Table 1.

Comparisons of and indications for VMAT-IMRT, PSPT, and IMPT

Technique	Pros	Cons	Clinical scenarios beneficial to proton therapy
IMRT-VMAT	High conformity between prescription isodose line and target	Higher low to medium dose to normal tissues limiting the ability for dose escalation
	Robust with respect to changes in motion or anatomy
	Lower cost and higher availability
PSPT	Limited low or medium dose to normal tissues enabling target dose escalation	Possibly higher lung mean dose and volume receiving 20 Gy and higher for complicated anatomy, lack of proximate conformation to target	Centrally located stage I disease
	Can be made robust with respect to changes in motion or anatomy	Poor conformality of prescription isodose line to target due to 3D planning, lack of conformity in the proximal end of the target volume and range uncertainty	Stage II to III disease without contralateral hilar lymph node involvement
IMPT	High conformity between prescription isodose line and target	Because of range uncertainty, less robust with respect to motion and/or changes in anatomy, making the treatment of mobile targets difficult	Centrally located stage I disease
	Spares more normal tissues than IMRT or PSPT including the heart, cord, lung, esophagus, and so on	Complexity of motion management, plan optimization, and quality assurance	Stage II to III disease with adequate motion management, robustness optimization, and strict quality assurance

Abbreviations: IMPT = intensity modulated proton therapy; IMRT = intensity modulated radiation therapy; PSPT = passive scattering proton therapy; 3D = 3-dimensional; VMAT = volumetric intensity modulated arc therapy.