# Breast cancer radiotherapy: analysis of unintended internal mammary node doses and influencing factors

## TL;DR

This study examines unintended radiation doses to internal mammary lymph nodes in breast cancer patients and identifies factors influencing these doses.

## Contribution

The study provides new insights into dose variability and factors affecting internal mammary lymph node radiation in breast cancer radiotherapy.

## Key findings

- Internal mammary lymph node doses varied, with no correlation to volume, radiotherapy field, or tumor stage.
- Nodal stage significantly impacted D95 doses, with higher doses observed in N1 patients.
- Wider radiotherapy fields increased D95 doses to internal mammary lymph nodes.

## Abstract

Breast cancer is a prevalent malignancy requiring ongoing treatment advancements. Radiotherapy is vital for reducing recurrence and improving survival. This study evaluates unintended doses to internal mammary lymph nodes and influencing factors in patients at Ankara Bilkent City Hospital's Radiation Oncology Clinic.

We analyzed 44 right-sided breast cancer patients treated with radiotherapy between November 2019 and April 2023. Data on demographics, treatment, and dose–volume histograms were reviewed using various statistical tests.

Median age was 54 years; 88.6% had invasive ductal carcinoma, and 11.4% had ductal carcinoma in situ. Patients received conventional (54.5%) or hypofractionated radiotherapy (45.5%) using intensity-modulated radiotherapy or three-dimensional conformal radiotherapy. Median internal mammary lymph node volume was 7.3 cc with dose variability. Internal mammary lymph nodes V45 dose showed no correlation with internal mammary lymph nodes volume, radiotherapy field, pT stage, or pN stage. However, the nodal stage significantly impacted the internal mammary lymph nodes D95 dose, with higher doses in N1 patients. Wider radiotherapy fields led to increased D95 doses.

The findings highlight the variability in internal mammary lymph nodes doses and the impact of nodal stage and radiotherapy field on dose distribution. Advanced techniques like intensity-modulated radiotherapy can reduce risks, but careful planning is essential.

Understanding internal mammary lymph nodes dose factors can enhance treatment planning and outcomes. Future research should focus on refining guidelines and leveraging technology to improve radiotherapy efficacy.