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Purpose To evaluate the impact of beam quality in terms of distal fall off DFO, 90 10 and lateral penumbra LP, 80 20 of single beam ocular proton therapy OPT and to derive resulting ideal requirements for future systems. Methods Nine different beam models with DFO varying between 1 and 4 mm and LP between 1 and 4 mm were created. Beam models were incorporated into the RayStation with RayOcular treatment planning system version 10 B RaySearch Laboratories, Stockholm, Sweden . Each beam model was applied for eight typical clinical cases, covering different sizes and locations of uveal melanoma. Plans with and without an additional wedge were created, resulting in 117 plans with a total prescribed median dose of 60 Gy RBE to the clinical target volume. Treatment plans were analyzed in terms of V20 V80 penumbra volume, D1 dose to 1 of the volume for optic disc and macula, optic nerve V30 volume receiving 30 Gy RBE , i.e., 50 of prescription , as well as average dose to lens and ciliary body. An LP dependent aperture margin was based on estimated uncertainties, ranging from 1.7 to 4.0 mm. Results V20 V80 showed a strong influence by LP, while DFO was less relevant. The optic disc D1 reached an extra dose of up to 3000 cGy RBE , comparing the defined technical limit of DFO LP 1 mm with DFO 3 mm LP 4 mm. The latter may result from a pencil beam scanning PBS system with static apertures. Plans employing a wedge showed an improvement for organs at risk sparing. Conclusion Plan quality is strongly influenced by initial beam parameters. The impact of LP is more pronounced when compared to DFO. The latter becomes important in the treatment of posterior tumors near the macula, optic disc or optic nerve. The plan quality achieved by dedicated OPT nozzles in single or double scattering design might not be achievable with modified PBS systems

Purpose To commission the treatment planning system (TPS) RayStation for proton therapy including beam models for spot scanning and for uniform scanning. Methods Tests consist of procedures from ESTRO booklet number 7, the German DIN for constancy checks of TPSs, and extra tests checking the dose perturbation function. The dose distributions within patients were verified in silico by a comparison of 65 clinical treatment plans with the TPS XiO. Dose-volume parameters, dose differences, and three-dimensional gamma-indices serve as measures of similarity. The monthly constancy checks of Raystation have been automatized with a script. Results The basic functionality of the software complies with ESTRO booklet number 7. For a few features minor enhancements are suggested. The dose distribution in RayStation agrees with the calculation in XiO. This is supported by a gamma-index (3 mm/3%) pass rate of >98.9% (median over 59 plans) for the volume within the 20% isodose line and a difference of V 95 of the PTV (median over 59 plans). If spot scanning is used together with a range shifter, the dose level calculated by RayStation can be off by a few percent. Conclusions RayStation can be used for the creation of clinical proton treatment plans. Compared to XiO RayStation has an improved modelling of the lateral dose fall-off in passively delivered fields. For spot scanning fields with range shifter blocks an empirical adjustment of monitor units is required. The computation of perturbed doses also allows the evaluation of the robustness of a treatment plan.

Aim To verify the consistency of dose and range measurement in an interinstitution comparison among proton therapy institutions in Germany which use the pencil-beam scanning technique. Methods Following a peer-to-peer approach absorbed dose and range have been intercompared in several missions at two hosting centers with two or three visiting physics teams of participating institutions using their own dosimetry equipment. A meta-analysis has been performed integrating the results of the individual missions. Dose has been determined with ionization chambers according to the dosimetry protocol IAEA TRS-398. For determination of the depth of the distal 80% dose the teams used either a scanning water phantom, a variable water column or a multi-layer ionization chamber. Results The systematic deviation between measured doses of the participating institutions is less than 1%. Ranges differ systematically less than 0.4 mm. Conclusions The match of measured dose and range is better than expected from the respective uncertainties. As all physics teams agree on the assessment of absorbed dose and range, an important prerequisite for a start of joint clinical studies is fulfilled.

Acquisition of quasi‐monoenergetic ("pristine") depth‐dose curves is an essential task in the frame of commissioning and quality assurance of a proton therapy treatment head. For pencil beam scanning delivery modes this is often accomplished by measuring the integral ionization in a plane perpendicular to the axis of an unscanned beam. We focus on the evaluation of three integral detectors: two of them are plane‐parallel ionization chambers with an effective radius of 4.1 cm and 6.0 cm, respectively, mounted in a scanning water phantom. The third integral detector is a 6.0 cm radius multilayer ionization chamber. The experimental results are compared with the corresponding measurements under broad field conditions, which are performed with a small radius plane‐parallel chamber and a small radius multilayer ionization chamber. We study how a measured depth‐dose curve of a pristine proton field depends on the detection device, by evaluating the shape of the depth‐dose curve, the relative charge collection efficiency, and intercomparing measured ranges. Our results show that increasing the radius of an integral chamber from 4.1 cm to 6.0 cm increases the collection efficiency by 0%–3.5% depending on beam energy and depth. Ranges can be determined by the large electrode multilayer ionization chamber with a typical uncertainty of 0.4 mm on a routine basis. The large electrode multilayer ionization chamber exhibits a small distortion in the Bragg Peak region. This prohibits its use for acquisition of base data, but is tolerable for quality assurance. The good range accuracy and the peak distortion are characteristics of the multilayer ionization chamber design, as shown by the direct comparison with the small electrode counterpart. PACS number: 87.55.Qr

We present here a novel method for using a single device in the daily quality assurance (QA) of pencil beam scanning (PBS) proton beams and an improved method for uniform scanning (US). The device can be used to measure the spot position, spot sigma, range, output, collinearity of the X‐ray system and proton beam, and to QA the first scatterers and a number of other imaging and mechanical checks. We have performed the daily QA according to this procedure for more than six months in both a PBS gantry and a US gantry. All of the tests were found to be sensitive and accurate enough to determine if the property being tested is within the tolerance. The output has remained within the ±2% tolerance, with the majority of measurements within ±1%, and the range was within ±0.5mm. The collinearity of the proton beam in both gantries is within the ±1mm tolerance in both X and Y directions for all measurements. A novel procedure to measure the functionality of the first scatterers in the US gantry is included in the QA procedure. It was found to be sensitive enough to pick up the thinnest scatterer of 0.6 mm in both possible failure methods — when it always remains in the beam or in the case when it never goes into the beam. The daily QA procedure presented here can be implemented at PBS or US proton therapy centers with a minimal outlay for equipment and setup time. The procedure can be performed in less than 30 min, and has been found to be accurate and reliable enough for the QA of a proton therapy gantry before patient treatment every day. PACS number: 87.55.Qr