Dosimetric comparison of dose accumulation between rigid registration and deformation registration in intensity-modulated radiation therapy for large volume non-small cell lung cancer

RAdiotherapy Dose Accumulation Routine (RADAR)-A Novel Dose Accumulation Script With Built-In Uncertainty

PURPOSE

To incorporate uncertainty into dose accumulation for reirradiation.

METHODS AND MATERIALS

The RAdiotherapy Dose Accumulation Routine (RADAR) script for the Eclipse treatment planning system (Varian Medical Systems) is described, and the voxel-wise ellipsoid search algorithm is introduced as a means of incorporating uncertainty. RADAR is first demonstrated on a test patient reirradiated to the spine, illustrating the effect of the uncertainty algorithm. A summary of initial evaluation testing conducted by 11 users, each of whom ran a separate spine reirradiation case, follows. Finally, RADAR run times are reported for various conditions.

RESULTS

In the demonstration case in which a 3-mm ellipsoid search was used, the maximum RADAR 2-Gy equivalent (EQD2) accumulated spinal cord dose increased from 7244 to 12,689 cGy because the ellipsoid search pulled dose from closer to the adjacent target structure. When the ellipsoid search was restricted to voxels within the spinal cord, the maximum accumulated cord dose was reduced to 6523 cGy and did not exceed the sum of the maximum EQD2 spinal cord doses of the individual plans (6730 cGy). In the evaluation cases, the RADAR EQD2 maximum dose for the spinal cord increased by an average of 31.6% with uncertainty applied compared to a conventional dose accumulation and decreased by an average of 16.7% compared to a conventional dose accumulation when the uncertainty calculation was restricted to voxels within the spinal cord. RADAR run times vary depending on the number of plans added and the type of uncertainty used.

CONCLUSIONS

RADAR offers a novel way to directly account for uncertainty in dose accumulation through a voxel-wise ellipsoid search algorithm. EQD2 dose accumulation with and without dose discounts is also available.

Quantifying the Effect of 4-Dimensional Computed Tomography-Based Deformable Dose Accumulation on Representing Radiation Damage for Patients with Locally Advanced Non-Small Cell Lung Cancer Treated with Standard-Fractionated Intensity-Modulated Radiation Therapy

PURPOSE

The aim of this study was to investigate the dosimetric and clinical effects of 4-dimensional computed tomography (4DCT)-based longitudinal dose accumulation in patients with locally advanced non-small cell lung cancer treated with standard-fractionated intensity-modulated radiation therapy (IMRT).

METHODS AND MATERIALS

Sixty-seven patients were retrospectively selected from a randomized clinical trial. Their original IMRT plan, planning and verification 4DCTs, and ∼4-month posttreatment follow-up CTs were imported into a commercial treatment planning system. Two deformable image registration algorithms were implemented for dose accumulation, and their accuracies were assessed. The planned and accumulated doses computed using average-intensity images or phase images were compared. At the organ level, mean lung dose and normal-tissue complication probability (NTCP) for grade ≥2 radiation pneumonitis were compared. At the region level, mean dose in lung subsections and the volumetric overlap between isodose intervals were compared. At the voxel level, the accuracy in estimating the delivered dose was compared by evaluating the fit of a dose versus radiographic image density change (IDC) model. The dose-IDC model fit was also compared for subcohorts based on the magnitude of NTCP difference (|ΔNTCP|) between planned and accumulated doses.

RESULTS

Deformable image registration accuracy was quantified, and the uncertainty was considered for the voxel-level analysis. Compared with planned doses, accumulated doses on average resulted in <1-Gy lung dose increase and <2% NTCP increase (up to 8.2 Gy and 18.8% for a patient, respectively). Volumetric overlap of isodose intervals between the planned and accumulated dose distributions ranged from 0.01 to 0.93. Voxel-level dose-IDC models demonstrated a fit improvement from planned dose to accumulated dose (pseudo-R2 increased 0.0023) and a further improvement for patients with ≥2% |ΔNTCP| versus for patients with <2% |ΔNTCP|.

CONCLUSIONS

With a relatively large cohort, robust image registrations, multilevel metric comparisons, and radiographic image-based evidence, we demonstrated that dose accumulation more accurately represents the delivered dose and can be especially beneficial for patients with greater longitudinal response.

Applied research of a four-dimensional CT localization technique in radiotherapy and treatment planning for early lung cancer

BACKGROUND

To study the feasibility of target contouring and the potential benefits to radiotherapy of four-dimensional computed tomography (4D-CT) for early stage lung cancer.

METHODS

We applied Brilliance CT to scan 24 lung cancer patients for 4D localization. Treatment plannings based on different breath phase CT images were designed in the Monaco 5.2 treatment planning system. Different planning was compared to find the difference of target volume, center, and dose.

RESULTS

Target volume composed of 10-breath phases (Sum) was considered as the reference volume, which was slightly larger than the volume contouring obtained by the maximum intensity projection (Mip) and extreme phase images (Exs). Target centers for Sum, Mip and Exs of CT images showed little deviation in the X, Y and Z directions. The V20 and V5 for the 4D-CT-based treatment plan showed a markedly lower dose delivered to normal tissues than those based on 3D-CT.

CONCLUSIONS

For target contouring, a target contouring by 10-breath phases was superior to Mip and Exs. As the gross target volume (GTV) contouring obtained by the maximum intensity projection and extreme phase were similar to that of the reference target, they can support the contouring target and reduce the time and work. Treatment plan comparisons indicated that normal lung tissues received a remarkably lower dose when a 4D-CT-based plan was used.