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A pilot study assessing the use of a novel LDR intracavitary brachytherapy applicator for carcinoma of the cervix uteri
Abstracts / Brachytherapy 5 (2006) 78–117 GYNECOLOGY P-63 Comparative analysis of CT-based 3D volumetric dosimetry and radiography-based 2D dosimetry for high-dose-rate intracavitary applications Nikhilesh G Patil, M.D., D.N.B.,1 Sherly Saju, M.Sc., D.R.P.,2 S V Jamema, M.Sc., D.R.P.,2 Umesh Mahantshetty, M.D., D.N.B.,1 Sudesh Deshpande, M.Sc., D.R.P.,2 Siddanna Palled, M.D., D.N.B.,1 Deepak D Deshpande, Ph.D.,2 Shyam K Shrivastava, M.D., D.N.B.,1 Ketayun A Dinshaw, D.M.R.T., F.R.C.R.1 1Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India; 2Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India. Purpose: Intracavitary brachytherapy is an integral component of any radical radiotherapy regimen for carcinoma cervix. Conventionally, dosimetry of intracavitary application is carried out using orthogonal radiographs where point doses to critical structures such as rectum and bladder are calculated according to the ICRU 38 specifications, but the point doses need not represent exactly the dose received by the volume of the organ. In the modern era of three dimensional volume based dosimetry, dose to rectum and bladder can be calculated using dose volume histograms. We undertook this study of comparing conventional 2D with CT-based 3D volumetric dosimetry. Methods and Materials: In this study, 22 intracavitary high-dose-rate (HDR) applications were analyzed and the doses received by the critical structures from the 3D planning were compared with the ICRU 38 point doses. Conventional planning was obtained from the orthogonal radiographs. After plan evaluation and approval, dose to Manchester points A, ICRU rectal and bladder reference points were estimated and recorded for each application. All the intracavitary applications were simultaneously taken up for CT planning. For each application the corresponding optimized source positions used in 2D planning were duplicated for 3D planning. Cumulative dose volume histograms were obtained for rectum and bladder and compared with corresponding 2D plans. Results: In the case of rectum, the mean contoured volume is 38 cm3. The mean dose for D5% and the ICRU rectal points were 73.8% and 66.2% of the prescription dose, respectively. The mean dose D5% is 1.11 times more than the maximum ICRU reference points in 2D planning. In the case of bladder, the mean contoured volume is 76 cm3. The mean dose for D5% and the ICRU bladder points were 101.7% and 66.9% of the prescription dose, respectively. The mean dose D5% is 1.52 times more than the ICRU reference point 2D planning. Conclusions: Correlation with the late reactions of normal tissue complications is necessary before concluding that 2D planning underestimates dose to bladder in the treatment of intracavitary application.
P-64 ICRU reference points underestimate rectal and bladder doses in interstitial HDR brachytherapy of locally advanced cervix cancer Ravindra Yaparpalvi, M.S., Madhur Garg, M.D., Giridhar Gorla, M.D., James Butler, M.D., Shalin Shah, M.D., Rajiv Sharma, M.D., Mark J Engler, Ph.D., Shalom Kalnicki, M.D., Subhakar Mutyala, M.D. Radiation Oncology, Montefiore Medical Center, Bronx, NY. Purpose: Bladder and rectal doses delivered from brachytherapy are defined by universal points (ICRU). We compared rectal and bladder doses using traditional ICRU points with CT-planning based custom dose evaluation in patients treated for advanced cervix cancers with interstitial HDR brachytherapy. Methods and Materials: We retrospectively analyzed 30 individual implants from 10 patients treated with external beam (EB) followed by HDR interstitial brachytherapy with concomitant chemotherapy (weekly Cisplatin 6) for locally advanced cervix carcinoma. The mean age was 57 years (44–71). FIGO stage distribution was: IIB (3), IIIA (1), IIIB (5), and IV A (1). EB consisted of 45 Gy to the pelvis followed by 9–14.4 Gy boost to the parametria in 1.8 Gy fractions. Brachytherapy consisted of
99
a total of 21 Gy in 7 Gy fractions. Patients underwent CT-simulation and image-guided planning (Plato). Treatments were delivered using a microselectron HDR unit. For all 30 implants, ICRU-rectal/bladder point doses, the maximal dose and doses to contiguous 1, 2, and 5 cm3 of rectum and bladder were calculated. Results: Doses resulting from CT-dosimetry were higher than ICRU point estimates. For bladder, the mean CT-maximum dose was 95.2% of the prescribed dose (SD 18.9) compared with 63.9% (SD 17.2) using ICRU point (p 5 0.066). Median bladder volume that received higher than ICRU point estimated dose was 6.98 cm3. The ICRU reference point and contiguous 5 cm3 bladder doses were not significantly different (p 5 0.94). For rectum, the mean CT-maximum dose was 77.5% of the prescribed dose (SD 18.6) compared with 58.8% (SD 16.9) to ICRU rectal point (p!0.0001). Median rectal volume that received higher than the ICRU point dose was 2.67 cm3. The ICRU reference and contiguous 2 cm3 rectal doses were not significantly different (p 5 0.24). Bladder and rectal doses did not correlate with point A dose (mean 5 8.05 Gy, p 5 0.06). Median rectal BED (including EB RT) was 126.7 Gy3 based on CT-dosimetry compared to 100.1 Gy3 using ICRU rectal dose. In our followup (median 15 months, range 10–24), no Grade 3 or higher rectal and bladder complications were observed. Conclusions: In cervix cancer interstitial HDR brachytherapy, ICRU points for rectal and bladder dose consistently and significantly underestimated the delivered dose, as compared to CT planned DVHs. Despite the fact that in our relatively small series there was no increase in Grade 3 or higher rectal or bladder toxicity, median rectal BED as estimated by DVHs is extremely close to complication inducing threshold (125 Gy3). We strongly advocate CT-derived DVHs be routinely used for estimating rectal and bladder doses in pelvic interstitial HDR brachytherapy.
