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.

Understanding Prostate Cancer

The prostate is a small organ, typically described as being walnut sized, present only in males. It lies at the base of the urinary bladder; the passage for excreting urine i.e. the urethra, passes through it. The size of the prostate, specifically the part adjacent to the urethra, increases in most men as they grow older. This non cancerous condition is called benign prostatic hypertrophy(BPH). The other reason for increase in size is prostate cancer.

q. What complaints or problems are an indication that the prostate requires to be investigated?

a. Presence of blood in the urine, frequent urination both during the day and/or night and inability to hold urine once the urge to pass has been felt, should prompt a visit to the doctor. Similarly, the inability to pass urine or the development of impotence should lead to medical consultation.  It is important to stress that these symptoms are not a definite indication of prostate cancer, but instead of a problem in the prostate. Besides prostate cancer, benign enlargement of the prostate (BPH) or an inflammation/ infection of the urinary tract may also give rise to the above symptoms.

Symptoms of a more general nature, such as weight loss and low backache are also important.

It is essential to know that prostate cancer arises most often from a part of the gland that is away from the urinary passage, and may hence produce no symptoms at all.

q. What steps are to be taken once symptoms relevant to a prostate problem have been noted?

a. A combination of steps are to be taken in consultation with a doctor. These are the measurement of Prostate Specific Antigen (PSA) in the blood and a Digital Rectal Examination (DRE), with or without an Ultrasound examination of the urinary tract. The ultrasound examines, among other parameters, the size, shape  and abnormalities of the prostate gland, as well as the amount of urine within the urinary bladder, before and after passing urine. DRE is a physical examination of the prostate via the rectum.

In case prostate cancer is suspected in the above investigations, a biopsy of the prostate gland may be planned. When the suspicion is very strong, the doctor may choose to get an MRI examination done even before a biopsy, so as to carry out the assessment before creating artifacts by the biopsy procedure. 

q. What is PSA?

a. PSA is a protein  produced by the  prostate gland. The blood level of this substance increases in the presence of prostate cancer; this fact is used to diagnose prostate cancer as well as to monitor its status. This is true of most but not all prostate cancers. PSA blood levels may also increase, to small degree, in benign enlargement of the prostate (BPH) or prostatic inflammation, as well as after particular activities and medical interventions.

q.How is prostate cancer diagnosed?

a.Once prostate cancer is suspected on the basis of a raised PSA value and an abnormal finding on clinical examination, a needle biopsy is performed via the rectal route, using an ultrasound to guide the needle into the prostate. Multiple cores of tissue are drawn out and examined under the microscope to document the presence of cancer cells. In addition, the grade of the cancer is determined, which is in turn a measure of the aggressiveness of the cancer

q.What happens after diagnosis?

a.The stage of the cancer is determined; broadly speaking the cancer may be confined to the prostate, be locally advanced or may have spread outside the confines of the prostate and its vicinity.

Following this, organ confined and locally advanced cancers are classified into low, intermediate and high risk categories. One of three options of treatment may be chosen, on the basis of multiple factors, the stage and grade of cancer, age, health status and desire of the patient.

Patients who are noted to have prostate cancer that has spread to other organs are treated with hormone therapy; occasionally they may also require chemotherapy.

q.Which are the three treatment options, mentioned above, for local and locally advanced prostate cancer?

a.Surgical removal of the diseased prostate gland, along with seminal vesicles that are attached to it as well removal of lymph glands in the pelvis is curative for early prostate cancer. It is now possible to perform this surgery, called radical prostatectomy, using the assistance of a robot that magnifies the surgical field up to 40 times and also allows the surgeon to reach difficult to access regions in the pelvis, while restricting discomfort and hospital admission time of the patient.

The cancer can also be treated non invasively using radiotherapy, i.e., x-rays.  A combination of sophisticated comuputerised planning and equipment called linear accelerator allow the radiation oncologist to focus radiotherapy on the prostate accurately while avoiding radiation to neighbouring urinary bladder and rectum. The technique used is Image Guided Radiotherapy ( IGRT) wherein the prostate’s position is confirmed prior to daily treatment; RapidArc or Intensity Modulated Radiotherapy ( IMRT) help ensure that radiotherapy dose to adjacent normal organs is minimized. This method of treatment is effective for organ confined as well as locally advanced prostate cancer, in addition to also working for failure after surgery or in post operative situations where the risk of failure is deemed high.  Radiotherapy is administered along with hormone therapy.

RapidArc Radiotherapy Plan for Prostate Cancer

Patients with poor life expectancy because of advanced age or ailments such as a heart disease or diabetes and the presence of low risk prostate cancer, it may be reasonable to follow a treatment plan which primarily aims at keeping the disease under observation, with regular assessment to document its growth.  This is called active surveillance. Treatment is carried out if the disease appears to progress. This option has to be chosen   very carefully as while this approach avoids unnecessary treatment, it also results in a small chance that the cancer may progress into an incurable stage in between two assessments.

q.How is prostate cancer treated by you?

a. My patients with prostate cancer that has remained confined to the prostate or its vicinity are typically treated in 28 sessions. This treatment is delivered over 5 - 6 weeks. In certain situations, such as when  a patient has many urinary complaints, a more protracted course of radiotherapy is advised.
Radiotherapy is administered in a carefully controlled condition, with due attention to positioning of the patients and application of protocols for bladder filling and rectal emptying, under daily image guidance.

In addition, patients receive Androgen Deprivation Therapy, i.e. drugs to prevent formation of the male hormone. This therapy may last for a period ranging from 6 months to 2 years, depending on the nature of the patient's ailment.

Patients are able to carry on their daily routine during radiotherapy. Some patients may experience urgency while passing urine, and occasionally, some may also encounter mild burning sensation while passing urine. Discomfort in passing stools occurs rarely. These symptoms are transient.