A study on the influence of breathing phases in intensity-modulated radiotherapy of lung tumours using four-dimensional CT

Abstract

ABSTRACT. During gated intensity-modulated radiotherapy (IMRT) treatment for patients with inoperable non-small cell lung cancer (NSCLC), the end-expiration (EE) phase of respiratory is more stable, whereas end-inspiration (EI) spares more normal lung tissue. This study compared the relative plan quality based on dosimetric and biological indices of the planning target volume (PTV) and organs at risk (OARs) between EI and EE in gated IMRT. 16 Stage I NSCLC patients, who were scanned by four-dimensional CT, were recruited and re-planned. An IMRT plan of a prescription dose of 60 Gy per respiratory phase was computed using the iPlan treatment planning system. The heart, spinal cord, both lungs and PTV were outlined. The tumour control probability for the PTV and normal tissue complication probability for all OARs in the EE and EI phases were nearly the same; only the normal tissue complication probability of the heart in EE was slightly lower. Conversely, the conformation number of the PTV, V 20 of the left lung, V 30 of both lungs, D max of the heart and spinal cord, V 10 of the heart and D 5% of the spinal cord were better in EE, whereas D mean of the PTV, V 20 of the right lung and maximum doses of both lungs were better in EI. No differences reached statistical significance (p,0.05) except D max of the spinal cord (p50.033). Overall, there was no expected clinical impact between EI and EE in the study. However, based on the practicality factor, EI is recommended for patients who can perform breath-hold; otherwise, EE is recommended. Non-small cell lung cancer (NSCLC) [1,2] accounts for 80% of all lung cancers for which radiotherapy (RT) is the treatment of choice for inoperable cases. However, the survival rate with RT is low. This, in part, is a result of respiratory motion [3], which may cause a planning target volume (PTV) displacement of more than 2.5 cm [4], leading to a geographic miss or unnecessary irradiation of adjacent normal tissues and organs at risk (OARs). This phenomenon involves different sizes and motion of the PTV at different phases of the breathing cycle, and therefore results in different PTV dose coverage [5].With the development of four-dimensional CT (4D-CT), intensity-modulated radiotherapy (IMRT) and gating, it is possible to achieve better accuracy, precision and clinical outcomes. At present, there are two different philosophies for applying gating phases: during expiration [6] and during inspiration [7,8]. The former approach advocates that tumour motion is comparatively stable during exhalation, which minimises the respiratory-induced target motion and allows better reproducibility of margin size. Conversely, the latter approach is based on the argument that, during lung inflation, more normal lung tissue can be spared during the irradiation [7]. In this study, a comparison is made between the use of endinspiration (EI) and end-expiration (EE) gated IMRT treatment for a set of NSCLC patients using dosimetric and associated biological indicators. Methods and materials SubjectsThis...

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“…Indeed, radiation therapy has undergone many improvements in treatment planning and radiation delivery. Nonetheless, a significant subset of patients with thoracic cancers, including those of the lung, esophagus, and proximal stomach, still receive considerable doses of radiation to the heart [19–21]. Moreover, radiation therapy is often combined with chemotherapeutic agents that have their own side effects in the heart.…”

Dynamic gating window for compensation of baseline shift in respiratory‐gated radiation therapy

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“…8,9,16,25 In addition, the position of the EOE window is more reproducible. 3,19,20,25,26 EOI gating is often used with a breath-hold technique ͑deep-inspiration breath-hold͒ to increase reproducibility and stability. 5,26,27 EOI gating has the advantage of lower lung toxicity to surrounding normal tissue than EOE gating; 2,8,9,19,25,26 however, EOI gating has more residual motion than EOE gating.…”

“…3,19,20,25,26 EOI gating is often used with a breath-hold technique ͑deep-inspiration breath-hold͒ to increase reproducibility and stability. 5,26,27 EOI gating has the advantage of lower lung toxicity to surrounding normal tissue than EOE gating; 2,8,9,19,25,26 however, EOI gating has more residual motion than EOE gating. 19 One metric for evaluating respiratory gating is the duty cycle, which is the fraction of total treatment time during which radiation is being delivered.…”

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