Myonggeun Yoon

Dosimetric comparison of four different external beam partial breast irradiation techniques: Three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, helical tomotherapy, and proton beam therapy

BACKGROUND AND PURPOSE As an alternative to whole breast irradiation in early breast cancer, a variety of accelerated partial breast irradiation (APBI) techniques have been investigated. The purpose of our study is to compare the dosimetry of four different external beam APBI (EB-APBI) plans: three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), helical tomotherapy (TOMO), and proton beam therapy (PBT). METHODS AND MATERIALS Thirty patients were included in the study, and plans for four techniques were developed for each patient. A total dose of 30Gy in 6Gy fractions once daily was prescribed in all treatment plans. RESULTS In the analysis of the non-PTV breast volume that was delivered 50% of the prescribed dose (PD), PBT (mean: 16.5%) was superior to TOMO (mean: 22.8%), IMRT (mean: 33.3%), and 3D-CRT (mean: 40.9%) (p<0.001). The average ipsilateral lung volume percentage receiving 20% of the PD was significantly lower in PBT (0.4%) and IMRT (2.3%) compared with 3D-CRT (6.0%) and TOMO (14.2%) (p<0.001). The average heart volume percentage receiving 20% and 10% of the PD in left-sided breast cancer (N=19) was significantly larger with TOMO (8.0%, 19.4%) compared to 3D-CRT (1.5%, 3.1%), IMRT (1.2%, 4.0%), and PBT (0%, 0%) (p<0.001). CONCLUSIONS All four EB-APBI techniques showed acceptable coverage of the PTV. However, effective non-PTV breast sparing was achieved at the cost of considerable dose exposure to the lung and heart in TOMO.

A new homogeneity index based on statistical analysis of the dose–volume histogram

The goal of the present study was to develop a new dose–volume histogram (DVH)– based homogeneity index for effectively evaluating the dose homogeneity of intensity‐modulated radiotherapy plans. The new index, called the sigma‐index (“S‐index”) is defined as the standard deviation of the normalized differential DVH curve. In a study of 16 patients with brain tumors at our institution, the S‐index was found to vary from 0.80 to 3.15. Our results showed that the S‐index provides a more reliable and accurate measure of dose homogeneity than that given by conventional methods. A guideline for evaluating the dose homogeneity of treatment plans based on the S‐index and its relation to equivalent uniform dose is discussed. PACS numbers: 87.53.Xd, 87.53.Tf

Radiation-Induced Cancers From Modern Radiotherapy Techniques: Intensity-Modulated Radiotherapy Versus Proton Therapy

PURPOSE To assess and compare secondary cancer risk resulting from intensity-modulated radiotherapy (IMRT) and proton therapy in patients with prostate and head-and-neck cancer. METHODS AND MATERIALS Intensity-modulated radiotherapy and proton therapy in the scattering mode were planned for 5 prostate cancer patients and 5 head-and-neck cancer patients. The secondary doses during irradiation were measured using ion chamber and CR-39 detectors for IMRT and proton therapy, respectively. Organ-specific radiation-induced cancer risk was estimated by applying organ equivalent dose to dose distributions. RESULTS The average secondary doses of proton therapy for prostate cancer patients, measured 20-60 cm from the isocenter, ranged from 0.4 mSv/Gy to 0.1 mSv/Gy. The average secondary doses of IMRT for prostate patients, however, ranged between 3 mSv/Gy and 1 mSv/Gy, approximately one order of magnitude higher than for proton therapy. Although the average secondary doses of IMRT were higher than those of proton therapy for head-and-neck cancers, these differences were not significant. Organ equivalent dose calculations showed that, for prostate cancer patients, the risk of secondary cancers in out-of-field organs, such as the stomach, lungs, and thyroid, was at least 5 times higher for IMRT than for proton therapy, whereas the difference was lower for head-and-neck cancer patients. CONCLUSIONS Comparisons of organ-specific organ equivalent dose showed that the estimated secondary cancer risk using scattering mode in proton therapy is either significantly lower than the cases in IMRT treatment or, at least, does not exceed the risk induced by conventional IMRT treatment.

Craniospinal Irradiation Techniques: A Dosimetric Comparison of Proton Beams With Standard and Advanced Photon Radiotherapy

