Anatomy‐based definition of point A utilizing three‐dimensional volumetric imaging approach for high‐dose‐rate (HDR) intracavitary brachytherapy dose prescription when treating cervical cancer using limited resources

Abstract

This study was designed to determine whether volumetric imaging could identify consistent alternative prescription methods to Manchester/point A when prescribing radiation dose in the treatment of cervical cancer using HDR intracavitary brachytherapy (ICBT). One hundred and twenty‐five treatment plans of 25 patients treated for carcinoma of the cervix were reviewed retrospectively. Each patient received 5 fractions of HDR ICBT following initial cisplatin‐based pelvic chemoradiation, and radiation dose was originally prescribed to point A (ICRU‐38). The gross tumor volume (GTV) and high‐risk clinical target volume (HR‐CTV) were contoured in three dimensions on the CT datasets, and inferior–superior, anterior–posterior, and left–right dimensions HR‐CTV were recorded along with multiple anatomic and skeletal dimensions for each patient. The least square–best fit regression lines were plotted between one half of the HR‐CTV width and pelvic cavity dimension at femoral head level and at maximum cavity dimension. The points in both plots lie reasonably close to straight lines and are well defined by straight lines with slopes of 0.15 and 0.17; intercept on y‐axes of ‐0.08 and ‐0.03, point A, at the same level as defined based on applicator coordinates, is defined using this correlation, which is a function of distance between femoral heads/dimensions of maximum pelvic cavity width. Both relations, defined by straight lines, provide an estimated location of point A, which provides adequate coverage to the HR‐CTV compared to the point A defined based on applicator coordinates. The point A defined based on femoral head distance would, therefore, be a reasonable surrogate to use for dose prescription because of subjective variation of cavity width dimension. Simple surrogate anatomic/skeletal landmarks can be useful for prescribing radiation dose when treating cervical cancer using intracavitary brachytherapy in limited‐resource settings. Our ongoing work will continue to refine these models.PACS number(s): 87.55.D‐, 87.55.ne

Comparison of point a based plans with clinical target volume-based three-dimensional plans using dose–volume parameters in small lesion of cervical cancer brachyterapy

“…Traditional ICBT planning based on the ICRU 38 reference points and CT/MRI-guided ICBT planning have been evaluated in previous studies that compared 2D plans and 3D plans according to both tumor volume coverage and D 1cc , D 2cc of the bladder and rectum, and the superiority of 3D plans has been demonstrated [21][22][23][24]. In the current study, we compared two different plans normalized to point A and HR-CTV in terms of the target volume and doses for OAR.…”

“…In the current study, we compared two different plans normalized to point A and HR-CTV in terms of the target volume and doses for OAR. Although the GEC-ESTRO working group published guidelines that included 3D dose-volume parameters used for the brachytherapy of cervical carcinoma, the high-dose-rate ICBT dose is normalized to point A, defined in reference to the applicator location in several radiation therapy centers [24]. Studies show that this utilization is effective only if the HR-CTV width contains bilateral point A's.…”

“…However, whether the target volume receives the prescribed dose and OAR are protected with plans normalized to point A is unclear. Goyal et al [24] reported that the dose prescription defined by point A may be below or overdose in terms of the variable size of the tumor and the patients' anatomy. A total of 125 treatment plans of 25 patients (5 fractions/25 patients) were re-analyzed.…”

“…In each plan, the radiation dose was originally prescribed to point A (ICRU-38), and the tumor volumes and HR-CTVs were retrospectively remade for all plans. The results showed that the dose prescription of point A relative to HR-CTV caused a risk of a low dose in large tumor sizes or of an overdose in small tumor sizes [24]. In another study, Shin et al [25] demonstrated that CT-guided CTV planning was superior to standard point A planning, according to the consistency of target coverage and avoidance of overdose in normal tissue volume.…”

Comparison of dose volume parameters evaluated using three forward planning – optimization techniques in cervical cancer brachytherapy involving two applicators

“…For locally advanced disease, point A based prescription can result in under dosage or geographic misses as has been documented on CT images [ 15 , 18 , 19 ]. Image-guided brachytherapy with 3D volume contouring and assessment of dose volume parameters should be done to ensure good coverage to target and sparing of organs at risk.…”