ESTRO 2024 - Abstract Book

S3625

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

ESTRO 2024

1. Rassiah P, Esiashvili N, Olch AJ, Hua CH, Ulin K, Molineu A, Marcus M, Gopalakrishnan M, Pillai S, Kovalchuk N, Liu A, Niyazov G, Pe nagar ıcano JA, Cheung F , Olson AC, Wu CC, Malhotra H, MacEwan IJ, Faught J, Breneman JC, Followill DS, FitzGerald TJ, Kalapurakal JA. Practice patterns of pediatric total body irradiation techniques: A Children’s Oncology Group survey. Int J Radiat Oncol Biol Phys, 2021

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Poster Discussion

A simple parameter to guide plan optimization for robotic pancreas SBRT

Margherita Zani 1 , Tommaso Zoppi 2 , Raffaela Doro 3 , Mauro Loi 4 , Lorenzo Livi 4,5 , Laura Masi 3

1 Azienda Ospedaliero-Universitaria Careggi, Medical Physics Unit, Florence, Italy. 2 University of Trento, Department of Information Engineering & Computer Science, Povo, Italy. 3 IFCA, Department of Medical Physics and Radiation Oncology, Florence, Italy. 4 Azienda Ospedaliero-Universitaria Careggi, Radiation Oncology Unit, Florence, Italy. 5 University of Florence, Department of Experimental and Clinical Biomedical Sciences ‘Mario Serio’, Florence, Italy

Purpose/Objective:

Pancreatic SBRT plans are challenging due to the proximity of sensitive organs at risk (OARs). CyberKnife (CK) offers steep dose gradients and real time tracking, often representing the system of choice [1]. Automated planning is not available for CK system, and an expert planner is needed to obtain the ‘best’ achievable plan. Even in this case the creation of a sub-optimal plan is still possible. This work provides a tool to guide plan optimization, based on simple parameters and on the experience gained in our center with pancreatic patients treated in the last few years.

Material/Methods:

A set of 37 patients with pancreatic cancer was considered. Treatments were performed with a CK equipped with a multileaf collimator (MLC) (InCise2™). The prescription was 40/50Gy (PTV/GTV) in 5 fractions. OAR doses were kept below dose limits and, for the most critical organs (duodenum, stomach, and bowel) the dose constraint was V35Gy < 0.5 cc.

To quantify the target to OARs proximity, a parameter was defined, computed as the intersection volume between the PTV expanded by 5 mm and duodenum, stomach, and bowel: the expansion-intersection volume (EIV).

We first investigated whether, while respecting the above-mentioned dose constraints, EIV could predict PTV/GTV coverage. Outputs taken into account were PTV percentage coverage at 35Gy and at 40 Gy (PTV V35 [%] and PTV V40 [%]), the volume of PTV not included in the 40 Gy isodose (PTV Vout40 [cc]), GTV percentage coverage at 47,5Gy and at 50 Gy (GTV V47,5 [%] and GTV V50 [%]), and GTV volume not included in the 47,5Gy isodose (GTV Vout47,5 [cc]).

As a second step, we designed a tool to help the planner during optimization. The tool is part of the open-source framework MACARON [2], and uses a 3-uple (EIV, PTV dimension, GTV dimension) of a new plan to: