Benefit of [18F] FDG PET/CT in the diagnosis and salvage treatment of recurrent nasopharyngeal carcinoma.

PURPOSE: To compare PET/CT, MRI and ultrasonography in detecting recurrence of nasopharyngeal carcinoma and identify their benefit in staging, contouring and overall survival (OS). METHODS: Cohort A included 1453 patients with or without histopathology-confirmed local recurrence, while cohort B consisted of 316 patients with 606 histopathology-confirmed lymph nodes to compare the sensitivities and specificities of PET/CT, MRI and ultrasonography using McNemar test. Cohorts C and D consisted of 273 patients from cohort A and 267 patients from cohort B, respectively, to compare the distribution of PET/CT-based and MRI-based rT-stage and rN-stage and the accuracy of rN-stage using McNemar test. Cohort E included 30 random patients from cohort A to evaluate the changes in contouring with or without PET/CT by related-samples T test or Wilcoxon rank test. The OS of 61 rT3-4N0M0 patients staged by PET/CT plus MRI (cohort F) and 67 MRI-staged rT3-4N0M0 patients (cohort G) who underwent similar salvage treatment were compared by log-rank test and Cox regression. RESULTS: PET/CT had similar specificity to MRI but higher sensitivity (93.9% vs. 79.3%, P < 0.001) in detecting local recurrence. PET/CT, MRI and ultrasonography had comparable specificities, but PET/CT had greater sensitivity than MRI (90.9% vs. 67.6%, P < 0.001) and similar sensitivity to ultrasonography in diagnosing lymph nodes. According to PET/CT, more patients were staged rT3-4 (82.8% vs. 68.1%, P < 0.001) or rN + (89.9% vs. 69.3%, P < 0.001), and the rN-stage was more accurate (90.6% vs. 73.8%, P < 0.001). Accordingly, the contours of local recurrence were more precise (median Dice similarity coefficient 0.41 vs. 0.62, P < 0.001) when aided by PET/CT plus MRI. Patients staged by PET/CT plus MRI had a higher 3-year OS than patients staged by MRI alone (85.5% vs. 60.4%, P = 0.006; adjusted HR = 0.34, P = 0.005). CONCLUSION: PET/CT more accurately detected and staged recurrence of nasopharyngeal carcinoma and accordingly complemented MRI, providing benefit in contouring and OS.

Accumulated Dose Deviation of Rotational and Residual Setup Errors on Nasopharyngeal Carcinoma Using MIM Treated by Helical Tomotherapy.

BACKGROUND: To analyze the relationship between the rotational and residual setup errors and the dose deviation on nasopharyngeal carcinoma (NPC) treated by helical tomotherapy (HT). METHODS: From 25 July 2017 to 20 August 2019, 16 treated NPC patients were enrolled in the study. These patients were scanned with full target range megavoltage computed tomography (MVCT) every other day. Adaptive radiotherapy function application software MIM7.1.3 were used to accumulate the actual dose. The dose deviation with the initial plan dose of the patients' target and organs at risk (OAR) were compared, and the correlation between the dose change and the setup errors (rotational setup errors and neck residual setup error) was analyzed. RESULTS: Translational setup errors increased farther away from the head. Statistically significant difference among 3 groups was achieved in the directions of left-right (P < .001) and anteroposterior (P < .001) by analysis of variance test. Compared with the initial plan dose, the actual accumulated dose of the target area decreased with the actual exposure dose of the OAR increased. However, most of the dosimetric parameters differed by less than 5%. No correlation was found between dose deviation values and the translational setup errors of target. However, sagittal rotational setup errors (pitch) had a positive relationship (P < .05) with the avearge dose of PTVnd (L) (r = 0.885), PTVnd(R) (r = 0.547) PTV1(r = 0.633) and PTV2(r = 0.584). Transverse rotational setup errors (roll) had a positive relationship (P < .05) with the avearge dose of PTVnd(R) (r = 0.593), PTV1(r = 0.505) and PTV2(r = 0.662). CONCLUSIONS: Dose deviation between the actual accumulated and initial plan is not negligible, but most indicators difference is less than 5%, NPC patients treated by HT with MVCT correction setup errors every other day did not need adaptive radiotherapy model unless got rapid tumor shrinkage or weight loss. Moreover, to minimize the dose deviation, more attention should be paid to the reduction of pitch, roll, and residual error of cervical vertebrae during body positioning.

Comparison of set up accuracy among three common immobilisation systems for intensity modulated radiotherapy of nasopharyngeal carcinoma patients.

INTRODUCTION: In intensity modulated radiotherapy (IMRT) of nasopharyngeal carcinoma (NPC) patients, an effective immobilisation system is important to minimise set up deviation. This study evaluated the effectiveness of three immobilisation systems by assessing their set up deviations. METHODS: Patients were randomly assigned to one of the three immobilisation systems: (1) supine on head rest and base plate (HB); (2) supine with alpha cradle supporting the head and shoulder (AC); (3) supine with vacuum bag supporting the head and shoulder (VB). CBCT was conducted weekly for each patient on the linear accelerator. Image registration was conducted at the nasopharynx (NP) and cervical regions. The translational displacements (latero-medial, antero-posterior and cranio-caudal), rotational displacements (pitch, yaw and roll) and 3D vectors obtained at the NP and cervical regions were recorded and compared among the three systems. RESULTS: The mean translational and rotational deviations were within 3 mm and 2°, respectively, and the range of 3D vector was 1.53-3.47 mm. At the NP region, the AC system demonstrated the smallest translational and rotational deviations and 3D vector. The differences were significant except for the latero-medial, yaw and roll directions. Similarly, at the cervical region, the AC system showed smaller translational and rotational deviations and 3D vector, with only the cranio-caudal and yaw deviations that did not reach statistical significance. CONCLUSIONS: Set up deviation was greater in the neck than the NP region. The set up accuracy of the AC system was better than the other two systems, and it is recommended for IMRT of NPC patients in our institution.

Evaluating the therapeutic dose distribution of intensity-modulated radiation therapy for head and neck with cone-beam computed tomography image: a methodological study.

An approximate correction method for the CT value-electron density curve of CBCT was established, through comparison and fitting with FBCT images, and applied to evaluate the therapeutic dose of IMRT. The precision of using CBCT for plan calculation was validated by comparing the dose distribution between CBCT- and FBCT-based IMRT plans. Also setup deviations were simulated to evaluate the ability of the CBCT-based calculation for detecting the dose errors caused by positioning deviation. The gamma comparison between CBCT- and FBCT-based dose computations showed that the pass rates of (2%, 2 mm) criteria were better than 97.60 ± 0.83% and 97.74 ± 2.08% in the phantom and 10 NPC cases. When setup deviation was introduced into CBCT-based dose calculation, the gamma pass rate significantly decreased while the volumetric doses of the targets and some normal organs exhibited different changes compared to the original plan. Our results validated the above CT value-electron density correction which reduced the difference between CBCT- and FBCT-based IMRT plan calculation for NPC to less than 2%. Online CBCT-based dose calculation can be used to reflect and evaluate the dose distribution discrepancy caused by setup deviation and structure changes during the treatment, ensuring more effective quality control of IMRT treatment.