Longitudinal study on the correlations of thyroid antibody and thyroid hormone levels after radiotherapy in patients with nasopharyngeal carcinoma with radiation-induced hypothyroidism.

BACKGROUND: The purpose of this study was to evaluate the correlations of thyroid antibody and thyroid hormone in postradiotherapy (post-RT) patients with nasopharyngeal carcinoma (NPC). METHODS: Serum thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), thyroperoxidase antibody (anti-TPO), and thyroglobulin antibody (anti-TG) levels of 55 patients with NPC were taken before RT and at 3, 6, 12, and 18 months after RT. Patients with hypothyroidism at 18 months after RT and those with normal thyroid function were categorized into the hypo and normal groups, respectively. The thyroid antibody levels were compared between the 2 groups, and the correlations of thyroid antibody and thyroid hormone were evaluated for the hypo group. RESULTS: The anti-TPO and anti-TG of the hypo group were higher than the normal group. In the hypo group, there was a positive correlation (r = 0.51) between TSH and anti-TG and a negative correlation between fT4 and anti-TPO (r = -0.55). CONCLUSION: There were correlations of the thyroid antibody and thyroid hormone levels in patients with radiation-induced hypothyroidism.

Advanced nasopharyngeal carcinoma radiotherapy with volumetric modulated arcs and the potential role of flattening filter-free beams.

PURPOSE: The purpose of this study is to investigate the dosimetric characteristics of volumetric modulated arc therapy (VMAT) with flattening filter-free (FFF) beams and assess the role of VMAT in the treatment of advanced nasopharyngeal carcinoma (NPC). METHODS: Ten cases of CT data were randomly selected from advanced NPC patients. Three treatment plans were optimized for each patient, RapidArc with FFF beams (RA-FFF), conventional beams (RA) and static gantry intensity-modulated radiation therapy (IMRT). The doses to the planning target volumes (PTVs), organs at risk (OARs), skin and normal tissue were compared. All the plans were delivered on a Varian TrueBeam linear accelerator and verified using the Delta4 phantom. Technical delivery parameters including the mean gamma score, treatment delivery time and monitor units (MUs) were also analyzed. RESULTS: All the techniques delivered adequate doses to the PTVs. RA-FFF gave the highest D(1%) (dose received by 1% of the volume), but the poorest conformity index (CI) and homogeneity index (HI) among the PTVs except for the planning target volume of involved regional lymph nodes (PTV66) CI, which showed no significant difference among three techniques. For the planning target volume of the primary nasopharyngeal tumor (PTV70), RA-FFF provided for higher mean dose than other techniques. For the planning target volume receiving 60 Gy (PTV60) and PTV66, RA delivered the lowest mean doses whereas IMRT delivered the highest mean doses. IMRT demonstrated the highest percentage of target coverage and D(99%) for PTV60. RA-FFF provided for the highest doses to the brain stem, skin and oral cavity. RA gave the highest D(1%) to the right optic nerve among three techniques while no significant differences were found between each other. IMRT delivered the highest mean doses to the parotid glands and larynx while RA delivered the lowest mean doses. Gamma analysis showed an excellent agreement for all the techniques at 3%/3 mm. Significant differences in the MUs were observed among the three techniques (p < 0.001). Delivery times for RA-FFF and RA were 152 ± 7s and 153 ± 7s, respectively, nearly 70% lower than the 493 ± 24s mean time for IMRT. CONCLUSIONS: All treatment plans met the planning objectives. The dose measurements also showed good agreement with computed doses. RapidArc technique can treat patients with advanced NPC effectively, with good target coverage and sparing of critical structures. RA has a greater dosimetric superiority than RA-FFF.

Volumetric modulation arc radiotherapy with flattening filter-free beams compared with conventional beams for nasopharyngeal carcinoma: a feasibility study.

There is increasing interest in the clinical use of flattening filter-free (FFF) beams. In this study, we aimed to investigate the dosimetric characteristics of volumetric modulated arc radiotherapy (VMAT) with FFF beams for nasopharyngeal carcinoma (NPC). Ten NPC patients were randomly selected to undergo a RapidArc plan with either FFF beams (RA-FFF) or conventional beams (RA-C). The doses to the planning target volumes (PTVs), organs at risk (OARs), and normal tissues were compared. The technical delivery parameters for RapidArc plans were also assessed to compare the characteristics of FFF and conventional beams. Both techniques delivered adequate doses to PTVs. For PTVs, RA-C delivered lower maximum and mean doses and improved conformity and homogeneity compared with RA-FFF. Both techniques provided similar maximum doses to the optic nerves and lenses. For the brain stem, spinal cord, larynx, parotid glands, oral cavity, and skin, RA-FFF showed significant dose increases compared to RA-C. The dose to normal tissue was lower in RA-FFF. The monitor units (MUs) were (536 ± 46) MU for RA-FFF and (501 ±25) MU for RA-C. The treatment duration did not significantly differ between plans. Although both treatment plans could meet clinical needs, RA-C is dosimetrically superior to RA-FFF for NPC radiotherapy.