Assessment of Treatment Plan Quality between Flattening Filter and Flattening Filter Free Photon Beam for Carcinoma of the Esophagus with IMRT Technique

Background

As compared to the flattened photon beam, removing the flattening filter (FF) from the head of a gantry decreases the average energy of the photon beam and increases the dose rate, leading to an impact on the quality of treatment plans.

Objective

This study aimed to compare the quality of intensity-modulated radiation therapy (IMRT) treatment plans for esophageal cancer with and without a flattened filter photon beam.

Material and Methods

In this analytical study, 12 patients, who had already been treated with a 6X FF photon beam, were treated based on new IMRT methods using a 6X the flattening filter-free (FFF) photon beam. Both 6X FF IMRT and 6X FFF IMRT plans used identical beam parameters and planning objectives. All plans were evaluated with planning indices and doses for organs at risk (OARs).

Results

Insignificant dose variation was for HI, CI, D_98%, and V_95% between FF and FFF photon beam IMRT plans. FF-based IMRT plan delivered a 15.51 % and 11.27% higher mean dose to both lungs and heart than the FFF plan, respectively. The integral dose (ID) for the heart and lungs was 11.21% and 15.51%, respectively, less in the IMRT plan with an FFF photon beam.

Conclusion

In contrast to the FF photon beam, a filtered photon beam-oriented IMRT plan provides significant OAR sparing without losing the quality of the treatment plan. High monitor units (MUs), low ID, and Beam on Time (BOT) are major highlights of the IMRT plan with FFF beam.

Does Fluence Smoothing Reduce the Complexity of the Intensity-Modulated Radiation Therapy Treatment Plan? A Dosimetric Analysis

Background

Intensity-modulated radiation therapy (IMRT) may have too many peaks and valleys, making the treatment plan undeliverable. When there are too many fluency differences between adjacent pixels in the X or Y directions, the X and Y smoothing factors are utilized as weighting factors to penalize this behavior. Generally, a high degree of complexity is accompanied by many monitor units (MUs), large number of segments, small sized segments, and complex segment shapes. The degree of plan delivery uncertainty can all increase with a higher detailed fluence map.

Aim

This study aims to evaluate the dosimetric effects of various smoothing levels on the planning target volume (PTV) and organs at risk (OARs) for cervix cancer.

Materials and Methods

IMRT treatment plans were re-optimized by combining several values of the X and Y penalty between 0 and 100. The dose-volume histogram assessed various dosimetric indicators for PTV and OARs. Additionally, gamma passing rates were evaluated and noted as an indicator of the complex treatment plan.

Results

At X = 60, Y = 60 fluence map penalty, the conformity index (CI) value reached its highest value of 0.996 ± 0.004. At X = 0, Y = 0, the homogeneity index (HI) was determined to have a maximum value of 0.0628 ± 0.0235. The highest and lowest MU values were 2424.30 ± 471.12 and 1087.80 ± 91.57, respectively, with X = 0, Y = 0 and X = 100, Y = 100. At X = 100, Y = 100, the gamma passing rate reaches its highest value of 99.28% ± 0.44% and minimum value of 85.93% ± 3.87% at X = 0, Y = 0.

Conclusion

The CI and HI values showed no discernible fluctuation, and the OAR doses were barely affected as smoothing was increased. When the smoothing factor was raised, the number of MUs sharply dropped, and a decrease in the number of segments and higher gamma passing rates were also seen.

Estimation and comparison of integral dose to target and organs at risk in three-dimensional computed tomography image-based treatment planning of carcinoma uterine cervix with two high-dose-rate brachytherapy sources: 60Co and 192Ir

Background

Iridium-192 (¹⁹²Ir) has been a widely accepted radioisotope for high-dose-rate (HDR) brachytherapy. Recently, Cobalt-60 (⁶⁰Co) radioisotope with a longer half-life (5.26 years) has been gaining popularity due to economic and logistical reasons as compared with the traditional ¹⁹²Ir.

Aim

This study aimed to evaluate and compare the integral dose (ID) to the target and organs at risk (OARs) with two HDR brachytherapy sources in brachytherapy treatment of carcinoma uterine cervix to find appropriate HDR radioisotopes for clinical benefit.

Materials and Methods

This is a retrospective analysis of 52 computed tomography image-based brachytherapy plans of 52 patients who have received intracavitary treatment with ¹⁹²Ir HDR source. For each patient plan, one additional set of plan was created using ⁶⁰Co source in place of ¹⁹²Ir source keeping the same dwell position, and again dose was optimized. The volume and mean dose for target, OARs, and volume structures of 400%, 200%, 150%, 100%, and 50% were recorded for the estimation and comparison of ID.

Results

The mean ID to high-risk clinical target volume was significantly higher by 5.84% in ⁶⁰Co plan than that in ¹⁹²Ir plan. For OARs, the mean ID to the rectum was significantly higher by 2.60% in ⁶⁰Co plan as compared to ¹⁹²Ir plan, whereas for bladder and sigmoid colon, it was lower in ⁶⁰Co plan than that in ¹⁹²Ir plan. The mean ID of central dose volume structures of 400%, 200%, 150%, 100%, and 50% was higher by 12.97%, 9.77%, 8.16%, 6.10%, and 3.22%, respectively, in ⁶⁰Co plan than that of ¹⁹²Ir plan.

Conclusion

The results of our study concluded that ¹⁹²Ir HDR radioisotope should be preferred for intracavitary brachytherapy due to its ideal physical characteristics for better clinical outcomes.

Interfraction physical dose variations in high-dose-rate brachytherapy for carcinoma cervix based on computed tomography image dataset to find the compatibility of the first fraction plan to treat successive fractions

Context

Due to limited resources and/or affordability by majority of the patients, many centers in low- and middle-income countries are still not able to adapt three-dimensional image-based brachytherapy planning in their routine practice.

Aim

The aim of the study was to see the feasibility of using computed tomography (CT)-based plan of the first fraction to treat successive fractions of intracavitary brachytherapy based on the estimation of the physical dosimetric differences between successive applications.

Materials and Methods

CT image-based brachytherapy plans of 38 patients who received three insertions of intracavitary application with high-dose-rate brachytherapy have been analyzed. Revised plans for the second and third insertions were generated by adapting dwell time and dwell position of the first insertion plan. The dose to point "A" and maximum doses to 2, 1, and 0.1 cc volumes of the rectum and bladder have been used for dosimetric comparison.

Results

The statistical differences of mean point "A" doses were observed insignificant except between original and revised plans for the second insertions. The dosimetric differences between consecutive original and revised plans for the bladder and rectum have not shown any significance except minimum dose to 0.1 cc volume of the rectum for the third insertions.

Conclusions

Dosimetric deviation for tumor and organs at risk is within acceptable limit while using CT image-based brachytherapy plan of the first fraction for treating successive fractions.