Intensity-modulated proton therapy versus helical tomotherapy in nasopharynx cancer: planning comparison and NTCP evaluation

Planning design of locally advanced pancreatic carcinoma using 4DCT and IMRT/IGRT technologies

BACKGROUND AND PURPOSE

to study the impact of the 4DCT imaging technique on radiotherapy planning for pancreatic carcinoma. To evaluate the possibility of IMRT/IGRT to increase the dose to PTV subvolume.

MATERIAL AND METHODS

contrast-enhanced 4DCT scans of 15 patients (PTs) with unresectable pancreatic cancer were acquired. A 4DCT based PTV (4D-PTV) was created by the convolution of contours and then expanded for geometric uncertainties; a standard PTV (STD-PTV) was derived from a single CTV plus conventional margins. Two 3D conformal treatment (3DCRT) plans and one Helical Tomotherapy (HT) plan were generated with a prescription of 60 Gy. Regarding the 3DCRT plans, the 4D-PTV was considered as the target volume for one, and the STD-PTV for the other; the HT plans were performed only for 4D-PTV. Twelve of 15 PTs were admitted to a Phase I hypofractionated study (15 fractions). The prescribed dose was 44.25 Gy to the 4D-PTV and the PTV subvolume around vascular involvement was boosted from 50 to 55 Gy; before treatment, daily patient position was corrected using MVCT.

RESULTS

4D-PTVs were smaller than STD-PTVs with a volume reduction equal to 37%. 3DCRT plans on 4D-PTV showed a significant sparing of most OARs, the use of IMRT allowed a further significant dose reduction. In the Phase I study the PTV subvolume received up to 55 Gy with modest increase in dose to OARs.

CONCLUSIONS

the 4DCT procedure decreases the overlap between PTV and OARs. HT technique, compared with 3DCRT, allows efficient dose sparing in particular for the duodenum. The IMRT/IGRT approach allows a safe dose escalation to PTV subvolume.

Clinical management of salivary gland hypofunction and xerostomia in head-and-neck cancer patients: successes and barriers

The most significant long-term complication of radiotherapy in the head-and-neck region is hyposalivation and its related complaints, particularily xerostomia. This review addresses the pathophysiology underlying irradiation damage to salivary gland tissue, the consequences of radiation injury, and issues contributing to the clinical management of salivary gland hypofunction and xerostomia. These include ways to (1) prevent or minimize radiation injury of salivary gland tissue, (2) manage radiation-induced hyposalivation and xerostomia, and (3) restore the function of salivary gland tissue damaged by radiotherapy.

Current treatment options for recurrent nasopharyngeal cancer

Loco-regional control rate of nasopharyngeal carcinoma (NPC) has improved significantly in the past decade. However, local recurrence still represents a major cause of mortality and morbidity in advanced stages, and management of local failure remains a challenging issue in NPC. The best salvage treatment for local recurrent NPC remains to be determined. The options include brachytherapy, external radiotherapy, stereotactic radiosurgery, and nasopharyngectomy, either alone or in different combinations. In this article we will discuss the different options for salvage of locally recurrent NPC. Retreatment of locally recurrent NPC using radiotherapy, alone or in combination with other treatment modalities, as well as surgery, can result in long-term local control and survival in a substantial proportion of patients. For small-volume recurrent tumors (T1–T2) treated with external radiotherapy, brachytherapy or stereotactic radiosurgery, comparable results to those obtained with surgery have been reported. In contrast, treatment results of advanced-stage locally recurrent NPC are generally more satisfactory with surgery (with or without postoperative radiotherapy) than with reirradiation.

Potential benefits of scanned intensity-modulated proton therapy versus advanced photon therapy with regard to sparing of the salivary glands in oropharyngeal cancer

PURPOSE

To test the hypothesis that scanned intensity-modulated proton therapy (IMPT) results in a significant dose reduction to the parotid and submandibular glands as compared with intensity-modulated radiotherapy with photons (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) for oropharyngeal cancer. In addition, we investigated whether the achieved dose reductions would theoretically translate into a reduction of salivary dysfunction and xerostomia.

