ESTRO 37 Abstract book

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ESTRO 37

adjacent normal tissues. The strict eligibility criteria of these trials raised important controversial issues concerning the appropriateness of HF-WBI for all breast cancer subtypes. Some uncertainties about the effectiveness of HF-WBI in aggressive tumor features or in young patients have slowed down the adoption of HF- WBI. ASTRO, ESTRO and NICE guidelines claimed the applicability of a moderate hypofractionation ( 2-3 Gy per fraction) for most patients with early breast cancer, recognizing the positive impact on social, economic and psycological aspects. In fact, considering the analysis of the cost-effectiveness of these treatments, HF-WBI should be preferred over CF-WBI, for a higher quality of life and lower costs. However, hypofractionation still meets with resistance and is adopted in varying degrees in clinical practice. Apart from controversies regarding tumor and patient sensitivity, concerns about tolerability of normal tissues might also be contributing to limit its utilization. Most ROs consider evidence still unsufficient to routinely adopt hypofractionation for regional node irradiation, even though in the only one neurologic injury in the arm receiving 41.6 Gy was reported. Admittedly, the randomized studies do not have a follow-up sufficiently long to allow a reliable assessment regarding cardiac toxicity. In addition, left- sided breast cancers very often require a certain level of technical complexity to minimise heart irradiation, especially in women with concomitant risk factors, and in this context the use of hypofractionation is considered an additional problem.In addition, HF-WBI is preferably delivered to small-moderate breast size, since large breast size may be more penalised by the so called “triple trouble” phenomenon, increasing the risk of fibrosis. Investigators from Spain highlighted how ROs were more likely to give HF-WBI to very old women, since elderly were deemed to be at lower risk of developing toxicity, being near the end of their lifespan.As a matter of fact, in most hypofractionated schedules, the total dose calculated in EQD2 (that is equivalent total dose delivered in 2 Gy fractions) is slightly reduced that that of CF-WBI. As Yarnod and coll. stated, a small decrease in total dose allows greater decrease in normal tissue toxicity under the acceptable compromise of local control. Therefore, hypofractionation should be gentler to normal tissue than conventional fractionation. Nevertheless, especially in case of very shortened hypofractionated schemes, the target population consists mostly of the elderly. Five fractions with high dose per fraction given once per week have been tested in several series, mainly including patients of advanced age or with co-morbidities. Only the UK FAST trial enrolled patients starting from the age of 50.There is a great variability in adopting hypofractionated schedules across countries and within the same country. These differences are due to different interpretation of the existing results and to a sort of reluctance and caution in the use of new schemes. While it is understandable to wait for more mature results in case of extreme forms of hypofractionation, there are few reasons not to apply moderate hypofractionation in almost all breast cancers. Three of the four randomized studies included early- and intermediate-stage breast cancer with a long follow-up. Of course, there might be several other reasons which contribute to slow adoption of hypofractionation. As part of the "Choosing Wisely" campaign by the American Board of Internal Medicine, aimed at avoiding unnecessary costs, ASTRO invited ROs to always consider HF-WBI in women aged over 50 with early breast cancer conservatively treated. Updated clinical guidelines could help to spread and homogenise hypofractionation.

Symposium: What is the limit of hypofractionation?

SP-0652 Extreme hypofractionation for prostate cancer: is single fraction a future? P. Blanchard 1 1 Institut Gustave Roussy, Radiation Oncology, Villejuif, France Abstract text The most widely used regimen for external beam radiotherapy for prostate cancer is a conventional fractionation schedule that spans over around eight weeks. But it has been suggested that prostate cancer is sensitive to high doses per fraction. In the recent years, large scale randomized trials have demonstrated the non- inferiority of moderately hypofractionated regimen, using typically 20 fractions of 3 Gy and hence cutting treatment duration by half. In the meantime, non- randomized studies have suggested the safety and efficacy of more severe hypofractionation regimens for low and intermediate risk patients using stereotactic body radiotherapy, with schedules typically using 5 fractions. The brachytherapy data, especially using high dose rate, have long demonstrated the efficacy of very hypofractionated schedules, which can typically use between two and five fractions for HDR brachytherapy. Many investigators are now embarking on the single fraction path, both using external beam and brachytherapy. However the adequate dose is yet to be defined and the efficacy/toxicity ratio of these single fraction regimens are to be tested in prospective trials. The goal of this talk is to discuss the rationale supporting extreme hypofractionation for prostate cancer, and to present recent results and ongoing trials that will soon support or invalidate this treatment option. SP-0653 Hypofractionation for breast cancer: 30, 15 or 5 fractions? M.C. Leonardi 1 , A. Morra 2 , S. Dicuonzo 2 , M. Gerardi 2 , V. Dell'Acqua 2 , D. Rojas 3 , A. Surgo 2 , S. Arculeo 3 , A. Casbarra 3 , C. Arrobbio 3 , R. Spoto 2 , F. Cattani 4 , R. Orecchia 5 , B. Jereczek Fossa 3 1 Leonardi Maria Cristina, Division of Radiotherapy, Milan, Italy 2 European Institute of Oncology, Division of Radiotherapy, Milan, Italy 3 European Institute of Oncology, Division of Radiotherapy and University of Milan, Milan, Italy 4 European Institute of Oncology, Division of Physics, Milan, Italy 5 European Institute of Oncology, Scientific Directorate, Milan, Italy Abstract text Since the early eighties interest in altered schedules for postoperative whole breast radiotherapy (WBI) has become considerable, in order to ease the burden of 5-7 weeks of treatment, even though the fractionation sensitivity of breast tumors was deemed to be high at that time (alfa/beta of 10 Gy), and, therefore, relatively insensitive to high dose per fraction. Four randomized trials (the Royal Marsden Hospital/ Gloucestershire Oncology Centre, the UK Standardisation of Breast Radiotherapy START A and B and the Canadian trials), all completed between 1986 and 2002, have pioneered and supported hypofractionation (HF-WBI) in breast cancer. The 10-year results of the above mentioned randomized studies have shown the equivalence in local control and tolerance between hypofractionated and conventional schedules. Amazingly, these studies have drawn the conclusion that breast cancer has an unexpected low alfa/beta of 3.5 Gy, which is similar to that of the