1. *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 ;80(4):515–23.

2. 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
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

3. 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

4. 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

5. 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,
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