Dosimetric Consequences Of The Prescription Point H Of Abs Recommendation In The Era Of Mri Guided Brachytherapy For Cervical Cancer: Based On Gyn Gec-Estro Recommendations Of Mri Guided Brachytherapy

Purpose/Objective(s)The GEC-ESTRO recommendations for MRI guided brachytherapy (BT) have strictly recommended not employing a solely volume-based prescription (Rx) before obtaining sufficient clinical data. Even in the era of MRI guided BT, the Rx point is still critical, incorporating MRI information in a hybrid way such as that the dose to the target volumes is increased to the Rx point dose. Hence, the dosimetric consequences of prescribing the radiation dose to different points were determined.Materials/MethodsThree different Rx points were explored: a revised Manchester Point A (Point A), the Point A utilized at the University of Iowa (Point A-UI: superiorly move from the tip of ovoids), and the Point H as proposed by the ABS. For stage I, II, and III cervical cancer, thirty high dose rate patients' plans prescribed to Point H were randomly selected. To remove the variations from anatomy changes through a treatment course, only the first fraction plans were retrospectively renormalized according to each Point A and Point A-UI. No variations were made other than the modification of the Rx points. A tandem and ovoid Fletcher Suit Delclos style applicator set (Varian) was utilized for all patients. Based on the GEC-ESTRO recommendations and ICRU Report 38, the values of total reference air kerma (TRAK) and the volume receiving 100% Rx dose (VOL100%Rx), both representing the delivered amount of radiation, were determined and the ICRU rectal and bladder point doses were quantified.ResultsPrescribing at Point H resulted in the minimal variations in a given geometry and using Point A-UI showed smaller variations than prescribing at Point A. The percent deviations against Rx doses were up to ±9.5% (mean ±2.2%, std dev ±3.0%, p = 0.0001) for Point A, ±8.6% (mean ±2.1%, std dev ±2.4%, p < 0.0001) for Point A-UI, and ±6.7% (mean ±1.8%, std dev ±1.3%: p < 0.0001) for Point H. When normalized to the Point H values, the percent (absolute) differences in TRAK were found on average -2% (-110 cGy·cm2) and -1% (-65 cGy·cm2) for Point A and A-UI, respectively. The percent differences in VOL100%Rx were on average -3% (std dev 5.8%) and -2% (std dev 2.9%) for Point A and A-UI, respectively. For both the rectum and the bladder points the percent differences were determined as on average -2% for Point A and -1% for Point A-UI. Prescribing at Point H increased the total delivered radiation dose since Point H was superiorly located.ConclusionsA brachytherapy plan is minimally affected from geometrical variations when a radiation oncologist prescribes dose to Point H. Prescribing at Point H increased 1∼2% of total amount of radiation but its clinical impacts need further studies. Purpose/Objective(s)The GEC-ESTRO recommendations for MRI guided brachytherapy (BT) have strictly recommended not employing a solely volume-based prescription (Rx) before obtaining sufficient clinical data. Even in the era of MRI guided BT, the Rx point is still critical, incorporating MRI information in a hybrid way such as that the dose to the target volumes is increased to the Rx point dose. Hence, the dosimetric consequences of prescribing the radiation dose to different points were determined. The GEC-ESTRO recommendations for MRI guided brachytherapy (BT) have strictly recommended not employing a solely volume-based prescription (Rx) before obtaining sufficient clinical data. Even in the era of MRI guided BT, the Rx point is still critical, incorporating MRI information in a hybrid way such as that the dose to the target volumes is increased to the Rx point dose. Hence, the dosimetric consequences of prescribing the radiation dose to different points were determined. Materials/MethodsThree different Rx points were explored: a revised Manchester Point A (Point A), the Point A utilized at the University of Iowa (Point A-UI: superiorly move from the tip of ovoids), and the Point H as proposed by the ABS. For