Keywords:
Breast, Oncology, Digital radiography, Radiation therapy / Oncology, Radiotherapy techniques
Authors:
R. Estoesta, D. Naehrig, L. Attwood, E. Claridge-Mackonis, D. Martin, M. Pham, J. Toohey, S. Carroll; Sydney/AU
DOI:
10.1594/ranzcr2015/R-0081
Methods and materials
The vDIBH technique employed at Chris O’Brien Lifehouse does not use commercially available devices for treatment delivery.
We employ a vDIBH technique described by Jensen et al [9] wherein the patient’s breath-hold is assessed for adequacy whilst a marker is placed at the level of the patient’s lateral tattoo.
The level of the marker is measured from both FB and vDIBH computed tomography (CT) scans and this measurement is recorded for treatment.
The FB Planning CT-scan is analysed to see if the patient would benefit from vDIBH by assessing the heart’s location in relation to the posterior edge of the planning target volume (PTV) (Figure 1).
If the Radiation Oncologist decides that the patient would benefit then a vDIBH Planning CT-scan is performed.
Twenty patients with left-sided breast cancer underwent CT-simulation in FB and vDIBH.
Treatment plans were generated by using a conventional tangential technique.
A dosimetric comparison was made between the two techniques for the heart,
the LAD and the left lung.
The treatment set-up is performed normally then the recorded measurement between the FB and vDIBH planning CT scans is marked on the patients skin.
The patient is then instructed to breathe in and hold once the in-room lasers reach the same level as the reference mark on the patient’s skin.
The laser-mark alignment is checked to ensure that the laser remains at the same level for the entire breath-hold.
During beam delivery,
a Radiation Therapist provides instruction whilst watching the room camera which is focused on the laser-mark alignment.
If the laser-mark alignment strays outside tolerance then the beam is shut off.
Portal images are acquired on days 1-3 and every fifth fraction thereafter and matched to a digitally reconstructed radiograph (DRR) prior to treatment commencing.
Treatment set-up is verified using electronic portal imaging device (EPID) images taken prior to the treatment commencing as per department protocol.
To assess treatment position reproducibility 125 EPIs were collected for the 20 patients undergoing vDIBH,
and 129 EPIs for a control cohort of 20 patients who were undergoing FB treatment.
Setup errors were measured off-line for every fraction.
Positional reproducibility was assessed by measuring the distance of the central axis to the chest wall (Figure 2) on the DRR.
The distance was measured for the EPI,
and then the difference between both values was recorded (Figure 2).
Comparison of mean values was performed using a paired sample Student’s t-test.
Statistical analysis was performed using Excel 2003 (Microsoft Corp.,
Redmond,
WA,
USA).
A p-value of ≤0.05 was considered significant.