ESTRO 38 Abstract book

S717 ESTRO 38

implement DIBH (deep inspiration breath hold) techniques and formally assessed set up margins with the use of daily imaging to allow us to reduce the current 1cm PTV margin to SCF, and improve dose constraint conformity. EP-1310 Toxicity evaluation of a hypofractionated WBRT with SIB for breast cancer using TomoDirect S. Dicuonzo 1 , M.C. Leonardi 1 , S. Raimondi 2 , E. Miglietta 1 , M.A. Gerardi 1 , A. Morra 1 , V. Dell'Acqua 1 , A. Surgo 1 , D.P. Rojas 1 , F. Pansini 3 , R. Luraschi 3 , F. Cattani 3 , C. Fodor 1 , P. Veronesi 4,5 , R. Orecchia 6 , B.A. Jereczek-Fossa 1,5 1 European Institute of Oncology, Division of Radiation Oncology, Milan, Italy ; 2 European Institute of Oncology, Department of Epidemiology and Statistics, Milan, Italy ; 3 European Institute of Oncology, Unit of Medical Physics, Milan, Italy ; 4 European Institute of Oncology, Division of Breast Surgery, Milan, Italy ; 5 University of Milan, Department of Oncology and Hemato-oncology, Milan, Italy ; 6 European Institute of Oncology, Scientific Directorate, Milan, Italy Purpose or Objective To report tolerance of whole-breast radiotherapy (WBRT) with a simultaneous integrated boost (SIB) to the tumor bed (TB) using hypofractionated schedule delivered with intensity-modulated radiotherapy (IMRT) by means of Tomotherapy (Accuray Inc., Sunnyvale, CA) in Direct modality. Material and Methods A prospective cohort of patients with early breast cancer, operated on with breast conserving surgery, received 15- fraction schedule consisting of 40.05 Gy (2.67 Gy/fraction) to the whole breast and 48 Gy SIB (3.2 Gy/fraction) to the TB over the period 2013-2017. The purpose of this analysis was to evaluate acute and intermediate toxicity assessed at the end of radiotherapy (RT) and within 6 months after RT, according to RTOG scale, and at 12 months using the LENT-SOMA scale, alongside cosmesis based on the Harvard criteria. McNemar’s test was used to compare any grade of toxicity, while univariate and multivariate analysis were used to examine predictive factors for severe toxicity at any time. Results Two hundred and eighty-three patients were analyzed. Acute toxicity was recorded at the end of RT for all patients and in 183 women within the next 6 months: Grade 2 toxicity occurred in 34% and 25% of the patients, respectively (Table 1). No Grade>2 was reported. A significant reduction of any grade toxicity was observed between the end of RT and the first assessment within the 6-month period (median time 3 months). At univariate analysis, age <40 years, breast volume >1000 cm 3 and D max ≤115% of prescription dose were predictive factors of severe (Grade≥2) acute toxicity. At multivariate analysis, only age and breast volume were confirmed as predictive factors, with Relative Risks (95% Confidence Intervals): 2.02 (1.13-3.63) and 1.84 (1.26-2.67), respectively. Twelve-month toxicity was available in 113 patients, who showed Grade 0-1 toxicity in 54% of cases (Table 2). Cosmetic evaluation, performed in 102 pts, revealed good- excellent outcome in 86% of the population.

plans and which OAR (organ at risk) dose constraints were most at risk of compromise. Material and Methods With the ARIA System we identified all patients who had radical 3DCRT for breast cancer from March 2017 to March 2018. All plans were peer reviewed, each with their respective PTV and OAR doses and volumes documented. The standards set were by Trust guidelines derived from the RTOG, ESTRO and RCR consensus target volume delineation for breast cancer. Results A total of 228 3DCRT breast treatments were planned. 88 (38.6%) plans were non-conformal, with 165 OAR dose constraint occurrences. All 26 (100%) breast plans that included the SCF (supra- clavicular fossa) (Breast +SCF +/-Boost) breached OAR dose constraints: 100% exceeded optimal V18Gy dose constraints whilst 80.8% exceeded mandatory V18Gy dose constraints. The mean ipsilateral lung dose of these 26 Breast +SCF plans was 8.76Gy, exceeding mean dose constraint set at <7.5Gy; and the mean ipsilateral V18Gy volume was 19% (mandatory dose constraint <15%). However five of the Breast +SCF +/-Boost plans that did not exceed mandatory OAR dose constraints also did not achieve optimal PTV coverage either (mean PTV95 breast: 92.1% coverage). Treatment plans that included a boost (Breast + Boost) also had higher rates of OAR non-conformity. Right Breast +Boost: 47.3% compared to 20% of right Breast only plans; Left Breast +Boost: 40% compared with 21.6% of left Breast only plans. Ipsilateral lung was the most non-conformal OAR dose constraint, with V18Gy exceeding tolerances in 33.3% of 3DCRT plans. The mean lung dose exceeded tolerances in 24.9% of 3DCRT plans.

Conclusion Indubitably, the more radiotherapy that is delivered, the greater the risk of OAR dose constraint non-conformity. Concerning radical 3DCRT breast treatment plans, those necessitating an SCF field or boost will exceed constraints, despite greater allowances provided to achieve optimal PTV coverage. Thus are we asking too much of radiotherapy planning in achieving optimal PTV coverage, and should we consider planning margins to be tighter or relax dose constraints to OAR. On reflection, no patient who exceeded mandatory OAR dose constraints, namely ipsilateral lung V18Gy and mean lung dose, have encountered any pulmonary toxicity to date (range 9 months to 3 weeks), however we do plan to introduce pulmonary toxicity on post radiotherapy follow up assessment systemic questioning. Furthermore, we plan to