Recent Advances in Radiotherapy (Radiation Therapy)

More than half of oncology patients receive radiotherapy . Advances in diagnosis, treatment and supportive care improve cancer outcomes daily. Research continues to reduce treatment side effectsand duration and improve quality of life. Radiotherapy is used to treat benign or malignant tumors and in palliative care, together with systemic treatment and surgery.

Therapeutic radiotherapy is delivered in three ways: external radiotherapy, brachytherapy (internal radiotherapy) and intraoperative radiotherapy (during surgery).

One of the most important stages of radiotherapy is treatment planning before treatment begins.

Targeted radiation therapy

Accurately defining tumor boundaries is one of radiation therapy's most critical steps. Improved boundary definition has markedly reduced the exposure of healthy tissues. Boundary definition and treatment planning generally use imaging with computed tomography (CT) . Magnetic resonance imaging (MRI) and F-fluorodeoxyglucose positron emission tomography (FDG-PET) are among the oncological imaging methods that can be combined with CT or used alone.

Although computed tomography greatly facilitates defining boundaries, difficulties remain. Lung cancer, for example, may cause collapse called atelectasis due to airway obstruction. Distinguishing these areas from tumor on CT is very difficult. FDG-PET, however, shows areas of intense metabolic activity, allowing the tumor to be distinguished easily. It therefore plays an important role in defining lung cancer boundaries and radiation dose. Similarly, PET is widely used to define boundaries and adjust dose in many solid cancers, particularly lymphoma and head and neck cancers .

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Brain tumors, sarcomas and head and neck tumors are better visualized with MRI than CT, which also better defines risks to surrounding organs from treatment. Advances in imaging systems particularly improve external radiotherapy's success.

New Radiotherapy Technologies, Treatment Planning and Delivery

Conventional radiation treatment delivers a fixed amount of radiation to a particular area. The method called conformal therapy uses advanced calculations to adjust dose and deliver 3-dimensional treatment, increasing success. 3-dimensional conformal radiotherapyhas a more advanced form, Intensity-Modulated Radiotherapy (IMRT) , which uses multileaf collimators to deliver less radiation to healthy tissue and more intense radiation to tumor tissue, effectively treating the tumor while maximally protecting healthy tissue. Another method, Volumetric Modulated Arc Therapy (VMAT) , shortens treatment time compared with other methods.

Reference markers identifying tumor and normal tissue on CT images also improve targeting. Although the patient is immobilized during treatment, movements such as breathing and swallowing may shift the mass. Advanced 4-dimensional CT imaging obtains multiphase images and records breathing cycles to guide treatment. The device thus waits during one phase of breathing and irradiates during another.

Stereotactic radiotherapy techniques (Stereotactic Body Radiation Therapy, SBRT) allow the calculated total dose to be delivered in a few sessions, achieving both greater destruction and fewer radiation side effects. With outcomes approaching surgery in early-stage cancers, SBRT has become one of the most popular nonsurgical cancer treatments. It also offers effective results for isolated metastases, such as treatment of spinal cord compression due to spinal metastases. SBRT is thought to act against tumors through 3 mechanisms:

• Direct tumor destruction by radiation at a level almost equivalent to surgery,
• Vasoconstriction reducing blood flow to the tumor, and
• Stimulation of the immune system by substances released from damaged cancer cells

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In brachytherapy (internal radiotherapy) , radioactive seeds are placed in a body cavity or treatment area. The aim is prolonged low-dose radiation with minimal harm to healthy tissue. Brachytherapy is currently used for prostate and gynecological cancers.

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Combined Treatments in Radiotherapy

Radiotherapy is very successful in some cancers, particularly early-stage Hodgkin lymphoma . However, doses are being reduced because of side effects. Combining radiotherapy with systemic therapies (chemotherapy) reduces the irradiated field and dose, minimizing side effects. The side effects of surgery and chemotherapy must also be considered when evaluating the efficacy of combined treatment.

Increasing Radiotherapy's Effectiveness

Tumors in certain locations or some tumor types reduce radiotherapy effectiveness through features such as rapid mitosis (cell division).

To improve effectiveness, the total dose is divided into frequent, short radiation treatments. Diseased tissue is affected more than normal tissue, and its rapid division is inhibited.

Another way to increase effectiveness is concurrent chemotherapy and radiotherapy (chemoradiotherapy). This combination improves tumor control and significantly prolongs survival in some cancers. Unlike surgery, it also offers a chance to preserve organs. In some cases, however, it increases side effects such as dermatitis, diarrhea and hematological effects (low blood counts). Studies have shown concurrent chemotherapy and radiotherapy to be effective in certain head and neck, gynecological, central nervous system and lung cancers; it is now used as the initial treatment option, particularly for locally advanced disease.

Radiotherapy and Immunotherapy

Recently, laboratory studies combining immunotherapy and radiotherapy have shown exciting developments in metastatic cancers. Combining radiotherapy with antibodies specific to cytotoxic T-lymphocyte-associated antigen (CTLA-4) also caused regression in tumors not irradiated. Radiation does not merely damage cells; it also increases cancer cells' release of inflammatory substances and substances attracting the immune system to the tumor site. Irradiation was found to improve the defense system's recognition function.

In conclusion, radiotherapy technologies continue developing through daily innovations. Rapid technological progress aims to increase safely deliverable doses to achieve minimal tissue damage and maximal tumor treatment, while the search for more advanced treatments continues.

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