Clinical validation and applications for CT-based atlas for contouring the lower cranial nerves for head and neck cancer radiation therapy

Dosimetric investigation of radiation-induced trigeminal nerve toxicity in parotid tumor patients

PURPOSE

We aimed to describe the association between trigeminal nerve (TN) dose and toxicity and determine a threshold value that leads to TN toxicity in patients with parotid tumors treated with adjuvant conventional fractionated radiation therapy.

METHODS AND MATERIALS

Eighteen patients who underwent adjuvant radiotherapy (RT) between 2013 and 2018 were included in this retrospective study. TN and its branches were outlined subsequently on the planning CT scans. The doses received by TN were obtained based on the dose-volume histogram. The dose and toxicity relationship was investigated over the total prescribed dose. RT-related toxicity was graded according to Common Terminology Criteria for Adverse Events V4.0 (CTCAEv4.0).

RESULTS

The median follow-up was 29.5 months. After RT, 61% of patients had Grade I-II late TN toxicity divided into Grade I in 4 (22%) and Grade II in 7 (39%) patients. TN injury symptoms were as follows: loss of sensation in the chin area in 3, difficulty in jaw movements in 3, and paresthesia in 5 patients. The total RT dose (p = 0.001), Dmax (p = 0.001), PTV-TN Dmax (p = 0.001), D1cc (p = 0.004), D0.5cc (p = 0.001), and D0.1cc (p = 0.01) had a significant effect on TN toxicity. Cut-off values leading to toxicity were determined as 66, 65.5, 65.25, 63.6, and 62.7 Gy for Dmax, PTV-TN Dmax, D0.1cc, D 0.5cc, and D1cc, respectively.

CONCLUSIONS

Radiation-induced TN injury in head and neck cancer patients may further be investigated in clinically prospective trials by virtue of high toxicity rates with current RT doses in our retrospectively designed dosimetric study in parotid tumors.

Hypoglossal nerve delineation in nasopharyngeal carcinoma patients may reduce the radiation dose and damage to the nerve

This study aims to establish a delineation guideline for the contouring of the hypoglossal nerve by dividing the nerve into different segments, and to test the possibility of a radiation dose reduction to the hypoglossal nerve in NPC patients receiving radiotherapy. Twenty NPC patients were selected arbitrarily. The hypoglossal nerves were delineated using anatomic landmarks and divided into the cisternal, intracanalicular, carotid, and transverse segments. The tumor coverage by radiation and dose-volume parameters of the nerve with and without various dose constraints to the hypoglossal nerve were compared. The hypoglossal nerve, which is invisible on CT images, can be delineated accurately with the assistance of several anatomic landmarks. Without a dose constraint to the hypoglossal nerve, the carotid space, intracanalicular, and transverse segments had high radiation dose-volumes. The dose-volume to the nerve, however, can be reduced when the nerve was defined and a dose constraint was given. The delineation of the hypoglossal nerve with its different segments is feasible. The carotid space, intracanalicular, and transverse segments received the highest dose, where the nerve damage was most likely located. The dose to the nerve can be reduced to less than 70 Gy using the intensity-modulated radiotherapy technique.

Vertebral artery sparing volumetric modulated arc therapy in nasopharyngeal carcinoma

Vascular stenosis is a late radiation complication that develops in long-term survivors of nasopharyngeal carcinoma. Vertebral arteries (VAs) are major vessels responsible for posterior circulation. In this study, we evaluated the feasibility of VA-sparing volumetric modulated arc therapy (VMAT) techniques. A total of 20 patients with nasopharyngeal carcinoma treated by a TrueBeam linear accelerator were enrolled in this study. The original VMAT plan was designed without the contouring of VAs as organs at risk (OARs). The same image set of the original VMAT plan was used to contour the VAs for each patient. A new VA-sparing VMAT plan was developed by avoiding VAs as OARs. Finally, a paired t-test was used to compare the dosimetric differences. The VA-sparing VMAT plan had similar target coverage and dose to those of other OARs. The VA-sparing plan yielded a significantly low VA dose from 53 to 40 Gy, with V35Gy changing from 97% to 56%, V50Gy changing from 67% to 35%, and V63Gy changing from 15% to approximately 7%-10% (p < 0.001 for all comparisons). VAs should be correctly identified as OARs. Photon VMAT with VA sparing can help substantially decrease the VA dose.

Radiation Therapy for Adenoid Cystic Carcinoma of the Head and Neck

Simple Summary

Adenoid cystic carcinoma is a rare histology arising in the head and neck region that has a high propensity for perineural invasion. While surgical resection is the preferred primary treatment modality, adjuvant radiotherapy is often indicated to improve local control. For unresectable disease, definitive radiotherapy can be utilized. Given the predilection for perineural tumor spread, target volumes often must encompass relevant nerve pathways back to the base of skull. Treatment strategies for ACC must therefore balance the disease burden and risk of failure against the morbidity of treatment.