P-65 Comparison of 2D vs. 3D dosimetry for Rotte ‘Y’ applicator highdose-rate brachytherapy for medically inoperable endometrial cancer Sushil Beriwal, M.D., Hayeon Kim, M.D., Dwight Heron, M.D., Raj Selvaraj, M.D. Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, PA. Purpose: To compare CT-based volumetric calculations and ICRU reference-point estimates of radiation doses to the target volume, bladder, rectum and sigmoid colon in patients with carcinoma of the endometrium trated with high-dose-rate intracavitary ‘Y’ applicator radiotherapy (ICRT). Methods and Materials: Eleven patients with cancer of the endometrium were treated with CT-compatible HDR intracavitary ‘Y’ applicators (Nucletron) and underwent post-implant pelvic CT scans with applicators in place. All patients were treated using orthogonal radiography-based planning. The dose was prescribed to ‘‘uterine points’’ which were as follows: a point located 2 cm below the center of a line drawn between the tips of the 2 ends of the Rotte applicator extending laterally from the tandem by half the maximum uterine width, Point A, and 0.5 cm depth along the upper 3 cm vagina. CT-images were transferred to the PLATO treatment planning system version 14.2.6 and retrospectively planned for volumetric calculations. The clinical target volume included the entire uterus, cervix, and upper 3 cm vagina. The volumes of organs at risk (OAR) were digitized. Dwell positions were identified and registered in both the uterine tandem for each patient. For those receiving HDRB alone, the prescribed dose was 7 Gy 5 fractions. Patients who were treated following EBRT received 4 Gy 5 fractions. The interfraction interval was 6–8 hours. The DVHs were computed for the CTV, bladder, rectum, and sigmoid colon. To compare doses of OARs, 1.0 cm3, 2.0 cm3 and 5.0 cm3 volume receiving the highest dose (D1, D2, and D5, respectively) were calculated from DVHs. Results: The mean of percentage of prescribed dose G S.D of D1, D2 and D5 for the OARs of interest were as follows: Rectum 44 G 21, 39 G 18 and 33 G 15, bladder 104 G 36, 91 G 31, and 73.9 G 24 and sigmoid 124 G 35, 109 G 30 and 89 G 25, respectively. The corresponding dose to ICRU 38 bladder and rectal points were 98 G 55% and 50.5 G 32%, respectively. The mean dose to uterine point and point A was 99 G 17% and 98 G 3%, respectively. The mean CTV volume was 160 G 89 cm3
P-64 ICRU reference points underestimate rectal and bladder doses in interstitial HDR brachytherapy of locally advanced cervix cancer Ravindra Yaparpalvi, M.S., Madhur Garg, M.D., Giridhar Gorla, M.D., James Butler, M.D., Shalin Shah, M.D., Rajiv Sharma, M.D., Mark J Engler, Ph.D., Shalom Kalnicki, M.D., Subhakar Mutyala, M.D. Radiation Oncology, Montefiore Medical Center, Bronx, NY. Purpose: Bladder and rectal doses delivered from brachytherapy are defined by universal points (ICRU). We compared rectal and bladder doses using traditional ICRU points with CT-planning based custom dose evaluation in patients treated for advanced cervix cancers with interstitial HDR brachytherapy. Methods and Materials: We retrospectively analyzed 30 individual implants from 10 patients treated with external beam (EB) followed by HDR interstitial brachytherapy with concomitant chemotherapy (weekly Cisplatin 6) for locally advanced cervix carcinoma. The mean age was 57 years (44–71). FIGO stage distribution was: IIB (3), IIIA (1), IIIB (5), and IV A (1). EB consisted of 45 Gy to the pelvis followed by 9–14.4 Gy boost to the parametria in 1.8 Gy fractions. Brachytherapy consisted of
99
