Dose Accumulation for Multicourse Gynecological Reirradiation: A Methodological Narrative and Clinical Examples

Reirradiation (re-RT) is a suitable and potentially curative treatment option for in-field locoregional recurrences in gynecological malignancies. Lack of clear guidelines on prescription, dose-response relationship, and clinical outcomes limits its clinical use. This clinical narrative describes the methodology for integration of deformable image registration (DIR) for cumulative dose assessment in the setting of re-RT for gynecologic malignancies, using the tools available within a commercial treatment planning system.

Four patients who received re-RT for locoregional recurrence or second cancer within previously irradiated areas for a gynecologic primary were identified. Patient-specific DIR for deformable dose mapping and accumulation was retrospectively performed using intensity-based algorithm provided by the Varian Medical Systems Velocity AI version 4.1. Cumulative equivalent doses in 2 Gy fractions (EQD2) delivered to overlapping targets and organs at risk were generated and compared with the physically summated doses. For both approaches, brachytherapy (BT) component was physically summated in cases where the BT applicator caused significant anatomic distortion.

The mean maximum cumulative overlapping target dose was 119.4 Gy₁₀ (range, 84.7 Gy10-144.9 Gy₁₀). The mean cumulative doses received by 2 cm³ of bladder, rectum, sigmoid, and bowel were 114.6 Gy₃ (101.1-133.4 Gy₃), 98.7 Gy₃ (67-136.2 Gy₃), 92.5 Gy₃ (70.4-107 Gy₃), and 89.9 Gy₃ (81.1-102.8 Gy₃)_, respectively. In the setting of in-field nodal recurrence, DIR-based dose summation was associated with lower cumulative organs at risk doses than those estimated with physical summation, except in one case with a higher bowel dose. In cases where re-RT was given for local recurrence/second primary, variation in sigmoid doses was observed between the 2 dose-summation strategies across all 3 cases, but it was inconsistent with bladder, rectum, or the bowel.

DIR-based dose accumulation can be used to guide re-RT planning and can provide clinically relevant information, especially in cases with nodal recurrences. Registration of BT data sets remain challenging and requires an individualized assessment when applying these algorithms to clinical practice.