Percutaneous lung tumor ablation

Percutaneous lung tumor ablation techniques are an alternative to surgery or stereotactic body radiotherapy (SBRT) for the treatment of certain malignancies. They have specific indications and contraindications, but are mostly limited to small oligonodular and favourably located lesions. 

They potentially include both thermal (radiofrequency ablation (RFA), microwave ablation (MWA), and cryoablation) non-thermal ablation methods (irreversible electroporation (IRE)), with RFA being the technique most widely applied. 

Indications

Various societies and local guidelines differ on when and which ablation technique should play as a therapeutic option in tumors affecting the lungs. Common indications include:

• lung cancer

  • NSCLC in stages I to IIIA has surgical resection as the standard of care. SBRT is commonly offered as a second-line treatment when there is a contraindication for surgery (e.g. poor cardiopulmonary reserve) ⁹. As per the European Society of Medical Oncology and American College of Chest Physicians, percutaneous ablation should be played as an alternative when both surgery and SBRT are contraindicated ⁹

  • stage I NSCLC 

    • better outcomes are achieved in lesions inferior to 2 cm, therefore, percutaneous ablation is reserved for T1a and T1b NSCLC ⁹

  • salvage therapy when local recurrence occurs after SBRT

  • associated with treatment with tyrosine kinase inhibitors (TKI) aiming to control the residual tumoral volume, which is likely TKI resistant ³

    • advantage of also offering new histological confirmation of tumor mutation with a biopsy performed at the same time 

• lung metastases

  • oligometastatic disease to lungs: maximum number of lesions to be ablated has not been established, with most centers performing usually up to 3 lesions ⁹

  • lesions <2 cm ⁹

Contraindications

• patients with ECOG >2 ⁹

• tumor located close to large vessels/hilum, usually <1 cm

  • heat sink effect may lead to thermal ablation failure

  • vessel injury  

• uncorrectable bleeding diathesis (abnormal coagulation indices)

• pacemaker 

  • RFA may reset pacemakers or implanted defibrillators

    • cardiology consultation required

  • MWA and cryoablation are safe 

• small cell lung cancer ⁹

Procedure

Preprocedural evaluation

• recent CT chest is required for planning

• margins of treatment must be considered

  • NSCLC: ablation zone must be oversized by about 8-10 mm in all directions ⁴

Equipment

• imaging guidance

  • CT guidance 

  • fluoroscopy guidance - C-arm cone beam 

• ablation equipment 

  • RFA

    • advantages: air-filled space acts thermally and electrically insulating the treated area 

  • MWA

    • advantages: 

      • air-filled space acts thermally insulating the treated area 

      • cf. RFA: higher temperatures inside the lesion leading to larger and faster volumes of necrosis ⁵

  • cryoblation 

    • air limits this technique

      • requires an increase of water content in the treated area

      • short freezing and thawing performed to fill the alveoli with hemorrhage/fluid 

      • triple freeze cycle recommended ⁶

    • advantages: potentially less pain in lesions adjacent to diaphragm and pleura

  • IRE

    • not effective for the treatment of lung malignancies ⁷

Technique

• iatrogenic pneumothorax

  • used to ablate lesions that contact critical thoracic structures such as the pleural surface, mediastinum, or diaphragm

  • injection of gas via a puncture sheath and insertion of small pigtail catheter 

  • awareness of rapid pneumothorax decompression must be regarded

Postprocedural care

• clinical monitoring as per post-sedation or general anesthesia recovery

• chest radiograph recommended 4 hours after the procedure to assess for a pneumothorax 

Outcomes

The treatment response needs to be followed up on imaging as per local guidelines. Besides cryoablation, the involution of the thermal ablation zone takes a long time, getting stable usually after 6 months.

• CT chest monitoring in 3, 6, 9 and 12 months is an option

• expected imaging findings

  • stability or decrease in size

  • no enhancement 

• signs of residual/recurrent tumor

  • enlargement

  • growing margins of the ablation zone with irregularities or nodularity

  • enhancement 

For equivocal cases of recurrence, and if after 6 months since the treatment, PET-CT is recommended.