A simple method to account for skin dose enhancement during treatment planning of VMAT treatments of patients in contact with immobilization equipment

Dosimetric evaluation of a patient-specific 3D-printed oral positioning stent for head-and-neck radiotherapy

As head-and-neck radiotherapy treatments become more complex and sophisticated, and the need to control and stabilise the positioning of intra-oral anatomy becomes more important, leading the increasing use of oral positioning stents during head-and-neck radiotherapy simulation and delivery. As an alternative to the established practice of creating oral positioning stents using wax, this study investigated the use of a 3D printing technique. An Ender 5 3D printer (Creality 3D, Shenzhen, China) was used, with PLA+ "food-safe" polylactic acid filament (3D Fillies, Dandenong South, Australia), to produce a low-density 3D printed duplicate of a conventional wax stent. The physical and dosimetric effects of the two stents were evaluated using radiochromic film in a solid head phantom that was modified to include flexible parts. The Varian Eclipse treatment planning system (Varian Medical Systems, Palo Alto, USA) was used to calculate the dose from two different head-and-neck treatment plans for the phantom with each of the two stents. Examination of the resulting four dose distributions showed that both stents effectively pushed sensitive oral tissues away from the treatment targets, even though most of the phantom was solid. Film measurements confirmed the accuracy of the dose calculations from the treatment planning system, despite the steep density gradients in the treated volume, and demonstrated that the 3D print could be a suitable replacement for the wax stent. This study demonstrated a useful method for dosimetrically testing novel oral positioning stents. We recommend the development of flexible phantoms for future studies.

Dose distribution comparison in volumetric-modulated arc therapy plans for head and neck cancers with and without an external body contour extended technique

Aim

This study compared volumetric-modulated arc therapy (VMAT) plans for head and neck cancers with and without an external body contour extended technique (EBCT).

Background

Dose calculation algorisms for VMAT have limitations in the buildup region.

Materials and methods

Three VMAT plans were enrolled, with one case having a metal artifact from an artificial tooth. The proper dose was calculated using Eclipse version 11.0. The body contours were extended 2 cm outward from the skin surface in three-dimensional space, and the dose was recalculated with an anisotropic analytical algorithm (AAA) and Acuros XB (AXB). Monitor units (MUs) were set, and the dose distributions in the planning target volume (PTV), clinical target volume, and organ at risk (OAR) and conformity index (CI) with and without an EBCT were compared. The influence of a metal artifact outside of the thermoplastic head mask was also compared.

Results

The coverage of PTV by the 95% dose line near the patient's skin was increased drastically by using an EBCT. Plan renormalization had a negligible impact on MUs and doses delivered to OARs. CI of PTV with a 6-MV photon beam was closer to 1 than that with a 10-MV photon beam when both AAA and AXB were used in all cases. Metal artifacts outside the head mask had no effect on dose distribution.

Conclusions

An EBCT is needed to estimate the proper dose at object volumes near the patient's skin and can improve the accuracy of the calculated dose at target volumes.

Optimization of skin dose using in-vivo MOSFET dose measurements in bolus/non-bolus fraction ratio: A VMAT and a 3DCRT study

In‐phantom and in‐vivo three dimensional conformal radiation therapy (3DCRT) and volumetric modulated arc therapy (VMAT) skin doses, measured with and without bolus in a female anthropomorphic phantom RANDO and in patients, were compared against treatment planning system calculated values. A thorough characterization of the metal oxide semiconductor field effect transistor measurement system was performed prior to the measurements in phantoms and patients. Patients with clinical indication for postoperative external radiotherapy were selected. Skin dose showed higher values with 3DCRT technique compared with VMAT. The increase in skin dose due to the use of bolus was quantified. It was observed that, in the case of VMAT, the bolus effect on the skin dose was considerable when compared with 3DCRT. From the point of view of treatment time, bolus cost, and positioning reproducibility, the use of bolus in these situations can be optimized.