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Proton therapy dose distribution comparison between Monte Carlo and a treatment planning system for pediatric patients with ependymoma a)
Author(s) -
Jia Yingcui,
Beltran Chris,
Indelicato Daniel J.,
Flampouri Stella,
Li Zuofeng,
Merchant Thomas E.
Publication year - 2012
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4736413
Subject(s) - proton therapy , nuclear medicine , monte carlo method , penumbra , radiation treatment planning , medicine , ependymoma , field size , mean value , dosimetry , mathematics , radiology , radiation therapy , statistics , ischemia
Purpose : 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.