ESTRO 2024 - Abstract Book

S3480

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

with reduced complexity (“simple plan”) and one of higher complexity (“complex plan”). These additional plans were generated by altering the monitor unit constraint and the aperture shape controller level, while retaining a similar dose distribution. The fraction of penumbra dose was calculated for both the clinical and the newly generated plans creating in total 36 penumbra maps.

Results:

The generated penumbra maps were able to highlight anatomical regions with high fraction of penumbra dose (e.g., above 50%). These regions were mostly observed outside the planning target volume (PTV), regardless of treatment site and complexity level. Generally, the fraction of penumbra dose, both inside and outside the PTV, was increased with increased plan complexity. The average fraction of penumbra dose for the body, PTV and an example OAR are shown in Table 1 across all analyzed plans. For certain cases, the absorbed dose in parts of OARs originated from penumbra regions to a considerable degree, even for the least complex version of the plan. Examples are shown in Figure 1 featuring the rectum in a prostate plan and the parotid glands in a head & neck plan.

Figure 1: Representation of the fraction of penumbra dose for one prostate (A-F) and one head & neck (G-M) across three complexity levels—simple, clinical, and complex. The penumbra dose is visualized using a color wash ranging from 10% to 100%. Prostate plans show traversal (A-C) and sagittal (D-F) slices, while head & neck plans display transversal (G-I) and coronal (K-M) slices. Red and blue structures represent the PTV for tumor and lymph node sites, respectively. The rectum is delineated in dark green, and for head & neck, light green and orange structures indicate the right and left parotid glands, respectively.