Comparing proton treatment plans of pediatric XXXX in two @entity4653 nozzles with different spot sizes.

@entity1 @entity137 @entity1313 @entity1315 @entity4653
Target coverage and organ-at-risk sparing were compared for 22 pediatric @entity1 with primary @entity1313 treated using two distinct nozzles in @entity4653 ( @entity4653 ) proton therapy. Consecutive @entity1 treated at our institution using a @entity4653 -dedicated nozzle (DN) were replanned using a universal nozzle (UN) beam model and the original DN plan objectives. Various cranial sites were treated among the @entity1 to prescription doses ranging from 45 to 54 Gy. Organs at risk (OARs) evaluated were @entity1 -dependent; 15 unique OARs were analyzed, all of which were assessed in at least 10 @entity1 . Clinical target volume (CTV) coverage and organ sparing were compared for the two nozzles using dose-volume histogram data. Statistical analysis using a confidence-interval approach demonstrates that CTV coverage is equivalent for UN and DN plans within    5% equivalence bounds. In contrast, average mean and maximum doses are significantly higher for nearly all 15 OARs in the UN plans. The average median increase over all OARs and @entity1 is approximately 1.7 Gy, with an increase in the 25%-75% of 1.0-2.3 Gy; the median increase to the @entity1315 and cochleas are 1.8, 1.7, 0.7, and 2.7 Gy, respectively. The CTV dose distributions fall off slower for UN than for the DN plans; hence, normal tissue structures in close proximity to CTVs receive higher doses in UN plans than in DN plans. The higher OAR doses in the UN plans are likely due to the larger spot profile in plans created with UN beams. In light of the high rates of @entity137 in pediatric @entity1 receiving cranial irradiation and in light of selected @entity1313 types having high cure rates, this study suggests the smaller DN beam profile is preferable for the advantage of reducing dose to OARs.
