ESTRO 37 Abstract book

S1041

ESTRO 37

photon plan showed dosimetric advantage to critical structures. In the other six cases, only minor dosimetric differences (<2 Gy) were found. In all cases where a cumulative dose exceeded 100Gy, the volume receiving >100 Gy (V100) was larger for protons compared to photons. On average, the median V100 was 2.85 (0.64 – 4.74) cc larger in the proton plans, due to inferior dose gradients caused by the range shifter. The integral dose and the dose to the brain excluding the PTV were higher in all photon plans. The mean decrease of integral dose by protons was 41.8% (±12.5). The mean decrease of dose to the brain excluding the PTV was 52.1% (±14.0).

(D-VMAT) plans for Internal Mammary Chain (ICM) irradiation in post-mastectomy implants adjuvant

Radiation Therapy (RT). Material and Methods

In our institution, 10 left advanced breast cancer patients with mastectomy and immediate prosthesis implants were evaluated for adjuvant RT on expanded chest wall by prosthesis and nodal areas (ICM and supraclavicular nodes) to treat simultaneously using h-VMAT vs D-VMAT modality planned with Treatment Planning System Monaco ® (Monte Carlo Photon Algorithm). According to ICRU 83, the prescribed total dose was 50 Gy (2 Gy, 25 fractions) to expanded chest wall and IMC and 48 Gy (1.92 Gy, 25 fractions) to supraclavicular nodes. Using the same structure set, h-VMAT and D-VMAT were generated for these targets and dosimetrically compared. VMAT plan consisted of dual-arc plan (from 170 to 340 degrees) with 6 MV photon beams. The h-VMAT planning involved two simultaneous steps. The first consists of three sliding-window IMRT photon beams (one 6 MV at 300 degrees and two 10 MV at 120 and 90 degrees) delivering about an half of the prescribed dose to minimize at maximum ipsilateral lung and heart doses. In the second step, the remaining dose was planned using a D-VMAT (from 170 to 340 degrees) by keeping the dose delivered in IMRT arrangement as the base dose plan. Both planning techniques were evaluated and compared using DVH Planning Target Volumes (PTVs) coverages (D95%), hot spots (D ≥ 108%), Conformity Index (CI), Homogeneity Index (HI). Results h-VMAT plans recorded the best results in terms of CI (p < 0.002), HI (p < 0.002). Both modalities showed similar dose coverage on expanded chest wall and supraclavicular area (D95 = 96%) while dose coverage of ICM improved with h-VMAT (D95 = 95% vs. 80%, p < 0.03). Furthermore, h-VMAT achieved a significant reduction in low dose regions of ipsilateral lung (V5 = 60% vs. 75%, p < 0.01) and heart (V7 = 24% vs. 42%). Conclusion This work shows that h-VMAT could be considered as a feasible method to obtain an optimal coverage of ICM, sparing low doses to ipsilateral lung and heart in comparison with D-VMAT. EP-1915 IMRT for breast cancer: a comparative dosimetric study between Tomotherapy, VMAT and proton therapy C. Adrien 1 , L. Bartolucci 1 , M. Lejars 2 , M. Vaillant 2 , S. Ribes 2 , F. Goudjil 2 , M. Robilliard 1 , E. Costa 1 , Y. Kirova 1 , A. Mazal 1 1 Institut Curie - Paris, Radiotherapy, Paris, France 2 Centre de Protonthérapie - Institut Curie, Radiotherapy, Orsay, France Purpose or Objective Since 2009, the use of Intensity-Modulated Radiation Therapy for the treatment of breast cancer with lymph node involvement has been considerably growing at our institution. Choice has been made to use as main technique Helical Tomotherapy (HT) with standard parameters such as a field width of 2.5 cm (HT_FW_2.5). It allowed us to meet stringent organs at risk (OAR) dose constraints but generally at the expense of a substantial treatment time which affect directly patient compliance. For that matter, two options are worth considering at our institution: HT with a wider field width of 5 cm (HT_FW_5) or Volumetric Modulated Arc Therapy (VMAT). However, patient care could also be improved by lowering the risk of side effects by using an alternative method of radiation treatment: proton therapy with Pencil Beam Scanning (PT_PBS). The aim of this study is

Bar plot of the integral dose to the brain by the single photon and proton plans

Conclusion Dose delivery using protons as compared to photons for intracranial re-irradiation will reduce the dose to the brain by approximately 50%. However, proton delivery did not reduce the high dose volumes (V100). Sparing of critical structures is very case specific and depends on target volume and shape as well as the distance of OARs to the target. This indicates the need for patient- individual evaluation of the optimal treatment modality. EP-1914 hHybrid VMAT As A Feasible Technique In Internal Mammary Chain Post-Mastectomy Adjuvant Radiotherapy A. Bruno 1 , D. Becci 1 , M. Leo 1 , A. Terlizzi 1 , G. Lazzari 2 , G. Silvano 2 , D. Mola 1 1 Azienda Ospedaliera SS. Annunziata Presidio Osped, Medical Physics, Taranto, Italy 2 Azienda Ospedaliera SS. Annunziata Presidio Osped, Radiology, Taranto, Italy Purpose or Objective To evaluate dosimetric advantages using hybrid Volu- metric Modulated Arc Therapy (h-VMAT) vs Dual-Arc VMAT