Radiation Induced Rib Fractures after Hypofractionated Stereotactic Body Radiation Therapy: The Risk Factors and Dose-Volume Relationship

Abstract

Results: With the1 min. irradiation, the neutron yield from brass is about a factor of 3 lower than that of W, and the decay of activities is about 10 times faster. For the second simulation, the neutron activity builds up slowly in brass, from about 7x10 3 Bq/cm 3 at the end of week one to a maximum of 10 4 Bq/cm 3 at the end of week 7. For W, the neutron activity builds up slowly from about 5.5x10 6 Bq/cm 3 at the end of week one, to about 9x10 6 Bq/cm 3 (0.24 mCi) at the end of week 5. The neutron activities at the beginning of the week (during irradiation) are due to nuclides with atomic numbers in the range Z = 8 -78. At the end of the week, the neutron activities are mostly due to nuclides in the range Z = 60-78, and a smaller contribution from nuclides in the range Z = 20-60. Conclusions: Our simulation showed that brass results in much lower neutron production than W. Although neutron activity slowly builds up in W, the activity is only about 0.24 mCi after 5 weeks at the surface of the metal. At the patient level, the activity will be smaller due to inverse square law. Our next step is to simulate a realistic treatment schedule with a commercial MLC to more accurately predict the neutron activities.Purpose/Objective(s): The purpose of this study is to clarify the incidence, the risk factors, and the dose-volume relationship of radiation induced rib fracture after hypofractionated stereotactic body radiation therapy (SBRT). consecutive patients treated with hypofractionated SBRT for primary or metastatic lung cancer were reviewed. The inclusion criteria were at least 3 months of follow-up by CT scan and no previous overlapped radiation exposure. Radiation induced rib fractures were defined as rib fractures located in the radiation field, detected by CT scan after treatment. The risk factors considered; age, gender, GTV diameter, chest wall -tumor distance were reviewed and each parameter was divided into two groups. Dose-volume histogram analysis was conducted on ribs received over 20 Gy at maximal point dose. The max dose and absolute volume received; $10 Gy, $20 Gy, $30 Gy and $40 Gy were determined for each ribs as the dosimetric parameters. The 3-and 5-year Kaplan-Meier (KM) estimates of rib fracture were calculated. Each risk factor was assessed by a log-rank test. The optimal cut off value for each dosimetric parameter was analyzed through the use of receiver-operating characteristic (ROC) curves. The area under the curve (AUC) values were also calculated. To estimate the cumulative risk of fracture, the ribs were divided into two groups according to the cutoff value and compared by log-rank test. S136 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010 Results: From 129 patients, 409 ribs met the inclusion criteria. Median follow-up period was 19 months. Among the 129 patients, 26 patients (44 ribs) experienced radiation induced rib fractures. The KM estimates of rib fracture at 3 years and 5 years were 35.3%, 53.7%, respectively. As a risk factor, chest wall -tumor d...

Dosemetric Parameters Predictive of Rib Fractures after Proton Beam Therapy for Early-Stage Lung Cancer

“…In our study, grade 2 RFs occurred in 12 patients following PBT (19.4%), with a three-year cumulative incidence rate of 30.2%. With regard to SRT, several groups reported RFs frequencies ranging from 4% to 37.7% after SRT for earlystage NSCLC; these rates were not much higher compared with those observed in our study (30.2%) (Pettersson et al 2009;Dunlap et al 2010;Andolino et al 2011;Welsh et al 2011;Asai et al 2012;Creach et al 2012;Mutter et al 2012;Stephans et al 2012;Taremi et al 2012;Nambu et al 2013). Although PBT reportedly offers advantages over SRT, it has not been reported to dramatically reduce RFs incidence (Georg et al 2008;Kadoya et al 2011).…”

“…In that study, BEDs for 50 and 65 Gy calculated with α/β = 3 Gy were 83 and 108 Gy 3 (RBE), respectively; these values were lower than our results for V120 with PBT. Using ROC curves for dosimetric parameters with SRT, Asai et al (2012) evaluated doses administered to 374 ribs and reported a 3-year fracture rate of 37.7%. Further, they reported that D max , V40, V30, and V20 were significantly higher in fractured ribs than in nonfractured ribs.…”

“…However, desired dose applications within target volumes are limited because of the proximity to critical normal tissues. Also, the incidence of rib fractures (RFs) following SRT for early-stage lung cancer ranges from 4% to 37.7% (Pettersson et al 2009;Dunlap et al 2010;Andolino et al 2011;Welsh et al 2011;Asai et al 2012;Creach et al 2012;Mutter et al 2012;Stephans et al 2012;Taremi et al 2012;Nambu et al 2013).…”

Feasibility and Efficacy of Adaptive Intensity Modulated Radiotherapy Planning according to Tumor Volume Change in Early Stage Non-small Cell Lung Cancer with Stereotactic Body Radiotherapy

“…Chest wall toxicity was significantly related to dose-volume parameters 9,10) and in our study, V30 Gy and V32 Gy of the chest wall were significantly reduced in the adaptive plan. Bhatt et al 14) reported that the doses of the chest wall and left ventricle were reduced in adaptive plans compared with initial plans.…”

“…[3][4][5] Several studies reported that higher biologically equivalent dose was related to improved local control and survival. 6,7) However, large fraction size may increase the toxicities of organs at risk (OARs), including the lung, 8) chest wall 9,10) and large bronchus. 11) Therefore, a smaller margin around the tumor is warranted in order to reduce radiation-induced normal tissue toxicities.…”