Passive Proton Beam Therapy Research Articles

Phantom Study of the Optimum Irradiation Angle for Proton Beam Therapy in Hepatocellular Carcinoma

<h3>Purpose/Objective(s)</h3> Passive proton beam therapy (PPBT) for hepatocellular carcinoma (HCC) has a higher local control rate than surgery or photon beam therapy. Moreover, it is attracting attention as one of the new treatment options. In the PPBT planning, the selection of the beam angle is determined according to the subjective judgment of the planner. Therefore, there are differences in the dose distribution depending on the planner. It has not yet been clarified which the irradiation angle can be selected to reduce unnecessary dose on the organ-at-risks and maintain the target coverage. The purpose of this study was to determining the optimal beam angle for liver S8 lesions. <h3>Materials/Methods</h3> The subjects were fifty-four treatment plans for HCC located in S8 irradiated using PPBT during the period of 2012.6-2021.3 at the National Cancer Center Hospital East. Tumor sizes were aggregated from the subjects. Clinical Target Volume (CTV) of the subject's liver ranged from 4 cm3 to 1370 cm3. Tumor sizes ranged from 132 cm to 655 cm3. From these results, the average CTV were represented on a virtual phantom, the dose distribution using PPBT was optimized using two irradiation angles. For the calculation of the optimum irradiation angle, the combination of the two beams rotated every 10 degrees and the best dose distribution was considered to be the optimum angle. The Conformity Index (CI) and Homogeneity Index (HI) of the CTV and the V30 (%) of the liver were calculated using the Dose volume histogram (DVH). <h3>Results</h3> The combination of beam angles showing 1 in the Conformity Index was 360 ° and 250 °, 350 ° and 230 °, 260 ° and 190 ° for small tumor volumes. Homogeneity Index and V30 averaged 1.06 and 28.0%, respectively. At the time of large tumor volume, it was 350 ° and 270 °, 350 ° and 250 °, 250 ° and 170 °. Homogeneity Index and V30 averaged 1.07 and 47.6%, respectively. The treatment schemes beam-arranged with a 70 ° difference in angle between the two beams were the most homogeneous with respect to the target. A significant difference was found in Conformity Index when compared to the most heterogeneous 190 ° difference (p <0.05). <h3>Conclusion</h3> Based on our findings, we recommend using a 2-beam configuration with a beam tilted by approximately 70 ° between the two beams for passive irradiation of hepatocellular carcinoma located in S8. This has the potential to achieve a uniform dose distribution within the target and at the same time reduce the hepatic dose. However, it should be noted that there is a difference in dose increase / decrease depending on the positional relationship of organs and tumors. Further treatment planning studies on aspects of respiration and organ movement need to be conducted.

SU-GG-T-465: Secondary Doses for the Treatment of Lung and Liver Cancers: IMRT vs. Proton Therapy

Purpose: To quantify and compare the secondary doses induced by advanced radiotherapy modalities, intensity‐modulated radiotherapy(IMRT) and proton beam therapy (PBT), for the treatment of lung and livercancers.Method and Materials:IMRT with 6 MV photon and proton beam therapy were planned for 3 lung and 3 livercancer patients. The treatment beams were delivered to phantom and corresponding secondary doses during irradiation were measured at various points from 20 cm to 50 cm apart from the beam isocenter using ion chamber and CR‐39 detectors for IMRT and PBT, respectively. Results: The average secondary doses of proton therapy for lung and livercancer patients, measured 20 to 50 cm from the isocenter, ranged from 1.73 mSv/Gy to 0.86 mSv/Gy. The average secondary doses of IMRT for lung patients, however, ranged between 5.8 mSv/Gy and 1.0 mSv/Gy, approximately three times higher than for proton therapy. The average internal neutrondoses of proton therapy for lung and livercancer patients, measured 20 to 50 cm from the isocenter, ranged from 0.21 mSv/Gy to 0.08 mSv/Gy. The result shows that internal neutrondose produced by proton interaction in the body is generally much less than external neutrondose produced by proton interactions in the scattering elements of the passively modulated beam line. Conclusion: By a comparison between passive proton beam therapy and IMRT for diseases of lung and livercancer, it was shown that the secondary doses using scattering mode in proton beam therapy is either significantly lower than the cases in IMRT treatment or, at least, does not exceed the secondary doses induced by conventional IMRT treatment.

SU‐FF‐T‐465: Study On Secondary Cancer Risk Induced by Intensity‐Modulated Radiotherapy and Passive Proton Beam Therapy

Purpose: Secondary cancer risk induced by radiation therapies, intensity‐modulated radiotherapy (IMRT) and passive proton beam therapy, was estimated and compared for prostate and head &amp; neck patients. Method and Materials: The concept of an organ equivalent dose (OED) for radiation‐induced cancer was applied to dose distributions of patients to estimate organ specific radiation‐induced cancer risk. IMRT with 6 MV photons and proton beam therapy were planned for 5 prostate and 5 head &amp; neck cancer patients. The treatment beams were delivered to humanoid phantom and secondary doses during irradiation were measured at various points from 20 cm to 60 cm apart from the beam isocenter on humanoid phantom using ion chamber and CR‐39 detectors for IMRT and passive proton beam therapy, respectively. Results: The average secondary doses for prostate cancer patients in passive proton beam therapy, which is neutron dose equivalent to the proton absorbed dose (H(10)/D) measured from 20 to 60 cm from the isocenter, ranged from 0.4 mSv/Gy to 0.1 mSv/Gy. The average secondary doses in IMRT for prostate patients, ranged between 3 mSv/Gy and 1 mSv/Gy whose values are approximately order of magnitude higher than the proton therapy. Although the average secondary doses for head &amp; neck cancer patients in proton therapy were less than the average secondary doses in IMRT, the difference was not significant as the prostate cases. Conclusion: By a comparison between passive proton beam therapy and IMRT for diseases of prostate and head &amp; neck, it was shown that the estimated secondary cancer risk using scattering mode in proton beam therapy is either significantly lower than the cases in IMRT treatment or, at least, does not exceed the risk induced by conventional IMRT treatment.