Analysis of an Image-Guided Radiotherapy Protocol with Exacradle without Fiducial Markers in Prostate SBRT

Purpose/Objective

The main objective of this study is to evaluate the validity of the protocol proposed by Anatge for image guided radiotherapy (IGRT) implemented in cases of SBRT for prostate cancer using Exacradle without fiducial markers. Additionally, we aim to characterize the magnitude of interfraction displacements during the first five sessions in the first three patients.

Material/Methods

We will describe the simulation and IGRT process, followed by detailing the analysis method. Patient simulation proceeds as follows:

1. Placement of the Exacradle indexed to the CT table (or MRI, as Exacradle is compatible) in a distant area from the irradiation field.
2. Substituting the headrest with a pillow.
3. Positioning the patient, fasting and having urinated, so their head is at the beginning of the Exacradle.
4. Placing the posterior actuators between the iliac crest and the costal arch (fig.1).
5. Positioning the arch at two stereotactic numbers below theposterior actuators to support the hands (fig.2).
6. Placing the medial actuator against the symphysis while the patient keeps their legs flexed (fig.3).
7. Placing a triangular Moldcare under the legs and indexing it with a vertex at the symphysis top.
8. Applying ankle antirotation.
9. Molding the bag to obtain the best patient imprint.
10.Inserting a small bladder catheter with contrast and filling the bladder with 180ml of saline and 20 ml of iodinated contrast at the end (fig.4).
11.Acquiring CT scans with 1mm thickness.
12.Avoiding tattoos due to Exacradle's stereotactic references and excellent immobilization and Moldcare imprint

Patient preparation in prostate SBRT is crucial. The initial step in patient simulation involves nursing care to understand the patient's scatological characteristics to control and reproduce the state of the rectum and bladder during simulation and treatment. The rectum should remain empty while the bladder is full, chosen for its reproducibility. The use of VMAT with high demands allows planning with doses below the tolerance of the empty rectum. The day before, intestinal emptying preparation involves administering sodium picosulfate and magnesium citrate. Subsequently, ensuring the patient maintains a regular bowel elimination pattern through
a tailored diet and lactulose laxative use. Micro-enemas may be utilized before each treatment session if necessary.

At the accelerator, a bladder catheter filled with contrast is reintroduced, ensuring the bladder contains a precise mixture of 180ml of saline and 20ml of iodinated contrast. This meticulous process optimizes visualization during imaging procedures, particularly as the contrast-filled intra-prostatic catheter functions as a fiducial marker in CBCT. Following this preparation, fifteen CBCT scans were meticulously scrutinized using the TRUEBEAM system, allowing for a comprehensive analysis of IGRT displacements, including their means and deviations, which were then tabulated for further examination.

Results

Table 1 offers an overview of IGRT displacements, highlighting the effectiveness of using the contrast-filled intra-prostatic catheter as a fiducial marker in CBCT for prostate localization, guiding treatment protocol improvements and enhancing radiotherapy precision in prostate cancer management.

Conclusion

In conclusion, Exacradle offers a promising solution for achieving reproducible, comfortable, and effective
Stereotactic Ablative Radiotherapy (SABR) treatments in patients with prostate cancer. Exacradle successfully
addresses fiducial marker concerns, ensuring consistent immobilization for precise tumor targeting while minimizing radiation exposure to healthy tissues. This approach not only enhances treatment efficacy but also improves patient comfort throughout the treatment process. By providing a comfortable and reliable setup, Exacradle promotes treatment compliance and reduces the risk of treatmentrelated side effects. Overall, Exacradle represents a promising advancement in SABR techniques for prostate cancer, offering a patient-centered approach to treatment delivery that prioritizes both efficacy and comfort.