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TU‐FF‐A2‐02: Dual‐Fields Rotational Total Skin Electron Irradiation/therapy
Author(s) -
Xu M,
Sethi A,
Glasgow GP,
Gao M,
Ke Y,
Rusu I,
Roeske J,
Chi A,
Garza R
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2962645
Subject(s) - imaging phantom , dosimetry , ionization chamber , nuclear medicine , materials science , linear particle accelerator , dose profile , irradiation , field size , beam (structure) , biomedical engineering , optics , physics , medicine , ionization , nuclear physics , quantum mechanics , ion
Purpose: We have developed a new technique for rotational total skin electron therapy (RTSET). The technique combines the rotational method of McGill University with the Stanford University angled dual‐fields method. We report dosimetry characteristics and in‐vivo dosimetry. Method and Materials: Patients stand on a rotational (0.9 rpm) platform at an extended SSD (332cm) with field‐size 133‐cm by 133‐cm. The gantry is angled 70° and 110° so that beam points above patient's head and below patient's feet, respectively, in order to minimize contaminant x‐ray dose. A “high‐dose‐rate” mode (600 MU/min) on a Varian‐21EX delivers a 6 MeV‐electron beam. Daily treatments require only about 0.5 h, one‐half of which is used for patient set‐up. Shields are used for eyes, nails, and toes. Dosimetry measurements include static dose‐rate at extended SSD, rotational dose‐rate for a rotating patient/phantom, and a power law correction for SSD variation. In‐vivo dose measurements are performed using XV‐films and MOSFET. Films strips are attached firmly on patient's skin to avoid any air gaps. Results: We obtained MU = Dose/(0.0751*0.39 *(332/SSD) 2.25 ). Therefore, a prescription dose of 125cGy at 325cm SSD required 4068 MU or 7.5 revolutions. The dose distribution along the vertical direction was measured by a parallel‐plate ionization chamber in a phantom. For a patient prescribed 116cGy daily, the average measured surface dose with film was 110cGy, within 5% of prescribed dose. In‐vivo MOSFET on a patient prescribed 125cGy daily, measured doses were distributed from 99% to 102% from the prescribed dose of 125cGy. Conclusion: The dual‐field RTSET offers combined advantages of shorter beam‐on time, uniform dose distribution, larger treatment fields, and less x‐ray contamination than other techniques. Our in‐vivo measurements revealed that delivered dose matched prescribed dose to < 5% and dose uniformity was within 6% variation.