SU‐E‐T‐411: Validation of Plan Dose Perturbation Software for Use in Patient Specific IMRT Quality Assurance

Abstract

Purpose: Patient‐specific IMRT quality assurance typically compares measured and calculated dose distributions in‐phantom. The clinical importance of disagreement between measured and calculated dose is often difficult to interpret. Recently, software has been developed (3DVH Sun Nuclear, Florida USA) that calculates the “delivered” dose distributions in patients by perturbing the calculated dose using errors detected in planar dose measurements. The aim of this work was to validate the accuracy of 3DVH versus commercial treatment planning software (Varian Eclipse 8.9). Methods: 17 DMLC prostate IMRT treatment plans were modified by Matlab script by adding randomly distributed positional errors of 1 or 3 mm in the planned MLC positions. These modified plans were delivered to a 2D diode array (MapCheck2, Sun Nuclear). Measured doses were compared to the dose planes from the original or recalculated MLC modified plans and 3DVH calculated a “delivered” dose in the patient. DVH comparisons were made based on mean dose and D99 for the PTV, and mean and maximum dose for the bladder and rectal for each patient and MLC error. Results: Paired Data showed good agreement for planning system and 3DVH dose volume histograms for both targets and organs at risk for both modified and unmodified plans, regardless of MLC error induced. Structure mean dose values as measured for PTV, Bladder and Rectum agreed to within 1% and dose maximum data showing a discrepancy of 2%. Conclusions: 3DVH is a potentially useful tool to calculate delivered dose distributions during patient specific IMRT quality assurance. The 3DVH data allows the user to analyze the difference between planned and delivered dose to given structures. By introducing random delivery errors, we showed that the 3DVH software was able to detect small fluence changes. This demonstrates the accuracy of 3DVH software against a commercial treatment planning system.

3D DVH‐based metric analysis versus per‐beam planar analysis in IMRT pretreatment verification

“…As a result, new approaches based on 3D dose reconstruction and DVH metrics have recently been developed and tested. [9][10][11] Although it has been suggested 8 that false positive and false negative can result from a per-beam gamma analysis, this hypothesis has not yet been clinically demonstrated.…”

“…First, we designed some in-phantom tests to elucidate the capabilities of new software based on DVH metrics and to highlight the flaws that can lead to false positives and false negatives in the conventional approach and to see if they were picked up in the 3DVH software. For the present study, real errors were created and delivered and they were measured with a commercial diode array; in contrast with previous studies 9,11 where errors were simulated and were quantified with an ideal planar detector. Second, we analyzed real patient verifications to highlight the information a DVH metric can typically provide compared to that of a 2D analysis and to see if differences could be related to gamma passing rates.…”

Using a Novel Dose QA Tool to Quantify the Impact of Systematic Errors Otherwise Undetected by Conventional QA Methods: Clinical Head and Neck Case Studies

“…In the process of validation of the 3DVH software (6,8,9,(15)(16)(17)(18)(19), other QA tools have also been used, including for D 95 of PTV 59. 4 and mean larynx dose, respectively.…”

“…Therefore, to predict clinically relevant patient dose errors, IMRT QA should include the evaluation of patient anatomy based metrics directly related to the clinical impact of the dose error. As a result, new approaches based on three-dimensional (3D) dose reconstruction and dose volume histogram (DVH) metrics have recently emerged and been tested (8,9). …”

Dependency of planned dose perturbation (PDP) on the spatial resolution of MapCHECK 2 detectors

“…A number of studies have shown the validity of 3DVH (9,10,12,14,15) . Zhen et al (12) used 24 error‐free IMRT plans and introduced four types of errors to create 96 plans with errors.…”