SRS for acoustic schwannoma

 What is an acoustic schwannoma ?

A benign tumour arising from Schwann cells enclosing the VIIIth cranial nerve. Schwann cells are not nerve cells themselves, but are responsible for protection and insulation of nerve cells. The VIIIth  nerve is the vestibulocochlear nerve, which is responsible for hearing and balance.

Coronal MRI images of acoustic schwannoma at the left CP angle ( arrow)

Is an acoustic schwannoma also called a vestibular schwannoma?

Yes. This tumour arises from the vestibulocohlear nerve. It is also called an acoustic neurinoma.

What symptoms does a patient suffering from an acoustic schwannoma feel:

·      Decreased hearing.

·      Tinnitus i.e. hearing a sound in the ear.

·      Loss of balance

·      Headache

·      In large tumours:

o   facial paralysis

o   impaired taste

o   symptoms arising from pressure on brain stem or other cranial nerves, such as deviation of tongue, difficulty in swallowing.

Axial images of acoustic schwannoma of left CP angle

Can acoustic schwannoma / vestibular schwannoma be treated with stereotactic radiosurgery (SRS)?

Stereotactic radiosurgery is an effective method of treating vestibular schwannomas, controlling the tumour in more than 90% of patients and hearing in more than 80 % of patients. The tumour does not disappear and in most patients either decreases slowly or remains the same size.

What is stereotactic radiosurgery?

Radiosurgery is the treatment of a lesion in the brain using X or gamma rays in a sharply focused manner, in a single or limited number of sessions, while ensuring strict attention to positioning and immobilization of the head.

How do you treat acoustic schwannomas using radiosurgery?

I treat patients with acoustic schwannoma using a technique called frameless radiosurgery. The treatment is delivered on a Novalis Tx linear accelerator, a very precise radiosurgery delivery platform installed at Indraprastha Apollo Hospital, New Delhi.

The patient’s head is immobilized in a thermoplastic cast, that molds into the shape of the head, and helps to hold it accurately in the same position. A special Brain Lab cast is used for radiosurgery. This is followed by scanning of the patients brain, using a CT scan as well as an MR, with  detailed imaging of the brain and neighbouring structures such as the middle and inner ear. These images are then fused to allow information regarding the anatomy to be extracted in detail. 

An acoustic schwannoma (green), and organs at risk, brainstem (purple), cochlea (sea-green), optic nerves and chiasm and eyes (red), in 3D

The lesion and surrounding normal structures are delineated by me and my team, following which a team of medical physicists creates multiple radiosurgery plans, targeting the lesion in a focused manner. The best plan is then chosen and a quality assurance test performed to assess whether the chosen plan can accurately be delivered on the linear accelerator.

Following this, the patient receives premedication with steroids to counter the effects of some swelling that may happen following radiosurgery, and is then transported to the Novalis Tx suite. The treatment is painless  and lasts about 40  to 60 minutes. The radiotherapy is delivered using  a sophisticated radiation plan comprising non co planar fields and arcs.

Acoustic Schwannoma (left) outlined in red,
in axial and coronal CT images;
SRS dose represented by colourwash,
closely conforms to the edges of the lesion.

Though headache, nausea and dizziness are possible immediate side effects of radiosurgery, they seldom occur.

Attention to detail, during planning and delivery of radiosurgery, is critical 

 What special techniques are used to preserve hearing ?

Hearing is preserved using sophisticated radiosurgery planning that restricts the dose to the cochlea , i.e. the inner ear and a specific component of the cochlea, the modiolus.

What is the usual dose schedule used in treating an acoustic schwannoma?

The most common schedule is a single fraction of radiosurgery, delivering 11-13 Gy to the edge of the lesion (and a higher dose centrally). Larger lesions may however be treated using more protracted schedules, comprising 3, 12 or 28 sessions.

Radiotherapy for Hepatocellular Carcinoma

Patients suffering from Hepatitis B and C  infection and, or, alcohol induced liver cirrhosis,  are more prone to develop hepatocellular carcinoma, i.e. liver cancer. Aflatoxin toxicity,   as well as fatty liver, may also make a person more prone to this aggressive cancer, considered among the top few causes of dying due to cancer.

Treatment of this cancer is linked to the general health status of the patient, the health of his liver, the number and size of the cancerous lesions, as well as the presence of the tumour in major vessels, nodes or other organs of the body.

Resection of a part of the liver, or removal of the entire liver, accompanied by transplanting the liver of a donor, has a high chance of resulting in cure. This treatment is, however, generally reserved for patients who  either have a  moderately sized single tumour, or  small tumours  less than 3 in number,  with good general health, and good functional capacity of the liver.

Patients with more extensive tumours, which are still confined to the liver, may undergo local treatments, with a view to controlling the tumour. This is done with the intent of making the  tumour amenable to  surgery  (downstaging), to buy time while the patient is on a waiting list for a donated liver, or, in some situations, as the sole therapy to prolong the life of a patient.

One of the therapies that is used is Trans Arterial Chemo Embolisation (TACE).  Performed by interventional radiologists, TACE involves  insertion of a catheter in the  blood vessel feeding the tumour, instillation of chemotherapy, locally into the tumours, and then closing off the blood supply to the tumour, thus allowing the drug to act locally.

Radiotherapy is the treatment of cancer using X rays. Various sophisticated techniques, that are an integration of advances in  computer software and in treatment machines called linear accelerators, enable safe radiotherapy. Tumours can be targeted better, notwithstanding their irregular shape, proximity to vital organs or movement with respiration or other bodily functions.

Radiotherapy was earlier considered ineffective for liver cancers; improvement in radiotherapy techniques has resulted in improvement in the therapeutic ratio, i.e. the chance of curing the tumour vis a vis the risk of damaging normal organs. With this improvement, high doses of radiotherapy can be administered, leading to  better chances of controlling tumours. Techniques used for this treatment are Intensity Modulated Radiotherapy ( IMRT) and  Volume Modulated Radiotherapy (VMAT), also called RapidArc. These treatments are delivered under image guidance, i.e. the patient is scanned, prior to each radiotherapy session, on the treatment couch itself, for accuracy. This is called Image Guided Radiotherapy ( IGRT). Since, with these mechanisms, the tumour is targeted accurately and the  bowel and normal liver spared well, very high doses of radiotherapy may be delivered in limited number of sessions; this is called Stereotactic Ablative Radiosurgery (SABR) or Stereotactic Body Radiotherapy  ( SBRT).

Stereotactic Ablative Radiosurgery dose colour wash for a lesion in the liver ( outlined in red).

Radiosurgery may be administered as the sole therapy for patients too unwell for surgery. It may also be used as bridge therapy for patients on a waitlist for liver transplant. This has the twin role of preventing progression during the waiting period as well as identifying patients with aggressive tumours that should not be treated with aggressive surgery, anyway.

Another application is as a treatment for patients with a portal vein tumour thrombus ( PVTT). Patient with any vascular involvement are thought to have a poor prognosis. Adding radiotherapy to the treatment protocol, alone , or along with TACE , is thought to improve the outcome for some patients suffering from HCC with PVTT. 

The treatment of HCC using  SABR/SBRT or the more protracted SHORT typically takes 2 - 3 weeks. In case surgery is planned following radiation, it may be performed anytime from 2 weeks to 6 months later.

In conclusion,  surgery is the ideal treatment for HCC. Non surgical options like TACE and SABR/SHORT help prepare patients for surgery as well as offer a possibility of controlling the disease for sometime, in case surgery is not possible.