Delivery accuracy of VMAT on two beam-matched linacs provided by accelerated go live service.

INTRODUCTION: Dosimetric accuracy is critical when a patient treated with volumetric modulated arc therapy (VMAT) is transferred to another beam-matched linac. To evaluate the performance of Accelerated Go Live (AGL) service, the measured beam characteristics and patient specific quality assurance (QA) results between two AGL-matched linacs were compared. MATERIALS AND METHODS: Two VersaHD linacs were installed using the AGL service. After the installation, the beam data such as percentage depth dose (PDD), lateral profiles and output factors for all photon beams were measured. Relative doses were also measured as a function of the multi-leaf collimator (MLC) leaf gap width. Subsequently, VMAT plans were created for prostate, pelvis, head and neck, liver, lung cancers and multiple brain metastases. Dose distributions and point doses were measured by multi-dimensional detectors and ionization chambers for patient specific quality assurance, and comparisons were made between the two linacs. RESULTS: Dose differences in PDDs were all within ± 1% except the entrance region, and the averaged gamma indices of the lateral profiles were within 0.3. The differences in doses as a function of the MLC leaf gap width between the two linacs were within ±0.5%. For all the plans, gamma passing rates were all higher than 95% with criteria of 2%/2 mm. The average and the SD of dose differences on the multi-dimensional detector between both measurements was 0.06 ± 2.12%, and the average of point dose differences was -0.03 ± 0.33%. CONCLUSION: We have evaluated the AGL performance in the context of beam characteristics and patient specific QA. It was demonstrated that the AGL service provides an accurate VMAT treatment reproducibility for many tumor sites with gamma pass rates greater than 95% under criteria of 2%/2 mm.

A new workflow of the on-line 1.5-T MR-guided adaptive radiation therapy.

PURPOSE: The aim of this study was to develop a new workflow for 1.5-T magnetic resonance (MR)-guided on-line adaptive radiation therapy (MRgART) and assess its feasibility in achieving dose constraints. MATERIALS AND METHODS: We retrospectively evaluated the clinical data of patients who underwent on-line adaptive radiation therapy using a 1.5-T MR linear accelerator (MR-Linac). The workflow in MRgART was established by reviewing the disease site, number of fractions, and re-planning procedures. Five cases of prostate cancer were selected to evaluate the feasibility of the new workflow with respect to achieving dose constraints. RESULTS: Between December 2021 and September 2022, 50 consecutive patients underwent MRgART using a 1.5-T MR-Linac. Of these, 20 had prostate cancer, 10 had hepatocellular carcinoma, 6 had pancreatic cancer, 5 had lymph node oligo-metastasis, 3 had renal cancer, 3 had bone metastasis, 2 had liver metastasis from colon cancer, and 1 had a mediastinal tumor. Among a total of 247 fractions, 235 (95%) were adapt-to-shape (ATS)-based re-planning. The median ATS re-planning time in all 50 cases was 17 min. In the feasibility study, all dose constraint sets were met in all 5 patients by ATS re-planning. Conversely, a total of 14 dose constraints in 5 patients could not be achieved by virtual plan without using adaptive re-planning. These dose constraints included the minimum dose received by the highest irradiated volume of 1 cc in the planning target volume and the maximum dose of the rectal/bladder wall. CONCLUSION: A new workflow of 1.5-T MRgART was established and found to be feasible. Our evaluation of the dose constraint achievement demonstrated the effectiveness of the workflow.

Independent assessment of source position for gynecological applicator in high-dose-rate brachytherapy.