Abstract

Adenoid cystic carcinoma of the head and neck is an uncommon malignancy that can arise in the major or minor salivary glands. Perineural invasion (PNI) is an extremely frequent finding in cases of adenoid cystic carcinoma (ACC) that can be associated with significant patient morbidity and poor prognosis. By contrast, ACC rarely demonstrates lymphovascular space invasion thereby making PNI the major avenue for metastasis and a driver of treatment rationale and design. Radiotherapy is often utilized post-operatively to improve locoregional control or as a primary therapy in unresectable disease. Here we aim to review the role of radiotherapy in the management of this malignancy with a focus on target delineation and treatment regimens in the definitive, recurrent, and metastatic settings.

Radiation-induced neuropathies in head and neck cancer: prevention and treatment modalities

Head and neck cancer (HNC) is the sixth most common human malignancy with a global incidence of 650,000 cases per year. Radiotherapy (RT) is commonly used as an effective therapy to treat tumours as a definitive or adjuvant treatment. Despite the substantial advances in RT contouring and dosage delivery, patients suffer from various radiation-induced complications, among which are toxicities to the nervous tissues in the head and neck area. Radiation-mediated neuropathies manifest as a result of increased oxidative stress-mediated apoptosis, neuroinflammation and altered cellular function in the nervous tissues. Eventually, molecular damage results in the formation of fibrotic tissues leading to susceptible loss of function of numerous neuronal substructures. Neuropathic sequelae following irradiation in the head and neck area include sensorineural hearing loss, alterations in taste and smell functions along with brachial plexopathy, and cranial nerves palsies. Numerous management options are available to relieve radiation-associated neurotoxicities notwithstanding treatment alternatives that remain restricted with limited benefits. In the scope of this review, we discuss the use of variable management and therapeutic modalities to palliate common radiation-induced neuropathies in head and neck cancers.

Characterization of very late dysphagia after chemoradiation for oropharyngeal squamous cell carcinoma

OBJECTIVES

Improved prognosis for p16+ oropharyngeal squamous cell carcinoma (OPSCC) has led to efforts to mitigate long-term complications of treatment, which remains poorly defined in late survivors. Here we characterize very late dysphagia in OPSCC.

MATERIALS AND METHODS

Long-term review of 93 p16+ OPSCC patients treated with chemoradiation was performed. We scored videofluoroscopic swallow studies (VFSS) according to the Dynamic Imaging Grade of Swallowing Toxicity (DIGEST) scale. Very late dysphagia was defined >2.5 years from end of treatment. Fine-Gray regression models were used to assess dysphagia with competing risk of death.

RESULTS

Median follow up was 10.5 years. 402 total VFSS were assessed (median 4 per patient, range 0-8). 15.1% of patients had a DIGEST score ≥2 very late after treatment. Very late DIGEST score ≥2 correlated with T-stage (HR 1.7, p = 0.049), second cancer (HR 6.5, p = 0.004), superior pharyngeal constrictor dose (HR 1.11, p = 0.050), total tongue dose (HR 1.07, p = 0.045), but not hypoglossal nerve dose (p > 0.2). Seven patients (7.5%) had late progressive dysphagia, defined as DIGEST score that increased by ≥2 beyond one year after treatment, and this correlated with higher ipsilateral hypoglossal nerve D1cc dose (75 vs 72 Gy, p = 0.037).

CONCLUSION

In p16+ OPSCC patients treated with definitive chemoradiation, at least 7.5% developed late progressive dysphagia, and 15.1% experienced moderate dysphagia >2.5 years from treatment. Our study suggests that dose to tongue musculature may be associated with very late dysphagia, and hypoglossal nerve dose may be associated with late progressive dysphagia. More intensive long-term dysphagia survivorship monitoring is suggested.

Application of hypoglossal nerve constraint in definitive radiotherapy for nasopharyngeal carcinoma: A dosimetric feasibility study

PURPOSE

Radiation-induced hypoglossal nerve palsy is an infrequent but debilitating late complication after definitive radiotherapy for head and neck cancers. D1cc < 74 Gy (equivalent dose in 2 Gy fractions, EQD2) has been proposed as a potential dose constraint that limits 8-year palsy risk to < 5%. This study sets to perform detailed dosimetric assessments on the applicability of this novel dose constraint in advanced nasopharyngeal carcinoma (NPC).

MATERIALS AND METHODS

This is a retrospective single-institution dosimetry study. NPC radiotherapy plans were identified from an institutional database, with an aim to select 10 eligible cases. Bilateral hypoglossal nerves were retrospectively contoured following a standard atlas. Cases with either one, or both, hypoglossal nerves D1cc exceeded 74 Gy EQD2 were included. Dosimetry of hypoglossal nerves, planning target volumes (PTV) and normal structures before and after application of the new hypoglossal nerve constraint were compared and analyzed.

