ESTRO 38 Abstract book

S600 ESTRO 38

There was no significant difference in outcomes for the three sites on subgroup analysis (Fig.1).

similar in both groups (LC 14%; HNC 9%), the deaths were higher in LC patients (19%). The schedule of RT treatment was 45-60 Gy (2-2.6 Gy/day, 5 days/week). Relative to control, both groups had significantly lower serum PON1 concentration, and arylesterase activity (p<0.001). We observed that after RT not only increased PON1 concentration in cancer patients but also arylesterase activity decreased. Intermediate density lipoprotein (IDL), triglycerides linked with different lipoprotein profiles and the VLDL particles size were significantly higher in cancer groups in comparison to control group. Whereas leucine, isoleucine, tyrosine, acetate, glutamine and formate metabolites were significantly lower in cancer groups, alanine, glucose and glutamate were significantly higher in the same groups. Only in HNC group showed significantly differences in glutamine and glutamate metabolites between before and after RT treatment. Conclusion Our study demonstrates that RT treatment can modulate anti-oxidant defense mechanisms and metabolites in cancer patients. These results could be useful as a biomarker to predict RT response and the prognosis of patients. PO-1080 Does hyperthermia clinically alter the α/β? Insights from thermoradiotherapy vs. radiotherapy trials N.R. Datta 1 , S. Bodis 1 1 Kantonsspital Aarau, Radio-Onkologie, Aarau, Switzerland Purpose or Objective Hyperthermia at 39-43°C is a known potent radiosensitizer, primarily due to its ability to radiosensitize hypoxic tumor cells and inhibit post radiation repair of the potentially lethal DNA damage. This should be expected to alter the α/β values of the linear- quadratic (L-Q) model. The present study has been carried out to clinically estimate the α/β from randomized studies of thermoradiotherapy (HTRT) vs. radiotherapy (RT) in recurrent breast (RBRT), head and neck (stages III/IV) (LAHNC) and cervix cancers (stages IIB-IVA) (LACC). Material and Methods Three r ecently published meta-analyses (2016) for HTRT vs. RT in RBRT, LAHNC and LACC, totaling 20 studies with 1,505 patients were evaluated for their complete response (CR). Only those studies with a specified RT dose (D), dose per fraction (d) and corresponding CRs in both groups were selected. Effect measures - odds ratio, risk ratio, risk difference (RD), tests for heterogeneity (I 2 ) and subgroup analysis were carried out for the included trials. The biological effective dose with RT (BED RT ) in these studies were individually computed using the L-Q equation without any time factor correction and assuming an α/β RT of 10 Gy for all sites. Since all trials had a positive outcome with HTRT over RT, the resultant enhanced thermoradiobiological BED for HTRT (BED HTRT ) was correspondingly computed as a product of the BED RT and %difference in CR between HTRT and RT. With the “D” and “d” of both HTRT and RT arms in each trial being similar, the α/β following HTRT (α/β HTRT ) was estimated as, α/β HTRT = Dd / (BED HTRT – D), derived from the L-Q model. Results 12 studies with 864 patients were shortlisted - RBRT (3 studies, n=259), LAHNC (5 studies, n=267) and LACC (4 studies, n=338). Mean RT dose was 53.4 Gy (SD: ±14.3) delivered in 2.2 Gy/fraction (SD: ±0.74). Mean temperature was 42.4°C (SD: ±0.9) and most patients received 2 sessions of HT per week for an average duration of 50 minutes, delivered mostly following RT. The overall risk difference of 0.28 was in favour of HTRT (p<0.001). Poster: Radiobiology track: DNA damage response

Mean BED RT was 64.7 Gy (SD: ±15.5) while the mean was estimated as 109.5 Gy (SD: ±32.1). The overall was 2.25 Gy (SD: ±0.79) and it revealed an inverse relation with the %improvement in CR with HTRT (r 2 : 0.71, p=0.001) (Fig.2). BED HTRT computed α/β HTRT

The α/β HTRT for RBRT, LAHNC and LACC were 2.05 Gy, 1.74 Gy and 3.03 Gy (p=0.027), reflecting a reduction in α/β by HTRT (range: 69.7% - 82%). On regression analysis, none of the treatment variables except %improvement in CR predicted for α/β HTRT (coeff: -0.74, p=0.001). Conclusion The reduction in the clinically estimated α/β HTRT corroborates with the in vitro studies. HT inhibits repair of RT induced DNA double strand breaks resulting in enhancing the β component of cell kill, consequently leading to a fall in α/β. This should be of practical use in optimizing RT time-dose-fractionation schedules with HT in the clinics. PO-1081 Biological interaction of a static magnetic field (SMF) with ionizing irradiation T. Schmid 1,2 , F. Hellmundt 2 , S. Lemmer 2 , K. Ilicic 1 , M. Melzner 2 , S. Bartzsch 1 , J.J. Wilkens 2 , S.E. Combs 1,2 1 Helmholtz Zentrum München, Institute of innovative Radiotherapy, Neuherberg, Germany ; 2 Klinikum rechts der Isar- Technical University of Munich, Radiooncology, Muenchen, Germany Purpose or Objective During the last decade there have been several technical developments in radiotherapy, like the development of integrated magnetic resonance imaging (MRI) in a linear accelerator. However, in literature the interaction of a static magnetic fields (SMFs) with radiation as part is still controversially discussed. Interactions could lead either to