# The implementation of knowledge‐based planning with partial OAR contours for prostate radiotherapy

## TL;DR

This paper proposes using partial organ contours in prostate radiotherapy to reduce contour uncertainty and improve treatment planning.

## Contribution

The novelty lies in using partial contours with knowledge-based planning to achieve dosimetry comparable to full contours.

## Key findings

- Partial contours showed higher concordance compared to full contours in geometric evaluations.
- RP_Part_Un plans reduced bladder doses in patients with SpaceOAR and rectum doses in those without.
- MIM AI_Part_Un plans showed lower rectum doses in both patient groups.

## Abstract

Intra‐ and inter‐observer contour uncertainty is a continuous challenge in treatment planning for radiotherapy. Our proposed solution to address this challenge is the use of partial contours for treatment planning, focusing on uninvolved or non‐overlapping portions of the organs‐at‐risk (OARs) with the planning target volume (PTV).

The partial contours systematically eliminate overlapping regions. The partial contours were evaluated against fully contoured OARs. We incorporated advanced tools like knowledge‐based planning (KBP) to create treatment plans and artificial intelligence (AI) to create auto‐segmented contours. We developed two models, Rapid Plan (RP) and Rapid Plan partial uninvolved (RP_Part_Un), using 70 previous clinically approved volumetric arc therapy (VMAT) plans each prescribed with 70 Gy/28 fractions. From these models, we created three plans, RP, RP_Part_Un, and MIM AI_Part_Un. In this retrospective study, 60 prostate patients were analyzed using the three plans. For determining OAR sparing, D
max and D
mean along the percent volume receiving a dose over a range (V10 Gy V70 Gy) between each plan were compared. Geometric evaluations, dice similarity coefficient (DSC), and overlay index (OI) between the OAR contours from partial‐contoured manual structure sets and partial‐contoured AI structure sets were analyzed.

When comparing the DSC and OI for full contours to the partial contours, in both groups, all comparisons were significantly increased for both organs. This indicated the partial contours had a higher degree of concordance. In patients with SpaceOAR, RP_Part_Un plans exhibited significantly reduced bladder D
max and D
mean compared to RP plans, while rectum D
max and Dmean showed no significant differences. For patients without SpaceOAR, RP_Part_Un significantly lowered rectum D
mean. MIM AI_Part_Un plans demonstrated lower rectum D
max in both patient groups.

Partial contours, defined at a specified distance from the PTV, yielded dosimetry comparable to fully contoured plans, highlighting their potential efficacy in treatment planning.