*Can the volume predict the acute reactions ? SLIDE 1 / 5 IMRT with Simultaneous Integrated Boost technique- popular technique in Head and neck cancer radiotherapy Also known as Dose Painting Simultaneous delivery of different dose levels ranging from 1.6 to 2.2 Gy per day to the targets based on their risk More than 1 Gy per volume is associated with differential gene expression and apoptosis - related with toxicity* 1Gy per day in 33 fractions EQ-D2 is 22Gy *Can 1 Gy per day be used as a constraint to reduce splay dosage in SIB IMRT ? *Can the volume predict the acute reactions ? *Jayashree B, Devasagayam TPA, Kesavan PC. Low dose radiobiology: mechanistic considerations. Curr Sci-BANGALORE-. 2001;80(4):515–23.

Methodology and results SLIDE 2 / 5 Methodology and results Retrospective review of plans of last 20 SIB IMRT treatments done in our institution in Head and neck cancer. 1Gy per day volume ( V1GD )created in ECLIPSE V 10.0.42 Low Dose Conformity Index (LDCI) = V1GD – PTV(in cc) / PTV THE LDCI of 20 patients mean median SD Min Max 1Gy volume 1824.5 1924.5 749.9 322 3187 PTV volume 579.2 612.5 276.4 100 1140 Index Score 2.3 2.105 .94 1.15 4.9

Red: 1Gy per day volume Blue: PTV volume SLIDE 3 / 5 LDCI as calculated for 20 patients with their treatment breaks No 1Gy volume PTV total LDCI =(1Gy-PTV)/PTV BREAK IN RT Patient 1 462 182 1.53 Patient 2 2180 672 2.24 Patient 3 1952 772 1.52 Patient 4 1569 262 4.98 Patient 5 1933 575.9 2.35 1 Patient 6 2457 1140 1.15 Patient 7 1916 762 1.51 Patient 8 2101 732 1.87 Patient 9 2014 729 1.76 Patient 10 1488 442 2.36 Patient 11 1472 478 2.07 Patient 12 3187 1056 2.01 Patient 13 2132 613 2.47 Patient 14 1764 570 2.09 Patient 15 501 190 1.63 Patient 16 1915 612 2.12 Patient 17 322 100 2.22 Patient 18 2642 735 2.59 Patient 19 2899 670 3.32 Patient 20 1584 293 4.4 Red: 1Gy per day volume Blue: PTV volume

Correlating LDCI and Toxicity 0.0073 0.012 SLIDE 4 / 5 Correlating LDCI and Toxicity Patient with Grade I or no mucositis Patient with Grade II or more mucositis 1 Gy volume PTV Index 462 182 1.53 1952 772 1.52 1916 762 1.51 1472 478 2.07 Median 1694 620 1.525 1 Gy volume PTV Index 2180 672 2.24 1569 262 4.98 1933 575.9 2.35 2457 1140 1.15 2101 732 1.87 1488 442 2.36 3187 1056 2.01 2132 613 2.47 1764 570 2.09 501 190 1.63 1915 612 2.12 322 100 2.22 2642 735 2.59 2899 670 3.32 1584 293 4.4 Median 2017 612.5 2.23 LDCI and Toxicity Correlation coefficient P-value Week 2 0.2053 0.3029 Week 3 0.2021 0.2924 Week 4 0.5120 0.0073 Week5 0.4816 0.012

LDCI predicts treatment breaks and acute toxicity SLIDE 5 / 5 Conclusion Low dose conformity index (LDCI)– can be calculated and Higher index values significantly correlated with greater treatment breaks after 4th week LDCI predicts treatment breaks and acute toxicity Prospectively , this index MAY be considered while analyzing IMRT plan to predict higher toxicities Lowering the Index (volume receiving 1 Gy) MAY decrease toxicity –requires further prospective studies LDCI may be used to compare rival IMRT plans when SIB technique is used 1. Schwartz et al – Accelerated radiotherapy with simultaneous integrated boost fractionation and IMRT for advanced head and neck cancer; Otolaryngology–Head and Neck Surgery (2007) 136, 549-555 2.Franceschini et al : Simultaneous Integrated Boost–Intensity-Modulated Radiotherapy in Head and Neck Cancer, The Laryngoscope, The American Laryngological, Rhinological and Otological Society, Inc 3. Studer et al - IMRT using simultaneously integrated boost (SIB) in head and neck cancer patients, Radiation Oncology 2006 4.Hervé Abdi, The Kendall Rank Correlation Coefficient