Acceptable fetal dose using flattening filter-free volumetric arc therapy (FFF VMAT) in postoperative chemoradiotherapy of tongue cancer during pregnancy

A phantom study investigating effective strategies for reducing fetal dose in pregnant patients with head and neck cancer

PURPOSE

To measure the out-of-field doses for various treatment planning techniques and assess the impact on fetal dose with and without the use of custom shielding.

MATERIALS AND METHODS

A total of six treatment plans were generated with different treatment techniques such as 3-dimensional conformal radiation therapy (3DCRT), intensity modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT), utilizing both 6 MV flattened beams and flattening filter-free (FFF) beams. The measurements were carried out both out-of-field at the surface and at depth to assess the dose reduction achieved by removing the flattening filter and incorporating shielding.

RESULTS

The custom-made frame shielding can effectively reduce the surface dose with a maximum reduction of 15.2% observed in VMAT plans and achieve a maximum reduction of 100% for cone beam computed tomography (CBCT) imaging. Out-of-field dose measurements conducted at depth, positioned 58 cm inferior to the target isocenter, reveal that the shielding effectiveness consistently remains the greatest for 3DCRT technique. A maximum reduction of 21% is observed when utilizing a flattening filter-free beam.

CONCLUSION

The results of this study indicate that the 3DCRT technique exhibits the least amount of scatter radiation both near and far from the treatment isocenter, which is the most suitable approach for radiation therapy of pregnant patients. In cases where meeting dose constraints for critical organs becomes challenging, VMAT technique emerges as the most suitable treatment technique for reducing out-of-field doses. Additionally, a flattening filter-free beam significantly reduces out-of-field doses due to lower contributions from head scatter.

Fetal dose estimation for Virtual Tangential-fields Arc Therapy whole breast irradiation by optically stimulated luminescence dosimeters

Breast cancer is the most frequently diagnosed tumor in pregnant women and radiation therapy should carefully be weighted up because of the dose to the fetus. The aim of this study was to investigate fetal dose in a patient treated with Virtual Tangential-fields Arc Therapy (ViTAT), an innovative technique for whole breast irradiation. Optically stimulated luminescence detectors (OSLDs) were calibrated on a Varian TrueBeam linac, with both a 6X and 6XFFF beam quality, and used for out-of-field measurements. Fetal dose related with ViTAT technique was compared to the standard 3D conformal radiation therapy technique (3DCRT). The fetal dose delivered with a ViTAT technique planned with 6XFFF beam was also investigated. Measurements were taken on a phantom composed of Rando Alderson Phantom slices and solid water slabs. OSLDs were placed in a region identified by the height of the fundus from conception to the twentieth week using a custom made PMMA grid. Due to the higher number of monitor units, the peripheral dose of ViTAT delivered with 6X beams is higher than that of 3DCRT. However, nanoDots measurements prove that ViTAT can be used in place of 3DCRT while maintaining similar fetal dose levels if 6XFFF beams are used.

Volumetric modulated arc therapy (VMAT): a review of clinical outcomes—what is the clinical evidence for the most effective implementation?

Modern conformal radiation therapy using techniques such as modulation, image guidance and motion management have changed the face of radiotherapy today offering superior conformity, efficiency, and reproducibility to clinics worldwide. This review assesses the impact of these advanced radiotherapy techniques on patient toxicity and survival rates reported from January 2017 to September 2020. The main aims are to establish if dosimetric and efficiency gains correlate with improved survival and reduced toxicities and to answer the question ‘What is the clinical evidence for the most effective implementation of VMAT?’. Compared with 3DCRT, improvements have been reported with VMAT in prostate, locally advanced cervical carcinoma and various head and neck applications, leading to the shift in technology to VMAT. Other sites such as thoracic neoplasms and nasopharyngeal carcinomas have observed some improvement with VMAT although not in line with improved dosimetric measures, and the burden of toxicity and the incidence of cancer related deaths remain high, signaling the need to further mitigate toxicity and increase survival. As technological advancement continues, large randomised long-term clinical trials are required to determine the way-forward and offer site-specific recommendations. These studies are usually expensive and time consuming, therefore utilising pooled real-world data in a prospective nature can be an alternative solution to comprehensively assess the efficacy of modern radiotherapy techniques.