TH-A-137-08: On the Validity of Target Density Overrides for RapidArc Lung SBRT Treatment Planning

Wiant, D; Yount, C; Pursley, J; Terrell, J; Mäurer, J; Sintay, B

doi:10.1118/1.4815690

Cited by 3 publications

(7 citation statements)

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“…Due to the density difference between the tumour and the lung tissue found within the PTV, inverse optimisation tends to cause an increased fluence at the PTV edge, which can cause increased dose deposition as the tumour moves within the PTV. This is typically mitigated using density overrides during optimisation [78,79].…”

Section: Imaging For Simulationmentioning

confidence: 99%

Image-guided Radiotherapy to Manage Respiratory Motion: Lung and Liver

et al. 2020

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Organ motion as a result of respiratory and cardiac motion poses significant challenges for the accurate delivery of radiotherapy to both the thorax and the upper abdomen. Modern imaging techniques during radiotherapy simulation and delivery now permit better quantification of organ motion, which in turn reduces tumour and organ at risk position uncertainty. These imaging advances, coupled with respiratory correlated radiotherapy delivery techniques, have led to the development of a range of approaches to manage respiratory motion. This review summarises the key strategies of image-guided respiratory motion management with a focus on lung and liver radiotherapy.

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Section: Imaging For Simulationmentioning

confidence: 99%

Image-guided Radiotherapy to Manage Respiratory Motion: Lung and Liver

et al. 2020

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“…One method to overcome the issues associated with inhomogeneity corrections in lung and tumor motion is to override the electron densities of the ITV/PTV . A study by Fu et al .…”

Section: Introductionmentioning

confidence: 99%

“…devised a method for overriding the density of the PTV to 0.8 g/cm 3 to reduce the planned MU while still delivering sufficient dose to the tumor for SBRT lung planning. Wiant et al . compared the use of free‐breathing CT scans, time average scans, and ITV/PTV tissue‐density overridden scans for lung SBRT to evaluate the accuracy of each method for predicting dose deposition in lung tissue.…”

Section: Introductionmentioning

confidence: 99%

“…compared the use of free‐breathing CT scans, time average scans, and ITV/PTV tissue‐density overridden scans for lung SBRT to evaluate the accuracy of each method for predicting dose deposition in lung tissue. Accuracy was assessed from measurements using Gafchromic film in a QUASAR phantom . A further study by Wiant et al .…”

Section: Introductionmentioning

confidence: 99%

“…The studies by Wiant et al . were performed using the Eclipse planning system, and the method has not currently been extended to any other dose calculating algorithms.…”

Section: Introductionmentioning

confidence: 99%

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The dosimetric effect of electron density overrides in 3DCRT Lung SBRT for a range of lung tumor dimensions

Healy

Marsh

Cousins

2018

J Applied Clin Med Phys

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The combined effects of lung tumor motion and limitations of treatment planning system dose calculations in lung regions increases uncertainty in dose delivered to the tumor and surrounding normal tissues in lung stereotactic body radiotherapy (SBRT). This study investigated the effect on plan quality and accuracy when overriding treatment volume electron density values. The QUASAR phantom with modified cork cylindrical inserts, each containing a simulated spherical tumor of 15‐mm, 22‐mm, or 30‐mm diameter, was used to simulate lung tumor motion. Using Monaco 5.1 treatment planning software, two standard plans (50% central phase (50%) and average intensity projection (AIP)) were compared to eight electron density overridden plans that focused on different target volumes (internal target volume (ITV), planning target volume (PTV), and a hybrid plan (HPTV)). The target volumes were set to a variety of electron densities between lung and water equivalence. Minimal differences were seen in the 30‐mm tumor in terms of target coverage, plan conformity, and improved dosimetric accuracy. For the smaller tumors, a PTV override showed improved target coverage as well as better plan conformity compared to the baseline plans. The ITV plans showed the highest gamma pass rate agreement between treatment planning system (TPS) and measured dose (P < 0.040). However, the low electron density PTV and HPTV plans also showed improved gamma pass rates (P < 0.035, P < 0.011). Low‐density PTV overrides improved the plan quality and accuracy for tumor diameters less than 22 mm only. Although an ITV override generated the most significant increase in accuracy, the low‐density PTV plans had the additional benefit of plan quality improvement. Although this study and others agreed that density overrides improve the treatment of SBRT, the optimal density override and the conditions under which it should be applied were found to be department specific, due to variations in commissioning and calculation methods.

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Assessment of a diaphragm override strategy for robustly optimized proton therapy planning for esophageal cancer patients

et al. 2021

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To ensure target coverage in the treatment of esophageal cancer, a density override to the region of diaphragm motion can be applied in the optimization process. Here, we evaluate the benefit of this approach during robust optimization for intensity modulated proton therapy (IMPT) planning.Materials and Methods: For ten esophageal cancer patients, two robustly optimized IMPT plans were created either using (WDO) or not using (NDO) a diaphragm density override of 1.05 g/cm 3 during plan optimization. The override was applied to the excursion of the diaphragm between exhale and inhale. Initial robustness evaluation was performed for plan acceptance (setup errors of 8 mm, range errors of ±3%), and subsequently, on all weekly repeated 4DCTs (setup errors of 2 mm, range errors of ±3%). Target coverage and hotspots were analyzed on the resulting voxel-wise minimum (Vw min ) and voxel-wise maximum (Vw max ) dose distributions. Results:The nominal dose distributions were similar for both WDO and NDO plans. However, visual inspection of the Vw max of the WDO plans showed hotspots behind the right diaphragm override region.For one patient, target coverage and hotspots improved by applying the diaphragm override. We found no differences in target coverage in the weekly evaluations between the two approaches. Conclusion:The diaphragm override approach did not result in a clinical benefit in terms of planning and interfractional robustness. Therefore, we don't see added value in employing this approach as a default option during robust optimization for IMPT planning in esophageal cancer.

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TH-A-137-08: On the Validity of Target Density Overrides for RapidArc Lung SBRT Treatment Planning

Cited by 3 publications

References 0 publications

Image-guided Radiotherapy to Manage Respiratory Motion: Lung and Liver

Image-guided Radiotherapy to Manage Respiratory Motion: Lung and Liver

The dosimetric effect of electron density overrides in 3DCRT Lung SBRT for a range of lung tumor dimensions

Assessment of a diaphragm override strategy for robustly optimized proton therapy planning for esophageal cancer patients

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