CT-guided intracavitary radiotherapy for cervical cancer: Comparison of conventional point A plan with clinical target volume-based three-dimensional plan using dose-volume parameters.
OBJECTIVE
To perform an intracavitary radiotherapy (ICR) plan comparison between the conventional point A plan (conventional plan) and computed tomography (CT)-guided clinical target volume-based plan (CTV plan) by analysis of the quantitative dose-volume parameters and irradiated volumes of organs at risk in patients with cervical cancer.


METHODS
Thirty plans for 192Ir high-dose-rate ICR after 30-40-Gy external beam radiotherapy were investigated. CT images were acquired at the first ICR session with artifact-free applicators in place. The gross tumor volume, clinical target volume (CTV), point A, and International Commission on Radiation Units and Measurements Report 38 rectal and bladder points were defined on reconstructed CT images. A fractional 100% dose was prescribed to point A in the conventional plan and to the outermost point to cover all CTVs in the CTV plan. The reference volume receiving 100% of the prescribed dose (V(ref)), and the dose-volume parameters of the coverage index, conformal index, and external volume index were calculated from the dose-volume histogram. The bladder, rectal point doses, and percentage of volumes receiving 50%, 80%, and 100% of the prescribed dose were also analyzed.


RESULTS
Conventional plans were performed, and patients were categorized on the basis of whether the 100% isodose line of point A prescription dose fully encompassed the CTV (Group 1, n = 20) or not (Group 2, n = 10). The mean gross tumor volume (11.6 cm3) and CTV (24.9 cm3) of Group 1 were smaller than the corresponding values (23.7 and 44.7 cm3, respectively) for Group 2 (p = 0.003). The mean V(ref) for all patients was 129.6 cm(3) for the conventional plan and 97.0 cm3 for the CTV plan (p = 0.003). The mean V(ref) in Group 1 decreased markedly with the CTV plan (p < 0.001). For the conventional and CTV plans in all patients, the mean coverage index, conformal index, and external volume index were 0.98 and 1.0, 0.23 and 0.34, and 3.86 and 2.15, respectively. Statistical analysis showed that the conformal index and external volume index improved significantly with the CTV plan, and this improvement was more marked in Group 1. The mean values of the bladder and rectal point doses and volume fractions receiving 50%, 80%, and 100% of the reference dose did not differ between plans for all patients. The reduction in the mean rectal and bladder point doses and irradiated volumes for the CTV plan was statistically significant in Group 1.


CONCLUSIONS
Computed tomography-guided CTV planning of ICR is superior to conventional point A planning in terms of conformity of target coverage and avoidance of overdosed normal tissue volume. To ascertain the potential benefit of treatment outcome, ICR with image-guided three-dimensional plans will be pursued and correlated with the dose-volume parameters.
Shin
Kyung Hwan
KH
Research Institute and Hospital, National Cancer Center, Goyang, Gyeonggi, Republic of Korea.
Kim
Tae Hyun
TH
Cho
Jung Keun
JK
Kim
Joo-Young
JY
Park
Sung Yong
SY
Park
Sang-Yoon
SY
Kim
Dae Yong
DY
Chie
Eui Kyu
EK
Pyo
Hong Ryull
HR
Cho
Kwan Ho
KH
D000970:Antineoplastic Agents / Q000627:therapeutic use; D001918:Brachytherapy / Q000379:methods*; D002945:Cisplatin / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007496:Iridium Radioisotopes; D011838:Radiation-Sensitizing Agents / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000532:radiotherapy*
D000970:Antineoplastic Agents; D007496:Iridium Radioisotopes; D011838:Radiation-Sensitizing Agents; D002945:Cisplatin