ESTRO 2020 Abstract book

S822 ESTRO 2020

For both prostate and head and neck IOA plans were selected in the blind scoring by clinician in 65% of cases; it was faster than GPS and certain dosimetric parameters were improved. PO-1449 A robust optimization algorithm for brachytherapy X. Wang 1 , P. Wang 1 , J. Li 1 , L. Clara Orlandini 1 1 Sichuan Cancer Hospital & Institute- Sichuan Cancer Center- School of Medicine- University of Electronic Science and Technology of China, Department of Radiation Oncology, Chengdu, China Purpose or Objective This paper presents a robust optimization algorithm for brachytherapy treatment planning and discusses the usefulness of this method for cervical cancer brachytherapy. Material and Methods The robust optimization model implemented, was based on the worst dose distribution method for considering the dose in the presence of source position uncertainties. For each iteration on optimization, apart from the nominal scenario (dose distribution with sources in the planned positions), we assumed that all sources move ±2 mm along the x, y, and z directions. In these 7 scenarios (D0-D6), the worst dose distribution for each voxel was identified as the one with the lowest dose in the target and the highest dose outside the target. The iterative objective function was calculated using the worst dose distribution. Twenty patients with radical cervical cancer who had completed the treatment were retrospectively selected. The conventional optimization plans (COPs) and robust optimization plans (ROPs) were compared. Dose Volume Histogram (DVH) parameters were used for the comparison, SPSS 19.0 software (IBM, Armonk, NY) was used for the statistical analyses, and p values of less than 0.05 were considered statistically significant. The robustneof the COPs and the ROPs was evaluated using the DVH bands. Results The dosimetric results obtained in the nominal scenario and in the worst dose distribution for the COPs and ROPs are reported in Table 1. It was noted that the results obtained for the ROPs are worse than the ones obtained for COPs. In the nominal scenario, the mean CTV D100%of the ROPs is 3.08% lower than the COPs, while the mean CTV V150% is 4.25% higher ( p < 0.05 ). For the bladder, rectum, and small intestine, the mean D2cc of the ROPs is 0.20 Gy, 0.19 Gy, and 0.12 Gy higher than the COPs ( p < 0.05 ), respectively. In the scenarios with shift source position, the mean CTV D100% of the ROPs is 1.47% lower than the COPs, while the mean CTV V150% is 3.77% higher. The mean CTV D90%of the ROPs is 0.35% higher than the COPs ( p > 0.05); however, the difference has a negligible difference. The mean D2cc of the bladder, rectum, and intestines is 0.12Gy, 0.17Gy, and 0.06Gy higher than the COPs ( p < 0.05 ), respectively.

Worst dose distribut ion

Nominal scenario

Parame ter

COPs ROPs

COPs

ROPs

p

p

CTV, D 100% CTV, D 90% CTV, V 150%

3.89±0. 30 6.00±0. 00 52.59±2 .13 4.62±0. 61 4.04±0. 69 3.05±1. 03

3.77±0.2 8 6.00±0.0 0 54.83±2. 44 4.82±0.7 2 4.23±0.7 2 3.17±1.0 5

0.00 3

3.40±0. 21

3.35±0.2 0 5.70±0.0 7 52.32±2. 58 5.39±0.8 1 4.75±0.8 5 3.48±1.1 9

0.02 1 0.09 3 0.00 0 0.00 1 0.00 1

- 5.68±0. 07

0.00 0 0.04 5 0.00 0 0.03 6

50.42±2 .70 5.27±0. 81 4.58±0. 82 3.42±1. 19

Bladder D 2cc Rectum D 2cc Sigmoid D 2cc

0.00 6

There was no remarkable difference in the DVH bands of the ROP and the COP in any of the patients studied.. Figure 1 reports the DVH bands for a representative patient.

Conclusion Robust optimization based on the worst dose distribution does not effectively improve the robustness of the brachytherapy plan for cervical cancer. Other methods are needed to reduce the dosimetric effect of uncertainties in brachytherapy. PO-1450 Analysis of breast radiotherapy plans generated by the EZFluence software J.F. Calvo Ortega 1 , C. Laosa-Bello 1 , S. Moragues- Femenia 1 , M. Hermida-López 2 , J. Casals 1 1 1.Servicio de Oncología Radioterápica- Hospital Quirónsalud- Barcelona- Spain & 2.Servicio de Oncología Radioterápica- Hospital Universitari Dexeus- Barcelona- Spain, 1.Servicio de Oncología Radioterápica- Hospital Quirónsalud- Barcelona- Spain & 2.Ser, ; 2 Servei de Física i Protecció Radiològica. Hospital Vall d'Hebron. Barcelona Spain, Servei de Física i Protecció Radiològica. Hospital Vall d'Hebron. Barcelona Spain, Barcelona, Spain Purpose or Objective To verify the quality and dosimetric accuracy of breast plans based on beam fluences provided by the commercially-available EZFluence (EZF) software (Radformation, Inc, New York, NY). Material and Methods Twenty hypofractionated (15 and 16 treatment fractions) breast treatment plans (8 right-side, 12 left-side) were retrospectively selected in a random way for this study. These treatments were planned in the Eclipse TPS (v. 13.7, AAA algorithm, 2.5 mm-calculation grid size) using the field-in-field (FiF) technique, consisting of two 6 MV tangential fields from a Varian Clinac 2100 CD equipped with a Millennium 120 MLC. Each FiF plan was re-planned by keeping the same tangential beam orientations and field sizes, but with its fluences generated by the scripted EZFluence software (v. 2.2.0). Fluences were optimized such that the maximum point dose was less than 105% of