In this research, it is shown that the lateral spread parameter σR(z) increases with cutout size. For radii of circular cutout sizes up to the equilibrium range of the electron beam, the increase of σR(z) with the cutout size is linear. The percentage difference of the calculated PDD curve from the measured PDD data for irregularly shaped cutouts was under 1.0% in the region between the surface and therapeutic range of the electron beam. Similar results were obtained for four electron beam energies (6, 9, 12, and 15 MeV).
The improved LBR method has been generalized to calculate the output factor of electron therapy at extended SSD. The percentage difference between the calculated and the measured output factors of irregularly shaped cutouts in a clinical useful SSD region was within 2%. Similar results were obtained for all available electron energies of both Varian 2100C and ELEKTA Synergy machines.
After radiotherapy (RT) of left-sided breast cancer patients, organs at risk (OARs) such as heart, left anterior descending (LAD) coronary artery, and left lung could be affected by radiation dose in the long term. The objective of this study was to perform a comprehensive meta-analysis and determine OARs dose reduction during left-sided breast cancer treatment using different RT modalities combined with deep inspiration breath-hold (DIBH) relative to free-breathing (FB). PubMed, Scopus, EMBASE, ProQuest, Google Scholar, and Cochrane Library electronic databases were used to search for studies until June 6, 2021. Nineteen eligible studies were selected and analyzed using the RevMan 5.3 statistical software package. The pooled weighted mean difference (MD) with their 95% confidence intervals for each of the three OAR mean doses were determined using a random-effects meta-analysis model to assess the dose reductions. From a total of 189 studies, 1 prospective study, 15 retrospective studies, and 3 randomized control trials (RCTs) with an overall of 634 patients were included. Reduction of doses to the heart (weighted MD = -1.79 Gy; 95% CI (-2.28, -1.30); P = 0.00001), LAD (weighted MD = -8.34 Gy; 95% CI (-11.06, -5.61); P = 0.00001), and left-lung (weighted MD = -0.90 Gy; 95% CI (-1.19, -0.61); P = 0.00001) were observed using DIBH combinations relative to FB combination. This study emphasizes that during the treatment of left-sided breast/chest wall (CW) ± supraclavicular (SCV) ± infraclavicular (ICV) ± internal mammary chain (IMC) lymph nodes (LN) ± axillary (Ax)/ cancer patients, different RT modalities combined with DIBH techniques are better options to reduce dose to OARs compared to FB, which benefits to minimize the long-term complications.
Purpose: To calculate the output factor of irregular shape electron beam at extended SSD using modified lateral build‐up‐ratio method. Methods: Circular cutouts from 2.0cm diameter to maximum possible sizes were prepared for applicator cone size of 15×15cm. In addition, different irregular cutouts were prepared. Percentage depth dose (PDD) curves were measured for each cutout using 6, 9, 12 and 16‐MeV at the standard SSD of 100cm. The scanning was done using Multidata system and Scanditronix diodes on 2100SC Varian LINAC. In addition, for each cutout and electron beam energy doses were measured at SSD values of 100, 105, 110, 115cm using EDR2 films and diodes. Results: The measured PDD were normalized to the depth of 1.0mm. The lateral build‐up‐ratio (LBR) and the lateral scatter parameter (sigma) were calculated for each circular cutout using the open 15×15‐cm2 field as the reference field. Taking the linear increase of sigma with cutout size into account, PDD of the irregular cutouts were calculated at 100 cm SSD. Furthermore, using the dose measured at different SSDs, the effective SSD value for each circular cutout and electron beam energy was determined. Employing the LBR and the effective‐SSD values of the circular cutouts along with the calculated PDD of the irregular cutouts, the output factors of the irregular cutout at different extended SSD values were calculated. Finally, the calculated output factors were compared with the measured values. Conclusion: In this research, it is shown that output factor of irregular shape electron beam at extended SSD can be determined by using the LBR and the effective SSD values of circular cutouts. The percentage difference of the calculated output factor from the measured output factor for irregular cutouts at extended SSD were within 3.0%.
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