Extrapulmonary Soft-Tissue Fibrosis Resulting From Hypofractionated Stereotactic Body Radiotherapy for Pulmonary Nodular Lesions

Brachial Plexus Tolerance to Single-Session SAbR in a Pig Model

PURPOSE

The single-session dose tolerance of the spinal nerves has been observed to be similar to that of the spinal cord in pigs, counter to the perception that peripheral nerves are more tolerant to radiation. This pilot study aims to obtain a first impression of the single-session dose-response of the brachial plexus using pigs as a model.

METHODS AND MATERIALS

Ten Yucatan minipigs underwent computed tomography and magnetic resonance imaging for treatment planning, followed by single-session stereotactic ablative radiotherapy. A 2.5-cm length of the left-sided brachial plexus cords was irradiated. Pigs were distributed in 3 groups with prescription doses of 16 (n = 3), 19 (n = 4), and 22 Gy (n = 3). Neurologic status was assessed by observation for changes in gait and electrodiagnostic examination. Histopathologic examination was performed with light microscopy of paraffin-embedded sections stained with Luxol fast blue/periodic acid-Schiff and Masson's trichrome.

RESULTS

Seven of the 10 pigs developed motor deficit to the front limb of the irradiated side, with a latency from 5 to 8 weeks after irradiation. Probit analysis of the maximum nerve dose yields an estimated ED₅₀ of 19.3 Gy for neurologic deficit, but the number of animals was insufficient to estimate 95% confidence intervals. No motor deficits were observed at a maximum dose of 17.6 Gy for any pig. Nerve conduction studies showed an absence of sensory response in all responders and absent or low motor response in most of the responders (71%). All symptomatic pigs showed histologic lesions to the left-sided plexus consistent with radiation-induced neuropathy.

CONCLUSIONS

The single-session ED₅₀ for symptomatic plexopathy in Yucatan minipigs after irradiation of a 2.5-cm length of the brachial plexus cords was determined to be 19.3 Gy. The dose-response curve overlaps that of the spinal nerves and the spinal cord in the same animal model. The relationship between the brachial plexus tolerance in pigs and humans is unknown, and caution is warranted when extrapolating for clinical use.

Combined Aortic Resection and Stent Graft Insertion for Local Recurrence of Metastatic Lung Carcinoma Following Stereotactic Radiotherapy: A Case Report

Stereotactic radiotherapy (SRT) is a useful treatment for malignant ling tumors. However, SRT is associated with complications such as high local recurrence rate and radiation-induced lung injury. Herein, we report a case of combined aortic resection for after SRT. An 82-year-old man underwent SRT for the metastatic lung carcinoma of rectal cancer at left lower lobe. Three years later, chest computed tomography showed local recurrence at the site of radiotherapy, with suspected invasion of the descending aorta. Thoracotomy was performed after metastatic lung carcinoma interpolation of a stent graft in the descending aorta. Because the tumor firmly adhered to the aorta, left lower lung lobe and aortic wall resection was performed. Pathological findings revealed fibrous hypertrophy and adhesion between the visceral pleura and aorta. As shown in our case, combined aortic resection and stent graft insertion is an effective minimally invasive and safe treatment for SRT-induced tissue damage.

Paralysis following stereotactic spinal irradiation in pigs suggests a tolerance constraint for single-session irradiation of the spinal nerve

BACKGROUND AND PURPOSE

Paralysis observed during a study of vertebral bone tolerance to single-session irradiation led to further study of the dose-related incidence of motor peripheral neuropathy.

MATERIALS AND METHODS

During a bone tolerance study, cervical spinal nerves of 15 minipigs received bilateral irradiation to levels C5-C8 distributed into three dose groups with mean maximum spinal nerve doses of 16.9 ± 0.3 Gy (n=5), 18.7 ± 0.5 Gy (n=5), and 24.3 ± 0.8 Gy (n=5). Changes developing in the gait of the group of pigs receiving a mean maximum dose of 24.3 Gy after 10-15 weeks led to the irradiation of two additional animals. They received mean maximum dose of 24.9 ± 0.2 Gy (n=2), targeted to the left spinal nerves of C5-C8. The followup period was one year. Histologic sections from spinal cords and available spinal nerves were evaluated. MR imaging was performed on pigs in the 24.9 Gy group.

RESULTS

No pig that received a maximum spinal nerve point dose ≤19.0 Gy experienced a change in gait while all pigs that received ≥24.1 Gy experienced paralysis. Extensive degeneration and fibrosis were observed in irradiated spinal nerves of the 24.9 Gy animals. All spinal cord sections were normal. Irradiated spinal nerve regions showed increased thickness and hypointensity on MR imaging.

CONCLUSION

The single-session tolerance dose of the cervical spinal nerves lies between 19.0 and 24.1 Gy for this model.

The role of stereotactic body radiotherapy in the management of non-small cell lung cancer: an emerging standard for the medically inoperable patient?

The standard of care for early-stage lung cancer is surgical resection. Many patients with this diagnosis have comorbidities that preclude oncologic resection. Randomized data show that limited resection is inadequate for local disease control and may negatively impact on survival. Stereotactic body radiotherapy (SBRT) has emerged as a novel radiation modality with significant applications in the inoperable, early-stage lung cancer population. Retrospective and prospective studies published in the past decade have established the feasibility, safety, and efficacy of SBRT in these patients using a variety of dose regimens and technologies. To date, lung SBRT results demonstrate excellent local control with very little acute toxicity, and suggest improved overall survival compared to historical controls of fractionated radiotherapy. Ongoing prospective trials are exploring dose and fractionation schedules in the inoperable population, and are starting to explore the role of SBRT for the operable patient.

Non-surgical management of stage I lung cancer

Stage I lung cancer has a high cure rate with surgery, although many patients are not surgical candidates due to comorbid conditions. Historically, non-operative treatment has been disappointing. New and promising ablative therapies offer a curative option.