The key challenge in radiotherapy of cancer patients is to balance the probability of tumour control and risk of radiation-induced side effects in the healthy tissue. This PhD thesis is based on four studies investigating different ways of optimising radiotherapy for breast cancer patients and patients with liver metastases.
Radiotherapy treatment plans are usually optimised based on doses to the target volume and organs at risk. In Study I, we demonstrated radiotherapy planning optimised solely by minimising the risk of cancer recurrence and radiation-induced mortality in breast cancer patients. The estimated benefit was modest in most patients compared to the clinically delivered radiotherapy plans.
Most breast cancer patients receive photon radiotherapy with low exposure of the heart and lung and thereby low risk of radiation-induced heart disease and lung cancer. We established dose thresholds for heart and lung to identify a subgroup of patients that may benefit from treatment with proton therapy in Study II. These dose thresholds are now used as patient selection criteria in the Danish Breast Cancer Group Proton Trial in which patients are randomised between proton therapy and photon radiotherapy.
For patients with synchronous cancer in both breasts, it can be difficult to obtain sufficient dose coverage of the target volume with photon radiotherapy, and these patients may benefit from proton therapy. In Study III, we created comparative proton therapy plans for patients with bilateral breast cancer already treated with photon radiotherapy, and we did comprehensive risk assessment of radiation-induced side effects in the photon radiotherapy
versus proton therapy plans. The proton therapy plans provided sufficient target coverage, reduced risk of radiation-induced heart disease and lung cancer but also increased risk of acute skin toxicity.
Liver metastases are subject to respiration-induced motion. This is often accounted for by irradiating a larger volume around the metastasis. The motion may be reduced by treating while the patients perform breath-hold. In Study IV, we evaluated the stability of breath-hold in ten patients with liver metastases treated at Rigshospitalet, and we found that the breath-holds were not always stable.