Field-in-Field Technique With Intrafractionally Modulated Junction Shifts for Craniospinal Irradiation Planning With Three-Dimensional Conformal Radiation Therapy

BACKGROUND

Planning craniospinal irradiation (CSI) with ''field-in-field'' (FIF) homogenization technique in combination with daily, intrafractional modulation of the field junctions is needed to avoid spinal cord overdose. Photon-based techniques for CSI may result in dose inhomogeneity within the treatment volume and usually require a weekly manual shift of the field junctions to minimize the possibility of spinal cord overdose. Nowadays, FIF technique is used to feather out the dose inhomogeneity caused by multiple fields. We have started using this technique after acquiring advanced technology machines in recent years.

METHODS AND MATERIALS

Sixteen patients treated with three-dimensional conformal radiation therapy (3D-CRT) for CSI were retrospectively chosen for analysis. These patients were treated during 2019-2020. Contouring of planning target volume (PTV) and organs at risk (OAR) was done, and planning was done on Varian Eclipse^TM Treatment Planning System (TPS) (Varian Medical Systems, Palo Alto, CA). These patients were planned with lateral craniocervical fields and posterior spinal fields using a forward-planned FIF technique. Field junctions were automatically modulated and custom-weighted for maximal homogeneity within each treatment fraction. Dose-volume histogram (DVH) was used for analysis of results. A corresponding plan without FIF technique was planned; then maximum dose at the junction was noted for each patient with both plans, and the readings were evaluated. Paired sample t-test was used to compute the p-values for the inferential statistics.

RESULTS

Without FIF technique, the volume receiving 110% of the prescribed dose ranged from 39% to 74% (mean: 62.12%) and volume receiving 120% dose ranged from 8% to 28% (mean: 17.68%), whereas with FIF technique, the thecal sac volume receiving 110% of dose ranged from 2% to 18% (mean: 11%) and volume receiving 120% ranged from 0% to 2%. Volume receiving 100% of the dose was also calculated in both techniques; mean values of this dose range was almost similar in both groups. Later p-value was calculated, and in both dose ranges of thecal sac volume receiving 110% and 120%, the difference in values was statistically significant. Therefore, it proved that plan inhomogeneity improved with FIF technique. This technique provided consistent dose delivery during each fraction of treatment across the junctions. The maximum doses calculated at the junction were higher in the CSI plans without FIF compared to those with FIF technique.

CONCLUSION

This study concludes that better dose homogeneity is achieved with FIF technique as compared to non-FIF technique, and the difference in values was statistically significant.

Dosimetric and clinical toxicity comparison of critical organ preservation with three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and RapidArc for the treatment of locally advanced cancer of the pancreatic head

PURPOSE

We compared dosimetry and clinical toxicity for 3-dimensional conformal radiotherapy (3D-crt), intensity-modulated radiotherapy (imrt), and RapidArc (Varian Medical Systems, Palo Alto, CA, U.S.A.) in locally advanced pancreatic cancer (lapcc). We hypothesized that the technique with better sparing of organs at risk (oars) and better target dose distributions could lead to decreased clinical toxicity.

METHODS

The study analyzed 280 patients with lapcc who had undergone radiotherapy. The dosimetry comparison was performed using 20 of those patients. Dose-volume histograms for the target volume and the oars were compared. The clinical toxicity comparison used the 280 patients who received radiation with 3D-crt, imrt, or RapidArc.

RESULTS

Compared with 3D-crt, RapidArc and imrt both achieved a better conformal index, homogeneity index, V95%, and V110%. Compared with 3D-crt or imrt, RapidArc reduced the V10, V20, and mean dose to duodenum, the V20 of the right kidney, and the liver mean dose. Compared with 3D-crt, RapidArc reduced the V35, and V45 of duodenum, the mean dose to small bowel, and the V15 of right kidney. The incidences of grades 3 and 4 diarrhea (p = 0.037) and anorexia (p = 0.042) were lower with RapidArc than with 3D-crt, and the incidences of grades 3 and 4 diarrhea (p = 0.027) were lower with RapidArc than with imrt.

CONCLUSIONS

Compared with 3D-crt or imrt, RapidArc showed better sparing of oars, especially duodenum, small bowel, and right kidney. Also, fewer acute grades 3 and 4 gastrointestinal toxicities were seen with RapidArc than with 3D-crt or imrt. A technique with better sparing of oars and better target dose distributions could result in decreased clinical toxicities during radiation treatment for lapcc.

Three-dimensional conformal planning with low-segment multicriteria intensity modulated radiation therapy optimization

PURPOSE

The purpose of this study was to evaluate automated multicriteria optimization (MCO), which is designed for intensity modulated radiation therapy (IMRT) but invoked with limited segmentation, to efficiently produce high-quality 3-dimensional (3D) conformal radiation therapy (3D-CRT) plans.

METHODS AND MATERIALS

Treatment for 10 patients previously planned with 3D-CRT to various disease sites (brain, breast, lung, abdomen, pelvis) was replanned with a low-segment inverse MCO technique. The MCO-3D plans used the same beam geometry of the original 3D plans but were limited to an energy of 6 MV. The MCO-3D plans were optimized with fluence-based MCO IMRT and then, after MCO navigation, segmented with a low number of segments. The 3D and MCO-3D plans were compared by evaluating mean dose for all structures, D95 (dose that 95% of the structure receives) and homogeneity indexes for targets, D1 and clinically appropriate dose-volume objectives for individual organs at risk (OARs), monitor units, and physician preference.

RESULTS

The MCO-3D plans reduced the mean doses to OARs (41 of a total of 45 OARs had a mean dose reduction; P << .01) and monitor units (7 of 10 plans had reduced monitor units; the average reduction was 17% [P = .08]) while maintaining clinical standards for coverage and homogeneity of target volumes. All MCO-3D plans were preferred by physicians over their corresponding 3D plans.

CONCLUSIONS

High-quality 3D plans can be produced by use of MCO-IMRT optimization, resulting in automated field-in-field-type plans with good monitor unit efficiency. Adoption of this technology in a clinic could improve plan quality and streamline treatment plan production by using a single system applicable to both IMRT and 3D planning.