Abstract Book

S1260

ESTRO 37

Results Our results show in two subpopulations of HNSCC-CSCs that photon irradiation increases migration and invasion capabilities while carbon ions decrease these metastatic processes. In addition, under hypoxic conditions, the increase in the migration/invasion observed in response to photons is abrogated while the C-ion irradiation decrease the migration/invasion capacities in non-CSC and CSCs subpopulations under normoxic and hypoxic conditions. In order to demonstrate the key role of HIF- 1α in the metastatic process in response to both type of radiation, the main signaling pathways conditioning the activation of HIF-1α (Akt/mTOR, STAT3 and MAPK) were studied in response to photon and C-ion irradiations under normoxic and hypoxic conditions. Compared with photons in which the 3 signaling pathways are activated, C-ion irradiation significantly decreases the signal transduction of these pathways leading to HIF-1α expression and then invasion/migration. Conclusion Our work has thus confirmed the key role of HIF-1α in the invasion-migration processes depending on the type of irradiation but also has contributed to identify a part of the underlying molecular mechanism under hypoxic conditions approaching the tumor microenvironment. EP-2282 Is radiobiologically better dose fractionation possible in head and neck radiotherapy? V.M. Gurusamy 1 , M. Ali 1 , Y. Bayoumi 1,2 1 King Fahad Medical city, Radiation oncology, Riyadh, Saudi Arabia 2 NCI-Cairo University, Radiation oncology, Cairo, Egypt Purpose or Objective Aim of these radiobiological calculations was to find out a better radiotherapy schedule for head and neck cancers in this Intensity modulated radiotherapy (IMRT) era. Material and Methods It has been shown that accelerated repopulation during radiotherapy treatment starts after 3 weeks of starting of radiotherapy, and it has been calculated that the dose increment of 0.6 Gy per day is needed to counteract the accelerated repopulation when radiotherapy is delivered more than 25 days. A new radiation schedule was proposed with 30 Gy in 15 fractions for first three weeks then 39 Gy in 15 fractions in 2.6 Gy per fraction radiotherapy. This extra 0.6 Gy per day would counteract tumour repopulation which is essential for effective tumor control. Four radiobiological parameters were analysed to evaluate this new schedule and were compared with clinically proven, standard radiotherapy schedules. 1.BED was calculated as follows BED=nd(1+d/α/β)- 0.693x(T-Tk)/ α x Tp Here, n = number of fractions per day, d= dose per fraction, α/β ratio = 10 for tumours, α = 0.35, Tk = tumour repopulation kick off time chosen as 21 days and Tp=3 days Electronic Poster: Radiobiology track: Radiobiology of head and neck cancer

4. Acute mucosa BED was calculated as follows: Acute mucosa BED Gy=nd(1+d/α/β)- 0.693x (T-Tk)/ α x Tp. Here Tk = mucosal repopulation kicks off time chosen as 7 days and Tp=2.5 days. Results BED, EQD doses and acute mucosal BED of different radiotherapy schedules in head and radiotherapy are displayed in Table no 1 for comparison.

To tal do se

Ove rall tim e

Acu te muc osa

Late complic ations

Fractio nation

Tum our

Schedule

BED

Time corre cted

EQD EQD

BED

Day s

Gy1 0/2

Gy1 0

Gy

Gy10

Gy3/2

Standard fractionati on Hyperfract ionation

2 Gy x 35

52.3 2

70 47 66.84 70 70

81. 6

1.2 Gy x 68 1.8 Gy x 30+1.5 Gy x 15 Gy x35, 6 days per week 2.25 Gyx 31 Gy x15+2.6 Gy x15 2 2

76.1 5

60.5 0

46 74.89

68.40

70.3 5

58.2 8

Concomita nt boost

67.90

72 40 71.88

Accelerate d radiothera py

57.8 6

70 40 71.46 70 70

56.9 2

Accelerate d IMRT

69. 75

43 70.9 71.2 73.05

70.9 5

59.0 0

Proposed IMRT

69 40 72.60

73.53

Conclusion These calculations have proven that a radiobiological modelled radiotherapy in head and neck cancers is feasible without any major complications. However, we need more research and clinical trials before implementing in clinical practise. EP-2283 Squamous cell carcinoma of the head and neck: a low α/β when treated with synchronous cisplatin? A. Hartley 1 , J. Best 1 , C. Fong 1 , H. Benhiat 1 , H. Mehanna 2 , J. Glaholm 1 1 Queen Elizabeth Hospital Birmingham, Hall-Edwards Radiotherapy Research Group, Birmingham, United Kingdom 2 University of Birmingham, InHANSE, Birmingham, United Kingdom Purpose or Objective The effect of synchronous chemotherapy in squamous cell carcinoma of the head and neck (SCCHN) has been modelled as additional Biologically Effective Dose (BED) or as a prolonged tumour cell turnover time during accelerated repopulation. Such models do not accurately predict the local control seen when hypofractionated accelerated radiotherapy is used with synchronous chemotherapy.

2. Tumour EQD was calculated as follows: Tumour EQD Gy 10/2= nd(1+d/α/β)/ 1.2. Here α/β ratio = 10.

3. Late complications EQD was calculated as follows: Late complications EQD Gy3/2 = nd(1+d/α/β)/ 1.67. Here α/β ratio = 3.