Beam specific PTV incorporating 4DCT for PBS proton therapy of thoracic tumors

Minglei Kang, PhD

Authors: Liyong Lin1, Minglei Kang1, Sheng Huang1, Rulon Mayer2, Andy Thomas2, James E McDonough1, Timothy D Solberg1, Charles Simone II1

1Department of Radiation Oncology, University of Pennsylvania2Henry Jackson Foundation

Supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17-W81XWH-07-2-0121 and W81XWH-09-2-

0174.

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Challenges for PBS to treat thoracic tumors Proton PBS treatment planning can achieve better organs

sparing than IMRT and DS techniques for thoracic tumors.

PBS is not a good choice.

Due to commercial TPSs are unable to calculate:

• (1). Accurate treatment margins to compensate for range uncertainties

• (2). PBS spots delivery interplay with organs motion

Chang, JY, Zhang X, Wang X et al. Int J Radiat Oncol Biol Phys., 65: 1087-1096, 2006Kang Y, Zhang X, Chang JY et al. Int J Radiat Oncol Biol.,67:906-914, 2007Lomax AJ. Phys Med Biol., 53: 1043, 2008Lomax AJ , Phys Med Biol; 53: 1027, 2008Zhang X, Li Y, Pan X et ,Int J Radiat Oncol Biol Phys., 77:357-366, 2010

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BSPTV: Beam specific planning target volume SPR: HU to stopping power ratio(SPR) conversion uncertainty Setup errors: cause cold or hot area. Motion: move the heterogeneity tissue into beam path to cause

overshoot or miss shootG=G300deg Slice No. 59 ,Y in Eclipse -508.5mm

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Park P C, Zhu X R, Lee AK et al. Int J Radiat Oncol Biol Phys; 82:329–36, 2012Flampouri S, Hoppe BS, Slopsema RL et al. Phys Med Biol; 59:4549-58. 2014

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iCTV

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BSPTV: SPR, Setup errors and Motion

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MIP-AVG

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iCTV

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Stopping power ratio: ± 3%, Setup errors: ±3 mm Motion quantification: 4DCT

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BSPTV: Sum 3 uncertainties Sum: linear or quadratic summation

• 3 uncertainties margins are displayed as Stopping power ratio, Setup and Motion, respectively.

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Magenta: Linear Sum Yellow: Quadratic Sum

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BSPTV: Contribution of 3 uncertainties BSPTV volume: Linear and quadratic summation The volume of BSPTV by linear summation can be ~7% larger

than that by quadratic.

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BSPTV: Gantry angle optimization Minimizing the overlapped volumes along with the BSPTV will help spare lung,

heart and cord before the start of plan optimization.

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BSPTV overlap lung beam overlap lung beam overlap cord

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BSPTV applied in PBS for lung tumor 10 patients were re-planed using PBS based on BSPTV method Evaluation: 12 Perturbations were applied on 8 CT phase for

both PBS and DS plans• ±3% uncertainty in stopping power ratio (2×)• ± 3 mm for setup errors in x, y and z direction (2×3)• 8 CT phases(8×)

Total 96=12*8 evaluation plans for each patient

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The robustness of PBS and DS plans were evaluated. The bands are displayed to show all perturbations of iCTV.

BSPTV PBS plans vs. DS

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BSPTV PBS plans vs. DS Average (solid lines) and 25th and 75th percentile (dashed lines)

OAR DVHs for PBS (red) and DS (blue) of 10 patient plans.• Average uncertainties of DVH per patient are represented separately with red and

blue error bars over the average DVH.

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Interplay effect Having a breathing cycle of ~3.5 seconds with delivery durations of ~60 seconds and ~46 seconds

for the involved two beams. The spots’ time sequence was read out from the beam delivery log files. For different treatment fractions or beam paintings in the same fraction, the beams randomly start from a position of the 3.5-second breathing period. PBS spots were therefore grouped into the eight different breathing phases. One treatment plan was split into eight plans outside of Eclipse using our in-house Matlab program.

All doses were deformed to CT-50.

Energy(MeV) Spots

8 CT Phases

0% 12.5% 25% 37.5% 50% 62.5% 75% 87%110 38 38122 78 78145 104 78 26160 151 138 13176 197 14 170 13180 232 60 169 3190 265 66 175 24199 260 25 172 63202 279 93 186210 298 178 72 48218 304 96 192 16

MUs 567.0 42.53 75.83 124.1 55.70 50.68 45.63 98.35 74.12

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Interplay effect110%100%95%50%

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Conclusion

1. BSPTV can give more accurate treatment target volumes.

2. BSPTV can give best gantry angle before the plan optimization.

3. PBS+ BSPTV could achieve better organ sparing and improve target coverage using a repainting or multi-fraction method for treating thoracic tumors.

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Thank you.