External beam planning module of Eclipse for external beam radiation therapy

TEAM participation in the irradiation of IROC phantoms for cooperative group clinical trials

The participation of radiation oncology team members in the irradiation of Imaging and Radiation Oncology Core (IROC) phantom for cooperative group clinical trials is essential to comply with the latest quality management philosophy. Medical dosimetrists are expected to develop treatment plans for the irradiation of IROC phantoms. For advanced treatment techniques, such as three-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT), the irradiation of the IROC phantoms serves as quality audit. If successful, the irradiation processes demonstrate that the institution has the knowledge of the protocol, and has the appropriate equipment to comply with the protocol requirements. This article describes three IROC phantoms used for credentialing external beam photon beam therapy, delivered using conventional medical linear accelerators, to the medical dosimetry community. Guidance and strategies for the development of treatment plans are discussed. Our institutional irradiation of the three IROC phantoms, delivered using the Truebeam medical linear accelerator, resulted in consistent dose accuracy to within ±1%. The participation of the team members may reduce the overall published failing rate stated to be about one-third of all participating institutions.

Tuning spatially fractionated radiotherapy dose profiles using the moiré effect

Spatially Fractionated Radiotherapy (SFRT) has demonstrated promising potential in cancer treatment, combining the advantages of reduced post-radiation effects and enhanced local control rates. Within this paradigm, proton minibeam radiotherapy (pMBRT) was suggested as a new treatment modality, possibly producing superior normal tissue sparing to conventional proton therapy, leading to improvements in patient outcomes. However, an effective and convenient beam generation method for pMBRT, capable of implementing various optimum dose profiles, is essential for its real-world application. Our study investigates the potential of utilizing the moiré effect in a dual collimator system (DCS) to generate pMBRT dose profiles with the flexibility to modify the center-to-center distance (CTC) of the dose distribution in a technically simple way.We employ the Geant4 Monte Carlo simulations tool to demonstrate that the angle between the two collimators of a DCS can significantly impact the dose profile. Varying the DCS angle from 10∘ to 50∘ we could cover CTC ranging from 11.8 mm to 2.4 mm, respectively. Further investigations reveal the substantial influence of the multi-slit collimator's (MSC) physical parameters on the spatially fractionated dose profile, such as period (CTC), throughput, and spacing between MSCs. These findings highlight opportunities for precision dose profile adjustments tailored to specific clinical scenarios.The DCS capacity for rapid angle adjustments during the energy transition stages of a spot scanning system can facilitate dynamic alterations in the irradiation profile, enhancing dose contrast in normal tissues. Furthermore, its unique attribute of spatially fractionated doses in both lateral directions could potentially improve normal tissue sparing by minimizing irradiated volume. Beyond the realm of pMBRT, the dual MSC system exhibits remarkable versatility, showing compatibility with different types of beams (X-rays and electrons) and applicability across various SFRT modalities.Our study illuminates the dual MSC system's potential as an efficient and adaptable tool in the refinement of pMBRT techniques. By enabling meticulous control over irradiation profiles, this system may expedite advancements in clinical and experimental applications, thereby contributing to the evolution of SFRT strategies.

The extent of unnecessary tooth loss due to extractions prior to radiotherapy based on radiation field and dose in patients with head and neck cancer

BACKGROUND AND PURPOSE

Prior to radiotherapy (RT), teeth with poor prognosis that pose a risk for post-RT osteoradionecrosis (ORN) are removed. To allow enough time for adequate wound healing prior to RT, decisions are made based on the estimated radiation dose. This study aimed to gain insight into (1) the overall number of teeth extracted and (2) the patient and tumor characteristics associated with the number of redundantly extracted teeth.

MATERIALS AND METHODS

Patients with head and neck cancer (HNC), treated with RT between 2015 and 2019, were included in this cross-sectional study. For each extracted tooth the radiation dose was calculated retrospectively. The cut-off point for valid extraction was set at ≥ 40 Gy in accordance with the national protocol. Potential factors for doses ≥ 40 Gy were identified, including age, sex, tumor location, tumor (T) and nodal stage (N), overall tumor stage and number of teeth extracted.

RESULTS

A total of 1759 teeth were removed from 358 patients. Of these 1759 teeth, 1274 (74%) appeared to have been removed redundantly, based on the mean dose (Dmean) of < 40 Gy. Using the maximum dose (Dmax) of < 40 Gy, 1080 teeth (61%) appeared to have been removed redundantly. Tumor location and N-classification emerged as the most important associative variables in the multivariable regression analysis.

CONCLUSION

To our knowledge this is the first study to provide insight into the amount of teeth redundantly extracted prior to RT and represents a step forward in de-escalating the damage to the masticatory system prior to RT.

