Longitudinal study using a diode phantom for helical tomotherapy IMRT QA.
OBJECTIVE
The Caribbean Radiation Oncology Center acquired a DELTA4 diode phantom for helical tomotherapy IMRT QA and presents the results of their first 264 clinical cases.


METHODS
The validation consisted of several case studies comparing existing ionization chamber and Gafchromic film IMRT QA results to diode phantom results, along with a longitudinal study analyzing the IMRT QA results against other machine QA procedures for a complete sample of IMRT patients.


RESULTS
The case studies resulted in a maximum observed difference of 0.7% between the diode phantom and the ionization chamber measurements in low dose-gradient regions. Over the longitudinal study, every IMRT QA plan passed a gamma specification of a 3%/3 mm and 98% of the diodes yielded a value of less than 1. In addition, the mean 90% isodose absolute difference for all plans was 0.05% with a (lsigma) standard deviation of 1.19%.


CONCLUSIONS
The phantom measurements closely match the planned dose distributions in high and low dose-gradient regions. In addition, a significant positive statistical correlation was determined between the IMRT QA, daily QA, and rotational variation output measurements. Together, these results signify high degree of accuracy of both the DELTA4 phantom as well as the TomoTherapy Hi-Art system.
Geurts
M
M
Caribbean Radiation Oncology Center, P.O. Box 958, Bayamon, Puerto Rico 00959, Puerto Rico. mgeurts@adioscancer.com
Gonzalez
J
J
Serrano-Ojeda
P
P
D006801:Humans; D008137:Longitudinal Studies; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care / Q000379:methods*; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*