EVALUATION OF SECONDARY DOSE AND CANCER RISK FOR OUT-OF-FIELD ORGAN IN ESOPHAGEAL CANCER IMRT IN A CHINESE HOSPITAL USING ATOM PHANTOM MEASUREMENTS

Monte Carlo study of organ doses and related secondary cancer risk estimations for patients undergoing prostate radiotherapy: Algerian population-based study

The present study aimed to assess organ doses and the associated cancer risks related to secondary radiation (photons and neutrons) exposure during 3D Conformational Radiotherapy (3D-CRT) for patients with prostate cancer in Algeria. To this purpose, a detailed geometric Monte Carlo (MC) modeling of the LINAC, combined with a hybrid whole-body phantom was carried out. The secondary radiation doses were calculated in patient's organs, both within and outside the field. The obtained doses were used to estimate the Lifetime Attributable Risks (LARs) for cancer incidence for out of field organs, using the Biological Effects of Ionizing Radiation VII (BEIR VII) risk model, considering the exposure age range according to the age of the treated patients in Algeria. The survival information and baseline cancer risks were based on relevant statistics for the Algerian population. The results revealed that secondary radiation equivalent doses mostly depend on the distance of organs from the treated volume. The highest and lowest equivalent doses of 5.77 mSv/Gy and 0.24 mSv/Gy were recorded in the small intestine and ocular lens, respectively. LARs decreased as the age of exposure increased, with the highest estimated value per 100,000 individuals identified at a 35-year exposure age (88 for the colon and 15 for the intestine). Conversely, the lowest risks were found at 70 years of age, specifically in rib bone and leg bone with value of (0). The current research could contribute to establishing a database concerning the incidence of secondary cancers induced by radiotherapy during 3D-CRT for prostate cancer in Algeria.

Monte Carlo study of organ doses and related risk for cancer in Algeria from scattered neutrons in prostate treatment involving 3D-CRT

The present study aimed to evaluate organ doses and related risk for cancer from scattered neutrons involving 3D Conformational Radiotherapy (3D-CRT) for patients with prostate cancer in Algeria based on Monte Carlo technique and to estimate the secondary cancer risks. To this purpose, a detailed geometric Monte Carlo (MC) modeling of the LINAC Varian 2100C combined with a computational whole-body phantom was carried out. The neutron equivalent doses were calculated in-field and out-of field of patient's organs using the phase-space method. The obtained neutron equivalent doses were used to estimate the Lifetime Attributable Risks (LARs) for cancer incidence in out of field organs. LARs was evaluated assuming Biological Effects of Ionizing Radiation VII (BEIR VII) risk model for exposure age in the range 35-70 years, according to the interval's age of treated patients in Algeria. The baselines cancer risks and survival data were associated with the statistical data for the Algerian population. The results showed that the neutrons equivalent doses per prescribed dose (Photon Dose) mostly depend on the distance of organs from the treated volume. The highest and lowest equivalent doses of 1.18 mSv/Gy and 0.25 mSv/Gy were recorded in the bladder and heart, respectively. The highest estimated lifetime attributable risk per 100,000 population was found for 35 yrs' exposure age in colon 49.94, lung 16.63 and stomach 11.17. The lowest risks were found for 70 yrs' age, in spine 0.06 and thyroid 0.14. The results showed that LARs values decrease with the increase of the exposure age and cancer incidence risk is lower than the baseline cancer risk incidence for all organs. The present study may help in providing a database on the impact of radiotherapy-induced secondary cancer incidence during 3D-CRT for prostate cancer in Algeria.

Out-of-field organ doses and associated risk of cancer development following radiation therapy with photons

Innovations in cancer treatment have contributed to the improved survival rate of these patients. Radiotherapy is one of the main options for cancer management nowadays. High doses of ionizing radiation are usually delivered to the tumor site with high energy photon beams. However, the therapeutic radiation exposure may lead to second cancer induction. Moreover, the introduction of intensity-modulated radiation therapy over the last decades has increased the radiation dose to out-of-field organs compared to that from conventional irradiation. The increased organ doses might result in elevated probabilities for developing secondary malignancies to critical organs outside the treatment volume. The organ-specific dosimetry is considered necessary for the theoretical second cancer risk assessment and the proper analysis of data derived from epidemiological reports. This study reviews the methods employed for the measurement and calculation of out-of-field organ doses from exposure to photons and/or neutrons. The strengths and weaknesses of these dosimetric approaches are described in detail. This is followed by a review of the epidemiological data associated with out-of-field cancer risks. Previously published theoretical cancer risk estimates for adult and pediatric patients undergoing radiotherapy with conventional and advanced techniques are presented. The methodology for the theoretical prediction of the probability of carcinogenesis to out-of-field sites and the limitations of this approach are discussed. The article also focuses on the factors affecting the magnitude of the probability for developing radiotherapy-induced malignancies. The restriction of out-of-field doses and risks through the use of different types of shielding equipment is presented.

