ESTRO 37 Abstract book

S1239

ESTRO 37

from the three fractions for the patient with the local recurrence - a), and those with biochemical failure –c) and d). The TCPs calculated based on the average DVH for these three special cases were given above each plot as well. For all of the patients the estimated TCPs were higher than 94%. The TCP corresponding to the average DVH is 98%.

The indices D 1% in the urethra did not show to be predictive of urinary morbidity. In contrast, the difference between them, especially between D 1% and D 50% : C 1-50 =D 1% -D 50% showed to be statistically related to the occurrence of urinary morbidity (p=0.009). Of the 28 patients with C 1-50 over 37.5Gy, only 2 developed urinary retention (7.1%), whereas 10 of the 18 patients with C 1-50 below 20.7Gy developed urinary morbidity (55.6%). Conclusion D 1% , D 5% , D 10% and D mean are usually used in LDR prostate brachytherapy to evaluate the dose received by the urethra. Therefore, we conclude that the contouring of an expanded urethra, with the objective of evaluating the same dose indices that are being evaluated in the urethra, would not contribute to decreasing the incidence of urinary retention. On the other hand, it may adversely affect the dose coverage of the prostate. The indices C 1-50 , C 1-30 and C 30-50 are descriptive of the DVH tendency. As shown in Figure 1, a high C 1-50 index indicates a low slope in the DVH curve. In this case, the patient without urinary morbidity received lower doses in around 80% of the volume of the urethra, despite having a higher D 1% . According to our results, once the D 1% in the urethra is below 150%, this index is not related to the occurrence of urinary morbidity. In this case, we reported the index C 1-50 as a predictive index of urinary retentions. , D 30% and D 50%

Conclusion An average dDVH was obtained. As could be seen from plots b)-c) the patients with failure in the local control have received doses higher than the average one. Their TCPs were estimated to be ~98%. The failure in the local control in these cases could be attributed to high cellular radioresistence. 1. B. Warkentin et al. Journal of Applied Clinical Medical Physics, Vol. 5, No. 1, 2004 L. Oliver Cañamás 1 , V. González Pérez 1 , J.L. Guinot 2 , C. Bosó 1 , J.C. Sánchez 1 , M. Peña 2 , V. De los Dolores 1 , C. Guardino 1 , V. Crispín 1 1 Fundación Instituto Valenciano de Oncologia, Radiophysics and Radiation Protection, Valencia, Spain 2 Fundación Instituto Valenciano de Oncologia, Radiotherapy, Valencia, Spain Purpose or Objective Controllable and observable parameters during the real- time planning of LDR prostate brachytherapy implants were studied with the aim of relating them to the occurrence of urinary morbidity. Material and Methods A total of 114 patients with prostate cancer, with I-125 seed implantation performed in our center from October 2007 to May 2014 were studied: a selection of 88 patients followed in our center with confirmation of an absence of long term urinary complications, 13 patients who developed an acute urinary retention and required a urinary catheter from 2 weeks to 7 months and 13 who required a transurethral resection of the prostate. Due to the restrictions of inclusion in the study, the percentage of complications in this sample is much higher than the actual one. The software used for the implants was Variseed 7.0 or 8.0 and the image was guided by a real-time US system. The prescribed dose was 145Gy. As indicated in our center’s protocol, the D 1% of the urethra was below 150% of the prescribed dose in all the patients. The dose plans were re-evaluated, and several data were taken from the cumulative DVH in the urethra, expansions of the urethra (2, 3 and 5 mm), prostate and rectum. All of these data were processed with the SPSS Software and the U Mann-Whitney test was applied to determine if they were statistically related to the occurrence of urinary morbidity. Results D 1% , D 5% , D 10% and D mean in the expanded urethra showed to be unrelated to the occurrence of urinary morbidity. EP-2241 Real-time planning of LDR prostate brachytherapy implants and urinary morbidity

EP-2242 Model for dosimetry heterogeneity assessment in breast interstitial brachytherapy V. Gonzalez-Perez 1 , J. Sánchez-Sánchez 2 , J. Guinot 3 , C. Bosó 1 , L. Oliver 1 , J. Sánchez 1 , D. Moratal 2 , V. Crispín 1 1 Fundación Instituto Valenciano de Oncología, Servicio de Radiofísica y Protección Radiológica., Valencia, Spain 2 Universitat Politècnica de València, Center for Biomaterials and Tissue Engineering, Valencia, Spain 3 Fundación Instituto Valenciano de Oncología, Servicio de Radioterapia., Valencia, Spain Purpose or Objective Hannoun-Levi et al. proposed a model to estimate the dose gradient effect in brachytherapy. In this model, the equivalent dose at 2 Gy (EQD2) that received every voxel in the clinical target volume (CTV) was considered. In this study, the previous model was modified to make it more stable against the treatment planning system (TPS) calculation characteristics and to include the cell repair effect. It was used to compare inter-patient dosimetry taking into account the dose in every CTV point. From now on, the equivalent dose at 2 Gy including the dose gradient effect calculated with our model will be High doses in the proximity of CTV have a high influence in EQD2 calculations in brachytherapy. Oncentra Brachy (Elekta, Sweden) allows the maximum dose calculation to be set to a maximum of 4, 8 or 16 times the prescription dose (PD). Depending on this value, EQD2 calculation following Hannoun-Levi model varied between 27.8%- 39.3% for 4 patients of our sample. referred to as EQD2g. Material and Methods