Clinical implication of different treatment techniques in glottic cancer
Laura Cardoso Rubio,
Spain
PO-1092
Abstract
Clinical implication of different treatment techniques in glottic cancer
Authors: Laura Cardoso1, Sofía Pena2, Laura Gómez1, Ángel Del Castillo2, María Luisa Del Valle1, Juan Francisco Gutiérrez1, María Herrera1, María Isabel Garavis1, Ana Casado1, Patricia Valencia1, Rocío Jaraíz1, Antonio Hurtado2, Pilar Alonso1, Ignacio Solis1, Iban Conles2, Daniel Rodríguez1, María Sánchez1, Patricia Diezhandino1
1Hospital Clínico Universitario de Valladolid, Radiation Oncology, Valladolid, Spain; 2Hospital Clínico Universitario de Valladolid, Medical Physics, Valladolid, Spain
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Purpose or Objective
Early stage glottic tumours (T1-T2 N0) have traditionally been treated with radical external radiotherapy (EBRT), showing 5 years local control rates of 80-90%. The classic treatment technique has been conformal 3D, but thanks to the emergence of techniques such as VMAT, the diversity in the choice of technique and treatment design has increased. The objective is to analyse the dosimetric discrepancies from data extracted from the DVH histogram for three types of treatment plans involving different techniques.
Material and Methods
Nineteen patients with early squamous cell carcinoma of the glottis (T1-T2 N0) who received EBRT in our centre between January-2019 and September-2021 were selected retrospectively. All the cohort have one prescribed dose level of between 63-66 Gy and for each of them we performed three treatment plans with different techniques: 3D opposite field (3D), a full arc of intensity-modulated volumetric arc therapy (F-VMAT) and two partial-arcs butterfly VMAT (B-VMAT). 50% was treated with 3D, 25% VMAT and 25% B-VMAT. The treatment planning system used was Eclipse v15.6 and the algorithm AAA for 3D and AcurosXB 15.6.04 for VMAT.
The median and the standard deviation of the maximum and of the average dose received by both carotids and the thyroid are analysed for the three treatment plans. Moreover, the median of the received by the spinal cord (SC) was also analysed. The volumes were contoured following RTOG guidelines, extending the volume of carotid arteries and spinal cord 2-1.5 cm above PTV and 1-1.5 cm below.
Results
The 3D technique provides good dose control to the SC with a median maximum dose received of 7.28 (±4.86 Gy). In contrast, the dose to the bilateral carotid arteries is high with a median mean dose of 47.12 (± 6.76Gy) and 45.28 (±7.44 Gy) to the right and left carotid arteries respectively.
The values of the VMAT plans are very similar at the carotid level, with a mean dose in the right carotid of 32.92 (±5.49 Gy) with a full arc and 35.88 (±5.96 Gy) with B-VMAT and mean doses of 33.61 (±7.16 Gy) and 34.80 (±6.92 Gy) in the left carotid. However, at SC we reduced the maximum dose with the two partial arcs from 31.09 (±3.28 Gy) to 20.01 (±6.59 Gy).
In the thyroid irradiation, the average dose is 28.33 (±10.73 Gy) with the 3D plan and 19.28 (±9.89 Gy) and 19.90 (±9.89 Gy) with VMAT and the proposed B-MAT, so we reduce the dose and the risk of hypothyroidism.
G2 skin toxicity was presented in 62,5% of patients treated with 3D and only in 25% of patients with VMAT and B-VMAT.
Conclusion
The VMAT technique compared to 3D provides better skin tolerance and greater dose conformity, reducing the dose received by the internal carotids and the thyroid but collaterally increasing the dose at the spinal cord. The proposed B-VMAT planning achieves smaller field sizes, shorter treatment time and associated dose reduction at the medullary level with similar doses in the other organs at risk compared to full arc VMAT, becoming a good choice of treatment option.