Investigation of the relative conformity and efficiency for ... - Wcenter.de

Conclusions• This study indicates that the sensitivity of dose conformity to beam size for IMPTdepends on the proximity of critical structures, their dose constraints, and the numberof beams delivered.• With the geometrically tight prostate phantom and only 2 fields, acceptable resultswere obtained with 3 and 6 mm beam σ, but not greater.• With the more forgiving lung phantom geometry, satisfactory results were obtainedwith beam σ up to 12 mm, but only with the addition of more fields.• Theoretically the time difference between 3 and 12 mm beam σ delivered fields in thetransverse direction is (3/12)^12=0,0625 a factor of 16 times. A longitudinal timedifferential also exists where the number of energy layers required scales linearly withbeam spot size.• This study suggests that there may be some clinical cases, such as prostate, wheredelivery time may be required to be longer to maintain conformity, and others, suchas lung, where a more efficient delivery of larger beam spots may be desirable. Thismay also reduce delivery sensitivity to target motion.• However, only two limited geometries were considered for this study. Hence, furtherinvestigation is suggested also with clinical cases before general conclusions can bemade regarding suggested beam σ’s for IMPT.