Treatment of extensive scalp lesions with segmental intensity-modulated photon therapy.
OBJECTIVE
To compare static electron therapy, electron arc therapy, and photon intensity-modulated radiation therapy (IMRT) for treatment of extensive scalp lesions and to examine the dosimetric accuracy of the techniques.


METHODS
A retrospective treatment-planning study was performed to evaluate the relative merits of static electron fields, arcing electron fields, and five-field photon IMRT. Thermoluminescent dosimeters (TLD) were used to verify the accuracy of the techniques. The required thickness of bolus was investigated, and an anthropomorphic phantom was also used to examine the effects of air gaps between the wax bolus used for the IMRT technique and the patient's scalp.


RESULTS
Neither static nor arcing electron techniques were able to provide a reliable coverage of the planning target volume (PTV), owing to obliquity of the fields in relation to the scalp. The IMRT technique considerably improved PTV dose uniformity, though it irradiated a larger volume of brain. Either 0.5 cm or 1.0 cm of wax bolus was found to be suitable. Air gaps of up to 1 cm between the bolus and the patient's scalp were correctly handled by the treatment-planning system and had negligible influence on the dose to the scalp.


CONCLUSIONS
Photon IMRT provides a feasible alternative to electron techniques for treatment of large scalp lesions, resulting in improved homogeneity of dose to the PTV but with a moderate increase in dose to the brain.
Bedford
James L
JL
Joint Department of Physics, The Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK. James.Bedford@icr.ac.uk
Childs
Peter J
PJ
Hansen
Vibeke Nordmark
VN
Warrington
Alan P
AP
Mendes
Ruheena L
RL
Glees
John P
JP
D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use*; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012189:Retrospective Studies; D012535:Scalp; D012878:Skin Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*