ESTRO 2024 - Abstract Book

S1263

Clinical - Head & neck

ESTRO 2024

of each cycle, the treating radiation oncologist would verify that the acquired CBCTs were adequate to visualize the GTV. Feasibility was defined as completion of this expedited adaptive quad shot workflow in at least 80% of patients, and patients were only evaluable for the primary endpoint if they received at least one adapted cycle.

Results:

Patient characteristics are shown in Table 1. 50% (5/10) of patients had no received prior radiotherapy, and 50% (5/10) of patients had received prior radiotherapy. Seven patients received a second cycle of quad shot and three patients received a third cycle of quad shot. The expedited adaptive quad shot workflow was feasible in 100% (7/7) of patients who received at least one adapted cycle, and was feasible in 100% (10/10) of attempted adapted cycles. For the second and third quad shot cycles, the average total workflow time for the first fraction adaptive treatments was 28 minutes (14 – 38). Median GTV volume changes from first cycle to second cycle were 13.57cc (- 35.56cc to 158.97cc) and -29.57cc (-114.42cc to 0.08cc) from second cycle to third cycle. Four dose constraint violations occurred across the ten adapted fractions when the simulation plan was applied on the anatomy-of-the day at the time of the online adaptation. All constraint violations were resolved with the use of online adaptation.

Table 1

Patient #

Age

Primary site

Histology

Location of disease

Prior radiotherapy

Number of quad shot cycles received

1

63

Hypopharynx

Squamous cell carcinoma (SCC)

Bilateral neck

No

2

2 3 4 5 6 7 8

67 63 84 56 56 62 84

Larynx

SCC SCC SCC SCC SCC SCC SCC

Right neck

Yes

3 2 3 3 2 2 1

Oropharynx Oropharynx Hypopharynx

Oropharynx Yes Oropharynx Yes

Right neck Right neck Right neck Right masticator space Right neck

No

Larynx

Yes

Oropharynx

No

Oral cavity

Yes

9

73 89

Oropharynx

SCC SCC

No No

1 1

10

Larynx

Larynx

Conclusion:

The expedited palliative quad shot radiotherapy workflow using online adaptive radiotherapy was found to be feasible for patients with head and neck malignancies. This workflow enabled quad shot treatment while eliminating the need for additional CT simulation appointments for subsequent cycles.

Keywords: Online adaptive radiotherapy, Quad shot