Point vs. volumetric bladder and rectal doses in combined intracavitary-interstitial high-dose-rate brachytherapy: Correlation and comparison with published Vienna applicator data

Yaparpalvi, Ravindra; Mutyala, Subhakar; Gorla, Giridhar R.; Butler, James; Mah, Dennis; Garg, Madhur K.; Kalnicki, Shalom

doi:10.1016/j.brachy.2008.05.005

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Volume 7, Issue 4 , Pages 336-342, October 2008

Point vs. volumetric bladder and rectal doses in combined intracavitary-interstitial high-dose-rate brachytherapy: Correlation and comparison with published Vienna applicator data

Ravindra Yaparpalvi
- Department of Radiation Oncology, Montefiore Medical Center and The Albert Einstein College of Medicine, Bronx, NY
- Corresponding author. Department of Radiation Oncology, Montefiore Medical Center, 111 E 210th Street, Bronx, NY 10467, USA. Tel.: +1-718-920-7750; fax: +1-718-882-6914.
Subhakar Mutyala
- Department of Radiation Oncology, Montefiore Medical Center and The Albert Einstein College of Medicine, Bronx, NY
Giridhar R. Gorla
- Comprehensive Blood and Cancer Center, Bakersfield, CA
James Butler
- Maimonides Cancer Center, Brooklyn, NY
Dennis Mah
- Department of Radiation Oncology, Montefiore Medical Center and The Albert Einstein College of Medicine, Bronx, NY
Madhur K. Garg
- Department of Radiation Oncology, Montefiore Medical Center and The Albert Einstein College of Medicine, Bronx, NY
Shalom Kalnicki
- Department of Radiation Oncology, Montefiore Medical Center and The Albert Einstein College of Medicine, Bronx, NY

Received 30 January 2007; received in revised form 2 May 2008; accepted 3 May 2008. published online 09 September 2008.

Abstract

Purpose

We correlated rectal and bladder point and volumetric dose data in patients treated for advanced cervix cancers with combined intracavitary-interstitial high-dose-rate (HDR) brachytherapy (BT). The results are compared with published Vienna applicator data.

Methods and Materials

We retrospectively analyzed 30 individual combined intracavitary plus interstitial implants from 10 patients treated with external beam radiation therapy (EBRT) followed by HDR BT for locally advanced cervix carcinoma. EBRT consisted of 45Gy to the pelvis followed by 9–14.4Gy boost to involved parametria. BT consisted of a total dose of 21Gy delivered in 7Gy fraction. For each implant, CT-image-based simulation and image-guided BT treatment planning was performed. Bladder and rectal doses were evaluated and analyzed using both International commission on Radiation Units and Measurements (ICRU) reference points and dose–volume histograms. The cumulative doses to the rectum and bladder were calculated by combining contributions from external beam therapy and BT. To facilitate comparison with published literature, the total doses were normalized to equivalent dose in 2-Gy fractions (EQD₂) using the equation EQD_2total=EQD_2EBRT+EQD_2BT.

Results

For the patient population considered, the mean ICRU bladder dose was 75 (±4) Gy₃ compared to bladder D_0.1_cc and D₂_cc doses of 84 (±4) and 78 (±3) Gy₃, respectively. The mean ICRU rectal dose was 73 (±4) Gy₃ compared to rectal D_0.1_cc and D₂_cc doses of 79 (±5) and 74 (±4) Gy₃, respectively. For rectum, the mean dose ratios (D_0.1_cc/D_ICRU) and (D₂_cc/D_ICRU) were 1.08 and 1.01, respectively, compared to Vienna applicator study mean dose ratios of 1.08 and 0.93, respectively. ICRU rectal dose correlated with volumetric rectal doses and best with volumetric D₂_cc dose (r_S=0.91, p=0.0003); however, ICRU bladder dose did not correlate with volumetric bladder dose.

Conclusions

Our study findings reveal a strong correlation between ICRU rectal reference dose and volumetric rectal D₂_cc dose in combined intracavitary-interstitial HDR brachytherapy. This surrogate rectal–dose relationship is valuable in establishing rectal tolerance dose levels in transitioning from traditional two-dimensional to image-based three-dimensional dose planning.

Keywords: ICRU reference dose, Bladder, Rectum, Volumetric dose, Cervix, Intracavitary-interstitial brachytherapy