ESTRO 2024 - Abstract Book

S5583

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

poorly fabricated shell and Moldcare cushion causes irreproducible HN position, irregular skin folds on the cushion and gaps between patient’s HN and device. Hence, this bring about to the evaluation of immobilization in stabilizing the head and neck region for proton beam therapy.

Material/Methods:

12 HN patients (6 photon and 6 proton) from May to October 2023 using HP PRO Nanor shell and Moldcare cushion were analyzed. The weekly CBCT image registration was performed using auto-matching algorithm tool in TrueBeam and PIAS system. The translational and rotational shifts were collated and analysed. The displacement of the clavicle was measured from the CBCT against the planning CT images. Secondary analysis was the observation done by the physicist and RTT on the fabricated Moldcare cushion along with the planning CT images. The re-setups related to the Moldcare were evaluated.

Results:

A total of 82 CBCTs were collected and the 6D shifts fell within the departmental HN imaging protocol tolerance of 5mm for translational shift and 2° for rotational shift. The setup errors were 1.3 ± 1.1mm for the translational shifts and 0.7 ± 0.5° for the rotational. The results showed strong reliability of the HP Pro and Moldcare immobilization.

Translation (mm)

Rotation (°)

Clavicle deviation (mm)

Shifts (mm) Percentage Mean±SD

Shifts (°)

Percentage

Mean±SD

Shifts (mm) Percentage Mean±SD

0

27%

0

43.3%

≤0.5

51.2%

1

37%

1

5.8%

2

23%

2

13.3%

1.3 ± 1.1

0.6-1.0

25.2%

3

7%

3

16.7%

0.7 ± 0.5

1.8 ± 1.9

4

7%

4

12.5%

1.1-1.5

17.5%

5

0

5

4.2%

6

2.5%

1.6-2.0

6.1%

7

1.7%

Table 1: Shifts collated from reviewing weekly CBCTs

The assessment for handgrip was credible because 95.8% < 5mm (1.8 ± 1.9), with the maximum displacement of 7mm. The displacement of clavicle > 5mm was due to weight loss of 5-10% from baseline. HN proton plan of the neck region is generated with robust optimization of range uncertainty: ± 3.5 and setup uncertainty: 5mm. All in all, the hand grips helped with the fixation of the shoulder position. Observation performed on the Moldcare cushions with the planning CT images were informative. Figure 1 showed a Moldcare with a ‘V-groove’ at the neck region. The filling of the gap was inconsistent on daily basis, resulted in a potential discrepancy of the dose. Figure 2 showed a comparison of a non-ideal Moldcare with irregular surface versus a perfectly made smooth Moldcare. Moreover, bulging skin was also noted on photo (a) while there was no ‘muffin’ of the skin seen on photo (c). It was not feasible to quantify the amount of skin folds that bulged out, but it will impact negatively on the planned beam.