A dosimetric comparison of intensity-modulated proton therapy optimization techniques for pediatric craniopharyngiomas: a clinical case study

BACKGROUND

To evaluate the dosimetric characteristics of intensity-modulated proton therapy (IMPT) optimization techniques and pencil-beam scanning (PBS) nozzle designs on pediatric craniopharyngiomas.

PROCEDURE

We compared a double-scatter (DS) plan with IMPT plans using single-field uniform dose (SFUD) optimization or multi-field optimization (MFO) and different PBS nozzles. The clinical impacts of SFUD versus MFO, range shifters, and two different PBS nozzles were compared. For target coverage assessment, the conformity index and inhomogeneity coefficient were evaluated.

RESULTS

Although both proton therapy techniques achieved adequate target coverage, IMPT achieved a better conformity index of 0.78 versus 0.60 for DS. For the inhomogeneity coefficient, IMPT with MFO performed better than using SFUD or DS. MFO with the dedicated nozzle (MFO-DN) achieved the best result of 0.023, as compared to values of 0.03 or higher for the other plans. IMPT achieved lower doses to the normal tissues, as compared to DS; MFO-DN had the best results. The DN provided the best beam-spot characteristics and the sharpest lateral penumbra. MFO reduced the need for range shifters.

CONCLUSIONS

As compared to DS proton therapy for pediatric craniopharyngiomas, IMPT achieved significantly better target coverage and dose sparing of normal tissue. Nozzle designs that provided small beam spots and sharp lateral penumbra allowed for better target coverage and reduced dose to normal tissue. In the case of shallow targets, MFO, in contrast to SFUD, required minimal use of range shifters, which preserved the penumbra and the dosimetric advantage. MFO-DN proved to be the optimal technique for IMPT.