ESTRO 2024 - Abstract Book

S4188

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

1 Aalborg University Hospital, 1) Department for Medical Physics, Aalborg, Denmark. 2 Aalborg University Hospital, 2) Department of Oncology, Aalborg, Denmark. 3 Aalborg University, 3) Department of Clinical Medicine, Aalborg, Denmark

Purpose/Objective:

Radiotherapy for Head and Neck (HN) cancer is often done by using daily Image Guided Radiotherapy (IGRT). However, concerns may arise regarding intra-fractional movement if these occurs frequently or exceed the planning target volume (PTV). This retrospective study aimed to assess the incidence of repositioning events triggered by Surface Guidance (SG) with verification by X-ray based IGRT.

Material/Methods:

Data was collected from 21 patients receiving treatment for head and neck cancer. The treatments were planned with three arc’s (field 1, 2 & 3), and a total of 695 treatment sessions were examined. The data for each fraction consisted of 6 Degrees of Freedom (6DOF) X-ray based IGRT match results and surface based monitoring during the sessions by using BrainLab Exactrac Dynamic V1.1. Surface deviations of up to 2 mm triggered an X-ray based IGRT procedure. The recorded data for analysis consisted of the number of recorded SGRT triggered verifications and the following applied couch shifts.

Results:

SGRT triggered repositioning were documented in 263 out of 695 sessions, which accounts for 38% of the sessions. The distribution among the three arcs was as follows: 55 sessions (21%) within Field 1, 113 sessions within Field 2 (43%) and 95 sessions (36%) within Field 3. The frequency of SGRT repositioning (in percent) for the 6DOF and for the 3 fields was computed in Table 1 and Figure 1. The results encompass the frequency of SGRT repositioning data for the three translational DOF: under 2 mm, under 5 mm, and exceeding 5 mm, as well as for the three rotational DOF: under 2 degrees (deg), under 5 degrees, and over 5 degrees. Mean absolute value for the 6DOF after SGRT repositioning were computed. The results show mean absolute value of VRT = 1.53 mm (sd= 3), LAT = 1.15 mm (sd = 1.74), LNG = 0.96 mm (sd = 1.5), Pitch = 0.43 deg (sd = 0.64) , Roll = 0.38 deg (sd = 0.48 ), and RNT = 0.35 deg (sd = 0.4). Of the instances where SGRT triggered verification procedures, up to 26 % of the images confirms deviations outside the tolerance of 2 mm, leading to minimum of 74 % of the cases as false positive. For the rotations, minimum 97 % of the verification images suggested correction within tolerance of 2 deg.

VRT

LAT

LNG

PITCH

ROLL

RNT

Field 1

Field 1

<2 mm

74%

82%

76%

<2 deg

97%

100%

98%

<5 mm

17%

15%

15%

<5 deg

3%

-

2%

>5 mm

9%

3%

9%

>5 deg

-

-

-