ESTRO 2024 - Abstract Book

S5466

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

Advancements in prostate radiotherapy and reporting of clinical trials such as PACE B will increasingly mandate the use of MRI-derived CTVs. Therefore, careful consideration will be required to ensure the improved accuracy of MRI CTVs is retained when verifying radiotherapy treatment using CBCT in the absence of fiducial surrogates. This study aimed to analyse the interobserver and intraobserver variation in match for MRI derived volumed for patients having stereotactic ablative body radiotherapy (SABR) for prostate cancer as publications have suggested MRI derived volumes are smaller when compared to CT [1].

Material/Methods:

A retrospective review of 5 patients who received 36.25Gy in 5 fractions inclusive of pre-treatment MRI for target volume delineation were reviewed.

10 radiographers were equally split into cohorts of trained (TR) or no training (NTR).

The difference in the image match shift values in 3D were calculated against a peer-reviewed gold standard.

1 radiographer in each of the groups also rematched the images a second time to explore intraobserver variation.

Descriptive statistics were calculated, and the Kappa (k) test was used to analyse the agreement of results.

Results:

An overview of the results can be found in Figure 1 and Table 1.

The standard deviation (SD) of the difference in match values were Vrt:0.11cm, Lng:0.09cm and Lat:0.03cm for both TR & NTR participants, with an interquartile range of <0.05.

k-value between NTR & TR overall was 1.00 (p<0.05), however comparison in the long shift was -0.019 (p<0.669) suggesting poor agreement between TR&NRT.

The SD for intraobserver variation was <0.3cm for both TR & NTR participants, with an interquartile range of <0.05.