WORKLOAD ANALYSIS FOR LINEAR ACCELERATORS AT RADIOTHERAPY DEPARTMENT OF THE CANCER INSTITUTE OF THE STATE OF SÃO PAULO - ICESP

The workload (W) indicates the weekly radiation performance of teletherapy equipment as linear accelerators. Although there are publications with default values for W, this parameter depends on the radiotherapy service and must be determined individually. This paper aims to analyze the weekly workload of six linear accelerators at Radiotherapy Department of a hospital in the State of Sao Paulo, from 2011 to 2018. The values found were compared to those used in the shielding calculations of the rooms, validating them. The equipment operates with different photon and electron energies (4, 6 and 15 MV for photons; 4, 6, 9, 12 and 15 MeV for electrons). The information was collected through the Institution Registration and Verifying System, obtaining the weekly values of Monitored Units (UM) and the dose delivered in Gray (Gy), performing the data analysis by Excel spreadsheet. Results present a mean dose value of (8.0 ± 1.1) × 10² Gy / week for (456 ± 33) patients and (9.1 ± 0.6) × 104 UM / week in 2011 for five of the linear accelerators, which use conformational (3DC) and modulated arc therapy (VMAT) techniques. In 2018 we obtained: (6.9 ± 0.9) × 10² Gy, (483 ± 69) patients and (1.4 ± 0.2) × 105 UM / week. For the sixth equipment, dedicated to high treatment technologies (VMAT and SBRT), we obtained: (3.3 ± 0.1) × 10² Gy / week for (220 ± 19) patients and (9.6 ± 0.9) × 104 UM / week from 2011 to 2018. The predicted values for the original shielding calculations were 2.25 × 10³ Gy / week and 2.25 x 105 UM / week for the five accelerators and 2.33 × 10³ Gy / week and 2.33 × 105 UM / week for the sixth accelerator. The highest Workload value found in this period was 1.14 × 10³ Gy / week and 1.86 × 105 UM / week for the five accelerators; for the sixth, it was 3.73 × 10²Gy / week and 1.25 × 105 UM / week. Therefore 50% and 82.6% of the previously determined dose value; 16% and 53.6% of the previously determined UM value, respectively. The predominant energies used were 6 and 15 MV for photons. A variation of UM is observed over the years. This can be attributed to the use of techniques such as VMAT, which requires more UM to perform the treatment, as well as increased opening hours and changes in the institutions fractionation protocols in the period.

Publication History

Article published online:
23 October 2019