Overcoming Problems Caused by Offset Distance of Multiple Targets in Single-isocenter Volumetric Modulated Arc Therapy Planning for Stereotactic Radiosurgery

Overview

Journal J Med Phys

Date 2024 Jan 15

PMID 38223796

Authors

Takaaki Ito

Kazuki Kubo

Hajime Monzen

Yuya Yanagi

Kenji Nakamura

Yusuke Sakai

Yasumasa Nishimura

Affiliations

Soon will be listed here.

Abstract

Purpose: The purpose of the study is to investigate the impact of large target offset distances on the dose distribution and gamma passing rate (GPR) in single-isocenter multiple-target stereotactic radiosurgery (SIMT SRS) using volumetric modulated arc therapy (VMAT) with a flattening filter-free (FFF) beam from a linear accelerator.

Methods: Two targets with a diameter of 1 cm were offset by "±2, ±4, and ±6 cm from the isocenter in a verification phantom for head SRS (20 Gy/fr). The VMAT plans were created using collimator angles that ensured the two targets did not share a leaf pair from the multi-leaf collimator. To evaluate the low-dose spread intermediate dose spill (R), GPRs were measured with a criterion of 3%/2 mm using an electronic portal imaging device and evaluated using monitor unit (MU), modulation complexity score for VMAT (MCS), and leaf travel (LT) parameters.

Results: For offsets of 2, 4, and 6 cm, the respective parameters were: R, 4.75 ± 0.36, 5.13 ± 0.36, and 5.11 ± 0.33; GPR, 95.01%, 93.82%, and 90.67%; MU, 5893 ± 186, 5825 ± 286, and 5810 ± 396; MCS, 0.24, 0.16, and 0.13; and LT, 189.21 ± 36.04, 327.69 ± 67.01, and 430.39 ± 114.34 mm. There was a spread in the low-dose region from offsets of ≥4 cm and the GPR negatively correlated with LT ( = -0.762). There was minimal correlation between GPR and MU or MCS.

Conclusions: In SIMT SRS VMAT plans with an FFF beam from a linear accelerator, target offsets of <4 cm from the isocenter can minimize the volume of the low-dose region receiving 10 Gy or more. During treatment planning, it is important to choose gantry, couch, and collimator angles that minimize LT and thereby improve the GPR.

Citing Articles

A multi-institutional trial evaluating the use of an integrated quality assurance phantom for frameless single-isocenter multitarget stereotactic radiosurgery.

Capaldi D, Skinner L, Pinkham D, Zavgorodni S, Stafford O, Shirmohammad M Front Oncol. 2024; 14:1445166.

PMID: 39544300 PMC: 11560902. DOI: 10.3389/fonc.2024.1445166.

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