METHODS AND MATERIALS

Ten patients with N0 oropharyngeal carcinoma were used. The intensity-modulated plans delivered simultaneously 70 Gy to the boost planning target volume (PTV2) and 54 Gy to the elective nodal areas (PTV1). The 3D-CRT technique delivered sequentially 70 Gy and 46 Gy to PTV2 and PTV1, respectively. Normal tissue complication probabilities were calculated for salivary dysfunction and xerostomia.

RESULTS

Planning target volume coverage results were similar for IMPT and IMRT. Intensity-modulated proton therapy clearly improved the conformity. The 3D-CRT results were inferior to these results. The mean dose to the parotid glands by 3D-CRT (50.8 Gy), IMRT (25.5 Gy), and IMPT (16.8 Gy) differed significantly. For the submandibular glands no significant differences between IMRT and IMPT were found. The dose reductions obtained with IMPT theoretically translated into a significant reduction in normal tissue complication probability.

CONCLUSION

Compared with IMRT and 3D-CRT, IMPT improved sparing of the organs at risk, while keeping similar target coverage results. The dose reductions obtained with IMPT vs. IMRT and 3D-CRT varied widely per individual patient. Intensity-modulated proton therapy theoretically translated into a clinical benefit for most cases, but this requires clinical validation.

Proton beam radiation therapy for head and neck malignancies

Proton beam radiation therapy (PBRT) has unique physical properties (e.g., Bragg Peak) that limit the amount of normal tissue irradiated in the head and neck region while maximizing the radiation delivered to the tumor. Radiation therapy is commonly used in both the primary and adjuvant setting for many head and neck malignancies. Limiting the unnecessary radiation to normal tissues within the head and neck region can result in a profound improvement in quality of life during and after treatment. Although PBRT was initially developed in the 1950s, recent technological advances have permitted the development of hospital-based facilities for proton delivery. PBRT has been shown to improve outcomes for patients with sinonasal tumors, chordomas, chondrosarcomas, ocular, and periocular malignancies. Further development of intensity-modulated proton therapy will permit comprehensive treatment for head and neck tumors.

Proton-beam therapy for tumors of the CNS

The focus of this review is proton radiotherapy for primary neoplasms of the brain. Although glial cells are among the most radioresistant in the body, the presence of sensitive critical structures and the high doses needed to control CNS tumors present a formidable challenge to the treating radiation oncologist. Treatment with conventional photon radiation at doses required to control disease progression all too often results in unacceptable toxicity. Protons have intrinsic properties that often allow radiation oncologists to deliver a higher dose to the tumor compared with photons, while at the same time offering better sparing of normal tissues. Recognition of these advantages has resulted in development of many new proton treatment facilities worldwide.

Dynamic jaws and dynamic couch in helical tomotherapy

PURPOSE

To investigate the next generation of helical tomotherapy delivery with dynamic jaw and dynamic couch movements.

METHODS AND MATERIALS

The new technique of dynamic jaw and dynamic couch movements is described, and a comparative planning study is performed. Ten nasopharyngeal cancer patients with skull base infiltration were chosen for this comparison of longitudinal dose profiles using regular tomotherapy delivery, running-start-stop treatment, and dynamic jaw and dynamic couch delivery. A multifocal simultaneous integrated boost concept was used (70.4Gy to the primary tumor and involved lymph nodes; 57.4Gy to the bilateral cervical lymphatic drainage pathways, 32 fractions). Target coverage, conformity, homogeneity, sparing of organs at risk, integral dose, and radiation delivery time were evaluated.

RESULTS

Mean parotid dose for all different deliveries was between 24.8 and 26.1Gy, without significant differences. The mean integral dose was lowered by 6.3% by using the dynamic technique, in comparison with a 2.5-cm-field width for regular delivery and 16.7% with 5-cm-field width for regular delivery. Dynamic jaw and couch movements reduced the calculated radiation time by 66% of the time required with regular 2.5-cm-field width delivery (199 sec vs. 595 sec, p < 0.001).

