Naslov
Evaluation of radiotherapy treatment dose distributions at University Hospital Rijeka – four-year experience

Autori
Obajdin, Nevena ; Smilović Radojčić, Đeni ; Švabić Kolacio, Manda ; Rajlić, David ; Jurković, Slaven

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, prošireni sažetak, znanstveni

Izvornik
Zbornik radova 12.simpozija Hrvatskog društva za zaštitu od zračenja / - , 2019, 86-91

Skup
12. Simpozij Hrvatskog društva za zaštitu od zračenja

Mjesto i datum
Varaždin, Hrvatska, 10.04.2019. - 12.04.2019

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Domaća recenzija

Ključne riječi
quality assurance, PSD, gamma test, tolerance criteria

Sažetak
INTRODUCTION Accurately calculated absorbed dose is essential for the outcome of radiotherapy treatment. Uncertainties in the calculation of absorbed dose should be as high as 3%. This requires development of a comprehensive quality assurance (QA) program which includes 2D dosimetric verification of calculated dose distributions, also known as Patient-Specific Dosimetry (PSD). At UH Rijeka, implementation of PSD started in 2015 for 3D Conformal Radiation Therapy (3D CRT) treatment plans and in 2016 for Intensity Modulated Radiation Therapy (IMRT) treatment plans. MATERIALS AND METHODS PSD is used for assessing agreement between calculated and measured absorbed dose distributions. Devices which are in clinical use at Radiotherapy Department of UH Rijeka were used to perform the verification: linear accelerators Siemens Oncor Impression and Siemens Oncor Expression, and CT simulator Siemens Somatom Open. Dose distributions were calculated using treatment planning systems XiOv5.10. and Monaco v5.11. Data were obtained using 2D ion chamber array IBA MatriXX which was placed in an IBA MultiCube homogeneous phantom. Agreement between measured and calculated dose distributions was evaluated using the gamma method. Gamma test is a composite of two tests: one that is relevant in the low dose gradient regions (dose difference) and one that is relevant in the steep dose gradient regions (distance-to-agreement). Tolerance criteria used were 3 %/3 mm and the tolerance limit was set so that 95 % of analyzed points pass the gamma test. For the purpose of additional research, 2 %/ 2 mm criteria were also applied. Following international guidelines, all QA plans are verified before the start of the treatment process. RESULTS AND DISCUSSION Average gamma passing rates for 3D CRT and IMRT treatment plans exceeded the tolerance limit of 95 % when 3 %/3mm criteria was used. Looking at 3D CRT dose distributions, passing rates range from 97.61 % for rectum anatomical site to 99.50 % for the prostate anatomical site. Average gamma passing rates for IMRT dose distributions range from 97.24 % (H&N) to 98.84 % (CNS). When 2 %/2 mm criteria were used, it was observed for IMRT plans that gamma passing rates deteriorate as the plan complexity increases. CONCLUSION Results presented in this work show how developing and conducting a good comprehensive QA program implies good results when conducting patient- specific QA program.

Izvorni jezik
Engleski

POVEZANOST RADA