Trajectory log analysis and cone‐beam CT‐based daily dose calculation to investigate the dosimetric accuracy of intensity‐modulated radiotherapy for gynecologic cancer

Abstract

This study evaluated unexpected dosimetric errors caused by machine control accuracy, patient setup errors, and patient weight changes/internal organ deformations. Trajectory log files for 13 gynecologic plans with seven‐ or nine‐beam dynamic multileaf collimator (MLC) intensity‐modulated radiation therapy (IMRT), and differences between expected and actual MLC positions and MUs were evaluated. Effects of patient setup errors on dosimetry were estimated by in‐house software. To simulate residual patient setup errors after image‐guided patient repositioning, planned dose distributions were recalculated (blurred dose) after the positions were randomly moved in three dimensions 0–2 mm (translation) and 0°–2° (rotation) 28 times per patient. Differences between planned and blurred doses in the clinical target volume (CTV) D98% and D2% were evaluated. Daily delivered doses were calculated from cone‐beam computed tomography by the Hounsfield unit‐to‐density conversion method. Fractional and accumulated dose differences between original plans and actual delivery were evaluated by CTV D98% and D2%. The significance of accumulated doses was tested by the paired t test. Trajectory log file analysis showed that MLC positional errors were −0.01 ± 0.02 mm and MU delivery errors were 0.10 ± 0.10 MU. Differences in CTV D98% and D2% were <0.5% for simulated patient setup errors. Differences in CTV D98% and D2% were 2.4% or less between the fractional planned and delivered doses, but were 1.7% or less for the accumulated dose. Dosimetric errors were primarily caused by patient weight changes and internal organ deformation in gynecologic radiation therapy.

Clinical commissioning of an adaptive radiotherapy platform: Results and recommendations

“…Additional tests could be considered, which would address common clinical scenarios experienced in other anatomical regions such as respiratory motion, or multiple scenarios could be combined and evaluated (e.g., simultaneous weight loss and changes in gas), as this commonly occurs clinically. 32 Furthermore, if clinics do have access to phantoms that can include known deformation, these would also be beneficial for validating online adaptive workflows and understanding limitations of adaptive platforms. However, the simple tests described in this study were essential to our understanding of the limitations and functionality of our adaptive platform.…”

Dose deviations induced by fractional image guidance system errors in intensity-modulated radiotherapy for brain tumor treatment

“…The results showed that the average dosimetric deviation of the PTV due to setup errors ranging from -2 to 2 mm per fraction were approximately -6% for D 98% , -4% for D 95% , and less than -1% for D 2% . Errors in fractional delivery dose led to a large underdose in the D 98% correlation, as found by Utena et al, 16 while dose deviation was caused by a high isodose line shift from the PTV. Siebers et al 17 have shown that the dose changes in gross target volume of head-and-neck squamous cell carcinomas treated with simultaneous integrated boost (SIB)-IMRT techniques were about 3-5% and the D 98% is the parameter that is most sensitive to patient position uncertainties.…”

Assessment of dosimetric impact of interfractional 6D setup error in tongue cancer treated with IMRT and VMAT using daily kV-CBCT

“…CBCT-based dose reconstruction could provide the actual dose delivered to the patient in the treatment fraction. Previous studies have reported on the feasibility and accuracy of CBCT for treatment dose simulation [35][36][37][38][39][40][41][42].…”