Patient and pretreatment assessment:
From February 2010 to March 2015, 181 patients were identified for inclusion in the study. The inclusion criteria were as follows: (1) laryngeal squamous cell carcinoma was confirmed by biopsy; (2) total laryngectomy and lymph node dissection had been performed; (3) postoperative pathology showed that lymph node biopsy was positive, and the positive lymph nodes were only in areas II and III while the rest of the lymph nodes were not metastatic; and (4) preoperative MRI scans of the larynx had been performed.
The pretreatment evaluation included medical history, physical examination, laryngoscope, whole blood cell count, liver and kidney function, chest CT, abdominal ultrasound, neck ultrasound and laryngeal MRI scans. PET-CT and bone scan were performed in symptomatic patients.
Radiotherapy:
Total neck prophylactic irradiation group:
The patient was fixed in the supine position with a thermoplastic mask, and a simulated CT location was performed with 3 mm thickness. The upper boundary of the location was the cranial crest, and the lower boundary was 3 cm below the sternoclavicular joint. PTVtb includes the primary tumour bed area with the prescription dose DT: 60 Gy/30 F; PTV is the whole neck prevention area with the prescription dose DT: 50 gy/25 F. The patients were treated once a day, five times a week.
Selective high-risk area irradiation group:
As shown in Fig. 1, PTVtb includes the primary tumour bed area with the prescription dose DT: 60 Gy/30 F; PTV is a selective high-risk area, i.e., areas II and III, with the prescription dose DT: 50 gy/25 F. Patients were treated once a day, five times a week. The other conditions were the same as the whole neck prophylactic irradiation group.
The difference between the two groups was mainly due to the difference of PTV range. Compared with the whole neck radiation group, the selective high-risk area irradiation group only included areas II and III with higher cervical lymph node metastasis rate of supraglottic laryngeal cancer.
From February 2010 to March 2015, 181 patients were identified for inclusion in the study.Among them, 100 patients received whole neck prophylactic irradiation and 81 patients received selective high-risk area irradiation.
Chemotherapy:
After the treatment, the two groups were given 4-6 cycles of TP sequential chemotherapy of paclitaxel 135 mg/m2, D1 and loplatin 30 mg/m2, D2.
Follow up:
In the first year, patients were rechecked every 1-3 months, and in the second year they were rechecked every 2-6 months.
Patients were rechecked every 4-8 months in years 3-5 and every 12 months in years >5. The examination items included chest X-ray or CT, abdominal ultrasound, neck ultrasound, laryngoscopy, laryngoscope, and routine blood work. If necessary, PET-CT and bone scans were performed.
The OS, PFS, NFS, recurrence rate, injury degree of normal tissue and incidence of late toxicity were counted. Recurrent cases diagnosed by imaging were completed by radiotherapists and radiologists. All endpoints were defined as the time interval from the beginning of treatment to failure or final follow-up. All the data were analysed by SPSS 24.0 statistical software after audit, and the counting data were analysed by chi square tests and t-tests, where significance was established at p = 0.05.
We designed and observed the following indexes of normal tissue injury.
1) Radiation-induced oral mucositis (ROM) is a common complication of radiotherapy for head and neck tumours6. Oral mucositis usually occurs 7 to 14 days after the start of chemotherapy or radiotherapy, presenting as erythema, ulcer, bleeding, edoema and pain7. These complications may cause oral discomfort in patients, thus delaying the treatment and failing to achieve good therapeutic effect. In addition, the loss of mucosal integrity also increases the chance of infection and endangers the life of patients8. With the increase in irradiation dose, there will be corresponding changes in the oral cavity. When the dose of irradiation is 20 Gy, the viscosity of saliva increases; when the dose is 30 Gy, erythema and ulcers occur in the oral mucosa, and the taste is abnormal, which can cause secondary infection and bleeding; when the dose is 40 Gy, saliva secretion stops; when the dose is 50 Gy, oral mucositis is aggravated, which affects eating; and when the dose is 60-70 Gy, it is difficult to speak and swallow.
The World Health Organization (WHO) evaluated radiation-induced oral mucositis. The evaluation of radiation-induced oral mucosal reaction recommended by WHO consists of 0-IV standard grades. Grade 0: no symptoms and signs; grade I: erythema, mild pain; grade II: painful erythema, edoema, or ulcer, but able to eat; grade III: painful erythema, edoema or ulcer, only able to feed with liquid; and grade IV: unable to eat, requiring parenteral or enteral support.
