ESTRO 2020 Abstract book

S853 ESTRO 2020

lumbar tract ± the third proximal femour(s). An option to conventional 3D isocentric radiotherapy modalities could be the VMAT modality in order to conform the dose and reduce toxicity to intrapelvic organs in frail , opioid analgesics refractory -pretreated patients (pts). Material and Methods Fifteen pts with widespread bone metastatic cancers entered into this study. Bone metastases from prostate cancer were found in 6 pts, from breast and lung cancers were recorded in 4 and 5 respectively. Palliative radiotherapy 3 Gy for 5 consecutive days was prescribed on a whole volume including the whole pelvis alone (2 pts) ± other bone districts : the lumbar spine from the top of L1 to the anatomic femoral neck (left 3 pts and right 2 pts); from the top of L3 to both superior third of femoral bone (5 pts); from the top of L2 to both femoral neck under 3 cm the intertotrochanter femoral bones (3pts). Three delivery modalities were adopted and compared in each pts : a 3D technique with 2 opposed isocentric AP-PA (3D- AP-PA) MLC customized fields and 10 MV photon beams ; a 3D isocentric MLC customized 4 fields box technique with 6-10 MV wedged photon beams (3D 4 F box) and a dual arch 6 MV photon VMAT( d-VMAT). PTV coverage and the median mean dose (MMD) to rectum , bladder and the peritoneal bag were analysed and compared in EQD2 system. To assess the effect on pain, the Numeric Pain Rating Scale was applied. Results The best dosimetry was observed in the d-VMAT modality. The median V95 in d-VMAT was 99.5% ± 0.3 vs 96.7% ± 0.5 in 3D-4F box vs 95% ± 0.2.5 in 3D-AP-PA (p < 0.03). According the EQD2 estimation , the MMD to rectum was 11. 5 Gy ± 0.5 in d-VMAT vs 13 Gy ± 0.8 in 3D-4F box vs 15 Gy ± 0.6 in 3D-AP-PA ( p < 0.04); the MMD to bladder was 14 Gy ± 0.6 in d-VMAT vs 17.5 Gy ± 0.5 in 3D-4F box vs 18.75 Gy ± 0.3 in 3D AP-PA. For the peritoneal bag V15 (EQD2) the MMD was 1.960 cc±1.50 in d-VMAT vs 2250 cc ± 100 for 3D- 4F box vs 2800 cc ± 150 for 3D-AP-PA ( p < 0.02). VMAT modality showed a dose distribution tight conformed to the target. This modality was chosen to treat all patients. No genitourinary and gastrointestinal acute toxicities were recorded. Pain and narcotic assumption were improved. Conclusion In terms of response and toxicity VMAT based complex whole pelvis radiation could be considered as a faster and much more easy HBI delivery in palliation of widespread complex pelvic bone metastatic cancers. PO-1494 Dose integration method of intensity- modulated arc therapy and HDR brachytherapy of prostate cancer G. Fröhlich 1 , P. Ágoston 1 , K. Jorgo 1 , C. Polgár 1 , T. Major 1 1 National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary Purpose or Objective To validate an alternative method for summing biologically effective doses of intensity-modulated-arc-therapy (IMAT) with interstitial HDR brachytherapy (BT) boost in prostate cancer. Material and Methods Fifteen intermediate or high-risk prostate cancer patients treated with IMAT and interstitial HDR BT boost were included in the study and additional plans using IMAT boost instead of BT were created. The prescribed dose was 2/44 Gy to the whole pelvis, 2/60 Gy to the prostate and vesicle seminals and 1x10 Gy BT or 2/18 Gy IMAT to the prostate gland. As the critical organs receive the maximal total dose in the region where the dose maximum is in BT, the teletherapy planning CT was registered with the US of the BT for every patient, and the most exposed volume of critical organs in BT were identified on these CT images. The minimal dose of these from IMAT was summed with their BT dose, and these biological total doses (EQD2) were

