Accelerated Partial Breast Irradiation: Dosimetric Parameters and Patient-Reported Outcomes of Acute Toxicity

Abstract

Accelerated partial breast irradiation (APBI) following breast conserving surgery offers a convenient and well-tolerated adjuvant radiotherapy option in comparison to whole breast irradiation. While several APBI regimens exhibit excellent disease control among appropriately selected patients, patient-reported outcomes and toxicity assessments may vary. We sought to describe patient-reported acute toxicity as a function of salient dosimetric parameters, during and after an APBI regimen of 40 Gy in 10 once-daily fractions.From June 2019 to July 2020 patients undergoing APBI were assigned a weekly, response adapted, PRO-CTCAE-based acute toxicity assessment. Symptoms assessed included pain, fatigue, breast enlargement, skin toxicity, and psychosocial concerns. Patients reported acute toxicity during treatment, and for up to 8-weeks following treatment. Socio-demographic characteristics and dosimetric treatment parameters were collected. Descriptive statistics were used to summarize patient-reported outcomes and corresponding dosimetric measures.Overall, 55 patients who received APBI (40 Gy in 10 fractions administered once-daily) completed more than one assessment during or after treatment. A total of 351 assessments were included in this analysis. Median patient age was 59 (range 37-78), and median planning target volume (PTV) was 210cc (range 64-580cc). Median PTV:ipsilateral breast volume ratio was 0.17 (range 0.05-0.44) and median maximum hotspot dose was 112% (range 108-115%). Breast V20 Gy ranged from 16% to 65% with a median of 45%. When queried weekly, 22% of patients reported moderate breast enlargement at least once, occurring at a median of 3 weeks after the initiation of treatment. More commonly, 71% reported maximum skin toxicity of moderate to very severe (42% moderate, 22% severe, 5% very severe) arising at a median of 3 weeks after the initiation of treatment. Furthermore, 70% of patients reported maximum fatigue as moderate to severe (42% moderate, 15% severe), and 44% patients reported maximum pain in the radiated area as moderate to very severe. Median time to first report of any moderate to very severe symptom was 10 days (IQR 6-27 days). By 8 weeks following APBI, 9 patients (16%) reported residual moderate symptoms and none endorsed severe or very severe symptoms.Weekly assessments during and after APBI revealed that several patients experienced severe or very severe toxicities by their estimation, but that these universally resolved by 8 weeks following treatment at which point a minority endorsed moderate symptoms. Depending on toxicity type, peak effect could be noted as early as 1 week from the initiation of treatment for fatigue, or as late as 4 weeks for skin toxicity. More comprehensive evaluations among larger cohorts will help to define the precise dosimetric parameters that correspond to each outcome of interest.