Radiation and Environmental Biophysics

Comparative analysis of simultaneous integrated boost and sequential boost radiotherapy in node-positive cervical cancer: dosimetric and radiobiological considerations

For locally advanced cervical cancer, the standard therapeutic approach involves concomitant chemoradiation therapy, supplemented by a brachytherapy boost. Moreover, an external beam radiotherapy (RT) boost should be considered for treating gross lymph node (LN) volumes. Two boost approaches exist with Volumetric Intensity Modulated Arc Therapy (VMAT): Sequential (SEQ) and Simultaneous Integrated Boost (SIB). This study undertakes a comprehensive dosimetric and radiobiological comparison between these two boost strategies. The study encompassed ten patients who underwent RT for cervical cancer with node-positive disease. Two sets of treatment plans were generated for each patient: SIB-VMAT and SEQ-VMAT. Dosimetric as well as radiobiological parameters including tumour control probability (TCP) and normal tissue complication probability (NTCP) were compared. Both techniques were analyzed for two different levels of LN involvement - only pelvic LNs and pelvic with para-aortic LNs. Statistical analysis was performed using SPSS software version 25.0. SIB-VMAT exhibited superior target coverage, yielding improved doses to the planning target volume (PTV) and gross tumour volume (GTV). Notably, SIB-VMAT plans displayed markedly superior dose conformity. While SEQ-VMAT displayed favorable organ sparing for femoral heads, SIB-VMAT appeared as the more efficient approach for mitigating bladder and bowel doses. TCP was significantly higher with SIB-VMAT, suggesting a higher likelihood of successful tumour control. Conversely, no statistically significant difference in NTCP was observed between the two techniques. This study's findings underscore the advantages of SIB-VMAT over SEQ-VMAT in terms of improved target coverage, dose conformity, and tumour control probability. In particular, SIB-VMAT demonstrated potential benefits for cases involving para-aortic nodes. It is concluded that SIB-VMAT should be the preferred approach in all cases of locally advanced cervical cancer.

Comparative dosimetric assessment of combined treatment modalities in cervical cancer radiotherapy for optimal organ protection

Abstract External radiotherapy combined with internal radiotherapy in cervical cancer can provide a boost to the target volume to increase tumour control. At the same time internal radiotherapy protects neighboring organs. The aim of the present study was to dosimetrically compare three external beam radiotherapy techniques each combined with internal radiotherapy to evaluate the combination that offers the best organ protection. Treatment plans of 20 cervical cancer patients were created for external (including three-dimensional conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT)) as well as brachytherapy. The prescribed dose was 50 Gy in 25 fractions for external and 21 Gy in three fractions for internal radiotherapy. The following organs at risk (OARs) were evaluated: bladder, rectum, sigmoid and bowel bag. The study analyzed the results of different treatment combinations in terms of dosimetric values for various parameters. The D90 for the clinical target volume was around 120 Gy, with the highest value seen in 3D-CRT + BT (brachytherapy) combination at 120.59 Gy. For the bladder, the D2cc remained below the recommended threshold of 90 Gy, with the lowest value obtained for the BT + IMRT combination at 79.2 Gy. For the rectum, both D2cc and D1cc remained below the recommended threshold of 75 Gy for both parameters. All techniques fell below the recommended dose of 75 Gy for the sigmoid. For the intestine, there were statistically significant differences between BT + IMRT and BT + 3D-CRT. The VMAT technique showed superiority over IMRT in tumour volume coverage and several organ-at-risk parameters. Generally, intensity-modulated techniques showed dosimetric advantage over the traditional 3D technique in cervical cancer. In addition to providing better compliance and homogeneity, they provided superior protection for organs at risk, especially for bowel bag. It is concluded that the BT + IMRT technique provided the best protection for organs at risk based on the lowest OAR dosimetric values, especially for the intestine.

Improving normal tissue sparing using scripting in endometrial cancer radiation therapy planning

The aim of this study was to improve the protection of organs at risk (OARs), decrease the total planning time and maintain sufficient target doses using scripting endometrial cancer external beam radiation therapy (EBRT) planning. Computed tomography (CT) data of 14 endometrial cancer patients were included in this study. Manual and automatic planning with scripting were performed for each CT. Scripts were created in the RayStation™ (RaySearch Laboratories AB, Stockholm, Sweden) planning system using a Python code. In scripting, seven additional contours were automatically created to reduce the OAR doses. The scripted and manual plans were compared to each other in terms of planning time, dose-volume histogram (DVH) parameters, and total monitor unit (MU) values. While the mean total planning time for manual planning was 368 ± 8 s, it was only 55 ± 2 s for the automatic planning with scripting (p < 0.001). The mean doses of OARs decreased with automatic planning (p < 0.001). In addition, the maximum doses (D2% and D1%) for bilateral femoral heads and the rectum were significantly reduced. It was observed that the total MU value increased from 1146 ± 126 (manual planning) to 1369 ± 95 (scripted planning). It is concluded that scripted planning has significant time and dosimetric advantages over manual planning for endometrial cancer EBRT planning.