# One Week Hypofractionated Adjuvant Radiation for Early Breast Cancer Patients Treated at a Tertiary Cancer Centre in South India: A Comparative Dosimetric Study of Forward Intensity-Modulated Radiotherapy (F-IMRT) and Volumetric Modulated Arc Therapy (VMAT)

## TL;DR

This study compares two radiation therapy techniques for breast cancer treatment, finding that one reduces radiation exposure to critical organs while maintaining effective treatment.

## Contribution

The study demonstrates dosimetric advantages of F-IMRT over VMAT in left-sided breast cancer treatment with hypofractionation and DIBH.

## Key findings

- F-IMRT significantly reduced mean left lung dose and left lung V8Gy compared to VMAT.
- F-IMRT resulted in lower mean heart dose and heart V1.5Gy compared to VMAT.
- F-IMRT showed lower mean right breast and right lung doses compared to VMAT.

## Abstract

Objective: This study is aimed at comparing the forward IMRT (F-IMRT) and VMAT techniques in the adjuvant treatment of left-sided breast cancer using hypofractionated radiation over 1 week with deep inspiration breath hold (DIBH) via the Elekta Active Breathing Coordinator (ABC) system.

Materials and Methods: Treatment plans for 26 patients receiving 26 Gy in five fractions (5.2 Gy/fraction), followed by a 10-Gy electron boost in five fractions, were analyzed. The boost phase was excluded from the comparison. F-IMRT and VMAT plans were evaluated for dose to 95% of the volume, conformity index (CI), mean left lung dose (MLLD), left lung V8 Gy, mean heart dose (MHD), heart V1.5Gy and V7Gy, mean right breast dose (MRBD), and mean right lung dose (MRLD). Statistical analysis was conducted using the Wilcoxon signed-rank test.

Results: PTV coverage was similar in F-IMRT and VMAT arms (95.83% vs. 95.38%), but CI was significantly improved with VMAT (1.31 vs. 1.04). F-IMRT significantly reduced MLLD (4.55 Gy vs. 5.95 Gy) and left lung V8Gy (18.78% vs. 25.87%) when compared to VMAT. MHD was lower with F-IMRT (1.79Gy vs. 2.47Gy), with significantly reduced heart V1.5Gy (21.6% vs. 54.4%) when compared to VMAT, with V7Gy not different (5.04% vs. 5.79%) between F-IMRT and VMAT. F-IMRT also resulted in lower MRBD (0.62 Gy vs. 2.4 Gy) and MRLD (0.38 Gy vs. 1.8 Gy) when compared to VMAT.

Conclusion: F-IMRT provides comparable target coverage to VMAT while significantly reducing radiation exposure to the heart, lungs, and contralateral breast for left-sided breast cancer treatment with DIBH and hypofractionation over 1 week. Given its dosimetric advantages, F-IMRT should be the preferred technique to enhance patient safety and minimize long-term toxicities.