Doctoral Dissertation

IMRT and Rotational IMRT (mARC) Using

Flat and Unflat Photon Beam

Doctoral DissertationOf

Amal Sheta

Klinik und Poliklinik für Strahlentherapie

AdvisorsProf. Ulrich WolfProf. Thomas Kuhnt

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Outline

Introduction

Aim of the WorkResults

IMRT using photon beam with and without FF mARC and IMRT

Conclusion

Effect of Flattening filter (FF) Treatment Techniques

Dosimetric characteristics of FF and FFF beams Two Planning comparison Studies

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INTRODUCTION

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Effect of Flattening Filter (FF)

Softening of the x-ray spectra Reduction in head scattered radiation

Non-uniform beam profile High dose rate

Uniform beam profile Significant decrease in output dose rate Beam hardening A major source of scatter and leakage radiation

Krieger, Hanno. Strahlenphysik, Dosimetrie und Strahlenschutz: Band 2: Strahlungsquellen, Detektoren und klinische Dosimetrie. Springer-Verlag, 2013.

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Treatment TechniquesStep and Shoot IMRT and Rotational IMRT (mARC)

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Aims of the work

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Determine the main dosimetric characteristics of FFF beams of Artiste linacs

Assess the effect of FFF beams on S&S-IMRT treatment plans in comparison with those of FF beams.

Estimate the performance of various mARC techniques and compare their performance with S&S-IMRT.

Aim of the Work

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Clinical Cases

prostate with LN H&N

prostate

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Planning Comparison Parameters

Plan quality

DVH-Analysis

Achievement of the clinical goals for PTV and

OAR

Conformity Number

Homogeneity Index

Treatment Eficiency

Treatment time

MUs required

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Dosimetric characteristicsof

FF and FFF beams

RESULTS

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6 MV FF, 7 MV FFF 10 MV FF, 11 MV FFF

Depth dose curves almost similar, match exactly at 10 cm ×10 cm F.S and slight differences are observed for larger and smaller F.S.

The beam softening due to flattening filter removal is compensated by the higher maximum photon energy (higher electron energy on the target) of FFF beams.

Dosimetric characteristics PDD Curves

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Dosimetric characteristics Dose Profile

The dose profiles for small F.S are almost identical and for larger F.S the difference

becomes more obevious.

For FFF beams the high photon energy shows profiles of steeper gradient.

At large F.S the out-of-field scatter is reduced due to removing the flattening filter.

.

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IMRT planning comparisonusing

FF and FFF Photon Beams

RESULTS

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Clinical Cases

PTVs Clinical Goals IMRT-FF IMRT-FFF

ProstateDmean = 74 GY 73.95 ±0.04 73.94 ±0.04

D98 ≥ 70.3 Gy 70.8 ±0.87 71.8 ±0.36

D2 ≤ 77.7 Gy 76.3 ±0.5 75.9 ±0.3

Prostate- LNDmean = 50.4 Gy 50.0 ±0.3 50.2 ±0.2

D98 ≥ 47.9 Gy 47.3 ±0.8 47.7 ±0.7

D2 ≤ 52.9 Gy 52.0 ±0.6 52.3 ±0.5

H&N Dmean = 50 Gy 50.1 ±0.30 50.1 ±0.2

D98 ≥ 47.5 Gy 47.8 ±0.7 47.7 ±0.6

D2 ≤ 52.5 Gy 52.2 ±0.45 52.3 ±0.35

The PTV clinical goals of the prostate, prostate-LN and H&N, in comparison with the calculated values IMRT FF and IMRT FFF

Plan Quality FF and FFF Beam

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Plan Quality FF and FFF Beam

FF Beam (10 MV)

FFF Beam (11 MV)

100 % = 50.4 Gy

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Bet

ter

Plan Quality FF and FFF Beam

HI & CN Prostate, Prostate-LN and H&N

Bet

ter

The dose homogeneity of IMRT-FFF is better than IMRT-FF plans for prostate and comparable for H&N and prostate-LN .

The IMRT FFF plans have better conformity than IMRT FF for all cases

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Treatment delivery time is the same for IMRT plans using FF beams and FFF beams

The number of MUs/Fx of IMRT plans with FFF beams is higher than with FF beams and the %-differences of the number of MUs increase with increasing the volume of PTV

Treatment Efficiency FF and FFF Beam

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Planning comparison between IMRT and mARC

RESULTS

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mARC Module

F.G.S

No of (OP) = No of segments = ⌠arc span / F.G.S⌡, Range: 4 – 15°

* Artiste mARC Treatment planning Guide

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Clinical Cases

PTVs Clinical Goals

SA (8) SA (4) DA (6) IMRT 7B IMRT 9B

ProstateDmean = 74.0 GY 74.1 ±0.06 73.9 ±0.13 73.8 ±0.1

D98 ≥ 70.3 Gy 70.7 ±0.5 70.8 ±0.75 70.7 ±0.7

D2 ≤ 77.7 Gy 76.6 ±0.4 76.0 ±0.2 75.9 ±0.24

Prostate-LN

Dmean = 50.4 Gy 50.4 ±0.0 50.5 ± 0.04 50.3 ±0.08 50.3 ±0.05

D98 ≥ 47.88 Gy 48 ±0.2 48.1 ± 0.14 47.6 ±0.13 47.9 ±0.30

D2 ≤ 52.9 Gy 52.3 ±0.12 52.2 ± 0.26 52.3 ±0.13 52.2 ±0.3

H&N Dmean = 50.0 Gy 49.9 ±0.02 49.9±0.05 49.9±0.05 49.9±0.06

D98 ≥ 47.5 Gy 47.8 ±0.15 47.7±0.22 47.6 ±0.13 47.6 ±0.17

D2 ≤ 52.5 Gy 51.7 ±0.15 51.7 ±0.2 51.8 ±0.13 51.7 ±0.24

Plan Quality IMRT and mARC

The PTV clinical goals of the prostate, prostate-LN and H&N, in comparison with the calculated values of SA (4), DA (6), IMRT 7B and IMRT 9B

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IMRT(9B) SA(4) DA(6)

DVH IMRT(9) SA(4)----- DA(6)…….

Plan Quality IMRT and mARC

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CN & HI of Prostate,Prostate-LN and H&N using IMRT(7&9B) and mARC (SA&DA)

Plan Quality IMRT and mARC

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The treatment delivery time of prostate, prostate-LN and H&N plans due to IMRT(7&9B) and mARC (SA&DA)

Treatment Efficiency IMRT and mARC

Technique Prostate Time(min)

Prostate-LN Time(min)

H&N time(min)

SA(4) (90seg) 6:22 8:26 8:10SA(6) (60seg) - 6:10 6:00SA(8) (45seg) 3:30 4:46 4:41

DA(6) (122seg) - 9:10 10:45IMRT 9B (50 or 60 segments) 6:21 8:00 6:47

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The number of MU required to deliver the planned dose for prostate, prostate-LN and H&N by using IMRT and mARC

Treatment Efficiency IMRT and mARC

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The shapes of the profiles of FFF beams were conical and affected by the field size and the photon beam energy.

The FFF beams produce PDD curves with similar characteristics to FF photon beams.

IMRT-FFF plans are clinically acceptable and comparable with IMRT-FF plans but need more MUs and the differences of TDT are between -20% to +25% in comparison with that of IMRT-FF plans.

mARC has a various options to create clinically acceptable treatment plans with comparable dose distribution with S&S-IMRT.

The main advantages of mARC technique are the lower MUs than IMRT and the possibility to shorten the TDT to the half.

Conclusions

Thank you for

your attention