Measurement of Ambient Dose Equivalent in Compact Proton Therapy using In-house Neutron Moderator-based Poly Allyl Diglycol Carbonate

Tanawat Tawonwong; Sivalee Suriyapee; Tanapol Dachviriyakij; Vithit Pungkun; Sirinya Ruangchan; Taweap Sanghangthum

doi:10.4103/jmp.jmp_35_23

Measurement of Ambient Dose Equivalent in Compact Proton Therapy using In-house Neutron Moderator-based Poly Allyl Diglycol Carbonate

J Med Phys. 2023 Jul-Sep;48(3):243-247. doi: 10.4103/jmp.jmp_35_23. Epub 2023 Sep 18.

Authors

Tanawat Tawonwong^{1

2

3}, Sivalee Suriyapee^{1

4}, Tanapol Dachviriyakij⁵, Vithit Pungkun⁵, Sirinya Ruangchan^{2

3}, Taweap Sanghangthum^{1

2

3

4}

Affiliations

¹ Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
² Her Royal Highness Princess Maha Chakri Sirindhorn Proton Center, Bangkok, Thailand.
³ Department of Radiology, Division of Radiation Oncology, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Bangkok, Thailand.
⁴ Department of Radiology, Division of Radiation Oncology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
⁵ Nuclear and Radiation Metrology Section, Regulatory Support Division, Office of Atoms for Peace, Bangkok, Thailand.

Abstract

Purpose: The high-energy proton produces the unwanted dose contribution from the secondary neutron. The main purpose of this study is to report the validation results of in-house neutron moderator based on poly allyl diglycol carbonate (CR-39) detector, Chulalongkorn University Neutron Moderator (CUMOD) through the ambient dose equivalent, H*(10) measurement.

Materials and methods: The Particle and Heavy Ion Transport code System (PHITS) Monte Carlo code was used to simulate the neutron response function. The CUMOD was calibrated with ²⁴¹AmBe source calibrator in the range of 100-1000 μSv. The variation of neutron fields was generated employing different proton treatment plans covering most of the clinical scenarios. The ambient dose equivalents, H*(10), evaluated employing CUMOD were compared to those obtained with WENDI-II dosimeter.

Results: The linear relationship between CUMOD and WENDI-II responses showed an R² value close to 1. The H*(10) per Gy delivered dose was in the range of 22-105 μSv for a 10 cm × 10 cm field.

Conclusion: The in-house CUMOD neutron moderator can expand the neutron detection dose range of CR-39 detector for ambient dose equivalent. The advantage of CUMODs is its capability to evaluate H*(10) in various positions simultaneously.

Keywords: Ambient dose equivalent; compact proton therapy; neutron moderator; polyallyl diglycol carbonate.