Out-of-field doses from radiotherapy using photon beams: A comparative study for a pediatric renal treatment

PURPOSE

First, this experimental study aims at comparing out-of-field doses delivered by three radiotherapy techniques (3DCRT, VMAT (two different accelerators), and tomotherapy) for a pediatric renal treatment. Secondly, the accuracy of treatment planning systems (TPS) for out-of-field calculation is evaluated.

METHODS

EBT3 films were positioned in pediatric phantoms (5 and 10 yr old). They were irradiated according to four plans: 3DCRT (Clinac 2100CS, Varian), VMAT (Clinac 2100CS and Halcyon, Varian), and tomotherapy for a same target volume. 3D dose determination was performed with an in-house Matlab tool using linear interpolation of film measurements. 1D and 3D comparisons were made between techniques. Finally, measurements were compared to the Eclipse (Varian) and Tomotherapy (Accuray) TPS calculations.

RESULTS

Advanced radiotherapy techniques (VMATs and tomotherapy) deliver higher out-of-field doses compared to 3DCRT due to increased beam-on time triggered by intensity modulation. Differences increase with distance to target and reach a factor of 3 between VMAT and 3DCRT. Besides, tomotherapy delivers lower doses than VMAT: although tomotherapy beam-on time is higher than in VMAT, the additional shielding of the Hi-Art system reduces out-of-field doses. The latest generation Halcyon system proves to deliver lower peripheral doses than conventional accelerators. Regarding TPS calculation, tomotherapy proves to be suitable for out-of-field dose determination up to 30 cm from field edge whereas Eclipse (AAA and AXB) largely underestimates those doses.

CONCLUSION

This study shows that the high dose conformation allowed by advanced radiotherapy is done at the cost of higher peripheral doses. In the context of treatment-related risk estimation, the consequence of this increase might be significative. Modern systems require adapted head shielding and a particular attention has to be taken regarding on-board imaging dose. Finally, TPS advanced dose calculation algorithms do not certify dose accuracy beyond field edges, and thus, those doses are not suitable for risk assessment.

A new Monte Carlo model of a Cyberknife® system for the precise determination of out-of-field doses

In a previous work, a PENELOPE Monte Carlo model of a Cyberknife system equipped with fixed collimator was developed and validated for in-field dose evaluation. The aim of this work is to extend it to evaluate peripheral doses and to determine the precision of the treatment planning system (TPS) Multiplan in evaluating the off-axis doses. The Cyberknife^® head model was completed with surrounding components based on manufacturer drawings. The contribution of the different head parts on the out-of-field dose was studied. To model the attenuation and the modification of particle energy caused by components not modelled, the photon transport was modified in one of the added components. The model was iteratively adjusted to fit dose profiles measured with EBT3 films and an ionization chamber for several collimator sizes. Finally, dose profiles were calculated using the two Multiplan TPS algorithms and were compared to our simulations. The contributions to out-of-field dose were identified as scattered radiation from the phantom and head leakage and scatter originating at the secondary collimator level. Particle transport in the additional pieces was modified to model this radiation. The maximum differences between simulated and measured doses are of 20.4%. Regarding the detector responses away from axis, EBT3 films and the Farmer chamber give similar response (less than 20% difference). The TPS Monte Carlo algorithm underestimates the doses away from axis more importantly for the smaller field sizes (up to 98%). Besides, RayTracing simplifies peripheral dose to a constant value with no inclusion of particle transport. A Monte Carlo model of a Cyberknife system for the determination of out-of-field doses up to 14 cm off-axis was successfully developed and validated for different depths and field sizes in comparison with measurements. This study also confirms that TPS algorithms do not model peripheral dose properly.

Monte carlo study of organ doses and related risk for cancer in Tanzania from scattered photons in cervical radiation treatment involving Co-60 source

PURPOSE

The present work aimed to evaluate organ doses and related risk for cancer from external beam radiation treatment (EBRT) and high-dose-rate (HDR) brachytherapy (BT) involving Co-60 source for patients with cervical carcinoma in Tanzania based on Monte Carlo methods and to evaluate the secondary cancer risks in their lifetime.

METHODS

EBRT and HDR-BR were modelled by using the MCNPX Monte Carlo (MC) code. The MC simulations were performed by using validated models and isocentric irradiation of an adult female computational phantom. The organ doses and cancer risks estimates were obtained.

RESULTS

The highest absorbed doses of 6.98 × 10^-2 and 5.74 × 10^-2 Sv/Gy were recorded in the bladder for BT and EBRT. The higher risk was found for colon at 1.06 × 10^-3 in the HDR-BT and 9.75 × 10^-5 in the EBRT per 100,000 population at exposure age of 35 years than in the other organs. The risk magnitude decreased with increasing age at exposure. In general, the secondary cancer risks in all sites considered from EBRT and HDR-BR for cervical cancer patient were lower than the baseline risks.

CONCLUSIONS

The chances of developing secondary cancer take years following radiation therapy are extremely low, but the results of present study can support to establish a future database on secondary cancer risks involving radiation therapy in patients with cervical cancer by using HDR-BR and EBRT with Co-60 source in Tanzania and other developing countries.