a total of 21 Gy in 7 Gy fractions. Patients underwent CT-simulation and image-guided planning (Plato). Treatments were delivered using a microselectron HDR unit. For all 30 implants, ICRU-rectal/bladder point doses, the maximal dose and doses to contiguous 1, 2, and 5 cm3 of rectum and bladder were calculated. Results: Doses resulting from CT-dosimetry were higher than ICRU point estimates. For bladder, the mean CT-maximum dose was 95.2% of the prescribed dose (SD 18.9) compared with 63.9% (SD 17.2) using ICRU point (p 5 0.066). Median bladder volume that received higher than ICRU point estimated dose was 6.98 cm3. The ICRU reference point and contiguous 5 cm3 bladder doses were not significantly different (p 5 0.94). For rectum, the mean CT-maximum dose was 77.5% of the prescribed dose (SD 18.6) compared with 58.8% (SD 16.9) to ICRU rectal point (p!0.0001). Median rectal volume that received higher than the ICRU point dose was 2.67 cm3. The ICRU reference and contiguous 2 cm3 rectal doses were not significantly different (p 5 0.24). Bladder and rectal doses did not correlate with point A dose (mean 5 8.05 Gy, p 5 0.06). Median rectal BED (including EB RT) was 126.7 Gy3 based on CT-dosimetry compared to 100.1 Gy3 using ICRU rectal dose. In our followup (median 15 months, range 10–24), no Grade 3 or higher rectal and bladder complications were observed. Conclusions: In cervix cancer interstitial HDR brachytherapy, ICRU points for rectal and bladder dose consistently and significantly underestimated the delivered dose, as compared to CT planned DVHs. Despite the fact that in our relatively small series there was no increase in Grade 3 or higher rectal or bladder toxicity, median rectal BED as estimated by DVHs is extremely close to complication inducing threshold (125 Gy3). We strongly advocate CT-derived DVHs be routinely used for estimating rectal and bladder doses in pelvic interstitial HDR brachytherapy.
P-65 Comparison of 2D vs. 3D dosimetry for Rotte ‘Y’ applicator highdose-rate brachytherapy for medically inoperable endometrial cancer Sushil Beriwal, M.D., Hayeon Kim, M.D., Dwight Heron, M.D., Raj Selvaraj, M.D. Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, PA. Purpose: To compare CT-based volumetric calculations and ICRU reference-point estimates of radiation doses to the target volume, bladder, rectum and sigmoid colon in patients with carcinoma of the endometrium trated with high-dose-rate intracavitary ‘Y’ applicator radiotherapy (ICRT). Methods and Materials: Eleven patients with cancer of the endometrium were treated with CT-compatible HDR intracavitary ‘Y’ applicators (Nucletron) and underwent post-implant pelvic CT scans with applicators in place. All patients were treated using orthogonal radiography-based planning. The dose was prescribed to ‘‘uterine points’’ which were as follows: a point located 2 cm below the center of a line drawn between the tips of the 2 ends of the Rotte applicator extending laterally from the tandem by half the maximum uterine width, Point A, and 0.5 cm depth along the upper 3 cm vagina. CT-images were transferred to the PLATO treatment planning system version 14.2.6 and retrospectively planned for volumetric calculations. The clinical target volume included the entire uterus, cervix, and upper 3 cm vagina. The volumes of organs at risk (OAR) were digitized. Dwell positions were identified and registered in both the uterine tandem for each patient. For those receiving HDRB alone, the prescribed dose was 7 Gy 5 fractions. Patients who were treated following EBRT received 4 Gy 5 fractions. The interfraction interval was 6–8 hours. The DVHs were computed for the CTV, bladder, rectum, and sigmoid colon. To compare doses of OARs, 1.0 cm3, 2.0 cm3 and 5.0 cm3 volume receiving the highest dose (D1, D2, and D5, respectively) were calculated from DVHs. Results: The mean of percentage of prescribed dose G S.D of D1, D2 and D5 for the OARs of interest were as follows: Rectum 44 G 21, 39 G 18 and 33 G 15, bladder 104 G 36, 91 G 31, and 73.9 G 24 and sigmoid 124 G 35, 109 G 30 and 89 G 25, respectively. The corresponding dose to ICRU 38 bladder and rectal points were 98 G 55% and 50.5 G 32%, respectively. The mean dose to uterine point and point A was 99 G 17% and 98 G 3%, respectively. The mean CTV volume was 160 G 89 cm3