IMRT technique for the treatment of non-small-cell lung cancer

IMRT technique for the treatment of non-small-cell lung cancer

ESTRO 33, 2014 cancer (BC) and to compare doses to the heart and other organs at risk (OAR) with different photon treatment planning techniques includ...

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ESTRO 33, 2014 cancer (BC) and to compare doses to the heart and other organs at risk (OAR) with different photon treatment planning techniques including gating. A newly published large case-control study by Darby et al (2013) showed that incidental exposure of the heart to ionizing radiation in radiotherapy for BC may increase the rate of major coronary events by 7.4% per Gy, with no apparent lower threshold and with earlier onset than previously known. The finite range of protons in tissue could be used to limit the irradiation of dose to the normal tissue, especially for certain subgroups of patients, e.g. with a priori risk for cardiac disease or with thoracic anatomic variations. Materials and Methods: Twenty patients with stage I-III BC (either after mastectomy or lumpectomy, left- or right-sided) were included in the study. The patients had been planned and treated with enhanced inspiration gated (EIG) technique or irregular surface compensator (ISC) technique with free breathing. The patients were identified from a larger group where high mean doses to the heart, left anterior descending coronary artery (LAD), or lung, qualified them for a retrospective re-planning study with protons. All volumes of interest (VOIs) were defined by a radiation oncologist. Clinical Target Volume (CTV) and Planning Target Volume (PTV) were defined as the volumes originally used in the photon plans, but the effect of changing the PTV margins to the lung was also evaluated. The prescribed dose for all patients was 50 Gy (RBE) in 2 Gy (RBE) fractions. The proton plans were generated using Eclipse version 11 (Varian Medical Systems, Palo Alto, CA), using 1 or 2 fields with spot scanning technique, either as single field uniform dose (SFUD) or as intensity-modulated proton therapy. Results: The proton plans showed comparable or better CTV and PTV coverage than the original photon plans. The main findings, however, were large and significant reductions in mean doses to the heart (from 1.27 Gy to 0.24 Gy), LAD (from 6.3 Gy to 0.84 Gy) and the ipsi-lateral lung. The dose to the skin could be reduced by using multi-field irradiations. No significant differences were found between SFUD and IMPT plans, but the dose distributions are very sensitive to variations in delineations of VOIs and the chosen constraints. Analysis of range and setup uncertainty and normal tissue complication probability will follow. Conclusions: Spot scanning technique with protons may further reduce doses to the OARs compared to advanced photon techniques. Further discussions and consensus on clinical relevant dose constraints to OAR including LAD are crucial. The results from this study indicate a potential for protons as adjuvant radiotherapy in BC and a further step towards the individualisation of treatment based on anatomic and comorbidity characteristics. References: Darby SC et al 2013 Risk of ischemic heart disease in women after radiotherapy for breast cancer. N Engl J Med 368:987-98 EP-1595 Clinical evaluation of treatment plans of Stereotactic Body Radiotherapy for liver tumors G. Boka1, O. Utehina1, I. Nemiro2, D. Purina1, M. Bukovska1, S. Bikova1, S. Popov1, V. Boka3 1 Riga East University Hospital, Clinic of Therapeutic Radiology and Medical Physics, Riga, Latvia 2 University of Latvia, Faculty of Medicine, Riga, Latvia 3 Riga East University Hospital, Clinic of Surgery, Riga, Latvia Purpose/Objective: The purpose of this study was to perform analysis of liver Stereotactic Body Radiotherapy (SBRT) treatment plans from point of view of target coverage and normal tissue constraints. Materials and Methods: 44 patients with 59 malignant lesions in liver were treated with SBRT between 2009 and 2013. Free breathing Fourdimensional Computed Tomography (4DCT) based planning was performed for all patients. No external fixation devices were used except a vacuum bag. The Gross Tumor Volume (GTV), the Clinical Target Volume (CTV), and the Internal Target Volume (ITV) were contoured on the basis of the MRI images co-registered with Maximum Intensity Projection (MIP) CT study. Planning Target Volume (PTV) was created by three-dimensional expansion of ITV by 3 to 5 mm. Dose delivery for all patients was performed using Image Guided Volumetric Modulated Arc Therapy (IGVMAT). Mean volume of CTV was 9.6 ccm (range0.4 – 51.1 ccm) and mean volume of ITV 26.4 ccm (range 2.3 – 120.0 ccm). In all cases dose was delivered on consecutive days. Prescribed dose per fraction varied from 7 to 18 Gy. Minimal dose in target volume was in range of 30 Gy to 48 Gy. Initial analysis of DoseVolume histograms demonstrated that Organs at Risk (OAR) adjacent to liver such spinal cord, kidney, stomach and duodenum received much lower radiation doses than respective tolerance doses. Therefore only doses for healthy liver tissue were analyzed and presented in this report. The following clinical plan parameters were included in analysis:

