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Exploring the role of proton therapy in sarcoma treatment.

Sarcoma is a rare cancer that develops in connective tissues such as fat, muscles, blood vessels, nerves and bone, and can appear in any part of the body and affects all age groups. Although it is not among the top 10 cancers diagnosed in Singapore, its impact is significant.

While there are no obvious risk factors, according to the American Cancer Society¹, possible causes of sarcoma include inherited DNA mutations and exposure to radiation from previous cancer treatments.

Treatment for sarcoma involves a skilled multidisciplinary team, comprising medical oncologists, oncology surgeons and radiation oncologists. Together, they develop comprehensive treatment plans aimed at maximising patient survival. Typically, sarcomas are surgically removed to achieve complete tumour removal. Adjunct therapies like radiation and chemotherapy may be administered before or after surgery to shrink tumours, prevent recurrence and improve outcomes. Other treatment options include targeted therapy and immunotherapy.

The Impact of Proton Therapy

Since its introduction in Singapore in mid-2023, proton therapy has emerged as a cutting-edge radiation option for some sarcomas.

Traditional radiation therapy uses X-ray beams that pass through a tumour, affecting both the target and surrounding areas. This ‘radiation spill’ can damage healthy tissue. Proton therapy, on the other hand, employs a distinct energy form that enters the body at a low dose and releases all its energy at the tumour site, with no exit dose, hence sparing healthy tissues.

The use of radiation in children and young adults can have additional long-term side effects, such as impact on fertility when targeted at the pelvic area and on growth and mental development when targeted at the brain. Children are also at a higher risk of radiation-induced future cancers. Proton therapy presents a less harmful alternative because it significantly reduces the exposure of normal tissues. Dr Lee Kuo Ann, Senior Consultant in Radiation Oncology at Parkway Cancer Centre, notes that proton therapy is particularly beneficial for sarcomas that affect critical organs or are inoperable, including:

• Ewing’s Sarcoma: Commonly found in children and young adults, Ewing’s Sarcoma may involve bones that are difficult to operate, such as the spine, pelvis or skull. Proton therapy limits the radiation’s impact on the growth and development of surrounding organs.
• Rhabdomyosarcoma: Affects skeletal muscles in children and teenagers; proton therapy helps preserve growth and development.
• Chondrosarcoma & Osteosarcoma: These sarcomas develop in cartilage and bone, respectively. If the sarcomas are located at the base of the skull, proton therapy reduces risks to the brain, cranial nerves, eyes and functions like speech and swallowing.
• Paraspinal Sarcoma: Located near the spine; proton therapy can protect the spinal cord.

Patients with soft tissue sarcomas in the abdomen and pelvis, such as leiomyosarcoma and liposarcoma, may also find proton therapy advantageous as it minimises radiation exposure to vital organs like the kidneys, liver, pancreas and intestines.

Prolonging Lives

Survival rates for sarcoma patients depend on several factors, including tumour size, aggressiveness and whether the cancer has spread. The expertise of the medical team also plays a critical role. Proton therapy — by reducing the side effects associated with conventional radiation — allows for treatments that patients are more likely to tolerate. Moreover, while high doses of conventional radiation can potentially lead to secondary cancers, proton therapy reduces this risk, thereby offering a promising pathway to long-term survival.

The National Association for Proton Therapy² in the United States reports that studies show patients undergoing proton therapy generally achieve better survival rates compared to those receiving other types of radiation therapy. Sarcoma patients should consider this when discussing treatment options with their medical team.

¹American Cancer Society, “Risk Factors for Soft Tissue Sarcoma”, accessed 5 June 2024, https://www.cancer.org/cancer/types/soft-tissue-sarcoma/causes-risks-prevention/risk-factors.html
²National Association for Proton Therapy, “Clinical Research”, accessed 5 June 2024, https://proton-therapy.org/clinical-research/