In the HOBBIT-trial by Vakaet et al. A protocol was developed to increase breath-hold time using (voluntary) hyperventilation and oxygenation to achieve DIBH times around 3 minutes.

Multiple non-medical interventions are being investigated to prolong a L-DIBH that are feasible in clinical practice. One of these methods will be to alter the time perception of the subjects. It has been noted in multiple studies (both medical and not) that slowing a person's perception of time results in an increase in breath-hold time. This alteration in time perception can be achieved with the use of a slowed clock as well as the usage of mental or physical exercises to preoccupy the subjects.

Volunteers will then be randomised into either the standard arm or the intervention arm. The intervention arm will follow standard protocol regarding DIBH preparation, though during the L-DIBH they will be asked to perform a simple mental exercise on a tablet. After 2 sessions of 3 L-DIBHs each, there will be a cross-over to the other arm in order to ascertain comfort and preference with each technique.

Adjuvant radiation therapy has a well-established role in the treatment of breast cancer complementing surgery and systemic treatment, improving survival and local control in both local and regional disease. The long-term follow-up, however, does show increased cardiac morbidity and mortality. The risk of heart disease is greatest in patients receiving a higher heart dosage i.e., left sided breast cancer and irradiation of the internal mammary lymph nodes and does not appear to have a threshold. Lowering heart dose can be achieved by improved planning methods as well as increasing the distance between the target volume and the heart. A deep inspiration breath-hold (DIBH) is often used to this end.

An unassisted DIBH is between 12 and 30 seconds; a simple breast irradiation averages 4 DIBHS for completion. More advanced radiotherapy plans (including lymph nodes) needs up to 20 DIBHs. This great amount is both physically and mentally exhausting.

A protocol was developed to increase breath-hold time using (voluntary) hyperventilation and oxygenation to achieve DIBH times around 3 minutes.

Multiple non-medical interventions are being investigated to prolong a L-DIBH that are feasible in clinical practice. One of these methods will be to alter the time perception of the subjects. It has been noted in multiple studies (both medical and not) that slowing a person's perception of time results in an increase in breath-hold time. This alteration in time perception can be achieved with the use of a slowed clock as well as the usage of mental or physical exercises to preoccupy the subjects.

Other important factors on the duration of breath holds are stress and anxiety, which may also be influenced by (relaxation) exercises (including Abdominal breathing).

The standard protocol for the first phase will be based on the results of the original HOBBIT trial.

40 Volunteers will be asked to perform 3 L-DIBHs each preceded by 3 minutes of hyperventilation at 16 breaths/min with 40L/min at FiO2 60%.

Volunteers will then be randomised into either the standard arm or the intervention arm. The intervention arm will follow standard protocol regarding DIBH preparation, though during the L-DIBH they will be asked to perform a simple mental exercise on a tablet.

Data regarding L-DIBH time, side-effects and volunteer reported stress and comfort will be reported.

Volunteers in each group will be asked to perform 2 series of 3 L-DIBHs on 2 separate days. After having finished these 2 series, there will be a cross-over to the other arm. This cross-over will evaluate the known effect of the learning bias that we see with breath-hold and show whether this effect has an impact on the anticipated benefit of the intervention. With the cross-over we can also ascertain volunteer comfort and preference with each the technique.

Inclusion Criteria:

• Volunteer
• Karnofsky index of at least 90
• Able to perform a single DIBH of at least twenty seconds without assistance
• Age ≥ 18 years
• Informed consent obtained, signed and dated before specific protocol procedures
• Female

Exclusion Criteria:

• Pregnant women
• Volunteers above WHO Obesity class II (BMI>35kg/m²)
• Subjects on oxygen treatment during day or night
• COPD or Asthma patients
• Volunteers with pulmonary hypertension
• Gastric tube present
• Smoking
• Previous and substantial breath-holding experience in the past year (e.g., diver, etc.)
• Mental condition rendering the volunteer unable to understand the nature, scope and possible consequences of the study