S201 Conformity Index (CI), Heterogeneity Index (HI), absolute volume of healthy liver tissue, and doses to 33%, 50% and 700 ccm of healthy liver tissue. Results: No one of the patients had any acute or late adverse effects after treatment. All SBRT plans are considered to be highly conformal with the mean CI 1.24 (range 1.01– 1.78). The dose HI was well inside acceptable range (mean HI = 1.24, range 1.07 – 1.38). The mean volume of liver was 1473 ccm (range 926 – 2530 ccm). 33% of healthy liver tissue received mean dose of 7.2 Gy (range 0.7 – 16.1 Gy) while 50% of healthy liver tissue received mean dose of 3.8 Gy (range 0.2 – 11.2 Gy). Doses delivered to 700 ccm of healthy liver tissue were well below the tolerance level (mean dose 5.4 Gy, range 0.3 – 13.9 Gy). Conclusions: SBRT for liver cancer is safe and well tolerated by the patients. The present study demonstrates that a further dose escalation can be achieved safely without compromising healthy tissue toxicity. EP-1596 A novel integrated VMAT/IMRT technique for the treatment of nonsmall-cell lung cancer N. Zhao1, R.J. Yang1, J.J. Wang1, N. Meng1, P. Jiang1, J.N. Li1, X.L. Zhang1 1 Peking University Third Hospital, Radiation Oncology, Beijing, China Purpose/Objective: To investigate a novel Integrated VMAT/IMRT technique which combines volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) for non-small cell lung cancer (NSCLC). Materials and Methods: 2 partial arcs VMAT, 5-field IMRT and Integrated VMAT/IMRT plans were created for 17 patients with NSCLC. The Integrated VMAT/IMRT plans were combination of 2 partial arcs VMAT plans and 5-field IMRT plans. The dose distribution of planning target volume (PTV) and organs at risk (OARs) for Integrated VMAT/IMRT was compared with IMRT and VMAT. The monitor units (MUs) and treatment delivery time were also evaluated. For each plan, a dry run was performed to assess the dosimetric accuracy with MatriXX from IBA. Results: Integrated VMAT/IMRT significantly improved the target conformity and homogeneity. The V30 of normal lung for Integrated plans was significantly lower than IMRT plans(8.4% vs 9.2%; p<0.05). The V5 and mean lung dose (MLD) of normal lung for Integrated plans were 9.8% and 4.6% lower than VMAT plans (p<0.05). The maximum dose of spinal cord for Integrated plans was 4.9 Gy lower than IMRT plans (p<0.05). The mean delivery time of IMRT, VMAT and Integrated plans was 280 s, 114 s, and 327 s, respectively. The mean MUs needed for IMRT, VMAT and Integrated plans were 933, 512, and 737, respectively. The gamma pass rates were beyond 90% at the 3%/3 mm criteria when the gantry angles were set to 0° for pretreatment verification.

