Room: Exhibit Hall | Forum 7
Purpose: Design of a remote in-vivo dosimetry program for patients treated with IMRT for locally advanced squamous cell carcinoma of the vulva to assess superficial vulvar doses.
Methods: IROC Houston supplied two OSLD dosimeters wrapped in plastic per patient to be placed on the patientâ€™s vulva. Each institution was to annotate on the irradiation form provided the location of the placement of the OSLD on the patient. The institution was to indicate whether bolus was used or if the OSLD were placed within any skin folds. The OSLD were to be irradiated during a complete single fraction of the patientâ€™s treatment. The irradiation form and OSLD were returned to IROC Houston to be read at a minimum of 5 days after irradiation. The expectation was that all patients would have vulvar doses within 10%.
Results: At the present time 29 patients have performed these in-vivo dosimetry assessments at 17 different institutions. Four of the patients did not report the calculated dose delivered to the OSLD. The AAPM Task Group Report 64 on in-vivo dosimetry states that one might use two action levels when evaluating in-vivo dosimetry. A suggested first level of 5% and a second level of 10%. Out of 25 patients analyzed, 64% fell within 5% agreement and 72% fell within 10% agreement. Seven patients (28%) had measured doses that disagreed with the institutionâ€™s calculated dose by greater than 10%.
Conclusion: The purpose of in-vivo dosimetry is to detect large errors. Through this remote audit tool we were able to potentially detect dosimetry errors greater than 10%. The results did not correlate with dosimeter placement on the patient and or treating institution. These data indicate a need to further improve the dose calculation models for superficial doses such as what might be encountered with vulvar treatments.