ESTRO 2022 - Abstract Book

S336

Abstract book

ESTRO 2022

E. Gort 1 , J.C. Beukema 1 , M.J. Spijkerman-Bergsma 1 , M.L. de Vries-de Groot 1 , S. Both 1 , J.A. Langendijk 1 , W.P. Matysiak 1 , C.L. Brouwer 2 1 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands; 2 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands Purpose or Objective When treating cervical cancer patients with VMAT, due to sensitivity to inter-fraction motion, adaptive strategies could be required to maintain target coverage. Manual segmentation of CTV and OARs on repeat-CT scans (reCTs) is time consuming and may delay decisions whether to perform plan adaptations. Our aim was to investigate differences in clinical decisions for re-planning based on manual vs automated dose accumulation. Materials and Methods Twelve cervical cancer patients were included in a prospective study undergoing 5 weekly reCTs. The primary and para- aortic lymph node target and OAR volumes were manually segmented on all CTs. Clinical re-planning was performed for 3 patients. Two-arcs VMAT plans for 25 fractions of 1.8 Gy were made on the planning CT scan (planCT) and recalculated as well as robustly evaluated on the reCTs [1]. Deformable hybrid intensity and structure based image registrations were performed using the manually segmented GTV, vagina, uterus and lymph nodes CTV as controlling ROIs (DIR_manual) and without controlling ROIs (DIR_automated). The target and OAR contours were warped using DIR_automated and resulting automated versus manually segmented dose and volume differences were evaluated. The voxelwise minimum (vox min) reCT doses were warped to the planCT using DIR_manual and DIR_automated, and the different accumulated doses were compared, where the criterion for acceptable coverage was ITV D98 > 95%. Results Manual vs automated segmented vox min lymph nodes D98 (Gy) at reCTs showed a significant difference (Table 1). For the other target volumes no significant dose differences were found. Regarding OAR doses, only bowel bag Dmean (Gy) showed a significant difference. Manual vs automated segments showed only a good concordance for lymph nodes, bone marrow and sacrum (concordance index ≥ 0.8). For 7 patients, conclusions on accumulated vox min D98 ITV target coverage were identical using DIR_automated vs DIR_manual. For 2 patients, DIR_manual showed correctly that ITV coverage was not maintained in contrast to using DIR_automated (Figure 1A, marked circular). For 1 patient’s evaluation, ITV coverage was correctly maintained using DIR_manual in contrast to using DIR_automated. Out of 10 clinically re-planned reCTs, manual in contrast to automated segmentation showed correctly that individual coverage was not maintained for 4 GTV and vagina, 3 uterus and 2 lymph nodes target volumes (Figure 1B, marked circular). The ratio between automated vs manual segmented OAR volumes (cc) was close to 1 for all OARs, except for bladder and rectum (Figure 1C). Automated contour warping of the bowel bag resulted in underestimation of the DVH (Figure 1D).