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What is better for medulloblastoma – Traditional radiotherapy or proton therapy?

What is better for medulloblastoma - Traditional radiotherapy or proton therapy? Proton therapy for the treatment of medulloblastoma. Cost of proton therapy in the treatment of medulloblastoma.

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Myeloblastoma is one of the most common childhood tumors. Among children under 10 years of age, the incidence rate is about 20% to 30% of all tumors. The peak age of onset is 5 years, and men are slightly more than women. The tumor is located in the posterior cervical fovea, near the cerebellar vermis and the fourth ventricle midline, and advanced tumors spread in the cerebrospinal fluid. Typical clinical manifestations are mainly related to the increased intracranial pressure caused by tumor occupying the posterior cranial fossa and blocking the fourth ventricle or midbrain aqueduct: headache, nausea, vomiting, blurred vision, and balance function caused by tumor compression on the cerebellum Obstacles, such as walking instability, ataxia, etc.

At present, the treatment of medulloblastoma should be based on the clinical stage and risk stage of the child, and comprehensive treatment methods: a reasonable combination of three treatment methods: surgery, radiation therapy and chemotherapy, to improve the cure rate of the tumor and reduce the damage to normal tissues. Growth and development, intellectual effects.
Since most medulloblastomas occur in children and are more sensitive to radiation, radiation therapy is one of the indispensable methods in the treatment of medulloblastomas. Children are in the stage of growth and development, radiation therapy inevitably causes damage to children’s growth, endocrine and intelligence. At present, three-dimensional conformal radiotherapy or intensity-modulated radiotherapy is mainly used to reduce the radiation dose of the brainstem, inner ear, temporal lobe, hypothalamus-pituitary region, and thyroid gland, and the anterior cranial fossa floor sieve plate area is determined to have a sufficient dose. Irradiation. The irradiation site was irradiated with whole brain, whole spinal cord and posterior cranial fossa.
The dose of traditional radiotherapy: whole brain and whole spinal cord according to the risk group, the preventive radiation dose is 1.8Gy / time, the total amount is 30-36Gy, the high-risk group is 36Gy, and the posterior cranial fossa is increased to 55.8Gy. When there is gross metastasis to the brain tissue and / or spinal cord, additional doses are also required. Whole brain whole spinal cord irradiation technology is a radiotherapy technology with a large irradiation range, which requires multiple isocenters and multiple fields, and requires high accuracy in positioning, planning, and positioning. The plan design generally uses 6MV X-rays. Due to the long target area, the design process generally requires three equal centers: the brain and brain centers, the cervical and thoracic centers, and the thoracic and abdominal centers. However, traditional radiotherapy cannot effectively control all cancer cells. The main reason is that the tumor site is too deep, the maximum radiation depth to the tumor is only 3 cm, the tumor cells are highly resistant to traditional radiotherapy, and the tumor is normally sensitive to traditional radiation. The tissue is surrounded and the tumor cannot be effectively controlled.
Protons are charged particles. The larger the ions, the greater their biological impact. Their mass is about 1836 times the mass of the electrons. Their energy transfer is inversely proportional to the square of the proton’s speed of motion. The energy loss is close to the end of the range. Here is The Bragg peak (named after its discoverer, the German Nobel Prize winner William Henry Prague), the dose after the Bragg peak is zero, and the lesion is placed in the peak area during treatment, which can obtain a high therapeutic gain ratio.
First, proton therapy is a type of external radiation using ionizing radiation. During treatment, the particle accelerator irradiates the tumor with a beam of protons. These charged particles cause single-strand breaks in DNA, destroy the DNA of tumor cells, and ultimately cause cancerous cells to die or interfere with their ability to reproduce. The high division rate of cancerous cells and the reduced ability to repair damaged DNA make their DNA particularly vulnerable to attack.
Second, the dosimetric properties of protons:
1) Strong penetration performance: Proton energy can be adjusted according to the location and depth of the lesion, so that the proton beam reaches any depth of the human body;
2) Normal tissue damage is small: the dose in front of the lesion is low, the dose in the rear is zero, and the normal tissue volume is reduced;
3) High dose in the target area: Spread out bragg peak (SOBP) is obtained through the Bragg peak broadening, so that the lesion is located in the SOBP peak area, thereby obtaining a high dose in the target area
4) Low side scattering: Due to the large mass of the protons, there is less scattering in the material, so the irradiation dose of the normal tissues around it is reduced.
Third, the proton energy tunability
In order to treat deep tumors, a proton accelerator must provide a proton beam of higher energy, and for superficial tumors a lower-energy proton beam is used. Proton therapy accelerators typically produce proton beams with energy between 70 and 250 megaelectron volts (MeV). By adjusting the proton energy during treatment, the proton beam can maximize the damage to tumor cells. Tissue closer to the body surface than the tumor receives lower doses of radiation and therefore less damage. The deep tissues of the human body are hardly exposed.
4. High conformity of tumor irradiation

Proton knife therapy

Modern proton-knife radiotherapy combines 3D-CRT and IMRT technology to achieve high tumor radiotherapy conformability. Proton intensity modulated radiotherapy (IMPT) integrates a full set of photon 3D-CRT and IMRT technologies, making proton radiotherapy achieve the highest conformity of tumor irradiation to date, and the dose of normal tissue surrounding the tumor is significantly reduced.

Therefore, compared with conventional radiotherapy, proton knife therapy has better physical and biological characteristics, and has sufficient radiation dose to reach tumors in deeper parts of the body. Heavy ions and protons can reach tissues 30 cm deep under the skin, which significantly improves the ability to control the tumor; compared with traditional radiation methods, the radiation energy reaching the tumor site can be greatly increased (proton knife can be increased by 20%), which significantly reduces the periphery of the tumor. Damage and side effects of normal tissues; reduce the toxicity of normal tissues with simultaneous application of radiotherapy and chemotherapy; significantly shorten the course of treatment by increasing the daily radiation dose; reduce the incidence of second primary tumors.

 

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