Overview

Breast cancer is the most common type of cancer in women, and it forms in the cells of the breast. It typically begins in the lining of the milk ducts, and over time, it can invade nearby tissues and spread to other parts of the body.¹ Approximately 55,000 people in the UK alone are diagnosed with breast cancer each year.² The most common treatment options for breast cancer include: 

• Surgery 
• Radiotherapy 
• Chemotherapy 
• Hormonal therapy 
• Targeted therapy¹

Proton therapy is an advanced form of radiotherapy that utilises protons - small atomic particles - fired in a controlled beam to target and destroy cancer cells, including breast cancer tissue.³ Exploring alternative treatments like proton therapy is crucial, especially given the fact that approximately 23% of individuals diagnosed with breast cancer do not survive.² By offering more precise targeting of cancer cells while minimising damage to surrounding healthy tissue, proton therapy represents a promising option in the fight against breast cancer.

What is proton therapy?

Proton therapy is an advanced form of radiation therapy that utilises protons, which are positively charged particles, to treat cancer. Unlike conventional radiation therapy, which uses photons (light particles), proton therapy employs protons for greater precision. In this treatment, a machine known as a cyclotron or synchrotron accelerates protons to high speeds, directing them with pinpoint accuracy onto the tumour. This allows proton therapy to deliver targeted radiation while minimising damage to surrounding healthy tissues.³

Why proton therapy for Breast Cancer?  

Advantages compared to X-ray therapy 

The advantages of proton therapy over conventional X-ray therapy include its ability to deliver high doses of radiation directly to the tumour while minimising exposure to surrounding healthy tissues, thereby reducing collateral damage. Because less radiation reaches healthy tissue, proton therapy is associated with fewer side effects. This precision makes it especially beneficial for treating cancers located near critical organs, such as the brain, spinal cord, or heart, as seen in cases of left-sided breast cancer.⁴

X-ray therapy for left-sided breast cancer carries a risk of cardiovascular complications, including arrhythmias, heart failure, pericardial disease, coronary artery disease, and heart valve damage. This risk arises from the proximity of the heart to the treatment area, which can result in unintended radiation exposure to the heart and surrounding tissues. Proton therapy, by contrast, offers a more precise radiation delivery that targets the tumour directly, significantly reducing exposure to the heart and minimising these cardiovascular risks.⁵

Limitations of surgery

While surgery is the most common treatment for breast cancer, as it is an effective method for removing growing tumours, it does have its limitations. In some cases, surgery alone may not eliminate all cancerous cells, leading to the possibility of cancer recurrence. Additionally, the physical and emotional toll of undergoing surgery can be significant, particularly with the removal of a breast, which may result in body image changes, loss of sensation, and emotional distress.⁶ Other risks and complications include:

• Infection 
• Bleeding 
• Lymphedema 
• Poor wound healing 
• Chronic pain⁶

Limitations of other therapies

Each treatment for breast cancer has limitations. Chemotherapy can cause significant side effects like nausea, fatigue, and hair loss, as it affects both cancerous and healthy cells, and some cancers may develop resistance. Hormonal therapy only works for hormone receptor-positive cancers and can cause menopausal symptoms and long-term issues like bone thinning. It also requires long-term use, which some patients find difficult. Targeted therapy is effective only for specific types of cancer, like HER2-positive, and can lead to resistance over time, with side effects like heart damage and high costs being additional concerns.⁷

Ideal candidates for Proton Therapy

Proton therapy is especially beneficial for individuals with tumours near critical organs like the brain, spinal cord, eyes, or heart.⁴ In cases of left-sided breast cancer, where the tumour is located in the left breast, proton therapy is ideal for minimising damage to the heart, which lies nearby. Left-sided breast cancer is more common and often more resistant to chemotherapy than right-sided breast cancer, making precise radiation crucial. Proton therapy’s ability to limit radiation exposure to surrounding healthy tissue helps protect heart function while effectively targeting the tumour.⁸

In addition to its standalone benefits, proton therapy can be used alongside other treatments like surgery. After surgery, proton therapy and radiotherapy can be applied to reduce the risk of cancer recurrence and improve survival rates. This combination approach enhances overall treatment effectiveness while minimising harm to vital organs.⁹