RESULTS

Ten NPC cases were replanned. All hypoglossal nerve contours overlapped with high-dose PTV, predominantly at regions of gross nodal diseases. D1cc in 15 out of 20 hypoglossal nerves exceeded 74G y EQD2 at initial plans. All nerves fulfilled the pre-specified constraint of 74Gy EQD2 after re-plan. Median hypoglossal nerve D1cc reduced from 74.8Gy (range, 74.1 to 77.4Gy) to 73.5Gy (range, 72.4 to 74.0Gy) (p < 0.001), corresponded to a projected reduction in 8-year palsy risk from 5%-14% to 3%-5%. PTV V100 was maintained above 95% in all cases. Dose increments in near-maximum (D2) and decrements in near-minimum (D98) were < 1 Gy. Safety dosimetric parameters of standard head and neck organs-at-risk showed no significant changes.

CONCLUSIONS

Hypoglossal nerve D1cc < 74 Gy EQD2 is a dosimetrically feasible constraint in definitive radiotherapy for NPC. Tumor target coverage and normal organ dosimetry were not compromised with its usage. Its routine application should be considered in definitive radiotherapy for head and neck cancers.

Radiation-induced hypoglossal nerve palsy after definitive radiotherapy for nasopharyngeal carcinoma: Clinical predictors and dose-toxicity relationship

BACKGROUND AND PURPOSE

Radiation-induced hypoglossal nerve palsy is a debilitating and irreversible late complication after definitive radiotherapy for nasopharyngeal carcinoma (NPC) and other skull base tumors. This study sets to evaluate its incidence and clinical predictive factors, and to propose relevant dosimetric constraints for this structure to guide radiotherapy planning.

MATERIALS AND METHODS

We undertook a retrospective review of 797 NPC patients who underwent definitive intensity-modulated radiotherapy (IMRT) between 2003 and 2011. Cumulative incidence and clinical predictors for radiation-induced hypoglossal nerve palsy were evaluated. Archived radiotherapy plans were retrieved and 330 independent hypoglossal nerves were retrospectively contoured following standardized atlas. Optimal threshold analyses of dosimetric parameters (Dmax, D0.5cc, D1cc, D2cc, Dmean) were conducted using receiver operating characteristic curves. Normal tissue complication probability was generated with logistic regression modeling.

RESULTS

With a median follow-up of 8.1 years, sixty-nine (8.7%) patients developed radiation-induced hypoglossal nerve palsy. High radiotherapy dose, premorbid diabetes, advanced T-stage and radiological hypoglossal canal involvement were independent clinical risk factors. Maximum dose received by 1 cc volume (D1cc) was the best predictor for the development of radiation-induced nerve palsy (AUC = 0.826) at 8 years after IMRT. Hypoglossal nerves with D1cc of 74 Gy EQD2 had an estimated palsy risk of 4.7%. Nerves with D1cc <74 Gy EQD2 had significantly lower risk of palsy than those ≥74 Gy EQD2 (2.4% vs 20.8%, p <0.001).

CONCLUSION

Incidence of radiation-induced hypoglossal nerve palsy was high after definitive IMRT for NPC. D1cc <74 Gy EQD2 can serve as a useful dose constraint to adopt during radiotherapy planning to limit palsy risk to <5% at 8 years after IMRT.

Radiation-induced lower cranial nerve palsy in patients with head and neck carcinoma

Radiation-induced cranial nerve palsy (RICNP) is a severe long-term complication in patients with head and neck cancer following high-dose radiation therapy (RT). We present the case report of a patient with bilateral RICNP of the hypoglossal and vagus cranial nerves (XII/X) following postoperative RT in the era prior to the introduction of intensity-modulated RT (IMRT), and an analysis of our IMRT patient cohort at risk including the case of a XII RICNP. A total of 201 patients whose glosso-pharyngeal (IX), X and XII cranial nerves had been exposed to >65 Gy definitive IMRT in our institution between January, 2002 and December, 2012 with or without systemic therapy, were retrospectively identified. A total of 151 patients out of 201 fulfilling the following criteria were included in the analysis: Locoregionally controlled disease, with a follow-up (FU) of >24 months and >65 Gy exposure of the nerves of interest. So far, one of the assessed 151 IMRT patients at risk exhibited symptoms of RICNP after 6 years. The mean/median FU of the entire cohort was 71/68 months (range, 27-145). The results were compared with literature reports. In conclusion, RICNP appears to be a rare complication. However, a longer FU and a larger sample size are required to draw reliable conclusions on the incidence of RICNP in the era of IMRT.