Introduction
Radio-induced malignancies were discovered early in radiology, and radiotherapy was linked as one of the causes of second cancer risk. Radiation oncologists' lack of concern for the carcinogenic risk of their therapy may be linked to low survival rates in the early years. When radiation oncologists were aware of a second cancer, it was attributed to chance, genetics, or lifestyle factors (for example, smoking, drinking) rather than the radiotherapy administered to the patient.
Clinical pioneers found an increase in second malignancies after radiation. The carcinogenic risk of radiation has been thoroughly investigated and must be considered while choosing a treatment and treating patients. This risk must be considered despite its smallness (and often negligibility).
What Are the Factors Related to Radiation Therapy Leading to Second Cancers?
Radiation therapy is a prevalent form of cancer treatment that has been associated with an increased risk of secondary cancer development. The likelihood of acquiring a solid tumor following radiation therapy is contingent upon various conditions, which encompass:
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Age: Individuals who receive radiation treatment during their early years face an elevated risk in comparison to those who undergo radiation treatment during adulthood. The risk diminishes with advancing age during radiation exposure.
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Radiation Dosage: The risk escalates with higher radiation doses.
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Targeted Region: Cancers typically arise in or near the radiated area. Specific regions or organs, such as the breasts and thyroid, are more susceptible to cancer development following radiation exposure.
What Are the Advantages of Reducing Radiation Exposure?
Radiation oncologists and physicists are well-informed about the advantages of reducing radiation exposure to different areas. They use modern techniques to achieve this.
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As a result, the deterministic effects have significantly dropped, which is anticipated to lower the chances of acquiring secondary radio-induced cancers in areas with high radiation exposure. These experts must thoroughly comprehend the magnitude of the dose levels beyond the volume being treated and be well-informed about ways to accommodate them efficiently.
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For a prolonged duration, the profession has disregarded the minimal doses beyond the desired quantities. A novel problem arises in mitigating the deterministic impacts and carcinogenic hazards near the desired volumes while concurrently diminishing the "low doses" situated considerably from the treated volume. This measure is implemented to mitigate the occurrence of radio-induced malignancies in specific regions.
What Are the Primary Guidelines for Mitigating the Likelihood of Radiation-Induced Cancer Following Radiotherapy?
1. Modifying the Irradiation Technique: Modern IMRT (intensity-modulated radiation therapy) treatments involve a trade-off between 3D conformal radiotherapy (CRT) and modifying the irradiation approach. Reducing the amount of tissue receiving a high dose, IMRT permits decreased treatment volume through enhanced conformality. Reduced use of MUs is possible with the more current VMAT (volumetric modulated arc treatment) approach, which lowers the integral dose;
2. Flattening Filter: In terms of lowering the integral dose, FFF (flattening filter free) administration is an advantage for both IMRT and stereotactic procedures since the out-of-field dosage is decreased when the flattening filter is removed from the beamline.
- A further trade-off between high- and low-energy therapies is photon energy, which the radiation oncologist must consider. Some (thankfully minimal) neutron generation is linked to high-energy therapy. Due to the increased number of MUs needed, low-energy photon treatment produces a larger stray photon dose. While the additional stray photon dose at low energy appears to balance out the enhanced neutron contamination at high energy, the exact amount is difficult to measure.
- Proton treatment usually results in a reduced integral dose compared to IMRT due to the significant dose reduction that may be achieved distal to the target. Using scanning proton treatment increases the patient's dosimetric benefit even further. Utilizing this method lowers the integral dosage to the patient by improving dose conformality compared to scattered proton treatment.
- Brachytherapy is most likely the finest radiation therapy available to reduce the chance of developing a second cancer. Compared with IMRT approaches, it reduces the volumes receiving low to intermediate doses, and the theoretical danger of second cancer outside the radiation beams is diminished.
3. Diminishing the Intended Quantities of Radiation: There is a positive correlation between the irradiated volume and the risk of subsequent radio-induced malignancy.
- In clinical practice, one of the most effective ways to lower the dose to non-target structures is to reduce the planned target volume (PTV); in many cases, the CTV has already been lowered.
- The treatment of the affected regions alone has mostly replaced the previous extensive field irradiation, which has already had a good effect on the risk of radio-induced cancers.
- Reducing the PTV margin is a straightforward technique for lowering the irradiated volume. However, doing so is usually linked to higher imaging.
4. Age Adaptation of the Patient: According to earlier studies, children are more likely than adults to develop a second cancer from radio exposure beyond a certain dose.
- Newborns are at high risk, although the risk decreases with age.
- When children must be irradiated, minimize the target volume and integral dosage. For young patients, brachytherapy can minimize dosage.
- Proton therapy is increasingly indicated. The balanced benefits of protons may outweigh the risk of subsequent cancer from particle radiotherapy in pediatric radiotherapy.
5. Adjustment to Particular Organs: The chance of developing a secondary radio-induced cancer varies among different organs. Certain organs, such as the small intestine, exhibit less sensitivity to cancer radio-induction. Conversely, the thyroid and breast are notable examples of organs that display heightened sensitivity to radio carcinogenesis. Age further exacerbates this sensitivity, with youngsters displaying a heightened susceptibility.
6. Effective Imaging Dose Administration: New exact treatment technologies require IGRT (image-guided radiotherapy). Accidental overdoses of eight to ten percent have been observed with unadapted portal imaging devices and ordinary controls. Radiation oncologists should know the IGRT dose and adjust the number of controls for each patient.
Conclusion
Radio-induced cancers, however rare, must be considered when planning radiotherapy. Even though there is no evidence linking new technologies to an increased incidence of second-kind radio-induced cancers compared to conventional methods, efforts should be made to reduce out-of-field doses to improve radiotherapy. This follows The International Commission on Radiological Protection optimization recommendations. Radio-induced secondary cancers are strongly correlated with age. Radiation may cause cancer in children three to six times more than in adults. Therefore, every effort should be made to reduce child risk. Elderly people have almost minimal risk of a second cancer. While secondary cancer is rare, it should be considered when designing treatment programs or prescribing radiation therapy.