PURPOSE To evaluate the dosimetric benefits of advanced radiotherapy techniques for craniospinal irradiation in cancer in children. METHODS AND MATERIALS Craniospinal irradiation (CSI) using three-dimensional conformal radiotherapy (3D-CRT), tomotherapy (TOMO), and proton beam treatment (PBT) in the scattering mode was planned for each of 10 patients at our institution. Dosimetric benefits and organ-specific radiation-induced cancer risks were based on comparisons of dose-volume histograms (DVHs) and on the application of organ equivalent doses (OEDs), respectively. RESULTS When we analyzed the organ-at-risk volumes that received 30%, 60%, and 90% of the prescribed dose (PD), we found that PBT was superior to TOMO and 3D-CRT. On average, the doses delivered by PBT to the esophagus, stomach, liver, lung, pancreas, and kidney were 19.4 Gy, 0.6 Gy, 0.3 Gy, 2.5 Gy, 0.2 Gy, and 2.2 Gy for the PD of 36 Gy, respectively, which were significantly lower than the doses delivered by TOMO (22.9 Gy, 4.5 Gy, 6.1 Gy, 4.0 Gy, 13.3 Gy, and 4.9 Gy, respectively) and 3D-CRT (34.6 Gy, 3.6 Gy, 8.0 Gy, 4.6 Gy, 22.9 Gy, and 4.3 Gy, respectively). Although the average doses delivered by PBT to the chest and abdomen were significantly lower than those of 3D-CRT or TOMO, these differences were reduced in the head-and-neck region. OED calculations showed that the risk of secondary cancers in organs such as the stomach, lungs, thyroid, and pancreas was much higher when 3D-CRT or TOMO was used than when PBT was used. CONCLUSIONS Compared with photon techniques, PBT showed improvements in most dosimetric parameters for CSI patients, with lower OEDs to organs at risk.

Secondary Neutron Doses for Several Beam Configurations for Proton Therapy

PURPOSE To compare possible neutron doses produced in scanning and scattering modes, with the latter assessed using a newly built passive-scattering proton beam line. METHODS AND MATERIALS A 40 x 30.5 x 30-cm water phantom was irradiated with 230-MeV proton beams using a gantry angle of 270 degrees , a 10-cm-diameter snout, and a brass aperture with a diameter of 7 cm and a thickness of 6.5 cm. The secondary neutron doses during irradiation were measured at various points using CR-39 detectors, and these measurements were cross-checked using a neutron survey meter with a 22-cm range and a 5-cm spread-out Bragg peak. RESULTS The maximum doses due to secondary neutrons produced by a scattering beam-delivery system were on the order of 0.152 mSv/Gy and 1.17 mSv/Gy at 50 cm from the beam isocenter in the longitudinal (0 degrees ) and perpendicular (90 degrees ) directions, respectively. The neutron dose equivalent to the proton absorbed dose, measured from 10 cm to 100 cm from the isocenter, ranged from 0.071 mSv/Gy to 1.96 mSv/Gy in the direction of the beam line (i.e., phi = 0 degrees ). The largest neutron dose, of 3.88 mSv/Gy, was observed at 135 degrees and 25 cm from the isocenter. CONCLUSIONS Although the secondary neutron doses in proton therapy were higher when a scattering mode rather than a scanning mode was used, they did not exceed the scattered photon dose in typical photon treatments.

Simultaneous Integrated Boost Intensity-Modulated Radiotherapy in Patients With High-Grade Gliomas

PURPOSE We analyzed outcomes of simultaneous integrated boost (SIB) intensity-modulated radiotherapy (IMRT) in patients with high-grade gliomas, compared with a literature review. METHODS AND MATERIALS Forty consecutive patients (WHO grade III, 14 patients; grade IV, 26 patients) treated with SIB-IMRT were analyzed. A dose of 2.0 Gy was delivered to the planning target volume with a SIB of 0.4 Gy to the gross tumor volume with a total dose of 60 Gy to the gross tumor volume and 50 Gy to the planning target volume in 25 fractions during 5 weeks. Twenty patients received temozolomide chemotherapy. RESULTS At a median follow-up of 13.4 months (range, 3.7-55.9 months), median survival was 14.8 months. One- and 2-year survival rates were 78% and 65%, respectively, for patients with grade III tumors and 56% and 31%, respectively, for patients with grade IV tumors. Age (≤50 vs. >50), grade (III vs. IV), subtype (astrocytoma vs. oligodendroglioma or mixed), and a Zubrod performance score (0-1 vs. >2) were predictive of survival. Of 25 (63%) patients who had recurrences, 17 patients had local failure, 9 patients had regional failure, and 1 patient had distant metastasis. Toxicities were acceptable. CONCLUSIONS SIB-IMRT with the dose/fractionation used in this study is feasible and safe, with a survival outcome similar to the historical control. The shortening of treatment time by using SIB-IMRT may be of value, although further investigation is warranted to prove its survival advantage.

