ESTRO 2020 Abstract book

S833 ESTRO 2020

irradiation: results of a Canada-wide survey, 2017, Current Oncology, 24, 3 [3] Private communication, Jim Cramb PO-1465 Automated versus manual LINAC stereotactic radiosurgery plans in patients with 4-10 brain metastases A. Petoukhova 1 , R. Snijder 1 , R. Wiggenraad 2 , L. De Boer- de Wit 2 , I. Mudde-van der Wouden 2 , M. Florijn 1 , J. Zindler 3,4 , J. Van Santvoort 1 1 Haaglanden Medical Centre, Department of Medical Physics, Leidschendam, The Netherlands ; 2 Haaglanden Medical Centre, Department of Radiation Oncology, Leidschendam, The Netherlands ; 3 Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands ; 4 Holland Proton Therapy Centre, Department of Radiation Oncology, Delft, The Netherlands Purpose or Objective Stereotactic radiosurgery (SRS) is a promising treatment option for patients with multiple brain metastases (BM). We studied whether automated planning or IMRT can make LINAC-based stereotactic radiosurgery plan quality with one isoc comparable or even better than a manually planned dynamic conformal arc (DCA) plan with a separate isocenter for each metastasis. Material and Methods For 12 patients with 4 up to 10 brain metastases (mean = 6), seven non-coplanar LINAC-based SRS plans with 6MV photons were created: a manually planned DCA plan with a separate isocenter for each metastasis (iPlan, BrainLAB), a dynamic IMRT plan (iPlan), a VMAT plan (Pinnacle, PHILIPS), two DCA plans with one isocenter for three (3 ∠ ) and five (5 ∠ ) couch angles (v1.6 Multiple Brain Mets SRS Elements, BrainLAB), two DCA plans with five couch angles with high and low sparing of normal tissue (NT) (v2.0 Multiple Brain Mets Elements). The last six plans were with one isocenter, of which five plans were automatically generated. In v2.0, a jaw tracking of Elekta Versa HD is possible. The maximum allowed gross tumour volume (GTV) to planning target volume (PTV) margin was 1 mm. The prescription dose was 21 Gy or 18 Gy in a single fraction or 8.5 Gy in 3 fractions depending on the PTV volume. All plans were calculated with Monte Carlo, except the VMAT, which was calculated with Collapsed Cone algorithm. The PTV coverage should be at least 98%. To assess SRS plan quality, the Paddick conformity index (CI), the Paddick gradient index (GI), the total V12Gy and V5Gy of uninvolved brain were studied and reported as MEAN±1SD. Additionally, the number of monitor units (MU) and irradiation time were compared. Results The mean total CI was the highest for dynamic IMRT and automated DCA with one isocenter (0.73±0.1) (see table). The lowest GI was for automatically generated DCA plans with one isocenter (v2.0 high and low NT sparing), whereas the highest GI was for VMAT plans (7.0±3.0). The total V12Gy of automatically generated DCA plans with one isocenter (3.3±3.2% and 3.6±3.5% for high and low NT sparing, respectively) were comparable with the manual DCA plans (3.6±3.7%). For the total V5Gy, the automatically generated DCA plans with one isocenter were comparable with the manual DCA plans. The number of MU was the smallest for VMAT plans, followed by automatically generated DCA and IMRT plans and much lower than the manual DCA plans. The irradiation time was the shortest for automatically planned DCA plans. Table: mean results

be helpful for clinics to determine future practice. We did a survey of TBI practice in Australia and New Zealand. Material and Methods We emailed 46 TBI related questions to clinics in Australia and New Zealand, using the ACPSEM (Australasian College of Physical Scientists and Engineers in Medicine) email distribution list. Results

Table 1 – selected data from the 2005 and the 2019 survey of total body irradiation practice in Australia and New Zealand. We received replies from 14 clinics. Some of the data, and data from a similar survey carried out in 2005 [3], are shown in Figure 1. 11 clinics participated in both surveys, 1 only in the 2005 survey and 3 only in the 2019 survey. 6 clinics are using similar linac dose rates in both surveys, 4 have lowered their linac dose rates, 1 has increased it. In 2019, 9 clinics use linac dose rates ≤ 200 MU/min, 3 use 200-300 MU/min and 1 uses 600 MU/min. In 2005, the patient dose rates were 9-25 cGy/min (the clinic using 600 MU/min did not report patient dose rate); in 2019, the patient dose rates were 5-15 cGy/min, with one outlier at 150 cGy/min, using an advanced technique (the clinic using 600 MU/min did not report patient dose rates). The most common prescriptions is 12Gy in 6 fractions over 3 days, though 3 clinics also use different prescriptions. 9 clinics use shielding, for various combinations of lungs, head, neck and/or kidneys. Most clinics use shielding to reduce the delivered dose to the prescription dose, however in two clinics the lung dose is 8 Gy while the prescription dose is 12 Gy. Lung doses vary considerably, from 8-14.4 Gy, for prescriptions of 12 Gy in 6 fractions. Conclusion The TBI practice in Australia and New Zealand remains varied, with considerable differences in lung doses and patient dose rates. [1] Quast, U.: Total body irradiation-review of treatment techniques in Europe, Radiotherapy and Oncology 1987, 9, 2, 91-106. https://doi.org/10.1016/S0167-8140(87)80197- 4 [2] Studinski, R.C.N., Fraser, D. J. , Samant, R. S. and MacPherson, M. S.: Current practice in total-body