2) Xerostomia also may occur. Saliva in the mouth mainly comes from the secretion of three glands, the parotid gland, the submandibular gland and the sublingual gland. The parotid gland secretes more than half of the saliva and is very sensitive to radiation. Because the parotid gland is located in the path of radiotherapy, radiotherapy will inevitably cause parotid gland injury. Severe xerostomia can even lead to mandibular necrosis, which seriously affects the quality of life of patients9, 10. The function of the parotid gland is to secrete saliva, and saliva secretion can decrease when the accumulative radiation dose reaches 10 Gy at the earliest; after the accumulative dose reaches 40 Gy, the production of parotid gland saliva has basically stopped; and 60 Gy will cause irreversible damage to the parotid gland. According to the RTOG/EORTC grading standard of acute radiation injury11, the evaluation standard of xerostomia in this study was determined as follows: Grade I: no significant change compared to before radiotherapy; grade II: Patients' subjective feeling of xerostomia, when they eat dry food, they do not need liquids; grade III: when they eat, they must take liquids, otherwise they cannot eat dry food; and grade IV: when they need to wake up and drink water or speak for a long time, and the mouth feels dry.
3) Taste change is one of the early reactions to radiotherapy for head and neck tumours. This phenomenon was first reported in 1955. In recent years, a large number of clinical and experimental studies have been carried out on this phenomenon12-15. More people think that the direct damage to the taste buds by radiation is the cause of taste change, but it may also damage the salivary glands and nerves, which indirectly leads to damage of taste buds, or they may exist at the same time13-15.
4) Difficulty in opening the mouth is a common complication of head and neck cancer patients after radiotherapy. The temporomandibular joint and masseter muscle degenerate and fibrose under the action of radiation, resulting in muscle atrophy and joint stiffness. The temporomandibular joint tightens and aches when the mouth is opened, and a severe case can have difficulty in pronunciation and eating. For the evaluation of difficulty in opening the mouth after radiotherapy, we used the subjective and objective treatment analysis standard, which is divided into four levels: Level I, limited opening of the mouth, 2.1-3.0 cm between the teeth; level II, difficulty in eating dry food, 1.1-2.0 cm between the teeth; level III, difficulty in eating soft food, 0.5-1.0 cm between the teeth; and level IV, less than 0.5 cm between the teeth, unable to eat, and requiring nasal feeding. Bhatiaks et al. defined the gap between the teeth ≤ 2.5 cm as opening difficulty16.
5) Cervical fibrosis: there are many factors affecting the occurrence of cervical fibrosis after radiotherapy for laryngeal malignant tumour. The higher the dose of radiotherapy, the more serious the degree of cervical fibrosis17. From 3 months to half a year after radiotherapy, the edoema of the face and neck gradually subside, and fibrosis of the neck begins to appear; from 1 to 2 years, severe fibrosis of the neck (grade III to IV) gradually forms; and from 4 to 5 years, the capillaries gradually expand. The mechanism of cervical fibrosis after radiotherapy is that the skin and muscle of the neck undergo an inflammatory reaction after irradiation, including vascular endothelial injury, endothelial cell necrosis and shedding, and increased vascular permeability. Leukocytes leak out of the blood vessels and gather at the site of infection and injury; releasing proteolytic enzymes and chemical mediators (tumour necrosis factor, interleukin-1, nitric oxide 5-hydroxytryptamine, histamine, etc.). In addition, oxygen free radicals play a role in phagocytosis and immunity, and cause normal tissue damage18. When the tissue damage is serious, a large amount of fibrinogen leaks out, but the leaking cellulose cannot be completely absorbed and gradually continues to deposit in the extracellular matrix, leading to mechanization. Over time, some blood vessels degenerate and the elasticity of the soft tissue disappears, which seriously affects the neck activity function. According to the criteria of late radiation injury, the degree of cervical fibrosis can be divided into the following categories: grade 0, no fibrosis; grade I, mild fibrosis; grade II, moderate fibrosis, no symptoms; grade III, severe fibrosis; and grade IV, tissue necrosis.
6) Laryngopharyngeal mucosa damage: the effects are similar to those of oral mucositis, the laryngopharyngeal mucosa will be damaged after radiotherapy19. The clinical manifestations are pharyngeal pain, dysphagia and hoarseness, which can form protracted radioactive pharyngitis. There are mucinous glands in the submucosa of oropharynx and laryngopharynx. The latter can secrete mucus and play a role in moistening mucosa. After irradiation, the secretion function of the salivary gland is inhibited. The mucous membrane is dry and it loses the ability to self-clean, so it is easily infected. Radiation may also directly damage the mucous membrane, resulting in erosion and ulceration of the mucous membrane. Different from the whole neck prophylactic irradiation group, the lower boundary of the target area in the selective high-risk area irradiation group is higher, so the damage to the throat mucosa is avoided. Through laryngoscopy, we can clearly and accurately evaluate the influence of different radiotherapy targets on the mucosa after radiotherapy. The grades of the oropharyngeal mucosa reaction are as follows: grade 0: normal mucosa; grade I: slight congestion of the pharyngeal mucosa; grade II: moderate congestion of the pharyngeal mucosa with edoema; grade III: severe congestion of the pharyngeal mucosa with scattered erosion of the oral mucosa; and grade IV: lamellar ulcer, haemorrhage and necrosis of the pharyngeal mucosa.