Potential side effects of Proton Therapy 

Proton therapy is generally safer than conventional radiation therapy, but it is not without potential side effects. Patients may still experience adverse reactions, including:  

• Skin reactions: Skin irritation includes redness, dryness and itchiness.
• Fatigue: Fatigue may build up throughout the treatment and last for several weeks post-treatment. 
• Swelling and soreness: Patients sometimes experience swelling or soreness in the treated area 
• Temporary hair loss: This can occur if the site being treated has hairs on the nearby region, such as the scalp  
• Changes in nearby tissues: Even though more precise than X-ray therapy, it still can affect nearby regions, potentially the heart, in some breast cancer patients.⁴

In some rare cases, patients may also experience nausea and vomiting after the procedure.¹⁰

Challenges and Limitations of Proton Therapy

The most significant limitation of proton therapy is its limited availability, making it inaccessible to many patients who might benefit, such as those with left-sided breast cancer. The high cost of establishing and maintaining proton therapy centres contributes to its restricted availability and makes the treatment more expensive than conventional radiation therapy.¹¹

Additionally, proton therapy, like other forms of radiation, has limitations in its application. While it is highly effective for localised tumours and cancers near vital organs, it may not be suitable for cancers that have spread throughout the body or those that progress rapidly.⁴

In some cases, proton therapy may also require more treatment sessions than traditional treatments such as surgery. This can present logistical challenges, particularly for patients who need to travel long distances to access a treatment centre.⁶

The Future of Proton Therapy for Breast Cancer 

The future of proton therapy for breast cancer is promising, with ongoing research and advancements aimed at improving its accessibility and effectiveness. As technology evolves, the cost of proton therapy equipment is expected to decrease, which could make it more widely available. Smaller, more affordable proton therapy units are being developed, potentially reducing the costs of establishing and operating treatment centres, thus broadening patient access.¹²

While proton therapy has shown significant benefits, research focuses on improving its precision to minimise collateral damage to healthy tissues further. Advances in imaging techniques and treatment planning are likely to enhance the accuracy of proton beam delivery, particularly in complex cases like left-sided breast cancer, where the heart is at risk.¹²

In addition to its use alongside surgery to reduce the risk of recurrence, proton therapy is being explored in combination with other treatments, such as chemotherapy. These combination therapies could lead to improved outcomes, especially for patients with more aggressive or metastatic breast cancer. By integrating proton therapy with other cancer treatments, researchers aim to enhance its overall effectiveness and expand its role in comprehensive breast cancer care.¹³

Summary 

Breast cancer, the most common cancer among women, affects around 55,000 people annually in the UK. Treatment options include surgery, radiotherapy, chemotherapy, hormonal therapy, and targeted therapy, each with benefits and limitations. Proton therapy, an advanced form of radiotherapy, offers a more precise approach by using protons to target tumours while minimising damage to surrounding healthy tissues. This is particularly useful for left-sided breast cancer, where conventional X-ray therapy may risk damaging the heart due to its proximity to the tumour.

While proton therapy shows significant promise, it comes with challenges such as high costs, limited availability, and the need for more treatment sessions in some cases. However, its ability to reduce collateral damage makes it especially valuable for patients with tumours near vital organs. Research is ongoing to improve accessibility and effectiveness, including integrating proton therapy with other treatments like surgery and chemotherapy to enhance outcomes for more aggressive breast cancers.

FAQs

What is the success rate of proton therapy for breast cancer?

A recent study indicated that proton therapy significantly improves survival rates in breast cancer patients, with an overall survival rate of approximately 97.2%. However, the findings should be interpreted cautiously, as the study involved a small sample size of just 42 patients. As more extensive studies are conducted, these results may evolve, providing more definitive insights into the effectiveness of proton therapy for breast cancer treatment.¹⁴

How many sessions of Proton Therapy for breast cancer?

Breast cancer patients undergoing proton therapy tend to  receive treatment once a day over five to six weeks. The exact duration depends on the characteristics of the tumor, such as its size, location, and response to therapy. This personalised approach ensures the most effective treatment while minimising damage to surrounding healthy tissues.¹⁵