Reply to the comment of S. VanDyk and K. Narayan on the editorial "IMRT, IGRT and other high technology become standard in external beam radiotherapy: But is image-guided brachytherapy for cervical cancer too expensive?" J Med Phys 2015;40:1-4.

Sir,

To begin with, the core point of the editorial (even the title) is about the general issue of the treatment of cervix cancer patients, where the main priority is to establish simple methods, while for other disease sites, the state of the art is constantly improving, especially with external beam methods. The short paragraph that was dedicated to the ultrasound (US) is well deserving, considering that the editorial is not about the US alone, but about the various other issues associated with the image-based brachytherapy (IGABT) of cervical cancer.

It has been very well acknowledged in the editorial, that, although magnetic resonance imaging (MRI) based BT is in principle appears promising, it has not been widely accepted for clinical practice, due to various reasons such as large patient numbers, lack of resources especially imaging, lack of training/expertise and other financial constraints, which makes implementation of this technique very challenging in the developing countries including India. There are certain widespread myths in India, about the cost of the IGABT, which need to be cleared out and hence the pragmatic approach is to use the easily available computed tomography (CT) scanners in the RT Department for BT, when it is being used in external beam radiotherapy extensively.

US Technology and its utilization in cervical brachytherapy are nothing new. It has been used to optimize the gynaecology BT application for both tandem and needle placements. However, unlike other sectional imaging trans-abdominal US (TAUS) has not been utilized for target volume and organs at risk (OAR) delineation and treatment planning. TAUS and trans-rectal ultrasound (TRUS) based target volume definitions to implement image-based BT approach is still an area of research. We do agree that some highly well-experienced departments have reported the US-based approach for BT planning,[1234] however, that does not mean that this technique can be adopted by everyone easily. The publications from Peter Mac on the utility of US information in principle seems to refine the conventional two-dimensional (2D) planning by defining and measuring various points representing the outer surface of cervix and uterus and normalise doses to these points. More importantly, authors also utilize MRIs at diagnosis and are repeated at BT, after delivery of first fraction to optimize doses in the subsequent applications. Hence, the authors of the letter cannot claim that their method of US Based BT planning is valid and be implemented easily. Moreover, there is no commercial solution available for BT planning for cervical cancer unlike the US based prostate cancer BT planning. We agree that performing rotations of the US probe results in an image with a different orientation, however, such as image would not be useful unless it is registered with an applicator co-ordinate system for BT planning. These images when used without registration to the applicator coordinate system or the real three-dimensional (3D) anatomy, may pose a substantial challenge for the spatial dose distribution, as no 3D volume is available. Hence, US technology if used without certain precautions may do more damage to the patients as compared to traditional 2D radiograph based planning or a state of the art 3D CT planning.

Second, there is a striking difference in the cervical cancer patient populations with respect to the stage at diagnosis. In India, two-third of the cervical cancers are diagnosed with advanced stages at presentation which means significant parametrial disease making the management more challenging.[5] Clinical outcome for Stage I and limited Stage II patients which represent the majority of their cohort is excellent.[6] This means a significant proportion of patients will have no parametrial disease at BT, which is the case in the two publications that have been referred.[46] In such situations, TAUS information in terms of points representing cervix and uterus and optimize the 2D planning may be sufficient which has been reported in the literature.[124]

In summary, TAUS has major limitations in terms of its inability (i) to implement target/organ volume concepts and dose volume parameters, (ii) to detect residual parametrial and vaginal disease, and (iii) to reconstruct catheters or utilization of applicator library. Moreover, TAUS guided BT planning assisted by MR and clinical outcome lacks robustness, hence needs further validation and larger studies. Hence, the US imaging for BT planning, whether TRUS or TAUS, is not a matured technology as on today as compared to 2D radiograph, 3D CT or MRI based planning with respect to 3D target/OAR volume delineation, applicator reconstruction, treatment planning and evaluation.