability (NTCP) modelling after SBRT for apical lung tumors. Two probit NTCP models were derived: one from 4 studies (including 221 patients with 229 targets and 18 events); and another from 3 studies (including 185 patients with 192 targets and 11 events) that similarly contoured the brachial plexus.

RESULTS

NTCP models suggest ≈10% risks associated with brachial plexus maximum dose (Dmax) of ∼32-34 Gy in 3 fractions and ∼40-43 Gy in 5 fractions. RIBP risks increase with increasing brachial plexus Dmax. Compared to previously published data from conventionally-fractionated or moderately-hypofractionated radiotherapy for breast, lung and head and neck cancers (which tend to utilize radiation fields that circumferentially irradiate the brachial plexus), SBRT (characterized by steep dose gradients outside of the target volume) exhibits a much less steep dose-response with brachial plexus Dmax > 90-100 Gy in 2-Gy equivalents.

CONCLUSIONS

A dose-response for risk of RIBP after SBRT is observed relative to brachial plexus Dmax. Comparisons to data from less conformal radiotherapy suggests potential dose-volume dependences of RIBP risks, though published data were not amenable to NTCP modelling of dose-volume measures associated with RIBP after SBRT.

Stereotactic Body Radiation Therapy for Spinal Metastases: Benefits and Limitations

Progress in biological cancer characterization, targeted systemic therapies and multimodality treatment strategies have shifted the goals of radiotherapy for spinal metastases from short-term palliation to long-term symptom control and prevention of compilations. This article gives an overview of the spine stereotactic body radiotherapy (SBRT) methodology and clinical results of SBRT in cancer patients with painful vertebral metastases, metastatic spinal cord compression, oligometastatic disease and in a reirradiation situation. Outcomes after dose-intensified SBRT are compared with results of conventional radiotherapy and patient selection criteria will be discussed. Though rates of severe toxicity after spinal SBRT are low, strategies to minimize the risk of vertebral compression fracture, radiation induced myelopathy, plexopathy and myositis are summarized, to optimize the use of SBRT in multidisciplinary management of vertebral metastases.

Adverse Events Following Limited Resection versus Stereotactic Body Radiation Therapy for Early Stage Lung Cancer

Rationale: Approximately a quarter of patients with early stage lung cancer are not medically fit for lobectomy. Limited resection and stereotactic body radiation therapy (SBRT) have emerged as alternatives for these patients. Given the equipoise on the effectiveness of the two treatments, treatment-related adverse events (AEs) could have a significant impact on patients' decision-making and treatment outcomes. Objectives: To compare the AE profile between SBRT versus limited resection. Methods: Data were derived from a prospective cohort of patients with stage I-IIA non-small cell lung cancer who were deemed as high-risk for lobectomy recruited from five centers across the United States. Propensity scores and inverse probability weighting were used to compare the rates of 30- and 90-day AEs among patients treated with limited resection versus SBRT. Results: Overall, 65% of 252 patients underwent SBRT. After adjusting for propensity scores, there was no significant difference in developing at least one AE comparing SBRT to limited resection (odds ratio [OR]: 1.00; 95% confidence interval [CI]: 0.65-1.55 and OR: 1.27; 95% CI: 0.84-1.91 at 30 and 90 days, respectively). SBRT was associated with lower risk of infectious AEs than limited resection at 30 days (OR: 0.05; 95% CI: 0.01-0.39) and 90 days posttreatment (OR: 0.41; 95% CI: 0.17-0.98). Additionally, SBRT was associated with persistently elevated risk of fatigue (OR: 2.47; 95% CI: 1.34-4.54 at 30 days and OR: 2.69; 95% CI: 1.52-4.77 at 90 days, respectively), but significantly lower risks of respiratory AEs (OR: 0.36; 95% CI: 0.20-0.65 and OR: 0.51; 95% CI: 0.31-0.86 at 30 and 90 days, respectively). Conclusions: Though equivalent in developing at least one AE, we found that SBRT is associated with less toxicity than limited resection in terms of infectious and respiratory AEs but higher rates of fatigue that persisted up to 3 months posttreatment. This information, combined with data about oncologic effectiveness, can help patients' decision-making regarding these alternative therapies.