Radiosurgery by X-Knife & Cyberknife

A Paradigm Shift in Radiation Treatment Schedule

Radiation Therapy involves the use of ionizing radiation (commonly X rays) for the treatment of malignant and some benign tumors. Since the discovery of X rays in late 19^th century, the technology of radiation delivery, understanding of tumor biology and radiobiology has grown by leaps and bounds.

Traditionally, the standard radiation therapy protocol involves, daily dose of 1.8-2Gy, one fraction a day, five fractions per week and five to seven weeks of treatment depending upon the tumor type, site and stage etc. The reason for this protracted course is to improve tumor kill and more important to give normal tissue time to undergo repair and undo the damage caused by radiation. With the availability of sensitive imaging modalities like PET/CT, MRI (for target and critical structure delineation), high precision techniques like Stereotactic Radiotherapy for treatment delivery, in room CT Scanners and Gating techniques (for accurate reproducibility and verification), Stereotactic Radiotherapy with X-knife & Cyberknife is being increasingly utilized in oncology practice, to reduce the overall treatment time, with equivalent or better tumor control rates and more importantly no normal tissue damage.

In the past decade, Stereotactic radiotherapy delivered in short course is being increasingly utilized to treat tumors with curative intent and to deliver very high ablative doses to tumors to achieve better long term control rates. The short course radiotherapy, not only gives better or equivalent control rates with acceptable late radiation induced toxicities, it’s also convenient from the patient’s perspective, where they can finish the treatment early, hence increasing the compliance and have to spend less on arranging the logistics of treatment and stay near the vicinity of the radiation centre. Another advantage of Hypofractionation (less number of Radiation treatment) is the increased throughput of the treatment machine.

The Novalis Tx Radiotherapy system with inbuilt X-knife technology is a versatile combination of advanced technologies, which can accurately deliver radiation doses anywhere in the body in just few minutes. Apart from brain, radiation can be safely and precisely delivered to the targets in lung, liver, prostate etc, while minimizing dose exposure to the surrounding normal tissue with the help of a unique technology called Exactrac System.

The tumors where the Hypofractionation is now increasingly used and showed a reasonable difference in the control rates and/or toxicities are discussed below –

• Benign Brain tumors: Acoutic Neuroma / Schwanoma / Pituitory adenoma etc.

This is a benign intracranial tumor that arises in the nerve that connects ear to the brain. Acoustic neuroma develops gradually over the years and cause hearing loss or deafness as the initial symptom. Failure to recognize may cause vertigo, altered gait and pressure effects on the brain stem. Surgical removal or radiotherapy is the main treatment modality. The availability of dedicated Radiosurgery systems has made possible to finish the treatment in single day only without any increase in toxicities.

• Asteio Venous Malformation (AVM):

This is an abnormal connection between arteries and veins in the nervous system. AVM may be asymptomatic or may cause headache, seizures or neurological deficits. Surgical removal, embolisation and radiation are the treatment options. Being a benign entity, Radiosurgery, where high dose is given in a single sitting, is a preferred option as it is non-invasive, less complications and a single day treatment.

• Brain Metastases:

The traditional standard treatment for brain metastases is Whole Brain Radiotherapy (WBRT) for five to ten days. In recent times, due to the availability of effective systemic treatment, survival of patients with brain metastases has increased. Post WBRT, the patients suffer from side-effects like alopecia, deterioration in neuro-cognitive functions like memory. In patients with 1-3 lesions in brain, Stereotactic Radiosurgery (SRS) is now increasingly used to deliver high dose of radiation to the lesions only in a single day, thus alleviating the toxicities associated with WBRT.

• Bone Metastases:

Stereotactic Radiosurgery (SRS) is one of the effective ways to deliver palliative radiation to the spinal metastases. It involves delivering the treatment in 1-5 days and rapid pain relief as compared to the standard radiation protocol of 5-10days.

• Lung Cancer:

Short course Radiotherapy like Stereotactic Body Radiotherapy (SBRT) (1 – 5 treatments) delivering short course treatment, is one of the standard options in Stage1, medically inoperable patients. The SBRT has shown better local control rates vis-à-vis standard radiotherapy protocol of 6 weeks. It also has reduced risk of morbidity and mortality as compared to Surgery in stage 1 patients. The treatment is delivered in three to five days.

• Breast Cancer:

In early breast cancer, radiotherapy delivered post Breast Conservation Surgery, improves both locoregional as well as overall survival rates. The standard protocol involves six weeks of radiation, which at times is too inconvenient to the patient and adds to the daily expenses also. In recent times Hypofractionated radiotherapy in node negative, early breast cancer has become an acceptable alternative with equivalent local control rates and cosmesis. In the selected patients, the radiation is completed in three weeks instead of six weeks of standard treatment.

• Prostate Cancer:

Radiotherapy plays an important role in the management of prostate cancer. The standard fractionation involves 7-8 weeks of treatment. In view of the slow dividing nature of prostate cancer cells, and availability of image guidance during radiation delivery, a hypofractionated regimen has been tried and tested, which shows equivalent local control and similar late toxicity profile especially, rectal toxicities. The short course radiotherapy can be safely completed in five weeks instead of 8 weeks in properly selected patients.

Though, the above short term hypofractionation protocols have shown equivalent results in terms of control rates and toxicities, but proper patient selection, availability of expertise and experience is imperative. The indiscriminate use of the above techniques may cause severe radiation induced sequelae and should be avoided at all costs. Stereotactic (Short Course) Radiotherapy, in future has a potential to become the standard protocol in radiation oncology practice in the properly selected patient cohort.

Dr. P. Vijay Anand Reddy
Sr. Consultant Oncologist
DIRECTOR, Apollo Cancer Institute, Hyderabad
Jubilee Hills, Hyderabad