Deintensification of Radiotherapy Use in Treatment of Ductal Carcinoma In Situ in the Netherlands–A Nationwide Overview From 2008 Until 2022

Aims: Ductal Carcinoma In Situ (DCIS) treated by breast-conserving surgery followed by radiotherapy aims to decrease the probability of locally recurrent disease. The role of whole breast irradiation, specifically in DCIS having low recurrence risk and low risk of becoming invasive, is increasingly debated. Also, the added value of applying boost irradiation in DCIS has been questioned. Hence, we evaluated the nationwide radiotherapy use in DCIS treatment in the Netherlands. Materials and Methods: Women diagnosed with DCIS in 2008–2022 were identified in the Netherlands Cancer Registry. Their primary treatment was presented over time and for age groups, stratified for DCIS grade I-II and III. Factors associated with radiotherapy use after breast-conserving surgery and boost irradiation use in whole breast irradiation after breast-conserving surgery were identified. Results: In women with DCIS grade I-II (N = 16,653), the use of breast-conserving surgery without radiotherapy increased from ∼11% in 2008–2013 to ∼26% in 2017–2022. Furthermore, post-breast-conserving surgery radiotherapy increasingly concerned whole breast irradiation without a boost or partial breast irradiation. Moreover, surgery was omitted more often in recent years (30% in 2022). In DCIS grade III (N = 13,534), the use of breast-conserving surgery without radiotherapy only slightly increased in the most recent years in older patients, while boost irradiation was increasingly omitted. Whole breast irradiation and boost irradiation following breast-conserving surgery were more often applied in case of a higher risk of recurrences: young age, larger lesions, or irradical resection. Variation was observed for hospital-characteristics but not for regions. Conclusion: In DCIS, the process of omitting breast irradiation after breast-conserving surgery is clearly ongoing. Boost irradiation was administered less frequently. Furthermore, the use of partial breast irradiation was introduced in recent years. These effects are more prominent in older women and those with grade I-II DCIS.