What is prostate radiation therapy?

Everyone must be familiar with radiotherapy. The full name of radiotherapy is radiation therapy. It is one of the very important means of treating local tumors. Especially for malignant tumors, radiotherapy is essential for patients. This treatment method has a wide range of adaptability, such as radiotherapy for the digestive system, respiratory system and urinary system. If a man has a prostate tumor, he needs to undergo prostate radiotherapy. The specific methods are as follows.

Prostate radiotherapy methods:

Radiotherapy methods include external irradiation and interstitial implantation. Three-dimensional conformal radiation therapy or intensity-modulated conformal radiation therapy can increase the tumor radiation dose and reduce early and late radiation complications.

1. Conventional external irradiation

(1) Treatment position and positioning: prone or supine, fixed position.

(2) Positioning under the simulator.

(3) Pelvic irradiation field: The four-field irradiation method is adopted, which includes the anterior, posterior and lateral fields. The irradiation field includes the prostate and pelvic lymph nodes.

(4) Prostate irradiation field: The four-field irradiation method of anterior, posterior and lateral fields is adopted, and the irradiation includes the prostate, while protecting the surrounding normal tissues such as the bladder and rectum as much as possible.

2. Intensity modulated radiation therapy and conformal radiation therapy

(1) Treatment position and immobilization: prone or supine position.

(2) CT simulation: After the phantom is fixed, a CT scan simulation is performed. The patient's position, radiation field center, skin reference point markings, etc. are determined under the CT simulator.

(3) Intensity-modulated conformal or three-dimensional conformal planning: Outline the target area, GTV, CTV, PTV and normal tissues and organs on CT. Reconstruct the target area and normal organs in three dimensions. The most commonly used irradiation field is 6 to 8 fields of coplanar irradiation. Calculate the isodose curve and dose volume histogram (DVH), use global lead shield or multileaf grating (MLC) for conformal radiotherapy or apply multileaf grating intensity-modulated therapy.

(4) Validation of the IMRT plan: dose intensity validation, dose distribution validation and absolute dose measurement validation.

(5) Calibration and field verification: A CT simulation positioning machine is used to calibrate the field isocenter and various irradiation parameters, and a field electronic imaging system is used under an accelerator to take field verification films.

(6) Plan implementation.

3. Radiation dose The total pelvic radiation dose is usually 45-50Gy/5 weeks, and then the field is narrowed to the prostate to add 20Gy. The total dose of conventional external irradiation is usually 65-70Gy/7-8 weeks. The daily PTV dose is 1.8-2.0Gy, 5 times a week, and the four fields are irradiated every day. During intensity-modulated conformal radiation therapy or conformal radiation therapy, the local radiation dose can exceed 70Gy.

4. Interstitial irradiation is suitable for early prostate cancer with good prognosis. Permanent seed implantation treatment sources include 125 iodine (125I) and 103 palladium (103Pd). Interstitial irradiation sources also include 192 irradiation (192Ir). When performing interstitial irradiation, a three-dimensional treatment plan should be made to ensure uniform distribution of the prostate dose. When performing seed implantation treatment, CT is performed after implantation for quality assessment (seed reconstruction and dose verification). If the dose is insufficient, external irradiation or seed implantation can be used to supplement the dose.