J Korean Med Sci.  2016 Feb;31(Suppl 1):S75-S87. 10.3346/jkms.2016.31.S1.S75.

Evolving Clinical Cancer Radiotherapy: Concerns Regarding Normal Tissue Protection and Quality Assurance

• Choi WH
• Cho J

• KMID: 2363384
• DOI: http://doi.org/10.3346/jkms.2016.31.S1.S75

Abstract

Radiotherapy, which is one of three major cancer treatment methods in modern medicine, has continued to develop for a long period, more than a century. The development of radiotherapy means allowing the administration of higher doses to tumors to improve tumor control rates while minimizing the radiation doses absorbed by surrounding normal tissues through which radiation passes for administration to tumors, thereby reducing or removing the incidence of side effects. Such development of radiotherapy was accomplished by the development of clinical radiation oncology, the development of computers and machine engineering, the introduction of cutting-edge imaging technology, a deepened understanding of biological studies on the effects of radiation on human bodies, and the development of quality assurance (QA) programs in medical physics. The development of radiotherapy over the last two decades has been quite dazzling. Due to continuous improvements in cancer treatment, the average five-year survival rate of cancer patients has been close to 70%. The increases in cancer patients' complete cure rates and survival periods are making patients' quality of life during or after treatment a vitally important issue. Radiotherapy is implemented in approximately 1/3 to 2/3s of all cancer patients; and has improved the quality of life of cancer patients in the present age. Over the last century, as a noninvasive treatment, radiotherapy has unceasingly enhanced complete tumor cure rates and the side effects of radiotherapy have been gradually decreasing, resulting in a tremendous improvement in the quality of life of cancer patients.

Keyword

Radiotherapy; Normal Tissues; 2D-Radiotherapy; 3D-Conformal Radiotherapy; Radiotherapy, Intensity-Modulated; Heavy Ion Radiotherapy; Radiobiology; Quality Assurance, Health Care

MeSH Terms

Humans
Magnetic Resonance Imaging
Neoplasms/*radiotherapy
*Quality Assurance, Health Care
Quality of Life
*Radiation Protection
Tomography, X-Ray Computed

Figure

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  Fig. 1 Principles and conceptual diagrams of 2D radiotherapy, 3D conformal radiotherapy, and intensity modulated radiotherapy. (A) 2D radiotherapy: Radiation is administered only anterior-posteriorly or laterally, precisely based on bone structures so that, when treating concave tumors (T), the distribution of prescribed dose (Dark Yellow) becomes rectangular and high dose radiation is focused on the center of the tumor and adjacent normal tissues (N). (B) 3D conformal radiotherapy: The patient’s body is simulated in the computer and radiation can be delivered at diverse angles so that radiation doses to normal tissues outside the tumor can be reduced but radiation dose to normal tissues in the center of tumors cannot be reduced. (C) Intensity modulated radiotherapy: In the case of intensity modulated radiotherapy, unlike 3D conformal radiotherapy in which single direction irradiation can be delivered with only one beam, radiation beams are divided into numerous beamlets to minutely adjust the intensity of radiation. The beams are delivered in 360 degree rotations or at diverse angles so that even normal tissues in the center of tumors can be irradiated with lower doses of radiation than the prescribed dose.

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  Fig. 2 4D-Radiotherapy concept diagram. (A) Radiotherapy during natural free breathing. In this case, the normal lung tissues in the whole range of the moving Y-axis are irradiated. (B) Gated radiotherapy (window period RT). Radiation beams are alternatingly turned on and off according to the patient’s respiration cycle so that radiation is not administered during the top and bottom parts of the respiration cycle, thereby excluding some normal tissues from irradiation. (C) Gated radiotherapy with active breath control. Although the respiration cycle is followed, radiation is delivered while the patient is holding his/her breath so that relatively small volumes of normal lung tissues are irradiated. (D) Tracking radiotherapy. This is the most ideal therapy, in which the patient breathes comfortably, and an image-guided or respiration sensor-based tracking system follows the patient’s tumors to only deliver radiation to the tumors. In this method, the least volume of surrounding normal lung tissues is irradiated. However, in this case, quite strict quality assurance programs are required because the error tolerance in this irradiation system is very small.

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  Fig. 3 Stereotactic ablative body radiotherapy (SABR) for a single metastatic lung tumor. The right figure shows the beam configuration of SBRT in which radiation is distributed in many diverse directions and the left figure shows the distributions of high-dose radiation confined to the tumor on axial, sagittal, and coronal images.

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  Fig. 4 Particle beams and Bragg’s Peaks. Usually, in the case of X-rays (photons), the doses are built up on the surface of the skin and absorbed doses are the highest at approximately 1-3 cm directly below the skin and attenuated thereafter to become gradually lower. On the other hand, particle radiotherapy using particles such as proton or carbon is characterized by Bragg’s Peaks, in which low absorbed doses are administered until a certain depth from the skin and radiation energy is concentrated at a certain depth. In this case, if the depth is adjusted well, radiation can be efficiently delivered to tumors with lower doses than normal tissues. Protons are advantageous in that radiation energy is almost completely dissipated after the Bragg’s Peak and carbon ions are advantageous in that radiation doses are lower than for protons from the skin until the radiation arrives at tumors. It is claimed that since carbon radiation has approximately three times larger biological effects, carbon ions can enhance treatment efficacy in terms of tumor control.

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  Fig. 5 Evolving clinical cancer radiotherapy over a century. Radiation has played important roles in cancer treatment over a long time, more than 100 years. Following the development of computers and machine engineering, an age of 3D treatment has come about only in the middle of the 1990s, when 3D conformal radiotherapy began to be diffused widely, and at the beginning of the New Millennium age, cutting edge treatment methods such as IMRT, SBRT, and particle therapy were commercialized and have widely diffused, so that the second act of the history of radiation cancer treatment could commence.

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