Design considerations for a computer controlled multileaf collimator for the Harper Hospital fast neutron therapy facility.
The d(48.5) + Be neutron beam from the Harper Hospital superconducting cyclotron is collimated using a unique multirod collimator (MRC). A computer controlled multileaf collimator (MLC) is being designed to improve efficiency and allow for the future development of intensity modulated radiation therapy with neutrons. For the current study the use of focused or unfocused collimator leaves has been studied. Since the engineering effort associated with the leaf design and materials choice impacts significantly on cost, it was desirable to determine the clinical impact of using unfocused leaves in the MLC design. The MRC is a useful tool for studying the effects of using focused versus unfocused beams on beam penumbra. The effects of the penumbra for the different leaf designs on tumor and normal tissue DVHs in two selected sites (prostate and head and neck) was investigated. The increase in the penumbra resulting from using unfocused beams was small (approximately 1.5 mm for a 5 x 5 cm2 field and approximately 7.6 mm for a 25 x 25 cm2 field at 10 cm depth) compared to the contribution of phantom scatter to the penumbra width (5.4 and 20 mm for the small and large fields at 10 cm depth, respectively). Comparison of DVHs for tumor and critical normal tissue in a prostate and head and neck case showed that the dosimetric disadvantages of using an unfocused rather than focused beam were minimal and only significant at shallow depths. For the rare cases, where optimum penumbra conditions are required, a MLC incorporating tapered leaves and, thus, providing focused collimation in one plane is necessary.
Maughan
Richard L
RL
Gershenson Radiation Oncology Center Karmanos Cancer Institute, Harper Hospital and Wayne State University, Detroit, Michigan 48201, USA. maughan@xrt.upenn.edu
Yudelev
Mark
M
Aref
Amr
A
Chuba
Paul J
PJ
Forman
Jeffrey
J
Blosser
Emanuel J
EJ
Horste
Timothy
T
D000230:Adenocarcinoma / Q000532:radiotherapy; D004867:Equipment Design; D005214:Fast Neutrons / Q000627:therapeutic use*; D006801:Humans; D008297:Male; D009502:Neutrons; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods*; D012542:Scattering, Radiation; D012984:Software; D001743:Urinary Bladder / Q000528:radiation effects; D014867:Water
D014867:Water