Proton therapy dose distribution comparison between Monte Carlo and a treatment planning system for pediatric patients with ependymoma.
OBJECTIVE
Compare dose distributions for pediatric patients with ependymoma calculated using a Monte Carlo (MC) system and a clinical treatment planning system (TPS).


METHODS
Plans from ten pediatric patients with ependymoma treated using double scatter proton therapy were exported from the TPS and calculated in our MC system. A field by field comparison of the distal edge (80% and 20%), distal fall off (80% to 20%), field width (50% to 50%), and penumbra (80% to 20%) were examined. In addition, the target dose for the full plan was compared.


RESULTS
For the 32 fields from the 10 patients, the average differences of distal edge at 80% and 20% on central axis between MC and TPS are -1.9 ± 1.7 mm (p < 0.001) and -0.6 ± 2.3 mm (p = 0.13), respectively. Excluding the fields that ranged out in bone or an air cavity, the 80% difference was -0.9 ± 1.7 mm (p = 0.09). The negative value indicates that MC was on average shallower than TPS. The average difference of the 63 field widths of the 10 patients is -0.7 ± 1.0 mm (p < 0.001), negative indicating on average the MC had a smaller field width. On average, the difference in the penumbra was 2.3 ± 2.1 mm (p < 0.001). The average of the mean clinical target volume dose differences is -1.8% (p = 0.001), negative indicating a lower dose for MC.


CONCLUSIONS
Overall, the MC system and TPS gave similar results for field width, the 20% distal edge, and the target coverage. For the 80% distal edge and lateral penumbra, there was slight disagreement; however, the difference was less than 2 mm and occurred primarily in highly heterogeneous areas. These differences highlight that the TPS dose calculation cannot be automatically regarded as correct.
St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, Tennessee 38120, USA.
Yingcui
Y
Jia
Chris
C
Beltran
Daniel J
DJ
Indelicato
Stella
S
Flampouri
Zuofeng
Z
Li
Thomas E
TE
Merchant
D000465:Algorithms; D001921:Brain / Q000473:pathology*; D001932:Brain Neoplasms / Q000532:radiotherapy; D002648:Child; D003198:Computer Simulation; D004806:Ependymoma / Q000532:radiotherapy*; D006801:Humans; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D061766:Proton Therapy; D018787:Radiation Oncology / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014867:Water / Q000737:chemistry
D014867:Water