ESTRO 2024 - Abstract Book

S4915

Physics - Quality assurance and auditing

ESTRO 2024

2678

Poster Discussion

A quantitative measure of plan quality for VMAT plans

Samuele Cavinato 1 , Francesca Dusi 1 , Badr El Khouzai 2 , Marco Krengli 2 , Marta Paiusco 1 , Chiara Paronetto 2 , Nicola Pivato 1 , Marco Andrea Rossato 1 , Matteo Sepulcri 2 , Alessandro Scaggion 1 1 Veneto Institute of Oncology IOV-IRCCS, Medical Physics Department, Padua, Italy. 2 Veneto Institute of Oncology IOV IRCCS, Radiation Oncology Department, Padua, Italy

Purpose/Objective:

The quality of a radiotherapy treatment plan should represent its suitability in terms of clinical acceptability, namely the fitness of the generated dose distribution, delivery accuracy and complexity [1-2]. An intimate relation exists between them: excessive plan complexity may degrade the delivery accuracy; conversely, a certain degree of complexity is necessary to achieve clinically acceptable plans. It is essential to find the optimal trade-off between these quantities, but this is always a challenge, particularly within the standard radiotherapy workflow where information on plan deliverability is not available during planning. To maximize the quality of radiotherapy VMAT plans, we propose a quantitative measure of the three-way relationship between clinical acceptability, delivery accuracy and complexity.

Material/Methods:

Thirty patients were retrospectively retrieved from our clinical database, including ten Head&Neck, ten Lung and ten Prostate patients. VMAT plans were generated using the Eclipse TPS v15.6.1 for a TrueBeamSTx with high-definition MLC and 6 MV energy (Varian Medical Systems). Each plan was created using different Aperture Shape Controller (ASC) penalties and maximum number of total Monitor Units (MUs) (Tab. 1). This procedure resulted in 190 plans with different levels of plan modulation.

Table 1. Summary of the ASC and MU/cGy values corresponding to the different strategies adopted to create the plans.

ASC ↓ \ MU/cGy →

<=3

<=4

<=5

Very High

VH_MU3

VH_MU4

VH_MU5 (Prostate)

Moderate

Mod_MU3

Mod_MU4

Off

Off_MU3

Off_MU4 (HN, Lung)

Off_MU5 (Prostate)

The clinical acceptability was assessed using the Plan Quality Metric (PQM%) score [3]. Delivery accuracy were assessed through dedicated patient-specific quality assurance (PSQA) sessions using the ArcCHECK TM detector array (Sun Nuclear Corporation). Dose comparisons were performed computing the γ-index passing rate PR γ %(3%G, 2 mm) as the AAPM TG-218 suggests [4]. A 10% threshold was set. Plan complexity was assessed using the indicators in the