Perspectives: Image guided Ablation

I listened to a great lecture by Dr David SK Lu on the primers of image guided ablation for tumors and it's so inspirational. Having been a former surgical resident, I know how morbid open surgical resection can be. I think the beauty of image guided ablation are as follows:

Allow non-surgical candidates an option for treatment: many patients are not operable because of disease burden, location or prior resection with local tumor progression. Image guided therapies can potentially help these patients.
Image guided therapies are less morbid. Most procedures are done on an outpatient basis. Therefore, patients usually have better quality of life and shorter hospital stay.
Additional procedures can be done. If patients develop more disease (for example, in the case of liver cancer), image guided therapies can be repeated without added complications. During my surgical residency days, we dreaded operating on patients who had prior surgeries because there was so much adhesion and scars. So, the surgical planes were obscured. This is not an issue with image guided ablations because it is performed subcutaneously. Many patients who have genetic predisposition of multiple cancers (liver cancer in the setting of hepatitis induced cirrhosis, or renal cell carcinoma in the setting of Von Hippel Lindau disease).
Ablations can be adjunct to systematic therapies (chemotherapies). Though the results are preliminary, combination ablation with chemotherapy show better results over chemo therapies alone for metastatic breast, ovarian, neuroendocrine cancers, etc.

Important variables considered for proper patient selection include:

Size: the ability to ablate depends on the size and number of the tumors.
Location: most lesions can be treated. Sub-capsular lesions are more challenging but with appropriate technique, the lesion can be adequately treated.
Access: most procedures are done subcutaneously, at UCLA. Some institutions use open or laproscopic approach as well.
Visibility: the lesion should be available by ultrasound, CT (or less commonly MRI).
Extra maneuvers: hydro-infusion, curved needle, combined with chemo-embolization, concurrent ethanol injection, adjuvant systemic therapies.

Types of ablation therapies:

Radiofrequency ablation: this is the mainstay and the original ablation modality. This was first described by Dr John McGahan at UC Davis in the 1990 and in 2000s, became the main ablation approach. Though there are different probes, RFA is limited to tumors that are smaller in size, usually <3 cm. At UCLA, RFA is the preferred method for treatment for renal and most liver lesions. RFA of renal lesions have shown to have effective intermediate to long term outcomes for renal cell carcinoma. RFA is also an option for cystic renal cell carcinoma.
Microwave ablation: this is the new kid on the block and was described by Dr Fred Lee at University of Wisconsin. It allows treatment of tumors are are larger, > 3 cm. This is becoming the preferred method due to its size coverage and ease of use.
Cryoablation: this uses cold to treat lesions. The border of the ablation can be seen well on image guidance. However, there is an increased risk of bleeding for certain organs such as renal ablations. Some internationalists prefer cryoablation for superficial treatment, like breast lesions or metastatic bone lesions. At UCLA, Dr Scott Genshaft prefers and uses image guided cryoblation for metastatic bone tumors for pain palliation.
Focused Ultrasound Surgery: unlike the other thermoablations, this approach is completely non-invasive. Individual elements of the transducers (up to 2000) are activated and focused on the region of the interest. So, the soundwaves pass through the skin like a normal ultrasound wave. However, at the focal point, the termperature reachs >90 Celcius and burns the tissue. FUS is available for osseous metastasis for pain palliation, symptomatic fibroid treatment and essential tremor. It's under investigation for prostate cancer.