Feasibility of Metal Testicle Shield By 3D Printing for CT Image-Based Treatment Planning

Abstract

This study aims to evaluate the feasibility of metal testicle shield for 3D CT image-based treatment planning using 3D dose calculation algorithm. The testicle shield was designed in the shape of box to minimize scatter radiation to the testicles and to be available in prone position. The testicle shield have two parts; cover and case. The dimension of case was 9.5 cm (length) × 7.5 cm (width) × 5.5 cm (height) with 2.0 cm thickness. The cover has 9.5 cm (length) × 9 cm (width) with 2.0 cm thickness. The one side of case was open sector to cover the scrotum of patient. A thin layer of silicon coating on inner surface was attached to allow comfortable attachment to the patient and to shield back-scattered electron dose from the shield. Each part was fabricated using 3D printer. The material of testicle shield was titanium which is allowed for the dose calculation using Acuros XB. To avoid metal artifact for CT image, the replica of the metal shield (dummy) was fabricated with a plastic using 3D printer for CT-sim. The rectal cancer patient underwent CT scan with dummy shield. In the treatment planning system (TPS), the dummy testicle shield was contoured, and material of dummy was assigned to titanium. Three-field box (two wedged opposing beams and 3rd beam at 90° with 15 MV) technique was used for treatment plans. The dose calculation was performed using Acuros XB and AAA. The dose distributions were also calculated in EGS4/DOSXYZnrc Monte Carlo (MC) for comparison. Optically stimulated luminescent dosimeter (OSLD) was used to measure dose of inside and outside shield for evaluating shield effect. We compared between OSLD measurement, MC simulation and TPS dose calculation. The inside dose of testicle shield was reduced to 48.1% inside dose by titanium testicle shield. The dose distribution of Acuros XB have good agreement with that of MC. The average difference was 2.1% in dose voxels containing greater than 50% the normalized dose. In contrast, the average difference between AAA and MC was 23.1%. For point dose inside the shield, MC calculation agreed with the OSLD measurements within 3.0%. The difference of MC and AAA are 10% and 30% for outside and inside surface of testicle shield, respectively. The radiation shielding ability of titanium was approximately 10% lower than that of lead. When the material of testicle shield is titanium and the plastic dummy is used for CT-sim, the dose distribution can be calculated using Acuros XB accurately in TPS.