The dose released to the patient skin during a radiotherapy treatment is important when the skin is an organ at risk, or on the contrary, is included in the target volume. Since most treatment planning programs do not predict dose within several millimeters of the body surface, it is important to have a method to verify the skin dose for the patient who is undergoing radiotherapy. A special type of metal oxide semiconductors field-effect transistors (MOSFET) was developed to perform in vivo skin dosimetry for radiotherapy treatments. Water-equivalent depth (WED), both manufacturing and sensor reproducibility, dependence on both field size and angulation of the sensor were investigated using 6 MV photon beams. Patient skin dosimetries were performed during 6 MV total body irradiations (TBI). The resulting WEDs ranged from 0.04 and 0.15 mm (0.09 mm on average). The reproducibility of the sensor response, for doses of 50 cGy, was within +/-2% (maximum deviation) and improves with increasing sensitivity or dose level. As to the manufacturing reproducibility, it was found to be +/-0.055 mm. No WED dependence on the field size was verified, but possible variations of this quantity with the field size could be hidden by the assessment uncertainty. The angular dependence, for both phantom-surface and in-air setups, when referred to the mean response, is within +/-27% until 80 degree rotations. The results of the performed patient skin dosimetries showed that, normally, our TBI setup was suitable to give skin the prescribed dose, but, for some cases, interventions were necessary: as a consequence the TBI setup was corrected. The water-equivalent depth is, on average, less than the thinnest thermoluminescent dosimeters (TLD). In addition, when compared with TLDs, the skin MOSFETs have significant advantages, like immediate both readout and reuse, as well as the permanent storage of dose. These sensors are also waterproof. The in vivo dosimetries performed prove the importance of verifying the dose to the skin of the patient undergoing radiotherapy.

Using in-house-designed phantoms, the authors evaluated radiation exposure rates in the vicinity of a newly acquired intraoperative radiation therapy (IORT) system: Axxent Electronic Brachytherapy System. The authors also investigated the perimeter radiation levels during three different clinical intraoperative treatments (breast, floor of the mouth and bilateral neck cancer patients). Radiation surveys during treatment delivery indicated that IORT using the surface applicator and IORT using balloons inserted into patient body give rise to exposure rates of 200 mR h(-1), 30 cm from a treated area. To reduce the exposure levels, movable lead shields should be used as they reduce the exposure rates by >95%. The authors' measurements suggest that intraoperative treatment using the 50-kVp X-ray source can be administered in any regular operating room without the need for radiation shielding modification as long as the operators utilise lead aprons and/or stand behind lead shields.

Purpose: The main objective was to evaluate and commission the Xoft Electronic Brachytherapy System for intraoperative treatments. Method and Materials: Using the manufacturer supplied phantom, we evaluated and commissioned the Xoft Electronic Brachytherapy system. We tested well‐chamber constancy and intercomparison, beam output stability with time, start/end effects, and performed radiation surveys. Other checks recommended by the AAPM TG152 were evaluated. Results The Ir‐192 calibrated well chamber is 3.7 times more sensitive when irradiated with the Xoft source than the Xoft calibrated well chamber. Expectation was that both chambers would give approximately the same reading because the Xoft integrated well chamber is cross calibrated in I‐125 source. It takes about 28s for the doserate from the Xoft Unit to ramp up to the treatment doserate. The unit delivers 9s worth of treatment during the ramp up phase. For treatment times less than 100s, this would introduce a dosimetry error of about 10% which will be repeated if there is a treatment interruption. Xoft Unit output may vary by up to 5% between 0.25 and 30 minutes. This variation is source dependent. So the minimum time used to collect charges for the AAPM‐TG61 calibration should be 1 minute, not 0.25 minute. Radiation surveys during treatment indicate that surface and intraoperative treatments give rise to exposure rates of 200mR/hr, 30cm from treatment area. Conclusions: Well chamber calibration inconsistency for Xoft Unit needs further investigation. Ramp up time accounts for 9s equivalent treatment time. Correction needed for treatment time less than 150 seconds. Charges for TG61 calibration should be collected for at least 1 minute, not 0.25 minute. Intraoperative and surface treatment produces exposure rate of 200mR/hr at distances of 30 cm. Exercise extreme caution by standing behind lead shield or wearing a lead apron.

Purpose: To compare two 3D Gamma Index calculation schemes for VMAT plans. Methods: VMAT (Volumetric Modulated Arc Therapy) treatment technique was commissioned for our clinic on an Elekta Synergy machine. We selected to use ScandiDos Delta4TM system for our VMAT patient QAs. Delta4 is a pseudo 3D diode detector array which calculates Gamma index from 3D dose distributions. Delta4 offers two ways to calculate Gamma Index: global Gamma Index and local Gamma Index. The global gamma calculates the dose difference relative to the normalization dose, which can be iso‐center dose, prescribed or maximum dose. The local gamma calculates the dose difference relative to the current measurement point under examination. Thirty two test plans for the treatments of different sites including prostates, HN, lung, abdomen, pancreas node, anus, brain post fossa, medium sternum and liver were selected for this study. Pass rates from the two Gamma Index calculation schemes with 3% and 3mm criterion were compared. Results: The pass rate from global Gamma Index calculation is high than those from the global Gamma Index (p<0.001). Correlation coefficient of the two pass rates is 0.78. The differences of pass rates range from 0% to 9.5%. The most dramatic differences happen for high modulated (more complex) plans and where there are some low dose plateau regions. Conclusions: Global Gamma Index doesnˈt describe the details of high modulated plans with some low dose regions. Pass rate of local Gamma Index should be examined in addition to global Gamma Index. Pass rates of local Gamma Index for different structures are desired.