ESTRO 2022

Session Item

Saturday

May 07

10:30 - 11:30

Room D5

Photon radiotherapy planning

Chair: , The Netherlands;

Co-Chair: Marcel Nachbar, Germany

Session Code: 1260

Session Type: Proffered Papers

Track: Physics

11:10 - 11:20

Adaptive Dose Painting vs standard IMRT in a randomized phase II trial: a dosimetric analysis.

Tom Vercauteren, Belgium

Presentation Number: OC-0129

Abstract

Abstract Title:

Adaptive Dose Painting vs standard IMRT in a randomized phase II trial: a dosimetric analysis.

Authors:

Tom Vercauteren¹, Aurélie De Bruycker¹, Fréderic Duprez¹, Jean-François Daisne², Ana Maria Luiza Olteanu¹, Stéphanie Deheneffe², Dieter Berwouts¹, Wilfried De Neve¹, Indira Madani³, Leen Paelinck¹, Bruno Speleers³, Ingeborg Goethals⁴, Werner De Gersem¹

¹Ghent University Hospital, Radiation Oncology, Ghent, Belgium; ²CHU-UCL, Radiation Oncology, Namur, Belgium; ³Ghent University, Radiation Oncology, Ghent, Belgium; ⁴Ghent University Hospital, Nuclear Medicine, Ghent, Belgium

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Purpose or Objective

In a two-centre randomized phase-II trial, Adaptive Dose-Painting-By-Numbers (A-DPBN) compared favourably to non-adaptive standard IMRT (S-IMRT) in head and neck cancer (HNC) in terms of short-term outcomes. This study presents the dosimetric evaluation.

Material and Methods

95 HNC were randomized. In A-DPBN, the treatment was given in 3‑phases (Figure 1), the first two treatment plans (fractions 1-10 and 11-20) being created with a dose-painting (DP) technique based on the ¹⁸F-FDG-PET-CTs acquired prior to the treatment and after the 8^th fraction. A CT acquired after the 18^th fraction was used to make the plan for fractions 21-30. The protocol dose prescription is given in Figure 1. Because of unexpected late grade 3-4 mucosal ulcers, the dose-escalation was reduced twice during the trial.

Two DP planning methods were applied in the two centres: voxel-intensity-based optimisation versus a technique using segmentation of the GTV in 3-4 regions of the uptake value.

Dose reporting was performed on the pretreatment CT, deformable image-registration being used to accumulate the adapted plan doses (RayStation, v6.1.1). Mann-Whitney U tests were calculated using SPSS (v27.0.1), p-values<0.05 were considered significant.

Results

No volume differences were observed between A-DPBN and S-IMRT in the primary GTV target (GTV-T) and the lymph node GTV (GTV-N) (p=0.386) on the pretreatment CT.

The mean D₂, D₅₀ were higher (p < 0.001) for GTV-T in A-DPBN (79.5±3.8, 72.5 ± 3.2 Gy) compared to the S-IMRT (70.9 ± 0.8, 69.4 ± 0.5 Gy). Conversely, mean D₉₈ was lower (66.9±2.6 and 68.0±0.9, respectively, p<0.001).

For GTV-N, D₂ and D₉₈ differed (p<0.001) in A-DPBN (75.5±5.5 and 64.0±3.2 Gy), compared to S-IMRT (71.0±0.9 and 66.6±2.7 Gy). No difference (p=0.112) was found for the D₅₀ (69.8±3.6 and 69.4±0.6 Gy, respectively).

The D₂ and D₅₀ of the ipsilateral parotid in A-DPBN (56.5±9.3 and 25.6±11.3 Gy) were lower (p<0.001 and 0.002) compared to S-IMRT (63.1±6.8 and 35.1±16.3 Gy). In the contralateral parotid, the D₂ and D₅₀ in A-DPBN (50.9±8.0 and 19.0±5.4 Gy) were lower (p<0.001 and 0.004) compared to S-IMRT (57.4±4.9 and 22.6±6.1 Gy)

The D₅₀ and D₉₈ in the union of the swallowing structures (47.3±10.2 and 27.8±12.3 Gy) were lower in A-DPBN compared with S-IMRT (59.4±10.4 and 41.1±14.0 Gy, p<0.001). No statistical difference (p=0.052) was observed between A-DPBN and S-IMRT for the D₂ (respectively 69.3±5.4 and 70.1).

Conclusion

The use of the A-DPBN technique enabled higher doses to the GTV. A combination of A-DPBN and a reduced dose prescription to the elective neck resulted in lower doses on the swallowing structures and parotids. Lower D₉₈ doses reported on the pretreatment GTV volumes by the anti-chronological dose accumulation was an effect of the treatment adaptation. A follow-up study of the disease control will provide more information regarding the long-term efficiency of the method.