Development of a Tongue Immobilization Device Using a 3D Printer for Intensity Modulated Radiation Therapy of Nasopharyngeal Cancer Patients

A Novel Immobilization Method for the Treatment of Head and Neck Cancer Using 3D Printing

Proper immobilization is critical for the delivery of high-quality radiation therapy. In cases when traditional immobilization is not feasible, 3-dimensional (3D) printing may provide a better-tolerated custom immobilization that is comparably effective. We present the successful treatment of a patient with inoperable oropharyngeal squamous cell carcinoma who was unable to tolerate traditional immobilization. To avoid covering the face, we created a 3D-printed cradle for the back of his head and neck. This design enabled the patient to tolerate traditional simulation scans with and without intravenous contrast and was subsequently able to undergo volumetric modulated arc therapy treatment. He successfully underwent treatment without evidence of disease more than 2 years after completion. The effect of 3D printing within the context of radiation oncology, as well as in other specialties, will undoubtedly continue to increase the variety of treatment options available to patients.

Novel tongue-positioning device to reduce tongue motions during radiation therapy for head and neck cancer: Geometric and dosimetric evaluation

This study aimed to assess the performance of a tongue-positioning device in interfractional tongue position reproducibility by cone-beam computed tomography (CBCT). Fifty-two patients treated with radiation therapy (RT) while using a tongue positioning device were included in the study. All patients were treated with 28 or 30 fractions using the volumetric modulated arc therapy technique. CBCT images were acquired at the 1st, 7th, 11th, 15th, 19th, 23th, and 27th fractions. Tongues on planning computed tomography (pCT) and CBCT images were contoured in the treatment planning system. Geometric differences in the tongue between pCT and CBCT were assessed by the Dice similarity coefficient (DSC) and averaged Hausdorff distance (AHD). Two-dimensional in vivo measurements using radiochromic films were performed in 13 patients once a week during sessions. The planned dose distributions were compared with the measured dose distributions using gamma analysis with criteria of 3%/3 mm. In all patients, the mean DSC at the 1st fraction (pCT versus 1st CBCT) was 0.80 while the mean DSC at the 27th fraction (pCT versus 27th CBCT) was 0.77 with statistical significance (p-value = 0.015). There was no statistically significant difference in DSC between the 1st fraction and any other fraction, except for the 27th fraction. There was statistically significant difference in AHD between the 1st fraction and the 19th, 23th, and 27th fractions (p-value < 0.05). In vivo measurements showed an average gamma passing rate of 90.54%. There was no significant difference between measurements at the 1st week and those at other weeks. The tongue geometry during RT was compared between pCT and CBCT. In conclusion, the novel tongue-positioning device was found to minimize interfractional variations in position and shape of the tongue.

Dosimetric comparison between VMAT plans using the fast-rotating O-ring linac with dual-layer stacked MLC and helical tomotherapy for nasopharyngeal carcinoma

BACKGROUND

To compare the dosimetric profiles of volumetric modulated arc therapy (VMAT) plans using the fast-rotating O-ring linac (the Halcyon system) based on a dual-layer stacked multi-leaf collimator and helical tomotherapy (HT) for nasopharyngeal cancer (NPCa).

METHODS

For 30 NPCa patients, three sets of RT plans were generated, under the same policy of contouring and dose constraints: HT plan; Halcyon VMAT plan with two arcs (HL_2arc); and Halcyon VMAT plan with four arcs (HL_4arc), respectively. The intended dose schedule was to deliver 67.2 Gy to the planning gross target volume (P-GTV) and 56.0 Gy to the planning clinical target volume (P-CTV) in 28 fractions using the simultaneously integrated boost concept. Target volumes and organ at risks dose metrics were evaluated for all plans. Normal tissue complication probabilities (NTCP) for esophagus, parotid glands, spinal cord, and brain stem were compared.

RESULTS

The HT plan achieved the best dose homogeneity index for both P_GTV and P_CTV, followed by the HL_4arc and L_2arc plans. No significant difference in the dose conformity index (CI) for P_GTV was observed between the HT plan (0.80) and either the HL_2arc plan (0.79) or the HL_4arc plan (0.83). The HL_4arc plan showed the best CI for P_CTV (0.88), followed by the HL_2arc plan (0.83) and the HT plan (0.80). The HL_4arc plan (median, interquartile rage (Q1, Q3): 25.36 (22.22, 26.89) Gy) showed the lowest D_mean in the parotid glands, followed by the HT (25.88 (23.87, 27.87) Gy) and HL_2arc plans (28.00 (23.24, 33.99) Gy). In the oral cavity (OC) dose comparison, the HT (22.03 (19.79, 24.85) Gy) plan showed the lowest D_mean compared to the HL_2arc (23.96 (20.84, 28.02) Gy) and HL_4arc (24.14 (20.17, 27.53) Gy) plans. Intermediate and low dose regions (40-65% of the prescribed dose) were well fit to the target volume in HL_4arc, compared to the HT and HL_2arc plans. All plans met the dose constraints for the other OARs with sufficient dose margins. The between-group differences in the median NTCP values for the parotid glands and OC were < 3.47% and < 1.7% points, respectively.

CONCLUSIONS

The dosimetric profiles of Halcyon VMAT plans were comparable to that of HT, and HL_4arc showed better dosimetric profiles than HL_2arc for NPCa.