PurposeTo investigate the dosimetric impact of the calculation boundaries and dose calculation algorithms of radiotherapy in head and neck cancer patients with an opened oral cavity connected to the exterior by a hollow intraoral positioning stent.Methods and MaterialsA homemade silicone phantom with an opened oral cavity was placed in a CIRS head phantom to model head and neck cancer patients with a hollow intraoral positioning stent. 3D‐CRT plans were designed on CT images of the phantom in Monaco and Pinnacle3 treatment planning systems (TPSs) with the same beam parameters. The default boundary and manually extrapolated boundary were both adopted in these two TPSs to explore the dosimetric impact on treatment plans. The nanoDot™ optically stimulated luminescence dosimeters (OSLDs) were chosen to measure the planned dose surrounding the oral cavity of the head phantom after calibration.ResultThe doses in the air cavity and two measuring points at the joint area were dramatically changed from 0.0, 92.4 and 148.8 cGy to 177.8, 244.2 and 244.1 cGy in Monaco after adopting the extrapolated boundary. While the calculated doses at the same place were changed from 61.2, 143.7 and 198.3 cGy to 175.4, 234.7 and 233.2 cGy in Pinnacle3 with a similar calculation boundary. For the Monaco TPS, the relative errors compared to the OSLD measured doses were 2.94 ± 1.93%, 0.53 ± 8.64%, 2.65 ± 1.87% and 3.93 ± 1.69% at 4 measuring positions. In contrast, the relative errors 4.03 ± 1.93%, 4.85 ± 8.64%, 7.61 ± 1.87% and 5.61 ± 1.69% were observed in Pinnacle3.ConclusionThe boundary setting of an opened oral cavity in TPSs has a significant dosimetric impact on head and neck cancer radiotherapy. An extrapolated boundary should be manually set up to include the whole oral cavity in the dose calculation domain to avoid major dose deviations.

3D printing technology is widely used for fabricating bolus in post-mastectomy radiotherapy. 3D printed boluses are usually made from hard materials like Polylactic Acid, which can't adhere to patients' skin perfectly in clinical practice because of the patients' uneven surfaces of chest walls and large radiotherapy area. In this work, the feasibility of 3D printing soft selfadhesion boluses using water tissue equivalent silicone hydrogel material in post-mastectomy radiotherapy was studied, and intensity modulated radiotherapy plans were designed to study the performance of the water tissue equivalent silicone hydrogel bolus by comparing to the results of using virtual boluses with the relative electron density of 1.09 in radiotherapy. The comparison demonstrated that water tissue equivalent silicone hydrogel boluses have better adhesive property than boluses made from hard materials. The average air gap volume between the water tissue equivalent silicone hydrogel bolus and patients' skin is 9.5 cc. The average degree of adhesion and average maximuum air cavity dimension are 3.7% and 4.3 mm, respectively. The dose distribution of the virtual bolus and the water tissue equivalent silicone hydrogel bolus are roughly the same in Dose Volume Histogram.

Purpose: Lung tumor and affected lymph nodes may change their relative positions during treatment, manifesting in the deformation of the multi‐target tumor system. Comparing to the current standard care, this study aims to quantify the clinical benefit if the deformation is ideally tracked. Methods: Six lung cancer patients at stage IIIA were included in this study. For the current standard care treatment, an IMRT plan was created on the reference phase and dose of the same plan was calculated on each phase. The planning target volume (PTV) was 5 mm expansion of the internal target volume (ITV) defined as the summation of the clinical target volumes (CTV) of all phases. For the ideally‐tracked treatment, an individual IMRT plan was created for each phase with 5 and 2 mm CTV‐to‐PTV margins. Dose of each phase was deformed and summed to the reference phase. All plans were normalized so that the equivalent uniform dose (EUD) of the CTV was the same at 74 Gy. EUD and the normal tissue complication probabilities (NTCP) of the spinal cord, esophagus, heart and lung were compared for the three treatment scenarios. Results: The EUD of the spinal cord, esophagus, heart and lung was 31.3±9.9, 55.5±11.7, 32.6±16.1, and 16.8±3.2 Gy for the standard‐care plan, 30.9±10.1, 54.2±12.1, 31.2±15.7, and 15.6±2.6 Gy for the ideally‐tracked plan with 5 mm PTV margin, and 29.0±10.6, 50.7±13.6, 29.4±15.1 and 14.3±2.6 Gy for the ideally‐tracked plan with 2 mm PTV margin, respectively. The greatest NTCP reduction was 3.5% (9.5%) for esophagitis, 4.4% (20.5%) for pericarditis and 11.8% (16.2%) for pneumonitis in ideally‐tracked treatment with 5 (2) mm PTV margin. Conclusion: The toxicity to the critical organs can be greatly reduced if the tumor system deformation can be compensated with high accuracy and precision which allows PTV margin to be reduced to 2 mm. The authors acknowledge funding support from the Australian NHMRC Australia Fellowship, Sydney Medical School Summer Research Scholarships, NHMRC Project Grant APP1042375 and US NIH/NCI R01CA93626.