A clip-based protocol for breast boost radiotherapy provides clear target visualisation and demonstrates significant volume reduction over time.

Introduction The clinical target volume ( CTV) for early stage breast cancer is difficult to clearly identify on planning computed tomography ( CT) scans. Surgical clips inserted around the tumour bed should help to identify the CTV, particularly if the seroma has been reabsorbed, and enable tracking of CTV changes over time. Methods A surgical clip-based CTV delineation protocol was introduced. CTV visibility and its post-operative shrinkage pattern were assessed. The subjects were 27 early stage breast cancer patients receiving post-operative radiotherapy alone and 15 receiving post-operative chemotherapy followed by radiotherapy. The radiotherapy alone ( RT/alone) group received a CT scan at median 25 days post-operatively ( CT1rt) and another at 40 Gy, median 68 days ( CT2rt). The chemotherapy/ RT group (chemo/ RT) received a CT scan at median 18 days post-operatively ( CT1ch), a planning CT scan at median 126 days ( CT2ch), and another at 40 Gy ( CT3ch). Results There was no significant difference ( P = 0.08) between the initial mean CTV for each cohort. The RT/alone cohort showed significant CTV volume reduction of 38.4% ( P = 0.01) at 40 Gy. The Chemo/ RT cohort had significantly reduced volumes between CT1ch: median 54 cm³ (4-118) and CT2ch: median 16 cm³, (2-99), ( P = 0.01), but no significant volume reduction thereafter. Conclusion Surgical clips enable localisation of the post-surgical seroma for radiotherapy targeting. Most seroma shrinkage occurs early, enabling CT treatment planning to take place at 7 weeks, which is within the 9 weeks recommended to limit disease recurrence. [ABSTRACT FROM AUTHOR]