Claim 1. 1^'he method of preparation of yttrium phosphate particles comprising:

step 1-· preparing reagents:

step 1.1. weighing out a noil-radioactive (i .e., Y -89) yttrium salt from the group of yttrium chloride, yttrium nitrate, yttrium sulfate, and yttrium bromide and transferring quantitatively to a volumetric flask; adding deionized water; agitating to mix completely; and step 1.2 drawing up the ⁸⁹Y⁺³ solution from the volumetric flask into a syringe and pushing the solution through a filter and collecting the solution in a sterile container: and step 1.3 preparing and filtering 0.15 M NaaHPO* and 0.05M BCI reagents; storing the reagents at room temperature; and step 2-preparing a radioactive ⁹⁰YCb solution:

adding to a source vial containing ⁹⁰YCb a sufficient volume of 0.05 M HCI, to achieve recovery of the desired quantity of radioactive material from the source vial: and step 3. radioactive ( Y +⁸ Y) PO₄ synthesis procedure; step 3.1 adding H₂O to the to a microwave reaction vial with a sterile magnetic stir bar; and placing the reaction vessel on a stir plate; and with continuous stirring step 3.2. adding 0.15 M Na₂HPO₄; and

step 3 3. adding ⁸⁹Y⁺³ solution; and

step 3.4. adding ⁹⁰Y in 0.05 M HC1 from a Source vial: and

step 3.5. recording the final pH and

step 3.6 transferring the vial to a microwave reactor; and

step 3.7 setting the reaction temperature to a temperature in the range of 1 10°C to

160°C and reaction time to between one hour and 20 hours and starting the reactor; and

step 4 final steps:

step 4.1. placing the microwave vial with the particles in a centrifuge, subjecting the particles to centrifugation; and

step 4.2. remove the supernatant liquid and replace with sterile phosphate buffered saline, and repeating steps 4. i and 4.2 two additional times; and

step 4.3. removing excess supernatant liquid from the vial; and

step 4.4 labeling the via! with identity, lot number, and date of manufacture

Claim 2. The method of preparation of yttrium phosphate particles depending from claim 1 and further comprising: step 1.1. 1.0 M ⁸⁹YC1₃: weighing out Don-radioactive (i.e., Y -89) YC1₃6H₂0 and transferring quantitatively to a volumetric flask; adding deionized water to the volumetric flask; agitating to mix completely; and step 1.2 drawing up the 1.0 M ⁸⁹YC1₃ solution into a syringe and pushing the solution through a filter and collecting the solution in a sterile container; and step 3. radioactive (⁹⁰Y +⁸⁹Y)P0₄ synthesis procedure;

step 3.1. adding 1.0 ml ofH2₀ to the to a microwave reaction vial with a sterile magnetic stir bar; and placing the reaction vessel on a stir plate; and with continuous stirring

step 3.2. adding 2.67 mi of 0.15 M Na₂.HPO_4; and

step 3.3. adding 0.32 mi of ⁸⁹YC1₃ solution, and

step 3.4 adding up to 0.05 ml of ⁹⁰Y in 0.05 MHCI front a Source vial: and step 3.5. recording the final pH and

step 3.6. transferring the vial to a microwave reactor; and

step 3 7 setting the reaction temperature to 150°C and reaction time to one hour and starting the reactor, and

step 4 final steps:

step 4.1. adjusting the pH of the product solution with 1.0 N NaOH to pH range of less than l .S to 8; and

step 4.3. removing supernatant leaving 01.0 ml, in the vial for each scheduled tumor treatment. Claim 3. The method of preparation of a volume of yttrium phosphate particles depending from claim 2 and further comprising:

step 1.1. 1.0 M ⁸⁹YC1₃: weighing out non-radioactive (i.e., Y -89) YC1₃-6H₂0, for a single scheduled tumor treatment, to the nearest 0.01 g) 3.03±0.15 g and transferring quantitatively to a 10 mL volumetric flask; adding lOmL deionized water to the 10 mL mark; agitating to mix completely, and step 1.2 drawing up ~ 8-10 mL of 1.0 M ⁸⁹YC1₃ into a syringe and pushing the solution through a filter and collecting the solution in a sterile container; and step 1.3 preparing and filtering 0.15 M NaaHPCL and 0.05 M HC1 reagents; and step 3. Radioactive (^9oY +⁸⁹Y)P0₄ synthesis procedure;

artd

step 4 final steps:

step 4.1. adjusting the pH of die product solution with 1.0 N NaOH to pH range of 7 to 8; and

step 4.3. removing supernatant leaving 1.0 mL in the vial for each scheduled tumor treatment.

Claim 4 A method of preparing a radioactive yttrium phosphate particle suspension comprising: using a hydrothermal process where in a solution of yttrium salts from the group of yttrium chloride, ytrium nitrate, yttrium sulfate, and yttrium bromide is combined with a solution of sodium phosphate having a stoichiometric excess of phosphate and a pH when combined in the range of 1.5 to 7.4 and preferably in the range of 7 to 8;

combining the solutions with continuous stirring and rapidly heating in a closed vessel to the range of 110°C to 160⁰€ and held for I to 20 hours to yield greater than 99.99% conversion of soluble yttrium to insoluble YPCri and to achieve the desired particle size distribution and;

creating the desired particle size distribution of YPO₄ particles suspended in buffered saline at neutral pH suitable for direct injection into human or animal tissue.

Claim 5. The method depending from Claim 4 further comprising; the radioactive particle suspension wherein the particle size is less than 2 um.

Claim 6. The method depending from claim 5 further comprising: the radioactive particle suspension comprised of at least 90 percent of the total particle volume consisting of particles in the range of 0.1 um to 2 urn.

Claim 7. The method depending from claim 6 and further comprising; wherein the starting concentration of soluble yttrium in the combined solution is in the range of 0.5 to 3.0 mole/liter and the stoichiometric excess of phosphate ranges from 10 to 100%. Claim 8. The method depending from claim 6 and further comprising: the starting concentration of soluble yttrium in the combined solution is 0.08 moles/liter and the stoichiometric excess of phosphate is 25%.

Claim 9. The method of claim 4 further comprising: the particle suspension formed by preparing the particle precursor solution of claim 4, mixing and heating to form the YPO₄ particles by controlled precipitation followed by post-processing the particles to achieve a suspension of YPO₄ particles in phosphate buffered saline solution at neutral pH suitable for injection into human or animal tissue.

Claim 10. The method of claim 9 further comprising: the particle suspension wherein the post processing consists of rinsing the particles 3 times with sterile phosphate buffered saline (PBS) solution and removing or adding PBS to achieve the final desired volume.

Claim 11. The method of claim 9 further comprising: the particle suspension wherein the post processing consists of adjusting the pH of the final solution with sodium hydroxide then removing excess solution or adding sterile PBS to achieve the final desired volume.

Claim 12. The method of claim 4 further comprising: the particle suspension of claim 4 wherein the yttrium phosphate particles are radioactive to serve as distributed sources of therapeutic radiation for treating cancerous tumors and other diseases; and making the particles radioactive by adding a small mass of soluble radioactive isotope to the particle precursor solution of claim 4 that becomes homogeneously incorporated into the insoluble yttrium phosphate particle matrix. Claim 13. The method of claim 4 further comprising; the yttrium phosphate particle suspension of claim 4 wherein the particle concentration is in the range of 40 mg/mI to 125 mg/ml to facilitate imaging by x-ray computed tomography after being combined in a ratio of 1 to 4 by volume with biocompatible hydrogel or other suitable liquid carrier solution and injection into human or animal tissue.