MICROSCOPIC GOLD PARTICLE-BASED FIDUCIAL MARKERS FOR PROTON THERAPY OF PROSTATE CANCER

PURPOSE We examined the feasibility of using fiducial markers composed of microscopic gold particles and human-compatible polymers as a means to overcome current problems with conventional macroscopic gold fiducial markers, such as dose reduction and artifact generation, in proton therapy for prostate cancer. METHODS AND MATERIALS We examined two types of gold particle fiducial marker interactions: that with diagnostic X-rays and with a therapeutic proton beam. That is, we qualitatively and quantitatively compared the radiographic visibility of conventional gold and gold particle fiducial markers and the CT artifacts and dose reduction associated with their use. RESULTS The gold particle fiducials could be easily distinguished from high-density structures, such as the pelvic bone, in diagnostic X-rays but were nearly transparent to a proton beam. The proton dose distribution was distorted <5% by the gold particle fiducials with a 4.9% normalized gold density; this was the case even in the worst configuration (i.e., parallel alignment with a single-direction proton beam). In addition, CT artifacts were dramatically reduced for the gold particle mixture. CONCLUSION Mixtures of microscopic gold particles and human-compatible polymers have excellent potential as fiducial markers for proton therapy for prostate cancer. These include good radiographic visibility, low distortion of the depth-dose distribution, and few CT artifacts.

Inter- and Intrafractional Movement–Induced Dose Reduction of Prostate Target Volume in Proton Beam Treatment

PURPOSE To quantify proton radiotherapy dose reduction in the prostate target volume because of the three-dimensional movement of the prostate based on an analysis of dose-volume histograms (DVHs). METHODS AND MATERIALS Twelve prostate cancer patients underwent scanning in supine position, and a target contour was delineated for each using a proton treatment planning system. To simulate target movement, the contour was displaced from 3 to 15 mm in 3-mm intervals in the superior-to-inferior (SI), inferior-to-superior (IS), anterior-to-posterior (AP), posterior-to-anterior (PA), and left-to-right (LR) directions. RESULTS For both intra- and interfractional movements, the average coverage index and conformity index of the target were reduced in all directions. For interfractional movements, the magnitude of dose reduction was greater in the LR direction than in the AP, PA, SI. and IS directions. Although the reduction of target dose was proportional to the magnitude of intrafractional movement in all directions, a proportionality between dose reduction and the magnitude of interfractional target movement was clear only in the LR direction. Like the coverage index and conformity index, the equivalent uniform dose and homogeneity index showed similar reductions for both types of target movements. CONCLUSIONS Small target movements can significantly reduce target proton radiotherapy dose during treatment of prostate cancer patients. Attention should be given to interfractional target movement along the longitudinal direction, as image-guided radiotherapy may be ineffective if margins are not sufficient.

Imaging doses and secondary cancer risk from kilovoltage cone-beam ct in radiation therapy

AbstractThe authors assessed the radiation-induced cancer risk due to organ doses from kilovoltage (kV) cone beam computed tomography (CBCT), a verification technique in image-guided radiotherapy (IGRT). CBCTs were performed for three different treatment sites: the head and neck, chest, and pelvis. Using a glass dosimeter, primary doses versus depth were measured inside a homemade phantom, and organ doses were measured at various locations inside an anthropomorphic phantom. The excess relative risk (ERR), excess absolute risk (EAR), and lifetime attributable risk (LAR) for cancer induction were estimated using the BEIR VII models based on dose measurement. The average primary (i.e., in-field) doses at the center of the phantom for standard imaging options were 1.9, 5.1, and 16.7 cGy for the head and neck, chest, and pelvis, respectively. The average secondary dose per scan for the pelvis measured 20–50 cm from the isocenter and ranged from 0.67–0.02 cGy, whereas the secondary dose per scan for the head and neck ranged from 0.07–0.003 cGy, indicating that CBCT for treatment of the head and neck is associated with a smaller secondary radiation dose than CBCT for treatment of the pelvis. The estimation of LAR from CBCT in IGRT indicated that the lifetime cancer risk for major organs can reach approximately 400 per 10,000 persons if 30 CBCT scans are performed to position a patient during radiation treatment of the pelvis site.

Secondary radiation doses of intensity-modulated radiotherapy and proton beam therapy in patients with lung and liver cancer

PURPOSE To compare the secondary radiation doses following intensity-modulated radiotherapy (IMRT) and proton beam therapy (PBT) in patients with lung and liver cancer. METHODS AND MATERIALS IMRT and PBT were planned for three lung cancer and three liver cancer patients. The treatment beams were delivered to phantoms and the corresponding secondary doses during irradiation were measured at various points 20-50 cm from the beam isocenter using ion chamber and CR-39 detectors for IMRT and PBT, respectively. RESULTS The secondary dose per Gy (i.e., a treatment dose of 1Gy) from PBT for lung and liver cancer, measured 20-50 cm from the isocenter, ranged from 0.17 to 0.086 mGy. The secondary dose per Gy from IMRT, however, ranged between 5.8 and 1.0 mGy, indicating that PBT is associated with a smaller dose of secondary radiation than IMRT. The internal neutron dose per Gy from PBT for lung and liver cancer, 20-50 cm from the isocenter, ranged from 0.03 to 0.008 mGy. CONCLUSIONS The secondary dose from PBT is less than or compatible to the secondary dose from conventional IMRT. The internal neutron dose generated by the interaction between protons and body material is generally much less than the external neutron dose from the treatment head.