Monte Carlo evaluation of out-of-field dose in 18-MV pelvic radiotherapy using a simplified female MIRD phantom

This study was devoted to determining the unwanted dose due to scattered photons to the out-of-field organs and subsequently estimate the risk of secondary cancers in the patients undergoing pelvic radiotherapy. A typical 18-MV Medical Linear Accelerator (Varian Clinac 2100 C/D) was modeled using MCNPX® code to simulate pelvic radiotherapy with four treatment fields: anterior-posterior, posterior-anterior, right lateral, left lateral. Dose evaluation was performed inside Medical Internal Radiation Dose (MIRD) revised female phantom. The average photon equivalent dose in out-of-field organs is 8.53 mSv/Gy, ranging from 0.17 to 72.11 mSv/Gy, respectively, for the organs far from the Planning Treatment Volume (Brain) and those close to the treatment field (Colon). Evidence showed that colon with 4.3049 % and thyroid with 0.0020 % have the highest and lowest risk of secondary cancer, respectively. Accordingly, this study introduced the colon as an organ with a high risk of secondary cancer which should be paid more attention in the follow-up of patients undergoing pelvic radiotherapy. The authors believe that this simple Monte Carlo (MC) model can be also used in other radiotherapy plans and mathematical phantoms with different ages (from childhood to adults) to estimate the out-of-field dose. The extractable information by this simple MC model can be also employed for providing libraries for user-friendly applications (e.g. “.apk”) which in turn increase the public knowledge about fatal cancer risk after radiotherapy and subsequently decrease the concerns in this regard among the public.

Excluding Lung Tissue from the PTV during Internal Mammary Irradiation. A Safe Technique for OAR-Sparing?

The current study aims to determine whether exclusion of lung tissue from planning treatment volume (PTV) is a valid organ at risk (OAR)-sparing technique during internal mammary irradiation (IMNI). Twenty patients with left-sided breast cancer undergoing adjuvant radiotherapy including IMNI after mastectomy or lumpectomy with daily ConeBeam CT (CBCT; median n = 28) were enrolled in the current study. The daily dose distribution of the patients was estimated by recalculating treatment plans on CBCT-scans based on a standard PTV (PTV margin: 5mm-STD) and a modified PTV, which excluded overlapping lung tissue (ExLung). Using 3D-deformable dose accumulation, the dose coverage in the target volume was estimated in dependence of the PTV-margins. The estimated delivered dose in the IMN-CTV was significantly lower for the ExLung PTV compared to the STD PTV: ExLung: V95%: 76.6 ± 22.9%; V90%: 89.6 ± 13.2%, STD: V95%: 95.6 ± 7.4%; V90%: 99.1 ± 2.7%. Daily CBCT imaging cannot sufficiently compensate the anatomic changes and intrafraction movement throughout the treatment. Therefore, to ensure adequate delivery of the prescribed dose to the IMN-CTV, exclusion of lung tissue from the PTV to spare the OARs is not recommended.

Stereotactic body radiotherapy for T1 glottic cancer: dosimetric data in 27 consecutive patients

Aim: Because the clinical feasibility of stereotactic body radiotherapy (SBRT) for early glottic cancer (T1) is controversial, we report dosimetric results in 27 consecutive patients from a prospective phase I and II study that started in 2017. Methods: In our approach, only the parts of the true vocal cord containing cancer and those immediately adjacent are planned to be treated to 36 Gy and 30 Gy, respectively, in 3 fractions. Several dosimetric metrics for both target volumes and organs at risk were extracted from individual plans and results were compared to those achieved by other authors in a similar setting. Results: Proper coverage was reached at planning in 2/3 of planning treatment volume 30 Gy, but only 4 planning treatment volume 36 Gy; conversely, the maximum dose objective was met for most of the patients on either arytenoid cartilage, but this was not the case for 51.9% and 96.3% of cricoid and thyroid cartilages, respectively. Our dosimetric results are similar to if not better than those achieved by others. Conclusion: SBRT in 3 fractions for T1 glottic lesions is dosimetrically challenging. Clinical validation is awaited.

The stability of seeds in external beam prostate radiotherapy and implications of migration in current practice: a systematic review

PurposeTo determine and summarise the literature on prostatic seed stability by investigating seed marker migration and loss in prostate cancer patients. In addition, documenting the implications of significant seed migration and loss in clinical practise.MethodsPubMed and Sciencedirect databases were used to locate papers on the stability of gold seed markers in prostate patients treated with external beam radiation therapy. The search found 3,238 articles and ten articles were selected and reviewed based on inclusion and exclusion criteria for the scope of this literature review.ResultsMinimal migration and loss of seeds was observed in the literature reviewed, with the majority of authors reporting <2·0 mm migration within the prostate; however, there were individual cases reported outside of the 2·0 mm threshold. It was also found that significant migration had an impact on image matching, as well as, planning treatment volume margins.ConclusionSeed stability within the prostate has been proven, with most authors reporting minimal migration within a 2·0 mm threshold and minimal loss of seeds. Although individual cases can have significant migration and loss, if marker migration exceeds the 2·0 mm threshold, a protocol is required to deal with both non-significant and significant migration.