To fractionate or not to fractionate? That is the question for the radiosurgery of hypoxic tumors

• Purpose: This study aimed to investigate the impact of tumour hypoxia on treatment outcome for metastases commonly treated with radiosurgery using one fraction of radiation. It also aimed to investigate the gain that could be expected from reoxygenation if the treatment is delivered in few radiation fractions.Methods: In silico metastases-like radiosurgery targets were modelled with respect to size, density of clonogenic cells and oxygenation. Treatment plans were produced for the targets using Leksell GammaPlan delivering clinically relevant doses and evaluating the tumour control probability (TCP) that could be expected in each case. Fractionated schedules with 3, 4 and 5 fractions resulting in similar biological effective doses were also considered for the larger target and TCP was determined under the assumption that local reoxygenation takes place between fractions.Results: The results showed that well-oxygenated small and medium-size metastases are well controlled by radiosurgery treatments delivering 20 or 22 Gy at the periphery, the TCP ranging from 90% to 100%. If they are moderately hypoxic the TCP could decrease to 60%. For large metastases, the TCP ranges from 0 to 19% depending on tumour oxygenation. However, for fractionated treatments, the TCP for hypoxic tumours could significantly increase up to 51%, if reoxygenation occurs between fractions.Conclusion: This study shows that hypoxia worsens the response to single-fraction radiosurgery, especially for large tumours. However, fractionated therapy for large hypoxic tumours might considerably improve the TCP and might constitute a simple way to improve the outcome of radiosurgery for patients with hypoxic tumours.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Cancer och onkologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Cancer and Oncology (hsv//eng)

Nyckelord

radiosurgery

metastases

tumour hypoxia

fractionation

Radiation Physics

radiofysik

Medical Radiation Physics

medicinsk strålningsfysik

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