CONCLUSIONS

The current delivery mode of helical tomotherapy produces dose distributions with conformal avoidance of parotid glands, brain stem, and spinal cord. The new technology with dynamic jaw and couch movements improves the plan quality by reducing the dose penumbra and thereby reducing the integral dose. In addition, radiation time is reduced by 66% of the regular delivery time.

A comparison of treatment plans using linac-based intensity-modulated radiation therapy and helical tomotherapy for maxillary sinus carcinoma

This study evaluated whether helical tomotherapy (TOMO) planning could achieve better isodose distribution for the maxillary sinus while concomitantly sparing the adjacent _critical normal organs than linac-based step-and-shoot IMRT (s-IMRT) planning. TOMO and s-IMRT were established for 10 patients with maxillary sinus cancer. The prescription (66 Gy, 30 fractions) was used to cover the planning target volume (PTV) with a 95% isodose line. Each plan was independently optimized using the CORVUS planning system and Tomotherapy Hi-Art system. The treatment plans were compared using dose volume histogram (DVH), a dose homogeneity index (DHI) of the PTV, and equivalent uniform dose (EUD) and DVH of organs at risk (OARs). The TOMO plans demonstrated better dose homogeneity compared to the s-IMRT plans. The average V95% of the TOMO plans was similar to that of the s-IMRT (92.92% vs. 95.07%, respectively), but the average V107% was 0% for TOMO compared with 18.74% for s-IMRT. The average maximum dose reduction was 7 Gy, and DHI increased by 8% for PTV1 in TOMO compared with s-IMRT (79 Gy vs. 71 Gy and, 89% vs. 97%, respectively). The average EUD reduction for the optic nerve was 17%. In summary, planning with TOMO was superior to s-IMRT planning with respect to dose homogeneity within the PTV and sparing of the optic nerve.

NTCP modeling of subacute/late laryngeal edema scored by fiberoptic examination

PURPOSE

Finding best-fit parameters of normal tissue complication probability (NTCP) models for laryngeal edema after radiotherapy for head and neck cancer.

METHODS AND MATERIALS

Forty-eight patients were considered for this study who met the following criteria: (1) grossly uninvolved larynx, (2) no prior major surgery except for neck dissection and tonsillectomy, (3) at least one fiberoptic examination of the larynx within 2 years from radiotherapy, (4) minimum follow-up of 15 months. Larynx dose-volume histograms (DVHs) were corrected into a linear quadratic equivalent one at 2 Gy/fr with alpha/beta = 3 Gy. Subacute/late edema was prospectively scored at each follow-up examination according to the Radiation Therapy Oncology Group scale. G2-G3 edema within 15 months from RT was considered as our endpoint. Two NTCP models were considered: (1) the Lyman model with DVH reduced to the equivalent uniform dose (EUD; LEUD) and (2) the Logit model with DVH reduced to the EUD (LOGEUD). The parameters for the models were fit to patient data using a maximum likelihood analysis.

RESULTS

All patients had a minimum of 15 months follow-up (only 8/48 received concurrent chemotherapy): 25/48 (52.1%) experienced G2-G3 edema. Both NTCP models fit well the clinical data: with LOGEUD the relationship between EUD and NTCP can be described with TD50 = 46.7 +/- 2.1 Gy, n = 1.41 +/- 0.8 and a steepness parameter k = 7.2 +/- 2.5 Gy. Best fit parameters for LEUD are n = 1.17 +/- 0.6, m = 0.23 +/- 0.07 and TD50 = 47.3 +/- 2.1 Gy.

CONCLUSIONS

A clear volume effect was found for edema, consistent with a parallel architecture of the larynx for this endpoint. On the basis of our findings, an EUD <30-35 Gy should drastically reduce the risk of G2-G3 edema.