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
(* Equally contributing authors)
Supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17-W81XWH and W81XWH

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: , 2006
Kang Y, Zhang X, Chang JY et al. Int J Radiat Oncol Biol.,67: , 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: , 2010

3. 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 shoot
BSPTV
iCTV
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:

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

5. BSPTV: Sum 3 uncertainties
Sum: linear or quadratic summation
3 uncertainties margins are displayed as Stopping power ratio, Setup and Motion, respectively.
Stopping power ratio(SPR)
Motion
Setup
Magenta: Linear Sum Yellow: Quadratic Sum

6. 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.

7. 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

8. 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

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

10. 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.

11. Interplay effect Energy (MeV) Spots 8 CT Phases 0% 12.5% 25% 37.5% 50%
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
122 78
145
104 26
160
151
138 13
176
197 14
170
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

12. Interplay effect
110%
100%
95%
50%

13. 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.

14. Thank you.