Conformity index: A review

Institut Curie, Orsay, France.
International Journal of Radiation OncologyBiologyPhysics (Impact Factor: 4.26). 03/2006; 64(2):333-42. DOI: 10.1016/j.ijrobp.2005.09.028
Source: PubMed


We present a critical analysis of the conformity indices described in the literature and an evaluation of their field of application. Three-dimensional conformal radiotherapy, with or without intensity modulation, is based on medical imaging techniques, three-dimensional dosimetry software, compression accessories, and verification procedures. It consists of delineating target volumes and critical healthy tissues to select the best combination of beams. This approach allows better adaptation of the isodose to the tumor volume, while limiting irradiation of healthy tissues. Tools must be developed to evaluate the quality of proposed treatment plans. Dosimetry software provides the dose distribution in each CT section and dose-volume histograms without really indicating the degree of conformity. The conformity index is a complementary tool that attributes a score to a treatment plan or that can compare several treatment plans for the same patient. The future of conformal index in everyday practice therefore remains unclear.

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Available from: Ge Noël, Jan 27, 2014
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    • "The reference isodose corresponds to 95% of the prescribed dose. This CN definition was chosen because it simultaneously takes into account irradiation of the target volume and irradiation of healthy tissue [19]. Finally, the homogeneity index (HI) of the PTV was calculated as HI ¼ D2ÀD98 D50 [20]. "
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    ABSTRACT: To determine the optimum combination of treatment parameters between pitch, field width (FW) and modulation factor (MF) for extremity sarcomas in tomotherapy. Six patients previously treated for extremity sarcomas (3 arms and 3 legs) with tomotherapy were included in this study. 288 treatment plans were recalculated, corresponding to all combinations between 2 FW (2.5 and 5 cm), 4 MF (1.5, 2, 2.5 and 3) and 6 pitches (0.215, 0.287, 0.43 and 3 off-axis pitches). The treatment parameters (MF, FW or pitch) are modified between each plan, and the calculation is relaunched for 400 iterations, without modifying the optimisation constraints of the plan under which the patient has been treated. We suggest eliminating the 0.43 pitch and never combining a 0.215 pitch with an MF ≤ 2. We also do not recommend using an MF = 1.5 unless treatment time is an absolute priority over plan quality. We did not see any advantage in using Chen off-axis pitches, except for targets far from the axis (>15 cm) treated with a high pitch. A combination of MF = 2/FW = 5 cm/pitch = 0.287 gives plans of acceptable quality, combined with reduced treatment times. These conclusions are true only for extremity sarcomas treated in 2 Gy/fraction. We have shown that the choice of pitch/MF/FW combination is crucial for the treatment of extremity sarcomas in tomotherapy: some produce good dosimetric quality with a reduced irradiation time, while others may increase the time without improving the quality. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
    Physica Medica 05/2015; 31(5). DOI:10.1016/j.ejmp.2015.05.005 · 2.40 Impact Factor
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    • "where TV is target volume, ie, PTV, TVRI is the target volume covered by the reference isodose, and VRI is the volume of the reference isodose.28 "
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    ABSTRACT: Background Prone positioning for breast radiotherapy is preferable when the aim is a reduction of the dose to the ipsilateral lung or the heart in certain left-sided cases. Materials and methods In 100 breast cancer cases awaiting postoperative whole-breast radiotherapy, conformal radiotherapy plans were prospectively generated in both prone and supine positions. The axillary nodal region (levels I–III) and internal mammary (IM) lymph-node region in the upper three intercostal spaces were retrospectively contoured. The mean doses to the nodal regions and the volume receiving 25 Gy (V25Gy), V45Gy, and V47.5Gy were compared between the two treatment positions. Results In most cases, the doses to axillary levels I–III and the IM lymph nodes were inadequate, regardless of the treatment position. The nodal doses were significantly lower in the prone than in the supine position. The radiation doses to levels II–III and IM nodes were especially low. The V45Gy and V47.5Gy of the level I axillary lymph nodes were 54.6% and 40.2%, respectively, in the supine, and 3.0% and 1.7%, respectively, in the prone position. In the supine position, only 17 patients (17%) received a mean dose of 45 Gy to the axillary level I nodes. Conclusion The radiation dose to the axillary and IM lymph nodes during breast radiotherapy is therapeutically insufficient in most cases, and is significantly lower in the prone position than in the supine position.
    Therapeutics and Clinical Risk Management 05/2014; 10(1):367-72. DOI:10.2147/TCRM.S59483 · 1.47 Impact Factor
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    • "The homogeneity index was defined as the maximum isodose in the target divided by the reference isodose (HIRTOG = Imax/RI), which is the maximum point dose divided by the prescribed dose of 30.6 Gy. HIRTOG ≤ 2 is considered complaint with protocol [12]. V107% was defined as the volume receiving at least 107% of the prescribed dose. "
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    ABSTRACT: High cure rates for Hodgkin’s lymphoma must be balanced with long-term treatment-related toxicity. Here we report an intensity-modulated radiation therapy (IMRT) technique that achieves adequate target coverage for mediastinal disease while minimizing high- and low-dose exposure of critical organs. Methods and materials Treatment plans for IMRT and conventional anteroposterior-posteroanterior (AP-PA) techniques, with comparable coverage of the planning target volume (PTV), were generated for 9 female patients with mediastinal Hodgkin’s lymphoma assuming use of inclined positioning, daily breath-hold, and CT-on-rails verification. Our “butterfly” IMRT beam arrangement involved anterior beams of 300°−30° and posterior beams of 160°−210°. Percentages of normal structures receiving 30 Gy (V30), 20 Gy (V20), and 5 Gy (V5) were tabulated for the right and left breasts, total lung, heart, left and right ventricles, left anterior descending coronary artery (LAD), and spinal cord. Differences in each variable, conformity index, homogeneity index, and V107% between the two techniques were calculated (IMRT minus conventional). Use of IMRT generally reduced the V30 and V20 to critical structures: −1.4% and +0.1% to the right breast, −1.7% and −0.9% to the left breast, −14.6% and −7.7% to the total lung, −12.2% and −10.5% to the heart, −2.4% and −14.2% to the left ventricle, −16.4% and −8.4% to the right ventricle, −7.0% and −14.2% to the LAD, and −52.2% and −13.4% to the spinal cord. Differences in V5 were +6.2% for right breast, +2.8% for left breast, +12.9% for total lung, −3.5% for heart, −8.2% for left ventricle, −1.5% for right ventricle, +0.1% for LAD, and −0.1% for spinal cord. Use of IMRT significantly reduced the volume of tissue receiving 107% of the dose (mean 754 cm3 reduction). This butterfly technique for IMRT avoids excess exposure of heart, breast, lung, and spinal cord to doses of 30 or 20 Gy; mildly increases V5 to the breasts; and decreases the V107%.
    Radiation Oncology 04/2014; 9(1):94. DOI:10.1186/1748-717X-9-94 · 2.55 Impact Factor
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