ESTRO 2021 Abstract Book

S215

ESTRO 2021

they were understood as intended. Results

133 centres, mostly European, responded to the survey. Response numbers for each separate question varied. Centres reported considering complexity most challenging for modulated treatments, particularly in head-and- neck plans, and using mainly the number of monitor units and visual assessment of aperture shapes to control and evaluate it (Fig.1). Responses regarding evaluation of dosimetric quality showed a great variability in the methods centres reported using. The reported use of margins, RO, and RE is shown in the table below. Figures in brackets are the total number of responses to a question. Photons Protons Optimization 105 (106) 5 (10) Use PTV 18 (85) 8 (10) Use RO 17 (18) 3 (8) Of those using RO also use PTV

Use PRV

68 (91) 5 (10)

Use RO for OAR

11 (18) 8 (8)

Of those using RO also use PRV

8 (11)

3 (8)

Evaluation Use PTV/PRV

78 (83) 1 (7)

Use RE

11 (81) 8 (10)

Answered "No" to RE but commented "Occasionally" or similar 4 (81) Of those using RE also use PTV/PRV 11 (11) 1 (8) Fig. 2 shows the methods for margin calculation and RO, as well as the types of uncertainties considered, reported by photon clinics. All centres using both margins and RO/RE reported different sizes for RO/RE shifts than margins in at least one of four queried anatomical sites.