This document describes a method called Beam Specific Planning Target Volume (BSPTV) for proton therapy of thoracic tumors. BSPTV incorporates uncertainties from stopping power ratio, setup errors, and organ motion into the target volume. It generates individual beam-specific target volumes and optimizes gantry angles to minimize volume overlaps and spare organs. When applied to 10 patient plans using proton pencil beam scanning, BSPTV resulted in more robust target coverage and reduced doses to organs-at-risk compared to double scattering plans, especially when evaluated under various perturbation scenarios.

1. 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 Pennsylvania
2Henry 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.

2. 2
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, 2006
Kang Y, Zhang X, Chang JY et al. Int J Radiat Oncol Biol.,67:906-914, 2007
Lomax AJ. Phys Med Biol., 53: 1043, 2008
Lomax AJ , Phys Med Biol; 53: 1027, 2008
Zhang 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, 2012
Flampouri S, Hoppe BS, Slopsema RL et al. Phys Med Biol; 59:4549-58. 2014
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BSPTV
iCTV

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BSPTV: SPR, Setup errors and Motion
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MIP-AVG
Mim IP-AVG
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iCTV
Distal M
Proximal M
 Stopping power ratio: ± 3%, Setup errors: ±3 mm
 Motion quantification: 4DCT

5. 5
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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Stopping power ratio(SPR)
Motion
Setup
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.
G270
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 38
122 78 78
145 104 78 26
160 151 138 13
176 197 14 170 13
180 232 60 169 3
190 265 66 175 24
199 260 25 172 63
202 279 93 186
210 298 178 72 48
218 304 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 effect
110%
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.