The influence of radiotherapy techniques on the plan quality and on the risk of secondary tumors in patients with pituitary adenoma

Abstract

Background: This planning study compares different radiotherapy techniques for patients with pituitary adenoma, including flatness filter free mode (FFF), concerning plan quality and secondary malignancies for potentially young patients. The flatness filter has been described as main source of photon scatter.Material and methods: Eleven patients with pituitary adenoma were included. An Elekta Synergy™ linac was used in the treatment planning system Oncentra® and for the measurements. 3D plans, IMRT, and VMAT plans and noncoplanar varieties were considered. The plan quality was evaluated regarding homogeneity, conformity, delivery time and dose to the organs at risk. The secondary malignancy risk was calculated from dose volume data and from measured dose to the periphery using different models for carcinoma and sarcoma risk.Results: The homogeneity and conformity were nearly unchanged with and without flattening filter, neither was the delivery time found substantively different. VMAT plans were more homogenous, conformal and faster in delivery than IMRT plans. The secondary cancer risk was reduced with FFF both in the treated region and in the periphery. VMAT plans resulted in a higher secondary brain cancer risk than IMRT plans, but the risk for secondary peripheral cancer was reduced. Secondary sarcoma risk plays a minor role. No advantage was found for non-coplanar techniques. The FFF delivery times were not shortened due to additional monitor units needed and technical limitations. The risk for secondary brain cancer seems to depend on the irradiated volume. Secondary sarcoma risk is much smaller than carcinoma risk in accordance to the results of the atomic bomb survivors. The reduction of the peripheral dose and resulting secondary malignancy risk for FFF is statistically significant. However, it is negligible in comparison to the risk in the treated region.Conclusion: Treatments with FFF can reduce secondary malignancy risk while retaining similar quality as with flattening filter and should be preferred. VMAT plans show the best plan quality combined with lowest peripheral secondary malignancy risk, but highest level of second brain cancer risk. Taking this into account VMAT FFF seems the most advantageous technique for the treatment of pituitary adenomas with the given equipment.

Recommendations for reducing exposure to medical X‑ray irradiation (Review)

“…Following the discovery of X-rays, it was found that frequent exposure experienced by physicians increased their risk of developing cancer (13)(14)(15)(16)(17)(18). Studies on atomic bomb survivors (19)(20)(21)(22)(23)(24) and patients with cancer receiving radiation therapy (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35) have found that the risk of tumorigenesis is associated with acute or fractionated high-dose radiation exposure. although opinions differ as regards the harm of low-dose radiation to the human body, the impact of low-dose radiation on cancer risk has gained scientific attention.…”

Treatment plan comparison of proton vs photon radiotherapy for lower-grade gliomas

“…Data on SC in the brain originates mainly from paediatric cohorts treated with cranial radiotherapy, where excess odds ratios (EOR) of 0.33 and 0.079 per Gy have been reported for gliomas and 1.06 and 5.1 per Gy for non-malignant and malignant meningiomas by the North American and British Cancer Survivor Study respectively [20] . Different photon techniques have been shown to have a theoretical impact on the risk of secondary tumours [21] . The rapid distal dose fall-off of protons may significantly reduce the integral dose and thus reduce the risk of SC.…”

Secondary malignancy risk for patients with localized prostate cancer after intensity‐modulated radiotherapy with and without flattening filter

“…Only a few investigations using model calculations have been published about the impact of the FFF mode on SMR. Besides works about patients with breast cancer, 11 ependymoma, 12 and pituitary adenoma 13 there is only one paper evaluating the SMR for patients with prostate cancer treated with linacs with and without flattening filter 14 which confined to only three patients at cost of statistical significance. Additionally, they used another therapy planning system (TPS) which can affect the out‐of‐field dose 15 …”