Plan quality score to evaluate the dwell time deviation restricted inverse planning by simulated annealing and graphically optimized treatment plans for template based interstitial brachytherapy

PURPOSE

To evaluate the impact of dwell time deviation constraint (DTDC) on the quality of IPSA-optimized treatment plans in comparison with graphical plans using plan quality scores (PQS).

MATERIAL AND METHODS

Seventy optimized plans (graphical & IPSA with different DTDC values) of ten cervical cancer patients were generated. Various DVH parameters like D₉₀, V₁₀₀, V₁₅₀, V₂₀₀, V₃₀₀ were compared to evaluate the impact of DTDC on target coverage and high dose regions inside target for different plans. Similarly, for the OAR dose, values of D_2cc were compared. Various planning parameters like CI, COIN, DHI, DNR, ODI, EI and gain factor (GF) for different OARs were calculated. Based on these indices a plan quality score (PQS) was formulated and calculated. PQS values were used to see the impact of DTDC on plan quality of IPSA in comparison with dosimetric quality of graphical plan.

RESULTS

We have found that target coverage is similar for IPSA and graphically optimized treatment plans. However, dose homogeneity was improved in IPSA compared to graphical optimization whereas conformality was better in graphically optimized plans. OAR dose was less in IPSA plans. High-dose regions inside the target were also reduced in IPSA comparatively. However, IPSA plans optimized with various values of DTDC did not necessarily reduce high-dose regions beyond 0.6. Plan quality scores (PQS) were 6.31, 6.31, 6.34, and 6.17 for the graphically optimized plan, IPSA with DTDC values of 0.0, 0.4, and 1.0 respectively.

CONCLUSION

We found that IPSA is dosimetrically advantageous over graphical optimization. IPSA with a DTDC value of 0.4 improved overall plan quality. However, DTDC value beyond 0.6 produces dosimetrically sub-optimal plans hence the use of DTDC should be very selective and limited.

Image-guided high-dose-rate interstitial brachytherapy boost in the radical radiotherapy for a huge metastatic carcinoma of cervical lymph nodes from an unknown primary site

The purpose of this article was to report the treatment effect of image-guided high-dose-rate interstitial brachytherapy boost in the radical radiotherapy for a huge metastatic carcinoma of cervical lymph nodes from an unknown primary site. The patient was a 75-year-old male. A diagnostic biopsy showed metastatic squamous cell carcinoma and the tumour size was 7.5×6.5×11.5cm³ before treatment (N3; AJCC 7th). After external beam radiotherapy with a dose of 60Gy in 30 fractions, the residual tumour (6.2×4.7×6.0cm³) was treated with image-guided high-dose-rate interstitial brachytherapy boost under ultrasound guidance. The brachytherapy dose was 16Gy in four fractions of 4Gy each. Removal of the huge metastatic tumour was securely achieved by high dose rate interstitial brachytherapy guided with ultrasound scanning. The refractory tumour in the patients healed uneventfully after image-guided high-dose-rate interstitial brachytherapy without recurrence during the 24 months of follow-up. The image-guided high-dose-rate interstitial brachytherapy boost may be a proposed treatment strategy for metastatic carcinoma of cervical lymph nodes from an unknown primary site with radical radiotherapy, especially for huge residual tumour.