Detector Selection Impact on Small-Field Dosimetry of Collecting Beam Data Measurements among Versa HD 6 MV FFF Beams: A Multi-Institutional Variability Analysis
Cemile CEYLAN1,Boran GÜNGÖR2,Abdullah YEŞİL3,Sinem GÜNGÖR2,Serpil YÖNDEM İNAL4,Esil KARA5,Aykut KONUK6,Özcan ÖZDEN7,Özgür KARA8,Volkan AVCI9,Tamer BAŞER10,Timur UĞUR11,Yücel SAĞLAM12,Sümeyra CAN13,İsmail Faruk DURMUŞ14
1Department of Radiation Oncology, Istanbul Oncology Hospital, İstanbul-Türkiye
2Department of Radiation Oncology, Balikesir Atatürk City Hospital, Balıkesir-Türkiye
3Department of Radiation Oncology, Bursa Medicana Hospital, Bursa-Türkiye
4Department of Radiation Oncology, Bahçeşehir Memorial Hospital, İstanbul-Türkiye
5Department of Radiation Oncology, Koru Hospital, Ankara-Türkiye
6Department of Radiation Oncology, Kocaeli University Hospital, Kocaeli-Türkiye
7Department of Radiation Oncology, Bursa City Hospital, Bursa-Türkiye
8Department of Radiation Oncology, Manisa City Hospital, Manisa-Türkiye
9Department of Radiation Oncology, Eskişehir City Hospital, Eskisehir-Türkiye
10Department of Radiation Oncology, Ankara Memorial Hospital, Ankara-Türkiye
11Department of Radiation Oncology, Yedikule Chest Disease Hospital, İstanbul-Türkiye
12Department of Radiation Oncology, Vehbi Koç University Hospital, İstanbul-Türkiye
13Department of Radiation Oncology, Çam and Sakura City Hospital, İstanbul-Türkiye
14Department of Radiation Oncology, Yeni Yüzyil University Hospital, İstanbul-Türkiye
DOI : 10.5505/tjo.2023.4115 OBJECTIVE
The objective of the present study was to assess the impact of detector type on measurements of small fields for the 6MV-FFF beam within 13 institutes of Elekta Versa HD linear accelerator users.

Using various ion chambers, measurements of the percent depth dose (PDD), off-center ratio (OCR), and output factor (OF) datasets in square areas between 2×2 and 50×50 mm2 for beam modelling in Monaco TPS were collected, and dosimetric differences were compared. The types of used detectors were PTW PinPoint 31014, IBA CC04, IBA CC01, IBA CC13 and Exradin A16, respectively. The effect of the detector type on the OCR was evaluated by including penumbra width of fields, full width half maximum value (FWHM) and FFF beam specific unflatness value. The PDDs were compared using depth of dmax, d5 and d10. Also, the differences between OFs of each field and institution were analyzed with and without correction factor.

The largest observed variance in dmax was 3 mm for a few institutions, whereas the majority of institutions agreed with GBD dmax values within 2 mm. The agreement of the median PDD values with GBD was all within ±2%. The maximum deviation was under 2% for the shoulder part and 1% for the center part of the OCR profiles for all field sizes. The maximum deviation of the penumbra and FWHM value observed for all field sizes at certain institute OCR data was considered a user-dependent effect instead of a detector. The relative percent difference both the OFuncorr and the OFcorr compared with GBD for all field sizes was within ±3%.

The findings of this study obtained via a large multicentre study can be considered as an external crossverification for Versa HD users doing beam data collection of Monaco and should help to offer accurate TPS modelling of small fields and minimize the uncertainty of SRS and SBRT. Our results emphasized that the use of several dosimetric systems, comparison of golden beam data, and multi-institutional review are required. Keywords : Beam data commissioning; FFF; small-field dosimetry