Main Session
Sep 30
PQA 07 - Genitourinary Cancer, Patient Safety, Nursing/Supportive Care

3376 - Impact of CT Calibration Method on Proton Plan Dosimetry

12:45pm - 02:00pm PT
Hall F
Screen: 33
POSTER

Presenter(s)

Li Zhao, PhD - Medical College of Wisconsin, Milwaukee, WI

L. Zhao, E. E. Ahunbay, M. Huang, and E. S. Paulson; Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI

Purpose/Objective(s): CT calibration is crucial for accurate proton dose calculations. We investigated the dosimetric impact of four methods: Hounsfield Unit (HU)-mass density with tissue substitutes (HU-MDts), HU-relative proton stopping power (RSP) with tissue substitutes (HU-RSPts), HU-mass density with biological tissues (HU-MDbio), and HU-RSP with biological tissues (HU-RSPbio).

Materials/Methods: Four curves were generated using a technology company scan on a different technology company's scanner. Dosimetric differences (global percentage) were evaluated in a treatment planning system using constant planning parameters for six disease sites: brain, spine, prostate, pelvis, craniospinal, and lung.

  • Curve 1 (HU-MDts): HU and manufacturer-provided density of tissue substitutes.
  • Curve 2 (HU-RSPts): HU and calculated RSP values using the Bethe-Bloch formula.
  • Curve 3 (HU-MDbio): Stoichiometric calibration with derived HU for ICRU44 human tissues.
  • Curve 4 (HU-RSPbio, reference): Derived HU for biological tissues and calculated RSP.

Results: Most CTV coverage remained within ±0.5%, consistent across different methods. However, HU-RSPts showed larger deviations in spine CTV (+5.22%), as well as mean doses for lung (+11.34%), eye (+7.65%), and uterus (+5.70%). Variations in mean doses were observed in the temporal lobe (+2.55%), kidney (+1.58%), and right lung (+7.37%) in HU-RSPts, while HU-MDts exhibited mean dose reductions in the uterus (-5.93%) and eye (-3.09%). Overall, organs at risk showed greater variability than target volumes. Our MD-to-SPR conversion agrees with the treatment planning system's conversion for human tissue.

Conclusion: While all calibration methods yielded consistent CTV coverage, HU-RSPts demonstrated the greatest deviations, particularly in heterogeneous regions. Stoichiometric calibration with biological tissues (HU-RSPbio or HU-MDbio) offers more stable and reliable dose estimations. Further research is recommended to refine CT calibration for improved proton therapy accuracy.

Abstract 3376 - Table 1

Treatment site

HU-MDts / HU-RSPbio (%)

HU-RSPts /HU-RSPbio (%)

HU-MDbio /HU-RSPbio (%)

Brain

CTV

D95|AVG|D1

0.01

0.02

0.05

-0.03

-0.12

-0.06

-0.02

-0.02

-0.02

Brainstem

AVG

-0.29

0.49

-0.05

Temporal Lobe_L

AVG

-1.62

2.55

-0.12

Spine

CTV

D95|AVG|D1

-0.04

0.11

0.11

5.22

-0.60

-0.55

0.15

-0.01

0.06

Lung

AVG

-0.45

11.34

0.00

Prostate

CTV

D95|AVG|D1

0.15

0.18

0.35

-0.30

-0.27

-0.18

0.01

0.03

0.10

Bladder

AVG

-0.49

0.35

-0.18

Rectum

AVG

0.15

-0.30

0.10

Pelvis

CTV

D95|AVG D1

-0.02

-0.04

-0.09

0.00

0.03

0.04

0.00

-0.01

-0.02

Femur_R

AVG

-0.26

0.37

-0.03

Uterus

AVG

-5.93

5.70

-1.23

Craniospinal

CTV Brain

D95|AVG|D1

0.04

0.04

0.05

-0.07

-0.08

-0.02

0.00

-0.01

0.03

CTV Spine

D95|AVG|D1

0.01

0.03

0.03

0.30

-0.11

1.34

0.02

0.00

-0.01

Eye_L

AVG

-3.09

7.65

0.52

Lung_L

AVG

0.10

0.94

-0.10

Kidney_L

AVG

-0.36

1.58

0.12

Lung

CTV

D95| AVG|D1

-0.06

0.01

0.26

-2.95

-2.14

-1.01

-0.13

0.04

0.00

Lung_R

AVG

1.40

7.37

-0.08

Chest wall

AVG

0.45

-0.10

0.00