Individual 3D-printed fixation masks for radiotherapy: first clinical experiences

Purpose To show the feasibility of 3D-printed fixation masks for whole brain radiation therapy in a clinical setting and perform a first comparison to an established thermoplastic mask system. Methods Six patients were irradiated with whole brain radiotherapy using individually 3D-printed masks. Daily image guidance and position correction were performed prior to each irradiation fraction. The vectors of the daily position correction were compared to two collectives of patients, who were irradiated using the standard thermoplastic mask system (one cohort with head masks; one cohort with head and neck masks). Results The mean systematic errors in the experimental cohort ranged between 0.59 and 2.10 mm which is in a comparable range to the control groups (0.18 mm–0.68 mm and 0.34 mm–2.96 mm, respectively). The 3D-printed masks seem to be an alternative to the established thermoplastic mask systems. Nevertheless, further investigation will need to be performed. Conclusion The prevailing study showed a reliable and reproducible interfractional positioning accuracy using individually 3D-printed masks for whole brain irradiation in a clinical routine. Further investigations, especially concerning smaller target volumes or other areas of the body, need to be performed before using the system on a larger basis.

Does Thermoplastic Mask Alleivates Skin Sparing Effect of Photons in Head and Neck Cancer Patients: A Pilot study

Introduction: Head and Neck tumors are mainly treated with concurrent chemoradiation. Treatment delivery with Megavoltage beam has the advantage of skin sparing effect but still skin reactions have been a major side effect since 2D era. Initially these reactions were due to the delivery with bilateral opposed portals but with advent of IMRT/ VMAT, it has been possible to escalate the tumor dose with the need of strict immobilization with thermoplastic mask. This thermoplastic mask may have a bolus effect and can result in increase in surface dose resulting in skin reactions. The aim of this study was to evaluate if any bolus effect of thermoplastic mask exists. Materials and Methods: A total of 15 patients of histologically proven carcinoma oropharynx and hypopharynx were taken. Patients were scanned for planning CT with thermoplastic mask. Another scan was taken in the same position but without thermoplastic mask. Same contouring and planning were done on both the scans. Plans were made and ascertained that all OAR’s and target volumes should get similar doses. Skin contoured on both the scans was evaluated for the dose received. Results: Mean dose received by skin in patients with thermoplastic mask was 48.15 GY while Mean dose received by skin in patients without thermoplastic mask was 43.18 GY. A paired t-test was applied on the dataset which revealed a statistically significant difference between the skin doses with and without mask with a p value of < 0.05. Conclusion: Increase in skin dose can be attributed of the bolus effect of thermoplastic mask. This bolus effect should be considered once high dose to skin is observed during planning or patient develops skin reaction.

A novel rabbit fixator made of a thermoplastic mask for awake imaging experiments

This study aimed to develop and validate a novel rabbit fixator made from a thermoplastic mask for awake imaging experiments. When heated in a hot-water bath at 65–70 °C for 2–5 min, the thermoplastic mask became soft and could be molded to fit over the entire body of an anesthetized rabbit (4 ml of 3% pentobarbital sodium solution by intramuscular injection). Twenty rabbits were randomly divided into fixator (n = 10) and anesthesia (n = 10) groups. The animals’ vital signs, stress hormones (cortisol and adrenaline), and subjective image quality scores for the computed tomography (CT), positron emission tomography (PET), and magnetic resonance imaging (MRI) scanning were measured and compared. Phantom CT, MRI and PET studies were performed to assess the performance with and without the thermoplastic mask by using image agents at different concentrations or with different radioactivity. The respiration rate (RR), systolic blood pressure (SBP), diastolic blood pressure (DBP), peripheral capillary oxygen saturation (SpO2) and body temperature (T) decreased after anesthesia (all P < 0.05) but did not significantly decrease after fixation (all P > 0.05). The heart rate (HR), cortisol and adrenaline did not significantly decrease after either anesthesia or fixation (all P > 0.05). The subjective image quality scores for the CT and MRI images of the head, thorax, liver, kidney, intestines and pelvis and the subjective image quality scores for the PET images did not significantly differ between the two groups (all P > 0.05). For all examined organs except the muscle, 18F-FDG metabolism was lower after fixation than after anesthesia, and was almost identical of liver between two groups. The phantom study showed that the CT values, standard uptake values and MR T2 signal values did not differ significantly with or without the mask (all P > 0.05). A novel rabbit fixator created using a thermoplastic mask could be used to obtain high-quality images for different imaging modalities in an awake and near-physiological state.

Compare of Interfractional Setup Reproducibility Between Vacuum-Lock Bag and Thermoplastic Mask in Radiotherapy for Breast Cancer

Background: This study aimed to analyze the difference of setup reproducibility between Vacuum-lock bag and Thermoplastic mask in the radiotherapy for breast cancer. Methods: A total of 100 invasive breast carcinoma patients were collected, among whom 50 patients were immobilized with Vacuum-lock bag (VB group), and the other 50 patients were immobilized with Thermoplastic mask (TM group). Set up reproducibility in different axes and comfort levels between two groups at three treatment progress points during the radiation therapy were collected and analyzed. Results: The linear regression model showed that fixed device was an independent factor of radiotherapy setup error (SE). Further subgroup analysis based on different axes showed that the SE caused by the fixed device was obvious in all directions. The comfort level in the VB group was significantly larger than that in the TM group at the beginning of treatment, reduced as the treatment progress going on, and finally disappeared within three weeks. Conclusions: Thermoplastic mask could significantly reduce positioning errors in the radiotherapy of breast cancer. Although more discomfort was found in the TM group, it could be eliminated as the treatment progresses.