stage I, II, and III cervical cancer, thirty high dose rate patients' plans prescribed to Point H were randomly selected. To remove the variations from anatomy changes through a treatment course, only the first fraction plans were retrospectively renormalized according to each Point A and Point A-UI. No variations were made other than the modification of the Rx points. A tandem and ovoid Fletcher Suit Delclos style applicator set (Varian) was utilized for all patients. Based on the GEC-ESTRO recommendations and ICRU Report 38, the values of total reference air kerma (TRAK) and the volume receiving 100% Rx dose (VOL100%Rx), both representing the delivered amount of radiation, were determined and the ICRU rectal and bladder point doses were quantified. Three different Rx points were explored: a revised Manchester Point A (Point A), the Point A utilized at the University of Iowa (Point A-UI: superiorly move from the tip of ovoids), and the Point H as proposed by the ABS. For stage I, II, and III cervical cancer, thirty high dose rate patients' plans prescribed to Point H were randomly selected. To remove the variations from anatomy changes through a treatment course, only the first fraction plans were retrospectively renormalized according to each Point A and Point A-UI. No variations were made other than the modification of the Rx points. A tandem and ovoid Fletcher Suit Delclos style applicator set (Varian) was utilized for all patients. Based on the GEC-ESTRO recommendations and ICRU Report 38, the values of total reference air kerma (TRAK) and the volume receiving 100% Rx dose (VOL100%Rx), both representing the delivered amount of radiation, were determined and the ICRU rectal and bladder point doses were quantified. ResultsPrescribing at Point H resulted in the minimal variations in a given geometry and using Point A-UI showed smaller variations than prescribing at Point A. The percent deviations against Rx doses were up to ±9.5% (mean ±2.2%, std dev ±3.0%, p = 0.0001) for Point A, ±8.6% (mean ±2.1%, std dev ±2.4%, p < 0.0001) for Point A-UI, and ±6.7% (mean ±1.8%, std dev ±1.3%: p < 0.0001) for Point H. When normalized to the Point H values, the percent (absolute) differences in TRAK were found on average -2% (-110 cGy·cm2) and -1% (-65 cGy·cm2) for Point A and A-UI, respectively. The percent differences in VOL100%Rx were on average -3% (std dev 5.8%) and -2% (std dev 2.9%) for Point A and A-UI, respectively. For both the rectum and the bladder points the percent differences were determined as on average -2% for Point A and -1% for Point A-UI. Prescribing at Point H increased the total delivered radiation dose since Point H was superiorly located. Prescribing at Point H resulted in the minimal variations in a given geometry and using Point A-UI showed smaller variations than prescribing at Point A. The percent deviations against Rx doses were up to ±9.5% (mean ±2.2%, std dev ±3.0%, p = 0.0001) for Point A, ±8.6% (mean ±2.1%, std dev ±2.4%, p < 0.0001) for Point A-UI, and ±6.7% (mean ±1.8%, std dev ±1.3%: p < 0.0001) for Point H. When normalized to the Point H values, the percent (absolute) differences in TRAK were found on average -2% (-110 cGy·cm2) and -1% (-65 cGy·cm2) for Point A and A-UI, respectively. The percent differences in VOL100%Rx were on average -3% (std dev 5.8%) and -2% (std dev 2.9%) for Point A and A-UI, respectively. For both the rectum and the bladder points the percent differences were determined as on average -2% for Point A and -1% for Point A-UI. Prescribing at Point H increased the total delivered radiation dose since Point H was superiorly located. ConclusionsA brachytherapy plan is minimally affected from geometrical variations when a radiation oncologist prescribes dose to Point H. Prescribing at Point H increased 1∼2% of total amount of radiation but its clinical impacts need further studies. A brachytherapy plan is minimally affected from geometrical variations when a radiation oncologist prescribes dose to Point H. Prescribing at Point H increased 1∼2% of total amount of radiation but its clinical impacts need further studies.