ESTRO 2024 - Abstract Book

S5600

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

ESTRO 2024

Purpose/Objective:

In prostate radiotherapy, the aim is to treat patients with a comfortably filled bladder, as small bladder size is associated with increased dose and, consequently, increased risk of late bladder toxicity [1]. However, many of our patients struggle to achieve the treatment planning bladder (PB) volume consistently over the treatment course. Our standard prostate regime includes urination 30-45 minutes before treatment time, followed by quickly drinking 300-400 ml liquid. Physicists analyze the first five fractions and contour the smallest observed bladder that still fulfills national dose constraints, the so-called "match bladder" (MB). On subsequent matching, if bladder volume is smaller than MB, a physicist is called and decision is made to either treat or remove patient from couch to drink more and wait 15-30 minutes before resuming treatment. However, it is difficult for an RTT to know whether dose at MB volume is barely or well within constraints: treating each fraction with MB bladder size can lead to significantly higher bladder dose than initially accepted during treatment planning. Alternatively, where MB is well within constraints, we risk removing patient unnecessarily from couch if bladder is slightly less full than MB. In addition, changing RTTs and physicists over a treatment course make it difficult to base decisions on knowledge of previous fractions.

Our project's aim is two-fold: to identify ways to help patients more consistently achieve an acceptable treatment bladder volume as well as develop tools to help RTTs assess bladder volume acceptability when matching daily CBCTs.

Material/Methods:

The project consists of two phases: Phase 1 is complete; Phase 2 finishes in January 2024.

Phase 1: Physicians hypothesized that increasing wait time after drinking to 60-75 minutes would lead to patients more consistently achieving a bladder volume greater than MB.

We added three steps sequentially to our treatment workflow, including six randomly selected patients (78Gy in 39 fractions) in each step:

A. Retrospective documentation: A worksheet (see Fig. 1) was developed to score bladder volume using the current definition of MB, filled in by RTTs using offline CBCTs.

B. Daily patient communication about bladder volume throughout treatment course: Same worksheet now filled in prospectively with urination time, liquid amount, pre-treatment CBCT time and bladder volume, as well as any actions taken after match. C. New regime standards implemented: Same worksheet used. New regime includes increased bladder filling time plus additional patient information regarding hydration, pelvic floor exercises, importance of proper filling and necessity of working in partnership with RTTs.

Worksheets were evaluated to assess the impact of these measures on patients’ bladder size. Bladder sizes were also re-scored by a second RTT to assess consistency in scoring.