Breast Dose in Young Women Treated for Hodgkin Lymphoma Between 2007 and 2018: A Single Institutional Study

Abstract

<h3>Purpose/Objective(s)</h3> Women receiving supradiaphragmatic radiotherapy (RT) for Hodgkin Lymphoma (HL) aged ≤ 36y have a greater risk of breast cancer (BC) than the general population. Although RT fields have reduced in recent years, breast tissue (BT) is unavoidably irradiated in many women. Despite the long-term risk, dose to BT is not routinely nor consistently reported: published studies report inconsistent breast dose metrics, or only point dose to the site of a subsequent BC. We hypothesize breast dose from HL RT has decreased since the implementation of CT based RT, due to an increased awareness of BC risk. This study also aims to assess the correlations between dose metrics of suspected importance to RT induced BC. <h3>Materials/Methods</h3> All female patients with available RT plans aged ≤ 36y treated with supradiaphragmatic RT from 2007 to 2018 were included. Patients received 3D conformal RT to 30-36 Gy (8/68 received 20 Gy). BT was retrospectively contoured. Dose metrics V4 Gy (volume receiving ≥4 Gy) and V30 Gy (in % and cm³) and mean breast dose (MBD, Gy) were extracted for both breasts to consider total BT at risk. Correlations between dose metrics, and with the target volume (CTV, cm³), were assessed using Pearson's correlation coefficient. Time trends were investigated using chi-square analysis of linear fit. <h3>Results</h3> 68 patients were available for analysis. 1 patient was excluded from % volume and MBD analysis due to truncated BT. MBD was strongly positively correlated with V4 Gy_% (r > 0.9) and moderately positively correlated with V4 Gy_cm³ (r = 0.8), V30 Gy_% (r = 0.5) and V30 Gy_cm³ (r = 0.5). Results suggest no decrease over time for V4 Gy_cm³ or V30 Gy_cm³ (linear regression coefficients of 12 and 0.4; both χ² > 1000). For the 63 patients with CTV available, weak positive linear correlation was seen between CTV and V4 Gy_cm³ (r = 0.2), MBD (r = 0.4), and V30 Gy_cm³ (r = 0.4). Large variations in breast dose were seen between patients (see table). <h3>Conclusion</h3> This is believed to be the first systematic retrospective evaluation of individual breast dose in modern HL RT. Despite increased awareness, our data gives no evidence of reduction in breast dose over time. The large variation in breast dose suggests individualized risk assessment and follow up strategies are needed. This data supports the importance of developing optimized screening strategies through initiatives such as the Breast screening After Radiotherapy Dataset (BARD). Our analysis suggests V4 Gy, V30 Gy and MBD cannot be considered independent. Until there is more evidence of the dose level associated with BC risk, it is recommended that all three are reported with V4 Gy and V30 Gy expressed in cm³ to consider total breast tissue at risk.