The incidence and mortality of lung cancer ranks first among cancers in the world, and the five-year survival rate of lung cancer patients is only 15% to 30%. Lung cancer patients bear a great psychological pressure, prone to anger, isolation, anxiety, depression, self-esteem and other psychological problems. The incidence of psychological disorders in lung cancer patients was 24.2 to 73.4%. A diagnosis of cancer not only causes physical and mental pain to the patient, but also has a huge impact on the family and their caregivers. As patients'primary coping resources, caregivers have to bear both physical and mental pressures. Therefore, it is worth to attention the mental health of lung cancer patients and their caregivers.

With the further deepening of self-concept research and the integration of Buddhist thought and psychology, the new concept of 'self-compassion' was proposed and developed. Self-compassion means that individuals treat themselves like their friends, with a friendly and tolerant attitude; maintains an objective and rational attitude towards the individual's own situation at all times; thinks that pain is a common experience shared by others, and everyone should be understood and sympathized. At the same time, self-compassion not only includes acceptance and affirmation of oneself, but also connects oneself with others, advocating that one should sympathize with oneself as sympathizing with others, providing the possibility of emotional connection between patients and their caregivers. Therefore, the study of mindfulness and self-compassion is expected to provide a reference for improving the dyadic mental health of lung cancer patient-caregiver dyads in China.

Mindfulness Self-Compassion (MSC) is a positive psychology intervention method that covers the concept of self-compassion developed by Neff and Germer on the basis of Mindfulness-based Stress Reduction. MSC is a 2.5-hour weekly, 8-week standardized training course. Some studies have shown that MSC can promote the emotional health of cancer patients and buffer their mental symptoms.

To sum up, the current mindfulness self-compassion training program has been applied to some cancer patients, and shows that the intervention has a positive effect, while the research in China has only been initially applied in the student population, and has not been applied in the field of cancer. Therefore, for lung cancer patient-caregiver dyad, the researchers can learn from the experience of mindfulness self-compassion training and develop a dyadic mental health intervention program based on Chinese condition. The current study aims to verify the effect of the dyadic mindfulness self-compassion intervention program for lung cancer patients and their caregivers, and explore its mechanism.

The study was a single blind, follow-up, randomized, controlled trial. Researchers recruited subjects from two general tertiary hospitals in Changsha, Hunan province, China. And the whole trail was on the basis of the CONSORT statements. The two hospitals provided similar conventional care for lung cancer patients. Study procedures were approved by the institutional review boards of all participating centers before data collection began. All patients were screened by researchers for eligibility and then enrolled in the study if eligible and if the provided consent.

Potential eligible participants were identified by researchers according to medical records at the colorectal surgery unit in each hospital. The participants were recruited with informed consent, and researchers explained the study purposes, procedures, benefits, and risks involved orally. The participants were then randomly allocated to the intervention or the control group according to a computer-generated block randomization list. A sequentially numbered and opaque , sealed envelope system was used by a non-investigator. The generated random numbers were put into consecutively numbered and opaque sealed envelopes. When enrolling and randomising a new participant, the enrolling investigators opened the sealed envelope after participant's name was written on next available envelopes; the enrolling investigators were blinded to the trial design and study hypotheses.

The researcher will recruit 74 lung cancer patient-caregiver dyads and randomly divide them into 2 groups: the control group, the dyadic intervention group. Among them, patients in the control group and caregivers received routine psychological care programs; patients in the intervention group had access to conventional care, in addition to receiving the 8-week dyadic MSC intervention sessions. The intervention was provided by trained nurses, including one researcher and one MSC therapist. The researcher was regarded as primary leader of the intervention sessions. The leader informed patients of the schedule for each session using the educational manual'Caring for ourselves, we are together' (developed by psychologists, nursing managers, experienced MSC therapist, oncology Nurse, and researchers).

The MSC techniques include body scanning, breathing meditation, sitting meditation, walking meditation, loving-kindness practice, and self-compassion writing expression. Intensive training once a week, 1 hour each time, encourage students to use 15-20 minutes a day to learn these skills, the total training time per week is 2.5 hours. The intervention is mainly out-of-hospital intervention, supplemented by short-term in-hospital intervention (1-2 weeks, adjusted according to the patient's hospital stay). The in-hospital stage focuses on guiding the research subjects to understand the content of mindful self-compassion and emotions, and conduct basic mindful self-compassion training; the outside of the hospital focuses on the maintenance of mindful self-compassion training and the promotion of mindful life.

Data were collected by a research assistant who was blind to the study design and allocation of participants. At baseline, before randomization, sociodemographic and clinical characteristics were collected from medical records and personal interviews. The two groups of participants completed surveys after each follow-up via face to face interviews at baseline (T0) and immediately after intervention (T1). The next two evaluations were performed at 1-month (T2) and 3-months (T3) after intervention via telephone contact.

For lung cancer patients

Inclusion Criteria:

• Diagnosed with lung cancer by pathological biopsy or cytology;
• The disease condition is relatively stable;
• Must be conscious, with normal communication ability;
• Must be volunteered to join the study.

Exclusion Criteria:

• Share a hospital room with a current study participant;
• With other types of cancer;
• Alcoholics and/or drug addicts;
• Disabilities and cannot take care of themselves.

For caregivers

Inclusion Criteria:

• A primary caregiver designated by a lung cancer patient who has been included in this study, with a cumulative care time of more than 72 hours;
• One of the family members of a hospitalized lung cancer patient, such as their spouse, children, parents or other relatives
• must be conscious, with normal communication ability;
• must be volunteered to join the study.

Exclusion Criteria:

• Have an employment relationship with the patient, such as nurses and nanny；
• Alcoholics and/or drug addicts;
• Disabilities and cannot take care of themselves.

The process of data collection cost a lot of human and material resources, some of the data was privacy information of participants, and so on. Considering this, it is improper to share these data.

Potential eligible participants were identified by researchers according to medical records at the oncology departments in each hospital. They were recruited with informed consent, and researchers explained the study purposes, procedures, benefits, and risks involved orally. The participants were then randomly allocated to the intervention or the control group according to a computer-generated block randomization list. The generated random numbers were put into consecutively numbered and opaque sealed envelopes. When enrolling and randomising a new participant, the enrolling investigators opened the sealed envelope after participant's name was written on next available envelopes. A sequentially numbered and opaque , sealed envelope system was used by a non-investigator. Additionally, all data collection was conducted by another research assistant who was blind to the study design and allocation of participants.