CyberKnife for Lung Cancer

Early Stage Disease

For early stage (I, II), operable cancers in healthy patients, surgical removal is normally accepted as the treatment of choice, with reported cure rates as high as 70% or more (1, 2). If a patient has an early stage cancer, but their ability to withstand surgery is in question because of coexisting medical problems (a condition generally referred to as “medically inoperable”), they may be offered radiation therapy instead of surgery. Extended disease-free survival is also observed with radiation therapy, though the reported rates tend to be lower compared with surgical results (3 -5).

Limitations with Conventional Radiation Therapy Approaches

Although considerable technical progress in radiation Therapy has occurred in the past decade, including Three-Dimensional Conformal radiotherapy (3DCRT) and Intensity Modulated Radiation Therapy (IMRT), there are a number of reasons why even sophisticated  Radiation Therapy may still produce a suboptimal result for bronchogenic carcinoma. Briefly, these include:

Increased Dose of Radiation

It is difficult to deliver a large enough radiation dose to a lung cancer to completely exterminate it, even using contemporary sophisticated treatment techniques, without also risking serious injury to a critical adjacent structure such as normal lung, bronchus, heart, spinal cord or esophagus. If there were a method of safely intensifying the radiation dose without increasing the risk of injury to adjacent tissues, the treatment would become more effective (8).

Breathing motion of tumor

Lung cancers actually move along a sometimes variable and unpredictable path during the respiratory cycle, sometimes moving several centimeters or more (9). To compensate for this breathing motion using conventional radiotherapy, a larger volume of normal tissue around the cancer needs to be treated with full dose radiation, which limits the total dose of radiation that may be safely given.

Limited number of targeting angles

Depending upon the exact location of a lung cancer, it may be difficult to deliver the necessary high dose of radiation to that cancer using “conventional” radiation techniques, without also delivering a substantial dose to the normal tissue traversed by any given radiation beam path, sometimes even affecting normal tissue that resides far away from the target lesion.

The CyberKnife Radiosurgery Solution for Early Stage Lung Cancer

Surgery remains the “gold standard” for operable early stage lung carcinoma in healthy patients. For early stage patients that may not be healthy enough to withstand the operation though, the CyberKnife® device is uniquely designed to deliver an ablative radiation dose to a moving cancer target in the chest, while preserving the maximum possible adjacent tissue, making it an ideal device to treat these patients.

Stereotactic radiosurgery, sometimes also referred to as stereotactic radiotherapy, is a new technique that shows great promise in the treatment of early stage lung cancer, in patients who may not be healthy enough to withstand the customary curative surgical procedure (10 - 13).

CyberKnife® radiosurgery effectively addresses all of the technical limitations of standard radiotherapy, resulting in a very sophisticated method to deliver a far more biologically potent dose of radiation to an early stage lung cancer, with surgical precision. Briefly, these include:

Increased Dose of Radiation

Due to its unique tumor tracking capability, the CyberKnife® device has a published accuracy of one millimeter (14), with a much sharper dose fall off at the target volume margin compared with “standard radiation,” effectively rendering the high dose radiation margin more “scalpel-like.” This allows a far smaller normal tissue expansion around the cancer, resulting in much better sparing of critical adjacent tissues from the high dose volume, allowing a substantial radiobiologic dose increase to the cancer (12).

Breathing motion of tumor

The CyberKnife® device is the only radiosurgery or radiotherapy device that tracks and treats a moving cancer throughout the entire breathing cycle (15). This enables an even smaller margin of normal tissue around the cancer to be treated, increasing the safety of treatment.

More Information on Synchrony Respiratory Tracking:

Virtually unlimited number of targeting angles

The CyberKnife® device treats a lung cancer from up to several hundred different directions, all designed on the computer to intersect through the cancer volume, compared with 2-6 directions using “conventional” radiotherapy. Because the CyberKnife® radiation beams come from so many different directions, there is very little radiation dose to normal tissues far away from the cancer target area, again increasing the safety of the treatment, even as its power against the cancer itself is increased, due to the extreme concentration of radiation dose within the target cancer itself.

Metastatic Disease to Lungs

The lungs serve as a common site of secondary spread (known as metastatic disease, or metastases) for a wide variety of primary cancers, including colorectal cancer, upper gastrointestinal cancers, kidney cancer, sarcomas (primary soft tissue or bone cancers) and pediatric cancers. Sometimes lung metastases are the only area of cancer spread, without evidence of relapse elsewhere in the body. When this is the case, if the lung metastases are not too numerous or advanced, some patients will be cured with surgical resection of their metastatic disease (16-19).

As with primary lung cancer, there are patients that might otherwise be candidates for surgery, but prevented by unsatisfactory co-existing health, or surgically inaccessible metastatic cancer location. In these cases, for exactly the same reasons listed for early stage primary lung cancer patients, CyberKnife® radiosurgery may serve as a safe and effective treatment alternative for them (10). If a patient has limited lung metastases and no active disease elsewhere in the body, CyberKnife® radiosurgery may be a very reasonable treatment method, offering them the possibility of extended disease-free survival or cure.

Advanced Lung Cancer

The primary treatment for more advanced lung cancer patients (stage III) usually consists of chemotherapy and radiotherapy (8,9). There is also evidence that surgery added to the treatment regimen may further increase the disease-free survival (20), although this represents a very aggressive treatment approach with an added risk of complications, and is not considered the standard of care for all stage III patients.

At this time, there is no specific evidence that CyberKnife® radiosurgery improves the outcome in stage III patients, primarily because its use in this setting has not been well evaluated.

Relapse of the cancer in its original area(s) of involvement (known as “local failure”) remains a prominent failure pattern in stage III patients though, as traditional radiotherapy and chemotherapy are sometimes insufficient to sterilize all chest disease. As such, one envisions a potential role for CyberKnife® radiosurgery to areas of residual cancer in these patients, potentially providing a benefit comparable to surgical resection in stage III patients (20), ideally under the auspices of a clinical research trial, until its utility in this setting has been proven.

Recurrent Disease

Unfortunately, it is not unusual for lung cancer to relapse following attempted curative treatment. These recurrent cancers often prove inoperable and poorly responsive to additional chemotherapy, with additional “conventional radiation” usually considered dangerous and ineffective.

CyberKnife® radiosurgery offers a new treatment alternative for these patients, who have traditionally had very few remaining options, and may be considered in selected patients for symptom relief, in some cases translating to additional long-term disease-free survival.

Conclusion

CyberKnife® radiosurgery represents a very powerful and precise radiation technique, for patients with primary or recurrent lung cancer, or for those with metastases to the lung from cancers that arise elsewhere in the body. The treatment is safe to administer to patients that are not healthy enough to withstand definitive surgery, and offers a new option to patients with recurrent disease, who may have previously had little if any additional effective treatment option available to them.

Bibliography

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