Implementation of automated personalised breast radiotherapy planning techniques with scripting in Raystation.

OBJECTIVE: Implement scripted automatic breast planning (AP) for breast techniques within Raystation. METHODS: Manual plans (MPs) were re-planned and compared with AP plans for whole breast (WB), partial breast (PB), hybrid volumetric modulated arc therapy simultaneous integrated boost (VMAT SIB) and VMAT nodal plans. RESULTS: WB AP plans took 7 min comparing well to MP. One WB AP failed a mandatory dose constraint. Small statistically significant differences showed improved coverage for AP at expense of slightly hotter plans, however absolute differences were small (mean differences < 1% or D 0.5cc<0.2 Gy). PB AP plans took 9 min, showing improved coverage (V 24.7Gy97.6 vs 96.4 %). One PB AP case failed a mandatory constraint. Other dosimetric differences were non-significant. SIB AP plans took 14 min with one case failing a mandatory constraint with minor differences compared with MP except larger V 42.8Gy (3 vs 1.5 %) and more MU. VMAT AP plans took 12 min and were hotter for PTVp_4000 but had higher nodal coverage. Contra_Lung V 2.5Gy was higher (8.8 %) than MP plans (6.5 %). CONCLUSION: Automatic planning of modern breast techniques has been successfully introduced using a commercial planning system. AP plans are very similar to MP, requiring little manual interaction for most cases with significant timesaving potential. ADVANCES IN KNOWLEDGE: Scripted breast plans produced within minutes for WB, PB, SIB and VMAT. Successfully introduced into large busy department. Plans similar to manual plans, requiring little manual interaction.

Neutron Radiation Dose Measurements in a Scanning Proton Therapy Room: Can Parents Remain Near Their Children During Treatment?

Purpose: This study aims to characterize the neutron radiation field inside a scanning proton therapy treatment room including the impact of different pediatric patient sizes. Materials and Methods: Working Group 9 of the European Radiation Dosimetry Group (EURADOS) has performed a comprehensive measurement campaign to measure neutron ambient dose equivalent, H*(10), at eight different positions around 1-, 5-, and 10-year-old pediatric anthropomorphic phantoms irradiated with a simulated brain tumor treatment. Several active detector systems were used. Results: The neutron dose mapping within the gantry room showed that H*(10) values significantly decreased with distance and angular deviation with respect to the beam axis. A maximum value of about 19.5 µSv/Gy was measured along the beam axis at 1 m from the isocenter for a 10-year-old pediatric phantom at 270° gantry angle. A minimum value of 0.1 µSv/Gy was measured at a distance of 2.25 m perpendicular to the beam axis for a 1-year-old pediatric phantom at 140° gantry angle.The H*(10) dependence on the size of the pediatric patient was observed. At 270° gantry position, the measured neutron H*(10) values for the 10-year-old pediatric phantom were up to 20% higher than those measured for the 5-year-old and up to 410% higher than for the 1-year-old phantom, respectively. Conclusions: Using active neutron detectors, secondary neutron mapping was performed to characterize the neutron field generated during proton therapy of pediatric patients. It is shown that the neutron ambient dose equivalent H*(10) significantly decreases with distance and angle with respect to the beam axis. It is reported that the total neutron exposure of a person staying at a position perpendicular to the beam axis at a distance greater than 2 m from the isocenter remains well below the dose limit of 1 mSv per year for the general public (recommended by the International Commission on Radiological Protection) during the entire treatment course with a target dose of up to 60 Gy. This comprehensive analysis is key for general neutron shielding issues, for example, the safe operation of anesthetic equipment. However, it also enables the evaluation of whether it is safe for parents to remain near their children during treatment to bring them comfort. Currently, radiation protection protocols prohibit the occupancy of the treatment room during beam delivery.

Ion recombination and polarity correction factors for a plane-parallel ionization chamber in a proton scanning beam.

PURPOSE: To evaluate the effect on charge collection in the ionization chamber (IC) in proton pencil beam scanning (PBS), where the local dose rate may exceed the dose rates encountered in conventional MV therapy by up to three orders of magnitude. METHODS: We measured values of the ion recombination (ks ) and polarity (kpol ) correction factors in water, for a plane-parallel Markus TM23343 IC, using the cyclotron-based Proteus-235 therapy system with an active proton PBS of energies 30-230 MeV. Values of ks were determined from extrapolation of the saturation curve and the Two-Voltage Method (TVM), for planar fields. We compared our experimental results with those obtained from theoretical calculations. The PBS dose rates were estimated by combining direct IC measurements with results of simulations performed using the FLUKA MC code. Values of ks were also determined by the TVM for uniformly irradiated volumes over different ranges and modulation depths of the proton PBS, with or without range shifter. RESULTS: By measuring charge collection efficiency versus applied IC voltage, we confirmed that, with respect to ion recombination, our proton PBS represents a continuous beam. For a given chamber parameter, e.g., nominal voltage, the value of ks depends on the energy and the dose rate of the proton PBS, reaching c. 0.5% for the TVM, at the dose rate of 13.4 Gy/s. For uniformly irradiated regular volumes, the ks value was significantly smaller, within 0.2% or 0.3% for irradiations with or without range shifter, respectively. Within measurement uncertainty, the average value of kpol , for the Markus TM23343 IC, was close to unity over the whole investigated range of clinical proton beam energies. CONCLUSION: While no polarity effect was observed for the Markus TM23343 IC in our pencil scanning proton beam system, the effect of volume recombination cannot be ignored.