Abstract Book

S1236

ESTRO 37

this patient group, compared to free breathing [figure1].

dose with a

plan (P<0.01). All patients had a lower D 2cc

breath hold treatment plan. Only the mean dose to the lungs increased 0.4Gy with a breath hold technique (P=0.13).

Conclusion A breath hold technique combined with a VMAT plan reduces the mean heart dose significantly for a local recurrence of left sided breast cancer patient in previously irradiated area, compared to a free breathing VMAT technique. EP-2362 Optimization strategies for stereotactic radiosurgery plans in Eclipse S. Ehlert Tvile 1 , N.K. Jensen 2 , L. Ohlhues 2 , L.S. Fog 2 1 Rigshospitalet, Finsenscenteret- Dep. of Oncology, Roedovre, Denmark 2 Rigshospitalet, Finsenscenteret- Dep. of Oncology, Copenhagen, Denmark Purpose or Objective Determine which optimization strategy in Eclipse provides optimal normal tissue sparing without compromising target coverage for stereotactic radiosurgery (SRS) plans for single and multiple brain metastases. Material and Methods 18 patients with 21 plans treated for one or multiple brain metastases after February 1 st , 2017 were reviewed by two medical physicists and two dosimetrists. Each reviewer independently evaluated each plan and noted if they agreed with the chosen gantry, collimator and couch angles. Any plan flagged by at least one reviewer was replanned with a different choice of arc span, collimator angle and/or couch angle to better avoid nearby OARs. All planning was done in Eclipse version 13.7 with the Photon Optimizer and AcurosXB on a 1x1x1 mm 3 resolution grid. All flagged plans originally planned with VMAT (Ten plans from eight patients) were replanned with 13 different normal tissue optimization strategies: DVH objective only on brain-GTV, DVH objective only on ring support structure (4 mm from GTV, 30 mm wide), and 11 normal tissue objective (NTO) parameter sets (Table). Each plan was normalized to 100% isodose to cover GTV. The following doses were extracted from each plan: GTV Dmax, brain–GTV V10Gy, Dmax to optic chiasm, brainstem, and both optic nerves, eyes, hippocampi, cochlea and lenses. V10Gy for brain was chosen as it has been shown to predict radionecrosis (Minniti G. et al., Radiat Oncol. 2011). All plans generated with automatic NTO were reoptimized four times iteratively to determine if the possible benefit of reoptimization.

In this study we investigated if there is a potential gain for heart and lung dose with a VMAT breath hold treatment for a local recurrence of left sided breast cancer in previously irradiated area. Material and Methods We retrospectively selected twenty patients who were treated at our clinic and had a free breathing and breath hold CT-scan. For the breath hold CT-scan we used the SpiroDynr’X system (Dyn'r Society) to receives a reproducible breath hold with visual feedback for the patient. For both scans the GTV, CTV and also heart and lungs were delineated. Using a CTV-PTV margin of 1cm, a dual arc VMAT, Elekta Agility, 6MV treatment plan, with a total dose of 46Gy in 23 fractions, was made for both CT- scans. For planning multi criterial optimization [MCO] within Raystation (Raysearch) was used. The mean dose to the heart was reduced as much as possible without compromising the target coverage. The V 43.7Gy (95% of prescribed dose) of the PTV; the D 2cc , D mean and V 43.7Gy of the heart; V 20Gy , V 10Gy and D mean of the lungs were compared using a paired sampled T-test. Results The average mean heart dose was reduced with 2.2Gy (10.3Gy vs. 8.1Gy) comparing breath hold with free breathing (P<0.01). However the difference per patient is widely spread ranging from -6.1Gy to 0.5Gy in favor of breath hold [table1]. Only 4 out of 20 patients had a difference less than 1Gy. The mean high dose(D 2cc ) in the heart is 4.2Gy lower for breath hold compared to the free breathing treatment