Radiation Therapy for Metastatic Cancer

Overview 

Imagine a rebel cell in our body, multiplying out of control. That is known as cancer. Imagine some of these rebels breaking free and taking a ride through our bloodstream or lymphatic system, like hidden invaders travelling throughout the body. This is metastatic cancer when cancer spreads from its origin to other parts of the body. It's a tough enemy, but don’t panic! We have a powerful weapon in our arsenal and it’s known as radiation therapy.

What is cancer metastasis?

Cancer occurs when an abnormal cell inside the human body multiplies, often forming a mass called tumour.¹

Cancer that has spread from its origin to a distant part of the body is called metastatic cancer and this process is called metastasis. It is also known as stage IV cancer. This type of cancer mainly occurs when cells break away from the original tumour, travel through the blood or lymphatic system, and form new tumours in other organs. Metastatic cancer is classified by where it originates, no matter where it spreads. For example, breast cancer that starts in the breast and spreads to the lungs is diagnosed as metastatic breast cancer, not lung cancer.

Common sites for metastasis

Metastatic cancer can spread to practically any organ of the body, although the adrenal glands, bones, brain, liver, lungs, lymph nodes, and peritoneum are some of the most common metastases.

Symptoms of metastatic cancer

Metastatic cancer does not necessarily present with specific symptoms, which are primarily determined by the size and location of the tumours. Some common signs of metastatic cancer ² include:

• Shortness of breath; when cancer has spread to the lungs
• Pain and fractures, mostly when cancer has spread to the bone
• Headache, seizures, or dizziness are very common symptoms when cancer has spread to the brain and 
• jaundice or swelling in the belly, when cancer has spread to the liver

Effect on normal cells

While radiation targets cancer cells, it can also harm nearby healthy tissue.³ Doctors minimise this by precisely aiming the beam or efficiency of radiation, but some side effects are unavoidable. This can lead to localized irritation, like skin problems or mouth ulcers, in areas exposed to radiation during treatment. Several reports showed that while many patients survive their first cancer, some also face the possibility of a second, separate tumour later in life. This is because radiation therapy, used to fight cancer, can damage healthy cells' DNA, potentially triggering new cancers. This risk depends on factors like radiation dose and area treated. Leukaemia is a common second cancer, often appearing within 10 years of therapy, whereas any other solid tumours may take 10-20 years to develop.

Role of radiation therapy in metastatic cancer

Radiotherapy may be used in the early stages of cancer or after it has started to spread or metastasise. It can be used either for curative intent which means to try and cure the cancer completely using multiple small doses while making other treatments more effective; for example, it can be combined with chemotherapy or used before surgery (neoadjuvant radiotherapy). On the other hand, palliative radiotherapy aims at symptom relief and the improvement of quality of life. It may be effective in conferring a reasonable quantum of local control as well as possibly prolonging survival in the short term.⁴

Goals of radiation therapy in cancer management 

The major goals of radiation therapy can be broken down into three key steps:

1. Pain Management: Metastatic tumours can cause notable pain by pressing on bones or nerves. Radiation therapy targets these tumour cells, aiming to shrink them and alleviate the pressure they create. This can provide significant pain relief and improve a patient's quality of life.

2. Tumor Control: Radiation disrupts further growth and division of cancer cells. By directing high-energy beams at the metastatic tumours, radiation therapy can slow down their growth or even stop them from growing altogether. This helps to control the spread of cancer and can sometimes lead to tumour shrinkage.

3. Preventing Complications: Metastatic tumours in certain locations can lead to serious complications. For example, bone metastases can weaken bones, increasing the risk of fractures. Radiation therapy can strengthen these bones and prevent fractures from occurring. This proactive approach helps to manage the disease and improve a patient's overall well-being.

Radiation therapy manages symptomatic metastasis, aiming to relieve pain and improve quality of life. It's also used for high-risk lesions, targeting aggressive tumours to prevent further spread. Additionally, radiation can be a powerful partner with other treatments, working alongside surgery or chemotherapy to enhance overall effectiveness.

