ESTRO 2024 - Abstract Book

S4049

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Figure 2: Plot of the change in the V36Gy dose constraint value (from P-CT to the CBCT) against the change in the B_Ht (from the P-CT to the CBCT).

The results for Patient A show poor correlation between all dose constraints and B_Ht. It is thought that this due to the patient having a hernia, meaning the position of their bowels was less constrained when bladder size increased.

Conclusion:

This retrospective study looked at CBCT data for 5 PIVOTAL Boost Prostate and Node patient. Results demonstrated a very strong correlation between B_Vol and B_Ht, where B_Ht could potentially be a quantitative way of monitoring B_Vol on set. The results also demonstrated that as B_Vol decreased, the difference in bowel doses/ dose constraints values increased (for 4/5 patients). Further investigation is required to establish how this impacts bowel toxicity. However, it reiterates the need to keep B_Vol consistent with the P-CT. 4/5 patients showed moderate to very strong correlation between the difference in B_Ht and the difference in maximum bowel Dose and the PIVOTAL Boost lower dose constraints. The other patient, did not show as good correlation as the other results, possibly due to the patient having a hernia. Emphasising the need for further investigation, with an increased number of patients.

The next stage of this study is to increase study size allow us to determine whether it is possible to use CBCT’s to predict the actual dose received based on the change in B_Ht.

Keywords: PIVOTALBoost, Bowel dose, Prostate and nodes

References:

[1] Syndikus I, Cruickshank C, Staffurth J, Tree A, Henry A, Naismith O, Mayles H, Snelson N, Hassan S, Brown S, Porta N, Griffin C, Hall E. PIVOTALboost: A phase III randomised controlled trial of prostate and pelvis versus prostate alone radiotherapy with or without prostate boost (CRUK/16/018). Clin Transl Radiat Oncol. 2020 Sep 1;25:22-28.

[2] Kong, V., Dang, J., Wan, V., & Rosewall, T. (2023). The dosimetric underpinning of bladder filling criteria for prostate image-guided volumetric modulated arc therapy. British Journal of Radiology.

1664

Poster Discussion

Assessing overall and fractional CTV coverage in breast cancer radiotherapy based on daily imaging

Elske M. Gort 1 , Sabine Visser 2 , Tristan C.F. Van Heijst 1