title: AMBIENT DOSE EQUIVALENT VERSUS EFFECTIVE DOSE FOR QUANTIFYING STRAY RADIATION EXPOSURES TO A PATIENT RECEIVING PROTON THERAPY FOR PROSTATE CANCER.
abstract: The purpose of this study was to evaluate the suitability of the quantity ambient dose equivalent H*(10) as a conservative estimate of effective dose E for estimating stray radiation exposures to patients receiving passively scattered proton radiotherapy for cancer of the prostate. H*(10), which is determined from fluence free-in-air, is potentially useful because it is simpler to measure or calculate because it avoids the complexities associated with phantoms or patient anatomy. However, the suitability of H*(10) as a surrogate for E has not been demonstrated for exposures to high-energy neutrons emanating from radiation treatments with proton beams. The suitability was tested by calculating H*(10) and E for a proton treatment using a Monte Carlo model of a double-scattering treatment machine and a computerized anthropomorphic phantom. The calculated E for the simulated treatment was 5.5 mSv/Gy, while the calculated H*(10) at the isocenter was 10 mSv/Gy. A sensitivity analysis revealed that H*(10) conservatively estimated E for the interval of treatment parameters common in proton therapy for prostate cancer. However, sensitivity analysis of a broader interval of parameters suggested that H*(10) may underestimate E for treatments of other sites, particularly those that require large field sizes. Simulations revealed that while E was predominated by neutrons generated in the nozzle, neutrons produced in the patient contributed up to 40% to dose equivalent in near-field organs.
authors.affiliation: The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard Unit 94, Houston, Texas 77030.
authors.forename: Jonas D
authors.initials: JD
authors.lastname: Fontenot
authors.forename: Phillip
authors.initials: P
authors.lastname: Taddei
authors.forename: Yuanshui
authors.initials: Y
authors.lastname: Zheng
authors.forename: Dragan
authors.initials: D
authors.lastname: Mirkovic
authors.forename: Wayne D
authors.initials: WD
authors.lastname: Newhauser