S1855
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
improved survival outcomes in high-risk endometrial cancer (HREC) but increases gastrointestinal adverse events (GIAE). In our department, an inverse PORTEC protocol induction paclitaxel carboplatin chemotherapy followed by concurrent CT_WPRT was implemented, showing improved metastasis-free and overall survival. However, this approach further sensitizes the intestinal mucosa, increasing the risk of treatment-related GIAE. In this setting, we aimed to determine rectal and peritoneal cavity (PC) dose acceptance thresholds predictive of grade ≥ 2 GIAE. Material/Methods: Patients with HREC treated with AdCT and 45-48.6 Gy VMAT WPRT were analysed. Treatment plans were approved based on established doses acceptance, including rectal limits of V40Gy < 85%, V30Gy < 95%, and Dmax < 47.3 Gy, and a PC doses acceptance of V45Gy < 195 cc. GIAE were assessed according to CTCAE version 5.0. Receiver operating characteristic (ROC) curve was applied to evaluate the significance of V30Gy, V40 Gy, Dmax rectum and V45 Gy PC on grade 2 or more GIAE. We used a logistic regression model, then displayed the precision, the sensitivity and the specificity. We also visualised the roc curve, and measured the optimal cut-off value and the air under the curve (P < 0.05). Results: Fifty two patients were included. GIAE occurred in 28 patients(53,8%). Grade ≥ 2 enterocolitis, abdominal pain, abdominal distension, rectal pain, and diarrhea were observed in 1, 5, 8, 7, 5, and 13 patients, respectively.Mean rectal and peritoneal cavity doses were 40.2 Gy [24.3–46.4 Gy] and 23.5 Gy [14–41 Gy], respectively. Mean rectal V30Gy and V40Gy were 86.1% [40.3–100%] and 67.2% [17.8–98.9%], respectively. For the peritoneal cavity, Dmax averaged 47.4 Gy [46.3–51.6 Gy], while the median V45Gy was 273 cc [ 6–1229 cc].Selected cut-off values for V30Gy ( ≥ 77.256%, p = 0.005), V40Gy ( ≥ 61.21%, p = 0.003) and Dmax( ≥ 46,11Gy p=0.019) appear to have good discriminating power to predict GIAE grade ≥ 2. (Figure 1, Table1). PC dose acceptance values predicting GIAE grade ≥ 2 were V45Gy ( ≥ 144,2 cc p = 0.002).(Figure 1, Table1).
Conclusion: Our results show that adjuvant chemotherapy in HREC cancer patients is associated with an increased incidence of grade ≥ 2 GIAE, particularly in the inverse PORTEC. In this setting, ROC curve analysis identified PC V45 Gy and rectal Dmax thresholds consistent with published data; however, V30 Gy and V40 Gy constraints should be lowered to <75% and <60%, respectively, as higher values were associated with increased GIAE. Keywords: Gastro Intestinal Adverse Events, Dose Acceptance Digital Poster 1799 Developing an illustrative handbook of accurate superficial radiotherapy dose calculations Scott B Crowe 1,2 , Jane Bennett 1 , Jemma Blyth 1 , Tanya Kairn 1,2 1 Cancer Care Services, Royal Brisbane and Women's Hospital, Brisbane, Australia. 2 School of Chemistry and Physics, Queensland University of Technology, Brisbane, Australia Purpose/Objective: Superficial radiotherapy is an effective technique for skin cancer treatment. Manual dose calculations for
superficial treatments are comparatively straightforward, however results have high uncertainties due to heterogeneous and
topographically complex anatomical targets. The lack of accurate 3D dose calculations has complicated comparisons between superficial radiotherapy and other radiotherapy treatment modalities. This study used the OrthoPlan open-source 3D Monte Carlo superficial dose calculation system [1] to develop an educational handbook as a useful reference when considering superficial radiotherapy for future patients. Material/Methods: The OrthoPlan software was adapted to use an in- house model of the WOmed T-300 superficial radiotherapy system, commissioned against water tank measurements, and validated with phantom measurements. Monte Carlo simulations prepared
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