PURPOSE: The aim of this study is to describe a phantom designed for independent examination of a source position in brachytherapy that is suitable for inclusion in an external auditing program. MATERIAL AND METHODS: We developed a phantom that has a special design and a simple mechanism, capable of firmly fixing a radiochromic film and tandem-ovoid applicators to assess discrepancies in source positions between the measurements and treatment planning system (TPS). Three tests were conducted: 1) reproducibility of the source positions (n = 5); 2) source movements inside the applicator tube; 3) changing source position by changing curvature of the transfer tubes. In addition, as a trial study, the phantom was mailed to 12 institutions, and 23 trial data sets were examined. The source displacement ΔX and ΔY (reference = TPS) were expressed according to the coordinates, in which the positive direction on the X-axis corresponds to the external side of the applicator perpendicular to source transfer direction Y-axis. RESULTS: Test 1: The 1σ fell within 1 mm irrespective of the dwell positions. Test 2: ΔX were greater around the tip of the applicator owing to the source cable. Test 3: All of the source position changes fell within 1 mm. For postal audit, the mean and 1.96σ in ΔX were 0.8 and 0.8 mm, respectively. Almost all data were located within a positive region along the X-axis due to the source cable. The mean and 1.96σ in ΔY were 0.3 and 1.6 mm, respectively. The variance in ΔY was greater than that in ΔX, and large uncertainties exist in the determination of the first dwell position. The 95% confidence limit was 2.1 mm. CONCLUSIONS: In HDR brachytherapy, an effectiveness of independent source position assessment could be demonstrated. The 95% confidence limit was 2.1 mm for a tandem-ovoids applicator.

Initial experience of radiotherapy plus cetuximab for Japanese head and neck cancer patients.

In Japan, cetuximab with concurrent bioradiotherapy (BRT) for squamous cell carcinoma of head and neck (SCCHN) was approved in December 2012. We herein report our initial experience of BRT, with special emphasis on acute toxicities of this combination therapy. Thirty-one non-metastatic SCCHN patients who underwent BRT using cetuximab between July 2013 and June 2014 were retrospectively evaluated. All patients received cetuximab with a loading dose of 400 mg/m(2) one week before the start of radiotherapy, followed by 250 mg/m(2) per week during radiotherapy. The median cycle of cetuximab was seven cycles and the median dose of radiotherapy was 70 Gy. Twenty-five patients (80.6%) accomplished planned radiotherapy and six cycles or more cetuximab administration. Six patients (19.4%) discontinued cetuximab. Grade 3 dermatitis, mucositis and infusion reaction occurred in 19.4%, 48.3% and 3.2%, respectively. One patient experienced Grade 3 gastrointestinal bleeding caused by diverticular hemorrhage during BRT. Grade 3 drug-induced pneumonitis occurred in two patients. The response rate was 74%, including 55% with a complete response. BRT using cetuximab for Japanese patients with SCCHN was feasible as an alternative for cisplatin-based concurrent chemoradiation, although longer follow-up is necessary to evaluate late toxicities.

Examination of beam profile measurement using an imaging plate by the light exposure fading method for quality assurance of external radiation therapy.

High-resolution film dosimetry has been used for several decades to check and to measure two-dimensional dose distributions. However, in recent years, the automatic processor has been replaced by the spread of computed radiography, or has been little used hospitals. In this study, we measured the off-center ratio (OCR) of the open field, after an irradiating radiation beam was delivered to the imaging plate (IP) under conditions in which the IP was exposed to a fixed amount of light with fading, and compared these data with the OCR measured by an ionization-chamber dosimeter, which is the standard method used for measuring radiation dose. Profile measurement using IP could be achieved by performing light fading, even at a range of more than 100 MU. Further, by using a metallic filter, we succeeded in demonstrating that the profile measurement of IP in an open irradiation field could approximate the values of those obtained by an ionization chamber dosimeter. This method can serve as a simple, easy-to-use method for evaluating the QA of dose distribution in radiation therapy.

[Characteristic evaluation of a real-time silicon dosimeter and measurement of entrance surface dose at radiography].

It is important to grasp how much radiation exposure has occurred through radiation diagnosis, in respect to patient explanations and radiation protection. In this examination, we used a patient skin dosimeter (PSD) that measures entrance surface dose (ESD) in real time using a fluoroscopy procedure. The PSD has the ability to display results beginning at 1 microGy. We focused our attention on the X-ray detectability of the PSD, and performed a representative evaluation with the X-ray equipment. We measured ESD under various radiographic parameters at our facility. Although the measurements were dependent on energy, we were able to measure ESD to within an accuracy of about a 5% error by putting a calibration value on energy. The PSD can measure ESD easily without requiring preparation. It is important to be aware of the exposure dose to the radiation staff, and the PSD is a very effective radiation dose-measuring tool when daily business is active.