ESTRO 2020 Abstract book

S496 ESTRO 2020

volume was 13.11 ± 11.77 ml compared to 16.58 ± 22.42 ml in the group with disease specific mortality (P-value = 0.794). In the group without disease recurrence, the mean tumor volume was 14.31 ± 12.69 ml compared with 15.89 ± 23.82 ml in the group with recurrence (P-value = 0.755). In dividing the patients into two groups according to the median volume (10.4 ml), there were differences in survival between the two groups, but not statistically significant. In addition, a negative correlation was found between male sex and overall survival (P-value = 0.048), and treatment with Cetuximab was negatively correlated to disease-free survival (P-value = 0.042). And positively correlated to metastatic spread (P-value = 0.011). In addition, alcohol use was positively associated with local recurrence of the disease (P-value = 0.034). Conclusion Although the volume of the tumor was greater in the group with recurrence of the disease, but did not reach statistical significance. It is necessary to perform future works with a larger number of patients, in more homogeneous populations. PO-0834 Tumor regression during intensity-modulated radiotherapy of nasopharyngeal carcinoma H. Daoud 1 , M. Wafa 1 , F. Nejla 1 , S. Tarak 1 , S. Wicem 1 , F. Leila 1 , D. Jamel 1 1 Hbib Bourguiba Hospital, radiotherapy, sfax, Tunisia Purpose or Objective The association of radiotherapy and chemotherapy is the standard treatment for nasopharyngeal carcinoma(NPC). TumorRegression during radiotherapy has been suggested to be correlated with radio responsiveness. We proposed in this study to evaluate the response degree of nasopharyngeal carcinoma. Material and Methods Twenty patients with NPC receiving IMRT treatment were included. For each patient, a second dosimetric CT was performed at 38 Gy, which was fused with the initial planning dosimetric CT. Manual contouring of the gross tumor volume (GTV) of the primitive tumor (T) and the lymph nodes (N)was performed on the second scanner. We recorded the volume and the isocenter position in the three planes of space (X, Y, Z) of both GTVs.We calculated the volume percent change. Statistical mean differences were calculated using the Wilcoxon signed-rank’ test and SPSS 20 software was used for data analysis. Results We observed a significant decrease in the GTV T volume by -8.9 cc ± 6.2. The average percentage of regression was -29.5% ± 15.3. For the GTV N, it was -16.2 cc± 27.3and a percentage of -58.2% ± 12.5. GTV N migration averages were +1.5 mm ±8.5in the medial direction (X) and +2.4 mm ±6.4 in the craniocaudal (Z). For the GTV T, it was +1.3 mm ±1.1 in the anteroposterior direction. The migration in the other directions was less than one millimeter. Conclusion The nasopharyngeal carcinoma is known to be radiosensitive. That was attested by our study with more than 50% of lymph node regression after only 38 Gy. Moreover, there was heterogeneity between the responses of all patients. It could be explained by the different radiobiological behaviors of the tumors during radiotherapy. PO-0835 Which are the most tooth bearing areas at risk after IMRT for nasopharyngeal carcinoma ? S. Wicem 1 , F. Mariem 1 , D. Amine 2 , S. Tarek 1 , N. Fourati 1 , M. Wafa 1 , F. Leila 1 , D. Jamel 1 1 Habib Bourguiba Hospital, Oncology Radiotherapy, Sfax, Tunisia ; 2 Liberal practice, Oral surgery specialist, Sfax, Tunisia

To analyse the dosimetric distribution on tooth-bearing areas of intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) patients in order to optimize the pre-radiation and post-radiation dental management. Material and Methods We conducted a retrospective study on 40 patients treated with (IMRT ) for nasopharyngeal carcinoma and received a tumoricide dose of 69.9 Gy in 33 daily fractions . The IMRT plan consisted of 7 fixed-filed dynamic 6 MV photon beams . Contouring was done by dividing the tooth-bearing area in the maxilla and the mandible. Each of them was divided into anterior and median right , median left, posterior right, posterior left area. Mean dose (Dmean) was reported for each area. Paired – samples T test was used to compare mean doses of Dmean. Results Doses in different regions of maxilla and mandible were recorded in table I .

Table I

Righ t Post erio r man dibl e

Rig ht

Left Post erio r man dibl e

Med ian righ t

Righ t med ian man dibl e

Left Pos teri or max illa

Left med ian man dibl e

Ant erio r man dibl e

Ant erio r max illa

Med ian left max illa

Pos teri or max illa

ma xill a

Mean Dme an ( Gy)± stan dard devia tion of p atien ts Dme an> 35 Gy num ber

47. 7±4 .3

47. 4±5 .4

46. 3±7 .2

45. 9±6 .1

33.3 ±3.8 9

27. 6±6 .3

20. 2±3 .6

34. 3±4 .4

29.3 ±4.3 7

27. 0±5 .9

39 37 39 37 12 13 11 6 4 0

No significant difference was observed between the right and the left side of the regions. Whereas, Posterior regions received the largest doses (p<0.001) The right median and the left median region of the maxilla received a relatively more important dose than the anterior region on the maxilla and it was superior to the doses on the median region of the mandible. the lower doses were noticed on the anterior region compared to the median and posterior regions in both the maxilla and the mandible (p<0.001). Conclusion The Dosimetric distribution showed that the posterior regions of tooth bearing areas received the largest dose and,thus, are exposed to a higher risk of toxicity especially osteoradionecrosis wich is correlated with radiation D mean > 35 Gy Therefore , Predicting radiation dosimetric distribution in different regions is an important indicator for a personalized dental management prediction and preservation process and would minimize risk of osteonecrosis of the jaws.

Purpose or Objective