Purpose or Objective To assess which Volumetric Modulated Arc therapy modality could be suitable for postmastectomy implants CTVs adjuvant radiotherapy (aRT) according the ESTRO- ACROP guidelines in cases including the supraclavicular (SVC) and the internal mammary chain (IMC). Material and Methods Since these guidelines have been published, in our institution 25 advanced breast cancer patients (pts) treated with postmastectomy immediate breast reconstruction (IBRi) have been studied for aRT planning. Single postmastectomy right CTVs in 4 pts and left in 6 pts were included togheter to 15 advanced postmastectomy CTVs (7 right and 8 left) requiring the SVC (5) and IMCiaRT (10). Postmastectomy implants CTVs were delineated according the ESTRO-ACROP consensus guidelines with a 0.5 cm margin to the posterior -medio-lateral sides to obtain the IBRi- PTV. The implant was considered as an organ at risk as the controlateral breast. The prescribed total dose was 50 Gy , 2 Gy/25 frs to the IBR PTV and IMC PTV and 48 Gy, 1.92 Gy/25 frs to supraclavicular nodes using a SIB modality delivery. For each case, three VMAT modalities were generated: hybrid-VMAT (h-VMAT) , multi arc (m-VMAT) and dual arc-VMAT (d-VMAT) plans and then compared on the basis of DVHs for PTVs coverages in terms of D95%, hot spots ( D ≥ 108%), Conformity Index, Homogeneity index and OARs constraints The m-VMAT consisted of 3-4 small 6MV photon beams arcs of 50°-60° degree ( start from 200°-220° in right side and from 300°- 310° in left side). The d-VMAT plan provided a dual-arc combination of 6-10 MV photon beams (for left from 170° to 340°; for right from 60° to -195° ). The h-VMAT plan included two delivery steps. The first step consisted of 3- 6 sliding-window IMRT 6-10 MV photon beams delivering more than 1 half of the prescribed dose to spare the ipsilateral lung, the implant and the heart. In the second step the remaining dose was delivered using a d-VMAT (from 170°to 340°for left; from 230° to 180 for right). Results In cases of single IBRi-PTV the m-VMAT resulted an optimal solution in terms of PTV coverage showing a D95 = 98% vs 85% vs 83% for d-VMAT and h-VMAT respectively (p < 0.002 ), CI ( p < 0.003) and HI ( p < 0.002) for both right or left sided PTVs. In scenarios with nodal irradiation , the d- VMAT resulted in the best dose coverage for implant and supraclavicular area in right sided PTVs (p < 0.003). Dosimetry by h-VMAT improved also for IMC ( D95= 95% vs 85% , p < 0.002) and left sided PTVs. Moreover, with h- VMAT a significant low dose region involvement was achieved with sparing of ipsilateral lung ( V5 = 60% vs 75% , p < 0.01) and heart ( V17 = 8% vs 12% p < 0.03). Conclusion This study shows that combining different VMAT modalities each other, a customized satisfactory dosimetry to irradiate the ESTRO-ACROP defined iBRi-PTV in different scenarios are suitable in order to spare the underlying implant. PO-1493 VMAT half-body palliative irradiation in widespread complex pelvic bone metastatic cancers G. Lazzari 1 , D. Becci 2 , A. Bruno 3 , M.G. Leo 3 , A. Terlizzi 3 , D. Mola 3 , G. Silvano 1 1 Azienda Ospedaliera SS. Annunziata Presidio Osped, Radiology, Taranto, Italy ; 2 Azienda Ospedaliera SS. Annunziata Presidio Osped, Fisica Sanitaria Department, Taranto, Italy ; 3 Azienda Ospedaliera SS. Annunziata Presidio Osped, Department of Fisica Sanitaria, Taranto, Italy Purpose or Objective Fractionated half-body irradiation (HBIRT) for widespread and symptomatic bone metastatic cancers has shown a fast and effective palliative role using a schedule of 15 Gy/5Fr/5 days . The most common feature to treat consists of wide volumes involving the bone pelvis ± the