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SU‐E‐T‐348: Measurement‐Guided 4D VMAT Dose Reconstruction on an Arbitrary Homogeneous Dataset
Author(s) -
Opp D,
Robinson J,
Nelms B,
Zhang G,
Feygelman V
Publication year - 2012
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 - 10.1118/1.4735435
Subject(s) - imaging phantom , nuclear medicine , homogeneous , ionization chamber , sagittal plane , cube (algebra) , materials science , biomedical engineering , medicine , physics , mathematics , radiology , ion , geometry , quantum mechanics , thermodynamics , ionization
Purpose: To develop and validate a VMAT QA tool that takes as input a 2D, low‐density (∼10 mm) empirical dose map from a commercial helical diode array, and outputs a high density, volumetric, time‐resolved (4D) dose matrix on an arbitrary patient dataset. At first, the method validation is limited to a homogeneous ‘patient’. Methods: A VMAT treatment is delivered to a diode array (ArcCHECK, Sun Nuclear Corp., Melbourne, FL). 3DVH software (Sun Nuclear) derives the high‐density volumetric dose using measurement‐guided dose reconstruction (MGDR). MGDR cylindrical phantom results are then used to perturb the 3D TPS dose on the patient dataset, producing a semi‐empirical volumetric dose grid. Four‐dimensional dose reconstruction on the patient is also possible by morphing the sub‐beam instead of composite dose. For validation, TG‐119 structures and objectives were used. 3DVH and TPS cumulative point doses were compared to ion chamber in a cube water‐equivalent phantom (‘patient’). The shape of the phantom is different from the ArcCHECK and the targets were placed asymmetrically. Ion chamber dose sampled at 10Hz was compared to time‐resolved 3DVH point doses. Coronal and sagittal absolute film dose distributions in the cube were compared with 3DVH and TPS. Results: Across four TG‐119 plans, the average PTV point dose difference in the cube between 3DVH and ion chamber is 0.0±0.9%. Average film vs. 3DVH gamma analysis passing rates are 88.6, 96.1, and 99.5% for 1%/2mm, 2%/2mm, and 3%/3mm criteria, respectively. 4D MGDR was also sufficiently accurate. Conclusions: Even for a well‐commissioned TPS, comparison metrics show on average better agreement between MGDR and measurement compared to MGDR and TPS on the arbitrary‐shaped phantom (‘patient’). The method requires no more accelerator time than standard QA, while producing more clinically relevant information. Validation in a heterogeneous thoracic phantom is under way, as is ultimate application to virtual motion studies. Supported in part by a grant from Sun Nuclear Corp.