Abstract P1-15-07: Simultaneous integrated boost incorporated into a hypofractionated regimen using tomoDirect: Acute toxicity assessment

Aim: We report on acute toxicity, which is the secondary endpoint of a phase II clinical trial specifically addressed to assess the chronic toxicity of a hypofractionated scheme including a simultaneous integrated boost, with intensity modulated radiotherapy. Materials and methods: From 2/2012 to 12/2013 194 patients with early breast cancer entered a phase II study on hypofractionated radiotherapy including a boost dose to the tumor bed. All patients were operated on conservatively. The whole breast and the tumor bed are planned to receive a dose of 45 Gy and 50 Gy, respectively, in 20 fractions, over 4 weeks. Treatment plans are generated using the TomoDirect modality,which is available on Tomotherapy Hi-Art System (Madison,WI). Acute toxicity was evaluated according to the RTOG acute toxicity scale, up to 6 months after the treatment. Afterwards, chronic toxicity is evaluated using LENT/SOMA scale. Results: 95% of the volume of the breast and boost PTVs received 99% and 100% of the planned dose, as median values, respectively and 0.1% (median value) of the entire breast volume received 100% of the boost dose. The median maximum dose to the breast and to the boost PTVs was 113% and 103.3 %, respectively. At the end of treatment, the acute toxicity, was distributed as follows. As far as erythema was concerned, at the end of treatment, 58% of the patients experienced grade 1 erythema, which dropped to 23% one month later. Grade 2 erythema affected 37% of the cases, and after one month, it decreased to 2%.Only 1 patient (0.5%) complained of Grade 3 erythema at the end of the treatment, which rapidly disappeared afterwards. With regard to breast oedema, at the end of treatment grade 1 was observed in 16% of the cases, for whom it tended to remain stable after one month, while grade 2 oedema was noted in 4% of the cases, decreasing to 1.5% on the first month- follow-up visit. Regarding desquamation, dry desquamation ( grade 1) was observed in less than 10% of cases at the end of treatment, but it tended to increase to 17% one month later. Patchy moist desquamation (grade 2) was present in 1.9% of the patients at the end of radiotherapy, and in 1% of them, one month afterwards. Confluent desquamation (grade 3) was noted only in 1 patient (0.5%), who was receiving concomitant chemotherapy with cyclophospamide, methotrexate and fluoruracil: it was still present 1 month after the radiotherapy completion, as the patient continued to be on chemotherapy. No significantly different side effects were observed between the whole breast and the boost area. No patients experienced any lung and cardiac symptoms. Conclusion: The clinical results of this SIB hypofractionated scheme showed low acute toxicity. In spite of the high dose per fraction, with the tumor bed receiving an even higher dose /per fraction, acute toxicity was within the limit acknowledged by literature for conventional fractionation. This non-rotational treatment option allows us to deliver treatment with a traditional tangent-like dose, without spreading low doses to the adjacent structures. Chronic toxicity will be assessed after 2 years. Therefore, a longer follow-up is needed to assess the effective tolerance to the SIB schedule. Citation Format: Maria Cristina Leonardi, Anna Morra, Federica Cattani, Luigi Santoro, Samantha Dicuonzo, Raffaella Cambria, Rosa Luraschi, Alessia Bazani, Roberta Lazzari, Veronica Dell'Acqua, Roberto Orecchia. Simultaneous integrated boost incorporated into a hypofractionated regimen using tomoDirect: Acute toxicity assessment [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-15-07.