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ESTRO 33, 2014 EP-1597 A dosimetric comparison of Helical Tomotherapy and VMAT in the treatment of high risk prostate cancer T. Lacornerie1, F. Cavillon2, R. Hardhuin3, P. Compte1, N. Reynaert1, E.F. Lartigau4, D. Pasquier4 1 Centre Oscar Lambret, Medical Physics, Lille, France 2 Université Catholique de Lille, Faculté de Médecine, Lille, France 3 Centre Galilée, Radiothérapie, Lille, France 4 Centre Oscar Lambret, Radiotherapy, Lille, France Purpose/Objective: To compare the dosimetric results of helical tomotherapy (HT) (V5.1 VoLo algorithm for optimization) and volumetric modulated arc therapy (VMAT) (Elekta Synergy 6 MV and Pinnacle3 v9, 2 arcs) in the treatment of high-risk prostate cancer with pelvic nodal radiotherapy. Materials and Methods: Plans were generated for ten consecutive patients treated for high-risk prostate cancer with prophylactic whole pelvic radiotherapy (WPRT, PTV1) and concomitant boost (PTV2) using VMAT and HT for 28 sessions of 1.8 Gy and 2.55 Gy respectively (a comparison was made and published previously for sequential treatments). The physicists were blinded to the dosimetric results generated by the other technique. Plan quality was assessed according to the ICRU 83 report's criteria: the near-minimal (D98%), near-maximal (D2%) and median (D50%) doses, the homogeneity index (HI) and the Dice similarity coefficient (DSC). Several organs at risk (OAR) dosimetric indexes were compared, the goals were V39 Gy < 33%, V54 Gy < 20% for rectal and bladder walls. Results: For the 10 patients both techniques reach goals so we had the possibility to consider mean DVH. HT was able to provide a higher D98% than VMAT for PTV1 (48.2±0.5 Gy and 46.4±0.6 Gy, respectively; p=0.002) and PTV2 (68.3±0.7 Gy and 66.3±1 Gy, respectively; p=0.002), leading to a better HI. HT and VMAT provided quite similar OAR sparing. For rectum wall V39 were 24.0±3.9 Gy and 26.3±3.9 Gy for HT and VMAT respectively. For bladder wall V39 were 27.8±4.8 Gy and 28.6±2.9 Gy for HT and VMAT respectively. For small bowel D2% were 40.0±6.5 Gy and 43.7±5.1 Gy for HT and VMAT respectively (p=0.039) but VMAT deliver significantly less dose under 18 Gy. Some differences statistically significant are probably without clinical consequence.

Conclusions: HT and VMAT provided similar and highly conformal plans that complied well with OAR dose-volume constraints. Although some dosimetric differences are statistically significant, they remained small. HT provided a more homogeneous dose distribution and OAR sparing was very similar for the two techniques. Conclusions: Integrated VMAT/IMRT technique significantly reduced V5, V10 and MLD of normal lung compared with VMAT, and the irradiated volume of the OARs receiving medium to high dose with fewer MUs compared with IMRT. Integrated VMAT/IMRT technique can be a feasible radiotherapy technique with better plan quality and accurately delivered on the linear accelerator.

EP-1598 Total scalp irradiation using Helical Tomotherapy with a helmet bolus printed using a 3D printer J.S. Kim1, S.G. Ju1, M.K. Kim1, D.H. Lim1, C.S. Hong1, D.H. Choi1, K.Z. Chung1, Y.I. Han1, J.S. Kim1, S.H. Ahn1 1 Samsung Medical Center, Radiation Oncology, Korea seoul, Korea Republic of Purpose/Objective: A new technique for manufacturing a helmet bolus (HB) using a 3D printer (3DP) was developed for total scalp irradiation with Helical Tomotherapy (HT). The usefulness and dosimetric characteristics of the new helmet bolus (HB-3DP) were evaluated for clinical implementation.