Monte Carlo evaluation of tissue heterogeneities corrections in the treatment of head and neck cancer patients using stereotactic radiotherapy

Abstract

The purpose of this study was to generate Monte Carlo computed dose distributions with the X-ray voxel Monte Carlo (XVMC) algorithm in the treatment of head and neck cancer patients using stereotactic radiotherapy (SRT) and compare to heterogeneity corrected pencil-beam (PB-hete) algorithm. This study includes 10 head and neck cancer patients who underwent SRT re-irradiation using heterogeneity corrected pencil-beam (PB-hete) algorithm for dose calculation. Prescription dose was 24-40 Gy in 3-5 fractions (treated 3-5 fractions per week) with at least 95% of the PTV volume receiving 100% of the prescription dose. A stereotactic head and neck localization box was attached to the base of the thermoplastic mask fixation for target localization. The gross tumor volume (GTV) and organs-at-risk (OARs) were contoured on the 3D CT images. The planning target volume (PTV) was generated from the GTV with 0 to 5 mm uniform expansion; PTV ranged from 10.2 to 64.3 cc (average = 35.0±17.5 cc). OARs were contoured on the 3D planning CT and consisted of spinal cord, brainstem, optic structures, parotids, and skin. In the BrainLab treatment planning system (TPS), clinically optimal SRT plans were generated using hybrid planning technique (combination of 3D conformal noncoplanar arcs and nonopposing static beams) for the Novalis-Tx linear accelerator consisting of high-definition multileaf collimators (HD-MLCs: 2.5 mm leaf width at isocenter) and 6 MV-SRS (1000 MU/min) beam. For the purposes of this study, treatment plans were recomputed using XVMC algorithm utilizing identical beam geometry, multileaf positions, and monitor units and compared to the corresponding clinical PB-hete plans. The Monte Carlo calculated dose distributions show small decreases (< 1.5%) in calculated dose for D 99 , D mean , and D max of the PTV coverage between the two algorithms. However, the average target volume encompassed by the prescribed percent dose (V p ) was about 2.5% less with XVMC vs. PB-hete and ranged between -0.1 and 7.8%. The averages for D 100 and D 10 of the GTV were lower by about 2% and ranged between -0.8 and 3.1%. For the spinal cord, both the maximal dose difference and the dose to 0.35 cc of the structure were higher by an average of 4.2% (ranged 1.2 to -13.6%) and 1.4% (ranged 7.5 to -11.3%), respectively, with XVMC calculation. For the brainstem, the maximal dose differences and the dose to 0.5 cc of the structure were, on average, higher by 2.4% (ranged 6.4 to -8.0%) and 3.6% (ranged 6.4 to -9.0%), respectively. For the parotids, both the mean dose and the dose to 20 cc of parotids were higher by an average of 3% (ranged -0.2 to -5.9%) and 4% (ranged -0.2 to -8%), respectively, with XVMC calculation. For the optic apparatus, results from both algorithms were similar. However, the mean dose to skin was 3% higher (ranged 0 to -6%), on average, with XVMC compared to PB-hete, although the maximum dose to skin was 2%

Clinical outcomes after local field conformal reirradiation of patients with retropharyngeal nodal metastasis

“…[4][5][6] The HN-SBRT treatment was delivered using the Varian TrueBeam STx system (Varian Medical Systems, Palo Alto, CA) with high definition (2.5 mm) leaflets and planned using the 2-3 arc VMAT technique with patients immobilized in a custom biteblock-mask-cushion system with image-guided on-line setup correction, as previously described. [7][8][9] The HN-SBRT was delivered in 5 fractions every other day over 2 weeks.…”

Validation of the RayStation Monte Carlo dose calculation algorithm using a realistic lung phantom

“…We searched articles available to the public from multiple journals concerning lung phantoms. Although a number of phantoms have been tested, including solid water, cork and solid water, balsa wood and solid water, balsa wood and cork, cork and plastic, cork and acrylic, polystyrene and cork, bolus and sponge, foam, and even wood, it appears that we are the first to report open‐access on the use of a cork‐and‐animal‐tissue lung tumor phantom.…”

HyperArc VMAT stereotactic radiotherapy for locally recurrent previously‐irradiated head and neck cancers: Plan quality, treatment delivery accuracy, and efficiency

“…[1][2][3][4][5][6][7][8] Some literature exists regarding the use of Linac-based SRT for head and neck recurrent cancers. [8][9][10][11][12] For instance, Unger and his colleagues presented a feasibility study concerning re-irradiating head and neck cancer patients using the CyberKnife technique with fractionated-SRT scheme. 2 For 65 patients, the median initial radiation dose was 67 Gy (in 33 fractions), and the median re-irradiation SRT dose was 30 Gy (21-35 Gy) in 2-5 fractions.…”

“…Many researchers have described the utilization of fractionated SRT for re‐irradiation of head and neck tumors, primarily using CyberKnife radiosurgery 1–8 . Some literature exists regarding the use of Linac‐based SRT for head and neck recurrent cancers 8–12 . For instance, Unger and his colleagues presented a feasibility study concerning re‐irradiating head and neck cancer patients using the CyberKnife technique with fractionated‐SRT scheme 2 .…”