Abstract Book

ESTRO 37

S374

Conclusion The relative risk of breast cancer in radiation treated patients with HD is 2.6. This risk has not lessened significantly despite a decrease in radiation field size and dose. PO-0731 Reducing toxicity of mediastinal RT for lymphoma: Combining butterfly VMAT and breath hold techniques R. Lynn 1 , J. Bowden 2 , A. Starke 2 , K. Hall 2 , K. Hudson 2 , A. Rato 2 , E. Aldridge 2 , D. Robb 2 , N.G. Mikhaeel 2,3,4 1 Guy's and St Thomas' NHS Trust, Medical Physics, London, United Kingdom 2 The London Radiotherapy Centre- Guy's Hospital, Radiotherapy, London, United Kingdom 3 Guy's and St Thomas' NHS Trust, Clinical Oncology, London, United Kingdom 4 King's College London University, London, London, United Kingdom Purpose or Objective Volumetric modulated arc therapy (VMAT) improves target coverage & heart sparing but at the expense of low-dose bath to lungs & breasts. Butterfly VMAT (BVMAT) uses non-co-planar partial arc VMAT, limiting doses to lungs and breasts, but heart sparing may be reduced. In addition, deep inspiration breath hold (DIBH) reduces lung and heart doses. The aim of this planning study was to investigate whether the dosimetric benefits of BVMAT & DIBH are additive. Material and Methods Sixty four plans for 16 consecutive patients (age: 22-63, 12 females) with mediastinal lymphoma were compared. A free-breathing (FB) scan & DIBH scan were acquired for all patients. Four VMAT plans were produced for each patient: 2 FB plans (2 full arcs [fVMAT] & BVMAT) and 2 DIBH plans (2 full arcs & BVMAT). The BVMAT used double 60 0 partial anterior & posterior arcs & 2 craniocaudal 60 0 anterior arcs. Dose prescription was 30.6Gy/17#. Plans were optimised to achieve comparable planning target volume (PTV) coverage. Dose to lungs, heart, spinal cord, oesophagus & female breasts were reduced as much as possible. Mean PTV coverage & doses to OARs were compared and differences were tested for statistical significance with Wilcoxon signed-rank test. Results Results are shown in table 1. The Mean Lung Dose (MLD) was lowest with BVMAT+DIBH (34% reduction). The lowest lung V30 to V20 were obtained by fVMAT+DIBH, while V5- V10 were lowest with BVMAT+DIBH. Lung V5 was reduced by 49% with BVMAT+DIBH. The lowest heart doses were for fVMAT+DIBH with a significant difference from FB plans. BVMAT+DIBH doses were marginally higher but the difference was not statistically significant apart from V15 & V20. BVMAT had more effect on reducing breast doses, particularly V4 with best doses obtained by BVMAT+DIBH (67% reduction in V4).

Conclusion Main benefit from DIBH is reduction of heart doses and lung medium-doses (V20-V30). BVMAT reduces low-dose bath to lungs (V5-V10) and breast without significant loss of heart sparing. The benefits of DIBH & B-VMAT are additive and result in maximum sparing of lungs, heart and breasts. PO-0732 First line low doses RT and chemoimmunotherapy in stage II/IV follicular lymphoma patients M. Galaverni 1 , P. Ciammella 2 , I. Renna 3 , E. Lattanzi 3 , A. Rosca 4 , F. Vigo 4 , L. Giaccherini 5 , F. Bellafiore 6 , G. Timon 7 , M. Galeandro 4 , M.P. Ruggieri 4 , C. Iotti 4 1 Università degli Studi di Parma – Scuola di specializzazione in Radioterapia, Medicine and surgery, Reggio Emilia, Italy 2 U.O.C. Radioterapia Oncologica – AUSL - IRCCS- Reggio Emilia, Oncology and advanced technologies, reggio emilia, Italy 3 Università degli Studi di Parma – Scuola di specializzazione in Radioterapia, MEDICINE AND SURGERY, parma, Italy 4 U.O.C. Radioterapia Oncologica – AUSL- IRCCS- Reggio Emilia, Oncology and advanced technologies, reggio emilia, Italy 5 U.O.C. Radioterapia Oncologica –AUSL- IRCCS- Reggio Emilia, Oncology and advanced technologies, reggio emilia, Italy 6 U.O.C. Radioterapia Oncologica – AUSL - IRCCS- Reggio Emilia, Oncology and advanced tecnologies, reggio emilia, Italy 7 U.O.C. Radioterapia Oncologica – AUSL- IRCCS- Reggio Emilia, Oncology and advanced technologies, raggio emilia, Italy Purpose or Objective Follicular indolent non-Hodgkin lymphomas (FL) are chronically progressive pathologies because, despite having a good response to initial therapies, they are characterized by frequent recurrences. In this area, standard immuno-chemotherapy (R-chemo) provides an excellent rate of response. The addition of a low-dose radiotherapy (LD-RT) treatment has already demonstrated a good tolerance profile without any reported toxicity prior to systemic treatment. To explore the feasibility and effectiveness of a LD-RT followed by standard R-chemo in patients with stage II-IV FL not previously treated. We present early results of a Phase 2, non-randomized, open-label, monocentric trial. Material and Methods The treatment schedule consists of 2 phases : 1. Radiation: 2 fractions of 2 Gy over 2 days at days 1 and 2, of all disease sites 2. Immuno-chemotherapy: 6 cycles of rituximab and bendamustine ( R - Benda ) q28 starting