Dose distribution assessment in human eye proton therapy by Monte Carlo method

1. Dose distribution assessment in human eye proton therapy by Monte Carlo method M. Tavakol1, A. Karimian 2* , S.M. Mostajab Aldaavati1 1 Department of Physics, Faculty of Science, University of Isfahan, Isfahan, Iran. 2* Department of Biomedical Engineering, Faculty of Engineering, University of Isfahan, Isfahan, Iran Karimian@eng.ui.ac.ir

2. Eye and its anatomic structure www.amazingeye.com

3. Eye Tumors • Tumors in the eye usually are secondary tumors caused by cancers that have spread from other parts of the body, especially the breast, lung, bowel or prostate. • Two types of primary tumors arise within the eye itself and are known as retinoblastoma in children and melanoma in adults http://www.hopkinsmedicine.org/wilmer/conditions/tumors.html

4. Retinoblastoma • Retinoblastoma is a cancer of the retina. This most common childhood eye cancer usually strikes children under age five, affecting 500 to 600 in the United States each year. In nearly a third of the cases, retinoblastoma occurs in both eyes. http://www.hopkinsmedicine.org/wilmer/conditions/tumors.html

5. melanoma • Malignant melanoma occurs most frequently in adults 60 to 65 years of age, arising from uncontrolled growth of cells called melanocytes. From 1,500 to 2,000 new cases are diagnosed annually in the United States

6. Eye tumors affects • In addition to damaging vision, eye tumors can spread to the optic nerve, the brain and the rest of the body. • Melanoma tends to spread via blood vessels to distant organs • Therefore, early diagnosis and treatment are extremely important.

7. Eye tumor treatment methods • There are various ways to treat eye tumors, depending on the size and aggressiveness of the tumor, and other factors. • Surgery, Radiation Therapy, laser and cryosurgery may use for eye tumor treatment

8. plaque therapy Internal radiation therapy Brachytherapy Tele-therapy (LINAC, …) Radiation therapy Proton therapy

9. Noninvasive Suitable Bragg Peak Small dimensions Advantags of proton particles Rather short-range Focal Proton Particles Energetic but controlled

10. Nozzle Individual mask Block-Bite [http://www.triumf.info/public/tech_transfer/treatment.php].

11. In spite of the advantages of proton therapy, during treatment, the tumor and also other components of vision like optic nerve, cornea, lens, anterior chamber are subjected to the radiation. • Malignant melanomas appear most commonly in the choroid

12. Materials and methods • In this research, one proton therapy system belonging to the Laboratori Nazionali del Sud- INFN as well as the human eye and its components were simulated by Monte Carlo method. • Maximum proton energy beam = 250 MeV • Proton beam radius = 0.5 cm • Modifier thickness = 1.5 cm • Number of particles per second = 1.25 E+10 • In this research: • Energy for eye = ( 50 – 65 ) MeV • Proton beam radius = ( 0.6 - 0.8 ) cm • Modifier thickness = ( 1 - 1.9 ) cm

13. To assess the absorbed dose in different parts of eye, the proton therapy system, the nuzzle aperture, modifier, different parts of eye such as choroid and sclera, retina and etc, also vision sense parts such as optic nerve, cornea, lens and anterior chamber were simulated by Monte Carlo method. • The eye was simulated by considering real materials and densities of eye components such as lens, cornea, retina, anterior chamber . Simulation of Eye and Proton therapy system

14. Lens Cornea Optic nerve Vitreous Anterior chamber

15. Optic Nerve

16. Treatment view of choroid and sclera cancer

17. The study was done in the following two stages, by changing the thickness of modifier in the range of 1.0 – 1.9 cm : • A tumor with the radius of 0.28 cm in choroid region (cell 23) • A tumor with the radius of 0.26 cm in choroid region and close to optic nerve (cell 27)

18. Radius tumor = 0.28 cm Volume tumor = 0.0914 cm3 39 29 20 30 23

19. cell No.23 Radius tumor = 0.28 cm Volume tumor = 0.0914 cm3 proton energy beam = 53.5 MeV Modifier thickness = 1.5 cm proton beam radius = 0.8 cm Dose (Gy) 23 Cell No

21. Radius tumor = 0.26 cm Volume tumor = 0.076 cm3 39 29 27 30 20

22. cell No.27 Radius tumor = 0.26 cm Volume tumor = 0.076 cm3 proton energy beam = 65 MeV modifier thickness = 1.5 cm proton beam radius = 0.5 cm Dose (Gy) 27 Cell No

24. Conclusion • This research showed in spite of the benefits of proton therapy in eye cancer treatment, the absorbed dose of healthy parts of eye specially the closed parts to the tumor are considerable and needs to reduce as much as possible. • The absorbed dose depends on the energy of proton beam, modifier thickness, size and location of tumor, radiation angle , etc, Which can modify and improve by Monte Carlo method.

25. Thank you