ESTRO 2023 - Abstract Book

S967

Digital Posters

ESTRO 2023

Aalst, Belgium; 8 Limburgs Oncologisch Centrum, Jessa Hospital and Ziekenhuis Oost-Limburg, Radiation Oncology, Hasselt and Genk, Belgium Purpose or Objective In the multicentric, prospective phase 2 randomized SEMIRAHN study (NCT04688528), sentinel lymph nodes (SLNs) are identified on 3-dimensional single photon emission computed tomography (SPECT)/computed tomography (CT) images to individually tailor the elective nodal irradiation (ENI) volume of head and neck squamous cell carcinomas (HNSCC). As a part of the mandatory patient-based radiotherapy (RT) dummy run, each center must handle SPECT/CT images. The aim is to test the ability to read, interpret and transfer the SLN drainage information to the selection and delineation of the ENI clinical target volume (CTV). Materials and Methods The anonymized data of a patient with a cT1N0M0 left hypopharyngeal SCC, treated in a previous RT study with SLN identification for ENI, were securely sent to the 7 participating centers. It encompassed the description of the clinical case, the description of the endoscopic examination, the simulation CT slices after iodine contrast injection and the hybrid SPECT/CT images after 99mTc-labelled nanocolloid endoscopic injection around the tumor and migration into the SLNs. Each local radiation oncologist (RO) and nuclear medicine specialist were asked to process the SPECT/CT images on the local infrastructure and to report all identified SLNs by decreasing order of activity and localization in the neck (level and laterality). Each RO was asked to delineate a mandatory list of organs at risk, the primary CTV and the ENI CTV (named “CTVn-LS”) encompassing the nodal levels containing up to the 4 hottest SLNs on the slices of the simulation CT. We report here the results of the SPECT/CT reading and its impact on the selection of the CTVn-LS levels. Results No center reported problems to read the SPECT/CT images. Four SLNs were identified by 5 centers (in levels 2 right (R), 2 left (L), 3L and 2L; by decreasing order of activity). Two centers did not identify the SLN in level 2L showing a low activity (about 10% of the SLN in level 2R with maximal activity, and about twice the background activity). All centers selected levels 2L, 3L and 2R for the CTVn-LS, and 1 center added level 5L (because of 3rd SLN in level 3L at its very posterior edge). Conclusion All centers could Identify and locate the 3 most active SLNs on the SPECT/CT images, and transfer the information to delineate the CTVn-LS on the slices of the simulation CT. One SLN with a very low activity was missed by 2 centers, showing that images saturation display and/or subjective interpretation of the images play a role. O. Nouri 1 , W. Mnejja 1 , F. Dhouib 1 , S. Zouari 1 , I. Charfeddine 2 , A. Khanfir 3 , W. Siala 1 , T. Sahnoun 1 , L. Farhat 1 , N. Fourati 1 , J. Daoud 1 1 Habib Bourguiba Hospital, Radiotherapy and oncology, Sfax, Tunisia; 2 Habib Bourguiba Hospital, Oto-Rhino-Laryngology, Sfax, Tunisia; 3 Habib Bourguiba Hospital, Medical Oncology, Sfax, Tunisia Purpose or Objective Intensity modulated radiation (IMRT) technique, associated with induction chemotherapy (IC) and/or concomitant chemotherapy (CC) is actually the recommended treatment modality for nasopharyngeal carcinomas (NPC). The aim of this study was to evaluate the loco regional relapse (LRR) rates and their patterns of relapse with this treatment protocol. Materials and Methods A retrospective study of 145 patients with NPC treated between June 2016 and July 2021. All patients received IMRT with integrated simultaneous boost (SIB) of 33 daily fractions at a dose of 69.96 Gy for high-risk volume, 60 Gy for intermediate risk volume and 54 Gy for low-risk volume. High risk volume dose was 66.5 Gy in children. For patients presenting a LRR, the CT scan showing the recurrence was merged with the initial dosimetric CT scan and the macroscopic volume of the recurrence was contoured (GTVr). An evaluation of the V95% received by the GTVr was made by reproducing the initial dosimetry on the new scanner. Thus, we have defined 3 situations: a recurrence “on the primary site” (V95% ≥ 95%), a “marginal recurrence” (20% ≤ V95% <95%) and an “out of field” recurrence (V95% <20%). Survival analysis was performed according to Kaplan-Meier method and Log-rank test was used to compare factors that may influence loco regional free survival (LRFS). Cox regression method was used for multivariate analyses. Results Median age was 48 years (11-80) with a sex ratio of 2.9. One hundred-twenty tumors (82.7%) were classified as stages III-IV according to the 2017 UICC TNM classification. Ten patients (6.9%) were metastatic at diagnosis. One hundred-thirty-five patients (93.1%) received IC and 138 (95.2%) received CC. After a median follow up of 48 months (24-83), 17 patients (11.7%) experienced LRR after a median of 18 months (6-43). Three years LRFS was 88.1%. A metastatic relapse was also noted for 5 of these patients (29.4%). Ten relapses (58.8%) were on the primary site, five (29.4%) were marginal and two pretragian relapses (11.7%) were “out of field”. Factors predicting LRR were a consultation delay of 6 months or more (p=0.042), histologic type other than undifferentiated (UCNT) (p<0.0001), a delay more than 14 days starting IC (p=0.029), number of CC courses (less than 4, p=0.013; less than 5, p=0.032, less than 6, p=0.05) and a total cumulative cisplatin dose < 380 mg/m ² (p=0.004). UICC TNM classification did not impact LRR. In multivariate analyses, histology other than UCNT (p=0.003) and total cumulative cisplatin dose (p=0.002) were significant prognosis factors of LRR. Conclusion For nasopharyngeal carcinoma, tumors with histologic type other than UCNT and that receive a low cumulative cisplatin dose, have a higher risk of LRR. Therefore, they require a more aggressive therapeutic approaches and a suitable monitoring protocol. PO-1210 Intensity modulated radiotherapy of nasopharyngeal carcinomas: locoregional failure patterns