Whole body gamma knife is innovated by advance technologies of multiple disciplines and is the world first stereo-directional radiation equipment for the treatment of whole body essential organ tumor. During the past years from 1998, eight different equipments have been developed, and some have been put into clinics as well as some still in the trial phrase. Statistics show that there are nearly 80 different whole body gamma knives in clinics to provide treatment for nearly 100,000 patients with different tumors. It has become one of important radiation treatment methods in China.

The development of whole body gamma knife is to improve the curative effect of radiation treatment, reduce radiation harm and own China’s proprietary intellectual property rights. Through the coordination between multiple disciplines and cross-discipline cooperation to promote technical innovation and system integration innovation, researchers can develop unique gamma ray whole body radiation treatment system (gamma knife) in China. Physicians from General Air Hospital used OUR-QGD type gamma knife to treat over 3,000 patients over 6 years, brought out unique dose distribution features and dose segmentation mode, set up clinical application and operation regulations, and achieved high local control rate at the tumor treatment and low side reaction.

Whole body gamma knife focuses -ray on a local area through multi-source dynamic rotation aggregation methods and technology. Its dose distribution features include:

1. Similar to the Bragg peak of proton ray. It has a high aggregation of doses, with maximum dose locating at the focus, possibly forming a plateau, and steep decrease in surrounding area (Fig. 1A).
   
   
2. Similar to radioactive particle implantation, radioactive particle-like high dose focuses formed through multi-source dynamic rotation aggregation, overlap in tumor and form a high dose area, with smaller dose range at surrounding area, and increasingly high dose at the center (Fig. 1B); it can treat tumor the size from 1 to 10 cm.
   
   
   
   
3. Similar to concentric circles with dose increasing at each layer, suitable for hypofractionated high-dose therapy. Take a 50% dose curve with a total dose of 50Gy (5Gy×10) for example, calculate the biological equivalent dose [BED = nd(1+d/a/ß), a/ß = 10]. The dose distribution will be: 75Gy in the PTV area, 100Gy (equivalent to 84Gy for regular radiotherapy) in the CTV-GTV interval, 119~131.3Gy (equivalent to 62Gy for regular radiotherapy) in the GTV area. This distribution fits both the requirement of BED>100Gy and a tolerable dose for normal tissue outside PTV area.
   
   
4. Better dose concentration than three-dimensional conformal radiotherapy technology (3D-CRT). The ϒ-ray overlay high dose points at targeted areas, with a highly concentrated dose distribution and a smaller range of 30%~50% dose curve. The 50% dose curve can be used as prescription dose line. 3D-CRT overlaps ray with an average dose of 70% from multiple fields to form a high dose area in tumor. Due to the limited number of radiation fields, 3D-CRT has a lower degree of concentration than ϒ-ray and a larger range of 30%~50% dose curve. Usually dose curve higher than 90% is used as prescription dose line.
   
   
5. Conformity and heterogeneous dose distribution are two of the distinctions between 3D-CRT and IMRI. As a result, there should be a strict limit on the choice of therapeutic indication of whole-body gamma knife.

a. Indications
The high dose concentration and heterogeneity of dose with target area determine that tumor of parenchymatous organ is the indication of whole-body gamma knife. Its clinical application includes the treatment of lung cancer, metastatic carcinoma of lung, liver cancer, metastatic carcinoma of liver, pancreatic cancer, abdominal lymph node metastasis, relapse after rectal cancer surgery, cholangiocarcinoma, retroperitoneal tumor and tumor of pelvis. In all the cases treated with whole-body gamma knife in our hospital, there are, peripheral lung cancer, metastatic carcinoma of lung, liver cancer, metastatic carcinoma of liver, pancreatic cancer and retroperitoneal tumor, according to orders of proportion.

b. Contraindications
In the following cases, application of whole-body gamma knife should be avoided:

1. Tumor located at or close to lumen organs, e.g. esophagus cancer, peptic cancer, cardiaoesophagus cancer, colon cancer etc (except local relapse after rectal cancer surgery); adhesion between tumor in abdominal cavity and intestine, etc. hypofractionated high-dose therapy usually cause radiation damages including, perforation, narrowing, hemorrhage, etc.
   
   
2. Tumor located in or close to spinal cord.
   
   
3. Huge tumor with extensive metastasis systemic failure.
   
   
4. Tumor with excessive pleural hydrothorax or ascites.

c. Prescription and dosages
Fractioned dose and total dose should be determined according to the size of target areas and the goal of treatment.

1. Eradicative treatment: small target area, tumor<3cm, 40~50Gy (5~10Gy × 4~10) at the 50% dose curve; medium target area, tumor 3~5cm, 48~56Gy (4~8Gy × 6~14) at the 50% dose cure; large target area, tumor 5~10cm, 3~4Gy at 40%~50% does line, and narrow down the filed and add another 10~20Gy after 40Gy. If the tumor is located in a parenchymatous organ but close to a radio-sensitive organ, then fractioned or total doses need to be lowered accordingly.
   
   
2. Palliative treatment: lower the fractioned dose or total dose appropriately on the basis of eradicative treatment in accordance with the overall situation of the patients and the goal of treatment, to reduce symptom and retard the growth of tumor.

Our hospital has more than 3,000 cases of tumor since our adoption of the technique in 2,000, with a complete response rate of primary locus of early stage non-small cell lung cancer 63% using hypofractioned high-dose, short-term therapy, and a overall response rate of 95%. The 1, 2 and 3 years tumor local control rates are all 95%. The Stage I survival rates of 1, 2 and 3 years are respectively, 100%, 91% and 91% for Stage I, 73%, 64% and 64% for Stage II, and 88%, 78% and 78% for Stage I/II; a relatively light response for early terminal stage, only 1 case of Grade III radiation pneumonia, accounting for 2%.

There is also an overall response rate of 88.7% and a 3-year survival rate of 40.6% for local liver cancer that can not be operated; an overall response rate of 88.4% for local pancreatic cancer that can not be operated, and 1, 2 years total survival rates of Stage II~IV are respectively 56.5% and 23.1%, and 76.9% and 46.7% for 1, 2 years total survival rates of Stage II~III. A general GI tract reaction of Grade I~II, Grade III reaction only accounts for 5% and can be completely relieved with symptom-targeting treatment. 1 year local control rate of metastatic carcinoma of both liver and lung is higher than 90%.

China’s unique whole body gamma knife has dose focus advantage and achieved inspiring local control rate and survival rate in treating essential organ tumor such as lung cancer, liver cancer and pancreas cancer. It is a safe and effective stereo-directional radiation treatment method with relatively low radiation reaction and worth to further research and promotion. Compared with other same-type technologies and equipments, the whole body gamma knife is low-cost, easy-to-operate, low treatment fee, easy-to-promote and can better satisfy the actual requirement at China’s current relatively low economic and scientific level. Further improving equipment and software performance can greatly promote the development of radiation equipment industrialization and save foreign exchange for China. The development of coordinative research between clinical centers and standardization of clinical applications has important meaning for the development of radiation oncology.