ESTRO 2023 - Abstract Book

S1785

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ESTRO 2023

PO-2011 Dosimetric correlates and acute toxicity for localized prostate cancer in hypofractionated schedules

J. GARRE CRISTAU 1 , X. Maldonado 2 , M. Altabas 3 , D. Sanchez 4 , M. Hermida 5 , A.A.A. Geng 2 , E. Recalde 2 , J. Giralt 2

1 HOSPITAL VALL D'HEBRON, RADIATION ONCOLOGY, BARCELONA, Spain; 2 Hospital Vall d'Hebron, Radiation Oncology, Barcelona, Spain; 3 Hospital Vall d'Hebron, Radiation Oncolgy, Barcelona, Spain; 4 Hospital Vall d'Hebron, Physics and Radiation Protection Department, Barcelona, Spain; 5 Hospital Vall d'Hebron, Physics and Radiation Protection Department , Barcelona, Spain Purpose or Objective To assess and compare the dosimetric correlates as well as ≥ grade 2 acute toxicity rates after two schemes of moderate hypofractionated radiotherapy for localized prostate cancer. To validate our critical organ dose constraints designed in terms of isotoxicity. Materials and Methods A total of 80 patients with localized prostate cancer (T1-T3N0M0) were treated with VMAT technique and IGRT (CBCT or fiducial markers triggered with kV images). All patients used androgen deprivation. Patients received a hypofractionation (HF) 60-62 Gy in 20 fractions (n=38), or moderate hypofractionation (MHF) 72 Gy in 30 fractions (n=42). CTVs were contoured according to the CHHIP clinical trial guidelines in HF. Acute toxicity was graded according to CTCAE 4.0. In order to compare dosimetric data we converted nominal doses in EQD2. The χ² test and t-student test were used to compare baseline characteristics of the two populations and the overall worst degree of toxicity. Two-tailed t-test of the two independent samples was calculated to compare dosimetric parameters with a significance level of p<0.05. In addition, a multivariate regression analysis was performed in pursuance of identifying dosimetric correlations which could predict acute toxicity. Results There weren’t statistical differences in patients characteristics between populations except clinical T (T1 78% in the HF group and 21% in the MHF group, p=0.024). Median age was 74 years old (p=0.24), 30% presented diabetes(p=0.9), 24% on oral anticoagulants (p=0.36), with an ISUP 2/3 grade in 71% of patients (p=0.61), median PSA 11 ng/ml (p=0.2). Use of ADT for 6 month in 35% and 24 month in 33% (p=0.75). IPSS score from 8-19 in 49.4% (p=0.53). Main acute GU and GI toxicity were grade 1-2 with no grade 3-4. Acute G2 GU toxicity was more frequent in MHF (10%) than in HF (4.7%) (p=NS). Regarding acute GI toxicity it has been mild with no grade 2, 3 or 4. No statistically significant differences between groups were observed in the PTV volume (cm3) (p=0.98) and OARs (bladder, rectum (cm3) p=0.97, p=0.069 respectively). In terms of EQD2 for rectal and bladder constraints, we observed statistical differences in favour of the HF group which are shown in Table 1 and 2. We have not found statistically significant dosimetric cut-off values in the multivariate regression analysis as toxicity predictors. Table 1.

Table 2.