ESTRO 2022 - Abstract Book

S803

Abstract book

ESTRO 2022

Conclusion The significant reduction of the GTV in LACC at 4-weeks of ERT results in a marked variation in the key DVH parameters when compared to the pre-IMRT plan. Continuing the same pre-ERT IMRT plan for the entire course of 5 weeks of ERT, would result in inadvertent hot or cold spots, irradiate higher normal tissue and thus defeat the very purpose of IMRT. Periodic assessment of the dynamic changes in GTV is thus mandatory by early incorporation of adaptive IMRT plans to optimize dose to the GTV. This would ensure adequate intended dose coverage to GTV that could finally translate into improved clinical outcomes (Fig). Thus, IMRT can not only precisely hit the target but could even precisely miss the target, if tumor regression dynamics are not timely supplemented by adaptive IMRT plans. Mere setup verifications and their corrections are grossly inadequate to ensure adequate GTV-PTV coverage as evident on snapshot pre-ERT IMRT plans in LACC.

PD-0908 Anatomy- versus margin-based prophylactic para-aortic radiotherapy in cervical cancer

J. Lee 1 , J. Lin 2 , C. Chang 3 , Y. Chen 1 , M. Wu 1

1 MacKay Memorial Hospital, Radiation Oncology, Taipei, Taiwan; 2 Changhua Christian Hospital, Radiation Oncology, Changhua, Taiwan; 3 MacKay Memorial Hospital, Obstetrics and Gynecology, Taipei, Taiwan Purpose or Objective Prophylactic para-aortic radiotherapy (PART) can mitigate the risk of para-aortic recurrence in locally advanced cervical cancer (LACC). However, target volume delineation for the para-aortic region is inconclusive. Based on studies evaluating the mapping of para-aortic nodes, margin expansions around the aorta and inferior vena cava (IVC) were suggested to achieve coverage of para-aortic region. However, anatomic principles that govern the distribution of lymphatics may more accurately define the para-aortic regions that determine the effectiveness and potentially reduce the dose to the intestine and further lower incidence of gastrointestinal (GI) toxicity. This study aimed to compare patient-reported GI toxicity and outcomes between anatomy- and margin-based prophylactic PART in patients with LACC. Materials and Methods We reviewed data of 160 patients with LACC who underwent CCRT with prophylactic PART during 2014–2019 at two tertiary medical centers. Para-aortic regions were drawn by margin expansion of 7–10 mm around aorta and IVC or anatomic para- aortic region atlas published by Takiar et al. (Figure 1). The upper border of PART was at the level of left renal vein. The prescribed dose of PART was 45 Gy. Patient-Reported Outcome version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE) was used to assess acute GI toxicity. Vx indicated the volume (mL) of small bowel or duodenum that received a radiation dose of x Gy.