Treatment planning and delivery of radiotherapy

Treatment planning and delivery in radiotherapy is a complex process that involves a multidisciplinary approach to ensure optimal patient outcomes. The planning process begins with imaging and simulations to accurately visualize the tumour and surrounding tissues, followed by dosimetry (measurement, calculation and assessment of the ionizing radiation dose) and treatment planning to determine the appropriate radiation dose.⁵ Various delivery techniques are employed based on the specific clinical scenario, including conventional radiotherapy, which uses standard radiation beams; stereotactic body radiotherapy (SBRT), which delivers high doses of radiation with precision to small targets; intensity-modulated radiotherapy (IMRT), which modulates the radiation intensity to conform to the tumour shape; and proton therapy, which uses protons for precise dose distribution, minimizing damage to surrounding healthy tissues. Each technique requires careful consideration and coordination among the medical team to achieve the best possible therapeutic outcome.

Side effects and management of radiation therapy

Patients undergoing radiotherapy often experience a range of side effects, both common and long-term. Common adverse effects include fatigue, skin reactions, gastrointestinal issues, bone marrow suppression, and anaemia, all of which can have a negative influence on a patient's quality of life. Long-term side effects, though less frequent, can be much more severe, including secondary cancers and organ damage leading to conditions like fibrosis (tissue scarring) and cardiopulmonary dysfunction.⁶

Effective management strategies are essential to ease these side effects. These strategies include medications to alleviate symptoms, supportive care to help patients cope with side effects, and regular follow-up and monitoring to detect and manaany complications early. Healthcare experts hope that these comprehensive management approaches would improve patient comfort and treatment outcomes.

Recent advances and innovations in radiation therapy 

Radiation therapy has seen significant advances and innovations, particularly in technological and clinical research areas globally. Technological advancements such as Image-Guided Radiation Therapy (IGRT) enhance accuracy by using imaging during treatment, while Adaptive Radiation Therapy (ART) allows for adjustments in treatment plans based on changes in tumour size and position. The combination of immunotherapy (using our immune system to fight cancer) and targeted therapy offers synergistic effects, improving treatment efficacy. Recent advancements include proton beam therapy, which provides accurate dose distribution with nominal damage to surrounding tissues, and FLASH radiotherapy (a technique involving the delivery of ultra-high dose rate radiation in milliseconds to the target.)potentially reducing side effects). In research and clinical trials, ongoing studies continuously evaluate new techniques and protocols, leading to emerging treatments that promise improved outcomes and reduced side effects.⁷ These innovations are paving the way for more effective and personalised radiation therapy options for patients.

Case studies and clinical outcomes

Recent studies have shown that hypo-fractionated ablative liver radiotherapy in patients with metastatic breast cancer (MBCa) is a safe and tolerable treatment with excellent one-year local control (LC) however, further studies are needed to identify which patients might benefit most from this therapy based on their metastatic class.⁸ Another study was able to demonstrate that patients with a single metastatic lesion and smaller brain tumours may benefit the most from an additional boost dose alongside whole-brain radiation therapy (WBRT).⁹ In a UK-based study, another study showed that at the 10-year mark, prostate cancer-specific deaths were minimal regardless of treatment type, showing no significant variation between treatments; surgery and radiotherapy resulted in lower rates of disease progression and metastasis compared to active monitoring.¹⁰

Summary 

Radiation therapy is a critical treatment mode for metastatic cancer, aimed at controlling symptoms, reducing tumour size, and improving the quality of the patient's life. It works by using high-energy radiation to target and destroy cancer cells in specific areas where the cancer has already spread or just started spreading. This therapy can be used alone or in combination with other treatments, such as chemotherapy and immunotherapy. While it may not cure metastatic cancer fully, it can significantly alleviate pain, prevent complications, and enhance survival.