Improved planning efficiency in multiple brain lesion SRS VMAT cases using Eclipse scripting

Though dosimetry has a multitude of treatment modalities, software, and workflows to aid in the treatment planning process, treatment planners are still responsible for several tedious and monotonous tasks that could decrease their planning efficiency. The purpose of this study was to determine if scripting could improve treatment planning efficiency for multiple brain lesion stereotactic radiosurgery (SRS) volumetric arc therapy cases by reducing planning time commitment. A script was developed for multiple brain lesion SRS cases using Eclipse scripting application programming interface with the intention of improving treatment planning efficiency by creating optimization structures and importing prescription and suggested OS dose metrics to the optimizer. Nine treatment planners were each provided with 3 different multiple brain lesion, single-isocenter SRS cases. Each planner created 2 plans for each case. One of these 2 plans used the SRS script, and the other did not. There were 54 treatment plans developed, totaling 27 plan comparisons. Each of the 54 treatment plans were considered clinically acceptable based on the participating institution's plan quality guidelines. Statistical analyses of planning time commitment with and without the SRS script were performed using RStudio. The mean and median planning times with and without the SRS script were compared using a paired T-test and Wilcoxon Signed Rank test, respectively, and effect size was evaluated using Cohen's classification. Using the SRS script resulted in statistically significant reduction in total contouring time (11.3 vs 2.8 minutes, p < 0.001), optimizer preparation time (7.7 vs 2.1 minutes, p < 0.001), and overall planning time (105.1 vs 77.9 minutes, p < 0.001). This study concluded that scripts developed using Eclipse scripting application programming interface offer an opportunity to improve treatment planning efficiency by reducing the planning time commitment for treatment planners.

Dosimetric evaluation of a treatment planning system using the AAPM Medical Physics Practice Guideline 5.a (MPPG 5.a) validation tests

Verifying the accuracy of the dose calculation algorithm is considered one of the most critical steps in radiotherapy treatment for delivering an accurate dose to the patient. This work aimed to evaluate the dosimetric performance of the treatment planning system (TPS) algorithms; the AAA (v. 15.6), AXB (v. 15.6) and eMC (v. 15.6) following the AAPM medical physics practice guideline 5.a (MPPG 5.a) validation tests package in a Varian iX Linear Accelerator (Linac). A series of tests were developed based on the MPPG 5.a. on a Varian's Eclipse TPS (v. 15.6) (Varian Medical Systems). First, the basic photon and electron tests were validated by comparing the TPS calculated dose with the measurements. Next, for heterogeneity tests, we verified the Computed Tomography number to electron density (CT-to-ED) curve by comparing it with the baseline values, and TPS calculated point doses beyond heterogeneous media were compared to the measurements. Finally, for IMRT/VMAT dose validation tests, clinical reference plans were re-calculated on ArcCheck's virtual phantom (Sun Nuclear Corporation, Melbourne, FL, USA) and exported to the Linac for delivery using the ArcCheck dosimetry system. All validation tests were evaluated following the MPPG 5.a recommended tolerances. In basic dose validation tests, the TPS calculated depth dose profiles agreed well with the measurements, with a minimum gamma passing rate of 95% at 2%/2 mm criteria. However, disagreements are seen in the build-up and penumbra region. Results for most point doses in homogeneous water phantoms were within the MPPG 5.a tolerance. For the heterogeneity tests, the CT-to-ED curve was established, and calculated point doses were all within 3% of the measurements for heterogeneous media for both photon algorithms at three energies. These results are within the MPPG5.a the recommended tolerance of 3%. Moreover, for electron beams, the differences between the calculated and measured point doses averaged 5% and 7%, but were just within the MPPG 5.a tolerance of 7%. For IMRT and VMAT validation tests using a gamma criteria of a 2%/2 mm, IMRT plans showed maximum and minimum passing rates of 98.2% and 97.4%, respectively. Whereas VMAT plans showed maximum and minimum passing rates of 100% and 94.3%, respectively. We conclude that the dosimetric accuracy of the Eclipse TPS (v15.6) algorithm is adequate for clinical use. The MPPG 5.a tests are valuable for evaluating dose calculation accuracy and are very useful for TPS upgrade checks, commissioning tests, and routine TPS QA.

Cochlea sparing with a stratified scheme of dose limitation employed in intensity-modulated radiotherapy for nasopharyngeal carcinoma: A dosimetry study

Hearing loss is 1 of the major complications after radiotherapy in nasopharyngeal carcinoma (NPC) patients, how to minimize dose to cochlea in order to reduce the incidence of sensorineural hearing loss is a critical task. This study is to investigate a stratified scheme of cochlea sparing based on T stage in intensity-modulated radiotherapy. We designed a comparison between 2 plans of cochlea sparing plan (C-Plan) and regular noncochlea sparing plan (R-Plan) from 19 NPC patients with 2, 3, 8, and 6 cases of T1, T2, T3, and T4 stage, respectively. The outcomes showed that target coverage parameters and dose-volume histogram features were of no significant difference, with a significant difference in dose distribution between C-Plan and R-Plan in cochlea and eustachian, e.g., ipsilateral cochlea D_mean 4619.75 ± 1134.09 cGy in C-Plan and 5061.03 ± 1121.09 cGy in R-Plan (p = 0.000), contralateral cochlea D_mean 4386.73 ± 945.14 cGy in C-Plan and 4991.38 ± 961.21 cGy in R-Plan (p = 0.000). Meanwhile, there was no significant difference in dose distribution in spinal cord, brainstem, and other OARs. Our dosimetry study showed cochlea sparing in intensity-modulated radiotherapy for NPC reduced cochlea dose to different extent, so we suggested a stratified scheme of cochlea sparing based on T stage could be a useful and practical tool for both physicists and radiation doctors.