A Comparative Dose-Escalation Analysis for the Head and Neck Reirradiation Patients with and without Appropriate DICOM Based Dose-Volume Information of Primary Radiotherapy

Abstract

<h3>Purpose/Objective(s)</h3> This study aims to compare the dose-escalation between two groups of head and neck reirradiation patients with or without availability of appropriate DICOM based dose-volume and planning information of primary RT <h3>Materials/Methods</h3> A total of 89 patients who received reirradiation for recurrent/second primary head and neck cancers between 2019-21 was included in the present study. Patients were categorized in two groups, with (D-group) and without (ND-Group) the DICOM based primary radiotherapy (RT1) information in planning system. For first group RT1 and re-irradiation (ReRT) in the present institution, for second group only ReRT in the present institution. For the D group, the dose to 0.2cc volume (D0.2cc) to the spine, brainstem, and optic apparatus was converted into structures in the RT1CT and these structures along with target volumes are copied to ReRTCT using deformable registration. Serial Structures in RT1CT and ReRTCT were merged to get the resultant structure with an intersection of D0.2 cc. A treatment plan was created using the baseline prescription (BRx) was defined by the treating physician. Further, a dose escalation (DERx) plan was created (66Gy/33fr for gross disease and 60Gy/30fr for post operative cases) respecting serial structures tolerance dose. For the ND group, no dose escalation was attempted over the BRx plan. <h3>Results</h3> 57 and 32 patients listed in D and ND-group. ReRT techniques were VMAT=72; IMRT=11, 3DCRT=6. For RT1, dose in D and ND groups 61±5.6 Gy and 30-66 Gy respectively. ReRT BRx doses for D and ND group were 52.5±10.7Gy and 50.6±6.9Gy (ΔDose=1.9±12.7 Gy). Dose escalated plan (DERx) was possible for 51 patients in D-Group with a mean DERx of 59.2±6.2Gy, and ΔDERx 6.7±12.4Gy from BRx plans. The maximum dose escalation from BRx was 21 Gy (D-Group). For 5 patients, dose escalation was not accepted for treatment due to other comorbidities, reducing actually delivered ΔDERx to 6.2± 14.4Gy. The average dose difference between D and ND-group were 8.6±9.3 Gy and 8.1±11.8 Gy on planned and accepted dose escalation. The spatial position of RT1 and ReRT Spine 0.2cc dose was within 5 mm only in 2 cases; for rest of the patients RT1 spine dose was not a big challenge for ReRT planning. It was possible to achieve the combined RT1 and ReRT Spine (<50Gy), Brainstem and Optic apparatus (<54 Gy) dose for 97% patients for D-group. For 86% cases Spine is the only challenged serial OAR for ReRT. <h3>Conclusion</h3> BRx was uniform for both the groups indicating the consistency in the institutional prescription policy. Appropriate dose mapping using DICOM information between RT1 and ReRT allows moderate to high dose escalation in recurrent Head neck re-irradiation which was otherwise not possible. Linear addition of maximum dose, without considering its spatial position, for serial structures (spine, brainstem) between RT1 and ReRT reduces dose escalation possibility as seen in the ND group and could not reach up to the recommended dose of 60/66Gy.