Vücut Içerisindeki Doku Eşdeğeri Olmayan Implant Materyallerinin Yoğunluk Ayarlı Radyoterapi ve Stereotaktik Radyocerrahi Tedavilerinde Doz Dağılımına Etkisinin İncelenmesi

Abstract

Several cancer patients, who have implant and filling material in their body, are treated with radiotherapy and those materials may cause dosimetric uncertainities during treatment which may not be estimated accurately by treatment planning systems(TPS). In this study we tried to evaluate those uncertainties caused by implant and filling materials, and also to assess the accuracy of the treatment planning systems in estimating those uncertainities. For this purpose we placed Ti-6A1-4V (TI), CoCrMo (CO) and composite filling material (KD) into the RW3 solid phantom. Treatment plannings using CyberKnife (Accuray Inc.,Sunnyvale,CA,USA) and Novalis (Brainlab AG) systems were made using standart radiation beams and the phantoms were irradiated accordingly. Point doses were measured with ionization chambers placed certain distances below and on the top of the implant material. In addition, dose profiles obtained from ionization chambers were compared with the dose profiles obtained from TPSs. The point doses at 0,5 cm above and 0,5 cm under the materials showed remarkable differences between the ionization chamber measurements and TPS values. In Novalis system the difference between the measured point doses 0,5 cm above the materials obtined from ionization chambers and the calculated values in TPS was up to 8±0,01% This difference was up to 6±0,01% when the ionization chamber was placed 0,5 cm under the materials. In CK system, on the other hand, this difference was up to 10±0,03% as ionization chamber was put 0,5 cm above the materials. This difference was up to 11±0,03% when ionization chamber was put 0,5 cm under the materials. However, ionization chamber and TPS values did not show remarkable differences in the lateral sides of the materials. The dose profile measurements with Novalis system showed that CO, TI and KD materials attenuated the radiation beam about 19%, 10% and 3,2% respectively. These results demostrated that TPSs do not estimate dosimetric uncertainities accurately when there is an implant or filling materials on the path of the photon beams. This failure may result underdosage in tumor tissues or overdosage in the surrounding healthy tissues. Underdosage in tumoral tissues may decrease local control rates and overdosage in surrounding healthy tissues may result in severe complications. These point dose and dose profile differences should be taken into consideration during treatment plannings.