External dosimetry audit for quality assurance of carbon-ion radiation therapy clinical trials.

PURPOSE: The QA team of the Japan carbon-ion radiation oncology study group (J-CROS) was organized in 2015 to enhance confidence in the accuracy of clinical dosimetry and ensure that the facility QA procedures are adequate. The team conducted onsite dosimetry audits in all the carbon-ion radiation therapy centers in Japan. MATERIALS AND METHODS: A special phantom was fabricated for the onsite dosimetry audit. Target volumes such as the GTV, CTV, and PTV were contoured to the obtained CT images, and two plans with different isocenter depths were created. The dose at the isocenter was measured by an ionization chamber, in the onsite audit and compared with the calculated dose. RESULTS: For all the centers, the average of the percentage ratio between the measured and calculated doses (measured/calculated) was 0.5% (-2.7% to +2.6%) and the standard deviation, 1.7%. In all the centers, the beams were within the set tolerance level of 3%. CONCLUSIONS: The audit demonstrated that the dose at a single point in the water phantom was within tolerance, but it is a big step to say that all doses are correct. In addition, this external dosimetry audit encouraged centers to improve the quality of their dosimetry systems.

The Usefulness of Using Fiducial Marker in Proton Therapy for Locally Advanced Pancreatic Cancer.

BACKGROUND: Though the dosimetric criteria for the gastrointestinal tract were met, late gastrointestinal toxicity was seen in several cases. Therefore, we thought that it was caused by the positional variation of gastrointestine surrounding pancreatic cancer because of peristalsis. METHOD: They were confirmed by CT image regularly. And we evaluated that how much the difference of matching methods for correcting the positional variation influenced dose distribution. RESULT: The fiducial markers could follow the position of pancreatic cancer and the duodenum. But it could reproduce the dose distribution to pancreatic cancer and the duodenum. DISCUSSION: In proton therapy, the reproducible improvement of the duodenum position did not make the dose of the duodenum same as planning dose because the matching of fiducial markers made the positional relations between beam compensator and the duodenum change. CONCLUSION: The fiducial markers are useful for correcting the position of pancreatic cancer and the duodenum. But in proton therapy, it could not reproduce the dose distribution to pancreatic cancer and the duodenum.

Preclinical biological assessment of proton and carbon ion beams at Hyogo Ion Beam Medical Center.

PURPOSE: To assess the biologic effects of proton and carbon ion beams before clinical use. METHODS AND MATERIALS: Cultured cells from human salivary gland cancer (HSG cells) were irradiated at 5 points along a 190 MeV per nucleon proton and a 320 MeV per nucleon carbon ion beam, with Bragg peaks modulated to 6 cm widths. A linac 4 MV X-ray was used as a reference. Relative biologic effectiveness (RBE) values at each point were calculated from survival curves. Cells were also irradiated in a cell-stack phantom to identify that localized cell deaths were observed at predefined depth. Total body irradiation of C3H/He mice was performed, and the number of regenerating crypts per jejunal section was compared to calculate intestinal RBE values. For carbon ion and referential 4 MV X-ray beams, mouse right legs were irradiated by four-fractional treatment and followed up for skin reaction scoring. RESULTS: RBE values calculated from cell survival curves at the dose that would reduce cell survival to 10% (D10) ranged from 1.01 to 1.05 for protons and from 1.23 to 2.56 for carbon ions. The cell-stack phantom irradiation revealed localized cell deaths at predefined depth. The intestinal RBE values ranged from 1.01 to 1.08 for protons and from 1.15 to 1.88 for carbon ions. The skin RBE value was 2.16 at C320/6 cm spread-out Bragg peak (SOBP) center. CONCLUSION: The radiobiologic measurements of proton and carbon ion beams at Hyogo Ion Beam Medical Center are consistent with previous reports using proton beams in clinical settings and carbon ion beams with similar linear energy transfer (LET) values.

Cell biological basis for combination radiotherapy using heavy-ion beams and high-energy X-rays.

We investigated the biological effect of combining carbon-beam and X-ray in vitro. The results showed that when we employed Gray equivalent as the indication of therapeutic dose, the effects could be explained with simple additive way in the treatment plan. This fact provides important information about the combined therapy of carbon-beam and X-ray.