Purpose: With a growing number of cancer survivors, there has been a steadily incidence of patients returning for external beam radiotherapy treatment (EBRT) to new or recurrent treatment sites. A special physics consult (SPC) evaluates the sum of radiation doses in the setting of re-irradiation. In this work, we present a systematic review of SPCs focusing on the clinical parameters used in these documents to assess the need for standardization.
Methods: An ARIA database search between April 2019 and July 2020 resulted in 436 SPCs performed by 13 physicists with different levels of clinical expertise. A subset of 147 SPCs was stratified according to: number of previous courses, time to re-irradiation, availability of previous treatment records, evaluation of CT registration, and dosimetric parameters. The data was organized in Excel-sheets and referenced publications were saved in a database for future SPCs.
Results: One third (33%) of patients presented for re-irradiation within 6 months and nearly two thirds (61%) within 2 years. The majority (78%) of patients had prior radiation treatment at NYU with treatment plans available in DICOM format. For patients treated at outside institutions, records were available as DICOM-data for only 24%, in paper for 33% and not available for 36%. The registration of DICOM-plans for dose-overlap-evaluation was rigid and only in few cases (2%) deformable. Maximum (57%) and mean dose (24%) were the most common reported dose-metrics with more than a third (39%) of these calculated using BED and EQD2, and volumetric measures (DVH, V20Gy, etc) used for 10% of SPCs.
Conclusion: The variation in SPCs performed to evaluate dose overlap in re-irradiation suggests a need for standardization through clearly structured site specific SPC templates with pre-defined clinical parameters, consensus-based dose limits and relevant peer-reviewed article references.