Dosimetry for ocular proton beam therapy at the Harvard Cyclotron Laboratory based on the ICRU Report 59

Abstract

The Massachusetts General Hospital, the Harvard Cyclotron Laboratory (HCL), and the Massachusetts Eye and Ear Infirmary have treated almost 3000 patients with ocular disease using high-energy external-beam proton radiation therapy since 1975. The absorbed dose standard for ocular proton therapy beams at HCL was based on a fluence measurement with a Faraday cup (FC). A majority of proton therapy centers worldwide, however, use an absorbed dose standard that is based on an ionization chamber (IC) technique. The ion chamber calibration is deduced from a measurement in a reference 60Co photon field together with a calculated correction factor that takes into account differences in a chamber's response in 60Co and proton fields. In this work, we implemented an ionization chamber-based absolute dosimetry system for the HCL ocular beamline based on the recommendations given in Report 59 by the International Commission on Radiation Units and Measurements. Comparative measurements revealed that the FC system yields an absorbed dose to water value that is 1.1% higher than was obtained with the IC system. That difference is small compared with the experimental uncertainties and is clinically insignificant. In June of 1998, we adopted the IC-based method as our standard practice for the ocular beam.

Monte Carlo calculations and measurements of absorbed dose per monitor unit for the treatment of uveal melanoma with proton therapy

“…The cause of the initial energy distribution is rooted in the design of the proton beam transport system as the proton bunches are created, accelerated and steered toward the treatment room. The mean proton energy of 159 MeV was taken from the literature (Newhauser et al 2002b). Given these parameters, the simulated and measured pristine peaks agreed to within 0.6% at depths proximal to the distal 90% dose level and to within 0.5 mm in the distal fall-off region.…”

“…Similarly, the D/MU values of the four modulated beams were measured at the center of the SOBP, per standard practice at NPTC (Newhauser et al 2002b). The water-equivalent depths of the eight D/MU measurements are also given in table 1.…”

Out-of-Field Dose Equivalents Delivered by Passively Scattered Therapeutic Proton Beams for Clinically Relevant Field Configurations

“…Prostate, cranial medulloblastoma, and spinal medulloblastoma fields were measured on the gantry treatment beam line, and an ocular melanoma field, on the MGH eye beam line (28). Additional measurements were completed with the patient-specific prostate aperture replaced with a solid brass beam block.…”

Effect of elemental compositions on Monte Carlo dose calculations in proton therapy of eye tumors

“…Despite the widespread use of ocular proton therapy with different suggested methods and designed systems, related literature has reported the dose calculations carried out with the water-equivalent phantoms with non-115 anatomically accurate geometries [22,[31][32][33][34]. Due to the importance of an accurate dose calculation to have a more realistic assessment of sufficiency of the available proton beam for a sensitive organ like the eye, this commonly used approach may make the dosimetry study unreliable.…”