Design, development, and implementation of the Radiological Physics Center's pelvis and thorax anthropomorphic quality assurance phantoms

Abstract

The Radiological Physics Center (RPC) developed two heterogeneous anthropomorphic quality assurance phantoms for use in verifying the accuracy of radiation delivery: one for intensity-modulated radiation therapy (IMRT) to the pelvis and the other for stereotactic body radiation therapy (SBRT) to the thorax. The purpose of this study was to describe the design and development of these two phantoms and to demonstrate the reproducibility of measurements generated with them. The phantoms were built to simulate actual patient anatomy. They are lightweight and water-fillable, and they contain imageable targets and organs at risk of radiation exposure that are of similar densities to their human counterparts. Dosimetry inserts accommodate radiochromic film for relative dosimetry and thermoluminesent dosimetry capsules for absolute dosimetry. As a part of the commissioning process, each phantom was imaged, treatment plans were developed, and radiation was delivered at least three times. Under these controlled irradiation conditions, the reproducibility of dose delivery to the target TLD in the pelvis and thorax phantoms was 3% and 0.5%, respectively. The reproducibility of radiation-field localization was less than 2.5 mm for both phantoms. Using these anthropomorphic phantoms, pelvic IMRT and thoracic SBRT radiation treatments can be verified with a high level of precision. These phantoms can be used to effectively credential institutions for participation in specific NCI-sponsored clinical trials.

Commissioning and verification of the collapsed cone convolution superposition algorithm for SBRT delivery using flattening filter‐free beams

“…The thorax phantom contains unit density targets imbedded in lung to allow direct verification of dosimetric calculations in heterogeneous media, but does not allow for planar film measurements in the vicinity of the lung targets. Additionally, prior to treating patients, the Radiological Physics Center's (RPC) lung phantom was irradiated as an independent check of the commissioning (15) . The National Cancer Institute (NCI) requires institutions wishing to participate in NCI‐sponsored clinical trials to image the phantom, create a plan to deliver 6 Gy to the PTV, perform their customary patient specific QA for the phantom plan, and irradiate the phantom.…”

Angular dependence of the nanoDot OSL dosimeter

“…This phantom has been shown to provide accurate and reproducible results using TLDs in photon beams. 23 The phantom's outer shell is composed of polystyrene and is hollow; the shell is filled with water at the time of irradiation. The inner section is a homogenous cylinder made of high-impact polystyrene that fits into the outer shell.…”

Commissioning and initial experience with the first clinical gantry‐mounted proton therapy system

“…The on‐site visit reviewed all the aspects of our practice, including CT calibration, treatment planning, delivery, QA, dosimetry, and workflow. In addition, dosimetric validation was performed on anthropomorphic phantoms representing four clinical sites including craniospinal, prostate, brain, and lung 13 , 14 . Irradiation of the IROC phantoms served both as an admission to NCI‐funded cooperative group clinical trials and a stringent test of our institute's capability of planning and delivering treatments with heterogeneity correctly accounted for.…”